A light-resistant biodegradable plastic, its preparation method, and its application in dustproof netting.

Abstract

This invention discloses a light-resistant biodegradable plastic, its preparation method, and its application in dustproof netting. The raw material composition of the light-resistant biodegradable plastic, by weight, includes: 60-70 parts polylactic acid (PLA), 10-15 parts lignin, 5-10 parts toughening agent, 5-8 parts UV-shielding agent, 3-5 parts compatibilizer, 1-2 parts composite nucleating agent, and 0-0.5 parts colorant. The UV-shielding agent is composed of sericite, glass microspheres, and fluorite powder. The layered structure of sericite and the spherical structure of glass microspheres reflect ultraviolet light from multiple angles, while the fluorite powder absorbs and converts the transmitted ultraviolet light, thereby shielding ultraviolet rays and increasing the light resistance of PLA. A compatibilizer is used to modify the nano-lignin, which absorbs ultraviolet light and converts the light energy into heat energy in a timely manner, preventing ultraviolet light from attacking the PLA chain segments. It has stable processability, low cost, and stable raw material supply, making it suitable for use in dustproof netting.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically relating to a light-resistant biodegradable plastic, its preparation method, and its application in dustproof netting. Background Technology

[0002] Driven by environmental protection requirements, dust control netting is widely used in various settings, including mining, construction sites, road projects, municipal pipeline renovation, landscaping, chemical raw material storage yards, sand and gravel plants, bulk cargo ports, coal collection and transportation stations, and landfills. Dust control netting reduces air pollution from dust, inhibits the spread of toxic and harmful dust, and prevents soil erosion. Traditional dust control netting is mostly made from high-strength plastics such as high-density polyethylene (HDPE) and polypropylene (PP). The process involves melt extrusion into thin sheets, longitudinal slitting, and oriented stretching to create filaments, which are then woven together. Because dust control netting is used outdoors in windy and sunny environments, it is easily damaged by sunlight, breaking down into plastic fragments that are difficult to recycle. For example, dust control netting used extensively at construction sites and in green belts is generally not recycled. Once damaged dust control netting seeps into the soil, it becomes a source of microplastic pollution. As the usage of dust control netting increases year by year, the secondary pollution problem caused by fragmented netting left in the soil is becoming increasingly serious.

[0003] With increasing environmental awareness, the upgrading and transformation of the dust control netting industry is urgently needed, and the use of biodegradable plastics to produce fully biodegradable dust control netting is gradually becoming a trend. After biodegradable plastics flow into the soil, they degrade into inorganic small molecules such as water and carbon dioxide in the soil's microbial environment. This degradation process is non-toxic and harmless, leaving no pollutants. Using biodegradable plastics in dust control netting eliminates the need for recycling after fulfilling its dust control function, thus preventing secondary pollution.

[0004] Polylactic acid (PLA) possesses excellent biodegradability and relatively low cost, making it a preferred material for biodegradable dustproof netting. However, while exhibiting excellent biodegradability, PLA is also prone to photodegradation. Dustproof netting made of PLA, when exposed to sunlight and subjected to ultraviolet (UV) radiation, suffers photodegradation due to the high energy of UV rays, resulting in decreased mechanical properties, rapid breakage, and a shortened lifespan. Its strength and lifespan are significantly lower than those of high-density polyethylene (HDPE) and polypropylene (PP) dustproof netting. When using conventional UV absorbers such as UV-531, UV-P, and UV-326 to improve the light resistance of PLA, an addition of more than 2% is generally required to achieve an effect, significantly increasing costs. Furthermore, UV absorbers are easily decomposed by processing temperatures. When zinc oxide and titanium dioxide are used to resist UV radiation in PLA, these semiconductors can reflect and absorb UV rays, primarily through electron transitions, absorbing UV energy and releasing it as heat, thus providing a certain degree of UV shielding. However, zinc oxide and titanium dioxide are also photocatalytic materials that can trigger a series of chemical reactions under light. For example, they can generate hydroxyl radicals with decomposition capabilities under light, which can lead to the breakage of polylactic acid chain segments. Summary of the Invention

[0005] This invention aims to solve the problem of easy photodegradation of polylactic acid (PLA), a biodegradable plastic. It enhances the light resistance and mechanical properties of PLA through low-cost improvements, enabling it to meet the requirements for dustproof netting. This allows PLA to resist ultraviolet radiation in light-exposed environments, maintaining good mechanical strength and preventing breakage.

[0006] In one aspect, the present invention proposes a light-resistant biodegradable plastic, the composition of which, by weight, includes: 60-70 parts of polylactic acid, 10-15 parts of lignin, 5-10 parts of toughening agent, 5-8 parts of UV shielding agent, 3-5 parts of compatibilizer, 1-2 parts of composite nucleating agent, and 0-0.5 parts of colorant.

[0007] The lignin is nanoscale lignin with a particle size of <300nm;

[0008] The toughening agent is at least one of polybutylene adipate terephthalate (PBAT), thermoplastic starch (TPS), polycaprolactone (PCL), polybutylene succinate (PBS), and polyhydroxyalkanoate (PHA).

[0009] The UV-shielding additive comprises sericite, glass microspheres, and fluorite powder;

[0010] The compatibilizer is glycidyl methacrylate;

[0011] The composite nucleating agent is composed of an inorganic nucleating agent and an amide nucleating agent in a mass ratio of (2-5):1.

[0012] Preferably, the lignin is nano-sized lignin with a particle size of <100nm. Nano-sized lignin is obtained from lignin separated from paper pulping waste through high-pressure homogenization and nano-sizing. It is low-cost, readily available for industrial use, and a renewable biomass resource. Because lignin is a biomass material and contains abundant ketone and phenolic hydroxyl groups, it possesses excellent UV resistance. When nano-lignin is dispersed in polylactic acid (PLA), under UV attack, the lignin absorbs UV light and converts the light energy into heat energy in a timely manner, preventing UV damage to the PLA chain segments. Given the difficulty in dispersing nano-sized lignin, this invention uses liquid glycidyl methacrylate (GMA) as a compatibilizer. Utilizing its ionic reactive epoxy groups and self-polymerizing properties, GMA is used to pre-disperse and modify lignin, causing the hydroxyl groups on the nano-lignin molecules to react and graft methacrylic acid, increasing the compatibility between lignin and PLA, and allowing the nano-lignin particles to be uniformly dispersed in PLA to form a UV barrier.

[0013] Preferably, the UV-shielding additive is a composite material made by grinding sericite, glass microspheres, and fluorite powder in a mass ratio of 10:5:2. First, the sericite and fluorite powder are ground in a ball mill until the D90 particle size is <10μm. Then, glass microspheres are added to the composite to obtain the UV-shielding additive; the glass microspheres are solid glass microspheres with a D50 particle size <5μm. Sericite has reflective properties due to its layered structure; glass microspheres have reflective properties due to their spherical structure; fluorite has certain fluorescent properties, capable of absorbing ultraviolet light and converting it into visible light. Through the composite of sericite, glass microspheres, and fluorite powder, the multilayer and spherical structures allow ultraviolet light irradiated on the polylactic acid (PLA) surface to be reflected from multiple angles, while the transmitted ultraviolet light is absorbed and converted, thereby shielding the PLA from ultraviolet radiation. Compared to using traditional UV absorbers, this method is lower in cost and more stable in processability.

[0014] More preferably, 0.5-1.0% of a dispersant by weight of the material being ground is added during grinding; the dispersant is selected from sodium hexametaphosphate or sodium pyrophosphate.

[0015] Preferably, the composite nucleating agent is composed of an inorganic nucleating agent and an amide-based nucleating agent in a mass ratio of 2:1. Polylactic acid (PLA) typically exhibits slow crystallization after processing and molding, remaining amorphous, brittle, and exhibiting reduced mechanical strength. By combining an inorganic nucleating agent and an amide-based organic nucleating agent, heterogeneous nucleation of PLA is promoted, enabling rapid crystallization during cooling after processing and molding, refining the grain size, reducing brittleness, and increasing strength. In particular, by increasing the crystallinity of PLA and refining the grain size, ultraviolet (UV) penetration can be effectively prevented, mitigating the penetrating attack of UV rays on PLA.

[0016] Further preferably, the inorganic nucleating agent is selected from at least one of talc, calcium carbonate, and kaolin with a particle size <2μm; the amide nucleating agent is preferably N,N′,N″-tricyclohexyl-1,3,5-benzenetricarboxamide (TMC-328). Through the combination of inorganic and organic nucleating agents, the nucleating agent is dispersed in polylactic acid in micrometers as heterogeneous crystal nuclei, inducing polylactic acid to accelerate crystallization during thermoforming cooling and promoting the refinement of grain size.

[0017] Preferably, the pigment is selected from one of cobalt green, iron oxide green, chromium oxide green, carbon black, iron black, or aniline black as needed.

[0018] In one aspect, the present invention proposes a method for preparing a light-resistant biodegradable plastic, comprising the following steps:

[0019] (1) Mix sericite and fluorite powder evenly, add dispersant and dry grind in ball mill until D90 particle size <10μm, then add glass microspheres to obtain UV shielding additive;

[0020] (2) Add 10-15 parts of lignin and 3-5 parts of compatibilizer to the kneader by weight and knead. Control the temperature below 60℃. After kneading evenly, transfer to the high-speed mixer. Then add 60-70 parts of polylactic acid, 5-10 parts of toughening agent, 5-8 parts of UV shielding agent, 1-2 parts of composite nucleating agent, and 0-0.5 parts of color powder. Control the temperature of the high-speed mixer at 90-100℃ and mix and disperse at low speed for 30-60 minutes. Then discharge the material to the cooling pot and stir to cool.

[0021] (3) The material cooled in step (2) is conveyed to a twin-screw extruder for hot melt extrusion, and then granulated by air-cooled die surface to obtain a light-resistant biodegradable plastic.

[0022] Preferably, when the ball mill is used for dry grinding, zirconia ceramic balls are added as grinding media, and the volume of the added grinding media is 1 / 3 of the total volume of sericite and fluorite powder.

[0023] Preferably, the kneading time of the kneader is controlled at 20-60 minutes to allow the liquid compatibilizer to fully penetrate the lignin.

[0024] Preferably, the twin-screw extruder is a co-rotating twin-screw extruder, with the temperature range of each section set to 170-220℃ during hot melt extrusion; the screw length-to-diameter ratio is 40:1; and the screw speed is 200-300 rpm.

[0025] Another aspect of the present invention provides an application of light-resistant biodegradable plastic in dust control nets. Through low-cost light-resistant and enhanced improvements to polylactic acid (PLA), it can be used in dust control nets in outdoor construction sites, road projects, mining operations, and landscaping maintenance. After long-term exposure to ultraviolet radiation, the dust control nets are not easily aged or damaged. After completing dust control, they are easily degraded in the soil's biological environment, thereby reducing environmental pollution.

[0026] This invention discloses a light-resistant biodegradable plastic, its preparation method, and its application in dustproof nets. Compared with existing technologies, the beneficial effects are as follows:

[0027] 1. Using glycidyl methacrylate as a compatibilizer, nano-lignin is modified. When the nano-lignin is dispersed in polylactic acid (PLA), it absorbs ultraviolet light and converts the light energy into heat energy in a timely manner when subjected to UV attack, thus preventing UV light from attacking the PLA chain segments. At the same time, the nano-lignin increases the strength of PLA, making the dustproof net more robust.

[0028] 2. A UV-shielding additive is obtained by combining sericite, glass microspheres, and fluorite powder. The layered structure of sericite and the spherical structure of glass microspheres can reflect UV light irradiating the surface of polylactic acid from multiple angles, while the fluorite powder absorbs and converts the transmitted UV light, thereby shielding the polylactic acid from UV attack and increasing the light resistance of polylactic acid.

[0029] 3. This invention simultaneously improves the light resistance and strength of polylactic acid. Compared with the use of traditional ultraviolet absorbers, it is lower in cost, more stable in processability, and all raw materials can be supplied industrially. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to specific examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Example 1

[0032] (1) Weigh sericite, glass microspheres and fluorite powder according to the mass ratio of 10:5:2; wherein, the glass microspheres are solid glass microspheres with a D50 particle size <5μm; first, mix sericite and fluorite powder evenly, add sodium hexametaphosphate dispersant at 1% of the total mass of sericite and fluorite powder, and dry grind and composite in a ball mill. The grinding medium is zirconia ceramic balls, and the volume of the grinding medium added is 1 / 3 of the total volume of sericite and fluorite powder; grind until the D90 particle size <10μm, and then add glass microspheres to the composite to obtain the UV shielding additive;

[0033] (2) Add 15 parts by weight of nano-sized lignin with a particle size <100nm and 5 parts by weight of compatibilizer glycidyl methacrylate to a kneader and knead for 30 minutes. Control the temperature to be below 60℃. After kneading evenly, transfer to a high-speed mixer. Then add 60 parts by weight of polylactic acid, 10 parts by weight of toughening agent PBAT, 8 parts by weight of UV shielding agent, 1.5 parts by weight of composite nucleating agent (talc powder with a particle size <2μm and TMC-328 are compounded at a mass ratio of 2:1), and 0.3 parts by weight of cobalt green (CAS:68186-85-6). Control the temperature of the high-speed mixer at 100℃ and mix and disperse at a low speed of 200rpm for 45 minutes. Then discharge the material to a cooling pot and stir to cool.

[0034] (3) The material cooled in step (2) is conveyed to a Φ65 co-rotating twin-screw extruder with a screw length-to-diameter ratio of 40:1 for hot melt extrusion. The temperature of the first and second feeding zones is controlled at 170℃; the temperature of the third, fourth and fifth plasticizing zones is controlled at 200℃; the temperature of the sixth, seventh and eighth homogenizing zones is controlled at 190℃; the temperature of the ninth and tenth compression zones is controlled at 220℃; the screw speed is 250 rpm. After extrusion, the die surface is directly air-cooled and pelletized at the die outlet. The pellets are collected after air cooling to obtain a light-resistant biodegradable plastic.

[0035] Example 2

[0036] (1) Weigh sericite, glass microspheres and fluorite powder according to the mass ratio of 10:4:3; wherein, the glass microspheres are solid glass microspheres with a D50 particle size <5μm; first, mix sericite and fluorite powder evenly, add sodium pyrophosphate dispersant at 1% of the total mass of sericite and fluorite powder, and dry grind and composite in a ball mill. The grinding medium is zirconia ceramic balls, and the volume of the grinding medium added is 1 / 3 of the total volume of sericite and fluorite powder; grind until the D90 particle size <10μm, and then add glass microspheres to the composite to obtain the UV shielding additive;

[0037] (2) Add 10 parts by weight of nano-sized lignin with a particle size <300nm and 3 parts by weight of compatibilizer glycidyl methacrylate to a kneader and knead for 30 minutes. Control the temperature to be below 60℃. After kneading evenly, transfer to a high-speed mixer. Then add 70 parts by weight of polylactic acid, 5 parts by weight of toughening agent TPS, 5 parts by weight of UV shielding agent, 2 parts by weight of composite nucleating agent (calcium carbonate with a particle size <2μm and TMC-328 are compounded at a mass ratio of 2:1), and 0.3 parts by weight of cobalt green (CAS:68186-85-6). Control the temperature of the high-speed mixer at 100℃ and mix and disperse at a low speed of 200rpm for 30 minutes. Discharge the material to a cooling pot and stir to cool.

[0038] (3) The material cooled in step (2) is conveyed to a Φ65 twin-screw extruder with a screw length-to-diameter ratio of 40:1 for hot melt extrusion. The temperature of the first and second feeding zones is controlled at 180℃; the temperature of the third, fourth and fifth plasticizing zones is controlled at 210℃; the temperature of the sixth, seventh and eighth homogenizing zones is controlled at 190℃; the temperature of the ninth and tenth compression zones is controlled at 220℃; the screw speed is 200 rpm. After extrusion, the die surface is directly air-cooled and pelletized at the die outlet. The pellets are collected after air cooling to obtain a light-resistant biodegradable plastic.

[0039] Example 3

[0040] (1) Weigh sericite, glass microspheres and fluorite powder according to the mass ratio of 8:7:2; wherein, the glass microspheres are solid glass microspheres with a D50 particle size <5μm; first, mix sericite and fluorite powder evenly, add sodium hexametaphosphate dispersant at 1% of the total mass of sericite and fluorite powder, and dry grind and composite in a ball mill. The grinding medium is zirconia ceramic balls, and the volume of the grinding medium added is 1 / 3 of the total volume of sericite and fluorite powder; grind until the D90 particle size <10μm, and then add glass microspheres to the composite to obtain the UV shielding additive;

[0041] (2) Add 12 parts by weight of nano-sized lignin with a particle size <100nm and 4 parts by weight of compatibilizer glycidyl methacrylate to a kneader and knead for 30 minutes. Control the temperature to be below 60℃. After kneading evenly, transfer to a high-speed mixer. Then add 65 parts by weight of polylactic acid, 8 parts by weight of toughening agent PBS, 6 parts by weight of UV shielding agent, 1.5 parts by weight of composite nucleating agent (kaolin with a particle size <2μm and TMC-328 are compounded at a mass ratio of 3:1) and 0.3 parts by weight of cobalt green (CAS:68186-85-6). Control the temperature of the high-speed mixer at 100℃ and mix and disperse at a low speed of 200rpm for 30 minutes. Then discharge the material to a cooling pot and stir to cool.

[0042] (3) The material cooled in step (2) is conveyed to a Φ65 twin-screw extruder with a screw length-to-diameter ratio of 40:1 for hot melt extrusion. The temperature of the first and second feeding zones is controlled at 170℃; the temperature of the third, fourth and fifth plasticizing zones is controlled at 200℃; the temperature of the sixth, seventh and eighth homogenizing zones is controlled at 190℃; the temperature of the ninth and tenth compression zones is controlled at 220℃; the screw speed is 300 rpm. After extrusion, the die surface is directly air-cooled and pelletized at the die outlet. The pellets are collected after air cooling to obtain a light-resistant biodegradable plastic.

[0043] Comparative Example 1

[0044] (1) Add 60 parts of polylactic acid, 10 parts of toughening agent PBAT, 2 parts of UV-531 ultraviolet absorber, 1.5 parts of composite nucleating agent (talc powder with a particle size <2μm and TMC-328 are compounded at a mass ratio of 2:1) and 0.3 parts of cobalt green (CAS:68186-85-6) to a high-speed mixer according to the weight, mix and disperse at a low speed of 200rpm for 20min, and then discharge the material to a cooling pot for stirring and cooling.

[0045] (2) The material cooled in step (1) is conveyed to a Φ65 co-rotating twin-screw extruder with a screw length-to-diameter ratio of 40:1 for hot melt extrusion. The temperature of the first and second feeding zones is controlled at 170℃; the temperature of the third, fourth and fifth plasticizing zones is controlled at 200℃; the temperature of the sixth, seventh and eighth homogenizing zones is controlled at 190℃; the temperature of the ninth and tenth compression zones is controlled at 220℃; the screw speed is 250 rpm. After extrusion, the die surface is directly air-cooled and pelletized at the die outlet. The pellets are collected after air cooling to obtain a light-resistant biodegradable plastic.

[0046] This comparative example uses the conventional ultraviolet absorber UV-531 to improve the light resistance of polylactic acid.

[0047] Comparative Example 2

[0048] (1) Weigh sericite and glass microspheres according to a mass ratio of 10:5; wherein the glass microspheres are solid glass microspheres with a D50 particle size <5μm; first, mix sericite with sodium hexametaphosphate, a dispersant of 1% of the mass of sericite, and dry grind them in a ball mill. The grinding medium is zirconia ceramic balls, and the volume of the grinding medium added is 1 / 3 of the volume of sericite; grind until the D90 particle size <10μm, and then add the glass microspheres to the composite to obtain the UV shielding additive;

[0049] (2) Add 15 parts by weight of nano-sized lignin with a particle size <100nm and 5 parts by weight of compatibilizer glycidyl methacrylate to a kneader and knead for 30 minutes. Control the temperature to be below 60℃. After kneading evenly, transfer to a high-speed mixer. Then add 60 parts by weight of polylactic acid, 10 parts by weight of toughening agent PBAT, 8 parts by weight of UV shielding agent, 1.5 parts by weight of composite nucleating agent (talc powder with a particle size <2μm and TMC-328 are compounded at a mass ratio of 2:1), and 0.3 parts by weight of cobalt green (CAS:68186-85-6). Control the temperature of the high-speed mixer at 100℃ and mix and disperse at a low speed of 200rpm for 45 minutes. Then discharge the material to a cooling pot and stir to cool.

[0050] (3) The material cooled in step (2) is conveyed to a Φ65 co-rotating twin-screw extruder with a screw length-to-diameter ratio of 40:1 for hot melt extrusion. The temperature of the first and second feeding zones is controlled at 170℃; the temperature of the third, fourth and fifth plasticizing zones is controlled at 200℃; the temperature of the sixth, seventh and eighth homogenizing zones is controlled at 190℃; the temperature of the ninth and tenth compression zones is controlled at 220℃; the screw speed is 250 rpm. After extrusion, the die surface is directly air-cooled and pelletized at the die outlet. The pellets are collected after air cooling to obtain a light-resistant biodegradable plastic.

[0051] Fluorite powder was not used in this comparative example of UV-shielding additives.

[0052] Comparative Example 3

[0053] (1) Weigh sericite and fluorite powder according to a mass ratio of 10:2; first, mix sericite and fluorite powder evenly, add sodium hexametaphosphate dispersant at 1% of the total mass of sericite and fluorite powder, and dry grind and compound them in a ball mill. The grinding medium is zirconia ceramic balls, and the volume of the grinding medium added is 1 / 3 of the total volume of sericite and fluorite powder; grind until the D90 particle size is <10μm to obtain the UV shielding additive;

[0054] (2) Add 15 parts by weight of nano-sized lignin with a particle size <100nm and 5 parts by weight of compatibilizer glycidyl methacrylate to a kneader and knead for 30 minutes. Control the temperature to be below 60℃. After kneading evenly, transfer to a high-speed mixer. Then add 60 parts by weight of polylactic acid, 10 parts by weight of toughening agent PBAT, 8 parts by weight of UV shielding agent, 1.5 parts by weight of composite nucleating agent (talc powder with a particle size <2μm and TMC-328 are compounded at a mass ratio of 2:1), and 0.3 parts by weight of cobalt green (CAS:68186-85-6). Control the temperature of the high-speed mixer at 100℃ and mix and disperse at a low speed of 200rpm for 45 minutes. Then discharge the material to a cooling pot and stir to cool.

[0055] (3) The material cooled in step (2) is conveyed to a Φ65 co-rotating twin-screw extruder with a screw length-to-diameter ratio of 40:1 for hot melt extrusion. The temperature of the first and second feeding zones is controlled at 170℃; the temperature of the third, fourth and fifth plasticizing zones is controlled at 200℃; the temperature of the sixth, seventh and eighth homogenizing zones is controlled at 190℃; the temperature of the ninth and tenth compression zones is controlled at 220℃; the screw speed is 250 rpm. After extrusion, the die surface is directly air-cooled and pelletized at the die outlet. The pellets are collected after air cooling to obtain a light-resistant biodegradable plastic.

[0056] Glass microspheres were not used in this comparative example of UV-shielding additives.

[0057] Comparative Example 4

[0058] (1) Weigh sericite, glass microspheres and fluorite powder according to the mass ratio of 10:5:2; wherein, the glass microspheres are solid glass microspheres with a D50 particle size <5μm; first, mix sericite and fluorite powder evenly, add sodium hexametaphosphate dispersant at 1% of the total mass of sericite and fluorite powder, and dry grind and composite in a ball mill. The grinding medium is zirconia ceramic balls, and the volume of the grinding medium added is 1 / 3 of the total volume of sericite and fluorite powder; grind until the D90 particle size <10μm, and then add glass microspheres to the composite to obtain the UV shielding additive;

[0059] (2) According to the weight parts, 60 parts of polylactic acid, 10 parts of toughening agent PBAT, 8 parts of UV shielding agent, 1.5 parts of composite nucleating agent (talc powder with a particle size <2μm and TMC-328 are compounded at a mass ratio of 2:1), and 0.3 parts of cobalt green (CAS:68186-85-6); the temperature of the high-speed mixer is controlled at 100℃, and the mixture is mixed and dispersed at a low speed of 200rpm for 45min. The mixture is then discharged into the cooling pot and stirred to cool.

[0060] (3) The material cooled in step (2) is conveyed to a Φ65 co-rotating twin-screw extruder with a screw length-to-diameter ratio of 40:1 for hot melt extrusion. The temperature of the first and second feeding zones is controlled at 170℃; the temperature of the third, fourth and fifth plasticizing zones is controlled at 200℃; the temperature of the sixth, seventh and eighth homogenizing zones is controlled at 190℃; the temperature of the ninth and tenth compression zones is controlled at 220℃; the screw speed is 250 rpm. After extrusion, the die surface is directly air-cooled and pelletized at the die outlet. The pellets are collected after air cooling to obtain a light-resistant biodegradable plastic.

[0061] This comparative example did not use modified lignin.

[0062] The light-resistant biodegradable plastics obtained from the embodiments of Examples 1-3 and Comparative Examples 1-4 were used to prepare dust nets, and their light resistance and degradation performance were tested. All process parameters were controlled to ensure that the resulting dust nets had the same density. The specific process was as follows: the light-resistant biodegradable plastic was added to a single-screw extruder for melt extrusion, passed through a T-die to form a sheet, calendered by multiple sets of rollers to form a film, slit into filaments by needle rollers, then heat-treated for orientation, stretched, and wound into filaments, and finally woven into dust nets using a six-needle weaving machine.

[0063] Light resistance performance verification:

[0064] The initial tensile strength of the dustproof net was tested, followed by a 500-hour accelerated UV aging test to assess the change in tensile strength. The accelerated UV aging was performed according to GB / T 16422.3-2022 (Plastics Laboratory Light Source Exposure Test Methods Part 3: Fluorescent Ultraviolet Lamps), using a UVA-340 fluorescent ultraviolet lamp that simulates sunlight. Tensile strength was tested according to GB / T 3923.1-2013 (Textiles Fabrics Tensile Properties Part 1: Determination of Breaking Strength and Elongation at Break (Strip Method)).

[0065] The color difference ΔE of the dustproof mesh before and after UV aging is tested to determine its light resistance performance. The smaller the color difference, the better the light resistance performance. When ΔE≤3, the color cannot be distinguished by the human eye, and it can be determined that it does not change color.

[0066] The changes in tensile strength and color difference ΔE of the dustproof net before and after UV aging are shown in Table 1.

[0067] Table 1: Test Table for Light Resistance Performance

[0068]

[0069] Biodegradability verification:

[0070] The dustproof net was buried in the soil at a depth of 30cm or more and in an environment with soil moisture greater than 70% for 6 months. The degradation characteristics of the dustproof net were observed and the mass loss rate was measured as the degradation rate, as shown in Table 2.

[0071] Table 2: Biodegradation rate

[0072]

[0073] Through testing, the light-resistant biodegradable plastic of this invention exhibits excellent light resistance. After 500 hours of accelerated aging under ultraviolet light, the tensile strength retention rate of the dustproof net is greater than 80%, meeting the requirements for long-term use of the dustproof net under light conditions. In particular, the UV-shielding additives composed of sericite, glass microspheres, and fluorite powder, along with nano-lignin, are dispersed in polylactic acid (PLA), enabling effective reflection and absorption of ultraviolet light, thus preventing UV damage to PLA chain segments. Furthermore, as a filler material, it enhances the mechanical properties of PLA. Compared to Comparative Example 1 using conventional UV absorbers, the light resistance of this invention is most significant, and the use of conventional UV absorbers negatively impacts the strength of PLA. Moreover, lignin facilitates the degradation of PLA in the soil bio-environment.

[0074] It should be understood that, although the embodiments have been described in detail, those skilled in the art will appreciate that the process parameters can be adjusted to achieve the technical objectives without departing from the inventive concept and spirit. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A light-resistant biodegradable plastic, characterized in that, The raw material composition by weight includes: 60-70 parts polylactic acid, 10-15 parts lignin, 5-10 parts toughening agent, 5-8 parts UV shielding agent, 3-5 parts compatibilizer, 1-2 parts composite nucleating agent, and 0-0.5 parts colorant. The lignin is nanoscale lignin with a particle size of <300nm; The toughening agent is at least one of polybutylene adipate terephthalate, thermoplastic starch, polycaprolactone, polybutylene succinate, and polyhydroxyalkanoate. The UV-shielding additive is obtained by dry grinding sericite and fluorite powder in a ball mill, and then combining them with glass microspheres. During grinding, 0.5-1.0% of a dispersant by weight of the material being ground is added. The dispersant is selected from sodium hexametaphosphate or sodium pyrophosphate. The mass ratio of sericite, glass microspheres and fluorite powder is 10:5:

2. The compatibilizer is glycidyl methacrylate; The composite nucleating agent is composed of an inorganic nucleating agent and an amide nucleating agent in a mass ratio of (2-5):

1.

2. The light-resistant biodegradable plastic according to claim 1, characterized in that, The lignin is nanoscale lignin with a particle size of <100nm.

3. The light-resistant biodegradable plastic according to claim 1, characterized in that, The composite nucleating agent is composed of an inorganic nucleating agent and an amide nucleating agent in a mass ratio of 2:

1.

4. The light-resistant biodegradable plastic according to claim 1, characterized in that, The inorganic nucleating agent is selected from at least one of talc, calcium carbonate, and kaolin with a particle size <2μm; the amide nucleating agent is N,N′,N″-tricyclohexyl-1,3,5-benzenetricarboxamide.

5. A method for preparing a light-resistant biodegradable plastic according to any one of claims 1-4, characterized in that, Includes the following steps: (1) Mix sericite and fluorite powder evenly, add dispersant and dry grind in ball mill until D90 particle size <10μm, then add glass microspheres to obtain UV shielding additive; (2) Add 10-15 parts of lignin and 3-5 parts of compatibilizer to the kneader by weight and knead. Control the temperature below 60℃. After kneading evenly, transfer to the high-speed mixer. Then add 60-70 parts of polylactic acid, 5-10 parts of toughening agent, 5-8 parts of UV shielding agent, 1-2 parts of composite nucleating agent, and 0-0.5 parts of color powder. Control the temperature of the high-speed mixer at 90-100℃ and mix and disperse at low speed for 30-60 minutes. Then discharge the material to the cooling pot and stir to cool. (3) The material cooled in step (2) is conveyed to a twin-screw extruder for hot melt extrusion, and then granulated by air-cooled die surface to obtain a light-resistant biodegradable plastic.

6. The method for preparing a light-resistant biodegradable plastic according to claim 5, characterized in that, The ball mill adds zirconia ceramic balls as grinding media during dry grinding, and the volume of the added grinding media is 1 / 3 of the total volume of sericite and fluorite powder.

7. The method for preparing a light-resistant biodegradable plastic according to claim 5, characterized in that, The twin-screw extruder is a co-rotating twin-screw extruder, with the temperature range of each section set to 170-220℃ during hot melt extrusion; the screw length-to-diameter ratio is 40:1; and the screw speed is 200-300 rpm.

8. The application of the light-resistant biodegradable plastic according to any one of claims 1-4 in dustproof netting.

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