A method for producing a polylactic acid-based polyurethane elastic fiber

Abstract

The application is a preparation method of polylactic acid-based polyurethane elastic fiber, comprising the following steps: step 1, reacting polylactic acid polyol, isocyanate compound and catalyst to obtain isocyanate group terminated prepolymer; step 2, fully reacting the prepolymer, chain extender and capping agent in the presence of a solvent in a reactor to obtain a polyurethane solution; step 3, using the polyurethane solution as a spinning solution to obtain polylactic acid-based polyurethane elastic fiber by dry spinning. The added nucleating agent and heat treatment technology are used to form a more perfect crystalline structure in the fiber, and the crystals act as physical crosslinking points, so that the fiber has higher modulus and breaking strength. The polylactic acid polyol with biodegradability is used to replace the traditional polymer polyol to synthesize polyurethane fiber, so that the prepared spandex is degradable, and the problems of difficult degradation and environmental pollution of waste spandex are effectively solved.

Description

Technical Field

[0001] This invention relates to methods for preparing polyurethane elastic fibers, and more particularly to a method for preparing polylactic acid-based polyurethane elastic fibers. Technical Background

[0002] Polyurethane urea elastic fiber (referred to as "spandex") is widely used in high-end clothing, sportswear, underwear, socks, and hygiene products due to its excellent mechanical properties and good resilience. However, the raw materials for ordinary spandex are derived from petrochemicals and are non-renewable. Furthermore, waste spandex is difficult to degrade, polluting the environment. In the future, spandex materials used in disposable products such as diapers and pull-ups will have even higher requirements for biodegradability.

[0003] In recent years, research and development of bio-based polyurethane materials has been rapid both domestically and internationally. Early bio-based polyurethane materials were mainly prepared by introducing biological components or groups through blending or copolymerization. With the successful synthesis of oligomeric polyols based on renewable resources, a completely new direction has been opened for the preparation of bio-based polyurethane materials. Among them, thermoplastic polyurethane elastomers (TPU) synthesized from polylactic acid polyols possess excellent biodegradability and ease of recycling and reprocessing, while also exhibiting high transparency and high damping properties (CN 110627985B). The polylactic acid-based TPU invented in patent CN201610046245.7 exhibits excellent wear resistance and biodegradability; its degradation cycle can be shortened by 10-50% compared to traditional TPU, and the degradation products are non-toxic and pollution-free.

[0004] The development of biodegradable spandex is also a research hotspot in the spandex industry. Patent CN109338504B uses readily biodegradable polyester polyols to synthesize spandex with readily biodegradable properties and high strength and high modulus. The preferred biodegradable polyester polyols used are polycaprolactone diols with a molecular weight of 2000 and aliphatic cyclic polycarbonate diols. Patent CN104630929B prepares spandex products for use in hygiene materials such as diapers by adding biodegradable compositions. However, to date, no relevant patent literature reports the use of polylactic acid polyols to prepare spandex products with readily biodegradable functions. Summary of the Invention

[0005] Technical Problem: This invention provides a method for preparing polylactic acid-based polyurethane elastic fibers. By using biodegradable polylactic acid polyols instead of traditional polymer polyols to synthesize polyurethane fibers, the prepared spandex becomes biodegradable, effectively solving the problems of difficult degradation and environmental pollution associated with waste spandex.

[0006] Technical solution: The preparation method of polylactic acid-based polyurethane elastic fiber of the present invention includes the following steps:

[0007] Step 1. React polylactic acid polyol and isocyanate compound to obtain isocyanate-terminated prepolymer;

[0008] Step 2. In the presence of a solvent in the reactor, the prepolymer reactants, chain extenders, and end-capping agents are fully reacted to obtain a polyurethane solution;

[0009] Step 3. Using the polyurethane solution described above as the polyurethane spinning solution, polylactic acid-based polyurethane elastic fibers are obtained by dry spinning.

[0010] The polylactic acid polyol is a polylactic acid diol with a number average molecular weight of 1000 to 3000.

[0011] The isocyanate compound is one or more of toluene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, isoflurone diisocyanate, dimethylbiphenyl diisocyanate, naphthalene diisocyanate, terephthalic diisocyanate, dicyclohexylmethane diisocyanate, and / or derivatives and / or modified polymers.

[0012] The molar ratio of polylactic acid polyol to isocyanate compound is 1.0:1.5 to 1.0:2.0.

[0013] The chain extender includes a diamine, including one or more of ethylenediamine, propylenediamine, butanediamine, and pentanediamine; the end-capping agent includes a monoamine, including one or more of diethylamine, dipropylamine, and n-hexylamine.

[0014] Nucleating agents are also added to the polyurethane spinning solution.

[0015] The nucleating agent is an organophosphate nucleating agent, preferably one or more of methyl bis(2,4-di-tert-butylphenoxy) phosphate, sodium methyl bis(2,4-di-tert-butylphenoxy) phosphate, and aluminum methyl bis(2,4-di-tert-butylphenoxy) phosphate, and its amount is equivalent to 0.1 to 1.0 wt% of the mass of the polyurethane solution.

[0016] The reactor in step 2 is a multi-stage static mixer.

[0017] The polyurethane spinning solution is used as the spinning solution to obtain polylactic acid-based polyurethane elastic fibers through dry spinning.

[0018] The dry spinning process yields polylactic acid-based polyurethane elastic fibers, which are then heat-treated at 50–80°C for 2–24 hours.

[0019] Beneficial effects: This invention uses polylactic acid diol as the main component for synthesizing polyurethane fibers. By utilizing added nucleating agents and heat treatment technology, a more complete crystalline structure is formed inside the fiber. These crystals act as physical cross-linking points, giving the fiber higher modulus and tensile strength. Furthermore, the polyurethane fibers prepared by this invention have excellent biodegradability, making them particularly suitable for use in disposable hygiene products such as diapers and pull-up pants. Detailed Implementation

[0020] The preparation method of polylactic acid-based polyurethane elastic fiber of the present invention includes the following steps:

[0021] 1) A prepolymerized product with isocyanate-terminated ends is obtained by reacting polylactic acid polyol and isocyanate compound;

[0022] 2) In the presence of a solvent, the prepolymer reactants, chain extenders, and end-capping agents are reacted to obtain a polyurethane solution.

[0023] 3) Polylactic acid-based polyurethane elastic fibers are obtained by dry spinning using the polyurethane solution described above as the spinning solution.

[0024] in:

[0025] The polylactic acid polyol is a polylactic acid diol with a number average molecular weight of 1000-3000;

[0026] The isocyanate compound is one or more of toluene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, isoflurone diisocyanate, dimethylbiphenyl diisocyanate, naphthalene diisocyanate, terephthalic diisocyanate, dicyclohexylmethane diisocyanate, and / or derivatives and / or modified polymers.

[0027] The molar ratio of the polylactic acid polyol to the isocyanate compound is 1.0:1.5 to 1.0:2.0;

[0028] The chain extender includes diamines, including one or more of ethylenediamine, propylenediamine, butanediamine, and pentanediamine;

[0029] The terminator includes a monoamine, including one or more of diethylamine, dipropylamine, and n-hexylamine;

[0030] Furthermore, the polylactic acid-based polyurethane elastic fiber also contains a nucleating agent, which is added to the polyurethane spinning solution;

[0031] The nucleating agent is an organophosphate nucleating agent, preferably one or more of methyl bis(2,4-di-tert-butylphenoxy) phosphate, sodium methyl bis(2,4-di-tert-butylphenoxy) phosphate, and aluminum methyl bis(2,4-di-tert-butylphenoxy) phosphate, and its amount is equivalent to 0.1 to 1.0 wt% of the mass of the polyurethane solution.

[0032] The solvent includes one or more of N,N-dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), and dimethylformamide (DMF).

[0033] Furthermore, conventional catalysts in the art can be added during the preparation process to accelerate the reaction rate, such as one or more of organotin catalysts, organozinc catalysts, and organobismuth catalysts; there are no special requirements for the timing and amount of catalyst addition, and it can be added according to actual production needs. For example, in some examples of this application, the catalyst is added to step 1) and / or step 2).

[0034] Furthermore, the polylactic acid-based polyurethane elastic fiber may also contain other functional additives commonly found in the art, as long as they do not degrade the performance of the product, such as one or more of lubricants, matting agents, dyeing auxiliaries, and chlorine-resistant auxiliaries.

[0035] Preferably, step 2) uses a multi-stage static mixer as the reactor;

[0036] In some embodiments of the present invention, the mixer comprises three sections, with the temperature of the first section set to 20–40°C, the temperature of the second section set to 60–90°C, and the temperature of the third section set to 40–60°C.

[0037] Preferably, after the polyurethane solution is cured, the cured polyurethane solution is used as the spinning solution to obtain polylactic acid-based polyurethane elastic fibers by dry spinning.

[0038] More preferably, the preparation method of the polylactic acid-based polyurethane elastic fiber further includes a heat treatment step, which includes placing the polylactic acid-based polyurethane elastic fiber in a dry heat treatment environment of 50-80°C for 2-24 hours, preferably in a dry heat treatment environment of 60-80°C for 8-24 hours.

[0039] The dry spinning process includes the steps of spraying, stretching, drying, false twisting, and winding into yarn;

[0040] Preferably, after the false twisting step, a spandex oil agent can be coated on the surface of the spandex, wherein the spandex oil agent includes mineral oil, silicone oil, etc.

[0041] The following embodiments are used to describe the production process of the present invention in detail, but these embodiments should not be construed as limiting the present invention in any way.

[0042] Example 1

[0043] Polylactic acid diol with a number average molecular weight of 2000 was mixed with diphenylmethane diisocyanate at a ratio of 1.0:

[0044] A 1.50 molar ratio was added to a reactor, along with an organotin compound as a catalyst. The mixture was stirred at 85°C for 2.0 hours to obtain an isocyanate-terminated (-NCO) prepolymer. The prepolymer was then thoroughly dissolved in an organic solvent to obtain a solution with a mass concentration of 25 wt%. The prepolymer solution and a mixture of ethylenediamine / pentanediamine / n-butylamine were added to a multi-stage static mixer for further mixing. The three stages were set at temperatures of 20°C, 60°C, and 45°C to obtain polyurethane. An ester solution was prepared; then 0.2 wt% of aluminum methyl bis(2,4-di-tert-butylphenoxy)phosphate, equivalent to the mass of the polyurethane solution, was added as a nucleating agent and magnesium stearate as a lubricant. The mixture was then matured for 24 hours to obtain a polyurethane urea spinning solution. The organic solvent of the spinning solution was evaporated through a 240℃ hot air tunnel system, then drawn by guide rollers, coated with spinning oil, and wound to obtain polyurethane fibers. Finally, the polyurethane fibers were placed in a 65℃ environment for dry heat treatment for 16 hours to obtain the final sample 1.

[0045] Example 2

[0046] Polylactic acid diol with a number average molecular weight of 2000 was mixed with diphenylmethane diisocyanate at a ratio of 1.0:

[0047] A 1.70 molar ratio was added to a reaction vessel, along with an organotin compound as a catalyst. The mixture was stirred at 85°C for 2.0 hours to obtain an isocyanate-terminated (-NCO) prepolymer. The prepolymer was then fully dissolved in an organic solvent to obtain a prepolymer solution with a mass concentration of 15 wt%. The prepolymer solution and a mixture of ethylenediamine / pentanediamine / n-butylamine were added to a multi-stage static mixer for mixing and reaction. The three stages were set at 20°C, 70°C, and 45°C to obtain a polyurethane solution. 0.2 wt% sodium methylenebis(2,4-di-tert-butylphenoxy)phosphate was added as a nucleating agent, and the mixture was matured for 24 hours to obtain a polyurethane urea spinning solution. The spinning solution was passed through a 250°C hot air duct system to evaporate the organic solvent, then drawn by guide rollers, coated with spinning oil, and wound to obtain polyurethane fibers. Finally, the polyurethane fibers were placed in an 80°C environment for dry heat treatment for 8 hours to obtain final sample 1.

[0048] Example 3

[0049] Polylactic acid diol with a number average molecular weight of 1000 and diphenylmethane diisocyanate were added to a reaction vessel at a molar ratio of 1.0:2.0, with an organozinc compound added as a catalyst. The reaction was stirred at 85°C for 2.0 hours to obtain an isocyanate-terminated (-NCO) prepolymer. The prepolymer was thoroughly dissolved in an organic solvent to obtain a prepolymer solution with a mass concentration of 15 wt%. The prepolymer solution and a mixture of ethylenediamine / pentanediamine / n-butylamine were added to a multi-stage static mixer for mixing and reaction. Polyurethane solutions were obtained by heating at temperatures of 20℃, 70℃, and 45℃. Then, sodium methylenebis(2,4-di-tert-butylphenoxy)phosphate (0.2 wt% of the polyurethane solution mass) was added as a nucleating agent, and the mixture was allowed to mature for 24 hours to obtain a polyurethane urea spinning solution. The spinning solution was then passed through a 250℃ hot air tunnel system to evaporate the organic solvent, followed by drawing with guide rollers, coating with spinning oil, and winding to obtain polyurethane fibers. Finally, the polyurethane fibers were subjected to a dry heat treatment at 80℃ for 8 hours to obtain final sample 1. The amount used was equivalent to 0.1–1.0 wt% of the polyurethane solution mass.

[0050] Example 4

[0051] Sample 3 was obtained by using the same experimental method as in Example 2, except that the proportion of nucleating agent added was equivalent to 0.5 wt% of the mass of the polyurethane solution.

[0052] Example 5

[0053] The same experimental method as in Example 2 was used, except that the proportion of nucleating agent added was equivalent to 1.0 wt% of the mass of the polyurethane solution, to obtain Sample 4.

[0054] Comparative Example 1

[0055] The same experimental method as in Example 2 was used, except that polytetramethylene ether glycol with a number average molecular weight of 2000 was used instead of polylactic acid diol, and the nucleating agent was removed, resulting in Comparative Sample 1.

[0056] Comparative Example 2

[0057] The same experimental method as in Example 2 was used, except that the nucleating agent was removed to obtain Comparative Sample 2.

[0058] Comparative Example 3

[0059] The same experimental method as in Example 2 was used, except that the dry heat treatment of polyurethane fibers at 80°C was omitted, resulting in Comparative Sample 3.

[0060] Test methods

[0061] The mechanical properties of the example samples and comparative samples were tested according to the textile industry standard "Test Method for Tensile Properties of Spandex Yarn" (FZ / T 5006-2013); the degradation performance of the samples was tested according to the national standard "Determination of Final Aerobic Biodegradation Capacity of Materials under Controlled Composting Conditions - Method for Determination of Released Carbon Dioxide Part 1: General Method" (GB / T19277.2-2011), with a degradation test period of 2 months. Specific test results are shown in Table 1 below:

[0062] Table 1. Comparison of unwinding tension between the example samples and the comparative samples.

[0063]

[0064] As shown in the table above, Comparative Sample 1, prepared using conventional polytetramethylene ether glycol, exhibits low modulus, high elongation, and poor degradation ability. Samples 1-4 all use polylactic acid diol, and their degradation ability is improved to over 40%. This indicates that the use of polylactic acid diol can effectively improve the biodegradability of polyurethane fibers. Comparative Sample 2, due to the elimination of the nucleating agent, shows a significant decrease in its mechanical modulus, indicating that the nucleating agent has a significant effect on improving fiber modulus and breaking strength. Comparative Sample 3, lacking the heat treatment process, shows a relatively low improvement in modulus and strength.

Claims

1. A method for preparing polylactic acid-based polyurethane elastic fibers, characterized in that, Includes the following steps: Step 1. React polylactic acid polyol and isocyanate compound to obtain isocyanate-terminated prepolymer; Step 2. In the presence of a solvent in the reactor, the prepolymer reactants, chain extenders, and end-capping agents are fully reacted to obtain a polyurethane solution; Step 3. Using the polyurethane solution described above as the polyurethane spinning solution, polylactic acid-based polyurethane elastic fibers are obtained by dry spinning; the polylactic acid-based polyurethane elastic fibers are then heat-treated at 50-80°C for 2-24 hours. The polyurethane spinning solution also contains an organophosphate nucleating agent, which includes one or more of methyl bis(2,4-di-tert-butylphenoxy) phosphate, sodium methyl bis(2,4-di-tert-butylphenoxy) phosphate, and aluminum methyl bis(2,4-di-tert-butylphenoxy) phosphate, and the amount of the nucleating agent is equivalent to 0.1 to 1.0 wt% of the mass of the polyurethane solution.

2. The method for preparing polylactic acid-based polyurethane elastic fiber according to claim 1, characterized in that, The polylactic acid polyol is a polylactic acid diol with a number average molecular weight of 1000-3000.

3. The method for preparing polylactic acid-based polyurethane elastic fiber according to claim 1, characterized in that, The isocyanate compound is one or more of toluene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, isoflurone diisocyanate, dimethylbiphenyl diisocyanate, naphthalene diisocyanate, terephthalic diisocyanate, and dicyclohexylmethane diisocyanate.

4. A method for preparing polylactic acid-based polyurethane elastic fiber according to claim 2 or 3, characterized in that, The molar ratio of polylactic acid polyol to isocyanate compound is 1.0:1.5 to 1.0:2.

0.

5. The method for preparing polylactic acid-based polyurethane elastic fiber according to claim 1, characterized in that, The chain extender includes diamines.

6. The method for preparing polylactic acid-based polyurethane elastic fiber according to claim 5, characterized in that, The diamine includes one or more of ethylenediamine, propylenediamine, butanediamine, and pentanediamine.

7. The method for preparing polylactic acid-based polyurethane elastic fiber according to claim 1, characterized in that, The capping agent includes a monoamine.

8. The method for preparing polylactic acid-based polyurethane elastic fiber according to claim 7, characterized in that, The monoamine includes one or more of diethylamine, dipropylamine, and n-hexylamine.

9. The method for preparing polylactic acid-based polyurethane elastic fiber according to claim 1, characterized in that, The reactor in step 2 is a multi-stage static mixer.

10. The method for preparing polylactic acid-based polyurethane elastic fiber according to claim 1, characterized in that, The polyurethane spinning solution is used as the spinning solution to obtain polylactic acid-based polyurethane elastic fibers through dry spinning.

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