Biodegradable polylactic acid composite material and preparation method thereof

Abstract

The invention discloses a biodegradable polylactic acid composite material and a preparation method thereof, and relates to the technical field of polylactic acid materials. The method comprises the steps that firstly, chitosan activated through hydrochloric acid is subjected to graft modification through a KH550 silane coupling agent, meanwhile, nano-zinc oxide is subjected to surface modification through stearic acid, the chitosan and the nano-zinc oxide are mixed, spray drying is conducted, and antibacterial composite powder is prepared; the preparation method comprises the following steps: performing hydrochloric acid activation and KH570 silane coupling agent modification on nano silicon dioxide, performing hydroxypropylation modification on alkali lignin, and performing reflux crosslinking reaction on the modified alkali lignin, KH570 modified nano silicon dioxide, polycaprolactone, methyl methacrylate and azodiisobutyronitrile to prepare a heat-resistant reinforcer; uniformly mixing polylactic acid, poly (butylene succinate), the antibacterial composite powder, the heat-resistant reinforcer, tributyl citrate, polyethylene glycol and talcum powder, and extruding and granulating by using a twin-screw extruder to obtain the heat-resistant antibacterial material. The composite material prepared by the invention has excellent antibacterial property, heat resistance and biodegradability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of polylactic acid materials, in particular to a biodegradable polylactic acid composite material and a preparation method thereof. BACKGROUND

[0002] With the improvement of global environmental awareness and the implementation of plastic restriction policy, biodegradable materials have become the core direction to replace traditional petroleum-based plastics. Among them, polylactic acid (PLA) has been widely used in food contact fields due to its advantages of renewable raw materials (derived from biomass fermentation lactic acid such as corn and potato), excellent biocompatibility, compostable degradation and good processability, especially in food packaging, tableware, straw and other products. Polylactic acid products not only can reduce environmental pollution caused by traditional plastics, but also have excellent transparency and odor barrier properties, which meet the basic needs of safety and practicality of materials in the food field. However, the application of polylactic acid materials in the food field is still limited by its inherent performance defects, especially the insufficient antibacterial performance and poor heat resistance: in terms of antibacterial performance, polylactic acid only has weak natural antibacterial effect, which cannot effectively inhibit the adhesion and reproduction of common food pathogenic bacteria such as Escherichia coli and Staphylococcus aureus, leading to microbial contamination of food during storage and transportation, shortening the shelf life and posing a potential risk to food safety. This problem is more significant in high temperature and high humidity environments; in terms of heat resistance, the glass transition temperature of polylactic acid is only 50-60℃, and the long-term use temperature is lower than 50℃. In the scenes of hot filling, high-temperature sterilization or daily contact with hot drinks, polylactic acid is prone to softening, deformation and even performance failure, for example, polylactic acid straw will quickly deform when it contacts hot drinks, which seriously affects the use experience and product reliability. SUMMARY

[0003] The present application aims to provide a biodegradable polylactic acid composite material and a preparation method thereof to solve the technical problems in the background art. The polylactic acid composite material prepared by the present application has good antibacterial performance and heat resistance on the basis of biodegradability.

[0004] To achieve the above-mentioned purpose, the present application provides the following technical solutions: A preparation method of a biodegradable polylactic acid composite material, comprising the following steps: S1, dispersing chitosan in hydrochloric acid aqueous solution and refluxing and stirring, adjusting the pH to neutral, and then separating and drying to obtain activated chitosan, and refluxing and reacting the activated chitosan with KH550 silane coupling agent in toluene, and then separating and drying to obtain KH550 grafted and modified chitosan; S2, stirring and reacting nano-zinc oxide and stearic acid in anhydrous ethanol, and then separating and drying to obtain surface-modified nano-zinc oxide, and then mixing and dispersing the KH550 grafted and modified chitosan and the surface-modified nano-zinc oxide, and then spray drying to obtain an antibacterial composite powder; S3, stirring reaction after adding nanosilica into hydrochloric acid solution, after separation, drying and calcination, obtaining activated nanosilica, refluxing reaction of activated nanosilica and KH570 silane coupling agent in toluene, after separation and drying, obtaining KH570 modified nanosilica; S4, reacting alkali lignin and propylene oxide in isopropyl alcohol, after separation and drying, obtaining hydroxypropylated modified lignin; mixing hydroxypropylated modified lignin, KH570 modified nanosilica, polycaprolactone and methyl methacrylate, then adding azobisisobutyronitrile for reflux crosslinking reaction, removing solvent and drying, obtaining heat-resistant reinforcing body; S5, mixing polylactic acid, polybutylene succinate, antibacterial composite powder, heat-resistant reinforcing body, tributyl citrate, polyethylene glycol and talc powder uniformly, obtaining mixed material, then granulating the mixed material by double screw extrusion, obtaining antibacterial heat-resistant biodegradable polylactic acid composite material.

[0005] In the technical scheme of the present application, the antibacterial composite powder realizes high-efficiency antibacterial effect through the synergistic effect of KH550 grafted and modified chitosan and surface modified nanometer zinc oxide, wherein the KH550 grafted and modified chitosan retains the natural antibacterial property of chitosan, and its molecular structure can interact with the cell membrane of microorganisms, destroy the integrity of the cell membrane, and inhibit the metabolism and reproduction of microorganisms; the surface modified nanometer zinc oxide has a small particle size and a large specific surface area, can fully contact with microorganisms, and the modification treatment avoids the agglomeration phenomenon, so that the nanometer zinc oxide is uniformly dispersed in the powder, further expanding the antibacterial contact range. After the two are loaded and combined in an optimized proportion, a synergistic system of natural antibacterial components and inorganic antibacterial components is formed, which not only plays a targeted inhibitory role of chitosan on microorganisms, but also covers common pathogenic bacteria such as Escherichia coli and Staphylococcus aureus by virtue of the broad-spectrum antibacterial property of nanometer zinc oxide, and the uniform dispersion structure ensures the sustained release of the antibacterial components in the composite material, realizes persistent and stable antibacterial effect, and protects the composite material from microbial breeding during use.

[0006] The heat-resistant reinforcing agent forms a stable heat-resistant system through multi-component cross-linking compounding, wherein the nano-silica modified by purification, activation and KH570 forms a rigid support structure with its small particle size and high specific surface area, which can hinder the thermal motion of molecular chains and reduce material deformation at high temperature; the hydroxypropyl-modified lignin retains the excellent thermal stability of its own aromatic ring conjugated structure, and the compatibility with other components is improved after modification, which can uniformly disperse in the system to form a heat-resistant skeleton; the polycaprolactone and methyl methacrylate are cross-linked to form a three-dimensional network structure under the action of an initiator, which firmly locks the heat-resistant components such as nano-silica and lignin, further limits the slip of molecular chains, and enhances the structural stability of the system. After modification, the interface bonding force of each component is significantly improved, forming a synergistic heat-resistant structure of rigid particles, heat-resistant skeletons and cross-linked networks, effectively improving the heat distortion temperature of the material, improving its heat-resistant performance, while maintaining the overall structural integrity and ensuring the use performance.

[0007] Preferably, in step S1, the mass ratio of activated chitosan to KH550 silane coupling agent is 8:(0.5-1.0).

[0008] Preferably, in step S2, the mass ratio of nano-zinc oxide to stearic acid is 5:(0.2-0.6).

[0009] Preferably, in step S2, the mass ratio of KH550 grafted modified chitosan to surface modified nano-zinc oxide is 4:(1-2).

[0010] Preferably, in step S3, the calcination temperature is 300-350°C, and the calcination time is 2-3h.

[0011] Preferably, in step S3, the mass ratio of activated nano-silica to KH570 silane coupling agent is 10:(1-2).

[0012] Preferably, in step S4, the mass ratio of alkali lignin to propylene oxide is 15:(3-6).

[0013] Preferably, in step S5, the mixture further contains polylactic acid-polyethylene glycol-polylactic acid block copolymer.

[0014] Preferably, the amount of polylactic acid-polyethylene glycol-polylactic acid block copolymer added is 0.5-1.0wt% of the mass of polylactic acid.

[0015] In the technical scheme of the present application, it is found through the research of the research and development team in the experiment process that there is a significant polarity difference between the antibacterial composite powder and the matrix material of the heat-resistant reinforcing body, wherein the chitosan derivative and the nano zinc oxide are biased to polarity, and the PCL-MMA copolymer is biased to hydrophobicity, resulting in weak interfacial bonding force between the two. In the composite forming stage, the antibacterial composite powder cannot completely integrate into the crosslinked network of the heat-resistant reinforcing body, forming an island structure, so that a significant thermal resistance barrier is generated at the interface; under high temperature environment, the heat transfer at the interface is hindered, local temperature is too high, and then the thermal aging of the crosslinked network of the heat-resistant reinforcing body is accelerated, and finally the overall heat-resistant performance of the composite material is reduced. In order to further solve this technical problem, polylactic acid-polyethylene glycol-polylactic acid block copolymer (PLA-PEG-PLA) is added to the mixture, the PLA segment of the block copolymer has good compatibility with polylactic acid and polybutylene succinate in the matrix of the composite material, and can be closely combined with the matrix material, and the PEG segment can form stable hydrogen bonds with the polar groups on the surface of the antibacterial composite powder, thereby building an efficient interface bridge between the antibacterial composite powder and the heat-resistant reinforcing body, effectively reducing the thermal resistance at the interface between the two, promoting the uniform transfer of heat in the composite material, avoiding the problem of thermal aging of the crosslinked network of the heat-resistant reinforcing body caused by local high temperature, and ensuring the stability of the overall heat-resistant performance of the material.

[0016] A biodegradable polylactic acid composite material is prepared by the method.

[0017] Compared with the prior art, the present application has the following advantages: 1. Through the synergistic effect of KH550 grafted modification 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, and the antibacterial components are uniformly dispersed to achieve sustained antibacterial effect.

[0018] 2. The heat-resistant reinforcing body uses nano silicon dioxide, hydroxypropylated modified lignin and multi-component crosslinked network to build a stable structure, which can hinder molecular chain movement at high temperature, improve the heat distortion temperature of the material, and maintain the overall structural integrity and performance.

[0019] 3. The addition of polylactic acid-polyethylene glycol-polylactic acid block copolymer as an interface bridge in the mixture enhances the bonding force between the antibacterial composite powder and the heat-resistant reinforcing body, reduces the thermal resistance, avoids the performance decline caused by local high temperature, and ensures the stability of the heat-resistant performance of the composite material. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 SEM image of the antibacterial composite powder prepared in Example 1 of the present application.

[0021] Figure 2SEM image of the heat-resistant reinforcing body prepared for Example 1 of the present application. DETAILED DESCRIPTION

[0022] The technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0023] Example 1 A preparation method of a biodegradable polylactic acid composite material, comprising the following steps: Step 1: 10 g of chitosan (degree of deacetylation 90%, molecular weight 80000) was weighed and added into 200 mL of 10% hydrochloric acid aqueous solution. After being dispersed by stirring at 300 rpm, it was refluxed at 85°C for 2 h in an oil bath. After cooling, 5% sodium hydroxide was added dropwise to adjust the pH to 7.2. After standing and filtration, it was washed with deionized water until the filtrate was neutral. Vacuum freeze-drying was performed at -50°C and 0.08 MPa until the weight was constant, to obtain activated chitosan.

[0024] 8 g of activated chitosan was weighed and added into 150 mL of toluene. After being dispersed by ultrasonic at 200 W for 35 min, 0.9 g of KH550 silane coupling agent was added. After the pH was adjusted to 4.0 by adding glacial acetic acid, it was refluxed at 108°C for 6 h under nitrogen protection. After cooling, it was centrifuged at 8000 rpm for 15 min. After being washed with toluene for 3 times, it was dried at 60°C and 0.09 MPa until the weight was constant, to obtain KH550 grafted chitosan.

[0025] Step 2: 5 g of nano-zinc oxide was weighed and added into 150 mL of anhydrous ethanol. After being dispersed by ultrasonic at 200 W for 25 min, 0.5 g of stearic acid was added and dissolved by stirring. After being reacted at 65°C for 2 h in a water bath, it was filtered and washed with anhydrous ethanol for 2 times. After being dried at 80°C by blowing air, the weight was constant, to obtain modified nano-zinc oxide.

[0026] 8 g of KH550 grafted chitosan and 3.5 g of modified nano-zinc oxide were weighed and added into 200 mL of deionized water. After being dispersed by ultrasonic at 200 W for 15 min, it was stirred at 48°C and 280 rpm for 3.5 h. After spray drying (inlet temperature 170°C and outlet temperature 85°C), the antibacterial composite powder was collected.

[0027] Step 3: 12 g of nano-silicon dioxide was weighed and added into 200 mL of 12% hydrochloric acid solution. After being refluxed at 85°C for 2.5 h, it was filtered and washed until neutral. After being dried at 105°C, it was calcined at 330°C for 2.5 h, to obtain activated nano-silicon dioxide.

[0028] Take 10 g of activated nano-silica and add it to 150 mL of toluene. Ultrasonic at 200 W for 45 min. Add 1.8 g of KH570 silane coupling agent, drop in glacial acetic acid to adjust pH to 3.8, and reflux at 108°C for 7 h under nitrogen protection. After centrifugal washing, dry at 80°C and 0.09 MPa vacuum to obtain KH570 modified nano-silica.

[0029] Step 4: Take 15 g of alkali lignin and add it to 150 mL of isopropyl alcohol. Stir and disperse, then add 0.75 g of sodium hydroxide and 5 g of propylene oxide. Place in an autoclave and react at 70°C and 0.6 MPa for 3.5 h. After pressure relief and cooling, filter and wash with isopropyl alcohol. Dry at 100°C to obtain hydroxypropylated lignin.

[0030] Take 1.5 g of KH570 modified nano-silica, 3.8 g of hydroxypropylated lignin, 7.5 g of polycaprolactone (molecular weight 50000), and 2.25 g of methyl methacrylate. Add to 200 mL of toluene, then add 0.15 g of azobisisobutyronitrile. Reflux at 110°C for 8 h under nitrogen protection. Evaporate toluene at 60°C and dry at 80°C under vacuum to obtain heat-resistant reinforcing agent.

[0031] Step 5: Take 55 g of polylactic acid (molecular weight 100,000, 98% optical purity), 20 g of polybutylene succinate (molecular weight 80,000), 7 g of antibacterial composite powder, 8 g of heat-resistant reinforcing agent, 5 g of tributyl citrate, 3 g of polyethylene glycol (molecular weight 4000), 2 g of talc, and 0.50 g of polylactic acid-polyethylene glycol-polylactic acid block copolymer. High-speed mix at 85°C and 550 rpm for 40 min to obtain a premix. Add the premix to a twin-screw extruder, set the temperature of each section to 150°C, 165°C, 180°C, 185°C, and the die head to 180°C. Set the screw speed to 220 rpm and the feeding rate to 50 g / min. Extrude the strip and cool it in water at 28°C, then cut it into particles to obtain the composite material particles.

[0032] Example 2 A method for preparing a biodegradable polylactic acid composite material, comprising the following steps: Step 1: Take 10 g of chitosan (deacetylation degree 90%, molecular weight 80000) and add it to 200 mL of 10% hydrochloric acid aqueous solution. Stir and disperse at 300 rpm, then reflux at 85°C for 2 h. After cooling, add 5% sodium hydroxide to adjust pH to 7.2. Let stand and filter, then wash with deionized water until the filtrate is neutral. Freeze-dry at -50°C and 0.08 MPa vacuum to constant weight to obtain activated chitosan.

[0033] Take 8 g of activated chitosan and add it to 150 mL of toluene, ultrasonic dispersion at 200 W for 35 min. Add 0.6 g of KH550 silane coupling agent, dropwise add glacial acetic acid to adjust the pH to 4.0, and reflux at 108°C for 6 h under nitrogen protection. After cooling, centrifuge at 8000 rpm for 15 min, wash with toluene for 3 times, and dry under vacuum at 60°C and 0.09 MPa until constant weight to obtain KH550 grafted chitosan.

[0034] Step 2: Take 5 g of nano zinc oxide and add it to 150 mL of anhydrous ethanol, ultrasonic dispersion at 200 W for 25 min. Add 0.3 g of stearic acid and stir to dissolve, and react at 65°C water bath for 2 h. After suction filtration, wash with anhydrous ethanol for 2 times, and dry at 80°C with air blowing until constant weight to obtain modified nano zinc oxide.

[0035] Take 8 g of KH550 grafted chitosan and 2.5 g of modified nano zinc oxide, add them to 200 mL of deionized water, and ultrasonic dispersion at 200 W for 15 min. After stirring at 48°C and 280 rpm for 3.5 h, spray drying (inlet temperature 170°C and outlet temperature 85°C) to collect the antibacterial composite powder.

[0036] Step 3: Take 12 g of nano silicon dioxide and add it to 200 mL of 12% hydrochloric acid solution, and reflux at 85°C for 2.5 h. Wash with water until neutral, dry at 105°C, and then calcine at 330°C for 2.5 h to obtain activated nano silicon dioxide.

[0037] Add 10 g of activated nano silicon dioxide to 150 mL of toluene, and ultrasonic dispersion at 200 W for 45 min. Add 1.2 g of KH570 silane coupling agent, dropwise add glacial acetic acid to adjust the pH to 3.8, and reflux at 108°C for 7 h under nitrogen protection. After centrifugal washing, dry under vacuum at 80°C and 0.09 MPa to obtain KH570 modified nano silicon dioxide.

[0038] Step 4: Take 15 g of alkali lignin and add it to 150 mL of isopropanol, stir to disperse, and then add 0.75 g of sodium hydroxide and 4 g of propylene oxide. Place in an autoclave and react at 70°C and 0.6 MPa for 3.5 h, then cool after pressure relief, suction filter, wash with isopropanol, and dry at 100°C to obtain hydroxypropylated lignin.

[0039] Take 1.5 g of KH570 modified nano silicon dioxide, 3.8 g of hydroxypropylated lignin, 7.5 g of polycaprolactone (molecular weight 50000), and 2.25 g of methyl methacrylate, add them to 200 mL of toluene, and then add 0.15 g of azobisisobutyronitrile, and reflux at 110°C for 8 h under nitrogen protection. Evaporate toluene at 60°C, and dry under vacuum at 80°C to obtain heat-resistant reinforcing agent.

[0040] Step 5: 55 g of polylactic acid (molecular weight 100,000, 98% optical purity), 20 g of polybutylene succinate (molecular weight 80,000), 7 g of antibacterial composite powder, 8 g of heat-resistant reinforcing agent, 5 g of tributyl citrate, 3 g of polyethylene glycol (molecular weight 4000), 2 g of talc, and 0.35 g of polylactic acid-polyethylene glycol-polylactic acid block copolymer were weighed. After high-speed mixing at 85°C and 550 rpm for 40 min, the pre-mixture was cooled to obtain a pre-mixture. The pre-mixture was added to a twin-screw extruder, and the temperature of each section was 150°C, 165°C, 180°C, 185°C, and the die head was 180°C. The screw rotation speed was 220 rpm, and the feeding rate was 50 g / min. After the extruded strip was cooled in water at 28°C, the composite particles were obtained by granulation.

[0041] Example 3 A method for preparing a biodegradable polylactic acid composite material, comprising the following steps: Step 1: 10 g of chitosan (deacetylation degree 90%, molecular weight 80,000) was added to 200 mL of 10% hydrochloric acid aqueous solution, and after stirring and dispersing at 300 rpm, it was refluxed at 85°C for 2 h. After cooling, 5% sodium hydroxide was added dropwise to adjust the pH to 7.2, and then it was left to stand and filtered. After washing with deionized water until the filtrate was neutral, it was freeze-dried at -50°C and 0.08 MPa vacuum to constant weight to obtain activated chitosan.

[0042] 8 g of activated chitosan was weighed into 150 mL of toluene and ultrasonically dispersed at 200 W for 35 min. Then, 0.7 g of KH550 silane coupling agent was added, and the pH was adjusted to 4.0 by adding glacial acetic acid. The reaction was carried out under nitrogen protection at 108°C for 6 h. After cooling, it was centrifuged at 8000 rpm for 15 min, washed with toluene 3 times, and dried at 60°C and 0.09 MPa vacuum to constant weight to obtain KH550 grafted chitosan.

[0043] Step 2: 5 g of nano-zinc oxide was added to 150 mL of anhydrous ethanol and ultrasonically dispersed at 200 W for 25 min. Then, 0.4 g of stearic acid was added and stirred to dissolve, and the reaction was carried out at 65°C water bath for 2 h. After filtration, it was washed with anhydrous ethanol 2 times, and dried at 80°C with air blowing to constant weight to obtain modified nano-zinc oxide.

[0044] 8 g of KH550 grafted chitosan and 3 g of modified nano-zinc oxide were weighed into 200 mL of deionized water and ultrasonically dispersed at 200 W for 15 min. After stirring at 48°C and 280 rpm for 3.5 h, it was spray dried (inlet temperature 170°C, outlet temperature 85°C) to collect the antibacterial composite powder.

[0045] Step 3: 12 g of nano-silicon dioxide was added to 200 mL of 12% hydrochloric acid solution and refluxed at 85°C for 2.5 h. After filtration and washing to neutral, it was dried at 105°C, and then calcined at 330°C for 2.5 h to obtain activated nano-silicon dioxide.

[0046] Take 10 g of activated nano-silica and add it to 150 mL of toluene, and ultrasonic at 200 W for 45 min. Add 1.5 g of KH570 silane coupling agent, drop in glacial acetic acid to adjust the pH to 3.8, and reflux at 108°C for 7 h under nitrogen protection. After centrifugal washing, dry at 80°C and 0.09 MPa vacuum to obtain KH570 modified nano-silica.

[0047] Step 4: Take 15 g of alkali lignin and add it to 150 mL of isopropyl alcohol, and stir to disperse. Add 0.75 g of sodium hydroxide and 4.5 g of propylene oxide. Place in an autoclave and react at 70°C and 0.6 MPa for 3.5 h. After pressure relief and cooling, filter, wash with isopropyl alcohol, and dry at 100°C to obtain hydroxypropylated lignin.

[0048] Take 1.5 g of KH570 modified nano-silica, 3.8 g of hydroxypropylated lignin, 7.5 g of polycaprolactone (molecular weight 50000), and 2.25 g of methyl methacrylate, and add them to 200 mL of toluene. Then add 0.15 g of azobisisobutyronitrile, and reflux at 110°C for 8 h under nitrogen protection. Evaporate toluene at 60°C, and dry at 80°C under vacuum to obtain heat-resistant reinforcing agent.

[0049] Step 5: Take 55 g of polylactic acid (molecular weight 100,000, 98% optical purity), 20 g of polybutylene succinate (molecular weight 80,000), 7 g of antibacterial composite powder, 8 g of heat-resistant reinforcing agent, 5 g of tributyl citrate, 3 g of polyethylene glycol (molecular weight 4000), 2 g of talc, and 0.40 g of polylactic acid-polyethylene glycol-polylactic acid block copolymer. High-speed mix at 85°C and 550 rpm for 40 min to obtain a premix. Add the premix to a twin-screw extruder, and set the temperature of each section to 150°C, 165°C, 180°C, 185°C, and the die head to 180°C. Set the screw speed to 220 rpm, and the feeding rate to 50 g / min. Extrude the strip and cool it in water at 28°C, and then pelletize to obtain composite particles.

[0050] Example 4 A method for preparing a biodegradable polylactic acid composite material, comprising the following steps: Step 1: Take 10 g of chitosan (deacetylation degree 90%, molecular weight 80000), add it to 200 mL of 10% hydrochloric acid aqueous solution, and stir to disperse at 300 rpm. Then reflux at 85°C for 2 h. After cooling, add 5% sodium hydroxide dropwise to adjust the pH to 7.2, and then stand and filter. Wash with deionized water until the filtrate is neutral, and then freeze-dry at -50°C and 0.08 MPa vacuum to constant weight to obtain activated chitosan.

[0051] Take 8 g of activated chitosan and add it to 150 mL of toluene, ultrasonic dispersion at 200 W for 35 min. Add 1.0 g of KH550 silane coupling agent, dropwise add glacial acetic acid to adjust the pH to 4.0, and reflux at 108°C for 6 h under nitrogen protection. After cooling, centrifuge at 8000 rpm for 15 min, wash with toluene for 3 times, and dry under vacuum at 60°C and 0.09 MPa until constant weight to obtain KH550 grafted chitosan.

[0052] Step 2: Take 5 g of nano zinc oxide and add it to 150 mL of anhydrous ethanol, ultrasonic dispersion at 200 W for 25 min. Add 0.6 g of stearic acid and stir to dissolve, and react at 65°C water bath for 2 h. After suction filtration, wash with anhydrous ethanol for 2 times, and dry at 80°C under blast until constant weight to obtain modified nano zinc oxide.

[0053] Take 8 g of KH550 grafted chitosan and 4 g of modified nano zinc oxide, add them to 200 mL of deionized water, and ultrasonic dispersion at 200 W for 15 min. After stirring at 48°C and 280 rpm for 3.5 h, spray dry (inlet temperature 170°C, outlet temperature 85°C) to collect the antibacterial composite powder.

[0054] Step 3: Take 12 g of nano silicon dioxide and add it to 200 mL of 12% hydrochloric acid solution, and reflux at 85°C for 2.5 h. Wash with water until neutral, dry at 105°C, and then calcine at 350°C for 3 h to obtain activated nano silicon dioxide.

[0055] Add 10 g of activated nano silicon dioxide to 150 mL of toluene, and ultrasonic dispersion at 200 W for 45 min. Add 2.0 g of KH570 silane coupling agent, dropwise add glacial acetic acid to adjust the pH to 3.8, and reflux at 108°C for 7 h under nitrogen protection. After centrifugal washing, dry under vacuum at 80°C and 0.09 MPa to obtain KH570 modified nano silicon dioxide.

[0056] Step 4: Take 15 g of alkali lignin and add it to 150 mL of isopropanol, stir to disperse, and then add 0.75 g of sodium hydroxide and 6 g of propylene oxide. Place in an autoclave and react at 70°C and 0.6 MPa for 3.5 h, then cool after pressure relief, suction filter, wash with isopropanol, and dry at 100°C to obtain hydroxypropylated lignin.

[0057] Take 1.5 g of KH570 modified nano silicon dioxide, 3.8 g of hydroxypropylated lignin, 7.5 g of polycaprolactone (molecular weight 50000), and 2.25 g of methyl methacrylate, add them to 200 mL of toluene, and then add 0.15 g of azobisisobutyronitrile, and reflux at 110°C for 8 h under nitrogen protection. Evaporate toluene at 60°C, and dry under vacuum at 80°C to obtain heat-resistant reinforcing agent.

[0058] 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.

[0059] Example 5 A method for preparing a biodegradable polylactic acid composite material includes the following steps: 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 10 g activated nano-silica was added into 150 mL toluene and ultrasonicated for 45 min at 200 W. 1.0 g of KH570 silane coupling agent was added, and the pH was adjusted to 3.8 by adding glacial acetic acid dropwise. The mixture was refluxed at 108°C for 7 h under nitrogen protection. After centrifugal washing, the mixture was dried at 80°C under 0.09 MPa vacuum to obtain KH570-modified nano-silica.

[0065] Step 4: 15 g of alkali lignin was added into 150 mL of isopropyl alcohol and stirred and dispersed. Then, 0.75 g of sodium hydroxide and 3 g of propylene oxide were added. The mixture was placed in an autoclave and reacted at 70°C under 0.6 MPa for 3.5 h. After pressure relief and cooling, the mixture was filtered and washed with isopropyl alcohol. The mixture was dried at 100°C to obtain hydroxypropylated lignin.

[0066] 1.5 g of KH570-modified nano-silica, 3.8 g of hydroxypropylated lignin, 7.5 g of polycaprolactone (molecular weight 50,000), and 2.25 g of methyl methacrylate were added into 200 mL of toluene, followed by the addition of 0.15 g of azobisisobutyronitrile. The mixture was refluxed at 110°C for 8 h under nitrogen protection. The toluene was evaporated at 60°C, and the mixture was dried at 80°C under vacuum to obtain a heat-resistant reinforcing body.

[0067] Step 5: 55 g of polylactic acid (molecular weight 100,000, 98% optical purity), 20 g of polybutylene succinate (molecular weight 80,000), 7 g of antibacterial composite powder, 8 g of heat-resistant reinforcing body, 5 g of tributyl citrate, 3 g of polyethylene glycol (molecular weight 4,000), 2 g of talc, and 0.28 g of polylactic acid-polyethylene glycol-polylactic acid block copolymer were weighed. The mixture was high-speed mixed at 85°C and 550 rpm for 40 min, and the cooled mixture was obtained as a premix. The premix was fed into a twin-screw extruder, and the temperature of each section was set to 150°C, 165°C, 180°C, 185°C, and the die head was set to 180°C. The screw rotation speed was 220 rpm, and the feeding rate was 50 g / min. The extruded strip was cooled in water at 28°C and then pelletized to obtain composite particles.

[0068] Comparative Example 1: The difference between Comparative Example 1 and Example 1 is that steps 1-2 are omitted in the preparation of the polylactic acid composite, and no antibacterial composite powder is added in step 5.

[0069] Comparative Example 2: The difference between Comparative Example 2 and Example 1 is that steps 3-4 are omitted in the preparation of the polylactic acid composite, and no heat-resistant reinforcing body is added in step 5.

[0070] Comparative Example 3: The difference between Comparative Example 3 and Example 1 is that no polylactic acid-polyethylene glycol-polylactic acid block copolymer is added in step 5 in the preparation of the polylactic acid composite.

[0071] Performance Test: 1. Antibacterial performance test: According to GB / T 31402-2015 standard, the composite particles were injection molded into 50mm x 50mm x 2mm smooth plaques, after sterilization at 121℃, 0.1MPa for 20min, 0.2mL of E. coli or S. aureus suspension with a concentration of 1x10 5 CFU / mL was added dropwise and evenly coated, and then incubated at 37℃, relative humidity ≥90% for 24h, followed by elution with 20mL of sterile normal saline for 10min, the eluate was gradient diluted and plated for counting, the antibacterial rate was calculated as (average bacterial count of blank sample-average bacterial count of sample) / average bacterial count of blank sample x 100%, antibacterial rate ≥90% was antibacterial effect, antibacterial rate ≥99% was excellent antibacterial effect.

[0072] 2. Heat resistance performance test: The heat distortion temperature test was carried out according to GB / T 1634.2-2004 "Determination of the heat distortion temperature of plastics, rigid rubbers and long fibre-reinforced composites Part 2: Plastics, rigid rubbers and long fibre-reinforced composites", the load was set to 1.80MPa, the temperature rising rate was 120℃ / h, and the temperature at which the sample deformation reached 0.2mm was recorded; The hot water immersion deformation rate test was carried out according to the relevant requirements of food contact materials, the standard sample (length 80mm x width 10mm x thickness 4mm) made of composite material was placed in a constant temperature water bath at 80℃ for 2h, then taken out and naturally cooled to room temperature, the length and width before and after immersion were measured, and the deformation rate was calculated, deformation rate (%)=(size after immersion-size before immersion) / size before immersion x 100%. The test results are shown in Table 1.

[0073] 3. Biodegradation performance test: According to GB / T 19277.1-2011 "Determination of the ultimate aerobic biodegradability of materials under controlled composting conditions - Method by measuring the evolution of carbon dioxide - Part 1: General method", the soil burial method was used, 5g of sample was buried in natural soil (humidity 60%, temperature 25℃), and the residual mass of the sample was measured periodically, and the biodegradation rate after 6 months was calculated. Degradation rate (%)=(initial mass-residual mass) / initial mass x 100%). The test results are shown in Table 1.

[0074] Table 1: Although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent substitutions for part of the technical features, any modification, equivalent substitution, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

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 8, 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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