Melt-spun spandex modified polylactic acid elastic fiber and preparation method thereof

Abstract

The invention provides a melt-spun spandex modified polylactic acid elastic fiber and a preparation method thereof, and belongs to the technical field of high polymer materials. The melt-spun spandex modified polylactic acid elastic fiber is prepared from the following raw materials in parts by weight: 60-80 parts of polylactic acid, 10-30 parts of polyester polyol, 2-15 parts of isocyanate, 1-5 parts of a chain extender and 5-10 parts of a compatibilizer, the polyester polyol, aromatic diisocyanate and the chain extender are fully reacted under the high-temperature shearing action of a double-screw extruder, and the melt-spun spandex modified polylactic acid elastic fiber is prepared from the following raw materials in parts by weight: 60-80 parts of polylactic acid, 10-30 parts of polyester polyol, 2-15 parts of isocyanate, 1-5 parts of a chain extender and 5-10 parts of a compatibilizer. And the PLA slices added at the rear end of the screw rod react with the compatibilizer and the trifunctional isocyanate at high temperature, so that the interfacial compatibility between the PLA and the melt-spun spandex is enhanced. According to the present invention, the polymerization reaction of the compatibilizer and the isocyanate and the multiple effects of shearing and stirring of the screw rod promote the molecular level mixing of the two materials, such that the elasticity of the polylactic acid is improved, and the breaking strength and the evenness stability of the polylactic acid are maintained;

Description

Technical Field

[0001] The invention belongs to the technical field of polymer materials, and in particular relates to a melt-spun spandex-modified polylactic acid elastic fiber and a preparation method thereof. Background Art

[0002] Polylactic acid (PLA) is a synthetic aliphatic polyester and a widely used fully degradable polymer. It uses starch raw materials to convert into lactic acid through fermentation, and then polymerizes and spins into polylactic acid with a melting point of over 170°C. Although polylactic acid fiber has many advantages such as biodegradability, excellent drape and smoothness, it also has the disadvantage of poor elasticity.

[0003] In recent years, there have been endless studies on the modification of polylactic acid. Patent CN 103255503 A subjects PLA slices to multiple melt-modified granulation, and finally melt-spinning to obtain elastic polylactic acid fibers. However, this method is cumbersome and complicated, and is not suitable for industrial production. In addition, multiple high-temperature screw shearing will cause a large loss of the physical properties of polylactic acid, causing the performance of the final fiber product to decay. Patent CN 109853084A introduces a method for preparing polylactic acid / polyester elastomer composite elastic fibers, but it is also achieved by melt blending finished PLA slices and finished polyester elastomer slices, and adding corresponding additives to achieve modification. The blending effect is limited, and the improvement in the elastic effect of the product is limited.

[0004] As an elastic fiber fabric, spandex fiber has high elasticity and recovery and is widely used in clothing and household items. Melt-spun spandex fiber is made by melt-spinning spandex slices. Its special molecular structure determines its high elasticity. However, there are few reports on the research related to melt-spun spandex modified PLA. Therefore, the present invention proposes a melt-spun spandex modified polylactic acid elastic fiber and a preparation method thereof. Summary of the invention

[0005] In order to solve the above technical problems, the present invention proposes a melt-spun spandex modified polylactic acid elastic fiber and a preparation method thereof. The melt-spun spandex modified polylactic acid elastic fiber prepared by the method of the present invention can significantly improve the elasticity of polylactic acid without affecting its breaking strength and strand stability.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] One of the technical solutions of the present invention:

[0008] A melt-spun spandex modified polylactic acid elastic fiber, the raw materials of which include, by weight: 60-80 parts of polylactic acid (PLA), 10-30 parts of polyester polyol, 2-15 parts of isocyanate, 1-5 parts of chain extender and 5-10 parts of compatibilizer;

[0009] The polyester polyol is a polyester polyol containing small molecular branches;

[0010] The isocyanate includes aromatic diisocyanate and trifunctional isocyanate.

[0011] Furthermore, the polyester polyol is one of poly(hexanediol adipate 2-methyl-2-propyl-1,3-propylene glycol ester diol), poly(butylene adipate 2-methyl-2-propyl-1,3-propylene glycol ester diol), poly(hexanediol adipate 2-methyl-1,3-propylene glycol ester diol) and poly(butylene adipate 2-methyl-1,3-propylene glycol ester diol) with a molecular weight of 2000-4000.

[0012] Furthermore, the polyester polyol is a polyester polyol added with a mixing auxiliary agent, and the mixing auxiliary agent includes a phosphite antioxidant, a hindered phenol antioxidant, a light stabilizer and an anti-hydrolysis agent.

[0013] Furthermore, the mass ratio of the aromatic diisocyanate to the trifunctional isocyanate is (2.5-14):1.

[0014] Furthermore, the aromatic diisocyanate includes one or more of toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), p-phenylene diisocyanate (PPDI), 1,5-naphthalene diisocyanate (NDI) and dimethyl diphenyl diisocyanate (TODI).

[0015] Furthermore, the chain extender is one of butanediol, hexanediol and 2-methyl-1,3-propanediol.

[0016] Furthermore, the compatibilizer is epoxy triglyceride.

[0017] Furthermore, the raw material of the melt-spun spandex modified polylactic acid elastic fiber also includes a catalyst, and the catalyst is an organic tin catalyst.

[0018] The second technical solution of the present invention:

[0019] A method for preparing the melt-spun spandex modified polylactic acid elastic fiber comprises the following steps:

[0020] Weigh each raw material by weight, inject polyester polyol, aromatic diisocyanate and chain extender into a twin-screw extruder for reaction, add a catalyst at the injection port, then add polylactic acid, a compatibilizer and a trifunctional isocyanate to the rear end of the screw, continue to add the catalyst, and the material extruded by the twin-screw extruder enters a single-screw extruder, and after a shearing and plasticizing reaction, enters a spinning assembly for melt spinning to obtain the melt-spun spandex modified polylactic acid elastic fiber.

[0021] Furthermore, the material temperature of the polyester polyol is 110-120°C, the material temperature of the aromatic diisocyanate is 70-80°C, and the material temperature of the chain extender is 60-70°C.

[0022] Furthermore, polylactic acid, a compatibilizer, a trifunctional isocyanate and the remaining catalyst are added at a distance of 2 / 3 of the total length of the screw from the feeding port of the twin-screw extruder.

[0023] Furthermore, the temperature of the front 2 / 3 of the twin-screw extruder is 220-240°C, and the temperature of the rear 1 / 3 is 180-190°C.

[0024] Furthermore, the temperature of the single screw in the single screw extruder is 210-220°C.

[0025] Compared with the prior art, the present invention has the following advantages and technical effects:

[0026] (1) The present invention mixes polyester polyol, aromatic diisocyanate and chain extender to obtain melt-spun spandex raw material. A small molecule alcohol with branched chains is added to the soft segment of the melt-spun spandex to make the soft segment non-crystalline, thereby ensuring the high resilience of the melt-spun spandex. The addition of the melt-spun spandex fully improves the elasticity and toughness of the polylactic acid fiber without affecting the dryness stability of the fiber. In addition, the addition of the compatibilizer and isocyanate makes PLA and the melt-spun spandex raw material fully compatible to obtain a homogeneous and stable material.

[0027] (2) The present invention uses the high-temperature shearing effect of the twin-screw extruder to fully react the polyester polyol, aromatic diisocyanate and chain extender to form a melt-spun spandex raw material. The PLA slices added at the rear end of the screw react with the compatibilizer and trifunctional isocyanate at high temperature. This in-situ reaction at high temperature enhances the interfacial compatibility between PLA and melt-spun spandex. The polymerization reaction of the compatibilizer and isocyanate, as well as the multiple effects of the screw shearing and stirring, promote the molecular mixing of the two materials, thereby improving the elasticity of the polylactic acid fiber while maintaining its breaking strength and strand stability.

[0028] (3) The preparation method of the present invention not only simplifies the process flow, but also optimizes the material properties by precisely controlling the reaction conditions, so that the prepared melt-spun spandex modified polylactic acid elastic fiber has better mechanical properties and processing properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0030] Figure 1 These are photos of Examples 1-2, Comparative Examples 1-4 and PLA fibers. DETAILED DESCRIPTION

[0031] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0032] It should be understood that the terms described in the present invention are only for describing special embodiments and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0033] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0034] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present invention description and examples are exemplary only.

[0035] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0036] The embodiment of the present invention provides a melt-spun spandex modified polylactic acid elastic fiber, wherein the raw materials include, by weight: 60-80 parts of polylactic acid (PLA), 10-30 parts of polyester polyol, 2-15 parts of isocyanate, 1-5 parts of chain extender and 5-10 parts of compatibilizer;

[0037] The polyester polyol is a polyester polyol containing small molecular branches;

[0038] The isocyanate includes aromatic diisocyanate and trifunctional isocyanate.

[0039] In a preferred embodiment of the present invention, the polyester polyol is one of poly(hexanediol adipate 2-methyl-2-propyl-1,3-propylene glycol ester diol) with a molecular weight of 2000-4000, poly(butylene adipate 2-methyl-2-propyl-1,3-propylene glycol ester diol) with a molecular weight of 2000-4000, poly(hexanediol adipate 2-methyl-1,3-propylene glycol ester diol) and poly(butylene adipate 2-methyl-1,3-propylene glycol ester diol) with a molecular weight of 3000. Exemplarily, the polyester polyol used in the embodiment of the present invention is poly(hexanediol adipate 2-methyl-2-propyl-1,3-propylene glycol ester diol) with a molecular weight of 3500 or poly(butylene adipate 2-methyl-1,3-propylene glycol ester diol) with a molecular weight of 3500.

[0040] In a preferred embodiment of the present invention, the polyester polyol is a polyester polyol added with a mixing auxiliary agent, and the mixing auxiliary agent includes a phosphite antioxidant, a hindered phenol antioxidant, a light stabilizer and an anti-hydrolysis agent. The anti-hydrolysis agent is a commercially available brand Stabaxol P200; the phosphite antioxidant is a brand BASF 168; the hindered phenol antioxidant is a brand BASF 1010 and BASF 1076; the light stabilizer is a brand BASF 770.

[0041] In a preferred embodiment of the present invention, the mixing aid is composed of Stabaxol P200, BASF 1010, BASF 1076, BASF 168 and BASF 770 in a mass ratio of 2:2:2:2:1. The amount of the mixing aid added is 1-1.5% of the mass of the polyester polyol, preferably 1.5%.

[0042] In a preferred embodiment of the present invention, the mass ratio of the aromatic diisocyanate to the trifunctional isocyanate is (2.5-14):1.

[0043] In a preferred embodiment of the present invention, the aromatic diisocyanate includes one or more of toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), paraphenylene diisocyanate (PPDI), 1,5-naphthalene diisocyanate (NDI) and dimethyl diphenyl diisocyanate (TODI). Exemplarily, the aromatic diisocyanate used in the embodiment of the present invention is diphenylmethane diisocyanate (MDI).

[0044] In a preferred embodiment of the present invention, the chain extender is one of butanediol, hexanediol and 2-methyl-1,3-propanediol. Exemplarily, the chain extender used in the embodiment of the present invention is 1,4-butanediol (BDO).

[0045] In a preferred embodiment of the present invention, the compatibilizer is epoxy triglyceride.

[0046] In a preferred embodiment of the present invention, the raw material of the melt-spun spandex modified polylactic acid elastic fiber further includes a catalyst, and the catalyst is an organic tin catalyst. Exemplarily, the catalyst is stannous octoate.

[0047] The embodiment of the present invention also provides a method for preparing the melt-spun spandex modified polylactic acid elastic fiber, comprising the following steps:

[0048] Weigh each raw material by weight, inject polyester polyol, aromatic diisocyanate and chain extender into a twin-screw extruder for reaction, add a catalyst to the injection port at the same time, react under the action of high temperature and catalyst to form polymer melt-spun spandex, then add polylactic acid, a compatibilizer and a trifunctional isocyanate to the rear end of the screw, continue to add the catalyst, continue to react under the combined action of high temperature, the catalyst and the compatibilizer, the material extruded by the twin-screw extruder enters a single-screw extruder, and after a shearing and plasticizing reaction, enters a spinning assembly for melt spinning to obtain the melt-spun spandex modified polylactic acid elastic fiber.

[0049] In a preferred embodiment of the present invention, the material temperature of the polyester polyol is 110-120°C, the material temperature of the aromatic diisocyanate is 70-80°C, and the material temperature of the chain extender is 60-70°C.

[0050] In a preferred embodiment of the present invention, polylactic acid, compatibilizer, trifunctional isocyanate and catalyst are added at a distance of 2 / 3 of the total length of the screw from the feeding port of the twin-screw extruder.

[0051] In a preferred embodiment of the present invention, the temperature of the front 2 / 3 of the twin-screw extruder is 220-240°C, the temperature of the rear 1 / 3 is 180-190°C, and the temperature of the single screw in the single-screw extruder is 210-220°C.

[0052] During the preparation process, the temperature of the first 2 / 3 of the screw extruder is set to 220-240°C, and the temperature of the last 1 / 3 is set to 180-190°C. The benefits of this temperature setting mainly include:

[0053] Promote material reaction and mixing: The high temperature (220-240℃) in the first 2 / 3 is conducive to the reaction and mixing of materials;

[0054] Control material flow and plasticization: Polylactic acid, compatibilizer and trifunctional isocyanate are added in the last 1 / 3. Polylactic acid is easy to degrade at high temperature. The lower temperature (180-190℃) in the last 1 / 3 helps to control the flow and further plasticization of the material while avoiding excessive thermal degradation. This temperature range can ensure that the material is evenly plasticized in the compression and metering section of the screw while maintaining a low viscosity for easy extrusion;

[0055] Prevent thermal degradation: Lower back-end temperature helps prevent thermal degradation caused by materials staying at high temperatures for too long, and maintains the molecular structure and physical properties of the polymer;

[0056] Optimize fiber molding quality: Through this temperature setting, the molding quality of the fiber can be optimized, the uniformity and strength of the fiber can be ensured, and defects such as burrs and breaks in the fiber molding process can be reduced;

[0057] Improve production efficiency: Appropriate temperature setting can improve production efficiency and reduce energy consumption, because high temperature can speed up the flow of materials, while appropriate low temperature can ensure the uniformity and stability of materials before extrusion.

[0058] In the embodiments of the present invention, "parts" are "parts by weight" unless otherwise specified.

[0059] The PLA used in the embodiments of the present invention is PLA slices, industrial grade, purchased from Anhui Fengyuan Futailai Polylactic Acid Co., Ltd., the trifunctional isocyanate used is Covestro Desmodur N3300, and the remaining raw materials are also commercially available.

[0060] It should be pointed out that the matters not described in detail in the present invention are conventional operating means in the art and are not the focus of the present invention.

[0061] The technical solution of the present invention is further illustrated by the following embodiments.

[0062] Example 1

[0063] Weigh the raw materials according to their weight, heat the poly(hexanediol adipate) 2-methyl-2-propyl-1,3-propanediol ester diol to a material temperature of 120°C, add 1.5% of the mass of the polyester polyol as a mixing aid for later use, heat the MDI to a material temperature of 75°C, and heat the BDO to a material temperature of 65°C for later use;

[0064] 20 parts of poly(hexanediol adipate) 2-methyl-2-propyl-1,3-propanediol) ester diol with a molecular weight of 3000, 6 parts of MDI and 1.5 parts of BDO were injected into a twin-screw extruder through a casting machine for reaction, and 50 ppm of stannous octoate was added to the injection port at the same time. Then, 65 parts of PLA chips, 6.5 parts of epoxy triglycerides and 1 part of N3300 were added at 2 / 3 of the total length of the screw from the feeding port of the twin-screw extruder, and 50 ppm of stannous octoate was continued to be added. The material extruded by the twin-screw extruder entered a single-screw extruder, wherein the temperature at the front 2 / 3 of the twin-screw extruder was 230°C, the temperature at the rear 1 / 3 was 190°C, and the temperature of the single screw in the single-screw extruder was 220°C. After shearing and plasticizing reaction, the material entered a spinning assembly for melt spinning to obtain a melt-spun spandex modified polylactic acid elastic fiber.

[0065] Example 2

[0066] Weigh the raw materials according to their weight, heat polybutylene adipate 2-methyl-1,3-propylene glycol ester diol to a material temperature of 120°C, add 1.5% of the mass of polyester polyol as a mixing aid for later use, heat MDI to a material temperature of 75°C, and heat BDO to a material temperature of 65°C for later use;

[0067] 12 parts of polybutylene adipate 2-methyl-1,3-propylene glycol ester diol with a molecular weight of 3500, 4 parts of MDI and 1 part of BDO are injected into a twin-screw extruder through a casting machine for reaction, and 50 ppm of stannous octoate is added at the injection port. Then, 80 parts of PLA chips, 2 parts of epoxy triglycerides and 1 part of N3300 are added at 2 / 3 of the total length of the screw from the feeding port of the twin-screw extruder, and 50 ppm of stannous octoate is continued to be added. The material extruded by the twin-screw extruder enters a single-screw extruder, wherein the temperature at the front 2 / 3 of the twin-screw extruder is 230°C, the temperature at the rear 1 / 3 is 190°C, and the temperature of the single screw in the single-screw extruder is 220°C. After shearing and plasticizing reaction, the material enters a spinning assembly for melt spinning to obtain a melt-spun spandex modified polylactic acid elastic fiber.

[0068] Comparative Example 1

[0069] Weigh the raw materials according to their weight, heat the poly(hexanediol adipate) 2-methyl-2-propyl-1,3-propanediol ester diol to a material temperature of 120°C, add 1.5% of the mass of the polyester polyol as a mixing aid for later use, heat the MDI to a material temperature of 75°C, and heat the BDO to a material temperature of 65°C for later use;

[0070] 20 parts of poly(hexanediol adipate 2-methyl-2-propyl-1,3-propanediol) ester diol with a molecular weight of 3000, 6 parts of MDI and 1.5 parts of BDO were injected into a twin-screw extruder through a casting machine for reaction, and 50 ppm of stannous octoate was added to the injection port at the same time. Then, 70 parts of PLA slices were added at 2 / 3 of the total length of the screw from the feeding port of the twin-screw extruder. The material extruded by the twin-screw extruder entered a single-screw extruder, wherein the temperature at the front 2 / 3 of the twin-screw extruder was 230° C., the temperature at the rear 1 / 3 was 190° C., and the temperature of the single screw in the single-screw extruder was 220° C. After shearing and plasticizing reaction, the material entered a spinning assembly for melt spinning to obtain a melt-spun spandex modified polylactic acid elastic fiber.

[0071] Comparative Example 2

[0072] Weigh the raw materials according to their weight, heat the poly(hexanediol adipate) 2-methyl-2-propyl-1,3-propanediol ester diol to a material temperature of 120°C, add 1.5% of the mass of the polyester polyol as a mixing aid for later use, heat the MDI to a material temperature of 75°C, and heat the BDO to a material temperature of 65°C for later use;

[0073] 20 parts of poly(hexanediol adipate) 2-methyl-2-propyl-1,3-propanediol) ester diol with a molecular weight of 3000, 6 parts of MDI and 1.5 parts of BDO were injected into a twin-screw extruder through a casting machine for reaction, and 50 ppm of stannous octoate was added at the injection port. Then, 70 parts of PLA chips and 1 part of N3300 were added at 2 / 3 of the total length of the screw from the feeding port of the twin-screw extruder. The material extruded by the twin-screw extruder entered a single-screw extruder, wherein the temperature at the front 2 / 3 of the twin-screw extruder was 230°C, the temperature at the rear 1 / 3 was 190°C, and the temperature of the single screw in the single-screw extruder was 220°C. After shearing and plasticizing reaction, the material entered a spinning assembly for melt spinning to obtain a melt-spun spandex modified polylactic acid elastic fiber.

[0074] Comparative Example 3

[0075] Weigh the raw materials according to their weight, heat the poly(hexanediol adipate) 2-methyl-2-propyl-1,3-propanediol ester diol to a material temperature of 120°C, add 1.5% of the mass of the polyester polyol as a mixing aid for later use, heat the MDI to a material temperature of 75°C, and heat the BDO to a material temperature of 65°C for later use;

[0076] 20 parts of poly(hexanediol adipate) 2-methyl-2-propyl-1,3-propanediol) ester diol with a molecular weight of 3000, 6 parts of MDI and 1.5 parts of BDO were injected into a twin-screw extruder through a casting machine for reaction, and 50 ppm of stannous octoate was added at the injection port. Then, 65 parts of PLA chips and 6.5 parts of epoxyglycerol triester were added at 2 / 3 of the total length of the screw from the feeding port of the twin-screw extruder. The material extruded by the twin-screw extruder entered a single-screw extruder, wherein the temperature at the front 2 / 3 of the twin-screw extruder was 230° C., the temperature at the rear 1 / 3 was 190° C., and the temperature of the single screw in the single-screw extruder was 220° C. After shearing and plasticizing reaction, the material entered a spinning assembly for melt spinning to obtain a melt-spun spandex modified polylactic acid elastic fiber.

[0077] Comparative Example 4

[0078] Weigh the raw materials according to their weight, heat the poly(hexanediol adipate) 2-methyl-2-propyl-1,3-propanediol ester diol to a material temperature of 120°C, add 1.5% of the mass of the polyester polyol as a mixing aid for later use, heat the MDI to a material temperature of 75°C, and heat the BDO to a material temperature of 65°C for later use;

[0079] 20 parts of poly(hexane adipate) diol with a molecular weight of 3000, 6 parts of MDI and 1.5 parts of BDO were injected into a twin-screw extruder through a casting machine for reaction, and 50 ppm of stannous octoate was added to the injection port at the same time. Then, 65 parts of PLA slices, 6.5 parts of epoxy triglyceride and 1 part of N3300 were added at 2 / 3 of the total length of the screw from the feeding port of the twin-screw extruder, and 50 ppm of stannous octoate was continued to be added. The material extruded by the twin-screw extruder entered a single-screw extruder, wherein the temperature at the front 2 / 3 of the twin-screw extruder was 230° C., the temperature at the rear 1 / 3 was 190° C., and the temperature of the single screw in the single-screw extruder was 220° C. After shearing and plasticizing reaction, the material entered a spinning assembly for melt spinning to obtain a melt-spun spandex modified polylactic acid elastic fiber.

[0080] Performance Testing

[0081] The usage of raw materials in each group of the embodiments and comparative examples is shown in Table 1.

[0082] Table 1 Usage of raw materials in each group of examples and comparative examples

[0083]

[0084]

[0085] Note: "+" means added, "-" means not added

[0086] PLA slices were melt-spun according to the method in Example 1 to obtain PLA fibers. Six melt-spun spandex-modified polylactic acid elastic fibers and PLA fiber samples were prepared according to the standard FZ / T 50006-2013 to test the fiber elongation at break. The fibers were magnified 300 times by a microscope to observe the fiber dryness. The results are shown in Tables 2 and Figure 1 .

[0087] Table 2 Test results of fiber properties in each group

[0088] Spinnability Elongation at break / % Breaking strength (cN / dtex) Dried PLA good 28.6 4.6 Uniform Example 1 good 135.2 4.2 Uniform Example 2 good 99.6 4.4 Uniform Comparative Example 1 Difference 66.7 2.3 Severe coarse details Comparative Example 2 Slightly worse 77.3 3.9 Hairy Comparative Example 3 good 80.5 2.6 Uniform Comparative Example 4 good 86.8 3.9 Uniform

[0089] The elongation at break of the fiber can reflect the elasticity of the fiber, especially the fiber with poor elasticity. Figure 1 It can be seen that:

[0090] The elongation at break of the fibers of Example 1 and Example 2 were greatly improved. Compared with Example 1, the fiber of Example 2 reduced the proportion of melt-spun spandex added, and the elongation at break of the obtained fiber decreased;

[0091] Compared with Example 1, the fiber of Comparative Example 1 removed the trifunctional isocyanate and the compatibilizer, and the final spinnability, evenness, elongation at break and specific strength at break all decreased. This is because the two materials of melt-spun spandex and PLA have poor compatibility and cannot be processed uniformly and stably, and the final fiber performance is also poor;

[0092] Compared with Example 1, the fiber of Comparative Example 2 removes the compatibilizer, and adds trifunctional isocyanate compared with the fiber of Comparative Example 1. The high temperature reaction improves the compatibility of the two components, but the final fiber still has fuzz. This is because without adding the compatibilizer, the compatibility of the two materials is limited, resulting in the appearance of fuzz. The addition of isocyanate improves the breaking strength of the final fiber, and because the yarn is relatively uniform, the elongation at break is slightly improved;

[0093] Compared with Example 1, the fiber of Comparative Example 3 removes the trifunctional isocyanate N3300, and compared with the fiber of Comparative Example 1, a compatibilizer is added. The final fiber has good spinnability and improved elongation at break, but the specific strength at break is low. This is because the lack of trifunctional isocyanate means there is no reactive group, and the later mechanical properties of the fiber cannot be improved.

[0094] Compared with Example 1, the fiber of Comparative Example 4 has a changed soft segment composition, and removes the branched small molecule alcohol, so that the final fiber elasticity is reduced.

[0095] Example 3

[0096] Weigh the raw materials according to their weight, heat polybutylene adipate 2-methyl-2-propyl-1,3-propylene glycol ester diol to a material temperature of 120°C, add 1.5% of the mass of polyester polyol as a mixing aid for later use, heat TDI to a material temperature of 70°C, and heat hexanediol to a material temperature of 60°C for later use;

[0097] 30 parts of polybutylene adipate 2-methyl-2-propyl-1,3-propanediol ester diol with a molecular weight of 4000, 4 parts of TDI and 1.8 parts of hexanediol were injected into a twin-screw extruder through a casting machine for reaction, and 50 ppm of stannous octoate was added to the injection port at the same time. Then, 80 parts of PLA chips, 5 parts of epoxy triglycerides and 1 part of N3300 were added at 2 / 3 of the total length of the screw from the feeding port of the twin-screw extruder, and 50 ppm of stannous octoate was continued to be added. The material extruded by the twin-screw extruder entered a single-screw extruder, wherein the temperature at the front 2 / 3 of the twin-screw extruder was 240°C, the temperature at the rear 1 / 3 was 190°C, and the temperature of the single screw in the single-screw extruder was 210°C. After shearing and plasticizing reaction, the material entered the spinning assembly for melt spinning to obtain melt-spun spandex modified polylactic acid elastic fiber.

[0098] Example 4

[0099] Weigh the raw materials according to their weight, heat the poly(hexanediol adipate) 2-methyl-1,3-propylene glycol ester diol to a material temperature of 110°C, add 1.5% of the mass of the polyester polyol as a mixing aid for later use, heat the PPDI to a material temperature of 80°C, and heat the 2-methyl-1,3-propylene glycol to a material temperature of 70°C for later use;

[0100] 10 parts of poly (hexanediol adipate 2-methyl-1,3-propylene glycol) ester diol with a molecular weight of 2000, 2.5 parts of PPDI and 1 part of 2-methyl-1,3-propylene glycol were injected into a twin-screw extruder through a casting machine for reaction, and 50 ppm of stannous octoate was added to the injection port at the same time. Then, 60 parts of PLA slices, 10 parts of epoxy triglycerides and 1 part of N3300 were added at 2 / 3 of the total length of the screw from the feeding port of the twin-screw extruder, and 50 ppm of stannous octoate was continued to be added. The material extruded by the twin-screw extruder entered a single-screw extruder, wherein the temperature at the front 2 / 3 of the twin-screw extruder was 220°C, the temperature at the rear 1 / 3 was 180°C, and the temperature of the single screw in the single-screw extruder was 220°C. After shearing and plasticizing reaction, the material entered the spinning assembly for melt spinning to obtain melt-spun spandex modified polylactic acid elastic fiber.

[0101] Example 5

[0102] Weigh the raw materials according to their weight, heat polybutylene adipate 2-methyl-2-propyl-1,3-propylene glycol ester diol and polyhexylene adipate 2-methyl-1,3-propylene glycol ester diol to a material temperature of 115° C., add 1.5% of the mass of the polyester polyol as a mixing aid for later use, heat NDI to a material temperature of 72° C., heat hexylene glycol and 2-methyl-1,3-propylene glycol to a material temperature of 68° C., and set aside;

[0103] 25 parts of poly (hexanediol adipate 2-methyl-1,3-propylene glycol) ester diol with a molecular weight of 3000, 10 parts of NDI, 2 parts of hexanediol and 2 parts of 2-methyl-1,3-propylene glycol were injected into a twin-screw extruder through a casting machine for reaction, and 50 ppm of stannous octoate was added to the injection port at the same time. Then, 66 parts of PLA chips, 8 parts of epoxy triglycerides and 1 part of N3300 were added at 2 / 3 of the total length of the screw from the feeding port of the twin-screw extruder, and 50 ppm of stannous octoate was continued to be added. The material extruded by the twin-screw extruder entered a single-screw extruder, wherein the temperature at the front 2 / 3 of the twin-screw extruder was 228°C, the temperature at the rear 1 / 3 was 185°C, and the temperature of the single screw in the single-screw extruder was 212°C. After shearing and plasticizing reaction, the material entered the spinning assembly for melt spinning to obtain melt-spun spandex modified polylactic acid elastic fiber.

[0104] Performance Testing

[0105] The melt-spun spandex modified polylactic acid elastic fiber samples prepared in Examples 3-5 were tested for fiber elongation at break according to standard FZ / T 50006-2013, and the evenness was observed. The results are shown in Table 3.

[0106] Table 3 Fiber performance test results of Examples 3-5

[0107] Spinnability Elongation at break / % Breaking strength (cN / dtex) Dried Example 3 good 110.5 4.2 Uniform Example 4 good 124.1 4.4 Uniform Example 5 good 100.7 4.3 Uniform

[0108] It can be seen from Table 3 that the melt-spun spandex modified polylactic acid elastic fibers prepared in Examples 3-5 of the present invention have better mechanical properties and processing properties, which are equivalent to those of Examples 1-2.

[0109] In combination with the embodiments of the present invention, it can be concluded that the present invention mixes polyester polyol, aromatic diisocyanate and chain extender to obtain melt-spun spandex raw material, and small molecule alcohol with branched chain is added to the soft segment of the melt-spun spandex to make the soft segment non-crystalline, thereby ensuring the high resilience of the melt-spun spandex. The addition of the melt-spun spandex fully improves the elasticity and toughness of the polylactic acid fiber, while not affecting the dryness stability of the fiber. In addition, the addition of the compatibilizer and isocyanate makes PLA and the melt-spun spandex raw material fully compatible to obtain a homogeneous and stable material. The present invention uses the high-temperature shearing action of a twin-screw extruder to fully react polyester polyol, aromatic diisocyanate and chain extender to form a melt-spun spandex raw material, and the PLA slice added to the rear end of the screw reacts with the compatibilizer and trifunctional isocyanate at high temperature, and the in-situ reaction at high temperature enhances the interface compatibility between PLA and the melt-spun spandex. The polymerization reaction of the compatibilizer and the isocyanate, as well as the multiple effects of the screw shearing and stirring, promote the molecular mixing of the two materials, thereby improving the elasticity of the polylactic acid fiber, while maintaining its breaking strength and strand stability. The preparation method of the present invention not only simplifies the process flow, but also optimizes the material properties by precisely controlling the reaction conditions, so that the prepared melt-spun spandex modified polylactic acid elastic fiber has better mechanical properties and processing properties.

[0110] The above are only preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A melt-spun spandex modified polylactic acid elastic fiber, characterized in that: The raw materials include, by weight: 60-80 parts of polylactic acid, 10-30 parts of polyester polyol, 2-15 parts of isocyanate, 1-5 parts of chain extender and 5-10 parts of compatibilizer; The polyester polyol is a polyester polyol containing small molecular branches; The isocyanate includes aromatic diisocyanate and trifunctional isocyanate.

2. The melt-spun spandex modified polylactic acid elastic fiber according to claim 1, characterized in that: The polyester polyol is one of poly(hexanediol adipate 2-methyl-2-propyl-1,3-propylene glycol ester diol), poly(butylene adipate 2-methyl-2-propyl-1,3-propylene glycol ester diol), poly(hexanediol adipate 2-methyl-1,3-propylene glycol ester diol) and poly(butylene adipate 2-methyl-1,3-propylene glycol ester diol) with a molecular weight of 2000-4000.

3. The melt-spun spandex modified polylactic acid elastic fiber according to claim 1, characterized in that: The mass ratio of the aromatic diisocyanate to the trifunctional isocyanate is (2.5-14):

1.

4. The melt-spun spandex modified polylactic acid elastic fiber according to claim 3, characterized in that: The aromatic diisocyanate includes one or more of toluene diisocyanate, diphenylmethane diisocyanate, p-phenylene diisocyanate, 1,5-naphthalene diisocyanate and dimethylbiphenyl diisocyanate.

5. The melt-spun spandex modified polylactic acid elastic fiber according to claim 1, characterized in that: The chain extender is one of butanediol, hexanediol and 2-methyl-1,3-propanediol.

6. The melt-spun spandex modified polylactic acid elastic fiber according to claim 1, characterized in that: The compatibilizer is epoxy triglyceride.

7. The melt-spun spandex modified polylactic acid elastic fiber according to claim 1, characterized in that: The raw material of the melt-spun spandex modified polylactic acid elastic fiber also includes a catalyst, and the catalyst is an organic tin catalyst.

8. A method for preparing the melt-spun spandex modified polylactic acid elastic fiber according to any one of claims 1 to 7, characterized in that: The following steps are involved: The raw materials are weighed according to their weight proportions, and polyester polyol, aromatic diisocyanate and chain extender are injected into a twin-screw extruder for reaction, and a catalyst is added at the injection port at the same time. Then, polylactic acid, a compatibilizer and trifunctional isocyanate are added to the rear end of the screw, and the catalyst is continued to be added. The material extruded by the twin-screw extruder enters a single-screw extruder, and after a shearing and plasticizing reaction, it is melt-spun to obtain the melt-spun spandex modified polylactic acid elastic fiber.

9. The method for preparing the melt-spun spandex modified polylactic acid elastic fiber according to claim 8, characterized in that: The material temperature of the polyester polyol is 110-120°C, the material temperature of the aromatic diisocyanate is 70-80°C, and the material temperature of the chain extender is 60-70°C.

10. The method for preparing melt-spun spandex modified polylactic acid elastic fiber according to claim 8, characterized in that: Add polylactic acid, compatibilizer, trifunctional isocyanate and catalyst at 2 / 3 of the total screw length from the feeding port of the twin-screw extruder; The temperature of the first 2 / 3 of the twin-screw extruder is 220-240°C, and the temperature of the last 1 / 3 is 180-190°C; The temperature of the single screw in the single screw extruder is 210-220°C.

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