Cellulose antibacterial modified degradable film and preparation method thereof

Abstract

The invention 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 at least comprises the following preparation steps: performing quaternization modification on nano cellulose to obtain antibacterial modified nano cellulose; polylactic acid is subjected to block copolymerization modification, and modified polylactic acid is obtained; carrying out melt blending on the antibacterial modified nanocellulose, the modified polylactic acid and polylactic acid to obtain a composite master batch; the composite master batch is subjected to single-screw hot-melt extrusion blow molding to form a film, and the cellulose antibacterial modified degradable film is obtained. The cellulose antibacterial modified degradable film prepared by the invention has excellent antibacterial property and mechanical property, and is low in blow molding difficulty.

Description

Technical Field

[0001] The invention relates to the technical field of film materials, and in particular to an antibacterial modified and degradable cellulose film and a preparation method thereof. Background Art

[0002] With the proposal of the national green sustainable development strategy and the implementation of the "plastic ban" and people's 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, and biodegradable food packaging materials have gradually become a new favorite. Among the commonly used biopolymers, polylactic acid (PLA) has been proven to have industrial application potential to replace petroleum-based polymers. Polylactic acid is a biodegradable polyester made from renewable resources and is commonly used in biomedicine, packaging and tissue engineering. PLA has an important position in the biopolymer industry due to its good mechanical properties, processability, biocompatibility, biodegradability and renewability, making it one of the most promising functional materials in the future. Although polylactic acid has the advantages of high mechanical strength and good thermal stability, it has problems such as brittleness, poor barrier properties and difficulty in single film blowing. Adding fibers, micro / nano fillers and other additives to the PLA matrix is ​​a feasible way to enhance its performance.

[0003] As the most abundant material in nature, cellulose and its derivatives have become important biomaterials due to their rich sources, naturalness, and many excellent physical and chemical properties. Nanocellulose (NCC) of a certain size is in the shape of short rods and can be added to materials to enhance the materials. Using PLA as the matrix and NCC as the filler can achieve the purpose of modifying PLA, make up for the shortcomings of the material, and prepare a degradable packaging material with high mechanical properties and high barrier properties. However, the hydroxyl groups on the surface of nanocellulose are polar, which limits its uniform distribution in polylactic acid and affects the toughening effect on the matrix. In addition, with the continuous enhancement of environmental protection, health and hygiene awareness in recent years, people have higher and higher requirements for the antibacterial properties of polylactic acid products. However, due to the poor antibacterial and mildew-proof properties of polylactic acid, mold will gradually grow on the surface of the material after long-term use. Therefore, the development of polylactic acid composite materials with antibacterial properties is of great significance to people's health. Therefore, the existing polylactic acid degradable film has defects such as poor antibacterial properties, poor mechanical properties, and difficulty in film blowing, which makes the use of this technology very limited. Summary of the invention

[0004] The purpose of the present invention is to provide a cellulose antibacterial modified degradable film and a preparation method thereof, to solve the following technical problems: The existing polylactic acid composite material blow molding method for preparing biodegradable films has the problems of poor antibacterial properties, poor mechanical properties and difficulty in film blowing.

[0005] The purpose of the present invention can be achieved through the following technical solutions: A method for preparing an antibacterial modified cellulose degradable film comprises at least the following preparation steps: The nanocellulose is modified by quaternization to obtain antibacterial modified nanocellulose; Modifying the polylactic acid by block copolymerization to obtain modified polylactic acid; Melting and blending the antibacterial modified nanocellulose, the modified polylactic acid and polylactic acid to obtain a composite masterbatch; The composite masterbatch is formed into a film by single-screw hot-melt extrusion blow molding to obtain a cellulose antibacterial modified degradable film.

[0006] As a further solution 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.

[0007] As a further solution of the present invention: the preparation method of the antibacterial modified nanocellulose comprises the following steps: The nanocellulose is dispersed in N,N-dimethylacetamide, 6-bromohexanoyl chloride is added, reacted, precipitated and washed to obtain surface-modified nanocellulose; The surface modified nanocellulose is dispersed in dimethyl sulfoxide, N,N-dimethyldodecylamine is added, reacted, dialyzed and dried to obtain antibacterial modified nanocellulose.

[0008] As a further embodiment 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.

[0009] As a further embodiment of the present invention: the preparation method of the modified polylactic acid comprises the following steps: Using dimethyl propionic acid as an initiator and stannous octoate as a catalyst, ε-caprolactone is initiated to undergo ring-opening polymerization to obtain a dihydroxy monocarboxyl polycaprolactone prepolymer; Using tetrabutyl titanate as a catalyst, catalyzing the self-condensation reaction of the dihydroxy monocarboxyl polycaprolactone prepolymer to obtain a long-chain branched polycaprolactone; The long-chain branched polycaprolactone is used as a macromolecular initiator and stannous octoate is used as a catalyst to initiate the ring-opening polymerization of the monomer L-lactide to obtain the modified polylactic acid.

[0010] As a further embodiment of the present invention: the mass ratio of the dimethylpropionic acid to the ε-caprolactone is 1:15-25.

[0011] As a further embodiment of the present invention: the mass ratio of the long-chain branched polycaprolactone to the L-lactide is 1:1-2.

[0012] As a further scheme of the present invention: the process conditions of the single-screw hot melt extrusion blow molding film are as follows: the processing temperatures of screw zones 1, 2, 3, 4 and 5 are 160°C, 175°C, 185°C, 190°C and 190°C respectively; the screw speed is 50r / min; the lower and upper die temperatures are 190°C and 19°C; the blowing ratio is 2.5 and the traction ratio is 3.

[0013] A cellulose antibacterial modified degradable film is prepared by any one of the preparation methods described above.

[0014] Beneficial effects of the present invention: The present invention adds antibacterial modified nanocellulose and modified polylactic acid to a polylactic acid base, melt blends, and blows into a film to obtain a cellulose antibacterial modified degradable film. In the present invention, the antibacterial modified nanocellulose is a quaternary ammonium modified nanocellulose, which gives the material excellent antibacterial properties, and the modified polylactic acid is a long-chain branched structure copolymer, which gives the material high melt strength, improves the subsequent film blowing process, and the antibacterial modified nanocellulose and modified polylactic acid not only synergistically improve the toughness of the degradable film, but also maintain the transparency of the polylactic acid film and the environmental protection performance of complete biodegradation, which is conducive to the wide application of polylactic acid film products. The cellulose antibacterial modified degradable film obtained by the present invention has excellent antibacterial properties and mechanical strength, and can be used for packaging film bags, cling film bags, disposable film bags and agricultural films in daily life.

[0015] The antibacterial modified nanocellulose prepared in the present invention is surface-modified by 6-bromohexanoyl chloride, and then quaternized by N,N-dimethyldodecylamine, so that the nanocellulose has antibacterial properties, and the quaternary ammonium salt is connected to the surface of the nanocellulose in the form of covalent bonding, and the antibacterial functional group quaternary ammonium salt does not dissolve, has excellent non-leaching stability, and prolongs the antibacterial time of the degradable film. After the modification, a long-chain alkane chain is also grafted on the surface of the nanocellulose, and the longer alkyl chain has higher hydrophobicity and lower wettability, which improves the dispersibility of the nanocellulose in polylactic acid, can effectively improve the mechanical properties, crystallization properties and light transmittance of polylactic acid, and ensures that the degradable properties of polylactic acid are not affected. After the antibacterial modified nanocellulose is added to the polylactic acid polymer matrix as a toughening agent and an antibacterial agent, the antibacterial property of the degradable film is improved, and the movement of the matrix molecular chain can be restricted, and nucleation sites are provided to promote crystallization, thereby improving the heat resistance and mechanical properties of the nanocomposite material.

[0016] The modified polylactic acid prepared in the present invention is a polycaprolactone-polylactic acid block copolymer containing a long-chain branched structure, which can improve the toughness and melt strength of PLA. The chain entanglement of the long-chain branched polycaprolactone segment in the modified polylactic acid after block copolymerization and the polylactic acid segment can produce a co-crystallization effect with the polylactic acid matrix, so that a physical cross-linked network similar to the chemical cross-linked structure is formed inside the modified cellulose antibacterial modified degradable film, thereby playing a good toughening effect, thereby improving its melt tensile strength, and the improvement of melt strength plays a very important role in improving the PLA blown film processing. And because the copolymer contains long-chain branched PCL segments and linear polylactic acid segments at the same time, there is good compatibility with the PLA matrix, and no larger-sized phase separation will occur, so the modified film still has a very good light transmittance. DETAILED DESCRIPTION

[0017] The following will be described clearly and completely in conjunction with the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0018] Example 1 The preparation method of antibacterial modified nanocellulose comprises the following steps: 10 g of nanocellulose powder was ultrasonically dispersed in 250 mL of N,N-dimethylacetamide, heated to 100 ° C, 20 g of 6-bromohexanoyl chloride was added, and the mixture was reacted at 100 ° C and stirred at 400 r / min for 1 hour. The mixture was poured into 2700 mL of ethanol, the reaction was terminated, and the precipitate was collected by centrifugation. The product was then washed alternately with dimethyl sulfoxide and ethanol to obtain surface-modified nanocellulose; 10 g of the above-mentioned surface-modified nanocellulose was dispersed in dimethyl sulfoxide, heated to 80°C, 40 g of N,N-dimethyldodecylamine was added, and after stirring at 80°C for 5 h, the reaction mixture was transferred to a dialysis bag, dialyzed in ethanol for 4 days, and then dialyzed in deionized water for 4 days, and then dried to obtain antibacterial modified nanocellulose.

[0019] Example 2 The preparation method of antibacterial modified nanocellulose comprises the following steps: 10 g of nanocellulose powder was ultrasonically dispersed in 250 mL of N,N-dimethylacetamide, heated to 100 ° C, 26 g of 6-bromohexanoyl chloride was added, and the mixture was reacted at 100 ° C and a stirring speed of 400 r / min for 1 hour. The mixture was poured into 2700 mL of ethanol, the reaction was terminated, and the precipitate was collected by centrifugation. The product was then washed alternately with dimethyl sulfoxide and ethanol to obtain surface-modified nanocellulose; 10 g of the above-mentioned surface-modified nanocellulose was dispersed in dimethyl sulfoxide, heated to 80°C, 52 g of N,N-dimethyldodecylamine was added, and after stirring at 80°C for 5 h, the reaction mixture was transferred to a dialysis bag, dialyzed in ethanol for 4 days, and then dialyzed in deionized water for 4 days, and then dried to obtain antibacterial modified nanocellulose.

[0020] Example 3 The preparation method of modified polylactic acid comprises the following steps: Under nitrogen protection, 100 g of ε-caprolactone and 5 g of dimethylpropionic acid were added to a dry three-necked flask, heated in an oil bath at 120°C to melt, 1.5 g of stannous octoate toluene solution was injected, vacuum-nitrogen-filling cycle was repeated 3 times to deoxygenate, the reaction was carried out at 130°C for 24 h, the reaction solution was dissolved in 200 mL of dichloromethane, dropped into 2000 mL of ice methanol for precipitation, centrifuged, and vacuum dried at 40°C for 48 h to obtain a dihydroxy monocarboxyl polycaprolactone prepolymer; 80 g of the above-mentioned dihydroxy monocarboxyl polycaprolactone prepolymer and 1.6 mL of catalyst tetrabutyl titanate were dissolved in 100 mL of anhydrous xylene, reacted at 160° C. for 12 h under nitrogen protection, then heated to 180° C. for 24 h, filtered and precipitated, and freeze-dried to obtain long-chain branched polycaprolactone; 50 g of the long-chain branched polycaprolactone and 72 g of initiator monomer L-lactide were mixed, melted and injected into a toluene solution containing 1.2 g of catalyst stannous octoate, reacted at 140° C. in vacuum for 36 h, precipitated and dried to obtain modified polylactic acid.

[0021] Example 4 A method for preparing an antibacterial modified cellulose degradable film is prepared by the following method: 5 parts by mass of the antibacterial modified nanocellulose prepared in Example 1, 15 parts by mass of the modified polylactic acid prepared in Example 3, and 100 parts by mass of polylactic acid were uniformly mixed and added into a twin-screw extruder for melt blending to obtain a composite masterbatch; The above-mentioned composite masterbatch was blown into film by single-screw hot melt extrusion. The processing temperatures of screw zones 1, 2, 3, 4 and 5 were set to 160°C, 175°C, 185°C, 190°C, 190°C respectively, the screw speed was 50r / min, the lower and upper die temperatures were 190°C and 19°C, the blowing ratio was 2.5, and the traction ratio was 3 to obtain a cellulose antibacterial modified degradable film.

[0022] Example 5 A method for preparing an antibacterial modified cellulose degradable film is prepared by the following method: 5 parts by mass of the antibacterial modified nanocellulose prepared in Example 2, 15 parts by mass of the modified polylactic acid prepared in Example 3, and 100 parts by mass of polylactic acid were uniformly mixed and added into a twin-screw extruder for melt blending to obtain a composite masterbatch; The above-mentioned composite masterbatch was blown into film by single-screw hot melt extrusion. The processing temperatures of screw zones 1, 2, 3, 4 and 5 were set to 160°C, 175°C, 185°C, 190°C, 190°C respectively, the screw speed was 50r / min, the lower and upper die temperatures were 190°C and 19°C, the blowing ratio was 2.5, and the traction ratio was 3 to obtain a cellulose antibacterial modified degradable film.

[0023] Example 6 A method for preparing an antibacterial modified cellulose degradable film is prepared by the following method: 8 parts by mass of the antibacterial modified nanocellulose prepared in Example 1, 12 parts by mass of the modified polylactic acid prepared in Example 3, and 100 parts by mass of polylactic acid were uniformly mixed and added into a twin-screw extruder for melt blending to obtain a composite masterbatch; The above-mentioned composite masterbatch was blown into film by single-screw hot melt extrusion. The processing temperatures of screw zones 1, 2, 3, 4 and 5 were set to 160°C, 175°C, 185°C, 190°C, 190°C respectively, the screw speed was 50r / min, the lower and upper die temperatures were 190°C and 19°C, the blowing ratio was 2.5, and the traction ratio was 3 to obtain a cellulose antibacterial modified degradable film.

[0024] Example 7 A method for preparing an antibacterial modified cellulose degradable film is prepared by the following method: 8 parts by mass of the antibacterial modified nanocellulose prepared in Example 2, 12 parts by mass of the modified polylactic acid prepared in Example 3, and 100 parts by mass of polylactic acid were uniformly mixed and added into a twin-screw extruder for melt blending to obtain a composite masterbatch; The above-mentioned composite masterbatch was blown into film by single-screw hot melt extrusion. The processing temperatures of screw zones 1, 2, 3, 4 and 5 were set to 160°C, 175°C, 185°C, 190°C, 190°C respectively, the screw speed was 50r / min, the lower and upper die temperatures were 190°C and 19°C, the blowing ratio was 2.5, and the traction ratio was 3 to obtain a cellulose antibacterial modified degradable film.

[0025] Comparative Example 1 The preparation method of antibacterial modified nanocellulose comprises the following steps: 10 g of nanocellulose powder was ultrasonically dispersed in 250 mL of N,N-dimethylacetamide, heated to 100 ° C, 20 g of 6-bromohexanoyl chloride was added, and the mixture was reacted at 100 ° C and stirred at 400 r / min for 1 hour. The mixture was poured into 2700 mL of ethanol, the reaction was terminated, and the precipitate was collected by centrifugation. The product was then washed alternately with dimethyl sulfoxide and ethanol to obtain surface-modified nanocellulose; 10 g of the above-mentioned surface-modified nanocellulose was dispersed in dimethyl sulfoxide, heated to 80°C, 40 g of N,N-dimethyl-n-butylamine was added, and after stirring at 80°C for 5 h, the reaction mixture was transferred to a dialysis bag, dialyzed in ethanol for 4 days, and then dialyzed in deionized water for 4 days, and then dried to obtain antibacterial modified nanocellulose.

[0026] Comparative Example 2 Compared with Example 4, Comparative Example 2 only replaces the antibacterial modified nanocellulose prepared in Example 1 added in Example 4 with the antibacterial modified nanocellulose prepared in Comparative Example 1, and the other components and preparation method are completely consistent with Example 4.

[0027] Comparative Example 3 Compared with Example 4, in Comparative Example 3, the antibacterial modified nanocellulose prepared in Example 1 is not added, and the remaining components and preparation method are completely consistent with those in Example 4.

[0028] Comparative Example 4 Compared with Example 4, in Comparative Example 4, the modified polylactic acid prepared in Example 3 is not added, and the other components and preparation method are completely consistent with those of Example 4.

[0029] Comparative Example 5 Compared with Example 4, in Comparative Example 5, pure polylactic acid was blown into a film.

[0030] Performance Testing Mechanical property test: The C41.103 electronic universal mechanical testing machine of Xinsansi (Shanghai) Enterprise Development Co., Ltd. was used to conduct mechanical tests on the degradable films in Examples 4-7 and Comparative Examples 2-5. The samples were cut into 1×4 cm specimens, the sensor used for the test was 200N, the test temperature was 23℃±2℃, and the humidity was 50%±10%. The tensile strength and elongation at break were tested, and each sample was tested five times, and the average value was taken as the test result; the test results are shown in Table 1; Melt extension rheological test: The raw materials were dried in a blast oven at 80°C for 6 h, and then melt extension rheological tests were performed on the degradable films in Examples 4-7 and Comparative Examples 2-5 using a melt extension rheometer (Gottfert, Germany, model RG50). The barrel temperature during the test was 190°C, the piston speed was 0.3 mm / s, the die aspect ratio was 30 / 1, the roller distance was 0.4 mm, the initial roller speed was 50 mm / s, and the acceleration was 2.4 mm / s. 2 ; The test results are shown in Table 1; Optical transmittance test: The transmittance of the degradable films in Examples 4-7 and Comparative Examples 2-5 was characterized by using a TU-195 UV-vis spectrophotometer (UV-vis) from Beijing Puxi General Instrument Co., Ltd. The test sample size was 4×4 cm, and the transmittance of the test sample at 550 nm was measured. The test results are shown in Table 1. Antibacterial performance test: Referring to GB / T 20944.3-2008, the antibacterial performance of the degradable films in Examples 4-7 and Comparative Examples 2-5 against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) was tested. The test time was 18 h. 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.

[0031] Y=(W t -Q t ) / W t ×100% Where: Y is the antibacterial rate, %; W t is the average number of colonies in the control sample; Q t is the average number of colonies of the test sample; the test results are shown in Table 1; Table 1: Statistical table of performance test data of degradable films in Examples 4-7 and Comparative Examples 2-5

[0032] As shown in Table 1, the cellulose antibacterial modified degradable film prepared in Examples 4-7 of the present invention, by adding antibacterial modified nanocellulose and modified polylactic acid, gives the polylactic acid degradable film excellent antibacterial and mechanical properties, reduces the difficulty of film blowing, and ensures that the transmittance of the degradable film at 550nm is greater than 90%. In Comparative Example 2, N, N-dimethyl n-butylamine containing a short carbon chain is used as a quaternary ammonium modifier, and the various properties of the degradable film obtained are reduced, indicating that the antibacterial nanocellulose prepared in the present invention is evenly dispersed in the polylactic acid substrate, and in Comparative Examples 3 and 4, polylactic acid is modified with antibacterial modified nanocellulose and modified polylactic acid, respectively, and the mechanical properties of the degradable film obtained are reduced, indicating that the antibacterial modified nanocellulose and modified polylactic acid in the present invention have a synergistic toughening effect on polylactic acid, and modified polylactic acid greatly improves the difficulty of film blowing, and Comparative Example 5 is a degradable film obtained by pure polylactic acid film blowing, which is a blank control, and the various properties of the degradable film obtained are all poor.

[0033] The above is a detailed description of an embodiment of the present invention, but the content is only a preferred embodiment of the present invention and cannot be considered to limit the scope of implementation of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims

1. A method for preparing an antibacterial modified cellulose degradable film, characterized in that: The method comprises at least the following preparation steps: The nanocellulose is modified by quaternization to obtain antibacterial modified nanocellulose; Block copolymerization is performed on polylactic acid to obtain modified polylactic acid; Melting and blending the antibacterial modified nanocellulose, the modified polylactic acid and polylactic acid to obtain a composite masterbatch; The composite masterbatch is formed into a film by single-screw hot-melt extrusion blow molding to obtain a cellulose antibacterial modified degradable film.

2. The method for preparing a cellulose antibacterial modified degradable film according to claim 1, characterized in that: The mass ratio of the antibacterial modified nanocellulose, the modified polylactic acid and the polylactic acid is 3-10:10-20:

100.

3. The method for preparing a cellulose antibacterial modified degradable film according to claim 1, characterized in that: The preparation method of the antibacterial modified nanocellulose comprises the following steps: The nanocellulose is dispersed in N,N-dimethylacetamide, 6-bromohexanoyl chloride is added, reacted, precipitated and washed to obtain surface-modified nanocellulose; The surface modified nanocellulose is dispersed in dimethyl sulfoxide, N,N-dimethyldodecylamine is added, reacted, dialyzed and dried to obtain antibacterial modified nanocellulose.

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

5. The method for preparing a cellulose antibacterial modified degradable film according to claim 1, characterized in that: The preparation method of the modified polylactic acid comprises the following steps: Using dimethyl propionic acid as an initiator and stannous octoate as a catalyst, ε-caprolactone is initiated to undergo ring-opening polymerization to obtain a dihydroxy monocarboxyl polycaprolactone prepolymer; Using tetrabutyl titanate as a catalyst, catalyzing the self-condensation reaction of the dihydroxy monocarboxyl polycaprolactone prepolymer to obtain a long-chain branched polycaprolactone; The long-chain branched polycaprolactone is used as a macromolecular initiator and stannous octoate is used as a catalyst to initiate the ring-opening polymerization of the monomer L-lactide to obtain the modified polylactic acid.

6. The method for preparing the antibacterial modified cellulose degradable film according to claim 5, characterized in that: The mass ratio of the dimethylpropionic acid to the ε-caprolactone is 1:15-25.

7. The method for preparing the antibacterial modified cellulose degradable film according to claim 5, characterized in that: The mass ratio of the long-chain branched polycaprolactone to the L-lactide is 1:1-2.

8. The method for preparing the antibacterial modified cellulose degradable film according to claim 1, characterized in that: The process conditions for the single-screw hot melt extrusion blow molding film are as follows: the processing temperatures of screw zones 1, 2, 3, 4 and 5 are 160°C, 175°C, 185°C, 190°C and 190°C respectively; the screw speed is 50r / min; the lower and upper die temperatures are 190°C and 19°C; the blowing ratio is 2.5 and the traction ratio is 3.

9. A cellulose antibacterial modified degradable film, characterized in that: The antibacterial modified cellulose degradable film is prepared by the preparation method described in any one of claims 1-8.

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