Modified polylactic acid chopped fiber suitable for spunlace non-woven fabric and manufacturing method of modified polylactic acid chopped fiber

Abstract

The invention relates to the technical field of fibers, in particular to a modified polylactic acid chopped fiber suitable for spunlace non-woven fabric and a manufacturing method of the modified polylactic acid chopped fiber. The modified polylactic acid chopped fiber comprises 90 to 95 wt% of polylactic acid, 5 to 8 wt% of epoxy grafted polylactic acid, 1 to 2 wt% of polyphosphate, 0.2 to 0.5 wt% of an external lubricant, 0.1 to 0.2 wt% of a heat stabilizer and 0.3 to 0.4 wt% of an anti-hydrolysis agent. According to the invention, the heat stability of the polylactic acid is improved, the thermal degradation of the polylactic acid in the melting processing heat process is inhibited, the viscosity of the polylactic acid melt tends to be consistent, the spinning stability is improved, and the consistency of the fiber diameter is ensured; the hygrothermal aging performance of the polylactic acid is improved. The crystallinity of the polylactic acid in the spinning process is reduced, but the tensile strength of the polylactic acid is still kept.

Description

Technical Field

[0001] The invention relates to a high molecular polymer, in particular to a modified polylactic acid chopped fiber suitable for spunlace nonwoven fabric and a preparation method thereof. Background Art

[0002] Nonwoven fabric is a kind of fabric that does not require spinning and weaving. It is formed by directional or random arrangement of textile short fibers or filaments to form a fiber mesh structure, and then reinforced by mechanical, thermal bonding or chemical methods. It can achieve customized functions and is one of the industrial products with extremely wide application range. Hydroentanglement is one of the main production methods of nonwoven fabrics. The short-cut fibers are entangled by high-speed water jets, and after drying, a continuous fabric with adjustable strength, softness and porosity can be obtained, which is suitable for a variety of occasions.

[0003] CN202111661135.9 discloses a method for preparing a moisture-absorbing and antibacterial spunlace non-woven fabric, but its main components are acetate fiber, polylactic acid fiber and polyethylene fiber. The preparation method is to first use an antioxidant and flame retardant solution to impregnate the polyethylene fiber, acetate fiber and polylactic acid fiber, and then lay four layers of fiber mesh in the order of polyethylene fiber-acetate fiber-polylactic acid fiber-polyethylene fiber, and reinforce them with double spunlace.

[0004] CN201810019723.4 discloses a spunlace nonwoven fabric, its preparation method and use, but its main components are graphene polylactic acid and graphene viscose fiber, and its production method includes mixing fibers of different finenesses.

[0005] Spunlace nonwovens usually use chemical synthetic fibers, such as polypropylene, nylon, polyester or spandex. The raw materials of the above chemical synthetic fibers are polypropylene, nylon 6, polyester and polyurethane, which have long-term chemical stability. The disadvantage is that they cannot be naturally decomposed after being discarded, and they remain in the environment to cause pollution and release a large number of microplastic particles.

[0006] Biodegradable plastics are one of the key solutions to current environmental issues, especially suitable for applications where reuse is not suitable and recycling is difficult or impossible. Under suitable conditions, biodegradable plastics can be rapidly degraded into carbon dioxide and water without producing additional pollutants.

[0007] Polylactic acid is an internationally recognized biodegradable plastic, which can be obtained as continuous fibers after melt spinning. However, polylactic acid has poor thermal stability and is prone to thermal degradation during melt processing, which affects spinning stability after degradation. As a typical polyester, the ester bonds of polylactic acid are easily hydrolyzed under high temperature and high humidity conditions, affecting fiber strength. In addition, polylactic acid is a semi-crystalline plastic, and the stretching process will strongly induce polylactic acid crystallization. The properties of polylactic acid fibers after crystallization change, with increased tensile strength, increased elastic modulus, and decreased elongation at break. After untreated polylactic acid is spun and used in non-woven fabrics, especially in the production of spunlace non-woven fabrics, it is easy to increase the proportion of fiber breakage, deteriorate entanglement tightness, and increase the fiber elastic modulus. The macroscopic manifestation is that the roughness of the non-woven fabric increases, the strength decreases, and the hardness increases, which has an adverse effect on the application of non-woven fabrics. Summary of the invention

[0008] The present invention aims to solve the above-mentioned defects and provides a modified polylactic acid chopped fibers suitable for spunlace nonwoven fabrics and a method for manufacturing the same.

[0009] In order to overcome the defects existing in the background technology, the technical solution adopted by the present invention to solve the technical problem is: the modified polylactic acid chopped fibers include 90-95wt% of polylactic acid, 5-8wt% of epoxy grafted polylactic acid, 1-2wt% of polyphosphate, 0.2-0.5wt% of external lubricant, 0.1-0.2wt% of heat stabilizer, and 0.3-0.4wt% of anti-hydrolysis agent.

[0010] According to another embodiment of the present invention, the weight average molecular weight of the polylactic acid is 150,000-200,000, and the melt mass flow rate under a load of 2.16 kg at 190 degrees Celsius is 15-20 g / 10 min.

[0011] According to another embodiment of the present invention, the epoxy grafted polylactic acid further comprises an epoxy group of R1-O-R2, wherein R1 and R2 are respectively one or more of methylene, hydroxyl, ether, and benzyl, the weight average molecular weight of the grafted polylactic acid in the epoxy grafted polylactic acid is 150,000-200,000, the melt mass flow rate at 190 degrees Celsius and a load of 2.16 kg is 15-20 g / 10 minutes, and the epoxy grafting rate of the grafted polylactic acid is 2-3%.

[0012] According to another embodiment of the present invention, the weight average molecular weight of the polyphosphate is 90,000-110,000, the phosphorus content is 9.5-11%, and the melt volume flow rate of the polyphosphate at 230 degrees Celsius and a load of 2.16 kg is 10-15 ml / 10 minutes.

[0013] According to another embodiment of the present invention, the external lubricant is a hydroxycarboxylate oligomer having the structure (COHCOOR)n , wherein R is one or more of sulfonic acid, amino, amide or carbonyl structures, and the relative molecular weight of the hydroxycarboxylate oligomer is 1500-3000.

[0014] According to another embodiment of the present invention, the heat stabilizer is further comprised of one or more of tetrakis(2,4-di-tert-butylphenyl)-4,4'-biphenyl bisphosphite, pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate or tris[2,4-di-tert-butylphenyl]phosphite.

[0015] According to another embodiment of the present invention, the anti-hydrolysis agent is further comprised of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide.

[0016] The method for producing modified polylactic acid chopped fibers comprises the following steps:

[0017] The first step is to mix polylactic acid, epoxy grafted polylactic acid and polyphosphate and then perform dew point drying. During drying, the dew point of the drying air is lower than -35°C, the drying temperature is 55°C, and the drying time is not less than 2 hours to ensure that the water content of the mixture is less than 200ppm;

[0018] The second step is to vacuum dry the heat stabilizer. During drying, the air pressure in the drying tank is not higher than 30Pa, the drying temperature is 50℃, and the drying time is not less than 1 hour to ensure that the water content of the heat stabilizer is less than 200ppm;

[0019] Step 3: The polylactic acid mixture, heat stabilizer, external lubricant and anti-hydrolysis agent after dew point drying in the first and second steps are respectively weighed by different weight loss scales, and nitrogen is used as a conveying medium to feed the weighed materials into the main feeding port of the co-rotating parallel twin-screw extruder for granulation;

[0020] Step 4: Dew point drying the modified polylactic acid after granulation in the third step. During drying, the dew point of the drying air is lower than -35°C, the drying temperature is 55°C, and the drying time is not less than 2 hours, ensuring that the water content of the modified polylactic acid is lower than 200ppm;

[0021] Step 5: sending the modified polylactic acid dried in the step 4 into a spinning machine with nitrogen as the medium for melt spinning to obtain modified polylactic acid continuous fibers;

[0022] Step 6: The modified polylactic acid continuous fibers obtained in the fifth step are cleaned and cut into short fibers with a length of 38 mm. After classification, modified polylactic acid short fibers with uniform length are obtained.

[0023] According to another embodiment of the present invention, the processing temperature during granulation in the third step is further comprised of 160-190°C, the length-to-diameter ratio of the co-rotating parallel twin-screw extruder is 56:1, it comprises 2 independent vacuum devolatilization chambers, and is divided into 13 independent temperature control zones, and the length-to-diameter ratio of each temperature control zone is 4:1.

[0024] According to another embodiment of the present invention, the fifth step further comprises a spinning temperature of 150-180° C., a winding temperature of 60-80° C., a winding speed of 1500-1800 m / min, and a stretching ratio of 10-12.

[0025] The beneficial effects of the present invention are:

[0026] (1) The thermal stability of polylactic acid is improved, the thermal degradation of polylactic acid during the melt processing is inhibited, the viscosity of the polylactic acid melt is made more consistent, the spinning stability is improved, and the consistency of the fiber diameter is ensured;

[0027] (2) Improved the wet heat aging performance of polylactic acid. The manufacturing process of polylactic acid spunlace nonwovens involves multiple dryings, all of which are in a high temperature and high humidity environment. After improving the wet heat aging performance of polylactic acid, in the above environment, the hydrolysis rate of polylactic acid short fibers is lower, and the elongation at break retention rate is higher, so that it can withstand greater processing pressure in the spunlace process, increase the fiber entanglement rate, and reduce the fiber breakage rate, thereby increasing the strength of the nonwoven fabric and reducing the surface roughness of the nonwoven fabric;

[0028] (3) The crystallinity of polylactic acid during the spinning process is reduced, but its tensile strength is still maintained. At a lower crystallinity, the elastic modulus of polylactic acid fiber is lower, and the macroscopic performance is that the nonwoven fabric is softer and has a wider range of applications. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] A modified polylactic acid chopped fiber suitable for spunlace nonwoven fabrics, comprising:

[0031] Polylactic acid 90-95wt%;

[0032] Epoxy grafted polylactic acid 5-8wt%;

[0033] Polyphosphate 1-2wt%;

[0034] External lubricant 0.2-0.5wt%;

[0035] Heat stabilizer 0.1-0.2wt%;

[0036] Anti-hydrolysis agent 0.3-0.4wt%.

[0037] The weight average molecular weight of the polylactic acid is 150,000-200,000, the melt mass flow rate under a load of 2.16 kg at 190 degrees Celsius is 15-20 g / 10 minutes, and the polylactic acid is poly-L-lactic acid or poly-D-lactic acid.

[0038] The content of polylactic acid is 90-95wt% of the modified polylactic acid fiber suitable for spunlace nonwoven fabric.

[0039] Preferably, poly-L-lactic acid with a weight average molecular weight of 170,000, a melt mass flow rate of 18 g / 10 min at 190 degrees Celsius and a load of 2.16 kg, and an optical purity of 98% can be selected.

[0040] Among them, the epoxy grafted polylactic acid contains an epoxy group R1-O-R2, wherein R1 and R2 are one or more of methylene, hydroxyl, ether, and benzyl. The weight average molecular weight of the polylactic acid used for grafted polylactic acid is 150,000-200,000, and the melt mass flow rate under 190 degrees Celsius and 2.16 kg load is 15-20 grams / 10 minutes. The polylactic acid used for grafted polylactic acid is poly-L-lactic acid or poly-D-lactic acid, but it should be consistent with the polylactic acid. The epoxy grafting rate of grafted polylactic acid is 2-3%.

[0041] Preferably, the epoxy group R1-O-R2, wherein R1 and R2 can be selected as hydroxyl and benzyl respectively, and can be selected as poly-L-lactic acid with a weight average molecular weight of 170,000, a melt mass flow rate of 18 g / 10 min at 190 degrees Celsius, an optical purity of 98%, and an epoxy grafting rate of 2.8%.

[0042] The content of the grafted polylactic acid is 5-8wt% of the modified polylactic acid fiber suitable for spunlace nonwoven fabric.

[0043] The weight average molecular weight of the polyphosphate is 90,000-110,000, the phosphorus content is 9.5-11%, the melt volume flow rate of the polyphosphate at 230 degrees Celsius and 2.16 kg load is 10-15 ml / 10 minutes, and the content of the polyphosphate is 1-2wt% of the modified polylactic acid fiber suitable for spunlace nonwoven fabrics.

[0044] Preferably, a polyphosphate with a weight average molecular weight of 110,000 and a phosphorus content of 10.5% can be selected, and its melt volume flow rate at 230 degrees Celsius and a load of 2.16 kg is 12 ml / 10 minutes.

[0045] Among them, the external lubricant is a hydroxycarboxylate oligomer, and its structure is (COHCOOR) n , wherein R is one or more of sulfonic acid, amino, amide or carbonyl structures, and the relative molecular weight of the hydroxycarboxylate oligomer is 1500-3000.

[0046] Preferably, the content of the external lubricant is 0.2-0.5wt% of the modified polylactic acid fiber suitable for spunlace nonwoven fabric.

[0047] Preferably, R is a hydroxycarboxylate oligomer of sulfonic acid group, and its relative molecular weight is 2,600.

[0048] The heat stabilizer is one or more of tetrakis(2,4-di-tert-butylphenyl)-4,4'-biphenyl bisphosphite, pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate or tris[2,4-di-tert-butylphenyl]phosphite.

[0049] Preferably, the content of the heat stabilizer is 0.1-0.2 wt % of the modified polylactic acid fiber suitable for spunlace nonwoven fabric.

[0050] Preferably, tetrakis(2,4-di-tert-butylphenyl)-4,4'-biphenyl bisphosphite and tris[2,4-di-tert-butylphenyl]phosphite are compounded in a weight ratio of 1:1.

[0051] Wherein, the anti-hydrolysis agent is 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide.

[0052] Preferably, the content of the anti-hydrolysis agent is 0.3-0.4wt% of the modified polylactic acid fiber suitable for spunlace nonwoven fabric.

[0053] This modified polylactic acid chopped fiber suitable for spunlace nonwoven fabrics improves the thermal stability of polylactic acid; it also improves the wet heat aging performance of polylactic acid. Under the conditions of 85°C and 85% RH, compared with the unmodified polylactic acid fiber, the time for the tensile strength of this modified polylactic acid fiber to be reduced by half is increased from 6 hours to 28 hours; it also improves the elongation at break of the polylactic acid fiber, reduces the crystallinity and elastic modulus of polylactic acid during the spinning process, and the tensile strength remains basically unchanged. Compared with the unmodified polylactic acid fiber, the elongation at break of this modified polylactic acid fiber is increased from 33% to 70%, the crystallinity is reduced from 44% to 22%, the elastic modulus is reduced from 3800Mpa to 2900Mpa, and the tensile strength is reduced from 3.4cN / dtex to 3.3cN / dtex.

[0054] The molecular weight of polylactic acid can be directly reflected by the melt index. When polylactic acid undergoes thermal degradation, its molecular weight decreases and the melt index increases. This modified polylactic acid fiber measures the thermal stability of polylactic acid by the change in the melt index of polylactic acid before and after heating. The heating process is simulated by banbury mixing. The specific indicators are: banbury mixing temperature 230°C, banbury mixing time 5 minutes, banbury mixing rotor, and banbury mixing speed 60rpm. The thermal stability of polylactic acid is evaluated by comparing the change rate of the melt index of the material before and after banbury mixing. The greater the change rate of the melt index of the material before and after banbury mixing, the worse the thermal stability of the material.

[0055] The wet heat aging performance test is based on the time-temperature equivalence principle. Taking the fiber tensile strength reduced by half as the performance index of fiber aging, a relatively accurate double 85 aging time can be obtained. The longer the time, the better the wet heat aging performance of the fiber.

[0056] The modified polylactic acid chopped fibers do not require any changes to the equipment in any processing link and are widely applicable to spunlace nonwoven fabrics of various specifications. The specific manufacturing method includes the following steps:

[0057] (1) After mixing polylactic acid, epoxy grafted polylactic acid and polyphosphate, dew point drying is performed. During drying, the dew point of the drying air is lower than -35°C, the drying temperature is 55°C, and the drying time is not less than 2 hours, ensuring that the water content of the mixture is less than 200 ppm.

[0058] (2) The heat stabilizer is vacuum dried. During drying, the air pressure in the drying tank is not higher than 30 Pa, the drying temperature is 50°C, and the drying time is not less than 1 hour, ensuring that the water content of the heat stabilizer is less than 200 ppm.

[0059] (3) Using nitrogen as the conveying medium, the dried polylactic acid mixture and the heat stabilizer are respectively fed into different weight loss scales 1 and 2 of the weight loss metering system. The above-mentioned weight loss metering system also includes two other weight loss scales, which are used to measure the external lubricant and the anti-hydrolysis agent respectively. The materials measured by the weight loss metering system enter the main feeding port of the co-rotating parallel twin-screw extruder.

[0060] (4) During granulation, the processing temperature is 160-190°C, the length-to-diameter ratio of the co-rotating parallel twin-screw extruder is 56:1, and it includes 2 independent vacuum devolatilization chambers and is divided into 13 independent temperature control zones. The length-to-diameter ratio of each temperature control zone is 4:1.

[0061] (5) The modified polylactic acid after granulation is subjected to dew point drying. During drying, the dew point of the drying air is lower than -35°C, the drying temperature is 55°C, and the drying time is not less than 2 hours, ensuring that the water content of the modified polylactic acid is lower than 200ppm.

[0062] (6) Using nitrogen as the medium, the dried modified polylactic acid is fed into a spinning machine for melt spinning to obtain modified polylactic acid continuous fibers. The spinning temperature is 150-180° C., the winding temperature is 60-80° C., the winding speed is 1500-1800 m / min, and the stretching ratio is 10-12.

[0063] The modified polylactic acid long fibers are cleaned and cut into short fibers with a length of 38 mm, and after classification, the modified polylactic acid short fibers with uniform length are obtained. The short fibers are suitable for the production of spunlace nonwoven fabrics.

[0064] The present invention is described in detail below by way of examples. It is necessary to point out that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements, adjustments or substitutions made by professionals and technicians in this field based on the content of the above invention still belong to the scope of protection of the present invention.

[0065] In addition, unless otherwise specified, the components used in the following materials are all weight percentages (wt %).

[0066] Embodiment 1:

[0067] A modified polylactic acid chopped fiber suitable for spunlace nonwoven fabrics, the modified polylactic acid chopped fiber comprising the following components in percentage by weight:

[0068] Component name Weight Percent Poly-L-lactic acid 90.1 Epoxy grafted polylactic acid 8 Polyphosphate 1 External lubricant 0.5 Heat Stabilizer 0.1 Anti-hydrolysis agent 0.3

[0069] The polylactic acid, epoxy grafted polylactic acid, polyphosphate and thermal stabilizer are dried according to the drying method of the present invention, and the water content of each component to be dried is ensured to be less than 200 ppm.

[0070] The feed ratio of the loss-in-weight metering system is set according to the ratio in the above table, and the above raw materials are added in proportion for granulation. During granulation, the processing temperature is 175℃.

[0071] The modified polylactic acid after granulation is dew-point dried. After the water content of the modified polylactic acid is less than 200ppm, the dried modified polylactic acid is sent to a spinning machine for melt spinning with nitrogen as the medium to obtain modified polylactic acid continuous fibers. The spinning temperature is 165°C, the winding temperature is 75°C, the winding speed is 1800 m / min, the stretching ratio is 12, and a continuous fiber with a fineness of 1.5D is obtained.

[0072] The modified polylactic acid long fibers were cleaned and cut into short fibers with a length of 38 mm, and modified polylactic acid short fibers with uniform length were obtained after classification.

[0073] The modified polylactic acid chopped fibers were tested and found that the melt index change rate at 230°C was 3.5%, the double 85 aging time was 24 hours, the elongation at break was 70%, the crystallinity was 27%, the elastic modulus was 3400 MPa, and the tensile strength was 3.4 cN / dtex.

[0074] Embodiment 2:

[0075] A modified polylactic acid chopped fiber suitable for spunlace nonwoven fabrics, the modified polylactic acid chopped fiber comprising the following components in percentage by weight:

[0076] Component name Weight Percent Poly-L-lactic acid 92.1 Epoxy grafted polylactic acid 5 Polyphosphate 2 External lubricant 0.5 Heat Stabilizer 0.1 Anti-hydrolysis agent 0.3

[0077] The polylactic acid, epoxy grafted polylactic acid, polyphosphate and thermal stabilizer are dried according to the drying method of the present invention, and the water content of each component to be dried is ensured to be less than 200 ppm.

[0078] The feed ratio of the loss-in-weight metering system is set according to the ratio in the above table, and the above raw materials are added in proportion for granulation. During granulation, the processing temperature is 175℃.

[0079] The modified polylactic acid after granulation is dew-point dried. After the water content of the modified polylactic acid is less than 200ppm, the dried modified polylactic acid is sent to a spinning machine for melt spinning with nitrogen as the medium to obtain modified polylactic acid continuous fibers. The spinning temperature is 165°C, the winding temperature is 75°C, the winding speed is 1800 m / min, the stretching ratio is 12, and a continuous fiber with a fineness of 1.5D is obtained.

[0080] The modified polylactic acid long fibers were cleaned and cut into short fibers with a length of 38 mm, and modified polylactic acid short fibers with uniform length were obtained after classification.

[0081] The modified polylactic acid chopped fibers were tested and found that the melt index change rate at 230°C was 4.3%, the double 85 aging time was 24 hours, the elongation at break was 50%, the crystallinity was 22%, the elastic modulus was 2900 MPa, and the tensile strength was 3.3 cN / dtex.

[0082] Example 3

[0083] A modified polylactic acid chopped fiber suitable for spunlace nonwoven fabrics, the modified polylactic acid chopped fiber comprising the following components in percentage by weight:

[0084] Component name Weight Percent Poly-L-lactic acid 93 Epoxy grafted polylactic acid 5 Polyphosphate 1 External lubricant 0.5 Heat Stabilizer 0.2 Anti-hydrolysis agent 0.3

[0085] The polylactic acid, epoxy grafted polylactic acid, polyphosphate and thermal stabilizer are dried according to the drying method of the present invention, and the water content of each component to be dried is ensured to be less than 200 ppm.

[0086] The feed ratio of the loss-in-weight metering system is set according to the ratio in the above table, and the above raw materials are added in proportion for granulation. During granulation, the processing temperature is 175℃.

[0087] The modified polylactic acid after granulation is dew-point dried. After the water content of the modified polylactic acid is less than 200ppm, the dried modified polylactic acid is sent to a spinning machine for melt spinning with nitrogen as the medium to obtain modified polylactic acid continuous fibers. The spinning temperature is 165°C, the winding temperature is 75°C, the winding speed is 1800 m / min, the stretching ratio is 12, and a continuous fiber with a fineness of 1.5D is obtained.

[0088] The modified polylactic acid long fibers were cleaned and cut into short fibers with a length of 38 mm, and modified polylactic acid short fibers with uniform length were obtained after classification.

[0089] The modified polylactic acid chopped fibers were tested and found that the melt index change rate at 230°C was 1.5%, the double 85 aging time was 25 hours, the elongation at break was 50%, the crystallinity was 26%, the elastic modulus was 3200 MPa, and the tensile strength was 3.5 cN / dtex.

[0090] Example 4

[0091] A modified polylactic acid chopped fiber suitable for spunlace nonwoven fabrics, the modified polylactic acid chopped fiber comprising the following components in percentage by weight:

[0092]

[0093]

[0094] The polylactic acid, epoxy grafted polylactic acid, polyphosphate and thermal stabilizer are dried according to the drying method of the present invention, and the water content of each component to be dried is ensured to be less than 200 ppm.

[0095] The feed ratio of the loss-in-weight metering system is set according to the ratio in the above table, and the above raw materials are added in proportion for granulation. During granulation, the processing temperature is 175℃.

[0096] The modified polylactic acid after granulation is dew-point dried. After the water content of the modified polylactic acid is less than 200ppm, the dried modified polylactic acid is sent to a spinning machine for melt spinning with nitrogen as the medium to obtain modified polylactic acid continuous fibers. The spinning temperature is 165°C, the winding temperature is 75°C, the winding speed is 1800 m / min, the stretching ratio is 12, and a continuous fiber with a fineness of 1.5D is obtained.

[0097] The modified polylactic acid long fibers were cleaned and cut into short fibers with a length of 38 mm, and modified polylactic acid short fibers with uniform length were obtained after classification.

[0098] The modified polylactic acid chopped fibers were tested and found that the melt index change rate at 230°C was 4.6%, the double 85 aging time was 28 hours, the elongation at break was 52%, the crystallinity was 27%, the elastic modulus was 3100 MPa, and the tensile strength was 3.4 cN / dtex.

[0099] Comparative Example:

[0100] Commercially available polylactic acid 38mm chopped fibers.

[0101] The modified polylactic acid chopped fibers were tested and found that the melt index change rate at 230°C was 9.8%, the double 85 aging time was 6 hours, the elongation at break was 33%, the crystallinity was 40%, the elastic modulus was 3800 MPa, and the tensile strength was 3.4 cN / dtex.

[0102] The following table summarizes the differences between the Examples and Comparative Examples.

[0103]

[0104]

[0105] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A modified polylactic acid chopped fiber suitable for spunlace nonwoven fabric, characterized in that: The modified polylactic acid chopped fibers comprise 90-95 wt % of polylactic acid, 5-8 wt % of epoxy grafted polylactic acid, 1-2 wt % of polyphosphate, 0.2-0.5 wt % of external lubricant, 0.1-0.2 wt % of heat stabilizer and 0.3-0.4 wt % of anti-hydrolysis agent.

2. The modified polylactic acid chopped fibers suitable for spunlace nonwoven fabrics according to claim 1, characterized in that: The weight average molecular weight of the polylactic acid is 150,000-200,000, and the melt mass flow rate under a load of 2.16 kg at 190 degrees Celsius is 15-20 g / 10 minutes.

3. The modified polylactic acid chopped fibers suitable for spunlace nonwoven fabrics according to claim 1, characterized in that: The epoxy group in the epoxy grafted polylactic acid is R1-O-R2, wherein R1 and R2 are respectively one or more of methylene, hydroxyl, ether, and benzyl. The weight average molecular weight of the grafted polylactic acid in the epoxy grafted polylactic acid is 150,000-200,000, and the melt mass flow rate under a load of 2.16 kg at 190 degrees Celsius is 15-20 g / 10 minutes. The epoxy grafting rate of the grafted polylactic acid is 2-3%.

4. The modified polylactic acid chopped fibers suitable for spunlace nonwoven fabrics according to claim 1, characterized in that: The weight average molecular weight of the polyphosphate is 90,000-110,000, the phosphorus content is 9.5-11%, and the melt volume flow rate of the polyphosphate at 230 degrees Celsius and a load of 2.16 kg is 10-15 ml / 10 minutes.

5. The modified polylactic acid chopped fibers suitable for spunlace nonwoven fabrics according to claim 1, characterized in that: The external lubricant is a hydroxycarboxylate oligomer, and its structure is (COHCOOR) n , wherein R is one or more of sulfonic acid, amino, amide or carbonyl structures, and the relative molecular weight of the hydroxycarboxylate oligomer is 1500-3000.

6. The modified polylactic acid chopped fibers suitable for spunlace nonwoven fabrics according to claim 1, characterized in that: The heat stabilizer is one or more of tetrakis(2,4-di-tert-butylphenyl)-4,4'-biphenyl bisphosphite, tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate]pentaerythritol or tris[2,4-di-tert-butylphenyl]phosphite.

7. The modified polylactic acid chopped fibers suitable for spunlace nonwoven fabrics according to claim 1, characterized in that: The anti-hydrolysis agent is 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide.

8. The method for producing modified polylactic acid chopped short fibers according to claim 1, wherein: The manufacturing method comprises the following steps: The first step is to mix polylactic acid, epoxy grafted polylactic acid and polyphosphate and then perform dew point drying. During drying, the dew point of the drying air is lower than -35°C, the drying temperature is 55°C, and the drying time is not less than 2 hours to ensure that the water content of the mixture is less than 200ppm; The second step is to vacuum dry the heat stabilizer. During drying, the air pressure in the drying tank is not higher than 30Pa, the drying temperature is 50℃, and the drying time is not less than 1 hour to ensure that the water content of the heat stabilizer is less than 200ppm; Step 3: The polylactic acid mixture, heat stabilizer, external lubricant and anti-hydrolysis agent after dew point drying in the first and second steps are respectively weighed by different weight loss scales, and nitrogen is used as a conveying medium to feed the weighed materials into the main feeding port of the co-rotating parallel twin-screw extruder for granulation; Step 4: Dew point drying the modified polylactic acid after granulation in the third step. During drying, the dew point of the drying air is lower than -35°C, the drying temperature is 55°C, and the drying time is not less than 2 hours, ensuring that the water content of the modified polylactic acid is lower than 200ppm; Step 5: sending the modified polylactic acid dried in the step 4 into a spinning machine with nitrogen as the medium for melt spinning to obtain modified polylactic acid continuous fibers; Step 6: The modified polylactic acid continuous fibers obtained in the fifth step are cleaned and cut into short fibers with a length of 38 mm. After classification, modified polylactic acid short fibers with uniform length are obtained.

9. The method for producing modified polylactic acid chopped short fibers according to claim 1, wherein: The processing temperature during granulation in the third step is 160-190° C., the length-to-diameter ratio of the co-rotating parallel twin-screw extruder is 56:1, and it includes 2 independent vacuum devolatilization chambers and is divided into 13 independent temperature control zones, and the length-to-diameter ratio of each temperature control zone is 4:

1.

10. The method for producing modified polylactic acid chopped short fibers according to claim 1, wherein: In the fifth step, the spinning temperature is 150-180° C., the winding temperature is 60-80° C., the winding speed is 1500-1800 m / min, and the stretching ratio is 10-12.

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