Degradable polyethylene masterbatch, preparation method and degradable linear low density polyethylene

Abstract

The application discloses a degradable polyethylene master batch, a preparation method and degradable linear low-density polyethylene. The degradable polyethylene master batch comprises the following components: 100 parts of LLDPE, 1.5-5 parts of an antioxidant, 0.5-3 parts of an acid absorbent, 25-35 parts of starch, 0.4-1.0 parts of a photosensitizer, 10-20 parts of an anti-aging modifier, 2-4 parts of a starch plasticizer and 8-15 parts of a modified filler. The anti-aging modifier is prepared by melt blending of maleic anhydride grafted polyolefin and amine-terminated polyamide at a mass ratio of 10:3-4, and the amine-terminated polyamide is obtained by polycondensation of bipyridine diacid and aromatic diamine at a molar ratio of 1:1.1-1.3. The application can effectively solve the problem of light aging of the current degradable polyethylene material during use, and reduce the negative influence of the antioxidant on the light degradation efficiency.

Description

Technical Field

[0001] This application relates to the field of biodegradable plastics, and in particular to a biodegradable polyethylene masterbatch, a preparation method thereof, and biodegradable linear low-density polyethylene. Background Technology

[0002] Polyethylene, as one of the most produced plastic products, is extremely difficult to degrade in the natural environment due to its excellent chemical stability, causing serious pollution problems. Developing environmentally degradable polyethylene materials is of great significance for ecological and environmental protection.

[0003] Currently, the preparation of biodegradable polyethylene mainly employs the following technical pathways: First, chemical modification introduces biodegradable structures into the polyethylene molecular chain. For example, copolymerization reactions are used to copolymerize monomers containing easily hydrolyzed or biodegradable groups such as ester bonds, ether bonds, and amide bonds with ethylene and α-olefins. Alternatively, grafting reactions are used to graft polar monomers such as maleic anhydride and acrylic acid onto the polyethylene backbone. The presence of these polar groups disrupts the stability of the C / C backbone, promoting material degradation in the natural environment. However, this pathway suffers from limitations in the selection of comonomers and the difficulty in precisely controlling the grafting rate, resulting in a complex process and high cost. Second, physical blending adds photosensitizers, such as benzophenones and transition metal salts, to the polyethylene matrix. The free radicals generated by the photosensitizers under light conditions trigger the breakage of the polyethylene molecular chain, achieving photodegradation. However, the degradation process of this type of material is heavily dependent on light conditions, exhibiting extremely low degradation efficiency in dark environments such as deep soil layers or inside sealed packaging, significantly limiting its applicability. Third, polyethylene is melt-blended with biodegradable polymers such as starch, chitosan, polylactic acid, and polybutylene adipate. The degradation properties of the biodegradable polymers drive the degradation of polyethylene and the matrix. Among them, starch is one of the most widely used biodegradable components in this pathway because it is widely available, inexpensive, completely biodegradable, and has good biocompatibility.

[0004] In practice, methods two and three are often combined, blending photosensitizers, starch, and polyethylene matrices to obtain composite materials that can undergo both photodegradation and further microbial degradation, thus achieving optimal degradation results. However, this method still faces many challenges in practical applications. For example, in outdoor applications such as packaging bags and agricultural films, materials need to be exposed to sunlight for extended periods, requiring sufficient stability throughout their service life. For most crop growth cycles, materials need to maintain a service life of 90-120 days to ensure that photodegradation does not lead to a significant decrease in mechanical properties or loss of function. Existing technologies only add antioxidants to inhibit photo-oxidation and delay material aging, but this approach typically has poor persistence and cannot meet the light stability requirements of degradable polyethylene within a 90-120 day service life. Summary of the Invention

[0005] This application provides a biodegradable polyethylene masterbatch, a preparation method, and biodegradable linear low-density polyethylene, which can effectively overcome the photoaging problem of current biodegradable polyethylene materials during use and alleviate the problem of traditional antioxidants having a negative effect on the photodegradation efficiency of waste biodegradable polyethylene materials.

[0006] In a first aspect, this application provides a biodegradable polyethylene masterbatch, comprising 100 parts of LLDPE, 1.5-5 parts of antioxidant, 0.5-3 parts of acid scavenger, 25-35 parts of starch, 0.4-1.0 parts of photosensitizer, 10-20 parts of aging resistant modifier, 2-4 parts of starch plasticizer, and 8-15 parts of modified filler; wherein the aging resistant modifier is obtained by melt blending maleic anhydride-grafted polyolefin and terminal amine polyamide in a mass ratio of 10:3-4, and the terminal amine polyamide is obtained by polycondensation of bipyridine dicarboxylic acid and aromatic diamine in a molar ratio of 1:1.1-1.3.

[0007] In any of the above technical solutions, the acid absorber is calcium stearate and / or zinc stearate.

[0008] In any of the above technical solutions, the bipyridine dicarboxylic acid is selected from 2,2'-bipyridine-3,3'-dicarboxylic acid, 2,2'-bipyridine-4,4'-dicarboxylic acid, or 2,2'-bipyridine-5,5'-dicarboxylic acid; preferably 2,2'-bipyridine-4,4'-dicarboxylic acid.

[0009] In any of the above technical solutions, the aromatic diamine is p-phenylenediamine.

[0010] In any of the above technical solutions, the maleic anhydride-grafted polyolefin is selected from any one or more of maleic anhydride-grafted polyethylene, maleic anhydride-grafted ethylene-vinyl acetate copolymer, maleic anhydride-grafted polypropylene, maleic anhydride-grafted ethylene-octene elastomer, and maleic anhydride-grafted ethylene-propylene rubber.

[0011] This application has no special requirements for starch; any product commonly used in the field may be selected, including but not limited to corn starch, potato starch, and tapioca starch.

[0012] This application's technical solution effectively suppresses photo-aging of biodegradable polyethylene materials during use through the synergistic effect of an anti-aging modifier and alkylated lignin, ensuring the material's mechanical properties while largely maintaining its photodegradation efficiency. Specifically, the anti-aging modifier is prepared by melt blending maleic anhydride-grafted polyolefin with a specific structured terminal amine polyamide, wherein the terminal amine polyamide is prepared by a polycondensation reaction of bipyridine dicarboxylic acid and aromatic diamine. The bipyridine structural unit and the benzene ring structure together constitute an extended conjugated π-electron system, which can effectively absorb near-ultraviolet light through π-π* transitions and convert it into visible light radiation or heat energy, significantly reducing the risk of ultraviolet-induced photo-oxidative degradation of polyethylene. It is worth noting that this conjugated system cannot be achieved by ordinary aliphatic dicarboxylic acids or other non-conjugated dicarboxylic acids. At the same time, the maleic anhydride-grafted polyolefin segments act as compatibilizers, ensuring that the anti-aging modifier is uniformly dispersed and well-bonded in the polyethylene matrix, thereby directly improving the material's anti-aging performance.

[0013] By incorporating biodegradable alkylated lignin, its active groups such as phenolic hydroxyl groups capture and consume free radicals generated during use, inhibiting the breakage of polyethylene molecular chains and further delaying material aging. Furthermore, alkylation modification of lignin significantly enhances its compatibility with the polyethylene matrix, effectively solving the problems of easy migration and uneven dispersion of traditional antioxidants, resulting in a more durable and stable antioxidant effect. The synergistic effect of both significantly improves the mechanical stability of the material during its 90-120 day service life.

[0014] Furthermore, in existing technologies that rely on antioxidants to ensure the anti-aging properties of materials, the amount of antioxidants used is difficult to control precisely. Insufficient use cannot effectively guarantee the service life of the material, while excessive use will excessively inhibit the degradation process. In particular, traditional antioxidants are significantly more effective than lignin, which will significantly delay the photodegradation time of the material after it is discarded.

[0015] In any of the above technical solutions, the antioxidant is alkylated lignin, and the preparation method of the alkylated lignin is as follows:

[0016] Alkali lignin is mixed with a sodium hydroxide solution and stirred at 40–50°C until the lignin dissolves to obtain a lignin solution, wherein the mass ratio of alkali lignin to sodium hydroxide is 3–5:1.

[0017] Tetrabutylammonium bromide was added to a lignin solution, and alkyl chloride was added dropwise after stirring. The temperature was raised to 70-80°C, and the mixture was stirred and refluxed for 3-4 hours. The reaction solution was cooled to room temperature, and hydrochloric acid was added dropwise to adjust the pH to 6.5-7.0. The crude product was obtained by filtration.

[0018] The crude product was washed repeatedly with anhydrous ethanol until the filtrate was colorless. The washed solid was then vacuum dried, pulverized, and sieved to obtain alkylated lignin.

[0019] In any of the above technical solutions, the starch plasticizer is selected from ethylene glycol, glycerin, or sorbitol; preferably glycerin.

[0020] In any of the above technical solutions, the photosensitizer is selected from tetraphenylporphyrin zinc and stearate metal salt in a mass ratio of 1:1 to 2.

[0021] In any of the above technical solutions, the stearate metal salt is selected from any one or more of iron stearate, cerium stearate or manganese stearate; preferably iron stearate.

[0022] This application uses a photosensitizer system composed of a complex of tetraphenylporphyrin zinc and stearic acid metal salt, both of which are coordination compounds. The advantage of this combination lies in the fact that its metal center can coordinate with the nitrogen atom on the bipyridine unit in the aging-resistant modifier, forming a "ligand-metal-ligand" network structure. This structure not only effectively immobilizes the photosensitizer and starch plasticizer molecules, inhibiting their migration and precipitation during processing and use, reducing negative impacts on the mechanical properties of the product and the environment, but also improves the overall stability of the system. In particular, the tetraphenylporphyrin zinc molecule has a large conjugated planar structure, which can enhance the compactness of the coordination network through π-π stacking.

[0023] In any of the above technical solutions, the modified filler is prepared by blending filler, carboxyl-terminated liquid polybutadiene and titanate catalyst in a mass ratio of 100:10~20:0.3~1 at 130~150℃.

[0024] In any of the above technical solutions, the titanate catalyst is selected from tetrabutyl titanate or tetraisopropyl titanate.

[0025] In any of the above technical solutions, the filler is selected from any one or more of silica, calcium carbonate, talc, montmorillonite, and alumina.

[0026] In any of the above technical solutions, the particle size of the filler is 0.1 to 5 micrometers, preferably 0.1 to 1 μm.

[0027] The modified filler used in this application involves esterification of the carboxyl groups of terminal carboxyl-terminated liquid polybutadiene with the hydroxyl groups on the silica surface via a tetrabutyl titanate catalyst, grafting flexible long chains with carboxyl groups onto the filler surface. During subsequent blending with the polyethylene matrix, these carboxyl groups can react with unreacted residual terminal amino groups in the aging-resistant modifier (some amino groups failed to participate in the amidation reaction due to steric hindrance) and the hydroxyl groups on the starch molecular chains, forming dispersed localized chemical crosslinking points. This localized micro-crosslinking structure significantly improves the melt strength of the composite material, especially in formulations with high starch content, effectively improving film-forming processability and reducing the problem of film bubble rupture due to insufficient melt strength. More importantly, compared to surface modification using short-chain carboxylic acids or epoxides, terminal carboxyl-terminated polybutadiene, as a flexible polymer long chain, can form a flexible connection between the filler particles and the matrix resin. It can deform and orient itself under stress, thereby strengthening the material while avoiding embrittlement and better maintaining the flexibility of the film.

[0028] Secondly, this application provides a method for preparing biodegradable polyethylene masterbatch, comprising:

[0029] According to the raw material ratio of any of the masterbatches described in the first aspect, starch and starch plasticizer are mixed and stirred at 80-100°C until a uniform starch paste is formed.

[0030] The product is obtained by melt-blending LLDPE, alkylated lignin, photosensitizer, anti-aging modifier, modified filler, and paste starch at 160–190°C and then extruding.

[0031] Thirdly, this application provides a biodegradable linear low-density polyethylene, comprising 100 parts of LLDPE powder and 1 to 5 parts of biodegradable polyethylene masterbatch; the biodegradable polyethylene masterbatch is any of the masterbatch described in the first aspect or the masterbatch obtained by the preparation method in the second aspect.

[0032] This biodegradable linear low-density polyethylene has a low masterbatch content, making it suitable for applications such as the preparation of biodegradable packaging materials with lower degradation performance requirements.

[0033] In summary, this application has the following beneficial effects:

[0034] This application utilizes the synergistic anti-aging effect of an aging-resistant modifier and alkylated lignin to effectively ensure the mechanical property stability of the material during its 90-120 day exposure period without requiring large amounts of traditional antioxidants. A specific photosensitizer system is anchored through coordination with the aging-resistant modifier, inhibiting migration and ensuring the normal triggering of photodegradation after disposal. The flexible long-chain modified filler enhances melt strength, solving the problem of easy film rupture in high-starch content formulations, while maintaining good toughness of the product. The components work synergistically to achieve a polyethylene material with good performance, processability, and controllable degradation characteristics, effectively resolving the contradiction between anti-aging and degradation-promoting properties in existing biodegradable polyethylene technologies. Detailed Implementation

[0035] Preparation Example

[0036] Preparation Example 1-1, an aging resistance modifier, was prepared according to the following method:

[0037] In a nitrogen-protected reactor, 5.0 mol (1.21 kg) of 2,2'-bipyridine-4,4'-dicarboxylic acid, 5.5 mol (0.594 kg) of p-phenylenediamine, and 1200 g of N,N-dimethylformamide were added as solvents. Stirring was initiated to completely dissolve the solids. Subsequently, 10.2 g of triphenyl phosphite was added as a catalyst. The mixture was heated in a temperature-controlled oil bath at a rate of 2 °C / min to 180 °C, and stirred at this temperature for 8 hours. During the reaction, water generated was removed via azeotropic extraction using a water separator. After the reaction was complete, heating was stopped, and the reaction system was cooled to below 50 °C. With stirring, the reaction solution was slowly poured into 10 L of deionized water, precipitating the product, which was then filtered through a Buchner funnel. The resulting solid was washed three times with ethanol to remove residual solvent and low-molecular-weight byproducts. The purified solid was dried in a vacuum drying oven at 85 °C (-0.1 MPa) for 24 hours to obtain amine-terminated polyamide.

[0038] 350g of terminal amine polyamide and 1000g of maleic anhydride-grafted linear low-density polyethylene (grade 41E1057) were placed together in an internal mixer. Under nitrogen protection, the mixture was melt-blended at 180°C and a rotor speed of 60 rpm for 8 minutes. The mixture was then discharged, pressed into tablets, cooled, and crushed into granules to obtain the aging-resistant modifier.

[0039] Preparation Examples 1-2, aging resistance modifiers, were prepared according to the following method:

[0040] In a nitrogen-protected reactor, 5.0 mol (1.21 kg) of 2,2'-bipyridine-4,4'-dicarboxylic acid, 5.2 mol (0.562 kg) of p-phenylenediamine, and 1200 g of N,N-dimethylformamide were added as solvents, and stirring was started to completely dissolve the solid. Then, 8.3 g of triphenyl phosphite was added as a catalyst. The mixture was heated in a temperature-controlled oil bath at a rate of 2 °C / min to 170 °C, and stirred at this temperature for 10 hours. During the reaction, water generated was removed by azeotropic extraction using a water separator. After the reaction was complete, heating was stopped, and the reaction system was cooled to below 50 °C. With stirring, the reaction solution was slowly poured into 10 L of deionized water, and the product precipitated and filtered through a Buchner funnel. The obtained solid was washed three times with ethanol to remove residual solvent and low-molecular-weight byproducts. The purified solid was dried in a vacuum drying oven at 85 °C (-0.1 MPa) for 20 hours to obtain amine-terminated polyamide.

[0041] 300g of amine-terminated polyamide and 1000g of maleic anhydride-grafted polyethylene (grade MC226) were placed together in an internal mixer. Under nitrogen protection, the mixture was melt-blended at 175℃ and a rotor speed of 70rpm for 10 minutes. The mixture was then discharged, pressed into tablets, cooled, and crushed into granules to obtain the aging-resistant modifier.

[0042] Preparation Examples 1-3, aging resistance modifiers, were prepared according to the following method:

[0043] In a nitrogen-protected reactor, 5.0 mol (1.22 kg) of 2,2'-bipyridine-5,5'-dicarboxylic acid, 6.2 mol (0.67 kg) of p-phenylenediamine, and 1400 g of N,N-dimethylformamide were added as solvents, and stirring was started to completely dissolve the solids. Then, 13.4 g of triphenyl phosphite was added as a catalyst. The mixture was heated in a temperature-controlled oil bath at a rate of 1.5 °C / min to 190 °C, and stirred at this temperature for 6 hours. During the reaction, water generated was removed by azeotropic extraction using a water separator. After the reaction was complete, heating was stopped, and the reaction system was cooled to below 60 °C. With stirring, the reaction solution was slowly poured into 15 L of deionized water to precipitate the product, which was then filtered through a Buchner funnel. The resulting solid was washed three times with ethanol to remove residual solvent and low-molecular-weight byproducts. The purified solid was dried in a vacuum drying oven at 90 °C (-0.1 MPa) for 26 hours to obtain amine-terminated polyamide.

[0044] 400g of amine-terminated polyamide and 1000g of maleic anhydride-grafted polyethylene (brand name ST-6) were placed together in an internal mixer. Under nitrogen protection, the mixture was melt-blended at 185℃ and a rotor speed of 50rpm for 12 minutes. The mixture was then discharged, pressed into tablets, cooled, and crushed into granules to obtain the aging-resistant modifier.

[0045] Preparation Examples 1-4, aging-resistant modifiers, differ from Preparation Example 1-1 in that 2,2'-bipyridine-4,4'-dicarboxylic acid is replaced with an equimolar amount of 2,6-pyridinedicarboxylic acid.

[0046] Preparation Examples 1-5, aging-resistant modifiers, differ from Preparation Example 1-1 in that p-phenylenediamine is replaced with an equimolar amount of hexamethylenediamine.

[0047] Preparation Example 2-1, Alkylated Lignin, was prepared by following these steps:

[0048] The alkali lignin was dried at 70℃ and under a vacuum of -0.09MPa for 4 hours, and then pulverized through an 80-mesh sieve. 100g of dried alkali lignin and 500mL of a 1mol / L sodium hydroxide aqueous solution were added to a reaction flask. Stirring was started, and the water bath temperature was controlled at 45±2℃. Stirring continued for 1.5 hours until a homogeneous lignin solution was obtained.

[0049] Add 3.0 g of tetrabutylammonium bromide as a phase transfer catalyst to the lignin solution and continue stirring for 15 minutes to ensure uniform dispersion. Slowly add 45 g of dodecane chloride dropwise over 30 minutes using a constant-pressure dropping funnel. After the addition is complete, raise the water bath temperature to 75 ± 2 °C and reflux the reaction mixture under stirring for 3.5 hours. After the reaction is complete, remove the water bath and allow the reaction mixture to cool naturally to room temperature (25 °C). While stirring, slowly add 10% hydrochloric acid (w / w) dropwise to adjust the pH to 7.0 ± 0.1, at which point a precipitate forms. Filter the precipitate using a Buchner funnel and collect the crude solid product. Wash the filter cake three times with 200 mL of anhydrous ethanol. Transfer the washed solid to a tray and dry it in a vacuum drying oven at 70 °C (-0.095 MPa) for 18 hours. Remove the dried solid blocks, pulverize them using a pulverizer, and pass them through a 200-mesh standard sieve to obtain alkylated lignin powder.

[0050] Preparation Example 2-2, Alkylated Lignin, was prepared by following these steps:

[0051] The alkali lignin was dried at 60℃ and under a vacuum of -0.09MPa for 5 hours, and then pulverized through an 80-mesh sieve. 100g of dried alkali lignin and 500mL of a 1mol / L sodium hydroxide aqueous solution were added to a reaction flask. Stirring was started, and the water bath temperature was controlled at 45±2℃. Stirring continued for 1.5 hours until a homogeneous lignin solution was obtained.

[0052] 2.0 g of tetrabutylammonium bromide was added to the lignin solution as a phase transfer catalyst, and the mixture was stirred for 10 minutes to ensure uniform dispersion. 30 g of chlorooctane was slowly added dropwise over 30 minutes using a constant-pressure dropping funnel. After the addition was complete, the water bath temperature was raised to 70 ± 2 °C, and the mixture was stirred and refluxed at this temperature for 4 hours. After the reaction was complete, the water bath was removed, and the reaction mixture was allowed to cool naturally to room temperature (25 °C). While stirring, 10% (w / w) dilute hydrochloric acid was slowly added dropwise using a dropping funnel to adjust the pH to 7.0 ± 0.1, at which point a precipitate formed. The product was filtered using a Buchner funnel, and the crude solid was collected. The filter cake was washed three times with 300 mL of anhydrous ethanol. The washed solid was transferred to a tray and dried in a vacuum drying oven at 65 °C (-0.095 MPa) for 24 hours. The dried solid blocks were then pulverized and passed through a 200-mesh standard sieve to obtain alkylated lignin powder.

[0053] Preparation Example 2-3, Alkylated Lignin, was prepared by following these steps:

[0054] The alkali lignin was dried at 70℃ and under a vacuum of -0.09MPa for 4 hours, and then pulverized through an 80-mesh sieve. 100g of dried alkali lignin and 500mL of a 1mol / L sodium hydroxide aqueous solution were added to a reaction flask. Stirring was started, and the water bath temperature was controlled at 50±2℃. Stirring was continued for 1 hour until a homogeneous lignin solution was obtained.

[0055] Add 4.0 g of tetrabutylammonium bromide as a phase transfer catalyst to the lignin solution and continue stirring for 20 minutes to ensure uniform dispersion. Slowly add 60 g of hexadecane chloride dropwise over 40 minutes using a constant-pressure dropping funnel. After the addition is complete, raise the water bath temperature to 80 ± 2 °C and reflux the reaction mixture under stirring for 3 hours. After the reaction is complete, remove the water bath and allow the reaction mixture to cool naturally to room temperature (25 °C). While stirring, slowly add 10% hydrochloric acid (w / w) dropwise to adjust the pH to 7.0 ± 0.1, at which point a precipitate forms. Filter the precipitate using a Buchner funnel and collect the crude solid product. Wash the filter cake three times with 200 mL of anhydrous ethanol. Transfer the washed solid to a tray and dry it in a vacuum drying oven at 75 °C (-0.095 MPa) for 15 hours. Remove the dried solid blocks, pulverize them using a pulverizer, and pass them through a 200-mesh standard sieve to obtain alkylated lignin powder.

[0056] Preparation Example 3-1, modified filler, was prepared according to the following operation:

[0057] 100g of fumed silica (D50=0.5μm), 13.5g of carboxyl-terminated liquid polybutadiene (number-average molecular weight Mn≈2500g / mol) and 0.6g of tetrabutyl titanate catalyst were poured into a high-speed heating mixer. The mixer speed was increased to 1000rpm and the temperature was maintained at 140℃. The mixture was stirred continuously for 2h. After the reaction was completed, the mixture was cooled and coarsely crushed to obtain the modified filler.

[0058] Preparation Example 3-2, modified filler, was prepared according to the following operation:

[0059] 100g of alumina (D50=0.8μm), 10g of carboxyl-terminated liquid polybutadiene (number-average molecular weight Mn≈1500g / mol) and 0.3g of tetrabutyl titanate catalyst were poured into a high-speed heating mixer. The mixer speed was increased to 1000rpm and the temperature was maintained at 150℃. The mixture was stirred continuously for 1.5h. After the reaction was completed, the modified filler was obtained by cooling and coarse crushing.

[0060] Preparation Example 3-3, modified filler, was prepared according to the following operation:

[0061] 100g of fumed silica (D50=0.3μm), 18.5g of carboxyl-terminated liquid polybutadiene (number-average molecular weight Mn≈3000g / mol) and 1g of tetrabutyl titanate catalyst were poured into a high-speed heating mixer. The mixer speed was increased to 1200rpm and the temperature was maintained at 130℃. The mixture was stirred continuously for 2.5h. After the reaction was completed, the modified filler was obtained by cooling and coarse crushing.

[0062] Preparation Examples 3-4: Modified fillers were prepared according to the following procedures:

[0063] Mix 13.5g of γ-glycidyl etheroxypropyltrimethoxysilane with 150mL of anhydrous ethanol, add glacial acetic acid dropwise to adjust the pH to 4, then slowly add 6g of deionized water and stir for 20min to obtain a hydrolysate for later use. Add 100g of silica to 250mL of anhydrous ethanol and stir for 20min to form a homogeneous suspension. Raise the temperature of the suspension to 75℃, and add the hydrolysate dropwise to the suspension through a dropping funnel over 40 minutes. Reflux the reaction for 4 hours. After the reaction is complete, cool to room temperature, filter out the solid, wash three times with deionized water, and dry to obtain the modified filler.

[0064] Preparation Example 3-5, modified filler, differs from Preparation Example 3-4 in that an equal amount of vinyltrimethoxysilane is used to replace γ-glycidoxypropyltrimethoxysilane.

[0065] Preparation Examples 3-6, modified fillers, were prepared according to the following procedures:

[0066] 100g of fumed silica (D50=0.3μm) was added to 200mL of adipic acid aqueous solution (containing 13.5g of adipic acid), and stirred for 15min to fully disperse the silica and form a homogeneous slurry. The system was heated to 95℃ and refluxed at this temperature for 4 hours. After the reaction was completed, the mixture was cooled to room temperature, the solid material was separated by vacuum filtration, and washed with deionized water at 50℃ until the filtrate was neutral. After drying, the modified filler was obtained.

[0067] Example

[0068] Example 1: A biodegradable polyethylene masterbatch was prepared according to the following steps:

[0069] Starch gelatinization: Premix 300g corn starch and 30g glycerol in a high-speed mixer for 2 minutes. Transfer the mixture to a reaction vessel and gelatinize at 90°C and 200rpm for 15 minutes to obtain a uniform starch paste.

[0070] Main ingredient mixing: 1000g of linear low-density polyethylene (brand name DFDA-7042), 40g of alkylated lignin from Preparation Example 2-1, 7g of photosensitizer (containing 3.5g of tetraphenylporphyrin zinc and 3.5g of ferric stearate), 150g of aging-resistant modifier from Preparation Example 1-1, 115g of modified filler from Preparation Example 3-1, and gelatinized starch were added together to a low-speed mixer and mixed at room temperature for 10 minutes until the material was homogeneous. The homogeneous mixture was then fed into a twin-screw extruder (screw diameter 45mm, L / D=40). The extruder processing temperatures from the feeding section to the die head were set sequentially as follows: 160℃, 170℃, 175℃, 180℃, 185℃, 185℃, 180℃. The screw speed was set to 300rpm. After melt extrusion, stranding, and water cooling (25℃), the material was granulated by a pelletizer.

[0071] Example 2: A biodegradable polyethylene masterbatch was prepared according to the following steps:

[0072] Starch gelatinization: Premix 250g potato starch and 20g sorbitol in a high-speed mixer for 2 minutes. Transfer the mixture to a reaction vessel and gelatinize at 85°C and 200rpm for 18 minutes to obtain a uniform starch paste.

[0073] Main ingredient mixing: 1000g of linear low-density polyethylene (brand name DEX-8302), 30g of alkylated lignin from Preparation Example 2-2, 4g of photosensitizer (containing 1.6g of tetraphenylporphyrin zinc and 2.4g of cerium stearate), 100g of aging-resistant modifier from Preparation Example 1-2, 80g of modified filler from Preparation Example 3-2, and gelatinized starch were added to a low-speed mixer and mixed at room temperature for 12 minutes until the material was homogeneous. The homogeneous mixture was then fed into a twin-screw extruder (screw diameter 45mm, L / D=40). The extruder processing temperatures from the feeding section to the die head were set sequentially as follows: 155℃, 165℃, 170℃, 175℃, 180℃, 180℃, 175℃. The screw speed was set to 350rpm. After melt extrusion, stranding, and water cooling (25℃), the material was granulated by a pelletizer.

[0074] Example 3: A biodegradable polyethylene masterbatch was prepared according to the following steps:

[0075] Starch gelatinization: Premix 350g corn starch and 40g glycerol in a high-speed mixer for 3 minutes. Transfer the mixture to a reaction vessel and gelatinize at 95°C and 200rpm for 12 minutes to obtain a uniform starch paste.

[0076] Main ingredient mixing: 1000g of linear low-density polyethylene (brand name DOWLEX 2045G), 50g of alkylated lignin from Preparation Examples 2-3, 10g of photosensitizer (containing 4g of tetraphenylporphyrin zinc and 6g of ferric stearate), 200g of aging-resistant modifier from Preparation Examples 1-3, 150g of modified filler from Preparation Examples 3-3, and gelatinized starch were added together to a low-speed mixer and mixed at room temperature for 15 minutes until the material was homogeneous. The homogeneous mixture was then fed into a twin-screw extruder (screw diameter 45mm, L / D=40). The extruder processing temperatures from the feeding section to the die head were set sequentially as follows: 165℃, 175℃, 185℃, 190℃, 195℃, 185℃, 185℃. The screw speed was set to 300 rpm. After melt extrusion, stranding, and water cooling (25℃), the material was granulated by a pelletizer.

[0077] Example 4, a biodegradable polyethylene masterbatch, differs from Example 1 in that it uses an equal mass of ferric stearate instead of zinc tetraphenylporphyrin.

[0078] Example 5, a biodegradable polyethylene masterbatch, differs from Example 1 in that ferric stearate and 2,2'-bipyridine-4,4'-dicarboxylic acid are replaced with an equal mass of benzophenone.

[0079] Example 6, a biodegradable polyethylene masterbatch, differs from Example 1 in that the modified filler of Preparation Example 3-1 is replaced with the modified filler of Preparation Example 3-4 by means of equal mass.

[0080] Example 7, a biodegradable polyethylene masterbatch, differs from Example 1 in that the modified filler of Preparation Example 3-1 is replaced with the modified filler of Preparation Example 3-5 by an equal mass.

[0081] Example 8, a biodegradable polyethylene masterbatch, differs from Example 1 in that the modified filler of Preparation Example 3-1 is replaced with the modified filler of Preparation Example 3-6 by an equal mass.

[0082] Comparative Example

[0083] Comparative Example 1, a biodegradable polyethylene masterbatch, differs from Example 1 in that the aging-resistant modifier of Preparation Example 1-1 is replaced with the aging-resistant modifier of Preparation Example 1-4 in equal mass.

[0084] Comparative Example 2, a biodegradable polyethylene masterbatch, differs from Example 1 in that the aging-resistant modifier of Preparation Example 1-1 is replaced with the aging-resistant modifier of Preparation Example 1-5 in equal mass.

[0085] Comparative Example 3, a biodegradable polyethylene masterbatch, differs from Example 1 in that an equal mass of maleic anhydride-grafted linear low-density polyethylene (grade 41E1057) replaces the aging-resistant modifier of Preparation Example 1-1.

[0086] Comparative Example 4, a biodegradable polyethylene masterbatch, differs from Comparative Example 3 in that it replaces alkylated lignin with an equal mass of antioxidant 1010.

[0087] Performance testing

[0088] Film preparation: The biodegradable polyethylene masterbatch (granules) of the embodiments and comparative examples of this application were used to make a film with a thickness of 0.03±0.005mm using a blown film machine under the same process conditions (blow-up ratio 2.5, processing temperature 170~190℃).

[0089] Experiment 1: Anti-aging performance test

[0090] Referring to GB / T 1040.3-2006 "Determination of Tensile Properties of Plastics - Part 3: Test Conditions for Films and Sheets", the film was cut into 10 Type 1B standard dumbbell-shaped specimens using a standard cutter. Each group of specimens was divided into two parts: one part (5 specimens) was directly subjected to tensile testing as the initial value, and the other part (5 specimens) was placed in a xenon lamp aging test chamber for artificial climate aging. Aging conditions (referring to GB / T 16422.3-2022 "Laboratory Light Source Exposure Test Methods for Plastics - Part 3: Fluorescent Ultraviolet Lamps"): Light source: Fluorescent ultraviolet lamp UVA-340; Irradiance: 0.76 W / m² 2Blackboard temperature: 60±3℃; Chamber temperature: 50±3℃; Irradiation / condensation cycle: 8 hours of UV irradiation, 4 hours of condensation; Aging time: set to 550 hours (to simulate 120 days of outdoor exposure).

[0091] After equilibration for 24 hours in a standard laboratory environment (23±2℃, 50±10%RH), both samples before and after aging were subjected to tensile testing using a universal testing machine. Test parameters: gauge length: 50mm; tensile speed: 500mm / min; tensile strength at break (MPa) and elongation at break (%) were recorded for each sample, and the average values ​​for each group were calculated. The performance retention rate was calculated using the formula: Retention rate (%) = (average value after aging / average value before aging) × 100%.

[0092] Experiment 2: Photodegradation Performance Test

[0093] Take the samples after 1500 hours of UVA aging in Experiment 1. Cut the aged sheets into 20mm × 20mm square samples. Prepare at least 12 parallel samples for each material. Number each sample and dry it in a vacuum drying oven at 40℃ until constant weight (usually 24 hours). After removal, place it in a desiccator to cool to room temperature, and weigh its initial mass using a microbalance with an accuracy of 0.01mg, accurately recording it as M0. Continue to place the samples in a UV fluorescence aging test chamber under the following aging conditions: light source: UVA-340 fluorescent UV lamp; irradiance: 0.5W / m². 2 The temperature was 40±3℃, and the humidity was 50±5%RH, with continuous exposure. Three parallel samples were removed from the chamber every 96 hours (4 days). Any loose material caused by degradation was gently removed from the sample surface using a soft brush or a blower. The samples were then placed in a 40℃ vacuum drying oven for 4 hours to remove absorbed moisture. After cooling, the samples were weighed and recorded as M. t Repeat this process until all samples have been taken or the mass loss rate of most samples has far exceeded 50%.

[0094] Calculate the mass loss rate of the sample at each sampling point using the following formula: WL(%) = (M0 - M) t ) / M0×100%. Calculate the average mass loss rate of three parallel samples at each sampling point. Plot the photodegradation curve for each group of materials with exposure time (days) on the x-axis and average mass loss rate (%) on the y-axis. Calculate the degradation rate: calculate the rate at which the mass loss rate reaches 50% (WL) by linearly fitting the rapid rise phase of the degradation curve. 50 The average time required (T) 50 T 50 The shorter the length, the faster the photodegradation rate.

[0095] Experiment 3: Film Formation Performance Test

[0096] The biodegradable polyethylene masterbatch (granules) of the embodiments and comparative examples of this application were blown into film on the same single-screw blown film unit. Each group of materials was continuously and stably operated for 1 hour. The number of film bubble ruptures that occurred during that hour was recorded.

[0097] Process parameters: Screw diameter φ45mm; L / D: 28:1; Processing temperature: 160-190℃ (from the feeding section to the die head); Die head diameter: φ100mm; Blow-up ratio: 2.5; Traction speed: 10m / min.

[0098] Table 1. Test Results of Performance

[0099]

[0100] Analysis of experimental results:

[0101] Compared to Example 1, Example 4 (replacing zinc stearate with zinc tetraphenylporphyrin) showed poorer photodegradation performance. This indicates that a complete photosensitizer compound system is crucial for achieving a balance between anti-aging and photodegradation. The reason may be that the lack of zinc tetraphenylporphyrin reduces the density and stability of the "ligand-metal-ligand" network structure, leading to increased migration of the photosensitizer and starch plasticizer. This weakens the durability of elongation at break and consumes some of the photosensitizer in the early stages of aging, affecting subsequent degradation efficiency. Example 5 (using benzophenone as a photosensitizer) showed further deterioration in photodegradation performance and elongation at break. This indicates that the specific photosensitizer system of this application is not only the core of photodegradation but also indirectly contributes to processing stability and mechanical properties through coordination with the anti-aging modifier. The reason may be that small-molecule benzophenone has poor compatibility with the system and is prone to migration and precipitation. It not only fails to form an effective network but its precipitation process also damages the phase interface, leading to processing difficulties and mechanical defects.

[0102] Compared to Example 1, Examples 6 (replacing the carboxyl-terminated liquid polybutadiene-modified filler with epoxy-silane-modified filler), 7 (replacing the carboxyl-terminated liquid polybutadiene-modified filler with vinylsilane-modified filler), and 8 (replacing the carboxyl-terminated liquid polybutadiene-modified filler with adipic acid-modified filler) all exhibited poorer film-forming properties and toughness, despite their similar aging resistance and photodegradation resistance. This indicates that the flexible long chains on the filler surface are crucial for maintaining film toughness. This may be because epoxy-silane, vinylsilane, and short-chain adipic acid-modified fillers exhibit high interfacial rigidity after bonding with the matrix, making them prone to stress concentration under stress, leading to increased material brittleness.

[0103] Compared to Example 1, Comparative Example 1 (replacing bipyridine dicarboxylic acid with 2,6-pyridinedicarboxylic acid) exhibited poorer anti-aging performance. This indicates that the extended conjugated π system formed by the bipyridine structure is crucial for UV shielding and subsequent coordination with photosensitizers. This may be because the conjugation range and electronic delocalization ability of a single pyridine ring are far inferior to those of bipyridine, leading to a decrease in its UV absorption efficiency. Comparative Example 2 (replacing p-phenylenediamine with hexamethylenediamine) also showed poor anti-aging performance. This indicates that the rigid benzene ring structure formed by aromatic diamines is a necessary component for constructing a large conjugated system and achieving efficient UV shielding. This may be because the aliphatic chain hexamethylenediamine cannot provide the conjugated structure of the benzene ring, resulting in a decrease in the UV absorption capacity of the synthesized polyamide, thereby deteriorating the performance of the anti-aging modifier.

[0104] Comparative Example 3 (using only maleic anhydride-grafted polyethylene, lacking terminal amine polyamide) showed faster photodegradation, but failed in anti-aging performance and film-forming properties, exhibiting cracking and damage during use, thus losing its effectiveness. This indicates that terminal amine polyamide is the core component providing anti-aging function. Without the UV shielding effect of terminal amine polyamide, the system relies solely on alkylated lignin to capture free radicals, resulting in insufficient anti-aging ability. Simultaneously, the lack of amino groups to form local crosslinks with the filler leads to decreased melt strength and difficulty in film formation.

[0105] Comparative Example 4 (using traditional antioxidant 1010 to replace alkylated lignin) showed extremely poor photodegradation performance, despite exhibiting the best anti-aging properties. This highlights the core contradiction of traditional antioxidants: they inhibit the degradation process. This is because the antioxidant's highly efficient free radical scavenging ability continues to function even after the material is discarded, strongly suppressing the photo-oxidative degradation reaction induced by photosensitizers, resulting in an extremely slow degradation rate.

[0106] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A degradable polyethylene masterbatch, characterized in that, The raw materials comprise the following parts by weight: 100 parts LLDPE, 1.5-5 parts antioxidant, 0.5-3 parts acid scavenger, 25-35 parts starch, 0.4-1.0 parts photosensitizer, 10-20 parts aging-resistant modifier, 2-4 parts starch plasticizer, and 8-15 parts modified filler; the aging-resistant modifier is obtained by melt blending maleic anhydride-grafted polyolefin and terminal amine polyamide in a mass ratio of 10:3-4, wherein the terminal amine polyamide is obtained by polycondensation of bipyridine dicarboxylic acid and aromatic diamine in a molar ratio of 1:1.1-1.3; the antioxidant is alkylated lignin, and the preparation method of the alkylated lignin is as follows: Alkali lignin is mixed with a sodium hydroxide solution and stirred at 40–50°C until the lignin dissolves to obtain a lignin solution, wherein the mass ratio of alkali lignin to sodium hydroxide is 3–5:

1. Tetrabutylammonium bromide was added to a lignin solution, and alkyl chloride was added dropwise after stirring. The temperature was raised to 70-80°C, and the mixture was stirred and refluxed for 3-4 hours. The reaction solution was cooled to room temperature, and hydrochloric acid was added dropwise to adjust the pH to 6.5-7.

0. The crude product was obtained by filtration. The crude product was washed repeatedly with anhydrous ethanol until the filtrate was colorless. The washed solid was then vacuum dried, pulverized, and sieved to obtain alkylated lignin.

2. The degradable polyethylene masterbatch according to claim 1, characterized in that, The bipyridine dicarboxylic acid is selected from 2,2'-bipyridine-3,3'-dicarboxylic acid, 2,2'-bipyridine-4,4'-dicarboxylic acid, or 2,2'-bipyridine-5,5'-dicarboxylic acid.

3. The degradable polyethylene masterbatch of claim 1, wherein, The aromatic diamine is p-phenylenediamine.

4. The degradable polyethylene masterbatch of claim 1, wherein, The starch plasticizer is selected from ethylene glycol, glycerin, or sorbitol.

5. The degradable polyethylene masterbatch of claim 1, wherein, The photosensitizer is selected from zinc tetraphenylporphyrin and metal stearate in a mass ratio of 1:1 to 2.

6. The biodegradable polyethylene masterbatch according to claim 1, characterized in that, The modified filler is prepared by blending filler, carboxyl-terminated liquid polybutadiene and titanate catalyst in a mass ratio of 100:10-20:0.3-1 at 130-150°C.

7. The biodegradable polyethylene masterbatch according to claim 6, characterized in that, The filler is selected from any one or more of silicon dioxide, calcium carbonate, talc, and alumina.

8. The method for preparing biodegradable polyethylene masterbatch according to any one of claims 1 to 7, characterized in that, include: Mix starch with starch plasticizer and stir at 80-100℃ until a uniform starch paste is formed; The product is obtained by melt-blending LLDPE, alkylated lignin, photosensitizer, anti-aging modifier, modified filler, and paste starch at 160–190°C and then extruding.

9. A biodegradable linear low-density polyethylene, characterized in that, It contains 100 parts of LLDPE powder and 1 to 5 parts of biodegradable polyethylene masterbatch; the biodegradable polyethylene masterbatch is any one of the masterbatch described in claims 1 to 7 or the masterbatch prepared in claim 8.

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