CN109553945B - Environment-friendly heat-insulating plastic film and preparation process thereof - Google Patents

Abstract

The invention discloses an environment-friendly heat-insulating plastic film which is prepared from the following raw materials in parts by weight: 30-40 parts of polylactic acid, 20-30 parts of polybutylene terephthalate adipate, 4-6 parts of glycerol, 8-12 parts of modified plant fiber, 1-2 parts of antibacterial agent and 60-80 parts of trichloromethane; the invention also discloses a preparation process of the environment-friendly heat-insulating plastic film. According to the invention, polylactic acid and polybutylene terephthalate adipate are used as plastic film substrates, both of which are biodegradable high polymers, and the polybutylene terephthalate adipate can effectively toughen the polylactic acid and overcome the defect that the polylactic acid is fragile; the flexural modulus of the PLA material is greatly improved by enhancing the modified plant fiber, and the mechanical property of the composite material is enhanced; the film has antibacterial performance by adding a trace amount of antibacterial agent; the heat-insulating plastic film which is green and biodegradable, has excellent mechanical property and antibacterial property is obtained by processing.

Description

Environment-friendly heat-insulating plastic film and preparation process thereof

Technical Field

The invention belongs to the technical field of plastic films, and particularly relates to an environment-friendly heat-insulating plastic film and a preparation process thereof.

Background

Today, the technological level is continuously developed, plastic film products become common and indispensable things in people's life, and plastic films such as disposable plastic bags and express packaging bags are visible everywhere. The raw materials of the traditional plastic film products are various derivatives of petroleum, and as is known, the petroleum belongs to non-renewable resources, so that the finding of suitable plastic substitutes with even better performance is not slow until the petroleum resources are exhausted. On the other hand, with the enhancement of the awareness of environmental protection, the times of simply pursuing product performance have passed, and now, the environmental friendliness of plastic products themselves is more required, so that biodegradable plastic products have come to be produced. Biodegradable plastic refers to plastic that can be degraded by the action of microorganisms such as bacteria, molds (fungi), and algae that are present in nature. Most of the existing biodegradable plastic films are prepared by blending or copolymerizing natural high molecular materials and various polyesters, and some of the prepared materials are biodegradable, but toxic and harmful catalysts, cross-linking agents and the like are used in the preparation process.

Many existing biodegradable plastic films cannot widely meet the requirements in use performance, for example, chinese patent CN101235156 discloses a fully biodegradable plastic film using polylactic acid as a matrix and a preparation method thereof. However, the polylactic acid has low glass transition temperature and is relatively brittle at normal temperature, the toughness and the tear strength of the product are poor, and the use temperature of the product is greatly limited. For another example, CN200810051415.6 discloses a fully biodegradable plastic film based on polypropylene carbonate and a preparation method thereof, the polypropylene carbonate has high flexibility and tear strength, but has a lower glass transition temperature than polylactic acid, which is only 35-40 ℃, and the prepared fully biodegradable plastic film can only be used in low temperature places.

Disclosure of Invention

The invention aims to provide an environment-friendly heat-insulating plastic film and a preparation process thereof, polylactic acid (PLA) and polybutylene terephthalate adipate (PBAT) are used as plastic film substrates, the PLA and the PBAT are biodegradable high polymers, and the polybutylene terephthalate can effectively toughen polylactic acid and overcome the defect that the polylactic acid is easy to crisp; the modified plant fiber is enhanced, so that the flexural modulus of the PLA material is greatly improved, and the mechanical property and the heat-insulating property of the composite material are enhanced; the film has good oxidation resistance by combining the tea polyphenol, and the antibacterial effect is enhanced in the aspect of oxidation resistance; the heat-insulating plastic film which is green and biodegradable, has excellent mechanical property and antibacterial property is obtained by processing.

The purpose of the invention can be realized by the following technical scheme:

an environment-friendly heat-insulating plastic film is prepared from the following raw materials in parts by weight: 30-40 parts of polylactic acid, 20-30 parts of polybutylene terephthalate adipate, 4-6 parts of glycerol, 8-12 parts of modified plant fiber, 1-2 parts of antibacterial agent and 60-80 parts of trichloromethane;

the environment-friendly heat-insulating plastic film is prepared by the following steps:

step S1, firstly, drying polylactic acid and polybutylene terephthalate adipate in a vacuum oven at 60 ℃ for 8 hours, putting the dried polylactic acid and polybutylene terephthalate into a double-screw extruder, adding glycerol, extruding and granulating by using the double-screw extruder, and extruding at 190 ℃ at a feeding speed of 100 g/min;

s2, drying the obtained plastic base particles in a vacuum oven at 70 ℃ for 6-7h, adding the dried plastic base particles into 2/3 of trichloromethane, and magnetically stirring the mixture at room temperature until the plastic base particles are completely dissolved to obtain a plastic base particle solution;

step S3, adding the modified plant fibers into the residual 1/3 of chloroform, and homogenizing for 15min to obtain a modified plant fiber suspension;

step S4, slowly adding the modified plant fiber suspension and the antibacterial agent into the plastic base particle solution, firstly, magnetically stirring for 10 hours to fully mix the suspension and the plastic base particle solution, and then, placing the mixture in an ice water bath for ultrasonic treatment for 30min to uniformly disperse all phases to obtain a mixed solution;

and step S5, pouring the mixed solution into a glass culture dish, naturally volatilizing for 24h at room temperature, then putting the glass culture dish into a vacuum oven at 60 ℃ for drying for 12h to completely remove the solvent, taking out the glass culture dish and uncovering the film to obtain the plastic film with the average thickness of 55-65 um.

Further, the antibacterial agent is prepared by the following method:

1) weighing 1.5g of tea polyphenol, adding into 200mL of absolute ethyl alcohol, and stirring to completely dissolve the tea polyphenol;

2) adding 3.6g of polyethylene glycol into the solution, continuing stirring for 15-20min, adding 0.8g of nano titanium dioxide, and performing normal-temperature ultrasonic treatment for 30min to obtain the antibacterial agent.

Further, the modified plant fiber is prepared by the following method:

1) chopping the plant fiber into small segments of 8-12cm, and mixing the plant fiber and the plant fiber according to the solid-liquid ratio of 1 g: 20-30mL of the filtrate is soaked in a NaOH solution with the concentration of 15g/L for 48 hours at room temperature, the filtrate is taken out and washed by a large amount of deionized water until the pH value of the filtrate is neutral, and the filtrate is dried at 80 ℃;

2) steam-exploding the treated fiber under the conditions of 12% of moisture content, 1.85MPa of steam explosion pressure and 85s of pressure maintaining time, then washing the fiber by deionized water until the pH value of the filtrate is neutral, and drying the fiber at 80 ℃;

3) bleaching the steam exploded fiber at a solid-to-liquid ratio of 1:15, wherein the bleaching solution contains 1% of Na₂SiO₃2% of NaOH, 1% of H₂O₂Treating at 60 deg.C for 3 hr, washing to neutrality, and oven drying at 80 deg.C;

4) and (3) carrying out heat treatment on the dried fiber at 145 ℃ for 14min, and then mixing the dried fiber with a solvent according to a material-liquid ratio of 1 g: 10-13mL of the fiber after heat treatment is added into deionized water, and the mixture is ultrasonically dispersed for 3 times in ice water bath, wherein each time lasts for 10min, so as to obtain fiber water suspension;

5) dissolving polyethylene glycol in deionized water to prepare a polyethylene glycol aqueous solution with the mass fraction of 20%, slowly pouring a fiber aqueous suspension into the polyethylene glycol aqueous solution according to the volume ratio of 1:5, magnetically stirring at room temperature for 2h, stirring in a water bath at 90 ℃ to evaporate the aqueous solution, and transferring to a vacuum oven at 60 ℃ for drying overnight after the solvent is reduced by 2/3-5/6 to obtain the modified plant fiber;

wherein the plant fiber is ramie, hemp, sisal, abaca, kapok or coconut fiber.

A preparation process of an environment-friendly heat-insulating plastic film comprises the following steps:

step S1, firstly, drying polylactic acid and polybutylene terephthalate adipate in a vacuum oven at 60 ℃ for 8 hours, putting the dried polylactic acid and polybutylene terephthalate into a double-screw extruder, adding glycerol, extruding and granulating by using the double-screw extruder, and extruding at 190 ℃ at a feeding speed of 100 g/min;

s2, drying the obtained plastic base particles in a vacuum oven at 70 ℃ for 6-7h, adding the dried plastic base particles into 2/3 of trichloromethane, and magnetically stirring the mixture at room temperature until the plastic base particles are completely dissolved to obtain a plastic base particle solution;

step S3, adding the modified plant fibers into the residual 1/3 of chloroform, and homogenizing for 15min to obtain a modified plant fiber suspension;

step S4, slowly adding the modified plant fiber suspension and the antibacterial agent into the plastic base particle solution, firstly, magnetically stirring for 10 hours to fully mix the suspension and the plastic base particle solution, and then, placing the mixture in an ice water bath for ultrasonic treatment for 30min to uniformly disperse all phases to obtain a mixed solution;

and step S5, pouring the mixed solution into a glass culture dish, naturally volatilizing for 24h at room temperature, then putting the glass culture dish into a vacuum oven at 60 ℃ for drying for 12h to completely remove the solvent, taking out the glass culture dish and uncovering the film to obtain the plastic film with the average thickness of 55-65 um.

Further, the twin-screw extruder in step S1 has a length-diameter ratio of 32:1, a screw diameter of 20mm, and a rotation speed of 100 rpm.

The invention has the beneficial effects that:

according to the invention, polylactic acid and polybutylene terephthalate adipate are subjected to poly blending, and polybutylene terephthalate adipate (PBAT) is a petroleum-based polyester copolymer with complete biocompatibility, has high ductility and low elastic modulus, and can effectively toughen polylactic acid (PLA); the glycerol is used as a chain extender, the glycerol is blended with the PLA and the PBAT, the compatibility of a polymer blend can be improved, the interfacial adhesion between a matrix and a dispersed phase is increased, the high molecular chains of the PLA and the PBAT and the glycerol are subjected to chemical reaction to form cavities, and the gaps between layers caused by the hollowing show good interfacial adhesion between the PLA and the PBAT, so that the prepared plastic film has good toughness;

according to the invention, the modified plant fiber reinforced film is adopted, the polarity of the plant fiber can be reduced by heat treatment, the interface adhesive property of the fiber and a base material is improved, the fiber after heat treatment is modified by polyethylene glycol, the polyethylene glycol can react with active groups such as hydroxyl on the surface of the fiber and cover the surface of the fiber, the polyethylene glycol can be completely compatible with polylactic acid, the fiber covered with the polyethylene glycol can be better dispersed in the polylactic acid, when the composite material is bent and deformed, the excellent tensile property of the plant fiber slows down the extension deformation of the lower part of the composite material, and the addition of the plant fiber greatly improves the bending modulus of the PLA material; after the plant fiber is modified, the defects of the section of the composite material are reduced, the compatibility of two phases is enhanced, the compactness of the obtained plastic film is enhanced, and the heat-insulating property of the plastic film can be effectively improved;

the invention adds antibacterial agent into film material, the antibacterial agent comprises nanometer titanium dioxide and tea polyphenol, the polyethylene glycol can be attached to the surface of nanometer titanium dioxide particle, so that nanometer TiO particle₂Uniformly dispersed in the film material, the nano titanium dioxide has excellent chemical stability and also has the antibacterial property of spectrum, and the nano TiO₂Added into the film material, on one hand, the nano titanium dioxide particles can be slowly released from the film to play the antibacterial property, and on the other hand, the nano TiO is doped into the film₂Can effectively prevent oxygen from penetrating from one side of the film to the other side, and the nano TiO₂The addition of the (B) compound gives the film excellent oxygen barrier property, and can greatly inhibit the growth of aerobic bacteria; the film has good oxidation resistance by combining the tea polyphenol, and the antibacterial effect is enhanced in the aspect of oxidation resistance;

according to the invention, polylactic acid (PLA) and polybutylene terephthalate adipate (PBAT) are used as plastic film substrates, both of which are biodegradable high polymers, and the polybutylene terephthalate can effectively toughen polylactic acid, so that the defect that the polylactic acid is fragile is overcome; the modified plant fiber is enhanced, so that the flexural modulus of the PLA material is greatly improved, and the mechanical property and the heat-insulating property of the composite material are enhanced; the film has good oxidation resistance by combining the tea polyphenol, and the antibacterial effect is enhanced in the aspect of oxidation resistance; the processing technology is simple, the raw materials are all green and environment-friendly, and the processed heat-insulating plastic film is green and biodegradable, has excellent mechanical property and antibacterial property, and has wide market application prospect.

Detailed Description

The technical solutions of the present invention will be described clearly and completely with reference to the following embodiments, and it should be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the 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.

An environment-friendly heat-insulating plastic film is prepared from the following raw materials in parts by weight: 30-40 parts of polylactic acid (PLA), 20-30 parts of polybutylene terephthalate adipate (PBAT), 4-6 parts of glycerol, 8-12 parts of modified plant fiber, 1-2 parts of antibacterial agent and 60-80 parts of trichloromethane;

the antibacterial agent is prepared by the following method:

1) weighing 1.5g of tea polyphenol, adding into 200mL of absolute ethyl alcohol, and stirring to completely dissolve the tea polyphenol;

2) adding 3.6g of polyethylene glycol into the solution, continuously stirring for 15-20min, adding 0.8g of nano titanium dioxide, and carrying out normal-temperature ultrasonic treatment for 30min to obtain an antibacterial agent;

polyethylene glycol can be attached to the surface of the nano titanium dioxide particles to ensure that the nano TiO₂Uniformly dispersed in the film material, the nano titanium dioxide has excellent chemical stability and also has the antibacterial property of spectrum, and the nano TiO₂Added into the film material, on one hand, the nano titanium dioxide particles can be slowly released from the film to play the antibacterial property, and on the other hand, the nano TiO is doped into the film₂Can effectively prevent oxygen from penetrating from one side of the film to the other side, and the nano TiO₂The addition of the (B) compound gives the film excellent oxygen barrier property, and can greatly inhibit the growth of aerobic bacteria; the film has good oxidation resistance by combining the tea polyphenol, and the antibacterial effect is enhanced in the aspect of oxidation resistance;

the modified plant fiber is prepared by the following method:

1) chopping the plant fiber into small segments of 8-12cm, and mixing the plant fiber and the plant fiber according to the solid-liquid ratio of 1 g: 20-30mL of the filtrate is soaked in a NaOH solution with the concentration of 15g/L for 48 hours at room temperature, the filtrate is taken out and washed by a large amount of deionized water until the pH value of the filtrate is neutral, and the filtrate is dried at 80 ℃;

2) steam-exploding the treated fiber under the conditions of 12% of moisture content, 1.85MPa of steam explosion pressure and 85s of pressure maintaining time, then washing the fiber by deionized water until the pH value of the filtrate is neutral, and drying the fiber at 80 ℃;

3) bleaching the steam exploded fiber at a solid-to-liquid ratio of 1:15, wherein the bleaching solution contains 1% of Na₂SiO₃2% of NaOH, 1% of H₂O₂Treating at 60 deg.C for 3 hr, washing to neutrality, and oven drying at 80 deg.C;

4) and (3) carrying out heat treatment on the dried fiber at 145 ℃ for 14min, and then mixing the dried fiber with a solvent according to a material-liquid ratio of 1 g: 10-13mL of the fiber after heat treatment is added into deionized water, and the mixture is ultrasonically dispersed for 3 times in ice water bath, wherein each time lasts for 10min, so as to obtain fiber water suspension;

5) dissolving polyethylene glycol in deionized water to prepare a polyethylene glycol aqueous solution with the mass fraction of 20%, slowly pouring a fiber aqueous suspension into the polyethylene glycol aqueous solution according to the volume ratio of 1:5, magnetically stirring at room temperature for 2h, stirring in a water bath at 90 ℃ to evaporate the aqueous solution, and transferring to a vacuum oven at 60 ℃ for drying overnight after the solvent is reduced by 2/3-5/6 to obtain the modified plant fiber;

wherein the plant fiber is ramie, hemp, sisal, abaca, kapok or coconut fiber;

the degumming effect of the pre-alkali treatment on the plant fiber is good, in the process of soaking in alkali liquor, the hemicellulose can be deacetylated under the action of alkali, and then sodium acetate is generated and dissolved, so that pores are gradually formed on the surfaces of cell walls and intercellular layers, the hydration effect is increased, and the treatment effect of steam explosion is favorably improved; after the plant fiber is subjected to steam explosion, the hemicellulose and lignin are hydrolyzed by the steam explosion treatment, the residual gum rate and the residual lignin are the lowest and are respectively 3.62-3.88 percent and 5.25-5.64 percent, the fiber crystallinity and the thermal stability are increased, the degummed fiber bundle is disintegrated and separated, fragments appear on the surface of the fiber, meanwhile, the fiber active area is increased, and the subsequent modification treatment performance of the fiber is improved; the heat treatment can reduce the polarity of the plant fiber and improve the interface adhesive property of the fiber and the matrix material, the fiber after the heat treatment is modified by the polyethylene glycol, the polyethylene glycol can react with active groups such as hydroxyl on the surface of the fiber and cover the surface of the fiber, the polyethylene glycol can be completely compatible with the polylactic acid, the fiber covered with the polyethylene glycol can be better dispersed in the polylactic acid, when the composite material generates bending deformation, the excellent tensile property of the plant fiber slows down the extension deformation of the lower part of the composite material, and the addition of the plant fiber can greatly improve the bending modulus of the PLA material; after the plant fiber is modified, the defects of the section of the composite material are reduced, the compatibility of two phases is enhanced, the compactness of the obtained plastic film is enhanced, and the heat-insulating property of the plastic film can be effectively improved;

the processing technology of the environment-friendly heat-insulating plastic film comprises the following steps:

step S1, firstly, drying polylactic acid and polybutylene terephthalate adipate in a vacuum oven at 60 ℃ for 8h (to avoid hydrolytic degradation), putting the dried polylactic acid and polybutylene terephthalate into a double-screw extruder, adding glycerol, extruding and granulating by using the double-screw extruder (the length-diameter ratio is 32:1, the diameter of a screw is 20mm, and the rotating speed is 100rpm), and extruding at 190 ℃ at a feeding speed of 100 g/min;

s2, drying the obtained plastic base particles in a vacuum oven at 70 ℃ for 6-7h, adding the dried plastic base particles into 2/3 of trichloromethane, and magnetically stirring the mixture at room temperature until the plastic base particles are completely dissolved to obtain a plastic base particle solution;

step S3, adding the modified plant fibers into the residual 1/3 of chloroform, and homogenizing for 15min to obtain a modified plant fiber suspension;

step S4, slowly adding the modified plant fiber suspension and the antibacterial agent into the plastic base particle solution, firstly, magnetically stirring for 10 hours to fully mix the suspension and the plastic base particle solution, and then, placing the mixture in an ice water bath for ultrasonic treatment for 30min to uniformly disperse all phases to obtain a mixed solution;

step S5, pouring the mixed solution into a glass culture dish, naturally volatilizing for 24h at room temperature, then putting into a vacuum oven at 60 ℃ for drying for 12h to thoroughly remove the solvent, taking out and uncovering the film to obtain the plastic film with the average thickness of 55-65 um;

polybutylene terephthalate adipate (PBAT) is a petroleum-based polyester copolymer with complete biocompatibility, has high ductility and low elastic modulus, and can effectively toughen polylactic acid (PLA); the glycerol is used as a chain extender, the glycerol is blended with the PLA and the PBAT, the compatibility of a polymer blend can be improved, the interfacial adhesion between a matrix and a dispersed phase is increased, the high molecular chains of the PLA and the PBAT and the glycerol are subjected to chemical reaction to form cavities, and the gaps between layers caused by the hollowing show good interfacial adhesion between the PLA and the PBAT, so that the prepared plastic film shows good toughness.

Example 1

An environment-friendly heat-insulating plastic film is prepared from the following raw materials in parts by weight: 30 parts of polylactic acid (PLA), 20 parts of polybutylene terephthalate adipate (PBAT), 4 parts of glycerol, 8 parts of modified plant fiber, 1 part of antibacterial agent and 60 parts of trichloromethane;

the environment-friendly heat-insulating plastic film is processed by the following steps:

step S1, firstly, drying polylactic acid and polybutylene terephthalate adipate in a vacuum oven at 60 ℃ for 8h (to avoid hydrolytic degradation), putting the dried polylactic acid and polybutylene terephthalate into a double-screw extruder, adding glycerol, extruding and granulating by using the double-screw extruder (the length-diameter ratio is 32:1, the diameter of a screw is 20mm, and the rotating speed is 100rpm), and extruding at 190 ℃ at a feeding speed of 100 g/min;

s2, drying the obtained plastic base particles in a vacuum oven at 70 ℃ for 6h, adding the dried plastic base particles into 2/3 of trichloromethane, and magnetically stirring the mixture at room temperature until the plastic base particles are completely dissolved to obtain a plastic base particle solution;

step S3, adding the modified plant fibers into the residual 1/3 of chloroform, and homogenizing for 15min to obtain a modified plant fiber suspension;

step S4, slowly adding the modified plant fiber suspension and the antibacterial agent into the plastic base particle solution, firstly, magnetically stirring for 10 hours to fully mix the suspension and the plastic base particle solution, and then, placing the mixture in an ice water bath for ultrasonic treatment for 30min to uniformly disperse all phases to obtain a mixed solution;

and step S5, pouring the mixed solution into a glass culture dish, naturally volatilizing for 24h at room temperature, then putting the glass culture dish into a vacuum oven at 60 ℃ for drying for 12h to completely remove the solvent, taking out the glass culture dish and uncovering the film to obtain the plastic film with the average thickness of 55-65 um.

Example 2

An environment-friendly heat-insulating plastic film is prepared from the following raw materials in parts by weight: 35 parts of polylactic acid (PLA), 25 parts of polybutylene terephthalate adipate (PBAT), 5 parts of glycerol, 10 parts of modified plant fiber, 1.5 parts of antibacterial agent and 70 parts of trichloromethane;

the environment-friendly heat-insulating plastic film is processed by the following steps:

step S1, firstly, drying polylactic acid and polybutylene terephthalate adipate in a vacuum oven at 60 ℃ for 8h (to avoid hydrolytic degradation), putting the dried polylactic acid and polybutylene terephthalate into a double-screw extruder, adding glycerol, extruding and granulating by using the double-screw extruder (the length-diameter ratio is 32:1, the diameter of a screw is 20mm, and the rotating speed is 100rpm), and extruding at 190 ℃ at a feeding speed of 100 g/min;

s2, drying the obtained plastic base particles in a vacuum oven at 70 ℃ for 6.5 hours, adding the dried plastic base particles into 2/3 of trichloromethane, and magnetically stirring the mixture at room temperature until the plastic base particles are completely dissolved to obtain a plastic base particle solution;

step S3, adding the modified plant fibers into the residual 1/3 of chloroform, and homogenizing for 15min to obtain a modified plant fiber suspension;

step S4, slowly adding the modified plant fiber suspension and the antibacterial agent into the plastic base particle solution, firstly, magnetically stirring for 10 hours to fully mix the suspension and the plastic base particle solution, and then, placing the mixture in an ice water bath for ultrasonic treatment for 30min to uniformly disperse all phases to obtain a mixed solution;

and step S5, pouring the mixed solution into a glass culture dish, naturally volatilizing for 24h at room temperature, then putting the glass culture dish into a vacuum oven at 60 ℃ for drying for 12h to completely remove the solvent, taking out the glass culture dish and uncovering the film to obtain the plastic film with the average thickness of 55-65 um.

Example 3

An environment-friendly heat-insulating plastic film is prepared from the following raw materials in parts by weight: 40 parts of polylactic acid (PLA), 30 parts of polybutylene terephthalate adipate (PBAT), 6 parts of glycerol, 8-12 parts of modified plant fiber, 2 parts of antibacterial agent and 80 parts of trichloromethane;

the environment-friendly heat-insulating plastic film is processed by the following steps:

step S1, firstly, drying polylactic acid and polybutylene terephthalate adipate in a vacuum oven at 60 ℃ for 8h (to avoid hydrolytic degradation), putting the dried polylactic acid and polybutylene terephthalate into a double-screw extruder, adding glycerol, extruding and granulating by using the double-screw extruder (the length-diameter ratio is 32:1, the diameter of a screw is 20mm, and the rotating speed is 100rpm), and extruding at 190 ℃ at a feeding speed of 100 g/min;

s2, drying the obtained plastic base particles in a vacuum oven at 70 ℃ for 7h, adding the dried plastic base particles into 2/3 of trichloromethane, and magnetically stirring the mixture at room temperature until the plastic base particles are completely dissolved to obtain a plastic base particle solution;

step S3, adding the modified plant fibers into the residual 1/3 of chloroform, and homogenizing for 15min to obtain a modified plant fiber suspension;

step S4, slowly adding the modified plant fiber suspension and the antibacterial agent into the plastic base particle solution, firstly, magnetically stirring for 10 hours to fully mix the suspension and the plastic base particle solution, and then, placing the mixture in an ice water bath for ultrasonic treatment for 30min to uniformly disperse all phases to obtain a mixed solution;

and step S5, pouring the mixed solution into a glass culture dish, naturally volatilizing for 24h at room temperature, then putting the glass culture dish into a vacuum oven at 60 ℃ for drying for 12h to completely remove the solvent, taking out the glass culture dish and uncovering the film to obtain the plastic film with the average thickness of 55-65 um.

The following performance tests were performed on the plastic films prepared in examples 1 to 3 and on the PLA films:

(1) mechanical properties: the tensile strength and the elongation at break are tested by an electronic universal tester according to the GB/T1040.3-2006 standard, and the test results are as follows:

	example 1	Example 2	Example 3	PLA film
					Tensile strength/MPa	43.2	43.1	43.4	31.1
Elongation at break/%	5.1	5.2	5.2	3.0

The tensile strength of the plastic film prepared by the invention is 43.1-43.4MPa, the elongation at break is 5.1-5.2%, and compared with a PLA film, the plastic film prepared by the invention has good mechanical properties;

(2) biodegradability: according to the GB/T19811-2005 standard of determination of the disintegration degree of the plastic material under the defined composting pilot test, the test is carried out by simulating the soil burying degradation experiment, and the weight loss ratio (%) at different times is tested, wherein the test results are as follows:

	example 1	Example 2	Example 3	PLA film
					10d	5.1	5.2	5.0	2.6
20d	14.8	15.3	15.2	4.1
					40d	30.5	30.4	30.6	10.2
80d	65.3	65.6	65.5	20.5

Therefore, the degradation rate of the plastic film prepared by the method reaches more than 5.0% in 10 days, more than 14.8% in 20 days and more than 65.3% in 80 days; compared with a PLA film, the plastic film prepared by the invention has high degradation speed and good biodegradability.

The preferred embodiments of the invention disclosed above are intended to be illustrative only. The preferred embodiments are not intended to be exhaustive or to limit the invention to the precise embodiments disclosed. Obviously, many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, to thereby enable others skilled in the art to best utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims (3)

1. The environment-friendly heat-insulating plastic film is characterized by being prepared from the following raw materials in parts by weight: 30-40 parts of polylactic acid, 20-30 parts of polybutylene terephthalate adipate, 4-6 parts of glycerol, 8-12 parts of modified plant fiber, 1-2 parts of antibacterial agent and 60-80 parts of trichloromethane;

the antibacterial agent is prepared by the following method:

1) weighing 1.5g of tea polyphenol, adding into 200mL of absolute ethyl alcohol, and stirring to completely dissolve the tea polyphenol;

2) adding 3.6g of polyethylene glycol into the solution, continuously stirring for 15-20min, adding 0.8g of nano titanium dioxide, and carrying out normal-temperature ultrasonic treatment for 30min to obtain an antibacterial agent;

the modified plant fiber is prepared by the following method:

1) chopping the plant fiber into small segments of 8-12cm, and mixing the plant fiber and the plant fiber according to the solid-liquid ratio of 1 g: 20-30mL of the filtrate is soaked in a NaOH solution with the concentration of 15g/L for 48 hours at room temperature, the filtrate is taken out and washed by a large amount of deionized water until the pH value of the filtrate is neutral, and the filtrate is dried at 80 ℃;

2) steam-exploding the treated fiber under the conditions of 12% of moisture content, 1.85MPa of steam explosion pressure and 85s of pressure maintaining time, then washing the fiber by deionized water until the pH value of the filtrate is neutral, and drying the fiber at 80 ℃;

3) bleaching the steam exploded fiber at a solid-to-liquid ratio of 1:15, wherein the bleaching solution contains 1% of Na₂SiO₃2% of NaOH, 1% of H₂O₂Treating at 60 deg.C for 3 hr, washing to neutrality, and oven drying at 80 deg.C;

4) and (3) carrying out heat treatment on the dried fiber at 145 ℃ for 14min, and then mixing the dried fiber with a solvent according to a material-liquid ratio of 1 g: 10-13mL of the fiber after heat treatment is added into deionized water, and the mixture is ultrasonically dispersed for 3 times in ice water bath, wherein each time lasts for 10min, so as to obtain fiber water suspension;

5) dissolving polyethylene glycol in deionized water to prepare a polyethylene glycol aqueous solution with the mass fraction of 20%, slowly pouring a fiber aqueous suspension into the polyethylene glycol aqueous solution according to the volume ratio of 1:5, magnetically stirring at room temperature for 2h, stirring in a water bath at 90 ℃ to evaporate the aqueous solution, and transferring to a vacuum oven at 60 ℃ for drying overnight after the solvent is reduced by 2/3-5/6 to obtain the modified plant fiber;

wherein the plant fiber is ramie, hemp, sisal, abaca, kapok or coconut fiber;

the environment-friendly heat-insulating plastic film is prepared by the following steps:

step S1, firstly, drying polylactic acid and polybutylene terephthalate adipate in a vacuum oven at 60 ℃ for 8 hours, putting the dried polylactic acid and polybutylene terephthalate into a double-screw extruder, adding glycerol, extruding and granulating by using the double-screw extruder, and extruding at 190 ℃ at a feeding speed of 100 g/min;

s2, drying the obtained plastic base particles in a vacuum oven at 70 ℃ for 6-7h, adding the dried plastic base particles into 2/3 of trichloromethane, and magnetically stirring the mixture at room temperature until the plastic base particles are completely dissolved to obtain a plastic base particle solution;

step S3, adding the modified plant fibers into the residual 1/3 of chloroform, and homogenizing for 15min to obtain a modified plant fiber suspension;

step S4, slowly adding the modified plant fiber suspension and the antibacterial agent into the plastic base particle solution, firstly, magnetically stirring for 10 hours to fully mix the suspension and the plastic base particle solution, and then, placing the mixture in an ice water bath for ultrasonic treatment for 30min to uniformly disperse all phases to obtain a mixed solution;

step S5, pouring the mixed solution into a glass culture dish, naturally volatilizing for 24h at room temperature, then putting into a vacuum oven at 60 ℃ for drying for 12h to thoroughly remove the solvent, taking out and uncovering the film to obtain the plastic film with the average thickness of 55-65 um;

the tensile strength of the prepared plastic film is 43.1-43.4MPa, and the elongation at break is 5.1-5.2%.

2. A preparation process of an environment-friendly heat-insulating plastic film is characterized by comprising the following steps:

step S1, firstly, drying polylactic acid and polybutylene terephthalate adipate in a vacuum oven at 60 ℃ for 8 hours, putting the dried polylactic acid and polybutylene terephthalate into a double-screw extruder, adding glycerol, extruding and granulating by using the double-screw extruder, and extruding at 190 ℃ at a feeding speed of 100 g/min;

s2, drying the obtained plastic base particles in a vacuum oven at 70 ℃ for 6-7h, adding the dried plastic base particles into 2/3 of trichloromethane, and magnetically stirring the mixture at room temperature until the plastic base particles are completely dissolved to obtain a plastic base particle solution;

step S3, adding the modified plant fibers into the residual 1/3 of chloroform, and homogenizing for 15min to obtain a modified plant fiber suspension;

step S4, slowly adding the modified plant fiber suspension and the antibacterial agent into the plastic base particle solution, firstly, magnetically stirring for 10 hours to fully mix the suspension and the plastic base particle solution, and then, placing the mixture in an ice water bath for ultrasonic treatment for 30min to uniformly disperse all phases to obtain a mixed solution;

and step S5, pouring the mixed solution into a glass culture dish, naturally volatilizing for 24h at room temperature, then putting the glass culture dish into a vacuum oven at 60 ℃ for drying for 12h to completely remove the solvent, taking out the glass culture dish and uncovering the film to obtain the plastic film with the average thickness of 55-65 um.

3. The process for preparing an environment-friendly heat insulation plastic film as claimed in claim 2, wherein in the step S1, the length-diameter ratio of the twin-screw extruder is 32:1, the diameter of the screw is 20mm, and the rotating speed is 100 rpm.