Pre-crosslinked sheath-core composite fiber reinforced polylactic acid material

Abstract

The invention discloses a pre-crosslinked sheath-core composite fiber reinforced polylactic acid material which has good toughness and strength and can be applied to the fields of extrusion and injection molding with requirements on high-strength and high-toughness polylactic acid materials. The material comprises the following components in parts by mass: 50-95 parts of polylactic acid and 5-50 parts of pre-crosslinked sheath-core composite fiber. And carrying out melt blending through a twin-screw extruder to obtain the reinforced polylactic acid material with good strength and toughness.

Description

Technical Field

[0001] The present invention relates to the field of polymer material modification, and particularly to a modified polylactic acid material with high strength and high toughness. Background Art

[0002] Polylactic acid is an aliphatic polyester formed by converting starch extracted from renewable plant resources such as corn and potatoes into glucose, fermenting it into lactic acid, and further polymerizing it. Polylactic acid has thermoplasticity and can be processed by extrusion, injection molding, thermoforming, etc., and can also be melt-spun into fibers. After degradation, polylactic acid materials can completely generate carbon dioxide and water, without causing pollution to the environment, and have broad application prospects. Polylactic acid is a semi-crystalline material and is brittle itself. After toughening, the strength of the material will drop significantly, limiting its scope of use.

[0003] The patent with publication number CN102690507A discloses a glass fiber reinforced polylactic acid composite material. By blending polylactic acid with polycarbonate and adding glass fiber for modification, the rigidity and heat resistance of the polylactic acid material are improved. However, the added polycarbonate is a non-degradable material, and the added glass fiber has poor compatibility with polylactic acid and will also reduce the fluidity of the material. The patent with publication number CN103467945A discloses a kenaf fiber reinforced polylactic acid degradable plastic, which enhances polylactic acid by adding kenaf fiber. The patent with publication number CN103467944A discloses a ramie fiber polylactic acid degradable plastic, which enhances polylactic acid by adding ramie fiber. The added kenaf fiber and ramie fiber both have problems of poor compatibility and poor processability. The patent with publication number CN107286614A discloses a polylactic acid sheet reinforced with pre-crosslinked polylactic acid fibers and its preparation method. By crosslinking polylactic acid fibers and using them as reinforcing materials to enhance polylactic acid, in the process of thermal mixing and processing, within a certain temperature range, the pre-crosslinked polylactic acid fibers will maintain their shape, form a pre-crosslinked region similar to an "island" structure, and impregnate with the polylactic acid matrix, increasing the interfacial bonding force and improving the strength of the composite material. However, while forming the pre-crosslinked region and impregnating with polylactic acid, the structure of the polylactic acid fibers has defects, reducing the strength and having a certain decline in the enhancement effect. Summary of the Invention

[0004] In view of the above problems, the present invention provides a pre-crosslinked skin-core composite fiber reinforced polylactic acid material to solve the problem of the decrease in strength after toughening of polylactic acid. First, polylactic acid is blended with different crosslinking agents and melt-extruded to prepare modified polylactic acid for the skin layer and the core layer respectively, then spun to prepare polylactic acid fibers with a skin-core structure, and then irradiated to obtain pre-crosslinked skin-core composite polylactic acid fibers. The prepared pre-crosslinked skin-core composite lactic acid fibers are blended with polylactic acid, a toughening material, and a compatibilizer and melt-extruded and pelletized to prepare a pre-crosslinked skin-core composite fiber reinforced polylactic acid material.

[0005] A pre-crosslinked skin-core composite fiber reinforced polylactic acid material, calculated by mass, the raw material composition includes: Polylactic acid: 50-95 Pre-crosslinked skin-core composite fiber: 5-50.

[0006] Preferably, a pre-crosslinked skin-core composite fiber reinforced polylactic acid material, calculated by mass, the raw material composition includes: Polylactic acid: 30-90 Toughening material: 5-30 Pre-crosslinked skin-core composite fiber: 5-50.

[0007] Preferably, a pre-crosslinked skin-core composite fiber reinforced polylactic acid material, calculated by mass, the raw material composition includes: Polylactic acid: 60-80 Toughening material: 10-20 Pre-crosslinked skin-core composite fiber: 10-20 Other additives: 0.1-30 parts; The other additives include antioxidants, chain extenders, lubricants, pigments, color powders, mineral fillers, etc.

[0008] Preferably, a pre-crosslinked skin-core composite fiber reinforced polylactic acid material, calculated by mass, the raw material composition includes: Polylactic acid: 60-80 Toughening material: 10-20 Pre-crosslinked skin-core composite fiber: 10-20 Antioxidant: 0.2-1 Chain extender: 0.1-0.8.

[0009] The polylactic acid is one or a combination of two of commercially available PLLA and PDLA.

[0010] The toughening material is one or a combination of several of commercially available PBAT, PBS, and PCL.

[0011] The pre-crosslinked core-shell composite fiber described above has a skin layer material composed of PLLA with a light purity of 96% or 98% and a crosslinking sensitizer, which are melt-blended and extruded into pellets. PLLA with a light purity of 96% is preferred.

[0012] The core layer material is PLLA with a light purity > 99% and a crosslinking sensitizer, which are melt-blended to form pellets.

[0013] The crosslinking sensitizer is one or a mixture of diallyl phthalate, triallyl benzene tricarboxylate, triallyl cyanurate, and triallyl isocyanurate. Then, the polylactic acid core-shell composite fiber is obtained by spinning, and finally, it is irradiated and crosslinked with electron beams or γ-rays.

[0014] The antioxidant described above is a hindered phenol main antioxidant and a phosphite auxiliary antioxidant, such as 1010, 168, etc.

[0015] The chain extender described above is a mixture of a polymeric epoxy-functionalized chain extender and an epoxy functional group ring-opening catalyst.

[0016] The above substances are mixed evenly and then put into a twin-screw extruder for melt extrusion. After cooling and pelletizing, a pre-crosslinked core-shell composite fiber-reinforced polylactic acid material is obtained.

[0017] Preferably, the polylactic acid has a melt index of 10 - 30 g / 10min PLLA.

[0018] Preferably, the toughening material is PBAT.

[0019] Preferably, for the pre-crosslinked polylactic acid core-shell composite fiber, the crosslinking agent is triallyl isocyanurate. The mass ratio of the skin layer material PDLA to the crosslinking sensitizer is 100:0.5 - 0.8; the mass ratio of the core layer material PLLA to the crosslinking sensitizer is 100:1 - 1.5, and the irradiation dose is 25 - 30 kGy.

[0020] Preferably, for the pre-crosslinked core-shell composite polylactic acid fiber-reinforced polylactic acid material, by mass, the raw material composition includes: PLLA: 59 - 74.5 PABT: 10 - 20 Pre-crosslinked core-shell composite polylactic acid fiber: 15 - 20 Antioxidant: 0.4 - 0.6 Chain extender: 0.1 - 0.4.

[0021] The present invention provides a pre-crosslinked skin-core composite fiber reinforced polylactic acid material, which comprises the following steps: 1. Prepare the materials required for the composite fiber skin layer and core layer respectively, and then carry out spinning to obtain the skin-core composite fiber; 2. After irradiating and crosslinking the obtained skin-core composite fiber, make it into short fibers to obtain the pre-crosslinked skin-core composite fiber; 3. Weigh the short-cut composite fibers in step 2 and polylactic acid according to the formula ratio, fully mix them and then put them into a twin-screw extruder for melt blending, draw and cool and pelletize to obtain the required reinforced polylactic acid material.

[0022] The temperature of the extruder is: 150~200 °C; preferably 160-180 °C,

[0023] Compared with the prior art, the present invention has the following characteristics: The pre-crosslinked polylactic acid skin-core composite fiber added in the present invention, by adding different contents of crosslinking sensitizers and different optical purities of PLA to the skin layer and core layer materials, while improving the strength and heat melting temperature of the fiber, the skin layer and the core layer have different thermal melting points. During melt blending processing, within a certain temperature range, the crosslinked part of the skin layer maintains the skeleton structure, and part of the amorphous region melts and is miscible with the polylactic acid matrix, forming pits on the surface of the core layer, which can improve the bonding force with the polylactic acid matrix. At the same time, there are no defects in the core layer fibers, and good strength is maintained while improving compatibility. Embodiment

[0024] The present invention will be further described below in conjunction with specific embodiments. These embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. All raw materials used in the following examples and comparative examples are commercially available unless otherwise specified.

[0025] Polylactic acid (PLA): FY801 Fengyuan (optical purity > 99%), FY802 Fengyuan (optical purity 98%), FY804 Fengyuan (optical purity 96%), L130 Total Corbion; Crosslinking sensitizer: Triallyl isocyanurate PBAT: TH801T Tunhe Antioxidant: 1010, 168 Chain extender: KL-E4370B, Shanxi Research Institute of Chemical Industry.

[0026] A pre-crosslinked sheath-core composite fiber reinforced polylactic acid material comprises the following steps: 1. Firstly prepare the materials required for the sheath layer and the core layer of the composite fiber respectively, and then perform spinning to obtain the sheath-core composite fiber; 2. After irradiating and crosslinking the obtained sheath-core composite fiber, prepare short fibers to obtain the pre-crosslinked sheath-core composite fiber; 3. The short-cut composite fiber and polylactic acid in the 2nd step are weighed according to the formula ratio in Table 1, fully mixed, and then put into a twin-screw extruder for melt blending, the temperature of the extruder is: 160-180 DEG C, and the drawing is cooled and pelletized to obtain the required reinforced polylactic acid material.

[0027] The skin material in step 1 is FY804 and the cross-linking sensitizer in a ratio of 100:0.6. After mixing evenly, it is put into a twin-screw extruder for melt blending. The extruder temperature is: 160-170°C, and the strands are cooled and pelletized to obtain the required pellets. The core material is FY801 and the cross-linking sensitizer in a ratio of 100:1.2. After mixing evenly, it is put into a twin-screw extruder for melt blending. The extruder temperature is: 170-180 degrees Celsius, and the strands are cooled and pelletized to obtain the required pellets. After the obtained skin material and core material are dried at 60°C for 6-8h, they are respectively put into two single-screw extruders, and then transported to the spinning assembly through a metering pump. After the two melts are combined at the spinneret of the composite spinning assembly, they are sprayed and rolled through the spinneret hole to obtain a skin-core composite polylactic acid fiber with a diameter of 0.2-0.4mm. The temperature of the skin layer single screw extruder is 180-200°C. The temperature of the core layer single screw extruder is 190-220°C.

[0028] The pre-crosslinked core-skin composite polylactic acid fiber in step 2: the core-skin composite polylactic acid fiber obtained in step 2 is irradiated with a 5MeV electron accelerator at a dose of 30 kGy. After irradiation, the fiber is chopped into 6 mm-12 mm.

[0029] The pre-crosslinked fibers in Comparative Examples 2 and 3 are core layer materials FY801, which are extruded through a single screw extruder and then transferred to a spinning assembly through a metering pump. The extruder temperature is 190-220°C, and the fibers are ejected and wound through a spinneret hole with a diameter of 0.2-0.4 mm. The fibers are then irradiated through a 5MeV electron accelerator with a dose of 30 kGy. After irradiation, the fibers are chopped into 6 mm-12 mm. The core layer materials of the pre-crosslinked core-skin composite fibers in Examples 1 to 4 and Comparative Example 4 are all FY801, the skin material of Example 4 is FY802, and the skin material of Examples 1 to 3 and Comparative Example 4 is FY804.

[0030] Table 1 Mass fractions of components in Examples 1-4 and Comparative Examples 1-4 Formulation Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 L130 74.3 64.3 59.3 59.3 79.3 74.3 59.3 54.3 TH801T 10 20 20 20 20 10 20 Pre-crosslinked skin-core composite fiber 15 15 20 20 / / / 25 Pre-crosslinked fiber / / / / / 15 20 / Antioxidant 1010 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Antioxidant 168 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Chain extender KL-E4370B 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 It can be seen from the comparison of the test results of the examples and comparative examples in Table 2 that the addition of pre-crosslinked skin-core composite polylactic acid fibers can significantly improve the performance of the composite material. With the increase of the content, the mechanical properties of the composite material all increase to a certain extent. Compared with the pre-crosslinked fibers, the pre-crosslinked skin-core composite fibers have better compatibility and thus have a better strengthening effect on the mechanical properties. When the content of the pre-crosslinked skin-core composite fibers exceeds 20 parts, the strengthening trend decreases, and bridging is likely to occur during the processing. Therefore, when the addition amount is 15-20 parts, it has better strengthening effect and processability.

[0031] Table 2 Test Results of Examples 1-4 and Comparative Examples 1-4 Test item Test standard Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Tensile strength GB / T 1040.2 74 71 79 70 45 66 69 81 Flexural strength GB / T 9341 98 96 113 95 56 86 93 115 Flexural modulus GB / T 9341 4836 4481 5139 4468 2885 4454 4832 5341 Notched Izod impact GB / T 1043.1 7.1 7.7 8.6 7.3 3.9 5.6 6.7 8.9 The above description of the embodiments is for the convenience of those of ordinary skill in the art to understand and apply the present invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative labor. Therefore, the present invention is not limited to the embodiments here, and the improvements and modifications made by those skilled in the art without departing from the scope of the present invention according to the disclosure of the present invention should be within the protection scope of the present invention.

Claims

1. A pre-crosslinked core-skin composite fiber reinforced polylactic acid material, calculated by weight, the raw material composition is include: Polylactic acid: 50-95 Pre-crosslinked sheath-core composite fiber: 5-50.

2. A pre-crosslinked core-skin composite fiber reinforced polylactic acid material, calculated by weight, the raw material composition is include: Polylactic acid: 60-80 Toughening material: 10-20 Pre-crosslinked sheath-core composite fiber: 10-20 Antioxidant: 0.2-1 Chain extender: 0.1-0.

8.

3. A pre-crosslinked skin-core composite fiber reinforced polylactic acid material according to claim 1 or 2, It is characterized in that The polylactic acid is one of commercialized PLLA and PDLA or a combination of both.

4. A pre-crosslinked skin-core composite fiber reinforced polylactic acid material according to claim 1 or 2, It is characterized in that The sheath material of the pre-crosslinked sheath-core composite fiber is PLLA with an optical purity of 96% or 98% and a crosslinking sensitizer; the core material is PLLA with an optical purity of more than 99% and a crosslinking sensitizer.

5. The pre-crosslinked core-skin composite fiber reinforced polylactic acid material according to claim 4, It is characterized in that The cross-linking sensitizer is one or a mixture of bisallyl phthalate, triallyl trimellitate, triallyl cyanurate and triallyl isocyanurate.

6. The pre-crosslinked core-skin composite fiber reinforced polylactic acid material according to claim 2, It is characterized in that The toughening material is one or a combination of commercialized PBAT, PBS, and PCL.

7. The pre-crosslinked core-skin composite fiber reinforced polylactic acid material according to claim 2, It is characterized in that The antioxidant is a hindered phenol type primary antioxidant and a phosphite type auxiliary antioxidant; the chain extender is a mixture of a polymeric epoxy functional chain extender and an epoxy functional group ring-opening catalyst.

8. The pre-crosslinked core-skin composite fiber reinforced polylactic acid material according to claim 4, It is characterized in that The pre-crosslinked polylactic acid sheath-core composite fiber has a crosslinking agent of triallyl isocyanurate, a mass ratio of the sheath material PDLA to the crosslinking sensitizer of 100:0.5-0.8, and a mass ratio of the core material PLLA to the crosslinking sensitizer of 100:1-1.

5.

9. The pre-crosslinked core-skin composite fiber reinforced polylactic acid material according to claim 4, It is characterized in that The method for preparing the pre-crosslinked sheath-core composite fiber is as follows:

1. Firstly, materials required for the sheath layer and the core layer of the composite fiber are prepared respectively, and then spinning is performed to prepare the sheath-core composite fiber; 2. The obtained core-skin composite fiber is irradiated and cross-linked to prepare short fibers, thereby obtaining a pre-cross-linked core-skin composite fiber; 3. The chopped composite fibers and polylactic acid in step 2 are weighed according to the formula ratio, mixed thoroughly, and then put into a twin-screw extruder for melt blending, and then drawn, cooled, and pelletized to obtain the desired reinforced polylactic acid material.

10. The pre-crosslinked core-skin composite fiber reinforced polylactic acid material according to claim 9, It is characterized in that The radiation cross-linking was performed at a dose of 25-30 kGy.