Cellulose antibacterial modified degradable film and preparation method thereof

Abstract

The application discloses a cellulose antibacterial modified degradable film and a preparation method thereof, and relates to the technical field of film materials. The preparation method of the cellulose antibacterial modified degradable film comprises the following steps: quaternary ammonium modification is performed on nanocellulose to obtain antibacterial modified nanocellulose; block copolymerization modification is performed on polylactic acid to obtain modified polylactic acid; the antibacterial modified nanocellulose, the modified polylactic acid and polylactic acid are melt blended to obtain a composite master batch; and the composite master batch is blown into a film by using a single-screw hot melt extrusion blow molding to obtain the cellulose antibacterial modified degradable film. The cellulose antibacterial modified degradable film prepared by the application has excellent antibacterial property and mechanical property, and has low blow molding difficulty.

Description

Technical Field

[0001] This invention relates to the field of thin film materials technology, specifically to a cellulose antibacterial modified biodegradable film and its preparation method. Background Technology

[0002] With the introduction of the national green and sustainable development strategy, the implementation of the "plastic restriction order," and the increasing awareness of environmental protection, health, and safety, the production and use of traditional plastic packaging materials have been restricted, prompting the industry to transform towards a more environmentally friendly and sustainable direction. Biodegradable food packaging materials are gradually becoming a new favorite. Among commonly used biopolymers, polylactic acid (PLA) has been proven to have the potential to replace petroleum-based polymers in industrial applications. PLA is a biodegradable polyester made from renewable resources and is commonly used in biomedicine, packaging, and tissue engineering. Due to its good mechanical properties, processability, biocompatibility, biodegradability, and renewability, PLA occupies an important position in the biopolymer industry and is one of the most promising functional materials for the future. Although PLA has advantages such as high mechanical strength and good thermal stability, it also suffers from problems such as brittleness, poor barrier properties, and difficulty in blown film production alone. Adding fibers, micro / nano fillers, and other additives to the PLA matrix is ​​a feasible method to enhance its performance.

[0003] As the most abundant material in nature, cellulose, with its rich and natural source and numerous excellent physical and chemical properties, has made cellulose and its derivatives important biomaterials. Nanocellulose (NCC) of a certain size, in the form of short rods, can be added to materials to reinforce them. Using PLA as a matrix and NCC as a filler, PLA can be modified to compensate for its shortcomings and produce biodegradable packaging materials with high mechanical and barrier properties. However, the polarity of the hydroxyl groups on the surface of nanocellulose limits its uniform distribution in polylactic acid (PLA) and affects its toughening effect on the matrix. Furthermore, with the increasing awareness of environmental protection, health, and hygiene in recent years, people have higher and higher requirements for the antibacterial properties of PLA products. However, due to the poor antibacterial and antifungal properties of PLA, mold will gradually grow on the surface of the material after long-term use. Therefore, the development of PLA composite materials with antibacterial properties is of great significance to human health. Thus, existing PLA biodegradable films suffer from defects such as poor antibacterial properties, poor mechanical properties, and difficulties in film blowing, which greatly limits the application of this technology. Summary of the Invention

[0004] The purpose of this invention is to provide a cellulose antibacterial modified biodegradable membrane and its preparation method, thereby solving the following technical problems:

[0005] Existing methods for preparing biodegradable films using polylactic acid composite material blow molding suffer from problems such as poor antibacterial properties, poor mechanical properties, and difficulties in blow molding.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A method for preparing a cellulose antibacterial modified biodegradable membrane includes at least the following preparation steps:

[0008] Antibacterial modified nanocellulose was obtained by quaternizing nanocellulose.

[0009] Modified polylactic acid was obtained by block copolymerization.

[0010] The antibacterial modified nanocellulose, the modified polylactic acid, and polylactic acid are melt-blended to obtain a composite masterbatch;

[0011] The composite masterbatch was blow-molded into a film using a single-screw hot melt extrusion to obtain a cellulose antibacterial modified biodegradable film.

[0012] As a further aspect of the present invention: the mass ratio of the antibacterial modified nanocellulose, the modified polylactic acid and the polylactic acid is 5-10:10-20:100.

[0013] As a further aspect of the present invention, the preparation method of the antibacterial modified nanocellulose includes the following steps:

[0014] Nanocellulose was dispersed in N,N-dimethylacetamide, 6-bromohexanoyl chloride was added, and the mixture was reacted, precipitated, and washed to obtain surface-modified nanocellulose.

[0015] The surface-modified nanocellulose was dispersed in dimethyl sulfoxide, N,N-dimethyldodecylamine was added, and the mixture was reacted, dialyzed, and dried to obtain antibacterial modified nanocellulose.

[0016] As a further aspect of the present invention, the mass ratio of the 6-bromohexanoyl chloride, the nanocellulose, and the N,N-dimethyldodecylamine is 1:2-3:3-6.

[0017] As a further aspect of the present invention, the preparation method of the modified polylactic acid includes the following steps:

[0018] Using dimethylpropionic acid as an initiator and stannous octoate as a catalyst, ε-caprolactone was initiated to undergo ring-opening polymerization to obtain a dihydroxy monocarboxylated polycaprolactone prepolymer.

[0019] Using tetrabutyl titanate as a catalyst, the dihydroxy monocarboxylated polycaprolactone prepolymer was catalyzed to undergo a self-condensation reaction to obtain long-chain branched polycaprolactone.

[0020] Using the long-chain branched polycaprolactone as a macromolecular initiator and stannous octoate as a catalyst, the monomer L-lactide is initiated to undergo ring-opening polymerization to obtain modified polylactic acid.

[0021] As a further aspect of the present invention, the mass ratio of the dimethylpropionic acid to the ε-caprolactone is 1:15-25.

[0022] As a further aspect of the present invention, the mass ratio of the long-chain branched polycaprolactone to the L-lactide is 1:1-2.

[0023] As a further aspect of the present invention: the process conditions for single-screw hot melt extrusion blow molding film formation are as follows: the processing temperatures of screw zones one, two, three, four, and five are 160℃, 175℃, 185℃, 190℃, and 190℃ respectively; the screw speed is 50 r / min; the lower and upper die temperatures are 190℃ and 19℃ respectively; the blow-up ratio is 2.5, and the traction ratio is 3.

[0024] A cellulose antibacterial modified biodegradable membrane, wherein the cellulose antibacterial modified biodegradable membrane is prepared by any one of the preparation methods described above.

[0025] The beneficial effects of this invention are:

[0026] This invention incorporates antibacterial modified nanocellulose and modified polylactic acid (PLA) into a PLA base, melt-blending and blow molding to obtain a cellulose antibacterial modified biodegradable film. In this invention, the antibacterial modified nanocellulose is quaternized modified nanocellulose, imparting excellent antibacterial properties to the material. The modified PLA is a long-chain branched copolymer, providing high melt strength and improving subsequent blown film processing. Furthermore, the antibacterial modified nanocellulose and modified PLA not only synergistically improve the toughness of the biodegradable film but also maintain the transparency and fully biodegradable environmental performance of the PLA film, facilitating the widespread application of PLA film products. The cellulose antibacterial modified biodegradable film obtained by this invention possesses excellent antibacterial properties and mechanical strength, making it suitable for use in everyday packaging bags, food preservation bags, disposable bags, and agricultural films.

[0027] The antibacterial modified nanocellulose prepared in this invention involves surface modification of nanocellulose with 6-bromohexanoyl chloride, followed by quaternization modification with N,N-dimethyldodecylamine. This process endows the nanocellulose with antibacterial properties, and the quaternary ammonium salt is covalently linked to the surface of the nanocellulose. The antibacterial functional group of the quaternary ammonium salt does not dissolve, exhibiting excellent non-leaching stability and extending the antibacterial duration of the biodegradable membrane. Long-chain alkyl chains are also grafted onto the surface of the modified nanocellulose. The longer alkyl chains have higher hydrophobicity and lower wettability, improving the dispersibility of nanocellulose in polylactic acid (PLA). This effectively improves the mechanical properties, crystallinity, and light transmittance of PLA while ensuring that the biodegradability of PLA remains unaffected. When antibacterial modified nanocellulose is added to the PLA polymer matrix as a toughening and antibacterial agent, it enhances the antibacterial properties of the biodegradable membrane, restricts the movement of matrix molecular chains, and provides nucleation sites to promote crystallization, thereby improving the heat resistance and mechanical properties of the nanocomposite material.

[0028] The modified polylactic acid (PLA) prepared in this invention is a polycaprolactone-PLA block copolymer containing long-chain branched polycaprolactone (PCL) segments, which can improve the toughness and melt strength of PLA. The chain entanglement of the long-chain branched PCL segments and the polylactic acid segments in the block copolymerized modified PLA can co-crystallize with the PLA matrix, resulting in a physical cross-linking network similar to a chemical cross-linking structure within the modified cellulose antibacterial biodegradable film. This provides excellent toughening and improves its melt tensile strength, which is crucial for improving PLA blown film processing. Furthermore, because the copolymer contains both long-chain branched PCL segments and linear polylactic acid segments, it exhibits good compatibility with the PLA matrix and does not undergo large-scale phase separation. Therefore, the modified film still maintains very good light transmittance. 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 some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Example 1: The preparation method of antibacterial modified nanocellulose includes the following steps:

[0031] 10g of nanocellulose powder was ultrasonically dispersed in 250mL of N,N-dimethylacetamide, heated to 100℃, and 20g of 6-bromohexanoyl chloride was added. After reacting for 1h at 100℃ and a stirring speed of 400r / min, the mixture was poured into 2700mL of ethanol to terminate the reaction and centrifuge to collect the precipitate. The product was then washed alternately with dimethyl sulfoxide and ethanol to obtain surface-modified nanocellulose.

[0032] 10g of the above surface-modified nanocellulose was dispersed in dimethyl sulfoxide, heated to 80°C, and 40g of N,N-dimethyldodecylamine was added. After stirring at 80°C for 5 hours, the reaction mixture was transferred to a dialysis bag and dialyzed in ethanol for 4 days, then dialyzed in deionized water for 4 days. After drying, antibacterial modified nanocellulose was obtained.

[0033] Example 2: The preparation method of antibacterial modified nanocellulose includes the following steps:

[0034] 10g of nanocellulose powder was ultrasonically dispersed in 250mL of N,N-dimethylacetamide, heated to 100℃, and 26g of 6-bromohexanoyl chloride was added. After reacting for 1h at 100℃ and a stirring speed of 400r / min, the mixture was poured into 2700mL of ethanol to terminate the reaction and centrifuge to collect the precipitate. The product was then washed alternately with dimethyl sulfoxide and ethanol to obtain surface-modified nanocellulose.

[0035] 10g of the above surface-modified nanocellulose was dispersed in dimethyl sulfoxide, heated to 80°C, and 52g of N,N-dimethyldodecylamine was added. After stirring at 80°C for 5h, the reaction mixture was transferred to a dialysis bag and dialyzed in ethanol for 4d, then dialyzed in deionized water for 4d. After drying, antibacterial modified nanocellulose was obtained.

[0036] Example 3: The preparation method of modified polylactic acid includes the following steps:

[0037] Under nitrogen protection, 100g of ε-caprolactone and 5g of dimethylpropionic acid were added to a dry three-necked flask and heated to melt in an oil bath at 120℃. A toluene solution of 1.5g of stannous octoate was then injected. The mixture was deoxygenated by vacuuming and nitrogen purging three times and reacted at a constant temperature of 130℃ for 24h. The reaction solution was dissolved in 200mL of dichloromethane and precipitated by adding it dropwise to 2000mL of ice-cold methanol. After centrifugation, the mixture was dried under vacuum at 40℃ for 48h to obtain the dihydroxy monocarboxylated polycaprolactone prepolymer.

[0038] 80g of the above-mentioned dihydroxy monocarboxylated polycaprolactone prepolymer and 1.6mL of the catalyst tetrabutyl titanate were dissolved in 100mL of anhydrous xylene. The reaction was carried out at 160℃ for 12h under nitrogen protection, and then the temperature was increased to 180℃ for 24h. The mixture was filtered and precipitated, and then freeze-dried to obtain long-chain branched polycaprolactone.

[0039] 50g of the above-mentioned long-chain branched polycaprolactone and 72g of initiating monomer L-lactide were mixed, melted, and then injected into a toluene solution containing 1.2g of catalyst stannous octoate. The mixture was reacted under vacuum at 140°C for 36h, precipitated, and dried to obtain modified polylactic acid.

[0040] Example 4: A method for preparing a cellulose antibacterial modified biodegradable membrane, which is made by the following method:

[0041] Five parts by weight of the antibacterial modified nanocellulose prepared in Example 1, 15 parts by weight of the modified polylactic acid prepared in Example 3, and 100 parts by weight of polylactic acid were mixed evenly and then added to a twin-screw extruder for melt blending to obtain a composite masterbatch.

[0042] The above-mentioned composite masterbatch was blow-molded into a film using a single screw hot melt extrusion. The processing temperatures of the screw zones 1, 2, 3, 4, and 5 were set to 160℃, 175℃, 185℃, 190℃, and 190℃ respectively, the screw speed was 50 r / min, the lower and upper die temperatures were 190℃ and 19℃ respectively, the blow-up ratio was 2.5, and the traction ratio was 3, to obtain a cellulose antibacterial modified biodegradable film.

[0043] Example 5: A method for preparing a cellulose antibacterial modified biodegradable membrane, which is made by the following method:

[0044] Five parts by weight of the antibacterial modified nanocellulose prepared in Example 2, 15 parts by weight of the modified polylactic acid prepared in Example 3, and 100 parts by weight of polylactic acid were mixed evenly and then added to a twin-screw extruder for melt blending to obtain a composite masterbatch.

[0045] The above-mentioned composite masterbatch was blow-molded into a film using a single screw hot melt extrusion. The processing temperatures of the screw zones 1, 2, 3, 4, and 5 were set to 160℃, 175℃, 185℃, 190℃, and 190℃ respectively, the screw speed was 50 r / min, the lower and upper die temperatures were 190℃ and 19℃ respectively, the blow-up ratio was 2.5, and the traction ratio was 3, to obtain a cellulose antibacterial modified biodegradable film.

[0046] Example 6: A method for preparing a cellulose antibacterial modified biodegradable membrane, which is made by the following method:

[0047] Eight parts by weight of the antibacterial modified nanocellulose prepared in Example 1, 12 parts by weight of the modified polylactic acid prepared in Example 3, and 100 parts by weight of polylactic acid were mixed evenly and then added to a twin-screw extruder for melt blending to obtain a composite masterbatch.

[0048] The above-mentioned composite masterbatch was blow-molded into a film using a single screw hot melt extrusion. The processing temperatures of the screw zones 1, 2, 3, 4, and 5 were set to 160℃, 175℃, 185℃, 190℃, and 190℃ respectively, the screw speed was 50 r / min, the lower and upper die temperatures were 190℃ and 19℃ respectively, the blow-up ratio was 2.5, and the traction ratio was 3, to obtain a cellulose antibacterial modified biodegradable film.

[0049] Example 7: A method for preparing a cellulose antibacterial modified biodegradable membrane, which is made by the following method:

[0050] Eight parts by weight of the antibacterial modified nanocellulose prepared in Example 2, 12 parts by weight of the modified polylactic acid prepared in Example 3, and 100 parts by weight of polylactic acid were mixed evenly and then added to a twin-screw extruder for melt blending to obtain a composite masterbatch.

[0051] The above-mentioned composite masterbatch was blow-molded into a film using a single screw hot melt extrusion. The processing temperatures of the screw zones 1, 2, 3, 4, and 5 were set to 160℃, 175℃, 185℃, 190℃, and 190℃ respectively, the screw speed was 50 r / min, the lower and upper die temperatures were 190℃ and 19℃ respectively, the blow-up ratio was 2.5, and the traction ratio was 3, to obtain a cellulose antibacterial modified biodegradable film.

[0052] Comparative Example 1: The preparation method of antibacterial modified nanocellulose includes the following steps:

[0053] 10g of nanocellulose powder was ultrasonically dispersed in 250mL of N,N-dimethylacetamide, heated to 100℃, and 20g of 6-bromohexanoyl chloride was added. After reacting for 1h at 100℃ and a stirring speed of 400r / min, the mixture was poured into 2700mL of ethanol to terminate the reaction and centrifuge to collect the precipitate. The product was then washed alternately with dimethyl sulfoxide and ethanol to obtain surface-modified nanocellulose.

[0054] 10g of the above surface-modified nanocellulose was dispersed in dimethyl sulfoxide, heated to 80°C, and 40g of N,N-dimethyl-n-butylamine was added. After stirring at 80°C for 5 hours, the reaction mixture was transferred to a dialysis bag and dialyzed in ethanol for 4 days, then dialyzed in deionized water for 4 days. After drying, antibacterial modified nanocellulose was obtained.

[0055] Compared with Example 4, Comparative Example 2 only replaced the antibacterial modified nanocellulose prepared in Example 1 with the antibacterial modified nanocellulose prepared in Comparative Example 1 in terms of mass. The remaining components and preparation methods were completely the same as those in Example 4.

[0056] Compared with Example 4, Comparative Example 3 did not contain the antibacterial modified nanocellulose prepared in Example 1, but the remaining components and preparation methods were completely the same as in Example 4.

[0057] Comparative Example 4: Compared with Example 4, the modified polylactic acid prepared in Example 3 was not added in Comparative Example 4, but the remaining components and preparation methods were completely the same as in Example 4.

[0058] Compared with Example 4, in Comparative Example 5, pure polylactic acid was blown into a film.

[0059] Performance testing

[0060] Mechanical property testing: The biodegradable films in Examples 4-7 and Comparative Examples 2-5 were mechanically tested using a C41.103 electronic universal testing machine from New Sansi (Shanghai) Enterprise Development Co., Ltd. Samples were cut into 1×4 cm specimens. The sensor used was 200N, the test temperature was 23℃±2℃, and the humidity was 50%±10%. Tensile strength and elongation at break were tested. Each sample was tested five times, and the average value was taken as the test result. The test results are shown in Table 1.

[0061] Melt tensile rheology test: The raw materials were dried in an 80℃ forced-air oven for 6 h, and then the biodegradable films in Examples 4-7 and Comparative Examples 2-5 were subjected to melt tensile rheology tests using a melt tensile rheometer (Gottfert GmbH, Germany, model RG50). The test conditions were: barrel temperature 190℃, piston speed 0.3 mm / s, die length-to-diameter ratio 30 / 1, roller gap 0.4 mm, initial roller speed 50 mm / s, and acceleration 2.4 mm / s². 2 The test results are shown in Table 1.

[0062] Optical transmittance test: The transmittance of the biodegradable films in Examples 4-7 and Comparative Examples 2-5 was characterized using a TU-195 UV-Vis spectrophotometer (UV-vis) from Beijing Purkinje General Instrument Co., Ltd. The sample size was 4×4cm, and the transmittance of the sample at 550nm was tested; the test results are shown in Table 1.

[0063] Antibacterial performance test: Referring to GB / T 20944.3-2008, the antibacterial performance of the biodegradable membranes in Examples 4-7 and Comparative Examples 2-5 against Escherichia coli and Staphylococcus aureus was tested. The test time was 18h. Each sample was weighed (0.75±0.05)g. The viable bacteria concentration and the antibacterial rate of the test sample were calculated according to the following formula. Each sample was tested 3 times and the average value was taken.

[0064] Y = (W t -Q t ) / W t ×100%

[0065] In the formula: Y is the antibacterial rate, %; W t Q is the average number of colonies in the control sample; t The average number of colonies in the test samples is shown in Table 1.

[0066] Table 1: Statistical table of biodegradable membrane performance test data in Examples 4-7 and Comparative Examples 2-5

[0067]

[0068] As shown in Table 1, the cellulose antibacterial modified biodegradable membranes prepared in Examples 4-7 of this invention, by adding antibacterial modified nanocellulose and modified polylactic acid, endow the polylactic acid biodegradable membrane with excellent antibacterial and mechanical properties, reduce the difficulty of blown film preparation, and ensure that the transmittance of the biodegradable membrane at 550 nm is greater than 90%. In Comparative Example 2, using N,N-dimethyl-n-butylamine containing short carbon chains as a quaternizing modifier, the properties of the obtained biodegradable membrane decreased, indicating that the antibacterial nanocellulose prepared in this invention is uniformly dispersed in the polylactic acid substrate. In Comparative Examples 3 and 4, polylactic acid was modified with antibacterial modified nanocellulose and modified polylactic acid, respectively, and the mechanical properties of the obtained biodegradable membranes decreased, indicating that the antibacterial modified nanocellulose and modified polylactic acid in this invention have a synergistic toughening effect on polylactic acid, and the modified polylactic acid greatly improves the difficulty of blown film preparation. Comparative Example 5 is a biodegradable membrane obtained by blown film preparation of pure polylactic acid, which serves as a blank control, and the properties of the obtained biodegradable membrane are all poor.

[0069] The foregoing has provided a detailed description of one embodiment of the present invention, but this description is merely a preferred embodiment and should not be construed as limiting the scope of the invention. All equivalent variations and modifications made within the scope of the claims of this invention should still fall within the patent coverage of this invention.

Claims

1. A method for preparing a cellulose antibacterial modified biodegradable membrane, characterized in that, It includes at least the following preparation steps: Antibacterial modified nanocellulose was obtained by quaternizing nanocellulose. Modified polylactic acid was obtained by block copolymerization. The antibacterial modified nanocellulose, the modified polylactic acid, and polylactic acid are melt-blended to obtain a composite masterbatch; The composite masterbatch was blow-molded into a film using a single-screw hot melt extrusion to obtain a cellulose antibacterial modified biodegradable film; The modified polylactic acid is a polycaprolactone-polylactic acid block copolymer containing a long-chain branched structure; the preparation method of the modified polylactic acid includes the following steps: Using dimethylolpropionic acid as an initiator and stannous octoate as a catalyst, ε-caprolactone was initiated to undergo ring-opening polymerization to obtain a dihydroxy monocarboxylated polycaprolactone prepolymer. Using tetrabutyl titanate as a catalyst, the dihydroxy monocarboxylated polycaprolactone prepolymer was catalyzed to undergo a self-condensation reaction to obtain long-chain branched polycaprolactone. Using the long-chain branched polycaprolactone as a macromolecular initiator and stannous octoate as a catalyst, the monomer L-lactide was initiated to undergo ring-opening polymerization to obtain modified polylactic acid. The preparation method of the antibacterial modified nanocellulose includes the following steps: Nanocellulose was dispersed in N,N-dimethylacetamide, 6-bromohexanoyl chloride was added, and the mixture was reacted, precipitated, and washed to obtain surface-modified nanocellulose. The surface-modified nanocellulose was dispersed in dimethyl sulfoxide, N,N-dimethyldodecylamine was added, and the mixture was reacted, dialyzed, and dried to obtain antibacterial modified nanocellulose. The mass ratio of the antibacterial modified nanocellulose, the modified polylactic acid, and the polylactic acid is 3-10:10-20:

100.

2. The method for preparing a cellulose antibacterial modified biodegradable membrane according to claim 1, characterized in that, The mass ratio of the 6-bromohexanoyl chloride, the nanocellulose, and the N,N-dimethyldodecylamine is 1:2-3:3-6.

3. The method for preparing a cellulose antibacterial modified biodegradable membrane according to claim 1, characterized in that, The process conditions for single-screw hot melt extrusion blow molding film formation are as follows: the processing temperatures of screw zones one, two, three, four, and five are 160℃, 175℃, 185℃, 190℃, and 190℃, respectively; the screw speed is 50 r / min; the lower and upper die temperatures are 190℃ and 19℃, respectively; the blow-up ratio is 2.5, and the traction ratio is 3.

4. A cellulose antibacterial modified biodegradable membrane, characterized in that, The cellulose antibacterial modified biodegradable membrane is prepared by the preparation method described in any one of claims 1-3.

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