CN112694591A - Preparation method of silane coupling agent modified solvent-free waterborne polyurethane - Google Patents

Abstract

The invention discloses a preparation method of silane coupling agent modified solvent-free waterborne polyurethane, which comprises the following preparation steps of 1) drying polyol, and controlling the water content in the polyol to be lower than 0.05%; 2) uniformly mixing the polyol dried in the step (1) with isocyanate, heating to react, then adding a chain extender, a hydrophilic chain extender and 1 part of catalyst, and uniformly mixing to obtain a solvent-free waterborne polyurethane prepolymer; 3) adding an alkaline aqueous solution into the solvent-free aqueous polyurethane prepolymer in the step (2), fully mixing and emulsifying under high-speed stirring to obtain an aqueous polyurethane emulsion; 4) and (3) reacting the solution system obtained in the step (3) with a compound containing two or more amino groups, then adding a silane coupling agent, and after complete reaction, dropwise adding a defoaming agent to obtain the silane coupling agent modified solvent-free waterborne polyurethane. The preparation method is simple in preparation process, and the prepared solvent-free waterborne polyurethane is excellent in mechanical property and heat resistance.

Description

Preparation method of silane coupling agent modified solvent-free waterborne polyurethane

Technical Field

The invention relates to the technical field of polymer synthesis, in particular to a preparation method of silane coupling agent modified solvent-free waterborne polyurethane.

Background

Polyurethane (PU) is a generic name for high-molecular polymers containing repeating urethane units (-NHCOO-) in their molecular structure. The Waterborne Polyurethane (WPU) is a transparent or opaque liquid formed by dispersing polyurethane particles in water serving as a dispersion medium, and is a high-performance high-molecular compound. The solvent type polyurethane paint not only retains the excellent performances of wear resistance, low temperature resistance, fatigue resistance and good flexibility of solvent type polyurethane, but also has the advantages of no toxicity, no flammability, no environmental pollution, easy modification and the like, and can be widely applied to the fields of paint, adhesive, automobile paint, fabric coating, leather finishing agent and the like.

However, because the aqueous polyurethane uses water as a solvent, and the surface tension of the medium water is large and the enthalpy is high, the problems of poor surface spreading, low film-forming hardness, poor mechanical properties, poor high-temperature resistance and the like of the polyurethane in the film-forming process can be caused. The silane coupling agent can be used for modifying waterborne polyurethane, and Si-O bonds in molecular chains of the silane coupling agent have strong cohesive energy and lower surface energy, so that the silane coupling agent is enriched to the surface in the drying process of an adhesive film, and can endow the modified products with excellent high temperature resistance and good mechanical property.

Disclosure of Invention

The technical problem to be solved by the invention is as follows: the method for preparing the waterborne polyurethane with better mechanical property and heat resistance by modifying the silane coupling agent is developed, the preparation process of the silane coupling agent modified solvent-free waterborne polyurethane is completely solvent-free, environment-friendly and pollution-free, and the preparation process is simple, and the prepared solvent-free waterborne polyurethane has the characteristics of excellent mechanical property and good heat resistance.

A preparation method of silane coupling agent modified solvent-free waterborne polyurethane comprises the following raw materials in parts by mass and reaction steps:

(1) drying 100-300 parts of polyhydric alcohol under the vacuum condition for 0.5-2 h at the temperature of 100-130 ℃, controlling the water content in the polyhydric alcohol to be lower than 0.05%,

wherein the polyol is one or more of polyol monomers such as polyether polyol, polyester polyol, polycarbonate polyol, polytetrahydrofuran polyol, polycaprolactone polyol and the like, and the number average molecular weight of the polyol is 500-4000;

(2) uniformly mixing the dried polyol in the step (1) with 30-80 parts of isocyanate, heating to 70-100 ℃, reacting for 1-2 hours, then adding 0-4 parts of chain extender, 5-10 parts of hydrophilic chain extender and 1 part of catalyst, uniformly mixing, reacting for 2-5 hours at 70-100 ℃, and obtaining the solvent-free waterborne polyurethane prepolymer,

wherein the chain extender, the hydrophilic chain extender and the catalyst are dried, the water content is lower than 0.05%, and the isocyanate is any one or more of isophorone diisocyanate, dicyclohexyl diisocyanate, hexamethylene diisocyanate and toluene diisocyanate.

(3) And (3) adding an alkaline aqueous solution into the solvent-free aqueous polyurethane prepolymer in the step (2), fully mixing and emulsifying for 10-30min under high-speed stirring to obtain the aqueous polyurethane emulsion.

Wherein, the alkali is one or more of triethylamine, diethanolamine, triethanolamine, sodium hydroxide, sodium bicarbonate, sodium acetate and ammonia water, the water is deionized water, and the solid content of the system is 20-50% in the emulsification process;

(4) and (3) reacting the solution system obtained in the step (3) with a compound containing two or more amino groups for 10-30min, then adding a silane coupling agent, dropwise adding a defoaming agent after complete reaction, reacting at a constant temperature of 50-70 ℃ for 1-1.5 h, cooling to room temperature, filtering the obtained final emulsion, and thus obtaining the silane coupling agent modified solvent-free waterborne polyurethane.

As a further improvement of the scheme, the polyol, the chain extender and the hydrophilic chain extender are dried by a vacuumizing method, the drying temperature is 100-130 ℃, the air pressure is more than or equal to-0.08 MPa, and the catalyst is dried by a blast drying oven at 100 ℃.

As a further improvement of the scheme, the dosage of the catalyst in the step (1) accounts for 0.1-0.5% of the total mass of the polyol and the isocyanate, and the solid content of reactants is 20-50%.

In a further improvement of the scheme, in the step (1), the polyol is one or more of polytetrahydrofuran ether glycol, polyethylene glycol, polypropylene glycol and polyglycerol, and the molecular weight of the polyol is 1000-4000.

As a further improvement of the scheme, in the step (2), the chain extender is any one or more of ethylene glycol, 1, 4-butanediol, trimethylolpropane and glycerol, the hydrophilic chain extender is any one or more of dimethylolpropionic acid and dimethylolbutyric acid, and the catalyst is any one or more of dibutyltin dilaurate, stannous octoate and organic bismuth.

As a further improvement of the scheme, in the step (4), the chain extender is one or more of isophorone diamine, diethylenetriamine and triethylene tetramine, and the silane coupling agent is at least one of vinyl trimethoxy silane, vinyl triethoxy silane, vinyl triisopropoxy silane, monoamino trimethoxy silicon, n-octyl triethoxy silane and gamma-aminopropyl triethoxy silane.

As a further improvement of the scheme, the reaction temperature in the step (2) is 80-100 ℃, the neutralization and emulsification temperature in the step (3) is 40-80 ℃, and the post-chain extension temperature in the step (4) is 60-90 ℃.

As a further improvement of the scheme, the solvent used in the steps (1), (2) and (3) is deionized water.

As a further improvement of the scheme, the solvent-free waterborne polyurethane is a segmented copolymer and is formed by alternately forming a hard segment consisting of isocyanate and chain extender micromolecules and a soft segment consisting of polyol, and the number average molecular weight of the solvent-free waterborne polyurethane is 5000-8000.

Compared with the prior art, the invention has the following beneficial effects:

according to the preparation method of the silane coupling agent modified solvent-free waterborne polyurethane, the solvent used in the whole process is only deionized water, and organic solvents such as toluene, acetone, butanone, N-methylpyrrolidone and the like are not used, namely, any organic solvent is not added in the synthesis process, so that the subsequent step of removing the organic solvent is omitted, the production cost is reduced, the preparation method is more environment-friendly, and the effects of no solvent, environment friendliness and no pollution are achieved;

compared with the prior art, the invention has the following beneficial effects:

1) the silane coupling agent is successfully connected into the waterborne polyurethane system in a chemical bond mode for modification, so that the defects of poor mechanical property and high temperature resistance of the original polyurethane are overcome;

2) the prepared silane coupling agent modified solvent-free waterborne polyurethane emulsion has the advantages of low viscosity, excellent storage stability, excellent mechanical property after film forming and good high temperature resistance. Tests show that the emulsion can be stably stored for more than 6 months, the tensile strength of a formed film can reach more than 50MPa, and the film is baked at 120 ℃ for 7 days without obvious yellowing and stickiness;

3) the preparation method of the amino silane coupling agent modified waterborne polyurethane has the advantages of simple process, easily controlled conditions and easy realization of large-scale production.

Drawings

FIG. 1 is a diagram showing the state of the resin of example 1 after baking at 120 ℃ for 7 days;

FIG. 2 is a state diagram showing the resin of example 2 after baking at 120 ℃ for 7 days;

FIG. 3 is a diagram showing the H-203NB resin film after baking at 120 ℃ for 7 days.

FIG. 4 shows that the silane coupling agent-modified solvent-free aqueous polyurethane obtained in examples 1 to 2 and a commercially available product H-203NB were applied to an impregnation process of an aqueous microfiber to prepare an aqueous suede microfiber product.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more clear, the present invention is further described with reference to the following embodiments:

the names, source manufacturers, specifications and types of raw materials used in the following examples are shown in Table 1.

TABLE 1 raw materials and raw material specifications

The viscosity of the present invention was tested according to GB/T2794-; the mechanical property of the invention is carried out according to GB/1040-; the high temperature resistance of the present invention was observed by allowing the polyurethane film to stand at 120 ℃ for 7 days to observe the change in appearance of the film.

The preparation method of the silane coupling agent modified solvent-free waterborne polyurethane comprises the following steps:

the method comprises the following steps: drying of polyether polyols

Weighing 100-300 g of polyether polyol into a four-neck flask provided with a stirrer, a thermometer, a constant pressure funnel and a vacuum pump, simultaneously opening the stirrer, an oil bath pot and the vacuum pump, raising the temperature to 100-130 ℃, adjusting the pressure to be less than or equal to-0.08 MPa, and keeping the conditions for constant-temperature and constant-pressure drying for 0.5-2 hours until the water content of the polyol is less than 0.05% (the mass of water in the polyol accounts for the total mass of the polyol).

Step two: preparation of solvent-free waterborne polyurethane prepolymer

And (2) reducing the temperature of the polyol obtained in the step (1) to be below 80 ℃, adding 30-80 g of diisocyanate into the polyol by using a constant-pressure funnel, uniformly stirring, gradually increasing the temperature to 70-100 ℃, reacting at a constant temperature for 1-3 h, then cooling to be below 80 ℃, adding 0-4 g of dried chain extender, 5-10 g of dried hydrophilic chain extender and 0.65-5 g of catalyst, uniformly stirring, gradually increasing the temperature to 70-100 ℃, and carrying out chain extension reaction for 2-5 h under the constant-temperature condition to obtain the solvent-free waterborne polyurethane prepolymer.

Note: in the synthesis method, the used chain extender and the water-based chain extender are dried until the water content is less than 0.05 percent; the used chain extender and the water-based chain extender can synthesize the polyurethane prepolymer with a certain molecular weight, and simultaneously can uniformly introduce hydrophilic functional groups into a molecular chain, thereby improving the emulsification of the polyurethane prepolymer in water.

Step three: neutralization and emulsification of prepolymer

Transferring the prepolymer into an emulsifying kettle, opening a stirring device, adding 3-8 g of neutralizing agent, stirring for 5-20 min for neutralization, then adjusting the rotating speed to high-speed stirring, quickly adding 400-700 g of deionized water, and stirring at high speed for 10-30min until the prepolymer is completely and uniformly dispersed.

Step four: back chain extension and silane coupling agent modification of solvent-free waterborne polyurethane

And (3) the polyurethane prepolymer and a rear chain extender are further subjected to chain extension reaction in an aqueous solution to further improve the molecular weight of the polyurethane, and the specific step is to slowly add 10-70 g of the rear chain extender with the mass fraction of 10-30% into the solution (3) to react for 10-30 min. And then slowly dripping 2-10 g of silane coupling agent and 3-8 g of defoaming agent, uniformly stirring, slowly heating to 50-80 ℃, carrying out heat preservation reaction for 1-1.5 h, stopping the reaction, then cooling until the temperature reaches room temperature, and finally filtering to obtain the silane coupling agent modified solvent-free waterborne polyurethane.

Example 1

The method comprises the following steps: drying of polyether polyols

Firstly, 25g of polytetrahydrofuran ether glycol (PTMG2000) and 155g of polyethylene glycol (PEG2000) are added into a 500ml four-neck flask with an electric stirring device, a thermometer, a constant pressure funnel and a vacuum pump, then the electric stirring device is started to stir, an oil bath pot is started to heat up, the vacuum pump is started to vacuumize the four-neck flask, when the temperature on the four-neck flask reaches 105 ℃ and the vacuum pressure is less than or equal to-0.08 MPa, the time is started, the temperature is kept between 105 ℃ and 110 ℃, and the pressure is less than or equal to-0.08 MPa, and the vacuum dehydration is carried out for 2 hours.

Step two: preparation of solvent-free waterborne polyurethane prepolymer

And when the water content in the polyol is less than 0.05%, closing the vacuum pump, reducing the temperature of the oil bath pot, when the temperature of the thermometer is reduced to 75 ℃, slowly adding 50g of isophorone diisocyanate through a constant-pressure funnel, stirring uniformly after the addition, starting to heat, and when the temperature reaches 90 ℃, starting to time and perform constant-temperature reaction for 1 hour. Then cooling to 75 ℃, adding 2g of dried 1, 4-butanediol, 9g of dried dimethylolpropionic acid and 8 drops (about 0.7g) of stannous octoate, stirring uniformly, gradually heating to 85 ℃, and carrying out constant-temperature chain extension reaction for 3 hours to obtain the solvent-free aqueous polyurethane prepolymer.

Step three: neutralization and emulsification of prepolymer

And immediately transferring the obtained prepolymer into an emulsifying kettle to obtain 228.54g of prepolymer, then adding 5g of dimethylethanolamine into the prepolymer, stirring for 5 minutes, increasing the stirring speed to 2000r/min after the prepolymer is completely neutralized, quickly adding 500g of deionized water, and stirring at a high speed for 10 minutes.

Step four: back chain extension and silane coupling agent modification of solvent-free waterborne polyurethane

And (3) slowly adding 31.6g of the isophorone diamine solution diluted to 20% by mass by using deionized water into the emulsion obtained in the third step, and stirring at a high speed for 10min after the addition is finished. Then slowly dripping 5.6g of gamma-aminopropyltriethoxysilane (KH-550), continuously stirring at high speed for 10min, dripping 0.2g of defoaming agent, reducing the stirring speed to 800r/min, and stirring for defoaming for 5 min. And then transferring the mixture into a 1000ml three-neck flask with a thermometer and a stirring device, opening the stirring device and an oil bath pot, heating while stirring, keeping the temperature constant for reaction for 1 hour when the temperature is raised to 60 ℃, turning off the oil bath pot to start cooling, and filtering the emulsion when the temperature is lowered to room temperature to obtain the silane coupling agent modified solvent-free waterborne polyurethane.

Example 2

The method comprises the following steps: drying of polyether polyols

50g of polytetrahydrofuran ether glycol (PTMG2000), 120g of polypropylene glycol (PPG3000) and 12g of polyethylene glycol monomethyl ether (YMR-N120) are added into a 500ml four-neck flask with an electric stirring device, a thermometer, a constant pressure funnel and a vacuum pump, then the electric stirring device is started to stir, an oil bath pot is started to heat up, the vacuum pump is started to vacuumize the four-neck flask, when the temperature on the four-neck flask reaches 110 ℃ and the vacuum pressure is less than or equal to-0.08 MPa, the timing is started, the temperature is kept between 110 ℃ and 120 ℃, and the pressure is less than or equal to-0.08 MPa, and the vacuum dehydration is carried out for 2 hours.

Step two: preparation of solvent-free waterborne polyurethane prepolymer

And when the water content in the polyol is less than 0.05%, closing the vacuum pump, reducing the temperature of the oil bath pot, when the temperature of the thermometer is reduced to 75 ℃, slowly adding 45g of hexamethylene diisocyanate through a constant-pressure funnel, stirring uniformly after adding, starting to heat, and when the temperature reaches 90 ℃, starting to time and perform constant-temperature reaction for 1 hour. Then cooling to 75 ℃, adding 1.04g of dried trimethylolpropane, 5.59g of dried dimethylolbutyric acid and 10 drops (about 0.8g) of stannous octoate, stirring uniformly, gradually heating to 85 ℃, and carrying out constant-temperature chain extension reaction for 3 hours to obtain the solvent-free aqueous polyurethane prepolymer.

Step three: neutralization and emulsification of prepolymer

And D, immediately transferring the prepolymer obtained in the step two to an emulsifying kettle to obtain 219.17g of prepolymer, then adding 3.25g of triethylamine into the prepolymer, stirring for 5 minutes, increasing the stirring speed to 2000r/min after the prepolymer is completely neutralized, quickly adding 450g of deionized water, and stirring at a high speed for 10 minutes.

Step four: back chain extension and silane coupling agent modification of solvent-free waterborne polyurethane

And (3) slowly adding 30.74g of diethylenetriamine solution diluted by deionized water to 20% in mass fraction into the emulsion obtained in the third step, and stirring at high speed for 10min after the addition is finished. Then slowly dripping 3.43g of monoamino trimethoxy silicon, continuously stirring at high speed for 10min, dripping 0.2g of defoaming agent, reducing the stirring speed to 800r/min, and stirring for defoaming for 5 min. And then transferring the mixture into a 1000ml three-neck flask with a thermometer and a stirring device, opening the stirring device and an oil bath pot, heating while stirring, keeping the temperature constant for reaction for 1h when the temperature is raised to 60 ℃, turning off the oil bath pot to start cooling, and filtering the emulsion when the temperature is lowered to room temperature to obtain the solvent-free waterborne polyurethane.

Table 2 the results of the tests of examples 1-2 were compared to resin H-203NB, grand deli resins ltd, taizhou, and the results were as follows:

test items	Unit of	Example 1	Example 2	H-203NB
					Temperature resistance	120 ℃/7 days	Without obvious change	Without obvious change	Yellow and sticky
Organic solvent content	PPM	0	0	40
					Elongation at break	％	436.5％	593.2％	265.7％
Breaking strength	MPa	64.97	83.17	41.69

From the above table, it can be seen that the silane coupling agent modified solvent-free waterborne polyurethane synthesized in the examples does not contain any organic solvent, and is superior to resin H-203NB of MacroDelhi resin Co., Ltd. in temperature resistance, elongation at break and breaking strength, i.e., the solvent-free waterborne polyurethane has excellent comprehensive performance.

FIG. 1 shows that the resin of example 1 was transparent and showed no significant change in color after being baked at 120 ℃ for 7 days;

FIG. 2 shows that the resin of example 2 was transparent and showed no significant change in color after being baked at 120 ℃ for 7 days;

as shown in FIG. 3, the H-203NB resin film turned yellow in color and was entirely sticky after being baked at 120 ℃ for 7 days.

The silane coupling agent modified solvent-free waterborne polyurethane obtained in the embodiment 1-2 and the commercially available product H-203NB are applied to an impregnation process of the waterborne microfiber (the specific manufacturing steps are impregnation, drying, weight reduction, washing, drying, sanding, washing, drying and finished product), the waterborne suede microfiber is prepared, and corresponding comparison tests are carried out on the waterborne suede microfiber, and the test results are as follows:

name of the product	Temperature resistance	Tensile strength	Tear strength	Colour fastness to rubbing
					Example 1 product	Without obvious change	153N	58N	4-5 stages
EXAMPLE 2 product	Without obvious change	144N	62N	4-5 stages
					H-203NB product	The color turns dark and yellow	132N	44N	Grade 3-4

Note: the temperature resistance is to be dried for 7 days at 120 ℃, and the appearance changes such as yellowing of the product are observed, and the specific figure is 4.

As can be seen from the above table data and FIG. 4, the products prepared in examples 1-2 of the present invention are superior to the products prepared from the commercial product H-203NB in terms of temperature resistance, tensile strength, tear strength and color fastness to rubbing, so that the silane coupling agent modified solvent-free waterborne polyurethane prepared by the method has excellent performance.

The above description is only for the preferred embodiment of the present invention, and not intended to limit the scope of the present invention, and all equivalent modifications made by the present invention are within the scope of the present invention.

Claims (9)

1. A preparation method of silane coupling agent modified solvent-free waterborne polyurethane is characterized by comprising the following steps: comprises the following raw materials in parts by mass and reaction steps:

(1) drying 100-300 parts of polyhydric alcohol under the vacuum condition for 0.5-2 h at the temperature of 100-130 ℃, controlling the water content in the polyhydric alcohol to be lower than 0.05%,

wherein the polyol is one or more of polyol monomers such as polyether polyol, polyester polyol, polycarbonate polyol, polytetrahydrofuran polyol, polycaprolactone polyol and the like, and the number average molecular weight of the polyol is 500-4000;

(2) uniformly mixing the dried polyol in the step (1) with 30-80 parts of isocyanate, heating to 70-100 ℃, reacting for 1-2 hours, then adding 0-4 parts of chain extender, 5-10 parts of hydrophilic chain extender and 1 part of catalyst, uniformly mixing, reacting for 2-5 hours at 70-100 ℃, and obtaining the solvent-free waterborne polyurethane prepolymer,

wherein the chain extender, the hydrophilic chain extender and the catalyst are dried, the water content is lower than 0.05%, and the isocyanate is any one or more of isophorone diisocyanate, dicyclohexyl diisocyanate, hexamethylene diisocyanate and toluene diisocyanate.

(3) And (3) adding an alkaline aqueous solution into the solvent-free aqueous polyurethane prepolymer in the step (2), and fully mixing and emulsifying for 10-30min under the high-speed stirring of 1500-3000r/min to obtain the aqueous polyurethane emulsion.

Wherein, the alkali is one or more of triethylamine, diethanolamine, triethanolamine, sodium hydroxide, sodium bicarbonate, sodium acetate and ammonia water, the water is deionized water, and the solid content of the system is 20-50% in the emulsification process;

(4) and (3) reacting the solution system obtained in the step (3) with a compound containing two or more amino groups for 10-30min, then adding a silane coupling agent, dropwise adding a defoaming agent after complete reaction, reacting at a constant temperature of 50-70 ℃ for 1-1.5 h, cooling to room temperature, filtering the obtained final emulsion, and thus obtaining the silane coupling agent modified solvent-free waterborne polyurethane.

2. The preparation method of the silane coupling agent modified solvent-free waterborne polyurethane as claimed in claim 1, wherein the polyol, the chain extender and the hydrophilic chain extender are dried by a vacuum pumping method, the drying temperature is 100-130 ℃, the air pressure is not less than 0.08MPa, and the catalyst is dried by a forced air drying oven at 100 ℃.

3. The method for preparing the silane coupling agent modified solvent-free waterborne polyurethane as claimed in claim 1, wherein the amount of the catalyst used in the step (1) is 0.1-0.5% of the total mass of the polyol and the isocyanate, and the solid content of the reactant is 20-50%.

4. The method for preparing silane coupling agent modified solvent-free waterborne polyurethane as claimed in claim 1, wherein the polyol in step (1) is one or more of polytetrahydrofuran ether glycol, polyethylene glycol, polypropylene glycol and polyglycerol, and the molecular weight of the polyol is 1000-4000.

5. The method for preparing the silane coupling agent modified solvent-free waterborne polyurethane as claimed in claim 1, wherein the chain extender in step (2) is one or more of ethylene glycol, 1, 4-butanediol, trimethylolpropane and glycerol, the hydrophilic chain extender is one or more of dimethylolpropionic acid and dimethylolbutyric acid, and the catalyst is one or more of dibutyltin dilaurate, stannous octoate and organic bismuth.

6. The method for preparing the silane coupling agent modified solvent-free waterborne polyurethane of claim 1, wherein the chain extender in step (4) is one or more selected from isophorone diamine, diethylene triamine and triethylene tetramine, and the silane coupling agent is at least one selected from vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriisopropoxysilane, monoamino-trimethoxysilane, n-octyltriethoxysilane and gamma-aminopropyltriethoxysilane.

7. The method for preparing silane coupling agent modified solvent-free waterborne polyurethane as claimed in claim 1, wherein the reaction temperature in step (2) is 80-100 ℃, the neutralization and emulsification temperature in step (3) is 40-80 ℃, and the post-chain extension temperature in step (4) is 60-90 ℃.

8. The method for preparing the silane coupling agent modified solvent-free waterborne polyurethane as claimed in claim 1, wherein the solvent used in the steps (1), (2) and (3) is deionized water.

9. The preparation method of the silane coupling agent modified solvent-free waterborne polyurethane as claimed in claim 1, wherein the solvent-free waterborne polyurethane is a block copolymer and is composed of hard segments composed of isocyanate and chain extender micromolecules and soft segments composed of polyol, and the number average molecular weight of the solvent-free waterborne polyurethane is 5000-8000.

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