CN115433383A - Biodegradable polylactic acid barrier film with multilayer structure and preparation method thereof - Google Patents

Biodegradable polylactic acid barrier film with multilayer structure and preparation method thereof Download PDF

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CN115433383A
CN115433383A CN202211077988.2A CN202211077988A CN115433383A CN 115433383 A CN115433383 A CN 115433383A CN 202211077988 A CN202211077988 A CN 202211077988A CN 115433383 A CN115433383 A CN 115433383A
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solution
plla
pdla
barrier film
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CN115433383B (en
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潘刚伟
蒋长妹
花铭
赵士友
姚理荣
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Nantong University
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    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J7/00—Chemical treatment or coating of shaped articles made of macromolecular substances
    • C08J7/04—Coating
    • C08J7/0427—Coating with only one layer of a composition containing a polymer binder
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J7/00—Chemical treatment or coating of shaped articles made of macromolecular substances
    • C08J7/04—Coating
    • C08J7/042—Coating with two or more layers, where at least one layer of a composition contains a polymer binder
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2367/00—Characterised by the use of polyesters obtained by reactions forming a carboxylic ester link in the main chain; Derivatives of such polymers
    • C08J2367/04—Polyesters derived from hydroxy carboxylic acids, e.g. lactones
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2467/00—Characterised by the use of polyesters obtained by reactions forming a carboxylic ester link in the main chain; Derivatives of such polymers
    • C08J2467/04—Polyesters derived from hydroxy carboxylic acids, e.g. lactones
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2487/00—Characterised by the use of unspecified macromolecular compounds, obtained otherwise than by polymerisation reactions only involving unsaturated carbon-to-carbon bonds
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
    • Y02W90/00—Enabling technologies or technologies with a potential or indirect contribution to greenhouse gas [GHG] emissions mitigation
    • Y02W90/10—Bio-packaging, e.g. packing containers made from renewable resources or bio-plastics

Abstract

The invention belongs to the technical field of barrier film materials, and discloses a biodegradable polylactic acid barrier film and a preparation method thereof. Firstly, grafting D-lactide and cellulose diacetate to obtain a CDA-g-PDLA graft copolymer, and then preparing the multi-layer structure barrier film by using polylactic acid and CDA-g-PDLA as raw materials. The PLA barrier film material prepared by the invention has the characteristics of excellent barrier property and high strength, can be completely biodegraded after being used and abandoned, and is environment-friendly.

Description

Biodegradable polylactic acid barrier film with multilayer structure and preparation method thereof
Technical Field
The invention belongs to the field of barrier film materials, and particularly relates to a biodegradable multilayer-structure polylactic acid barrier film and a preparation method thereof.
Background
In recent years, the environmental pollution problem caused by plastic products has seriously affected the living environment of human beings, and researchers have been devoted to the development of new materials to solve the environmental pollution problem caused by the products such as plastics. To avoid secondary pollution and excessive use of non-renewable resources, the use of degradable materials needs to be introduced. Therefore, the degradable high polymer material is selected as the raw material, and the preparation of the environment-friendly barrier film material has important significance.
Polylactic acid (PLA) is a high polymer material derived from renewable plant resources, has good biocompatibility, can be completely biodegraded into water and carbon dioxide, is nontoxic and does not pollute the environment, and has a certain antibacterial function. Cellulose Diacetate (CDA), which is an important organic ester of cellulose, is synthesized from natural cellulose and is biodegradable, non-toxic and harmless to the environment. In addition, cellulose acetate is inexpensive, has excellent properties such as spinnability, film-forming properties, and thermal stability, and is widely used in the fields of textile, tobacco filtration, water separation, and biomedical applications. Therefore, the preparation of the barrier film by using the biodegradable PLA and the CDA has important significance.
Chinese patent CN105729967A discloses a multilayer polylactic acid composite barrier high-strength film, which consists of an outer layer polylactic acid hydrophobic film, a middle layer polylactic acid barrier film and a bottom layer polylactic acid barrier film. Wherein the hydrophobic layer is formed by using polylactic acid and glycidyl methacrylate grafted copolymer single-layer melt extrusion film forming and then using glue for bonding. The polylactic acid barrier film prepared by the method has better strength and barrier property, but the preparation process is more complicated, and the glycidyl methacrylate is slightly toxic and has certain irritation to skin and mucous membrane.
Disclosure of Invention
Aiming at the defects and shortcomings of the prior art, the invention provides the biodegradable polylactic acid barrier film with the multilayer structure and the preparation method thereof.
In order to achieve the purpose, the invention is realized by the following technical scheme:
a method for preparing a biodegradable polylactic acid barrier film with a multilayer structure comprises the following steps:
s1, crushing cellulose diacetate into powder by using a crusher to obtain cellulose diacetate powder, and performing vacuum drying on the cellulose diacetate powder and D-lactide;
s2, placing the cellulose diacetate powder and the D-lactide in a reaction kettle heated to 110-140 ℃, and stirring and dissolving under the protection of nitrogen to obtain a first mixed solution;
s3, inAdding Sn (Oct) into the first mixed solution 2 A catalyst is obtained to obtain a reaction solution, the reaction solution is stirred under the protection of nitrogen until the reaction is finished, the heating is stopped, and a solid reaction product is taken out after the reaction kettle is cooled to room temperature;
s4, dissolving the solid reactant in chloroform, and stirring and dissolving the solid reactant by using a magnetic stirrer until the solid reactant is completely dissolved to obtain a second mixed solution;
s5, slowly pouring the second mixed solution into anhydrous methanol for precipitation, and performing suction filtration to obtain a solid product, and performing vacuum drying to obtain a light yellow solid crude product;
s6, placing the solid crude product in a Soxhlet extractor, refluxing for 24 hours by using toluene as a solvent, and drying to obtain a CDA-g-PDLA graft copolymer;
s7, respectively dissolving the CDA-g-PDLA graft copolymer and the PLLA in a mixed organic solvent to obtain a CDA-g-PDLA solution and a PLLA solution;
and S8, scraping the CDA-g-PDLA solution and the PLLA solution layer by layer to form the multi-layer structure polylactic acid barrier film, wherein the outer layer of the multi-layer structure polylactic acid barrier film is a PLLA layer.
Further, the degree of acetylation substitution of the cellulose diacetate is 2.0 to 2.6.
Further, the melting point of D-lactide is 93-95 ℃.
Further, in the step S2, the stirring time is 30 to 180min.
Further, in step S2, the usage ratio of the D-lactide to the cellulose diacetate powder is 5:5 to 7:3.
Further, in the reaction solution, sn (Oct) 2 The mass percentage of the catalyst is 1-4%.
Further, in step S4, the stirring time is 5 to 24 hours.
Further, in step S5, the drying temperature is 60 to 80 ℃.
Further, the mixed organic solvent is obtained by mixing trichloromethane and dimethylformamide, and the mass ratio of the trichloromethane to the dimethylformamide is 9:1.
Furthermore, the content of the CDA-g-PDLA in the CDA-g-PDLA solution is 10-15wt%.
Further, the content of PLLA in the PLLA solution is 8-13wt%.
The invention also provides the multilayer structure polylactic acid barrier film prepared by the preparation method, wherein the layer ratio of the PLLA layer to the CDA-g-PDLA layer in the multilayer structure polylactic acid barrier film is 5:5-9:1.
Further, the thickness of the polylactic acid barrier film with the multilayer structure is 0.1-0.3mm.
Furthermore, the tensile strength of the polylactic acid barrier film with the multilayer structure is 11.2-17.5 MPa, and the water vapor transmission capacity is 39.8173-45.1251 g/(m) 2 24 h), oxygen permeability of 178.56-358.65 cm 3 /(m 2 ·24h·0.1MPa)。
The biodegradable polylactic acid barrier film with the multilayer structure has the following advantages and beneficial effects:
(1) The PLLA and the CDA-g-PDLA have good interface compatibility, and the PLLA and the CDA-g-PDLA can form a stereo composite structure, so that a more compact structure can be formed between the PLLA and the CDA-g-PDLA, so that the polylactic acid barrier film has excellent mechanical properties and simultaneously exerts the barrier property of the CDA.
(2) The polylactic acid barrier film can be completely biodegraded and is environment-friendly.
(3) The preparation method is simple in manufacturing process and low in manufacturing cost, can be well applied to the field of environment-friendly functional materials, and meets the production requirements of the polymer material industry.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1
(1) Weighing D-lactide and CDA with the mass ratio of 5/5, drying in a vacuum drying oven at 60 ℃, heating a reaction kettle to 110 ℃, placing the dried CDA and D-lactide in the reaction kettle, and stirring and dissolving under the protection of nitrogen after completing the three-time gas replacement.
(2) Adding Sn (Oct) with the total mass fraction of 1 percent into the mixture obtained in the step (1) 2 And continuously stirring the catalyst for 30min under the protection of nitrogen, stopping heating after the reaction time is reached, and taking out the solid reaction product after the reaction kettle is cooled to room temperature.
(3) And (3) dissolving the solid reactant obtained in the step (2) in chloroform, and stirring and dissolving for 5 hours by using a magnetic stirrer until the solid reactant is completely dissolved. And slowly pouring the obtained solution into anhydrous methanol for precipitation, and performing vacuum drying on the solid product at 60 ℃ after suction filtration to obtain a light yellow solid crude product.
(4) And (4) using toluene as a solvent for the solid crude product obtained in the step (3), placing the solid crude product in a Soxhlet extractor, refluxing for 24 hours, and drying to obtain the CDA-g-PDLA graft copolymer.
(5) Dissolving the CDA-g-PDLA obtained in step (4) in a CHL/DMF mixed solvent at a mass ratio of 9/1 to prepare a solution accounting for 10% by weight, and dissolving the PLLA in a CHL/DMF mixed solvent at a mass ratio of 9/1 to prepare a solution accounting for 8% by weight.
(6) And (3) scraping the PLLA solution obtained in the step (5) on a glass plate by using a film scraper, and after the PLLA film is dried and formed, scraping the film again by using a CDA-g-PDLA solution on the basis of the PLLA film to form a film with a double-layer structure. The resulting film had a tensile strength of 13.1MPa and a water vapor transmission of 44.1591 g/(m) 2 24 h) oxygen permeability of 358.65cm 3 /(m 2 ·24h·0.1MPa)。
Example 2
(1) Weighing D-lactide and CDA with the mass ratio of 7/3, drying in a vacuum drying oven at 60 ℃, heating a reaction kettle to 140 ℃, placing the dried CDA and D-lactide in the reaction kettle, and stirring and dissolving under the protection of nitrogen after three times of gas replacement.
(2) Adding Sn (Oct) with the total mass fraction of 2 percent into the mixture obtained in the step (1) 2 And continuously stirring the catalyst for 90min under the protection of nitrogen, stopping heating after the reaction time is reached, and taking out the solid reaction product after the reaction kettle is cooled to room temperature.
(3) And (3) dissolving the solid reactant obtained in the step (2) in chloroform, and stirring and dissolving for 24 hours by using a magnetic stirrer until the solid reactant is completely dissolved. And slowly pouring the obtained solution into anhydrous methanol for precipitation, and after suction filtration, carrying out vacuum drying on the solid product at the temperature of 80 ℃ to obtain a light yellow solid crude product.
(4) And (3) taking toluene as a solvent for the solid crude product obtained in the step (3), placing the solid crude product in a Soxhlet extractor, refluxing for 24h, and drying to obtain the CDA-g-PDLA graft copolymer.
(5) Dissolving the CDA-g-PDLA obtained in step (4) in a CHL/DMF mixed solvent at a mass ratio of 9/1 to prepare a solution accounting for 10% by weight, and dissolving the PLLA in a CHL/DMF mixed solvent at a mass ratio of 9/1 to prepare a solution accounting for 8% by weight.
(6) And (3) scraping the PLLA solution obtained in the step (5) on a glass plate by using a film scraper, and after the PLLA film is dried and formed, scraping the film again by using a CDA-g-PDLA solution on the basis of the PLLA film to form a film with a double-layer structure.
(7) And (4) repeatedly scraping a layer of PLLA again on the basis of the PLLA and CDA-g-PDLA double-layer structure film obtained in the step (6) to obtain the polylactic acid barrier film with a three-layer structure. The resulting film had a tensile strength of 15.4MPa and a water vapor transmission of 41.6591 g/(m) 2 24 h) oxygen permeability of 298.34cm 3 /(m 2 ·24h·0.1MPa)。
Example 3
(1) Weighing D-lactide and CDA with the mass ratio of 5/5, drying in a vacuum drying oven at 60 ℃, heating a reaction kettle to 140 ℃, placing the dried CDA and D-lactide in the reaction kettle, and stirring and dissolving under the protection of nitrogen after three times of gas replacement.
(2) Adding Sn (Oct) with the total mass fraction of 2 percent into the mixture obtained in the step (1) 2 And continuously stirring the catalyst for 90min under the protection of nitrogen, stopping heating after the reaction time is reached, and taking out the solid reaction product after the reaction kettle is cooled to room temperature.
(3) And (3) dissolving the solid reactant obtained in the step (2) in chloroform, and stirring and dissolving for 24 hours by using a magnetic stirrer until the solid reactant is completely dissolved. And slowly pouring the obtained solution into anhydrous methanol for precipitation, and after suction filtration, putting the solid product into a vacuum drying oven for vacuum drying to obtain a light yellow solid crude product.
(4) And (3) taking toluene as a solvent for the solid crude product obtained in the step (3), placing the solid crude product in a Soxhlet extractor, refluxing for 24h, and drying to obtain the CDA-g-PDLA graft copolymer.
(5) Dissolving the CDA-g-PDLA obtained in step (4) in a CHL/DMF mixed solvent in a mass ratio of 9/1 to formulate 10% by weight solution, and dissolving the PLLA in a CHL/DMF mixed solvent in a mass ratio of 9/1 to formulate 8% by weight solution.
(6) And (3) scraping the PLLA solution obtained in the step (5) on a glass plate by using a film scraper, and after the PLLA film is dried and formed, scraping the film again by using a CDA-g-PDLA solution on the basis of the PLLA film to form a film with a double-layer structure.
(7) And (4) repeating the step (6) again on the basis of the PLLA and CDA-g-PDLA double-layer structure film obtained in the step (6) to obtain the polylactic acid barrier film with a four-layer structure. The resulting film had a tensile strength of 16.7MPa and a water vapor transmission of 40.5261 g/(m) 2 24 h) oxygen permeability of 213.95cm 3 /(m 2 ·24h·0.1MPa)。
Example 4
(1) Weighing D-lactide and CDA with the mass ratio of 5/5, drying in a vacuum drying oven at 60 ℃, heating a reaction kettle to 130 ℃, placing the dried CDA and D-lactide in the reaction kettle, and stirring and dissolving under the protection of nitrogen after three times of gas replacement.
(2) Adding Sn (Oct) with the total mass fraction of 3 percent into the mixture obtained in the step (1) 2 And continuously stirring the catalyst for 90min under the protection of nitrogen, stopping heating after the reaction time is reached, and taking out the solid reaction product after the reaction kettle is cooled to room temperature.
(3) And (3) dissolving the solid reactant obtained in the step (2) in chloroform, and stirring and dissolving for 24 hours by using a magnetic stirrer until the solid reactant is completely dissolved. And slowly pouring the obtained solution into anhydrous methanol for precipitation, and after suction filtration, putting the solid product into a vacuum drying oven for vacuum drying to obtain a light yellow solid crude product.
(4) And (4) taking the toluene obtained in the step (3) as a solvent, placing the solid crude product in a Soxhlet extractor, refluxing for 24 hours, and drying to obtain the CDA-g-PDLA graft copolymer.
(5) Dissolving the CDA-g-PDLA obtained in step (4) in a CHL/DMF mixed solvent at a mass ratio of 9/1 to prepare a 12% by weight solution, and dissolving the PLLA in a CHL/DMF mixed solvent at a mass ratio of 9/1 to prepare a 10% by weight solution.
(6) And (4) scraping the PLLA solution obtained in the step (5) on a glass plate by using a film scraper, and after the PLLA film is dried and formed, scraping the film again by using CDA-g-PDLA solution on the basis of the PLLA film to form a film with a double-layer structure.
(7) And (5) repeating the step (6) again on the basis of the PLLA and CDA-g-PDLA double-layer structure film obtained in the step (6) to obtain a polylactic acid barrier film with a four-layer structure. The resulting film had a tensile strength of 15.3MPa and a water vapor transmission of 40.3256 g/(m) 2 24 h) oxygen permeability of 225.67cm 3 /(m 2 ·24h·0.1MPa)。
Example 5
(1) Weighing D-lactide and CDA with the mass ratio of 6/4, drying in a vacuum drying oven at 60 ℃, heating a reaction kettle to 120 ℃, placing the dried CDA and D-lactide in the reaction kettle, and stirring and dissolving under the protection of nitrogen after three times of gas replacement.
(2) Adding Sn (Oct) with the total mass fraction of 3 percent into the mixture obtained in the step (1) 2 And continuously stirring the catalyst for 120min under the protection of nitrogen, stopping heating after the reaction time is reached, and taking out the solid reaction product after the reaction kettle is cooled to room temperature.
(3) And (3) dissolving the solid reactant obtained in the step (2) in chloroform, and stirring and dissolving for 24 hours by using a magnetic stirrer until the solid reactant is completely dissolved. And slowly pouring the obtained solution into anhydrous methanol for precipitation, and after suction filtration, putting the solid product into a vacuum drying oven for vacuum drying to obtain a light yellow solid crude product.
(4) And (4) taking toluene obtained in the step (3) as a solvent, placing the solid crude product in a Soxhlet extractor, refluxing for 24h, and drying to obtain the CDA-g-PDLA graft copolymer.
(5) Dissolving the CDA-g-PDLA obtained in step (4) in a CHL/DMF mixed solvent at a mass ratio of 9/1 to prepare a 12% by weight solution, and dissolving the PLLA in a CHL/DMF mixed solvent at a mass ratio of 9/1 to prepare a 10% by weight solution.
(6) And (3) scraping the PLLA solution obtained in the step (5) on a glass plate by using a film scraper, and after the PLLA film is dried and formed, scraping the film again by using a CDA-g-PDLA solution on the basis of the PLLA film to form a film with a double-layer structure.
(7) And (4) scraping 8 layers of PLLA on the basis of the PLLA and CDA-g-PDLA double-layer structure film obtained in the step (6) to obtain the polylactic acid barrier film with a ten-layer structure. The resulting film had a tensile strength of 16.3MPa and a water vapor transmission of 39.8173 g/(m) 2 24 h) oxygen permeability of 178.56cm 3 /(m 2 ·24h·0.1MPa)。
Example 6
(1) Weighing D-lactide and CDA with the mass ratio of 7/3, drying in a vacuum drying oven at 60 ℃, heating a reaction kettle to 120 ℃, placing the dried CDA and D-lactide in the reaction kettle, and stirring and dissolving under the protection of nitrogen after three times of gas replacement.
(2) Adding Sn (Oct) with the total mass fraction of 3 percent into the mixture obtained in the step (1) 2 And continuously stirring the catalyst for 180min under the protection of nitrogen, stopping heating after the reaction time is reached, and taking out the solid reaction product after the reaction kettle is cooled to room temperature.
(3) And (3) dissolving the solid reactant obtained in the step (2) in chloroform, and stirring and dissolving for 24 hours by using a magnetic stirrer until the solid reactant is completely dissolved. And slowly pouring the obtained solution into anhydrous methanol for precipitation, and performing vacuum filtration on the solid product at 60 ℃ to obtain a light yellow solid crude product.
(4) And (4) taking toluene obtained in the step (3) as a solvent, placing the solid crude product in a Soxhlet extractor, refluxing for 24h, and drying to obtain the CDA-g-PDLA graft copolymer.
(5) Dissolving the CDA-g-PDLA obtained in step (4) in a CHL/DMF mixed solvent in a mass ratio of 9/1 to 12% by weight, and dissolving the PLLA in a CHL/DMF mixed solvent in a mass ratio of 9/1 to 10% by weight.
(6) And (4) scraping the PLLA solution obtained in the step (5) on a glass plate by using a film scraper, and after the PLLA film is dried and formed, scraping the film again by using CDA-g-PDLA solution on the basis of the PLLA film to form a film with a double-layer structure.
(7) And (4) repeating the step (6) again on the basis of the PLLA and CDA-g-PDLA double-layer structure film obtained in the step (6), so as to obtain the polylactic acid barrier film with a four-layer structure. The resulting film had a tensile strength of 17.5MPa and a water vapor transmission of 40.8124 g/(m) 2 24 h) oxygen permeability of 181.27cm 3 /(m 2 ·24h·0.1MPa)。
Example 7
(1) Weighing D-lactide and CDA with the mass ratio of 5/5, drying in a vacuum drying oven at 60 ℃, heating a reaction kettle to 130 ℃, placing the dried CDA and D-lactide in the reaction kettle, and stirring and dissolving under the protection of nitrogen after three times of gas replacement.
(2) Adding Sn (Oct) with the total mass fraction of 4% into the mixture obtained in the step (1) 2 And continuously stirring the catalyst under the protection of nitrogen, stopping heating after the reaction time is reached, and taking out the solid reaction product after the reaction kettle is cooled to room temperature.
(3) And (3) dissolving the solid reactant obtained in the step (2) in chloroform, and stirring and dissolving for 24 hours by using a magnetic stirrer until the solid reactant is completely dissolved. And slowly pouring the obtained solution into anhydrous methanol for precipitation, and performing suction filtration, and then performing vacuum drying on the solid product at 70 ℃ to obtain a light yellow solid crude product.
(4) And (4) taking toluene obtained in the step (3) as a solvent, placing the solid crude product in a Soxhlet extractor, refluxing for 24h, and drying to obtain the CDA-g-PDLA graft copolymer.
(5) Dissolving the CDA-g-PDLA obtained in step (4) in a CHL/DMF mixed solvent at a mass ratio of 9/1 to prepare a 14% by weight solution, and dissolving the PLLA in a CHL/DMF mixed solvent at a mass ratio of 9/1 to prepare a 12% by weight solution.
(6) And (4) scraping the PLLA solution obtained in the step (5) on a glass plate by using a film scraper, repeatedly scraping the PLLA solution for 2 times after the PLLA film is dried and formed, and then scraping the film again on the basis of the solution of CDA-g-PDLA to form a film with a four-layer structure.
(7) Scraping the PLLA film twice on the basis of the PLLA and CDA-g-PDLA four-layer structure film obtained in the step (6), and finally scraping a layer of CDAg-PDLA and a PLLA film. The polylactic acid barrier film with the eight-layer structure is obtained. The resulting film had a tensile strength of 12.6MPa and a water vapor transmission of 43.1583 g/(m) 2 24 h) oxygen permeability of 281.79cm 3 /(m 2 ·24h·0.1MPa)。
Example 8
(1) Weighing D-lactide and CDA with the mass ratio of 7/3, drying in a vacuum drying oven at 60 ℃, heating a reaction kettle to 110 ℃, placing the dried CDA and D-lactide in the reaction kettle, and stirring and dissolving under the protection of nitrogen after three times of gas replacement.
(2) Adding Sn (Oct) with the total mass fraction of 4% into the mixture obtained in the step (1) 2 And continuously stirring the catalyst under the protection of nitrogen, stopping heating after the reaction time is reached, and taking out the solid reaction product after the reaction kettle is cooled to room temperature.
(3) And (3) dissolving the solid reactant obtained in the step (2) in chloroform, and stirring and dissolving for 24 hours by using a magnetic stirrer until the solid reactant is completely dissolved. And slowly pouring the obtained solution into anhydrous methanol for precipitation, and after suction filtration, putting the solid product into a vacuum drying oven for vacuum drying to obtain a light yellow solid crude product.
(4) And (4) taking toluene obtained in the step (3) as a solvent, placing the solid crude product in a Soxhlet extractor, refluxing for 24h, and drying to obtain the CDA-g-PDLA graft copolymer.
(5) Dissolving the CDA-g-PDLA obtained in step (4) in a CHL/DMF mixed solvent at a mass ratio of 9/1 to prepare a 15% by weight solution, and dissolving the PLLA in a CHL/DMF mixed solvent at a mass ratio of 9/1 to prepare a 13% by weight solution.
(6) And (4) scraping the PLLA solution obtained in the step (5) on a glass plate by using a film scraper, and after the PLLA film is dried and formed, scraping the film again by using CDA-g-PDLA solution on the basis of the PLLA film to form a film with a double-layer structure.
(7) And (4) repeating the step (6) again on the basis of the PLLA and CDA-g-PDLA double-layer structure film obtained in the step (6), so as to obtain the polylactic acid barrier film with a four-layer structure. The tensile strength of the resulting film was 11.2MPa, and the water vapor transmission rate was 45.1251 g/(m) 2 24 h) oxygen permeability of 302.61cm 3 /(m 2 ·24h·0.1MPa)。
Comparative example 1
(1) Weighing PLLA particles of corresponding mass, preparing into 8% wt solution in CHL/DMF solution at mass ratio of 9/1, scraping with a film scraper on a glass plate, and repeating for four times to obtain pure PLLA film with multilayer structure. The resulting film had a tensile strength of 12.8MPa and a water vapor transmission of 42.3168 g/(m) 2 24 h) oxygen permeability of 298.75cm 3 /(m 2 ·24h·0.1MPa)。
Comparative example 2
(1) The PLLA particles and CDA particles at a mass ratio of 7/3 were weighed, mixed with CHL/DMF solution at a mass ratio of 9/1 to prepare a solution of 10% by weight, and the resulting mixture was subjected to film scraping using a film scraper on a glass plate, and the above steps were repeated four times to obtain a polylactic acid barrier film having a multilayer structure. The resulting film had a tensile strength of 14.1MPa and a water vapor transmission of 80.3658 g/(m) 2 24 h) oxygen permeability of 746.35cm 3 /(m 2 ·24h·0.1MPa)。

Claims (10)

1. A preparation method of a biodegradable polylactic acid barrier film with a multilayer structure is characterized by comprising the following steps:
s1, crushing cellulose diacetate into powder by using a crusher to obtain cellulose diacetate powder, and performing vacuum drying on the cellulose diacetate powder and D-lactide;
s2, placing the cellulose diacetate powder and the D-lactide in a reaction kettle heated to 110-140 ℃, and stirring and dissolving under the protection of nitrogen to obtain a first mixed solution;
s3, adding Sn (Oct) into the first mixed solution 2 A catalyst is used to obtain a reaction solution, the reaction solution is stirred under the protection of nitrogen until the reaction is completed, the heating is stopped, and a solid reaction product is taken out after the reaction kettle is cooled to room temperature;
s4, dissolving the solid reactant in chloroform, and stirring and dissolving the solid reactant by using a magnetic stirrer until the solid reactant is completely dissolved to obtain a second mixed solution;
s5, slowly pouring the second mixed solution into anhydrous methanol for precipitation, and performing suction filtration to obtain a solid product, and performing vacuum drying to obtain a light yellow solid crude product;
s6, placing the solid crude product in a Soxhlet extractor, refluxing for 24 hours by using toluene as a solvent, and drying to obtain a CDA-g-PDLA graft copolymer;
s7, respectively dissolving the CDA-g-PDLA graft copolymer and the PLLA in a mixed organic solvent to obtain a CDA-g-PDLA solution and a PLLA solution;
s8, scraping the CDA-g-PDLA solution and the PLLA solution layer by layer to form the multi-layer structure polylactic acid barrier film, wherein the outer layer of the multi-layer structure polylactic acid barrier film is a PLLA layer.
2. The method according to claim 1, wherein the degree of acetylation substitution of the cellulose diacetate is 2.0 to 2.6.
3. The method according to claim 1, wherein the melting point of D-lactide is 93 to 95 ℃.
4. The method according to claim 1, wherein the D-lactide and the cellulose diacetate powder are used in a ratio of 5:5 to 7:3 in step S2.
5. The method according to claim 1, wherein Sn (Oct) is contained in the reaction solution 2 The mass percentage of the catalyst is 1-4%.
6. The preparation method according to claim 1, wherein the mixed organic solvent is prepared by mixing trichloromethane and dimethylformamide, and the mass ratio of the trichloromethane to the dimethylformamide is 9:1.
7. The method according to claim 1, wherein the content of CDA-g-PDLA in the CDA-g-PDLA solution is 10-15wt%.
8. The method according to claim 1, wherein the PLLA solution contains 8 to 13wt% of PLLA.
9. The polylactic acid barrier film with the multilayer structure prepared by the preparation method of any one of claims 1 to 8, wherein the layer ratio of the PLLA layer to the CDA-g-PDLA layer in the polylactic acid barrier film with the multilayer structure is 5:5-9:1.
10. The barrier film of claim 9, wherein the barrier film has a tensile strength of 11.2 to 17.5MPa and a water vapor transmission of 39.8173 to 45.1251 g/(m) m 2 24 h), oxygen permeability of 178.56-358.65 cm 3 /(m 2 ·24h·0.1MPa)。
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