A biodegradable polylactic acid composite material and its preparation method

Abstract

This invention discloses a biodegradable polylactic acid (PLA) composite material and its preparation method, relating to the field of PLA material technology. The method includes: firstly, grafting and modifying hydrochloric acid-activated chitosan with KH550 silane coupling agent, and simultaneously surface-modifying nano-zinc oxide with stearic acid; then mixing and spray-drying the two to obtain an antibacterial composite powder; secondly, activating nano-silica with hydrochloric acid and modifying it with KH570 silane coupling agent, and hydroxypropylating modifying alkali lignin; then performing a reflux crosslinking reaction with KH570-modified nano-silica, polycaprolactone, methyl methacrylate, and azobisisobutyronitrile to obtain a heat-resistant reinforcement; finally, uniformly mixing PLA, polybutylene succinate, the antibacterial composite powder, the heat-resistant reinforcement, tributyl citrate, polyethylene glycol, and talc, and granulating the mixture using a twin-screw extruder to obtain the final product. The composite material prepared by this invention possesses excellent antibacterial properties, heat resistance, and biodegradability.

Description

Technical Field

[0001] This invention relates to the field of polylactic acid materials technology, specifically to a biodegradable polylactic acid composite material and its preparation method. Background Technology

[0002] With increasing global environmental awareness and the implementation of plastic restriction policies, biodegradable materials have become a core direction for replacing traditional petroleum-based plastics. Among them, polylactic acid (PLA) has been widely used in the food contact field due to its advantages such as renewable raw materials (derived from fermented lactic acid from biomass such as corn and potatoes), excellent biocompatibility, compostability, and good processability. It has achieved large-scale promotion, especially in food packaging, tableware, straws, and other products. PLA products not only reduce the environmental pollution caused by traditional plastics, but also have excellent transparency and odor barrier properties, meeting the basic requirements of the food industry for material safety and practicality. However, the application of polylactic acid (PLA) materials in the food industry is still limited by its inherent performance defects, among which insufficient antibacterial properties and poor heat resistance are particularly prominent. In terms of antibacterial properties, PLA only has a weak natural antibacterial effect and cannot effectively inhibit the adhesion and reproduction of common food pathogens such as Escherichia coli and Staphylococcus aureus. This leads to microbial contamination of food during storage and transportation, shortens shelf life, and poses food safety risks. This problem is more pronounced in high temperature and high humidity environments. In terms of heat resistance, PLA's glass transition temperature is only 50-60℃, and the long-term use temperature is below 50℃. In scenarios such as hot filling, high-temperature sterilization, or daily contact with hot beverages, it is prone to softening, deformation, or even performance failure. For example, PLA straws deform rapidly when in contact with hot beverages, seriously affecting the user experience and product reliability. Summary of the Invention

[0003] The purpose of this invention is to provide a biodegradable polylactic acid (PLA) composite material and its preparation method, thereby solving the technical problems mentioned in the background section. The PLA composite material prepared by this invention possesses both good antibacterial and heat-resistant properties in addition to being biodegradable.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] A method for preparing a biodegradable polylactic acid composite material includes the following steps:

[0006] S1. Chitosan is dispersed in hydrochloric acid aqueous solution and refluxed with stirring. After adjusting the pH to neutral, it is separated and dried to obtain activated chitosan. The activated chitosan is reacted with KH550 silane coupling agent in toluene under reflux. After separation and drying, KH550 grafted modified chitosan is obtained.

[0007] S2. The nano zinc oxide and stearic acid were stirred and reacted in anhydrous ethanol, and the surface-modified nano zinc oxide was obtained by separation and drying. KH550 grafted modified chitosan and surface-modified nano zinc oxide were mixed, dispersed and spray-dried to obtain antibacterial composite powder.

[0008] S3. Add nano-silica to hydrochloric acid solution and stir to react. After separation and drying, calcine to obtain activated nano-silica. Reflux the activated nano-silica with KH570 silane coupling agent in toluene. After separation and drying, obtain KH570 modified nano-silica.

[0009] S4. Alkali lignin is reacted with propylene oxide in isopropanol, and the mixture is separated and dried to obtain hydroxypropylated modified lignin. The hydroxypropylated modified lignin, KH570 modified nano silica, polycaprolactone and methyl methacrylate are mixed and then azobisisobutyronitrile is added for reflux crosslinking reaction. The solvent is removed and the mixture is dried to obtain heat-resistant reinforced material.

[0010] S5. Polylactic acid, polybutylene succinate, antibacterial composite powder, heat-resistant reinforcement, tributyl citrate, polyethylene glycol and talc are mixed evenly to obtain a mixture. The mixture is then granulated by twin-screw extrusion to obtain an antibacterial, heat-resistant and biodegradable polylactic acid composite material.

[0011] In this invention, the antibacterial composite powder achieves highly efficient antibacterial effects through the synergistic effect of KH550 grafted modified chitosan and surface-modified nano-zinc oxide. KH550 grafted modified chitosan retains the natural antibacterial properties of chitosan, and its molecular structure can interact with microbial cell membranes, disrupting cell membrane integrity and inhibiting microbial metabolism and reproduction. The surface-modified nano-zinc oxide, with its small particle size, possesses a large specific surface area, allowing for sufficient contact with microorganisms. Simultaneously, the modification treatment avoids agglomeration, ensuring uniform dispersion within the powder and further expanding the antibacterial contact range. When the two are combined in an optimized ratio, a synergistic system of natural and inorganic antibacterial components is formed. This system leverages the targeted inhibitory effect of chitosan on microorganisms while utilizing the broad-spectrum antibacterial properties of nano-zinc oxide to cover common pathogens such as Escherichia coli and Staphylococcus aureus. The uniformly dispersed structure ensures the continuous release of antibacterial components within the composite material, achieving a long-lasting and stable antibacterial effect and guaranteeing effective inhibition of microbial growth during use.

[0012] The heat-resistant reinforcement constructs a stable heat-resistant system through multi-component cross-linking. Purified and activated nano-silica modified with KH570, with its extremely small particle size and high specific surface area, forms a rigid support structure that hinders the thermal motion of molecular chains and reduces material deformation at high temperatures. Hydroxypropylated lignin retains the excellent thermal stability of its aromatic ring conjugated structure, while modification improves its compatibility with other components, allowing it to be uniformly dispersed in the system to form a heat-resistant skeleton. Polycaprolactone and methyl methacrylate cross-link under the action of an initiator to form a three-dimensional network structure, firmly locking the heat-resistant components such as nano-silica and lignin, further restricting molecular chain slippage and enhancing the structural stability of the system. After modification, the interfacial bonding force of each component is significantly improved, forming a synergistic heat-resistant structure of rigid particles, a heat-resistant skeleton, and a cross-linked network. This effectively increases the material's heat distortion temperature, improves its heat resistance, and maintains overall structural integrity, ensuring performance in use.

[0013] Preferably, in step S1, the mass ratio of activated chitosan to KH550 silane coupling agent is 8:(0.5-1.0).

[0014] Preferably, in step S2, the mass ratio of nano zinc oxide to stearic acid is 5:(0.2-0.6).

[0015] Preferably, in step S2, the mass ratio of KH550 grafted modified chitosan to surface-modified nano zinc oxide is 4:(1-2).

[0016] Preferably, in step S3, the calcination temperature is 300-350°C and the calcination time is 2-3 hours.

[0017] Preferably, in step S3, the mass ratio of activated nano-silica to KH570 silane coupling agent is 10:(1-2).

[0018] Preferably, in step S4, the mass ratio of alkali lignin to propylene oxide is 15:(3-6).

[0019] Preferably, in step S5, polylactic acid-polyethylene glycol-polylactic acid block copolymer is also added to the mixture.

[0020] Preferably, the amount of polylactic acid-polyethylene glycol-polylactic acid block copolymer added is 0.5 to 1.0 wt% of the mass of polylactic acid.

[0021] In the technical solution of this invention, the research and development team discovered during experiments that there is a significant difference in polarity between the matrix materials of the antibacterial composite powder and the heat-resistant reinforcement. Chitosan derivatives and nano-zinc oxide are predominantly polar, while the PCL-MMA copolymer is predominantly hydrophobic, resulting in weak interfacial bonding between the two. During the composite molding stage, the antibacterial composite powder cannot be fully integrated into the cross-linked network of the heat-resistant reinforcement, forming an island structure. This creates a significant thermal barrier at the interface. Under high-temperature conditions, heat transfer at the interface is hindered, leading to excessively high local temperatures. This accelerates the thermal aging of the cross-linked network of the heat-resistant reinforcement, ultimately resulting in a decrease in the overall heat resistance of the composite material. To further address this technical problem, this invention incorporates a polylactic acid-polyethylene glycol-polylactic acid block copolymer (PLA-PEG-PLA) into the mixture. The PLA segments of this block copolymer exhibit good compatibility with polylactic acid and polybutylene succinate in the composite matrix, allowing for tight bonding with the matrix material. Meanwhile, its PEG segments can form stable hydrogen bonds with the polar groups on the surface of the antibacterial composite powder, thereby constructing an efficient interfacial bridge between the antibacterial composite powder and the heat-resistant reinforcement. This effectively reduces the thermal resistance at the interface, promotes uniform heat transfer within the composite material, avoids the thermal aging problem of the heat-resistant reinforcement crosslinking network caused by localized high temperatures, and ensures the stability of the overall heat resistance performance of the material.

[0022] A biodegradable polylactic acid composite material is prepared by the method described above.

[0023] Compared with the prior art, the beneficial effects of the present invention are:

[0024] 1. Through the synergistic effect of KH550 grafted modified chitosan and surface-modified nano zinc oxide, a composite system of natural and inorganic antibacterial components is formed, which can effectively inhibit common pathogenic bacteria such as Escherichia coli and Staphylococcus aureus. Moreover, the antibacterial components are evenly dispersed to achieve a continuous antibacterial effect.

[0025] 2. The heat-resistant reinforcement utilizes nano-silica, hydroxypropylated modified lignin, and a multi-component cross-linked network to construct a stable structure that can hinder molecular chain movement at high temperatures, increase the material's heat distortion temperature, and maintain the overall structural integrity and performance.

[0026] 3. Adding polylactic acid-polyethylene glycol-polylactic acid block copolymer to the mixture as an interfacial bridge enhances the bonding force between the antibacterial composite powder and the heat-resistant reinforcement, reduces thermal resistance, avoids performance degradation caused by local high temperature, and ensures stable heat resistance of the composite material. Attached Figure Description

[0027] Figure 1 This is a SEM image of the antibacterial composite powder prepared in Example 1 of the present invention.

[0028] Figure 2 This is a SEM image of the heat-resistant reinforcement prepared in Example 1 of the present invention. Detailed Implementation

[0029] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0030] Example 1

[0031] A method for preparing a biodegradable polylactic acid composite material includes the following steps:

[0032] Step 1: Weigh 10g of chitosan (90% deacetylation, molecular weight 80,000), add 200mL of 10% hydrochloric acid aqueous solution, stir and disperse at 300rpm, then reflux in an oil bath at 85℃ for 2h. After cooling, add 5% sodium hydroxide dropwise to adjust the pH to 7.2, allow to stand and filter, wash with deionized water until the filtrate is neutral, and freeze-dry at -50℃ and 0.08MPa under vacuum until constant weight to obtain activated chitosan.

[0033] Weigh 8g of activated chitosan and add it to 150mL of toluene. Disperse the mixture using ultrasonication at 200W for 35min. Add 0.9g of KH550 silane coupling agent, adjust the pH to 4.0 with glacial acetic acid, and reflux at 108℃ for 6h under nitrogen protection. After cooling, centrifuge at 8000rpm for 15min, wash three times with toluene, and dry under vacuum at 60℃ and 0.09MPa to constant weight to obtain KH550-grafted chitosan.

[0034] Step 2: Weigh 5g of nano zinc oxide and add 150mL of anhydrous ethanol. Disperse the mixture by ultrasonication at 200W for 25min. Add 0.5g of stearic acid and stir to dissolve. React in a water bath at 65℃ for 2h. After filtration, wash twice with anhydrous ethanol and dry at 80℃ to constant weight to obtain modified nano zinc oxide.

[0035] Weigh 8g of KH550-grafted chitosan and 3.5g of modified nano-zinc oxide, add 200mL of deionized water, and sonicate at 200W for 15min. After stirring at 48℃ and 280rpm for 3.5h, spray dry (inlet air 170℃, outlet air 85℃) and collect the antibacterial composite powder.

[0036] Step 3: Weigh 12g of nano-silica and add it to 200mL of 12% hydrochloric acid solution, reflux at 85℃ for 2.5h. Filter and wash until neutral, dry at 105℃, and calcine at 330℃ for 2.5h to obtain activated nano-silica.

[0037] 10g of activated nano-silica was added to 150mL of toluene and sonicated at 200W for 45min. 1.8g of KH570 silane coupling agent was added, and the pH was adjusted to 3.8 with glacial acetic acid. The mixture was refluxed at 108℃ for 7h under nitrogen protection. After centrifugation and washing, the mixture was dried under vacuum at 80℃ and 0.09MPa to obtain KH570 modified nano-silica.

[0038] Step 4: Weigh 15g of alkali lignin and add it to 150mL of isopropanol. Stir and disperse, then add 0.75g of sodium hydroxide and 5g of propylene oxide. Place in an autoclave and react at 70℃ and 0.6MPa for 3.5h. After depressurization and cooling, filter, wash with isopropanol, and dry at 100℃ to obtain hydroxypropylated lignin.

[0039] Weigh 1.5g of KH570 modified nano-silica, 3.8g of hydroxypropylated lignin, 7.5g of polycaprolactone (molecular weight 50000), and 2.25g of methyl methacrylate, add them to 200mL of toluene, then add 0.15g of azobisisobutyronitrile (AIBN), and reflux at 110℃ for 8h under nitrogen protection. Evaporate the toluene at 60℃, and vacuum dry at 80℃ to obtain the heat-resistant reinforced material.

[0040] Step 5: Weigh 55g of polylactic acid (molecular weight 100,000, 98% optical purity), 20g of polybutylene succinate (molecular weight 80,000), 7g of antibacterial composite powder, 8g of heat-resistant reinforcement, 5g of tributyl citrate, 3g of polyethylene glycol (molecular weight 4,000), 2g of talc, and 0.50g of polylactic acid-polyethylene glycol-polylactic acid block copolymer. Mix at 85℃ and 550rpm for 40min, then cool to obtain a premix. Add the premix to a twin-screw extruder with section temperatures of 150℃, 165℃, 180℃, 185℃, and die head temperature of 180℃, screw speed of 220rpm, and feed rate of 50g / min. After extruding the strip, water-cool it at 28℃ and then pelletize it to obtain composite material particles.

[0041] Example 2

[0042] A method for preparing a biodegradable polylactic acid composite material includes the following steps:

[0043] Step 1: Weigh 10g of chitosan (90% deacetylation, molecular weight 80,000), add 200mL of 10% hydrochloric acid aqueous solution, stir and disperse at 300rpm, then reflux in an oil bath at 85℃ for 2h. After cooling, add 5% sodium hydroxide dropwise to adjust the pH to 7.2, allow to stand and filter, wash with deionized water until the filtrate is neutral, and freeze-dry at -50℃ and 0.08MPa under vacuum until constant weight to obtain activated chitosan.

[0044] Weigh 8g of activated chitosan and add it to 150mL of toluene. Disperse the mixture using ultrasonication at 200W for 35min. Add 0.6g of KH550 silane coupling agent, adjust the pH to 4.0 with glacial acetic acid, and reflux at 108℃ for 6h under nitrogen protection. After cooling, centrifuge at 8000rpm for 15min, wash three times with toluene, and dry under vacuum at 60℃ and 0.09MPa to constant weight to obtain KH550-grafted chitosan.

[0045] Step 2: Weigh 5g of nano zinc oxide and add 150mL of anhydrous ethanol. Disperse the mixture by ultrasonication at 200W for 25min. Add 0.3g of stearic acid and stir to dissolve. React in a water bath at 65℃ for 2h. After filtration, wash twice with anhydrous ethanol and dry at 80℃ to constant weight to obtain modified nano zinc oxide.

[0046] Weigh 8g of KH550-grafted chitosan and 2.5g of modified nano-zinc oxide, add 200mL of deionized water, and sonicate at 200W for 15min. After stirring at 48℃ and 280rpm for 3.5h, spray dry (inlet air 170℃, outlet air 85℃) and collect the antibacterial composite powder.

[0047] Step 3: Weigh 12g of nano-silica and add it to 200mL of 12% hydrochloric acid solution, reflux at 85℃ for 2.5h. Filter and wash until neutral, dry at 105℃, and calcine at 330℃ for 2.5h to obtain activated nano-silica.

[0048] 10g of activated nano-silica was added to 150mL of toluene and sonicated at 200W for 45min. 1.2g of KH570 silane coupling agent was added, and the pH was adjusted to 3.8 with glacial acetic acid. The mixture was refluxed at 108℃ for 7h under nitrogen protection. After centrifugation and washing, the mixture was dried under vacuum at 80℃ and 0.09MPa to obtain KH570 modified nano-silica.

[0049] Step 4: Weigh 15g of alkali lignin and add it to 150mL of isopropanol. Stir and disperse, then add 0.75g of sodium hydroxide and 4g of propylene oxide. Place in an autoclave and react at 70℃ and 0.6MPa for 3.5h. After depressurization and cooling, filter, wash with isopropanol, and dry at 100℃ to obtain hydroxypropylated lignin.

[0050] Weigh 1.5g of KH570 modified nano-silica, 3.8g of hydroxypropylated lignin, 7.5g of polycaprolactone (molecular weight 50000), and 2.25g of methyl methacrylate, add them to 200mL of toluene, then add 0.15g of azobisisobutyronitrile (AIBN), and reflux at 110℃ for 8h under nitrogen protection. Evaporate the toluene at 60℃, and vacuum dry at 80℃ to obtain the heat-resistant reinforced material.

[0051] Step 5: Weigh 55g of polylactic acid (molecular weight 100,000, 98% optical purity), 20g of polybutylene succinate (molecular weight 80,000), 7g of antibacterial composite powder, 8g of heat-resistant reinforcement, 5g of tributyl citrate, 3g of polyethylene glycol (molecular weight 4,000), 2g of talc, and 0.35g of polylactic acid-polyethylene glycol-polylactic acid block copolymer. Mix at 85℃ and 550rpm for 40min, then cool to obtain a premix. Add the premix to a twin-screw extruder with section temperatures of 150℃, 165℃, 180℃, 185℃, and die head temperature of 180℃, screw speed of 220rpm, and feed rate of 50g / min. After extruding the strip, water-cool it at 28℃ and then pelletize it to obtain composite material particles.

[0052] Example 3

[0053] A method for preparing a biodegradable polylactic acid composite material includes the following steps:

[0054] Step 1: Weigh 10g of chitosan (90% deacetylation, molecular weight 80,000), add 200mL of 10% hydrochloric acid aqueous solution, stir and disperse at 300rpm, then reflux in an oil bath at 85℃ for 2h. After cooling, add 5% sodium hydroxide dropwise to adjust the pH to 7.2, allow to stand and filter, wash with deionized water until the filtrate is neutral, and freeze-dry at -50℃ and 0.08MPa under vacuum until constant weight to obtain activated chitosan.

[0055] Weigh 8g of activated chitosan and add it to 150mL of toluene. Disperse the mixture using ultrasonication at 200W for 35min. Add 0.7g of KH550 silane coupling agent, adjust the pH to 4.0 with glacial acetic acid, and reflux at 108℃ for 6h under nitrogen protection. After cooling, centrifuge at 8000rpm for 15min, wash three times with toluene, and dry under vacuum at 60℃ and 0.09MPa to constant weight to obtain KH550-grafted chitosan.

[0056] Step 2: Weigh 5g of nano-zinc oxide and add 150mL of anhydrous ethanol. Disperse the mixture by ultrasonication at 200W for 25min. Add 0.4g of stearic acid and stir to dissolve. React in a water bath at 65℃ for 2h. After filtration, wash twice with anhydrous ethanol and dry at 80℃ to constant weight to obtain modified nano-zinc oxide.

[0057] Weigh 8g of KH550-grafted chitosan and 3g of modified nano-zinc oxide, add 200mL of deionized water, and sonicate at 200W for 15min. After stirring at 48℃ and 280rpm for 3.5h, spray dry (inlet air 170℃, outlet air 85℃) and collect the antibacterial composite powder.

[0058] Step 3: Weigh 12g of nano-silica and add it to 200mL of 12% hydrochloric acid solution, reflux at 85℃ for 2.5h. Filter and wash until neutral, dry at 105℃, and calcine at 330℃ for 2.5h to obtain activated nano-silica.

[0059] 10g of activated nano-silica was added to 150mL of toluene and sonicated at 200W for 45min. 1.5g of KH570 silane coupling agent was added, and the pH was adjusted to 3.8 with glacial acetic acid. The mixture was refluxed at 108℃ for 7h under nitrogen protection. After centrifugation and washing, the mixture was dried under vacuum at 80℃ and 0.09MPa to obtain KH570 modified nano-silica.

[0060] Step 4: Weigh 15g of alkali lignin and add it to 150mL of isopropanol. Stir and disperse, then add 0.75g of sodium hydroxide and 4.5g of propylene oxide. Place in an autoclave and react at 70℃ and 0.6MPa for 3.5h. After depressurization and cooling, filter, wash with isopropanol, and dry at 100℃ to obtain hydroxypropylated lignin.

[0061] Weigh 1.5g of KH570 modified nano-silica, 3.8g of hydroxypropylated lignin, 7.5g of polycaprolactone (molecular weight 50000), and 2.25g of methyl methacrylate, add them to 200mL of toluene, then add 0.15g of azobisisobutyronitrile (AIBN), and reflux at 110℃ for 8h under nitrogen protection. Evaporate the toluene at 60℃, and vacuum dry at 80℃ to obtain the heat-resistant reinforced material.

[0062] Step 5: Weigh 55g of polylactic acid (molecular weight 100,000, 98% optical purity), 20g of polybutylene succinate (molecular weight 80,000), 7g of antibacterial composite powder, 8g of heat-resistant reinforcement, 5g of tributyl citrate, 3g of polyethylene glycol (molecular weight 4,000), 2g of talc, and 0.40g of polylactic acid-polyethylene glycol-polylactic acid block copolymer. Mix at 85℃ and 550rpm for 40min, then cool to obtain a premix. Add the premix to a twin-screw extruder with section temperatures of 150℃, 165℃, 180℃, 185℃, and die head temperature of 180℃, screw speed of 220rpm, and feed rate of 50g / min. After extruding the strip, water-cool it at 28℃ and then pelletize it to obtain composite material particles.

[0063] Example 4

[0064] A method for preparing a biodegradable polylactic acid composite material includes the following steps:

[0065] Step 1: Weigh 10g of chitosan (90% deacetylation, molecular weight 80,000), add 200mL of 10% hydrochloric acid aqueous solution, stir and disperse at 300rpm, then reflux in an oil bath at 85℃ for 2h. After cooling, add 5% sodium hydroxide dropwise to adjust the pH to 7.2, allow to stand and filter, wash with deionized water until the filtrate is neutral, and freeze-dry at -50℃ and 0.08MPa under vacuum until constant weight to obtain activated chitosan.

[0066] Weigh 8g of activated chitosan and add it to 150mL of toluene. Disperse the mixture using ultrasonication at 200W for 35min. Add 1.0g of KH550 silane coupling agent, adjust the pH to 4.0 with glacial acetic acid, and reflux at 108℃ for 6h under nitrogen protection. After cooling, centrifuge at 8000rpm for 15min, wash three times with toluene, and dry under vacuum at 60℃ and 0.09MPa to constant weight to obtain KH550-grafted chitosan.

[0067] Step 2: Weigh 5g of nano zinc oxide and add 150mL of anhydrous ethanol. Disperse the mixture by ultrasonication at 200W for 25min. Add 0.6g of stearic acid and stir to dissolve. React in a water bath at 65℃ for 2h. After filtration, wash twice with anhydrous ethanol and dry at 80℃ to constant weight to obtain modified nano zinc oxide.

[0068] Weigh 8g of KH550-grafted chitosan and 4g of modified nano-zinc oxide, add 200mL of deionized water, and sonicate at 200W for 15min. After stirring at 48℃ and 280rpm for 3.5h, spray dry (inlet air 170℃, outlet air 85℃) and collect the antibacterial composite powder.

[0069] Step 3: Weigh 12g of nano-silica and add it to 200mL of 12% hydrochloric acid solution, reflux at 85℃ for 2.5h. Filter and wash until neutral, dry at 105℃, and calcine at 350℃ for 3h to obtain activated nano-silica.

[0070] 10g of activated nano-silica was added to 150mL of toluene and sonicated at 200W for 45min. 2.0g of KH570 silane coupling agent was added, and the pH was adjusted to 3.8 with glacial acetic acid. The mixture was refluxed at 108℃ for 7h under nitrogen protection. After centrifugation and washing, the mixture was dried under vacuum at 80℃ and 0.09MPa to obtain KH570 modified nano-silica.

[0071] Step 4: Weigh 15g of alkali lignin and add it to 150mL of isopropanol. Stir and disperse, then add 0.75g of sodium hydroxide and 6g of propylene oxide. Place in an autoclave and react at 70℃ and 0.6MPa for 3.5h. After depressurization and cooling, filter, wash with isopropanol, and dry at 100℃ to obtain hydroxypropylated lignin.

[0072] Weigh 1.5g of KH570 modified nano-silica, 3.8g of hydroxypropylated lignin, 7.5g of polycaprolactone (molecular weight 50000), and 2.25g of methyl methacrylate, add them to 200mL of toluene, then add 0.15g of azobisisobutyronitrile (AIBN), and reflux at 110℃ for 8h under nitrogen protection. Evaporate the toluene at 60℃, and vacuum dry at 80℃ to obtain the heat-resistant reinforced material.

[0073] Step 5: Weigh 55g of polylactic acid (molecular weight 100,000, 98% optical purity), 20g of polybutylene succinate (molecular weight 80,000), 7g of antibacterial composite powder, 8g of heat-resistant reinforcement, 5g of tributyl citrate, 3g of polyethylene glycol (molecular weight 4,000), 2g of talc, and 0.55g of polylactic acid-polyethylene glycol-polylactic acid block copolymer. Mix at 85℃ and 550rpm for 40min, then cool to obtain a premix. Add the premix to a twin-screw extruder with section temperatures of 150℃, 165℃, 180℃, 185℃, and die head temperature of 180℃, screw speed of 220rpm, and feed rate of 50g / min. After extruding the strip, water-cool it at 28℃ and then pelletize it to obtain composite material particles.

[0074] Example 5

[0075] A method for preparing a biodegradable polylactic acid composite material includes the following steps:

[0076] Step 1: Weigh 10g of chitosan (90% deacetylation, molecular weight 80,000), add 200mL of 10% hydrochloric acid aqueous solution, stir and disperse at 300rpm, then reflux in an oil bath at 85℃ for 2h. After cooling, add 5% sodium hydroxide dropwise to adjust the pH to 7.2, allow to stand and filter, wash with deionized water until the filtrate is neutral, and freeze-dry at -50℃ and 0.08MPa under vacuum until constant weight to obtain activated chitosan.

[0077] Weigh 8g of activated chitosan and add it to 150mL of toluene. Disperse the mixture using ultrasonication at 200W for 35min. Add 0.5g of KH550 silane coupling agent, adjust the pH to 4.0 with glacial acetic acid, and reflux at 108℃ for 6h under nitrogen protection. After cooling, centrifuge at 8000rpm for 15min, wash three times with toluene, and dry under vacuum at 60℃ and 0.09MPa to constant weight to obtain KH550-grafted chitosan.

[0078] Step 2: Weigh 5g of nano-zinc oxide and add 150mL of anhydrous ethanol. Disperse the mixture by ultrasonication at 200W for 25min. Add 0.2g of stearic acid and stir to dissolve. React in a water bath at 65℃ for 2h. After filtration, wash twice with anhydrous ethanol and dry at 80℃ to constant weight to obtain modified nano-zinc oxide.

[0079] Weigh 8g of KH550-grafted chitosan and 2g of modified nano-zinc oxide, add 200mL of deionized water, and sonicate at 200W for 15min. After stirring at 48℃ and 280rpm for 3.5h, spray dry (inlet air 170℃, outlet air 85℃) and collect the antibacterial composite powder.

[0080] Step 3: Weigh 12g of nano-silica and add it to 200mL of 12% hydrochloric acid solution, reflux at 85℃ for 2.5h. Filter and wash until neutral, dry at 105℃, and calcine at 300℃ for 2h to obtain activated nano-silica.

[0081] 10g of activated nano-silica was added to 150mL of toluene and sonicated at 200W for 45min. 1.0g of KH570 silane coupling agent was added, and the pH was adjusted to 3.8 with glacial acetic acid. The mixture was refluxed at 108℃ for 7h under nitrogen protection. After centrifugation and washing, the mixture was dried under vacuum at 80℃ and 0.09MPa to obtain KH570 modified nano-silica.

[0082] Step 4: Weigh 15g of alkali lignin and add it to 150mL of isopropanol. Stir and disperse, then add 0.75g of sodium hydroxide and 3g of propylene oxide. Place in an autoclave and react at 70℃ and 0.6MPa for 3.5h. After depressurization and cooling, filter, wash with isopropanol, and dry at 100℃ to obtain hydroxypropylated lignin.

[0083] Weigh 1.5g of KH570 modified nano-silica, 3.8g of hydroxypropylated lignin, 7.5g of polycaprolactone (molecular weight 50000), and 2.25g of methyl methacrylate, add them to 200mL of toluene, then add 0.15g of azobisisobutyronitrile (AIBN), and reflux at 110℃ for 8h under nitrogen protection. Evaporate the toluene at 60℃, and vacuum dry at 80℃ to obtain the heat-resistant reinforced material.

[0084] Step 5: Weigh 55g of polylactic acid (molecular weight 100,000, 98% optical purity), 20g of polybutylene succinate (molecular weight 80,000), 7g of antibacterial composite powder, 8g of heat-resistant reinforcement, 5g of tributyl citrate, 3g of polyethylene glycol (molecular weight 4,000), 2g of talc, and 0.28g of polylactic acid-polyethylene glycol-polylactic acid block copolymer. Mix at 85℃ and 550rpm for 40min, then cool to obtain a premix. Add the premix to a twin-screw extruder with section temperatures of 150℃, 165℃, 180℃, 185℃, and die head temperature of 180℃, screw speed of 220rpm, and feed rate of 50g / min. After extruding the strip, water-cool it at 28℃ and then pelletize it to obtain composite material particles.

[0085] Comparative Example 1: The difference between Comparative Example 1 and Example 1 is that steps 1-2 are omitted in the preparation of polylactic acid composite material, and antibacterial composite powder is not added in step 5.

[0086] Comparative Example 2: The difference between Comparative Example 2 and Example 1 is that steps 3-4 are omitted in the preparation of polylactic acid composite material, and heat-resistant reinforcement is not added in step 5.

[0087] Comparative Example 3: The difference between Comparative Example 3 and Example 1 is that polylactic acid-polyethylene glycol-polylactic acid block copolymer is not added in step 5 of the polylactic acid composite material preparation process.

[0088] Performance testing:

[0089] 1. Antibacterial performance test: According to GB / T 31402-2015 standard, composite material particles were injection molded into smooth samples of 50mm×50mm×2mm. After sterilization at 121℃ and 0.1MPa for 20min, 0.2mL of a 1×10⁻⁶ solution was added. 5 A CFU / mL suspension of Escherichia coli or Staphylococcus aureus was prepared and spread evenly. The suspension was statically cultured at 37°C and relative humidity ≥90% for 24 hours. Then, the suspension was eluted with 20 mL of sterile physiological saline and shaken for 10 min. The eluent was serially diluted and spread for counting. The antibacterial rate was calculated as (average colony count of blank sample - average colony count of sample) / average colony count of blank sample × 100%. An antibacterial rate ≥90% was considered to have antibacterial effect, and an antibacterial rate ≥99% was considered to have excellent antibacterial effect.

[0090] 2. Heat Resistance Test: The heat distortion temperature test was conducted according to GB / T 1634.2-2004 "Determination of Load Deflection Temperature of Plastics - Part 2: Plastics, Hard Rubber and Long Fiber Reinforced Composite Materials". The load was set at 1.80 MPa, the heating rate was 120℃ / h, and the temperature at which the sample deformation reached 0.2 mm was recorded. The hot water immersion deformation rate test was conducted in accordance with the relevant requirements for food contact materials. A standard sample strip made of composite material (80 mm long × 10 mm wide × 4 mm thick) was immersed in an 80℃ constant temperature water bath for 2 hours. After removal, it was allowed to cool naturally to room temperature. The length and width before and after immersion were measured, and the deformation rate was calculated. Deformation rate (%) = (dimension after immersion - dimension before immersion) / dimension before immersion × 100%. The test results are shown in Table 1.

[0091] 3. Biodegradability Test: Following GB / T 19277.1-2011 "Determination of Final Aerobic Biodegradability of Materials under Controlled Composting Conditions—Method for Determining the Release of Carbon Dioxide—Part 1: General Method", the soil burial method was used. Samples were crushed into particles approximately 2 mm in size, and 5 g of sample was weighed and buried in natural soil (60% humidity, 25℃). Samples were periodically taken and the remaining mass was weighed. The biodegradation rate after 6 months was calculated. Degradation rate (%) = (Initial mass - Remaining mass) / Initial mass × 100%). Test results are shown in Table 1.

[0092] Table 1:

[0093]

[0094] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for producing a biodegradable polylactic acid composite material, characterized by, The method comprises the following steps: S1. dispersing chitosan in hydrochloric acid solution and refluxing and stirring, adjusting pH to neutral, separating and drying to obtain activated chitosan, refluxing and reacting the activated chitosan with KH550 silane coupling agent in toluene, separating and drying to obtain KH550 grafted and modified chitosan; S2. stirring and reacting nano zinc oxide with stearic acid in anhydrous ethanol, separating and drying to obtain surface modified nano zinc oxide, mixing and dispersing the KH550 grafted and modified chitosan with the surface modified nano zinc oxide, and spray drying to obtain antibacterial composite powder; S3. stirring and reacting nano silicon dioxide in hydrochloric acid solution, separating, drying and calcining to obtain activated nano silicon dioxide, refluxing and reacting the activated nano silicon dioxide with KH570 silane coupling agent in toluene, and separating and drying to obtain KH570 modified nano silicon dioxide; S4. reacting alkali lignin with propylene oxide in isopropyl alcohol, and separating and drying to obtain hydroxypropylated modified lignin; mixing the hydroxypropylated modified lignin, the KH570 modified nano silicon dioxide, polycaprolactone and methyl methacrylate, adding azobisisobutyronitrile, refluxing and crosslinking, removing solvent and drying to obtain heat-resistant reinforcing body; S5. mixing polylactic acid, polybutylene succinate, antibacterial composite powder, heat-resistant reinforcing body, tributyl citrate, polyethylene glycol, talc and polylactic acid-polyethylene glycol-polylactic acid block copolymer uniformly to obtain a mixture, and extruding and granulating the mixture by a double screw extruder to obtain antibacterial heat-resistant biodegradable polylactic acid composite material.

2. The method for preparing a biodegradable polylactic acid composite material according to claim 1, characterized in that, In the step S1, the mass ratio of the activated chitosan to the KH550 silane coupling agent is 8:(0.5-1.0).

3. The method for preparing a biodegradable polylactic acid composite material according to claim 1, characterized in that, In the step S2, the mass ratio of the nano zinc oxide to the stearic acid is 5:(0.2-0.6).

4. The method for preparing a biodegradable polylactic acid composite material according to claim 1, characterized in that, In the step S2, the mass ratio of the KH550 grafted and modified chitosan to the surface modified nano zinc oxide is 4:(1-2).

5. The method for preparing a biodegradable polylactic acid composite material according to claim 1, characterized in that, In the step S3, the calcination temperature is 300-350℃, and the calcination time is 2-3h.

6. The method for preparing a biodegradable polylactic acid composite material according to claim 1, characterized in that, In the step S3, the mass ratio of the activated nano silicon dioxide to the KH570 silane coupling agent is 10:(1-2).

7. The method for preparing a biodegradable polylactic acid composite material according to claim 1, characterized in that, In the step S4, the mass ratio of the alkali lignin to the propylene oxide is 15:(3-6).

8. A method for preparing a biodegradable polylactic acid composite material according to claim 1, characterized in that, In the step S5, the addition amount of the polylactic acid-polyethylene glycol-polylactic acid block copolymer is 0.5-1.0wt% of the mass of the polylactic acid.

9. A biodegradable polylactic acid composite, characterized by, The antibacterial heat-resistant biodegradable polylactic acid composite material is prepared by the method in any one of the above claims 1-8.

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