WO1992004410A1 - Films containing polyhydroxy acids and a compatibilizer - Google Patents

Abstract

This invention relates to certain compositions useful in making films and their preparation, which compositions comprise polyhydroxy acid (PHA) and a compatibilizer. It also relates to films comprising such compositions and other polymers.

Description

TITLE FILMS CONTAINING POLYHYDROXY ACIDS AND A COMPATIBILIZER

BACKGROUND OF THE INVENTION This invention relates to certain compositions useful in making films and their preparation, which compositions comprise polyhy^roxyacid (PHA) and a co patibilizer. It also relates to films comprising such compositions and other polymers- High molecular weight polymers of hydroxy acids and cyclic dimer products of esterification, of 2-hydroxy acids, particularly glycolic acid and lactic acid, are well known to be degradable. These materials can be useful in disposable packaging that will substantially and readily deteriorate to harmless by-products under conditions existing in the natural enviroment or employed in suitable waste treatment facilities. Highly useful films are made from many known polymers, such as polyolefins, polycarbonates, nylon and cellophane. The polyolefin films pose a waste disposal problem because by themselves they are not degradable in the environment. Polyolefin films have been rendered degradable to the extent of degeneration to polyolefin flakes, by incorporating starches into the polymer. While these polyolefin/starch blends have a number of uses such as garbage bags, their utility is limited because they are not transparen .

Schneider d iscloses in U.S. 2,703,316 the manufacture of film ro polymerized lactic acid, but does not disclose blends with compatabilizers and other polymers. The Encyclopedia of Polymer Science and Engineering, Mark, et al., 1987, discloses polymer blends and the use of compatibilizers but does not disclose any PHAs nor discuss degradability despite the long availibility of PHAs and their known degradability.

It is desirable to provide significantly degradable compositions which may be processed economically, and with high yield, into optically clear, robust, heat-sealable film for commercially useful packaging and other applications, which films may have a balance of physical properties that can be tailored for particular uses.

SUMMARY OF THE INVENTION According to the present invention, there is provided a composition comprising a polyhydroxy acid (PHA) and a compatibilizer. These compositions are useful to blend with another thermoplastic polymer resulting in a film that possesses to a substantial degree the properties of both polymers, particularly the transparency and degradability of the PHA.

There are further provided articles made by blending these ingredients.

DETAILED DESCRIPTION OF THE INVENTION

The significant degradability of the films produced by this invention is achieved by use of polyhydroxy acids. "Polyhydroxy acids" as used herein means polymers containing at least one hy^droxy acid unit selected from among:

(i) [0(CR'R")nCO)p (ii) (OCR'R"'COOCR^/R"CO)q (iii) (OCR'R"CR'R"OCR'R"CO)r (iv) (OCR'R"CR'R"ZCR'R CR'R"CO)s (v) copolymers of (i)-(iv) with non-hydroxy acid comonomers wherein n is 2, 4 or 5; p, q, r and s are integers, the total of which may range from about 50 to 5,000; R' and R^,/ independtly hydrogen, hydrocarbyl containing 1 to 12 carbon atoms, or substituted hydrocarbyl containing 1 to 12 carbon atoms; z is oxygen, sulphur, NH or PH. The PHA is present in amounts from 5-90 weight percent. The compatibilizer is present in amounts from 5 to about 75 weight % of the PHA/compatibilizer composition. As discussed in the Mark et al., reference above, compatibilizers are compositions that when introduced into a blend of substantially immiscible polymers will bring about an intimate blending of the polymers that does not exhibit gross symptoms of polymer segregation. The compatibilizer brings about a compatible blend that is homogeneous on a macroscopic level; a blend that is heterogeneous on a macroscopic level is not compatible. In its broadest concept, a compatibilizer is specific for specific polymer blends because it must contain chemical components that are compatible with each of the other polymers. In the present invention the compatibilizers must all contain a chemical or physical ability to be compatib-ilized with the PHA and also with the other part^ ular polymer component. Thus, depending on what ether polymer component is to be blended and rendered compatible with the particular PHA, the selection of an^effective compatibilizer will be made based on the know., chemical and physical characteristics of the other polymer component of the blend. If more than a single polymer is present in the other polymer component, more than one compatibilizer may be required to give a homogeneous blend. Examples of compatibilizers that, when mixed with PHAs will give compatible compositions, are listed in Table I.

TABLE I

PHA Composition Compatibilizer Other Polymer polyglycolic acid ethylene/vinyl polyethylene homopolymer acetate copo¬ lymer

polyglycolic/poly- ethylene/carbon polyethylene lactic copolymer monoxide co- polymers

polyglycolic/poly- ethylene/maleic polyethylene lactic copolymer anhydride graft polymer

polyglycolic/poly- ethylene-proply- polyethylene lactic copolymer ene/maleic anhy¬ dride graft polymer

polylactic acid ethylene/maleic polyethylene anhydride graft polymer

The amount of compatibilizer needed will vary depending on the relative amounts of PHA and the overall PHA/compatibilizer/polymer blend proportions.

The polymer other than those of formalae (i) to (v) in the preferred compositions is present in amounts up to about 90 weight % of the final 3 or more component product. The F ./compatibilizer compositions of this invention are p-...-.pared by dry mixing or melt blending the PHA with a compatibilizer that is compatbile with the PHA and the particular 3rd component other polymer.

The films of this invention are prepared by melt processing the PHA/compatibilizer/polymer compositions under sufficient mechanical agitation to obtain a uniform composition that is a solution or intimately homogeneous small particle blend. The film product is ther ormed by conventional techniques, such as solution casting, extruding, or tubular blowing, to produce a film of uniform thickness normally from about 0.01 to 2 mm. In formula (v) examples of suitable non-hydroxy acid comonomers include those capable of condensation pol^ aerization with ?- .-ctide or lactic acid; i.e., lactones such as epsilon-caprolactone, beta-propiolactone; alpha-dimethyl-beta-propiolactcne; glycolide; and dodecanolaσtone and lactams. For a ore complete list see U.S. 4,800,219 at column 9, line 27.

Polyhydroxy acid containing compositions of this invention have average molecular weights at le_^st high enough to provide sufficient viscosity and strength to form sustainable film from the total polymer melt. For the PHA, weight average molecular weights from about 2,000 to about 600,000 can be used. Preferably a molecular weight of the PHA from about 20,000 to about 450,000 is used where the PHA comprises over half of the polymer content of the final film produc containing the other compatibilizer polymer; and 4,00-. ro 20,000 where the PHA comprises less than half of the polymer content of the final film product. The term "degradable" as used here with respect to the polyhydroxy acids means that the polyhydroxy acid portion of the degradable material is biodegradable and, more importantly, degradable by hydrolysis. The degradation rate is consistent with its intended usage, i.e., the product does not degrade significantly in normal storage and usage, but will degrade in a reasonable time, after discarding.

The hydrolytic degradation of a polymer can be tailored readily to meet the requirements of use and disposal of the film. It depends primarily on the nature of groups in the chains.

Certain conditions such as moisture, pH, temperature, ion strength, sunlight, enzymes, polymer crystallinity and hydrophilicity of the polymer affect degradation of the polymer, as is well known.

Rate of degradation of polyhydroxy polymers can be too great for many typical packaging applications (i.e., the packaging film will deteriorate excessively in less time than the expected shelf-life of the package, which includes the warehousing time of the packaging film between its production and application of the product) . The reduced tensile strength of the film caused by the deterioration results in film ruptures while being processed on shrink-wrap machinery and would be unacceptable for commercial packaging applications. Also, the amount of shrinkage or the resistance of the films may be inappropriate for particular uses. These deficiencies can be controlled by incorporating a non-polyhydroxy polymer in the polymer composition. Non-polyhydroxy polymers are those which will produce films having clarity that does not obscure or distort graphics. Preferred non-polyhydroxy r lymers of this invention include polyolefins, polyet rs, polyesters, polyamides, polyvinyl chlorides, polycarbonates, polysulfones, copolyetheresters, polyurethanes, ethylene/vinyl alcohol copolymers, copolyamidoetheresters, ethylene/vinyl ester copolymers and terpolymers,ethylene/acrylic acid and terpolymers and their metal salts, ethylene-carbon monoxide copolymers, and copolyetherimidoesters. "Hazy" products, outside the scope of this invention, have impaired transparency caused by insufficient compatibilization, extruding of low molecular weight plasticizer to the surfaces of the films, high crystalline content of the starting polymer, and the like.

The term "ambient temperature" means the highest temperature at which the film product will be exposed during use or storage. Normally, this will range from room temperature (20"C) or below when under refrigeration, up to 40^βC or more when in warehouse storage.

Preferred polyhydroxy acids of this invention are those wherein 50-99 mol% is the PHA component composed of hydroxy acid units (i) wherein R' is hydrogen and R" is the methyl radical, and having 80-97 mol% of asymmetric carbon atoms R- configuration and 3-20 mol% S- configuration or 80-97 mol% S- configuration and 3-20 mol% R- configuration; and wherein 1-45 mol% is tfc-> minor component composed of either^hydroxy acid unit (i) of such asymmetric carbon content that the total R- or S- configuration in major and minor components do not exceed 97 mol% of asymmetric carbon atoms, or any hydroxy acid units (ii) to (iv) or suitable non-hydroxy acid comonomers. Explaination of these preferred polyhydroxy acids is effectively achieved by example. A preferred polyhydroxy acid may, for example, contain a major component of 67 mol% hydroxy acid unit (i) in which 90 mol% of asymmetric carbon atoms are S- configuration. In this example, the minor polyhydroxy acid component will be 35 mol%, and might be completely composed of hydroxy acid unit (ii) or a suitable non-hydroxy acid comonomer. In this same preferred example, the minor component of the PHA might be additional hydroxy acid unit (i) but the fraction of asymmetric carbon atoms which are S- configuration component can be no greater than that which when added to the S- atoms of the PHA component does not raise the S- atom content of the total above 97 mol%.

In more preferred embodiments of this invention, the range of R- and S- asymmetric carbon atoms in the polyhydroxy acid is 85-96 mol%.

In deciding the relative R- and S- contents, consideration must also be given to having a PHA that has a melting point close to the melting point of the other polymer so as to promote maximum processibility and ultimate product properties. Thus, in some compositions a very high content of R- may be less desirable.

The terms "R-" and "S-" refer to the standard nomenclature for identifying stereoisomer configurations on the asymmetrical carbon. The percentages of R- and S- carbons indicated herein refer only to fractions of asymmetrical carbon atoms in the PHA polymer chains and not to total carbon atoms in the polymer chains. Asymmetrical carbon atoms are those having less than four different substituent radical groups attached to them. The preferred compositions have narrow ranges of selected asymmetrical carbon atoms because polymers containing more equal fractions of R- and S- carbon atoms demonstrate accelerated degradation by hydrolysis, produce films adjacent layers of which often adhere to each other and which are prone to degradation during processing to form film.

Also, films made outside these ranges may be hazy and/or brittle. For example, polymer films having fractions above the S- carbon atom range are substantially crystalline after hot processing, such as in film production. Crystallinity is detrimental to film-forming capability, and to optical clarity of films formed from crystalline polymers. A method for reducing the negative effects of highly crystalline polymer on film properties is to plasticize the polymer by incorporating and dispersing monomeric, low molecular weight oligomeric^'species within the polymer matrix. Plasticizers for polyhydroxy acids of this invention are monomeric hydroxy acids, lactides of monomeric hydroxy acids, lactyl lactate non-cyclic dimers of monomeric hydroxy acids and other oligomers of monomoric hydroxy acids up to molecular weight of about 450. However, amounts of plasticizers produces films of uneven thickness. Where films are made by casting onto drums, excessive plasticizer may separate from the film, stick to and foul the drum, or may cause the film to stick to the drum. Thus, it has been found necessary to use polymer containing a minimal 3mount of plasticizer. The amount of plasticizers need ; to obtain useful films of this invention is from about 0.10 to about 8 wt%, and preferably from about 0.2 to 6 wt%. A highly preferable composition range is from about 0.2 to 0.4 wt% plasticizer. These plasticizer levels are based upon the concentrations of the polyhydroxy acid and plasticizer in the feedstock to the film production process and not necessarily to the concentrations of the plasticizer in the film produced from compositions of this invention. Plasticizer content may be determined by lactide content analysis methods taught in Journal of Applied Polymer Science, Kohn, Van den Berg, Van de Ridder and Feyen, volume 29, pages 4265-4277 (1984) . When necessary to reduce the concentration of plasticizers in a plasticizer-rich composition, a devolatilizing extruder can be used either as a separate step or during film extrusion.

EXAMPLES

The compatibilizers used in these Examples are: TRX-101 HF™ (Du Pont Co.), aleic anhydride grafted on ethylene-propylene copolymer; Elvax™ 360 (Du Pont Co.), a copolymer of ethylene and vinyl acetate; Fusabond™ D-100 and Fusabond™ D-111 (Du Pont Co.), maleic anhydride grafted on PE; and Nucrel™ 0407 (Du Pont Co.) and Nucrel™ 0903(Du Pont Co.) copolymer of ethylene and acrylic acid. Suryln™ Ionomer #1650 and #1601 (Du Pont Co.) are Nucrel™ salts. EMA™ 2205 and 2207 (Chevron) are ethylene and methylacrylic acid copolymers. These compatibilizers all have both hydrophyllic and hydrophobic end groups. Examples 1-5

A 50% polylactic acid/50% polyglycolic acid (PLA/PGA) copolymer is prepared by heating a mixture of 1667g of crystalline glycolic acid, 1894g of R-lactic acid, and 3.3g of stannous octoate. The reaction is heated from room temperature to 136^βC under atmospheric pressure. The pressure is then reduced to 100mm. while heating over 3 hrs. to 190^βC. -li¬ lt is then heated for an additional 5 hours at 190°C under 2mm v< αu . There is produced a 50/50 copolymer with an average molecular weight of 6000 with a softening point of about 120"C. Blends, as shown in Table I, are then prepared using low-density polyethylene (LDPE) , Exxon #3060, with a melt index of 2.0; and the compatibilizers listed in Table I. The above described 50/50 copolymer, the LDPE, and the compatibilizer are mixed together in a Banbury mixer above the melting points of the three ingredients and then is crushed to 1/4" average diameter particles. The particles are then dried in an oven.

Thereafter, blown films are prepared as follows: The particles are then fed to a screw feeder having a 1" dia eter die. It is maintained at 175-225*C in tht- heating and melt zones. The screw is run at 32 rpm. Films are tnen extruded ar. - conventionally blown to 2-4 mil. (.05-.lmm) thickness.

Examples 1, 4 and 5 are first tested and then are heated in distilled water for 28 days at 70°C. Table II shows the results of these tensile tests in PSI before and after the water treatment. MD is the extrusion direction; TD is the transverse or circumferential direction.

TABLE II - Tensile Properties

After H?Q Treatment MD TD

2706 2695 2654 1586

2940 2275

The tensile strength (at break) numbers of

Examples 4 and 5 this invention show high strengths as blown compared to Example 1 (100% PE) , and also shows lower strengths (degradation) after water treatment. Similar films are prepared by casting the film directly without blowing. These films have similar properties of strength, clarity and degradability.

Example 7 Several films are blown on commercial equipment .04-.05mm thickness from a blend containing 10% of 50/50% PLA/PGA copolymer, 10% of Elvax™ 360, and 80% of LDPE (Exxon 3060) . These films of the present invention are clear and flexible and have elongations at break and tensile strengths^' comparable to a 100% LDPE control. Accelerated tests are run on these films simulating exposure to municipal sewage in a treatment plant bio-digester. After 5 days exposure a biological oxygen demand is (BOD) of 300ppm is obtained. After 20 days the BOD is increased further to 1400ppm. The films are completely broken down by the biological degradation of + ιe PLA/PGA component of the films.

Comparative film of 100% LDPE has inferior strength and elongation properties and does not degrade in the simulated sewage test. Example 8

As in Example 1, PLA of inherent viscosity of 1.1 is blended in a Banbury mixer in a 1:2 ratio with Fusabond™ D-111. The resulting blend is crushed to 1/4" average diameter particles and blown films are made as in Example 1. The resulting films are significantly degradable.

Claims

We claim:

1. A composition comprising

(I) 5 to 95% of a polyhydroxy acid containing at least one unit selected from the group selected from: (i) [0(CR^,R")n CO)p (ϋ) (OCR'R"COOCR'R"CO)q (iii) (OCR'R"CR'R"OCR'R"CO)r (iv) (OCR'R"CR'R"ZCR'R"CR'R"CO)s

(v) copolymers of (i)-(iv) with non-hydroxy acid comonomers wherein n is 2 , 4 or 5; p, q, r and s are integers, the total of which are about 350-5,000; R' and R" are independently hydrogen, hydrocarbyl containing 1-12 carbon atoms, or substituted hydrocarbyl containing 1-12 carbon atoms; z is oxygen, sulfur, NR' or PR'; and

(II) 5 to 75% of a compatibilizer.

2. The composition of claim 1 containing up to 90% of another thermoplastic polymer that is compatible with the combination of ingredients (I) and (II).

3. The composition of claim 2 wherein the thermoplastic polymer is selected from the group consisting polyethylenes and polypropylenes.

4. The composition of claim 1 which contains polyhydroxy acid (I) in amount 30-60% and the compatibilizer in amount 40-70% of the total composition by weight.

5. The composition of claim 1 in which the polyhydroxy acid is selected from the group consisting of polyglycolic acid, polylactic acid and their copolymers.

6. The composition of claim 1 in which the compatibilizer is a selected from a ethylene/maleic anhydride graft polymer and a ethylene/oxide ethylene copolymer.

7. A film containing the composition of claim

2.

8. A film of claim 7 that is clear.

9. A film of claim 7 which comprise by weight polyhydroxy acid (I) 5-15%; compatibilizer (II) 5-20%, and thermoplastic polymer 60-90% of the film.

10. A process for producing films which compromises intimately blending the dry components of claim 2; heating to melt the blended components; forming a film from the melt; and cooling to solidify the film.

11. The process of claim 10 wherein the film is formed by extruding.

12. The process of claim 10 wherein the extruded film is blown.