PROSTHETIC DEVICES OF ULTRA HIGH MOLECULAR WEIGHT POLYETHYLENE TREATED WITH RADIATION AND FUSIONFIELD OF THE INVENTION The present invention relates to the orthopedic field and to the provision of prostheses such as hip and knee implants, as well as to methods for the manufacture of said devices and material used therein. BACKGROUND OF THE INVENTION The use of synthetic polymers, e.g., ultra high molecular weight polyethylene, with metal alloys has revolutionized the field of prosthetic implants, e.g., its use in replacements for total joints for the hip or knee. . The use of synthetic polymer against the metal of the joint, however, can result in severe adverse effects with predominant manifestation after several years. Several studies have concluded that such use can lead to the release of ultrafine polyethylene particles in periprosthetic tissues. It has been suggested that abrasion extends the chain-bent crystallites to form the anisotropic fibrillar structures on a joint surface. The stretched fibrils can then be broken leading to the production of submicron sized particles. In response to the progressive entry of these polyethylene particles between the prosthesis and the bone, the resorption induced by macrophages of the periprosthetic bone begins. The macrophage, being frequently unable to digest these polyethylene particles, synthesizes and releases large numbers of cytokines and growth factors that ultimately result in bone resorption by osteoclasts and monocytes. This osteolysis can contribute to the mechanical loss of the prosthesis components, sometimes requiring revision surgery with its concomitant problems. SUMMARY OF THE INVENTION It is an object of the invention to provide an implantable prosthesis device formed, at least in part, of ultra high molecular weight polyethylene (PEPMUA) treated with radiation having undetectable free radicals, so that production is reduced of fine particles of the prosthesis during the use of the prosthesis. It is another object of the invention to reduce osteolysis and inflammatory reactions resulting from prosthetic implants. It is still another object of the invention to provide a prosthesis that can remain implanted within a person for prolonged periods. It is still another object of the invention to provide improved UA PEPM which has a high density of entanglements and has undetectable free radicals. A still further objective of the invention is to provide improved PEPMUA having improved wear resistance. According to the invention, a medical prosthesis for use within the body that is formed with ultra high molecular weight polyethylene (PEPMUA) treated by radiation having substantially undetectable free radicals is provided. The radiation, for example, can be gamma or electronic radiation. The PEPMUA has an intertwined structure. Preferably the PEPMUA is substantially not oxidized and is substantially resistant to oxidation. Variations include, eg, , the PEPMUA that has three fusion peaks, two fusion peaks or a fusion peak. In certain embodiments, the PEPM UA has a polymeric structure with less than about 50% crystallinity, less than about 290A of laminar thickness and less than about 940 MPa of elastic modulus of tension, so that it reduces the production of fine particles of the prosthesis during the use of the prosthesis. Part of the prosthesis, for example, may be in the form of a cup-shaped article or tray having a load bearing surface made of this PEPM UA. This load bearing surface can be contacted with a second part of the prosthesis having a load bearing surface of equalization of a metallic or ceramic material. Another aspect of the invention is PEPMUA treated with radiation i having substantially no detectable free radicals. This PEPMUA has an intertwined structure. Preferably thisPEPMUA is substantially not oxidized and substantially resistant to oxidation. Variations include, v. gr. , the PEPM UA that has three fusion peaks, two fusion peaks or a peak of fusion I. i »Other aspects of the invention are fabricated articles, v. gr, with a load-bearing surface and wear-resistant coatings made of said PEPMUA. One embodiment is where the manufactured article has the shape of a bar post that is capable of being configured into articles by conventional methods, e.g., machining. Yet another aspect of the invention includes a method for forming an entangled PEPMUA that substantially does not have detectable free radicals. Conventional PEPMUA is provided which has 10 polymer chains. This PEPMUA is irradiated in a way that interlaces the polymer chains. The PEPMUA is heated above the melting temperature of the PEPMUA so that substantially no free radicals are detectable in it. The PEPMUA is then cooled to room temperature. In certain 15 modes, the cooled PEPMUA is machined and / or sterilized. A preferred embodiment of this method is called IRF-FS, i.e., cold irradiation and subsequent fusion. The PEPMUA that is provided is at room temperature below room temperature. Another preferred embodiment of this method is called IRC-FS, i.e. hot irradiation and subsequent fusion. The PEPMUA that is supplied is heated to a temperature below the melting temperature of the PEPMUA. Another preferred embodiment of this method is called IRC-FA, namely hot irradiation and adiabatic melting. In this embodiment, the supplied PEPMUA is heated to a temperature below the melting temperature of the PEPMUA, preferably between about 100 ° C below the melting temperature of the PEPMUA. Preferably, the PEPMUA is in an insulating material 5 so as to reduce the heat loss of the PEPMUA during the process. The preheated PEPMUA is then irradiated at a sufficiently high total dose and at a sufficiently rapid dose rate that generates sufficient heat in the polymer to melt substantially all the crystals in the material and thus ensure the removal of substantially all the free radicals detected by, v.gr., the irradiation step. It is preferred that the irradiation step uses electron irradiation so as to generate said adiabatic heating. Another aspect of this invention is the product made in accordance with the method described above.ßB In still another aspect of this invention, called IRF, i.e. fusion irradiation, is a method for forming interlaced PEPMUA. Conventional PEPMUA is provided. Preferably, the PEPMUA is surrounded with an inert material that is substantially free of oxygen. The PEPMUA is heated above the melting temperature of the PEPMUA so that it completely melts the entire crystal structure. The heated PEPMUA is irradiated and the irradiated PEPMUA is cooled to approximately 25 ° C. In an IRF mode, highly intricate and interlaced PEPMUA is formed. Conventional PEPMUA is provided.
* Preferably, the PEPMUA is surrounded with an inert material that is substantially free of oxygen. The PEPMUA is heated above the melting temperature of the PEPMUA for a sufficient time to allow the formation of intricate polymer chains in the PEPMUA. The heated PEPMUA is irradiated in a manner that traps the polymer chains in the intricate state and the irradiated PEPMUA is cooled to approximately 25 ° C. The invention also characterizes a method for forming a medical prosthesis of PEPMUA treated with irradiation havingsubstantially undetectable free radicals, the prosthesis resulting in reduced production of prosthetic particles during the use of the prosthesis. The radiation treated PEPMUA is provided having substantially undetectable free radicals. A medical prosthesis of this PEPMUA is formed in such a way thatreduces the production of particles of the prosthesis during the use of the prosthesis, the PEPMUA forming a surface that supports the load of the prosthesis. The formation of the prosthesis can be achieved by normal procedures known to those skilled in the art, e.g., machining. Also in this invention a method for treating a body in need of a medical prosthesis is provided. A shaped prosthesis formed by PEPMUA treated by radiation having substantially free radicals is provided. The prosthesis involves the body that needs the prosthesis. The prosthesis reduces productionof prosthesis particles during the use of the prosthesis. In preferred embodiments, the PEPMUA forms a surface that supports the loading of the prosthesis. The above and other aspects and advantages objectives of the present invention will be better understood from the following specification when read together with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a cross-sectional view through the center of a medical hip joint prosthesis according to a preferred embodiment of this invention. Figure 2 is a side view of an acetabular cup liner as shown in Figure 1; Figure 3 is a cross-sectional view through line 3-3 of Figure 2; Figure 4 is a graph showing the cpstatin and melting point of the irradiated PEPMUA with fusion at different irradiation doses; Figure 5 is an environmental scanning electron microphotograph of the recorded surface of conventional PEPMUA showing its crystallinity structure; Figure 6 is an environmental scanning electron microphotograph of the etched surface of the melted irradiated PEPMUA showing its crystalline structure at approximately the same magnification as in Figure 5; and Figure 7 is a graph showing the crystallinity and melting point at different depths of a melted irradiated PEPMUA cup. Figure 8 is a graph showing CBD melting endotherms for PEPMUA of Hoechst-Celanese GUR 4050 prepared using hot irradiation and partial adiabatic melting (IRC-EA), with and without subsequent heating. Figure 9 is a graph showing DSD melting endotherms for PEPMUA Hoechst-Celanese GUR 1050 prepared using hot irradiation and partial adiabatic melting (IRC-FA) with and without subsequent heating. Figure 10 is a graph showing adiabatic heating of PEPMUA treated by IRC-FA with a preheat temperature of 130 ° C. Figure 11 is a graph showing tension strain behavior of unirradiated PEPMUA, PEPMUA treated with IRF-FS and PEPMUA treated with IRC-FA. Detailed Description This invention provides a medical prosthesis for use within the body that is formed of ultra high molecular weight polyethylene (PEPMUA) treated with radiation having substantially undetectable free radicals. A medical prosthesis in the form of a hip joint prosthesis is generally illustrated at 10 in Figure 1. The prosthesis shown has a conventional ball head 14 connected by # a neck portion to a post 15 which is mounted by conventional cement 17 to the femur 16. The ball head may have the conventional design and be formed of stainless steel or other alloys as is known in the art. The radius of the ball head closely conforms to the radius of the inner cup of an acetabular cup 12 which may be mounted on cement 13 directly to the pelvis 11. Alternatively, a metal acetabular shell can be cemented to the pelvis 11 and the cup Acetabular 12 can form a lining or liner connected to the acetabular shellmetallic by the means known in the art. The specific shape of the prosthesis can vary greatly as is known in the art. Many constructions of hip joints are known and also other prostheses are known such as knee joints, joints ofshoulders, ankle joints, elbow joints and finger joints. All prostheses of the prior art can benefit by forming at least one surface that supports the loading of said prostheses of a high molecular weight polyethylene material according to this invention. Saidload-bearing surfaces can have the form of actual layers, linings or complete devices, as shown in Figure 1. In all cases, it is preferred that the load bearing surface act together with a metal equalizing member. or ceramic of the prosthesis so that a surface ofsliding between them. Said sliding surfaces are subject to rupture of polyethylene as known in the art. Such rupture can be decreased by the use of the materials in the present invention. Figure 2 shows the acetabular cup 12 in the form of a half-hollow ball-shaped device best observed in the cross-section of Figure 3. As previously described, the outer surface 20 of the acetabular cup need not be circular or hemispherical but may be be square or of any configuration to adhere directly to the pelvis or pelvis through a metal cover as is known in the art. The radius of the acetabular cup shown at 21 in Figure 3 of the preferred embodiment varies from about 20 mm to about 35 mm. The thickness of the acetabular cup from its generally hemispherical hollow portion to the outer surface is preferably about 8 mm. The external radius preferably is in the order of about 20 mm to about 35 mm. In some cases, the ball joint can be made from the PEPMUA of this invention and the acetabular cup formed of metal, although it is preferred to make the acetabular cup or acetabular cup liner of PEPMUA to match the metal ball. The particular method of joining the components of the prosthesis to the bones of the body can vary greatly as is known in the art. It is intended that the medical prostheses of this invention include whole prosthetic devices or portions thereof ^ - > v.gr., component, layer or liner. The medical prosthesis includes v.gr, orthopedic joint and bone replacement parts, for example replacements of hip, knees, shoulders, elbows, ankles or fingers. The prosthesis may have the shape, e.g., of a cup-shaped article 5 or tray having a surface that supports the load. Other forms known to those skilled in the art may also be included in the invention. It is also intended that medical prostheses include any wear surface of a prosthesis, e.g., a coating on a surface of a prosthesis in thewhich prosthesis is made of a material different from the PEPMUA of this invention. The prostheses of this invention are useful for contact with metal-containing parts formed of e.g., cobalt alloy, chromium, stainless steel, titanium alloy or nickel alloycobalt, or with parts that contain ceramic. For example, a hip joint is constructed in which a cup-shaped article having an internal radius of 25 mm is brought into contact with a metal ball having an outer radius of 25 mm, so as to closely match the cup-shaped article. TheThe load-bearing surface of the cup-shaped article of this example is made of the PEPMUA of this invention, preferably having a thickness of at least about 1 mm, more preferably having a thickness of at least 2 mm, more preferably having a thickness of at least 063 cm, and more preferably having a thickness of at least about 0.84 cm. The prostheses may have any shape, appearance or known normal configuration or may be a common design, but 5 have at least one surface that supports a load of the PEPMUA of this invention. The prostheses of this invention are not toxic to humans. They are not subject to deterioration by normal body constituents, eg, blood or interstitial fluids. They are capableto be sterilized by normal means, including, eg, heat or ethylene oxide. By PEPMUA, linear unbranched ethylene chains are understood to have molecular weights in excess of about 500,000, preferably in excess of about 1,000,000 andmore preferably above about 2,000,000. Frequently the molecular weights can be as high as# approximately 8,000,000. By initial average molecular weight is meant the average molecular weight of the PEPMUA starting material, before any irradiation. Conventional PEPMUA is usually generated by Ziegler-Natta catalysis and since the polymer chains are generated from the surface catalytic site, they crystallize and interweave like crystals folded into a chain. Examples of known PEPMUA powders include Hifax Grade 1900 polyethylene (obtained fromMontell, Wilmington, Delaware), having a molecular weight of% about 2 million g / mole and not containing calcium stearate; GUR 4150, also known as GUR 415, (obtained from Hoescht Celanese Corp., Houston, TX), having a molecular weight of about 4-5 million g / mole and not containing calcium stearate 5, GUR 4120 (obtained from Hoescht Celanese Corp., Houston, TX), having a molecular weight of about 2 million g / moles and containing 500 ppm of calcium stearate; GUR 4020 (obtained from Hoescht Celanese Corp. Houston, TX), having a molecular weight of approximately 2 million g / moles and not containingcalcium stearate; GUR 1050 (obtained from Hoescht Celanese Corp, Germany), having a molecular weight of approximately 4-5 million g / moles and without containing calcium stearate; GUR 1150 (obtained from Hoescht Celanese Corp., Germany), having a molecular weight of approximately 4-5 million g / mol and containing500 ppm of calcium stearate; GUR 102 (obtained from Hoescht Celanese Corp., Germany), having a molecular weight of approximately 2 million g / moles and without containing calcium stearate; and GUR 1120 (obtained from Hoescht Celanese Corp., Germany), having a molecular weight of approximately 2 million g / molesand containing 500 ppm of calcium stearate. The preferred PEPMUAs for medical applications are GUR 4150, GUR 1050 and GUR 1020. Resin is understood as powder. PEPMUA powder can be consolidated using a variety of different techniques, eg, hydraulic extrusion, moldingby compression or direct compression molding. The extrusion * hydraulic, the PEPMUA powder is pressurized through a heated barrel so it is consolidated into a bar steel, that is, a bar steel (obtainable, eg, from Westlake Plastics, Lenni , PA). In compression molding, the PEPMUA powder consolidates under high pressure in a mold (for example, from Poly-Hi Solidur, Fort Wayne, IN, or Perplas, Stanmore, U.K.). The shape of the mold can be, e.g., a thin sheet. Direct compression molding is preferably used to manufacture products in the form of a network, eg, acetabular components or knee insertstibial (obtainable e.g., from Zimmer, Inc. Warsaw, IN). In this technique, the PEPMUA powder is pressed directly into the final form. "Hockey disks" or discs are usually machined from hydraulically extruded bar steel or from a compression molded sheet. 15 PEPMUA treated by radiation means PEPMUA that has been treated with radiation, eg, gamma radiation or electron radiation, in a way that induces entanglement between the polymer chains of the PEPMUA. By substantially undetectable free radicals,understands substantially non-free radicals measured by electronic paramagnetic resonance, as described in Jahan et al., J. Biomedical Materials Research 25: 1005 (1991). Free radicals include, e.g., unsaturated trans-vinylene free radicals. The PEPMUA have irradiated below their point offusion with ionization radiation contains entanglements as well as free radicals trapped for a long time. These free radicals react with oxygen for a long time and result in the fragility of PEPMUA through oxidative degradation. One advantage of the PEPMUA and medical prostheses of this invention is that the PEPMUA treated by radiation is used which does not have detectable free radicals. The free radicals can be removed by any method from this result, e.g., by heating the PEPMUA above its melting point so that the substantially residual crystalline structure does not remain. Thus, the crystal structure remains substantially non-residual. By eliminating the crystalline structure, free radicals are able to recombine and therefore are eliminated. The PEPMUA that is used in this invention has an interlaced structure. An advantage of having an interlocking structure is that it will reduce the production of prosthesis particles during the use of the prosthesis. It is preferred that the PEPMUA be substantially non-oxidized. By substantially non-oxidized it is understood that the radius of the area under the carbonyl peak at 1740 cm "1 in the IRFT spectrum to the area 20 under the peak at 1460 cm" 1 in the IRFT spectrum of the interlaced sample is of the same order of magnitude than the radius of the sample before interlacing. It is preferred that the PEPMUA be substantially resistant to oxidation. By substantially resistant to oxidation itunderstands that it remains substantially non-oxidized for at least 10 years. Preferably, they remain substantially non-oxidized for at least about 20 years, more preferably for at least about 30 years and even more preferably throughout the life of the patient. In certain embodiments, the PEPMUA has three melting peaks, the first melting peak preferably being from about 105 ° C to about 120 ° C, more preferably from about 110 ° C to about 120 ° C, and even more preferably it is approximately 118 ° C. The second peakis preferably about 140 ° C, more preferably about 135 ° C and still more preferably about 137 ° C. The third type of melting preferably is from about 140 ° C to about 150 ° C, more preferably from about 140 ° C to about145 ° C and even more preferably about 144 ° C. In certain modalities, the PEPMUA has two melting peaks. The first* melting peak is preferably from about 105 ° C to about 120 ° C, more preferably it is from about 110 ° C around 120 ° C and even more preferably it is fromabout 118 ° C. The second melting peak is from about 125 ° C to about 140 ° C, more preferably it is from about 130 ° C to about 140 ° C, more preferably it is about 135 ° C and still more preferably it is about 137 ° C. C. In certainmodalities the PEPMUA has a melting peak. The melting peak is preferably from about 125 ° C to about 140 ° C, more preferably from about 130 ° C to about 140 ° C, more preferably it is from about 135 ° C and even more preferably from 137 ° C. Preferably, the PEPMUA has two melting peaks. The number of melting peaks is determined by differential scanning calorimetry (CBD) at a heating rate of 10 ° C / min. The polymeric structure of the PEPMUA used in the prosthesis of this invention results in the reduction of particles ofPEPMUA of the prosthesis during the use of the prosthesis. As a result of the limited number of particles diffusing in the body, the prosthesis exhibits longer implant life. Preferably the prosthesis can remain implanted in the body for at least 10 years, more preferably for at least 20 years andeven more preferably throughout the patient's life.* > The invention also includes other manufactured articles made with PEPMUA treated with alloy having substantially undetectable free radicals. Preferably, the PEPMUA that is used to form the manufactured articles has a structureInterlaced Preferably, the PEPMUA is substantially resistant to oxidation. In certain modalities, the PEPMUA has three melting peaks. In certain modalities, the PEPMUA has two melting peaks. In certain modalities, the PEPMUA has a melting peak. Preferably, the PEPMUA has two melting peaks. Themanufactured articles include shaped articles and non-configured items, including, eg, machined objects, eg, cups, gears, nuts, drive slides, bolts, fasteners, cables, pipes and the like and steel bars , films, cylindrical bars, laminates, panels and fibers. The configured articles 5 can be formed, eg, by machining. The manufactured article can have, for example, the form of steel bars that is capable of being configured in a second article by machining. The articles manufactured in particular are suitable for* applications that support load, eg, high applicationsresistance to use, e.g., as a load bearing surface, e.g., a joint surface and as metal replacement articles. The films or thin films of the PEPMUA of this invention can also be attached, eg, with glue on the support surfaces and therefore can be used as aload-bearing surface resistant to use. The invention also includes PEPMUA treated by radiation having substantially undetectable free radicals. The PEPMUA has an intertwined structure. Preferably, the PEPMUA is substantially non-oxidized and substantiallyresistant to oxidation. In certain modalities, the PEPMUA has three fusion spikes. In certain modalities, the PEPMUA has two melting peaks. In certain modalities, the PEPMUA has a melting peak. Preferably, the PEPMUA has two melting peaks. Depending on the particular processing used to formPEPMUA, certain impurities may be present in the PEPMUA of this invention, including eg, calcium stearate, molding release agents, extenders, anti-oxidants and / or other conventional additives for polyethylene polymers. The invention also provides a method for forming interlaced PEPMUA 5 having substantially undetectable free radicals. Preferably this PEPMUA is to be used as a load bearing article with high wear resistance. Conventional PEPMUA that has polymer chains is provided. The conventional PEPMUA fr may have the form of, e.g., a steel inbar, a bar steel configured, e.g., a disc, a liner or a manufactured article e.g., a cup-shaped article or tray for use in a medical prosthesis. By conventional PEPMUA it is understood commercially available high density (linear) polyethylene of molecular weights greater thanapproximately 500,000. Preferably, the starting material of i PEPMUA has an average molecular weight greater than about 2 million. By initial average molecular weight, we mean the average molecular weight for starting material of PEPMUA before any irradiation. The PEPMUA radiates fromThus, the polymer chains are interlocked. Irradiation can be done in an inert or non-inert environment. Preferably, the irradiation is done in a non-inert environment, eg, air The irradiated PEPMUA is heated above the melting temperature of the PEPMUA so that there are no free radicals substantially notdetectable in the PEPMUA. The hot PEPMUA is then cooled toVim * J * t. S? Rr? m? «- ^ - w - '" • «- ?? ar.emperatura am ente. Recently, the cooling step is at a rate greater than about 0.1 ° C / minute. Optionally, the cooled PEPMUA can be machined. For example, if the oxidation of PEPMUA occurs during the irradiation step, it can be machined if desired, by any method known to those skilled in the art. And optionally, the cooled PEPMUA, or the machined PEPMUA, can be sterilized by any method known to those skilled in the art.
* A preferred modality of this method is called IRF-FS, it issay, cold irradiation and subsequent fusion. In this modality, the PEPMUA that is provided is at room temperature, below the ambient temperature. Preferably, it is about 20 ° C. The irradiation of the PEPMUA can be with, e.g., gamma irradiation or electronic irradiation. In general, the gamma irradiation givesa high penetration depth but it does not take long, resulting in the possibility of deeper oxidation. In general, electron irradiation gives more limited penetration depths but it takes less and the possibility of extensive oxidation is reduced. The irradiation is done in a way that interlaces thepolymer chains The irradiation dose may vary to control the degree of entanglement and crystallinity in the final PEPMUA product. Preferably, the total absorbed dose of the irradiation is from about 0.5 to about 1,000 Mrad, more preferably about 1 to about 100.
Mrad, more preferably is from about 4 to about 20 Mrad and even more preferably about 15 Mrad. Preferably, a dose regime is used which does not generate enough heat to melt the PEPMUA. If gamma irradiation is used, the preferred dose regimen is from about 0.05 to about 0.2 Mrad / minute. If electron irradiation is used, preferably the dose rate is from about 0.05 to about 3,000 Mrad / minute, more preferably from about 0.05 to about 5 Mrad / minute, and even more preferably fromabout 0.05 to about 0.2 Mrad / minute. The dose regime in electron irradiation is determined by the following parameters (1) the power of the accelerator in kW, (n) the speed of the conveyor, (iii) the distance between the surface of the irradiated specimen and the scanning antenna, and (iv) the sweep width. HeThe dose regime in the e-ray installation is often measured in Mrad by passing under the tracking beam. The dose regimes indicated herein as Mrad / minute can be converted into Mrad / step using the following equation: DMrad / m? N = DMrad / step X Vc - = - I 20 where Dmrad.m? I, is the dose rate in Mrad / min, Dmrad / step is the dose regimen in Mrad / step, vc is the velocity of the transporter and I is the length of the specimen traveling through the tracking area of the ray e. When electron irradiation is used as the energy of electrons, it can vary to changethe penetration depth of electrons. Preferably from about 0.5 Mev to about 12 Mev, more preferably from about 5 MeV to about 12 Mev. Such manipulation is particularly useful when the irradiated object is an article of varying thickness or depth, eg, a joint cup for a medical prosthesis. The irradiated PEPMUA is heated above the melting temperature of the PEPMUA so that there are no detectable free radicals in the PEPMUA. The heating provides the molecules fr with sufficient mobility in a way that eliminates the restrictionsderived from the crystals of the PEPMUA so it allows essentially all residual free radicals to recombine. Preferably the PEPMUA is heated to a temperature from about 137 ° C to about 300 ° C, more preferably from about 140 ° C to about 300 ° C,More preferably still about 140 ° C to about 190 ° C, more preferably about 145 ° C to about 300 ° C, more preferably about 145 ° C to about 190 ° C, more preferably about 146 ° C to about 190 ° C and even more preferably about 150 ° C. FromPreferably the temperature in the heating step is maintained for about 0.5 minutes to about 24 hours, more preferably about 1 hour to about 3 hours, and even more preferably about 2 hours. The heating can be carried out, v.gr, in air, in an inert gas, v.gr,Nitrogen, argon or helium, in an atmosphere of sensitization, v. Gr.it prefers that for longer heating times, the heating is carried out in an inert gas or under vacuum. Another preferred embodiment of this method is called IRC-FS. is to say, hot irradiation and subsequent fusion. In this mode, the PEPMUA that is provided is preheated to a temperature below the melting temperature of the PEPMUA. The preheating can be done in an inert or non-inert environment. It is preferred that this preheating be carried out in air. Preferably, thePEPMUA is preheated to a temperature from about 20 ° C to about 135 ° C, more preferably at a temperature greater than about 20 ° C to about 135 ° C, and even more preferably at a temperature of about 50 ° C. other parameters are as described above for the modality ofIRC-FS, except that the dose regime for the irradiation stepwhich uses electron irradiation preferably is from about 0.05 to about 10 Mrad / minute, and more preferably from about 4 to about 5 Mrad / minute, and the dose regime for the irradiation step usingThe irradiation range is preferably from about 0.05 to about 0.2 Mrad / minute and more preferably from about 0.2 Mrad / minute. Another preferred embodiment of this method is called IRC-FA, that is, hot irradiation and adiabatic melting. In this modality, thePEPMUA that is provided is preheated to a temperature belowEPMUA The preheating can be done in an inert or non-inert environment. It is preferred that this preheating is carried out in air. The preheating can be carried out, e.g., in an oven. It is preferred that the preheat is at a temperature between about 100 ° C and below the melting temperature of the PEPMUA. Preferably, the PEPMUA is preheated to a temperature of about 100 ° C to about 135 ° C, more preferably the temperature is about 130 ° C and furtherpreferably is about 120 ° C. Preferably, the PEPMUA is an insulating material in a manner that reduces the heat loss of the PEPMUA during processing. The heat is intended to include eg, preheating supplied before irradiation and heat generated during irradiation. By isolating theMaterial is understood to be any type of material that has insulating properties, e.g., a fiberglass bag. The preheated PEPMUA is then irradiated at a total or sufficiently high dose and at a dose rate sufficiently fast so as to generate sufficient heat in the polymer tosubstantially melt all crystals in the material and thus ensure the removal of substantially all detectable free radicals generated by, v., The irradiation step. It is preferred that the irradiation step uses electron irradiation so as to generate said adiabatic heating. ByAdiabatic heating means that there is no loss of heat to n. Adiabatic heating results in adiabatic fusion if the temperature is above the melting point. Adiabatic fusion is understood to include complete or partial fusion. The minimum total dose is determined by the amount of heat needed to heat the polymer from its initial temperature (ie, the preheated temperature treated above) to its melting temperature and the heat needed to melt all the crystals and the heat necessary to heating the polymer to a predetermined temperature above its melting point. TheThe following equation describes how the total dose amount is calculated Total Dose = Cpp. (Tm - T,) +? Hm + Cpm (Tr-Tm) Where Cpp, (= 2 J / g / ° C) and Cpm (= 3 J / g / ° C) are heat capacities of the PEPMUA in the solid state and molten state,respectively,? Hm (= 146 J / g) is the heat of fusion of the bar post Hoescht Celanese GUR 415 not irradiated, T, is the initial temperature and Tf is the final temperature. The final temperature must be above the melting temperature of the PEPMUA. Preferably, the final temperature of the PEPMUA isabout 140 ° C to about 200 ° C, more preferably it is about 145 ° C to about 190 ° C, more preferably it is about 146 ° C to about 190 ° C and even more preferably it is about 150 ° C C. Above 160 ° C, the polymer starts to bubble and cracksPreferably, the dose regime of the electron irradiation fr is from about 2 to about 3,000 Mrad / minute, more preferably it is from about 2 to about 30 Mrad / minute, more preferably it is from about 7 to about 25 Mrad / minute, more preferably is about 5 Mrad / minute and even more preferably is about 7 Mrad / minute. Preferably the total dose absorbed is from about 1 to about 100 Mrad. Using the above equation, the absorbed dose for an initial temperature of 130 ° C and a final temperature of 150 ° C iscalculate that it is approximately 22 Mrad. In this embodiment, the heating step of the method results from the adiabatic heating described above. In certain modalities, adiabatic heating completely melts the PEPMUA. In certain modalities, warmingadiabatic only partially melts the PEPMUA. Preferably, further heating of the irradiated PEPMUA is made subsequent to the irradiation induced by adiabatic heating so that the final temperature of the PEPMUA after further heating is above the temperature offusion of PEPMUA in such a way as to ensure the complete fusion of PEPMUA. Preferably, the temperature of the PEMMA of the additional heating is from about 140 ° C to about 200 ° C, more preferably it is from about 145 ° C to about 190 ° C, more preferably it is from aboutfr 146 ° C to about 190 ° C and even more preferably is about 150 ° C. Still another embodiment of this invention is called IRC-FA, i.e., cold irradiation and adiabatic heating. In this mode,the PEPMUA at room temperature below room temperature is melted by adiabatic heating with or without subsequent additional heating, as described above. This invention also includes the product made in accordance with the method described above. Also disclosed in this invention is a method for forming a medical prosthesis of PEPMUA having substantially undetectable free radicals, the prosthesis resulting in reduced production of prosthesis particles during the use of the prosthesis. The PEPMUA treated with radiation that hasfree radicals not detectable. A medical prosthesis is formed from this PEPMUA in a way that reduces the production of prosthetic particles during the use of the prosthesis. The PEPMUA forming a load-bearing surface of the prosthesis. The formation of the prosthesis can be achieved through proceduresnormal known to those skilled in the art, e.g., machined. Also in this invention a method is provided for treating a body in need of a medical prosthesis. A configured prosthesis formed of PEPMUA treated with radiation is provided.free radicals substantially undetectable. This prosthesis is applied to the body that needs the prosthesis. The prosthesis reduces the production of fine particles of the prosthesis during the use of the prosthesis. In preferred embodiments, the ultra high molecular weight polyethylene forms a load bearing surface of the prosthesis. In yet another embodiment of this invention, a medical prosthesis is provided for use within the body that is formed of ultra high molecular weight polyethylene (PEPMUA) having a polymeric structure with less than about 50% crystallinity, less than about 290A laminar thickness andless than about 940 MPa of elastic modulus of tension, so that it reduces the production of fine particles of the prosthesis during the use of the prosthesis. The PEPMUA of this modality has a polymeric structure with less than about 50% crystallinity,preferably less than about 40% crystallinity.< | By crystallinity is meant the fraction of the polymer that is crystalline. The crystallinity is calculated by knowing the weight of the sample (p, in g), the heat absorbed in the sample in fusion (E in lime) and the calculated heat of the fusion of the polyethylene in statecrystalline at 100% (? H ° = 69.2 cal / g) and using the following equation% of cpstalinity = E w,? H °The PEPMUA of this modality has a polymeric structurewith at least about 290A of laminar thickness preferably less than about 290A of laminar thickness- - ^ ^^ ... ^^. ^^^, ... ". ^. ^^. ^ Aihi-jÉ.iaiA ^^ fr and more preferably less than about 100Á laminar thickness. By laminar thickness (1) is meant the calculated thickness of assumed laminar structures in the polymer using the following expression: 1 = 2-s "-Tm °? H ° - (Tm ° -Tm) -pwhere, s0 is the energy of the final free surface of polyethylene (2.22 x 106 cal / cm2),? H ° is the calculated heat of melting of fr 10 polyethylene in the crystalline state at 100% (69.2 cal / g), p is the density of the crystalline regions (1,005 g / cm3), Tm ° is the melting point of the perfect polyethylene crystal (418.15K) and Tm is the experimentally determined melting point of the sample The PEPMUA of this modality has less fromapproximately 940 MPa of elastic tension modulus preferably less than about 600 MPa of elastic tension modulus, more preferably less than about 400 MPa of elastic modulus of the invention and even more preferably less than about 200 MPa of modulustension elastic. The elastic voltage module is the ratio of the rated voltage to the corresponding voltage for voltages less than 0.5% as determined using the normal test. Preferably, the PEPMUA of this modality has apolymer structure with approximately 40% crystallinity••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• • The PEPMUA of this embodiment has free radicals not trapped, eg, trans-vinylene saturated free radicals. It is preferred that the PEPMUA of this embodiment have a hardness of less than about 65 on the Shore D scale, more preferably a hardness of less than about 55 on the Shore D scale, more preferably a hardness of less than 50 on the Shore D scale. Hardness is the hardness of foodsnapshot on the Shore D scale using a durometer described in ASTM D2240. It is preferred that the PEPMUA of this embodiment be substantially non-oxidized. The polymer structure has extensive entanglement so that a substantial portion of the polymer structure does not dissolve in Deca n. Per portionSubstantial is at least 50% of the dry weight of the polymer sample. By not dissolved in Decalin it is understood that it does not dissolve in Decalin at 150 ° C during a period of 24 hours Preferably, the PEPMUA of this modality has a high density of intricacy in a way that causes the formation ofimperfect crystals and reduced crystallinity. By intricacy density is meant the number of intricacy points of polymer chains in a unit volume. A higher density of intricacy being indicated by the inability of the sample of the polymer to crystallize to the same degree as conventional PEPMUA.thus leading to a lower degree of crystallinity.- * - - - - - ^ • «t * - ^ - *** '- - * - ^^^^ * The invention also includes other manufactured articles made of PEPMUA of this embodiment having a polymeric structure with less than about 50% crystallinity, less than about 290A of sheet thickness, and less than about 5,940 MPa of elastic modulus of tension. These articles include articles configured from non-configured items, including, eg, machined objects, for example, cups with gears, nuts, drag slides, bolts, fasteners, cables, pipes and the like, and bar steel, films, cylindrical bars, laminates, 10 panels and fibers The configured articles can be made, for example, by machining. The manufactured articles are particularly suitable for load bearing applications, v. Gr., As a load bearing surface and as metal replacement articles. These films or sheets of PEPMUA that have been irradiated by melting are also attached, eg, with glue on the supporting surfaces and are therefore used as a surface bearing a load resistant to transparent wear. The invention also includes an embodiment in which PEPMUA has a unique polymeric structure characterized by less than about 50% crystallinity, less than about 290A of sheet thickness, and less than about 940 MPa of elastic tension modulus. Depending on the particular processing used to form the PEPMUA, certain impurities may be present in the PEPMUA of this invention, including v.gr .. 25 calcium stearate, mold release agents, extendersAntioxidants and / or other conventional additives to ethylene polymers. In certain embodiments, the PEPMUA has high light transmissivity, preferably a light transmission, preferably a transmission greater than about 10% light at 517 nm through a 1 mm thick sample, more preferably a transmission greater than 30. % light at 517 nm through a 1 mm thick sample and even more preferably a transmission greater than about 40% light at 517 nm through a 1 mm thick fr sample. Said PEPMUA is particularly useful forthin films or sheets that can be attached to the support surfaces of various articles, the film or sheet being transparent and resistant to wear. In another embodiment of the invention, a method for forming interlaced PEPMUA is provided. This method is calledmerger (IRF). Conventional PEPMUA is provided. Preferably, the PEPMUA is surrounded with an inert material that is substantially free of oxygen. The PEPMUA is heated above the melting temperature of PEPMUA so that it completely melts the entire crystal structure. The hot PEPMUA is irradiated and the PEPMUAirradiated is cooled to approximately 25 ° C. Preferably, the PEPMUA made of this embodiment has a polymer structure that is less than about 50% crystallinity, less than about 290A of sheet thickness and less than about 940 MPa of elastic tension modulus.
The conventional PEPMUA, v.gr, a steel in the form ofonfigurado, a coating or a manufactured article. By conventional PEPMUA is meant commercially available (linear) high density polyethylene of molecular weights greater than about 500,000. Preferably, the PEPMUA starting material has an average molecular weight greater than about 2 million. By initial average molecular weight is meant the average molecular weight of the PEPMUA starting material, before any irradiation. It is preferred that»This PEPMUA is surrounded by an inert material that issubstantially free of oxygen, e.g., nitrogen, argon or helium. In certain modalities, a non-inert environment can be used. The PEPMUA is heated above its melting temperature for a sufficient time to allow all the crystals to melt. Preferably, the temperature is approximately 145 ° C toaround 230 ° C and more preferably is about* ^ 175 ° C to around 200 ° C. Preferably, the heating is maintained to have the polymer at the preferred temperature for about 5 minutes to about 3 hours and more preferably for about 30 minutes to about2 hours. The PEPMUA is then irradiated with gamma irradiation or electronic irradiation. In general, gamma irradiation gives a high penetration depth but takes longer, resulting in the possibility of some oxidation. In general, electronic irradiation gives depths of penetration morelimited but it takes less and therefore the possibility of¿M *, ** iiJL-,.-....... a ^ - ^, .- ^ - ^^. "., -.-.- ^ s ^^ fr oxidation. The irradiation dose can be varied to control the degree of entanglement and crystallinity in the final PEPMUA product. Preferably, a dose greater than about 1 Mrad is used, more preferably a dose greater than about 20 Mrad is used. When electronic irradiation is used, the energy of the electrons can vary to change the penetration depth of the electrons, thus controlling the degree of entanglement of crystallinity in the final product of PEPMUA. Preferably, the energy is from about 0.5 10 MeV to about 12 MeV. More preferably about 1 MeV at about 10 MeV and more preferably about 10 MeV. Said manipulation is particularly useful when the irradiated object is an article of variable thickness or depth, e.g., a particular arch for a prosthesis. The irradiated PEPMUA 15 is then cooled to about 25 ° C. Preferably, the cooling rate is equal to or greater than about 0.5 ° C / min, more preferably equal to or greater than about 20 ° C / min. In certain modalities, the irradiated PEPMUA can be machined. In the preferred embodiments, the cooled irradiated PEPMUA has substantially no detectable free radicals. Examples 1, 3 and 6 describe certain preferred embodiments of the method. Examples 2, 4 and 5 and Figures 4 to 7 illustrate certain properties of the molten irradiated PEPMUA obtained from these preferred embodiments compared to conventional PEPMUA.... 1,. ^ Z ^, ^^^^ .. ^^^? iimu mé lü i i üíiíí iffi - ^ i -r - nizátr ^ 1 fr This invention also includes the product made according to the method described above. In an IRF modality, it is made in highly intricate and interlaced PEPMUA. Conventional PEPMUA is provided. Preferably, the PEPMUA is surrounded by an inert material that is substantially free of oxygen. The PEPMUA is heated above the melting temperature of PEPMUA for a sufficient time to allow the formation of intrinsic fr polymer chains in the PEPMUA. The heated PEPMUA is irradiated in a manner that traps the polymer chains in the intricate state. The irradiated PEPMUA is cooled to approximately 25 ° C. This invention also includes the product made according to the method described above. Also provided in this invention is a method for forming a PEPMUA prosthesis so that the production of fine particles of the prosthesis is reduced during the use of the prosthesis. The PEPMUA having a pohmérica structure with less than about 50% of crystallinity, less than about 290A of sheet thickness and less than about 940 MPa of elastic tension modulus. A shape prosthesis of this PEPMUA, the PEPMUA forming a surface that supports the prosthesis load. The formation of the prosthesis can be achieved by normal procedures known to those skilled in the art, e.g., machiningThere is also provided in this invention a method for treating a body in need of a prosthesis. A shaped prosthesis formed of ultra high molecular weight polyethylene is provided having a polymeric structure with less than about 50% crystallinity, less than about 290A laminar thickness and less than about 940 MPa elastic tension modulus. This prosthesis applies to the body that needs the prosthesis. The prosthesis reduces the production of fine particles of the prosthesis during the use of the prosthesis. In preferred embodiments, theultra high molecular weight polyethylene forms a bearing surface of the prosthesis. The products and processes of this invention also apply to other polymeric materials such as high density polyethylene, low density polyethylene, low density polyethylene.linear and polypropylene.
The following non-limiting examples further illustrate the present invention EXAMPLESExample 1: Method for Forming Irradiated-Molten PEPMUA (IRF) This example illustrates irradiation of electrons from molten PEPMUA A cuboidal specimen (disc) of size 10 mm x 12 mm x 60 mm prepared from an extruded PEPMUA bar steelhydraulically conventional (bar steel Hoescht Celanese• "---" * - - • »» * • "GUR 415 obtained from Westlake Plastics, Lenni, PA) was placed in a chamber. The atmosphere inside the chamber consisted of nitrogen gas with low oxygen content (<0.5 ppm oxygen gas) (obtained from AIRCO, Murray Hill, NJ). The pressure in the chamber was 5 about 1 atm. The temperature of the sample and the manner of irradiation was controlled using a heater, an autotransformer and a thermocouple (manual) or temperature (automatic) reading controller. The chamber was heated with a heating mantle of 270 W. The chamber was heated (controlled by theautotransformer) at a rate such that the steady state temperature of the sample was approximately 175 ° C. The sample was kept at the temperature in a stable state for 30 minutes before starting the irradiation. The irradiation was performed using a van der Graaff generatorwith 2.5 MeV energy electrons and a dose rate of 1.67 Mrad / min. The sample was given a dose of 20 Mrad with the beam of fr electrons hitting the sample on the surfaces of 60 mm x 12 mm. The heater was turned off after irradiation and the sample was allowed to cool inside the chamber under an inert nitrogen gas atmosphere.20 to 25 ° C for approximately 0.5 ° C / minute As a control, similar specimens were prepared using a non-heated, unirradiated bar steel of conventional PEPMUA Example 2: Comparison of Steel Properties in bar GUR 415 and PEPMUA and Steel in bar (IRF) GUR 415 IrradiatedFade (20 Mrad)gJ «á ^ > ~ «& &.,., -, ^ t ^^ - a ^^ aat -a« -------- J - ¿?? Iaái ^ - ^ This example illustrates various properties of the samples irradiated and non-irradiated bar steel from PEPMUA (GUR 415) obtained from Example 1. The samples tested were the following: the test sample was bar steel that was melted and then irradiated while melting; the control was bar steel (without heating / melting, without irradiation). (A) Differential Scanning Calorimetry (CBD) A Perkin-Elmer CBD7 was used with a heat container with ice water ice under heating and cooling regime of10 ° C / minute with a continuous nitrogen purge. The crystallinity of the samples obtained from Example 1 was calculated from the weight of the sample and the heat of fusion of the polyethylene crystals (69.2 cal / g) the temperature corresponding to the peak of the endortem was taken as the melting point Laminar thickness was calculatedassuming a laminar crystalline morphology and knowing the? H ° of theheat of the fusion of 100% crystalline polyethylene (69 2 cal / g), the melting point of a perfect crystal (418.15 K), the density of the crystalline regions (1,005 g / cm3) and the final free surface energy of polyethylene (2.22 x 106 cal / cm2) The results are shown in theTable 1 and Figure 4. Table 1: CBD (10 ° C / min) GUR 415 GUR 415 (non-irradiated) (irradiated with Property 0 MRad fusion)t: i «*" • »• -» - ». > ~~ * < ^^ - ^^ '' * - * - ~ '***? Crystallinity (%) 50.2 37.8 Warm-up Point (C) 135.8 125.5 Laminar thickness 290 137The results indicate that the sample irradiated with fusion had an intricate and polymeric structure less crystalline than the unirradiated sample, as evidenced by lower crystallinity, lower laminar thickness and lower melting point. (B) Sponge Ratio Samples were cut into cubes of 2mm x 2mm x 2mm in size and kept immersed in Decalin at 150 ° C for a period of 24 hours. An antioxidant (1% N-phenyl-2-) was added. 10 naphthylamine) to Deca n to avoid degradation of the sample. The swelling ratio and percentage extract were calculatedmeasuring the weight of the sample before the experiment After the swelling for 24 hours and after the vacuum drying of the swollen sample The results are shown in Table 2. 15 Table 2 Sponging in Decalin with Antioxidant for 24 hours at 150 ° CGUR 415 GUR 415 (non-irradiated) (irradiated with Property 0 MRad fusion)^^^^^^^^^^^^ wn fr 20 MRad Foam ratio Dissolve 2.5 Extract (%) approx. 100% 0.0The results indicate that the sample of PEPMUA irradiated with fusion was highly interlaced and therefore did not allow the dissolution of the polymer chains that the solvent still heats up7 ^ after 24 hours, while the unirradiated sample completely dissolved in the hot solvent in the same period. (C) Elastic Stress Module The ASTM 638 M lll of the samples was followed. The displacement rate was 1 mm / minute. The experiment was carried outin this MTS machine. The results are as shown in Table 3 Table 3: Elastic test (ASTM 638 M lll, 1 mm / min.) GUR 415 GUR 415 fr (non-irradiated) (irradiated with Property 0 MRad fusion) 20 MRad Stress elastic module (MPa) 9407 200 8 Elastic fatigue 22.7 14.4 Stress at break (%) 9538 547.2 UTS Worked (MPa) 464 154- •• ^ - ^ • - * • - * .- - - '^^^. ^^? ^ T ^ i ^ ilai ^^ ^ m fr The results indicate that the sample of PEPMUA irradiated with fusion had an elastic modulus of voltage significantly lower than the non-irradiated control. The tension below the rupture of the sample of PEPMUA irradiated with fusion still more evidences the entanglement of the chains in that sample. (D) Hardness The hardness of the samples was measured using a durometer on the Shore D scale. The hardness was recorded for instantaneous fr infestation. The results are shown in Table 4 10 Table 4: Hardness (Shore D) GUR 415 GUR 415 (non-irradiated) (irradiated with Property 0 MRad fusion) 20 MRad Hardness (Scale D) 65.5 54 5The results indicate that the PEPMUA irradiated with fusion was smoother than the non-irradiated control. (E) Light Transmissivity (Transparency) 15 The transparency of the samples was measured as follows: the transmission of light for a light of wavelength of 517 nm was studied passing through a sample of approximately 1 mm thickness placed between two glass plates. The samples were prepared by polishing the surface against 600 granules paper. If oil was spread over the surfaces, the silicone oil was used in order to reduce diffuse light scattering due to the roughness of the surface of the surface. polymer sample. The reference used for this purpose was two similar glass plates separated by a thin film of silicone oil. Transmissivity was measured using a uv-vis Perkin Elmer Lambda 3B spectrophotometer. The absorption coefficient and the transmissivity of a sample of exactly 1 mm thickness was calculated using law Lambert-Beer. The results are# shown in Table 5. 10 Table 5: Transmissivity of light at 517 nm GUR 415 GUR 415 (non-irradiated) (irradiated with Property 0 MRad fusion) 20 MRad Transmission (%) 8.59 399 (1 mm sample) fr Coefficient of absorption 24.54 9 18 (cm1)The results indicate that the sample of PEPMUA irradiated with fusion transmitted much more light through it than the control and therefore it is much more transparent than the control 15 (F) Scanning Electron Microscopy (MEBA) It was carried out MEBA (ElectroScan, Model 3) in the samples at 10 kV (low voltage to reduce the radiation damage to the sample)fr with an extremely thin gold coating (approximately 20A to increase image quality). By studying the surface of the polymer under the MEBA with and without the gold coating, it was verified that the thin film coating 5 did not produce any artifact. The samples were recorded using a permanganate etch with a ratio of sulfuric acid to orthophosphoric acid of 1: 1 and a concentration of 07% (w / v) of fr potassium permanganate before being seen under the MEBA 10 Figure 4 shows a MEBA (10,000 x magnification) of a recorded surface of conventional PEPMUA (GUR 415, not heated, not irradiated). Figure 5 shows an MEBA (10,500 x magnification) of a recorded surface of melted irradiated PEPMUA (GUR 415; cast, 20 Mrad) MEBAs indicated a reduction inThe size of the crystallites and the perfect crystallization presentation in the PEPMUA irradiated with fusion compared to the conventional PEPMUA. (G) Fourier Transform Infrared Spectroscopy (IRTF) 20 The IRTF of the samples was carried out using a micromeshter on the samples rinsed with hexane to remove surface impurities. The peaks observed around 1740 to 1700 cm "1 are bands associated with oxygen-containing groups Therefore the ratio of the area under the carbonyl peak togj ^^^^^^^^^^^^^ g ^^ Hg ^^ tógj 1740 cm "1 to the area under the peak of rrtit leno to 1460 cm'1 is a measure fr of the degree of oxidation. IRTF indicates that the sample of PEPMUA irradiated with fusion showed more oxidation than the PEPMUA controlconventional non-irradiated, but less batch oxidation than a sample of PEPMUA irradiated in air at room temperature and given the same dose as irradiation as the sample irradiated by fusion. (H) Electronic Paramagnetic Resonance (RPE) was carried out RPE at room temperature on the samples fr 10 which were placed in a nitrogen atmosphere in an air-tight quartz tube. The instrument used was theBruker ESP 300 RPE spectrometer and tubes used were RPE Taperlok sample tubes obtained from Wilmad GlassCompany, Buena, NJ. 15 The unirradiated samples do not have any free radical in them because the irradiation in that process creates free radicals in the polymer. By irradiation, free radicals are created which can last for several years under the appropriate conditions. 20 The results of RPE indicate that the sample irradiated with fusion does not show free radicals when studied using aRPE immediately after irradiation, while the sample that is irradiated at room temperature under nitrogen atmosphere showed trans-vinylene free radicals after 266days of storage at room temperature. The absence of^ ÉssgÉ &^^^^ fr free radicals in the sample of PEPMUA irradiated with fusion means that no further oxidative degradation is possible. (I) Use Resistance to the use of the samples was measured using a biaxial screw-on-disk tester. The test of use involved the action of rubbing of PEPMUA bolts (diameter 9 mm, height = 13mm) against a Co-Cr alloy disc. These tests were carried out for a total of 2 million cycles. The bolt does notIrradiated radiation exhibited a use regime of 8 mg / million cycles, 10 while the irradiated bolt used a rate of use of 05 mg / million cycles. The results indicate that the melted irradiated PEPMUA has much higher resistance than the unirradiated control. Example 3: Method for Forming Conventional Articulated Cups 15 of Fused Irradiated PEPMUA (IRF) This example illustrates electron irradiation of a conventional fused PEPMUA particular fr cup. A conventional particular cup (non-sterilized high-compliant PEPMUA cup made by Zimmer, Inc., Warsaw, IN) 20 of internal diameter of 26 mm and made of GUR 415 hydraulically extruded bar steel, was irradiated under controlled atmosphere and temperature in an airtight chamber with a titanium cup holder at the base and a thin stainless steel blade (0.0025 cm thickness) at the top. The 25 atmosphere inside this chamber consisted of nitrogen gas with a low«Gg ^ ÉKi ^ ÉriÉéü *, oxygen content (<0.5 pt'n of oxygen gas) (obtained fromAIRCO, Murray Hill, NH). The pressure in the chamber was approximately 1 atmosphere. The chamber was heated using a 270 W heating mantle at the base of the chamber that was controlled using a temperature controller and an autotransformer. The chamber was heated so that the temperature on the top surface of the cup rose approximately 1.5 ° C to 2 ° C / min, finally asymptotically reaching a temperature in the idle state of about 175 ° C. Due to the thickness in the sample cup and the particular design of the equipment used, the temperature at rest of the cup varied between 200 ° C in the base to 175 ° C in the upper part. The cup was kept at this temperature for a period of 30 minutes before starting the irradiation. Irradiation was performed using a van generator fromGraaff with 2 5 MeV energy electrons and a dose rate of 1.67 Mrad / min. The beam entered the chamber through the thin sheet at the top and hit the concave surface of the cup. The dose received by the cup was such that a maximum dose of 20 Mrad was received approximately 5 mm below the surface of the cup being struck by the electrons After the irradiation the heating was stopped and the cup was allowed to cool to room temperature (approximately 25 ° C) while still in the chamber with nitrogen gas The cooling rate was about 0 5 ° C / m? n The sample was removed from the chamber after the chamber and sample reached the temperature ambient. The irradiated anterior cup that increases in volume (due to the decrease in density accompanying the reduction of crystallinity after fusion irradiation) can be re-machined to the appropriate dimensions. Example 4: Sponge Ratio and Percent Extract at Different Depths for Articulated Cups of Fused Irradiated PEPMUA (IRF) 10 This example illustrates the ratio of swelling and percentage extract to different depths of the particular cup irradiated with fusion obtained from Example 3 Samples with a size of 2mm x 2mm x 2mm were cut from the cup at various depths along the axis of the cup. These samples were then kept submerged in Decahn at 150 ° C for a period of 24 hours. An antioxidant (1% N-phenyl-2-naphthylamine) was added to the Decalin to prevent degradation of the sample. The swelling ratio and the percentage extract were calculated by measuring the weight of the sample before the experiment, after swelling for 24 hours, and after vacuum drying of the swollen sample The results are shown in Table 6. Table 6: The Sponge and Percent Extract Ratio at Different Depths on the Articular Cup of Fused Irritated PEPMUA¿Sb? Íauífa? A. ^ -. ^ U *****. ^ ^ É ^ MMitfi Sponge Ratio% Depth Extraction (Decalin 150 ° C 1 day) (mm) 0-2 2.43 0.0 2-4 2.52 0.0 4-6 2.52 0.0 6-8 2.64 0.0 8-10 2.49 0.0> 12 6.19 35.8 Not irradiated Dissolves Approx. 100%The results indicate that the PEPMUA in the cup has been interlaced to a depth of 12 mm due to the fusion irradiation process to such an extent that no polymer chains were dissolved in hot Decalin for 24 hours. Example 5: Crystallinity and Melting Point at Different Depths for Articulated Cups of Fused Irritated PEPMUA (IRF) This example illustrates the crystallinity and melting point at 10 different depths of the irradiated cup with fusion obtained from Example 3. Samples were taken of the cup at various depths along the axis of the cup. Crystallinity is the fraction of the polymer that is crystalline. The crystallinity was calculated knowing the weight of^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the sample (p, in g), the heat absorbed by the sample in fusion (E, in lime that was experimentally measured using Differential Scanning Calorimeter at 10 ° C / min.) And polyethylene heat fusion crystalline state at 100% (? H ° = 69.2 cal / g), using the following equation% of crystallinity = E w,? H °The melting point is the temperature that corresponds to the peak • t 10 in the CBD endotherm. The results are shown in Figure 7 The results indicate that the cpstatinity and melting point of the fusion-irradiated PEPMUA in the articular cups obtained from example 3 were much lower than the values corresponding to conventional PEPMUA, even at a depth of 15 1 cm (the thickness of the cup being 1.2 cm.).
Example 6: Second Method for Forming Artificial Cups of and Fused Irritated PEPMUA (IRF) This example illustrates a method for forming articular cups 20 with melted irradiated PEPMUA The conventional hydraulically extruded PEPMUA bar steel (GUR 415 bar steel obtained from West Lake Plastics, Lenni, PA) was machined to the shape of a cylinder, with 4 cm in height and 5.2 cm in diameter. A circular face of the cylinder was machined to include an exact hemispherical orifice of diameter of 2 6 cm, so that the axis of the hole and the cylinder coincided...... ^^^., ^^^ ^ ~ ¿^ ^ * .c ^^ - ** -, .j ^ fc. ^ M-- »^. ^ ...... ** ~ * 6A ~ .. .. ^ ..... ~ - .- ^ ... t ^ m.
This specimen was enclosed in an airtight chamber with a thin stainless steel blade (0.0025 cm thick) on top. The cylindrical specimen was placed so that the hemispherical orifice looked towards the leaf. The chamber was rinsed and filled with an atmosphere of nitrogen gas with low oxygen content (<0.5 ppm oxygen gas) obtained from AIRCO, Murray Hill, NJ). After this rinsing and filling, a slow continuous flow of nitrogen was maintained, while the pressure in the chamber was maintained at about 1 atm. The chamber was heated using a cloakheating d 270 W at the base of the chamber that was controlled using a temperature controller and an autotransformer. The chamber was heated so that the temperature on the upper surface of the cylindrical specimen was raised to approximately 1.5 ° C to 2 ° C / min., Reaching asymptotically at the end a temperature instate at rest of approximately 175 ° C. The specimen was then kept at this temperature for a period of 30 minutes before starting irradiation. The irradiation was performed using a van der Graaff generator with 2.5 MeV energy electrons and a dose regimeof 1.67 Mrad / min. The beam entered the chamber through the thin sheet at the top and hit the surface with the hemispherical hole. The dose received by the specimen was such that a maximum dose of 20 Mrad was received approximately 5 mm below the surface of the polymer being struck by the electronsAfter irradiation, the heating stopped and the specimen& a »* tiUM & Xlttti0S3 &&. -i- * A *» ^ lte ^ afe¿ ^^^^ fc ^ Baflft1 ^ «» A ~ g »?« »¿^ W'- - - - fr was allowed to cool to room temperature (approximately 25 ° C) while still in the chamber with nitrogen gas. The cooling rate was approximately 0.5 ° C / min. The sample was removed from the chamber after the chamber and sample 5 reached room temperature. The cylindrical specimen was then machined in a particular cup with the dimensions of a particular cup of high conformity of 26 mm internal diameter PEMMUA manufactured byZimmer, Inc., Warsaw, IN, such that the concave surface 10 of the hemispherical orifice was reworked at the joint surface. This method allows the possibility of relatively large changes in dimensions during fusion irradiation. Example 7: Electronic Discrimination of PEPMUA Disks 15 This example illustrates that the electron irradiation of PEPMUA disks gives a non-uniform absorbed dose profile. The conventional PEPMUA extruded bar steel was used (Hoescht Celanese bar steel GUR 415 obtained from Westlake Plastics, Lenni, PA) The GUR 415 20 resin used for the bar steel had a molecular weight of 5,000,000 g / mol and containing 500 ppm of calcium stearate The bar steel was cut into cylinders in the form of "hockey discs" (height 4 cm, diameter 8.5 cm) The discs were irradiated at room temperature with electronic beam incident to one of the circular bases of the discs withttltíifr '- • «' '•" - "- - * - ** ^ ****? **» * »-'-- ^ -utt-i-- .. l llllllllllllllllllllllllllllllllllllllllll ? ~ < *? ** »* * • * - ^. ^ ^ ^ ^ t at 10 MeV and 1 kW (AECL, Pinawa, Manitoba, Canada), with a sweeping width of 30 cm and a speed of 0.08 cm / sec conveyor Due to a cascade effect, electron irradiation results in a non-uniform absorbed dose profile Table 7 illustrates the values of absorbed dose by calculating various depths in a polymethylene specimen irradiated with 10 MeV The absorbed doses were the values measured on the lower surface (surface area of* incidence of e rays). 10 Table 7: The Variation of absorbed dose as a function of Depth in polyethylenezAbsorbed dose (M rad) 0 20 0.5 22 1.0 23 1.5 24 2.0 25 2.5 27 3.0 26 fr 3.5 23 4.0 20 4.5 8 5.0 3 5.5 1 6.0 0Example 8: Method for Forming PEPMUA Using Cold Irradiation and Subsequent Fusion (IRF-FS) This example illustrates a method for forming PEPMUA having interlaced structure and having substantially undetectable free radicals by irradiation and then fusion of the PEPMUA. The hydraulically extruded bar steel of conventional PEPMUA was used (bar steel from Hoescht Celanese GUR415 obtained from Westlake Plastics, Lenni, PA). The GUR 415 resin used for the bar steel had a molecular weight of 5,000,000g / mol and contained 500 ppm of calcium stearate. The bar steel was cut into cylinders in the form of "hockey pucks" (height 4 cm, diameter 8.5 cm). The discs were irradiated at room temperature at a dose rate of 2.5 Mrad per step at 2.5, 5, 7.5, 10, 12.5, 15, 17.5, 20, 30 7 50 Mrad of total absorbed dose measured on the upper surface (incidence of electron beams) (AECL, Pinawa, Manitoba, Canada). The discs were not packed and the irradiation was carried out in air. After irradiation the disks were heated to 150 ° C under vacuum for 2 hours so that the polymer melts and thus results in the recombination of free radicals leading to substantially undetectable residual free radicals. The discs were then cooled to room temperature at a rate of 5 ° C / min. 15 Residual free radicals were measured by electronic paramagnetic resonance as described in Jahan et al., J Biomedical Materials Research 25: 1005 (1991). Example 9: Method for Forming PEPMUA Using Subsequent Hot Melting and Fusion (IRC-FS) This example illustrates a method for forming PEPMUA which has an interlaced structure and has substantially undetectable free radicals, irradiating PEPMUA which has been heated below the melting point and then fusion of PEPMUA Conventional PEPMUA hydraulically extruded bar steel (Hoescht Celanese GUR bar steel)£ * - ^. ¿SiJÍÉí *. L ßa! * I? ßaS &? * ¿&&&3 '& amp; > > .415 obtained from Westlake Plastics, Lenni, PA). The ream of GUR 415 used for the bar steel had a molecular weight of 5,000,000 g / mol and contained 500 ppm of calcium stearate. The bar steel was cut into cylinders in the form of "hockey discs" (height 4 cm, diameter 8.5 cm). The discs were heated to 100 ° C in air in an oven. The hot disks were then irradiated with an electron beam at a total dose of 20 Mrad at a dose rate of 2.5 Mrad per step (E-Beam Services, Cranbury, NJ), with a sweep width of 30 cm and a speed of conveyor of 008 cm / sec. After irradiation, the discs were heated at 150 ° C under vacuum for 2 hours, thus allowing the free radicals to recombine leading to substantially undetectable residual free radicals. The discs were then cooled to room temperature at a rate of 5 ° C. / min Example 10: Method for Forming PEPMUA Using Hot Irradiation and Adiabatic Fusion (IRC-FA) This example illustrates a method for forming PEPMUA which has an interlaced structure and has substantially undetectable free radicals, irradiating PEPMUA which has been heated below of the melting point and then fusion of the PEPMUA in such a way as to generate adibatic fusion of PEPMUA. The conventional PEPMUA extruded bar steel was used (Hoescht Celanese bar steel GUR 415 obtained from Westlake Plastics, Lenni, PA). The ream of GUR 415to A? & amp; . ^^ g | g ^ ^ used for bar steel had a molecular weight of 5,000,000 g / mol and contained 500 ppm of calcium stearate. The bar steel was cut into cylinders in the form of "hockey pucks" (height 4 cm, diameter 8.5 cm). 5 Two discs were packed in a fiberglass bag (obtained from Fisher Scientific Co., Pittsburgh, PA) to minimize heat loss in subsequent processing steps. First, the wrapped discs were heated overnight in afr air conduction oven maintained at 120 ° C. As soon as thediscs removed from the oven were placed under an electron beam incident to one of the circular phases of the disks from a linear electronic accelerator operated at 10 MeV and 1 kW (AECL, Pinawa, Manitoba, Canada), and immediately irradiated to a total dose of 21 and 22.5 Mrad, respectively. The dose regimen was2.7 Mrad / min. Therefore, for 21 Mrad, the radiation was for 7.8 min., And for 22.5 the radiation was 8.3 minutes. After the irradiation, the discs were cooled to room temperature of 5 ° C / minute, at which point the fiberglass bag was removed and the specimens were analyzed. Example 11: Comparison of the Properties of Steel Discs in Bar PEPMUA GUR 415 and Bar Steel Discs Treated with IRF-FS and IRC-FA This example illustrates various properties of irradiated and non-irradiated samples of bar steel from PEPMUA GUR 415obtained from Examples 8 and 10. The samples tested were thefollowing- (i) test samples (discs) of bar steel that was irradiated at room temperature, subsequently heated to approximately 150 ° C for complete melting of polyethylene crystals, followed by cooling to room temperature (IRF-5 FS), ( ii) test specimens (discs) of bar steel that were heated to 120 ° C in a glass fiber bag in a manner that minimizes the heat loss of the discs, followed by immediate irradiation for general adiabatic melting of the discs. polyethylene fr glasses (IRC-FA), and (iii) steel in control rod (withoutheating / melting, without irradiation). A. Fourier Transform Infrared Spectroscopy (IRTF) The infrared (IR) spectroscopy of the samples was carried out using a BioRad UMA 500 infrared microscope.thin sections of the samples obtained from examples 8 and 10. The thin sections (50 μm) were prepared with a drag microtome. The IR spectra were collected at 20 μm, 100 μm and 3 mm low from the irradiated surface of the disks with an aperture size of 10 x 50 μm2. The peaks observed around 1740 a1700 cm "1 were associated with oxygen-containing groups, Therefore, the ratio of the area under the carbonyl peak to 1740 cm" 1 to the area under the methylene peak to 1460 cm "1, after subtracting the lines of The corresponding base was a measure of the degree of oxidation, Tables 8 and 9 summarize the degree of oxidation forspecimens described in Examples 8 and 10.,. ".«., - .. «s-a ^ .. ^. ^. ^^ j ^ -u ^ zdaa *. ^ * ^^ ff-fj9uÉ¡I? 9é9Í99? 9 9k These data show * that after the entanglement procedures there was some oxidation within a thin layer of approximately 100 μm in thickness. When machining this layer, the fine product could have the same oxidation levels as the non-irradiated control. Table 8: Degree of oxidation of specimens of Example 8 (IRF-FS) (with fusion after vacuum irradiation) Degree of Oxidation at various cold depths (AU) Specimen 20 μm 100 um 3 mm Non-irradiated control 0.01 0.01 0.02 Irradiated a 2.5 Mrad 0.04 0.03 0.03 Irradiated at 5 Mrad 0.04 0.03 0.01 Irradiated at 7.5 Mrad 0.05 0.02 0.02 Irradiated at 10 Mrad 0.02 0.03 0.01 Irradiated at 12.5 Mrad 0.04 0.03 0.01 fr Irradiated at 15 Mrad 0.03 0.01 0.02 Irradiated at 17.5 Mrad 0.07 0.05 0.02 Irradiated at 20 Mrad 0.03 0.02 0.01FA1 Oxidation degree a (A.U.) Specimen 20 μm 100 μm 3 mm Non-irradiated control 0.01 0.01 0.02 Irradiated at 21 Mrad 0.02 0.01 0.03 Irradiated at 22.5 Mrad 0.02 0.02 0.01* B. Differential Scanning Calorimetry (CBD) A Perkin-Elmer CBD7 was used with a heating vessel with ice water and a heating and cooling rate of 10 ° C / minute with a continuous nitrogen purge. The crystallinity of specimens is obtained from Examples 8 and 10 was calculated from the weight of the sample and the heat of fusion of the crystals ofPolyethylene was measured during the first heating cycle. Percent crystallinity is given by the following equation-% crystallinity = E w,? H °where E and w are the heat of fusion (J or lime) and weight (gram) of the tested specimen, respectively, and where? H ° is the heat of fusion of 100% crystalline polyethylene in Joules / grams (291 J / go 69.2 cal / g). The temperature corresponding to the peak of the endothermy was taken as the melting point In some cases where they aremultiple endothermic peaks, the multiple melting points corresponding to these endothermic peaks have been reported. Thecrystallinity and melting points for the specimens described in Examples 8 and 10 are reported in Tables 10 and 11. Table 10: CBD at a heating rate of 10 ° C / min. for specimens of Example 8 (IRF-FS) Specimen Crystallinity (%) Melting Point (° C) Non-Irradiated Control 59 137 Irradiated at 2.5 Mrad 54 137 Irradiated at 5 Mrad 53 137* Irradiated at 10 Mrad 54 137 Irradiated at 20 Mrad 51 137 Irradiated at 30 Mrad 37 137Table 11: CBD at a heating rate of 10 ° C / min. for specimens of Example 10 (IRC-FA) Specimen Crystallinity (%) Melting Point (° C) Non-irradiated control 59 137 Irradiated at 21 Mrad 54 120-135-145 Irradiated at 22.5 Mrad 48 120-135-145The data shows that the crystallinity does not changesignificantly at the absorbed doses of 20 Mrad. Therefore, the elastic properties of the interlaced material should remain substantially unchanged when interlaced. On the other hand, elastic properties could be created by changing theCold crystallinity with higher doses. The data also show that the IRC-FA material exhibited three fusion peaks. C. Disc Bolt Experiments for Use Regime Disc bolt experiments (PED) were performed on a biaxial disc bolt tester at a frequency of 2 Hz where the polymer bolts were tested by a rubbing action of the pin against a highly polished Co-Cr disc. Before preparing the bolts in cylindrical form (height 13 mm,fr diameter 9 mm), a millimeter of the surface of thediscs in order to remove the outer layer that had oxidized during irradiation and after and before processing. The bolts were machined from the disk array and tested on the PED so that the e-beam incident surface was on the Co-Cr disk. The tests of use were carried out at atotal of 2,000,000 cycles in bovine serum. The bolts were weighed every 500,000 cycles and the average weight loss values (regime of use) were reported in Tables 12 and 13 for specimens obtained from Examples 8 and 10 respectively. Table 12: PED use regimes for specimens of 20 Example 8 (IRF-FS)fr Specimen Usage regime (mg / million cycles) Non-irradiated control 9.78 Irradiated at 2.5 Mrad 9.07 Irradiated at 7.5 Mrad 4.80 Irradiated at 5 Mrad 2.53 Irradiated at 10 Mrad 1.54 Irradiated at 16 Mrad 0.51 Irradiated at 20 Mrad 0.05 Irradiated at 30 Mrad 0.11Table 12: PED use regimes for specimens of Example 10 (IRC-FA)Specimen Usage regime (mg / million cycles) Non-irradiated control 9.78 Irradiated to 21 Mrad 1.15The results indicate that the interlaced PEPMUA was much higher than the resistance of use than the non-irradiated control D. Gel Content and Sponge Ratio 10 Samples were cut into cubes of size 2 x 2 x 2 mm 3 and kept submerged in xylene at 130 ° C for a period of 24 hours An antioxidant (N-phenol-2-naphthylamine 1%) was added to the xylene to prevent degradation of the sample. The relationship of, - ^ w-. The amount of frubbing and gel content was calculated by measuring the weight of the sample before the experiment, after sponging for 24 hours. hours and after vacuum drying of the swollen sample. The results are shown in Tables 14 and 15 for the specimens obtained from Examples 8 and 10. Table 14: Gel content and swelling ratio for specimens of Example 8 (IRF-FS) Specimen Gel Content (%) Ratio of Sponge Control Non-irradiated 89.7 12.25 Irradiated at 5 Mrad 99.2 464 Irradiated at 10 Mrad 99.9 2.48 Irradiated at 20 Mrad 99.0 2.12 Irradiated at 30 Mrad 99.9 2.06Table 15: Gel content and swelling ratio for 10 specimens of Example 10 (IRC-FA)) Specimen Gel Content (%) Sponge Ratio Control Not irradiated 897 1225 Irradiated at 21 Mrad 999 2.84 Irradiated at 22.5 Mrad 100 2 36The results show that the swelling ratio decreased with the increase in absorbed dose indicating an increase in the interlacing density. The gel contentincrease indicating the formation of an interlaced structureExample 12: Concentration of Free Radicals for PEPMUA Prepared by Cold Irradiation with and without Subsequent Fusion (IRF-FS) This example illustrates the effect of the subsequent fusion to 5 cold irradiation of PEPMUA on the concentration of free radicals. The electronic paramagnetic resonance (RPE) was carried out at room temperature on the samples after placing them in a hydrogen atmosphere in a quartz tube. air tight. The instrument used of the RPE spectrometerBruker ESP 300 and the tubes used were sample tubes of RPE Taperlok (obtained from Wilmad Glass Co, Buena, NJ). The non-irradiated samples had no detectable free radicals in them. During the irradiation process, free radicals were created which can last for at least a few yearsunder appropriate conditions ** Cold-irradiated PEPMUA specimens exhibited a strong free radical signal when tested with the RPE technique. When the same samples were examined with RPE following a melting cycle, the RPE signal was found reduced toundetectable levels. The absence of these radicals in the sample of molten (recpstakhnized) PEPMUA subsequently radiated in cold means that any diminution of oxidative degradation can occur via the attack to the trapped radicals.
Example 13: Crystallinity and Fusion Point to DifferentDepths of PEPMUA Prepared by Cold Irradiation and Subsequent Fusion (IRF-FS) This example illustrates the crystallinity and melting point at different depths of the interlaced PEPMUA specimens obtained from Example 8 with total radiation dose of 20 Mrad. Samples were taken at various depths of the interlaced specimen. The crystallinity and the melting point were determined- £ &- using a Perkin Elmer Differential Scanning Calorimeter aswas described in Example 10 (B). The results are shown in Table 16. Table 16: CBD at a heating rate of 10 ° C for the specimen of Example 8 irradiated at a total dose of 20 Mrad (IRF-FS) Depth (mm) Cropiness (%) Point of Fusion I ° C) 0-2 53 137 6-8 54 137 9-11 54 137 14-16 34 137 20-22 52 137 26-28 56 137 29-31 52 137 37-40 54 137 Unirradiated Control 59 137 15 The results indicate that the variability varied as a function of depth away from the surface. The sudden fall in 15 mm is the consequence of the cascade effect. The peak in the absorbed dose is localized to around 16 mm where the level of 5 doses could be as high as 27 Mrad. Example 14: Comparison of PEPMUA Prepared by IRF-FS Using Air Fusion Against Low Vacuum Fusion This example illustrates that the oxidation levels of the PEPMUA disks prepared by IRF-FS, either melted in air or under vacuum, are equal that the discs are not irradiated to a depth of 3 mm below the surface of the discs. The conventional PEPMUA hydraulically extruded bar steel (Hoescht Celanese bar steel GUR 415 obtained from Westlake Plastics, Lenni, PA) was used. The GUR 415 15 resin used for the bar steel had a molecular weight of 5,000,000 g / mol and contained 500 ppm of calcium stearate. The steel in fr bar was cut into cylinders in the form of "hockey pucks" (height 4 cm, diameter 8.5 cm). Two disks were irradiated at room temperature with a dose regime of 2.5 Mrad per step at 17.5 Mrad total absorbed dose as measured on the upper surface (incidence of e-rays) (AECL, Pinawa, Manitoba, Canada), with a sweeping width of 30 cm and a conveyor speed of 0.07 cm / sec Discs were not packed and irradiation was carried out in air. 25 After irradiation, a disk was heated under vacuum at 150 ° CJ ** Jt? Sdh .Jtt - was heated in air at 150 ° C for 2 hours, so that a state of undetectable residual crystalline content and residual, undetectable free radicals is obtained. The discs were then cooled to room temperature at room temperature. 5 regime of 5 ° C / min. The discs were analyzed for the degree of oxidation as described in Example 11 (A) Table 17 summarizes the results obtained from the degree of oxidation. Table 17: Degree of oxidation of molten specimens in cold air against vacuum After Fusion Degree of oxidation at various depths (AU) Specimen Environment 20 μm 100 μm 3 mm Non Irradiated Control N / A 0.01 001 002 Irradiated at 17.5 Mrad Vacuum 0.07 0.05 0.02 Irradiated to 175 Air 0.15 0 15 0.01"2 10 The results indicated that within 3 mm of the free surfaces of the oxidation level in the specimens of PEPMUA, the observed oxidation levels of PEPMUA were decreased, this was the case independent of theFusion atmosphere after irradiation (air or vacuum) Therefore, fusion could be performed after irradiation in an air conduction oven without oxidizing the matrix of the irradiated disk Example 15. Method for forming PEPMUA Using Cold Irradiation and Subsequent Fusion Using Range Irradiation (IRF-FS) or to form PEPMUA which has an interlaced structure and has substantially undetectable free radicals by cold irradiation with gamma radiation and then melting the PEPMUA. 5 The conventional PEPMUA hydraulically extruded bar steel (Hoescht Celanese bar steel GUR 415 obtained from Westlake Plastics, Lenni, PA) was used. The GUR 415 resin used for the bar steel had a molecular weight of 5,000,000 g / mol and contained 500 ppm of calcium stearate.bar was cut into cylinders in the form of "hockey pucks" (height 4 cm, diameter 8.5 cm) The discs were irradiated at room temperature at a dose rate of 0.05 Mrad / minute at a total absorbed dose of 4 Mrad as measured on the upper surface (incidence of lightningrange) (Isomedix Northboro, MA) The peaks were not packaged and the irradiation was carried out in air After irradiation, the frits were heated at 150 ° C low vacuum for 2 hours so that the polymer was melted and thus results in the recombination of free radicals leading to residual free radicalsSubstantially Not Detectable Example 16 'I Method for Forming PEPMUA Using Hot Irradiation and Subsequent Complete Fusion Adiabatic Fusion (IRC-FA) This example illustrates a method for forming PEPMUA havingan interlaced structure, exhibits two fusion endotherms• Feto-a-jatciiifr- '' ^? ^^^ iAs & ^ itÁ i ^ ii ^ Ái.jíii ?? ti, -? ~ I different and a differential scanning calorimeter (CBD) and has substantially free radicals not detectable, irradiating PEPMUA that has been heated to below the melting point so as to generate partial adiabatic fusion of PEPMUA and subsequently melting the PEPMUA. A bar steel GUR 4050 (made of GUR 4050 resin from Hydraulically extruded Hoescht Celanese obtained from Westlake Plastics, Lenni, PA) was machined into a 8.5 cm diameter and 4 cm thick hockey puck. Twenty-five discs, 25 aluminum fasteners and 25 glass fiber blankets of 20 cm x 20 cm at 125 ° C were preheated overnight in an air-conduction oven. The preheated disks were each placed in a preheated aluminum fastener which was covered by a preheated fiberglass mat to minimize the loss of heat to the vicinity during irradiation. The discs were then irradiated in air using 10 MeV, electron beam of 1 kW with a scan width of 30 cm (AECL, Pinawa, Manitoba, Canada). The conveyor speed was 007 cm / sec. which gave a dose regimen of 70 kGy per step. The discs were irradiated in two passages under the beam to achieve a total absorbed dose of 140 kGy. For the second step, the movement of the conveyor belt was reversed as soon as the discs were out of the scanning area of the electron beam to avoid any loss of heat from the discs. After the hot irradiation, 15 discs were heated to^ j ^^^ ej ^^ - ^^^^ J • 150 ° C for 2 hours so that he obtained the complete fusion of the crystals and substantial elimination of the free radicals. A. Thermal Properties (CBD) of the specimens prepared in Example 16 A Perkin-Elmer CBD 7 was used with a heat container in ice water and a heating and cooling regime of 10 ° C / min. with a continuous nitrogen purge. The crystallinity of the samples obtained from Example 16 was calculated from the weight of the# sample and the heat of fusion of polyethylene crystals (69.2 cal / gm). 10 The temperature corresponding to the peak of the endotherm was taken as the melting point. In the case of multiple endothermic peaks, multiple melting points were reported. Table 18 shows the variations obtained in the melting behavior and the crystallinity of the polymer as adepth function of the e-beam incidence surface. Figure 8 shows representative CBD fusion endotherms obtained 2 cm below the surface of the incidence of e-rays obtained both before and after the subsequent fusion.
-Neither* These results indicate that the fusion behavior of PEPMUA changes drastically after the subsequent fusion step in this modality of the IRC-FA process. Prior to the subsequent fusion the polymer exhibited three melting peaks, whilethat after the subsequent fusion exhibited two melting peaks. B. Electronic Paramagnetic Resonance (RPE) of the specimens prepared in Example 16 The RPE was carried out at room temperature in the samples obtained from Example 16 after placing the samples in an air-tight quartz tube in an atmosphere of nitrogen. The instrument used was the Bruker ESP 300 RPE Spectrometry and the tubes used were Taperlok RPE Sample tubes (obtained from Wilmad Glass Co., Buena, NJ) The non-irradiated samples did not have detectable free radicals in them. During the irradiation process, free radicals were created which can last for at least several years under appropriate conditions. Under the subsequent fusion, the RPE results showed a complex free radical peak composed of peroxy 20 and primary free radicals. After the subsequent fusion the RPE free radical signal was reduced to undetectable levels. These results indicated that the induced free radicals were the irradiation process were substantially eliminated after the subsequent fusion step Therefore the PEPMUA was highly resistant to oxidation.
Example 17: II Method for Heating PEPMUA Using Hot Irradiation and Partial Adiabatic Fusion with Subsequent Full Fusion (IRC-FA) This example illustrates a method for PEPMUA form having an interlaced structure, exhibiting two different fusion endotherms in CBD, and has substantially undetectable free radicals, by irradiation of PEPMUA which has been heated below the melting point so as to generate the partial adiabatic fr fusion of the PEPMUA and by subsequent fusion of the PEPMUA. 10 A GUR 4050 steel bar (made of hydraulically extruded Hoescht Celanese GUR 4050 resin obtained from Westlake Plastics, Lenni, PA) was machined into 8.5 cm diameter and 4 cm thick discs. Twenty-five discs, 25 aluminum fasteners and 25 fiberglass blankets of 20 cm x 20 cm at 125 ° C were preheatedovernight in an air conduction oven. The preheated disks were each placed in a preheated aluminum fastener which was covered by a mantle of preheated fiberglass to minimize the loss of heat to the vicinity during irradiation. The discs were then irradiated in airusing an electron beam of 10 MeV, 1 kW with a sweeping width of 30 cm (AECL, Pinawa, Manitoba, Canada) The conveyor speed was 0.07 cm / sec which gave a dose rate of 70 kGy per step The discs were irradiated in two passages under the beam to achieve a total absorbed dose of 140 kGy. For the secondOn the other hand, the movement of the conveyor belt was reversed as soon as the discs were removed from the scanning area of the electron beam to avoid any loss of heat from the discs. After the hot irradiation, 15 disks were heated at 150 ° C for 2 hours in order to obtain complete melting of the crystals and substantial removal of the free radicals. Example 18: III. Method for forming PEPMUA Using Hot Irradiation and Partial Adiabatic Fusion with Subsequent Complete Fusion (IRC-FA) fr This example illustrates a method for forming PEPMUA that hasan interlaced structure, exhibits two different fusion endotherms in CBD and has substantially undetectable free radicals, irradiating PEPMUA which has been heated to below the melting point so as to generate adiabatic partial fusion of PEPMUA and subsequently melting the PEPMUA. 15 A GUR 1050 bar steel (made from hydraulically extruded Hoescht Celanese GUR 1050 resin obtained from Westlake Plastics, Lenni, PA) was machined into 8.5 cm diameter and 4 cm thick hockey pucks. 18 disks, 18 aluminum fasteners and 18 20 cm x 20 glass fiber blankets were preheatedcm at 125 ° C, 90 ° C or 70 ° C, in an air conduction oven at night. Six discs were used for each different preheat temperature. The preheated disks were each placed in a preheated aluminum fastener which was covered by a mantle of preheated fiberglass to minimizethe loss of heat in the vicinity during irradiation. The discsthen they were irradiated in air using an electron beam of 10 MeV and 1kW with a scan width of 30 cm (AELC, Pinawa, Manitoba, Canada). The conveyor speed was 0.06 cm / sec. which has a dose regime of 75 kGy per step. The disks were irradiated in two steps under the beam to accumulate a total of 150 kGy of absorbed dose. For the second step the movement of the conveyor belt was reversed as soon as the discs left the electron beam tracking area to avoid any loss of heat from the discs. After the hot irradiation, half of the discs were heated at 150 ° C for 2 hours so as to obtain complete melting of the crystals and substantial removal of the free radicals. A. Thermal Properties of Prepared Specimens in Example 18 A Perkin-Elmer CBD 7 with a heat container in ice water was used for a heating and cooling rate of 10 ° C / min. with a continuous nitrogen purge. The crystallinity of the samples obtained from Example 18 was calculated from the weight of the sample and the heat of fusion of the polyethylene crystals (69.2 cal / gm). The temperature corresponding to the peak of the endotherm was taken as the melting point. In the case of multiple endothermic peaks, multiple melting points were reported. Table 19 shows the effect of preheating temperature on melting behavior and cpstatinality of the polymer. Figure 9 shows the CBD profile of an RC-FA disc at a preheat temperature of 125 ° C both before and after the subsequent melting.
^«Ft-vi - iWJ The results indicate that the fusion behavior of PEPMUA changed drastically after the subsequent fusion step in this modality of the IRC-FA process. Before the subsequent fusion, the polymer exhibited three fusion peaks, 5 while after the subsequent fusion it exhibited two melting peaks. Example 19: IV. Method for Forming PEPMUA Using Hot Irradiation and Subsequent Full-Fused Adiabatic Fusion (IRC-FA) 10 This example illustrates a method for forming PEPMUA that has an interlaced structure, exhibits two distinct fusion endotherms in CBD, and has substantially free radicals not detectable, irradiating PEPMUA that has been heated below the melting point so as to generate partial adiabatic melting of thePEPMUA by subsequent fusion of the polymer. A bar steel of GUR 1020 (made of hydraulically extruded Hoescht Celanese GUR 1020 resin from Westlake Plastics, Lenni, PA) was machined into 7.5 cm diameter and 4 cm thick hockey pucks. Ten discs, 10 aluminum fasteners and20 cm x 20 cm glass fiber blankets were preheated at 125 ° C overnight in an air conduction oven. The preheated disks were each placed in a preheated aluminum fastener which was covered by a mantle of preheated fiberglass to minimize the heat loss to the vicinityduring irradiation. The discs were then irradiated in air.asÉfatefeft. ';using a linear electron beam accelerator of 10 MeV, 1kW (AECL, Pinawa, Manitoba, Canada). The scan width and conveyor speed were adjusted to achieve the desired dose rate per step. The disks were then irradiated at 61, 70, 80, 5 100, 140 and 160 kGy of the total absorbed dose. For the absorbed dose of 61, 70, 80 kGy, the irradiation was completed in one step, while it was completed for 100, 140 and 160 in two steps. For each level of absorbed dose, six disks were irradiated. During the two-step experiments, for the second step the movement ofThe conveyor belt was reversed as soon as the discs left the scanning area of the electron beam to avoid any loss of heat from the discs. After irradiation, half of the discs were heated at 150 ° C for 2 hours in an air conduction oven so that fusion was obtainedcomplete of the crystals and substantial elimination of free radicals. Example 20: V. Method for Forming PEPMUA Using Hot Irradiation and Partial Adiabatic Fusion with Subsequent Complete Fusion (IRC-FA) 20 This example illustrates a method for forming PEPMUA having an interlaced structure, exhibiting two different fusion endotherms in CBD and has substantially undetectable free radicals, irradiating PEPMUA that has been heated below the melting point so as to generate partial adiabatic melting forthe PEPMUA and subsequently melting the polymerfr A GUR 4150 bar steel (made from GUR 4150 from hydraulically extruded Hoescht Celanese obtained from Westlake Plastics, Lenni, PA) was machined into 7.5 cm diameter and 4 cm thick hockey disks. Ten discs, 10 aluminum clips and 5 20cm x 20cm glass fiber blankets were preheated at 125 ° C overnight in an air-conduction oven. The preheated disks were each placed in a preheated aluminum fastener which was covered by a pre-heated glass fiber blanket to minimize the loss of heat to the vicinityduring irradiation. The disks were then irradiated in air using a 10-MeV, 1 kW linear electron beam accelerator (AECL, Pinawa, Manitoba, Canada). The sweep width and conveyor speed were adjusted to achieve the desired dose rate per step. . The discs were irradiated at 61, 70 80, 100, 140 and160 kGy of the total absorbed dose For each dose level absorbed, six disks were irradiated For the absorbed dose of 61, 70, 80 kGy, the irradiation was completed in one step, for 160 kGy, it was completed in two steps. After the irradiation, three discs of eachlevel of absorbed dose other than 150 ° C for 2 hours to completely melt the crystals and reduce the concentration of free radicals to undetectable levels A. Properties of the Specimens Prepared in Example 20A Perkin-Elmer CBD 7 was used with a water-on-ice heat container and a heating and cooling rate of 10 ° C per minute with a continuous nitrogen purge. The crystallinity of the samples obtained from Example 20 was calculated from the weight of the sample and the heat of fusion of polyethylene crystals (692 cal / gm). The temperature corresponding to the peak of the endotherm was taken as the melting point. in the case of multiple endotherm peaks, multiple melting points were reported. The results obtained are shown in Table 20 as a function of the total absorbed dose level. They indicate that the cpstatinity decreases with the increasing dose level At the absorbed dose levels studied. , the polymer exhibited two melting peaks (Ti = -118 ° C, T2 = -137 ° C) after the subsequent melting step00 r-?Example 21: Temperature Elevation During the IRC-FA Process This example demonstrates that the temperature rises during the hot irradiation process leading to partial or complete adiabatic fusion of the PEPMUA. A bar steel 4150 (made of GUR 4150 resin from hydraulically extruded Hoescht Celanese obtained from Westlake Plastics, Lenni, PA) was machined into a 8.5 cm diameter and 4 cm thick hockey disc. A hole was drilled in the center of the disc body. A type K thermocouple was placed in this hole. The disc was preheated to 130 ° C in an air conduction oven. The disk was then irradiated using an electron beam of 10 MeV, 1 kW (AECL, Pinawa Manitoba, Canada). The irradiation was carried out in air with a sweeping width of 30 cm. The 15 dose regimen was 27 kGy / min. and the disk was left stationary under the beam. The temperature of the disc was constantly measured during irradiation. Figure 11 shows the temperature rise in the disk obtained during the irradiation process. Initially, the temperature is the preheat temperature (130 °). As soon as the beam is turned on, the temperature increases during that time the crystals of PEPMUA are melted. There is the fusion of smaller crystals starting at 130 ° C. indicating that partial melting occurs during heating. Around 25 145 ° C there was an abrupt change in the behavior offull After that point, the temperature continues to rise in the molten material. This example demonstrates that during the IRC-FA process, the level of absorbed dose (duration of irradiation) can be adjusted to 5 partial or complete melting of the polymer. In the first case the fusion can be contemplated with an additional melting step in an oven to eliminate the free radicals. Example 22 Method for Forming PEPMUA Using Hot Irradiation and Adiabatic Heating with Subsequent Complete Fusion (IRC-FA) This example illustrates a method for forming PEPMUA having an interlaced structure, and having substantially undetectable free radicals, by irradiation of PEPMUA at a sufficiently high dose rate to generate adiabatic heating for 15 PEPMUA and subsequent melting of polymer A GUR 4150 bar steel (made from GUR 4150 resin from hydraulically extruded Hoescht Celanese obtained from Westlake Plastics, Lenni, PA) was machined in a hockey disk 8 5 cm in diameter and 4 cm thick. Twelve stationary discs, 20 in air, were irradiated at a dose rate of 60 kGy / min. using 10 MeV, 30 kW electrons (E-Beam Services, Cranbury, NJ). Six of the discs were irradiated at a total dose of 170 kGy, while the other six were irradiated at a total dose of 200 kGy At the end of the irradiation the temperature of the discs was greater than 100 ° C. ^^^ > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ crystals and reduce the concentration of free radicals to undetectable levels. A. Thermal Properties of the Specimens Prepared in Example 22 A Perkin-Elmer CBD 7 was used with an ice water heating vessel and a heating and cooling rate of 10 ° C per minute with a nitrogen purge# keep going. The crystallinity of the samples obtained from Example 22 was calculated from the weight of the sample and the heat of fusion of polyethylene crystals (69.2 cal / gm). The temperature corresponding to the endothermic peak was taken as the melting point. Table 21 summarizes the effect of total absorbed dose on the thermal properties of PEPMUA of IRC-FA both before and after subsequent fusion processes. The results obtained indicate a single melting peak both before and after the subsequent melting peak. Table 21: GUR 4150 bar of IRC-FA Peak T peak T dose after Crystallinity Crystallinity irradiation (kGy) after fusion after subsequent fusion irradiation (° C) subsequent (° C) subsequent irradiation (%) (%) 170 143.67 13707 58.25 45.27 200 143.83 136.73 54.74 43.28 «Example 23: Comparison of Tension Deformation Behavior of Unirradiated PEPMUA. PEPMUA Cold Irradiated and Subsequently Melt (IRF-FS) and PEPMUA hot-radiated and melted Adiabatically and Partially and subsequently 5 Melt (IRC-FA) This example compares the strain deformation behavior of PEPMUA in its unirradiated form and the forms irradiated via the IRF-FS and IRC-FA methods. * Normal type V ASTM D638 was used to preparespecimens of dog bone for stress test. The voltage test is carried out in an Instron Universal 4120 universal tester at a crossing speed of 10 mm / minute. The stress-fatigue behavior of the work was calculated from the load displacement data following ASTM D638. 15 Dog bone specimens were machined for discs^^ B GUR 4150 hockey (made from reams GUR 4150 from Hoescht Celanese hydraulically extruded from Westlake Plastics, Lenni, PA) that were tested for the IRC-FS and IRC-FA methods. For the IRC-FS, the method described in Example 8 was followed,while for IRC-FA, the method described in Example 17 was followed. In both cases, the total dose administered was 150 kGy. Figure 12 shows the tension behavior obtained from the non-irradiated control, specimens treated with IRF-FS and IRC-FA. 25 The variation of deformation behavior of, .Ale • 4 & amp; & amp; amp; amp; amp; amp; amp; amp; amp; amp; amp; amp; amp; amp; amp; amp; fr in PEPMUA treated with IRC-FS and IRC-FA, although in both methods irradiation was carried out at 150 kGy. This difference is due to the two-base structure generated using the IRC-FA method. Those skilled in the art will be able to ensure the use of no more than routine experimentation, many equivalents of the specific embodiments of the invention described herein. These and the other equivalents are intended to be encompassed by the following claims 10^^^^^^^ tóg ^^^^^^^^^^ j! ^^^^^^^ tá # &alímtofáté * ^^ uá ^^ hg