Biodegradable heat sealing film and preparation method thereof

Abstract

The invention relates to a biodegradable heat-sealing film and a preparation method thereof, and belongs to the technical field of heat-sealing films, the biodegradable heat-sealing film is prepared from the following raw materials by weight: 45-55 parts of polylactic acid, 6-12 parts of modified tapioca flour, 5-12 parts of toughening fiber, 8-18 parts of glycerin, 0.5-1.5 parts of sorbitol, 3-5 parts of citric acid, and 4-8 parts of stearic acid; wherein the modified tapioca flour is obtained by performing heat-moisture treatment and oxidation treatment on tapioca starch, and the toughened fibers are prepared by performing blasting and purification treatment on plants serving as raw materials. The biodegradable heat-sealing film is prepared through the synergistic effect of the polylactic acid, the modified tapioca flour and the plant-based toughening fibers in a specific proportion, and the tapioca flour is modified through damp heat and oxidation, so that the compatibility and degradation performance of the tapioca flour and the polylactic acid are improved; the toughening fiber is obtained by steam explosion and purification of various plants, and the addition of the toughening fiber can provide an anchor point for the biodegradable heat-sealing film, so that the biodegradable heat-sealing film is not easy to generate a longer fracture when being pulled.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of heat-sealable film, and particularly relates to a biodegradable heat-sealable film and a preparation method thereof. BACKGROUND

[0002] The heat-sealable film is a functional film material widely used in the packaging industry, and its core function is to realize the adhesion and sealing between materials through heating, and it is commonly used in the packaging of food, medicine, daily chemical products and the like.

[0003] The existing biodegradable heat-sealable film is mostly prepared by using polylactic acid and the like, and has the defect of poor tear resistance in actual use, because the film body lacks effective stress anchor points inside, once a small crack occurs, it can be easily torn, and a long fracture is generated, which seriously affects the sealing performance and use reliability of the packaging, and limits the popularization and application of the film in the packaging field. SUMMARY

[0004] The application aims to provide a biodegradable heat-sealable film and a preparation method thereof to solve the above problems.

[0005] The application achieves the above-mentioned purpose by the following technical scheme:

[0006] The application provides a biodegradable heat-sealable film, which is prepared from the following raw materials by weight: 45-55 parts of polylactic acid, 6-12 parts of modified cassava powder, 5-12 parts of toughening fiber, 8-18 parts of glycerol, 0.5-1.5 parts of sorbitol, 3-5 parts of citric acid, and 4-8 parts of stearic acid.

[0007] The modified cassava powder is obtained by wet heat treatment and oxidation treatment of cassava starch, and the toughening fiber is prepared from plants by explosion and purification treatment.

[0008] As a further optimization scheme of the application, the specific steps of the wet heat treatment are as follows: the moisture content of the cassava starch is controlled to be 15-35%, and the cassava starch is heated at 70-130 DEG C for 5-7 hours, then the moisture content of the cassava starch is adjusted to 25-30%, and the cassava starch is heated at 95-100 DEG C for 5-8 hours.

[0009] As a further optimization scheme of the present application, the specific steps of the oxidation treatment are as follows: mixing deionized water with cassava starch, uniformly mixing to obtain starch milk; adjusting the pH of the starch milk to 9.0-11.0 by using sodium hydroxide, dropping sodium hypochlorite into the starch milk under the condition of 25-40℃, stirring at a speed of 350 r / min for 1-2 h, after the stirring is completed, adding 5-10% dilute hydrochloric acid to adjust the pH to 6.5-7.0, adding sodium sulfite, stirring at a speed of 120 r / min for 15-25 min, to obtain modified cassava starch milk; washing the modified cassava starch milk with deionized water until neutral, drying at 40-50℃, and crushing to obtain modified cassava powder.

[0010] As a further optimization scheme of the present application, the mass ratio of deionized water to cassava starch in the starch milk is 1:0.15; the mass ratio of sodium hypochlorite, sodium sulfite and the starch milk is 0.05-0.08:0.01-0.03:1.

[0011] As a further optimization scheme of the present application, the toughening fiber is made of the following raw materials by weight: 5-10 parts of dry branch of Zanthoxylum ailanthoides, 35-45 parts of side branch of Phyllostachys nuda, 6-12 parts of banana stem, 25-30 parts of wheat straw, 1-5 parts of vitamin C, 2-6 parts of citric acid, and 10-15 parts of sodium hypochlorite.

[0012] As a further optimization scheme of the present application, the preparation process of the toughening fiber is as follows:

[0013] (I) explosion pretreatment: after the dry branch of Zanthoxylum ailanthoides, the side branch of Phyllostachys nuda, the banana stem and the wheat straw are cleaned and dried, they are cut into 2-4 cm sections, placed in a sealed kettle, and subjected to steam infiltration under the condition of 180-200℃ and 1.0-2.0 MPa for 6-8 min, then instantaneously released at 0.01 second level, cooled, added with vitamin C and citric acid, and placed in dark for 1-3 d to obtain explosion crude fiber material;

[0014] (II) purification: the crude fiber material is added into 50% ethanol aqueous solution, the solid-liquid ratio is 1:10 (g:mL), extracted by reflux at 50℃ for 1.5-2 h, repeated for 1-3 times, washed with water for 3-5 times, added with sodium hypochlorite, stirred at a speed of 220 r / min for 1.5-2 h, washed with water for 3-5 times, filtered out the fiber, dried to obtain the toughening fiber.

[0015] As a further optimization scheme of the present application, the number average molecular weight of the polylactic acid is 80000-120000; the length of the toughening fiber is 0.1-0.3 mm, and the diameter is 5-15 μm.

[0016] The present application also provides a preparation method of a biodegradable heat-seal film, which comprises the following steps:

[0017] S1, raw material drying: dry polylactic acid in a vacuum drying oven at 85-95℃ for 8-10h, and prepare; dry modified cassava powder and toughening fiber respectively in a blast drying oven at 70-80℃ for 5-6h, and prepare;

[0018] S2, dry mixing: add the dried polylactic acid, modified cassava powder and toughening fiber into a high-speed mixer, and dry mix at a speed of 850-950rpm for 6-8min to obtain a mixture;

[0019] S3, preparation of pre-material: stir the mixture at a speed of 130-150rpm, and add stearic acid, glycerol and sorbitol in sequence, stir for 8-10min, and finally add citric acid, continue to stir for 3-5min to obtain a pre-material;

[0020] S4, granulation: add the pre-material into a twin-screw extruder for melt blending, set the temperature gradient from the feeding port to the die in sequence as follows: 145-155℃ for the feeding section, 155-165℃ for the melting section, and 160-170℃ for the die section, set the screw speed at 200-250rpm, extrude a strip-shaped melt, and granulate by a granulator to obtain a heat-seal film granule with a diameter of 2-3mm and a length of 3-5mm;

[0021] S5, add the granule into a casting film extruder, control the die temperature at 160-165℃, the cooling roller temperature at 25-30℃, and the traction rate at 3-5m / min, and prepare a biodegradable heat-seal film with a thickness of 20-50μm by a casting method.

[0022] The application has the advantages that: the biodegradable heat-seal film is prepared by the synergistic effect of polylactic acid, modified cassava powder and plant-based toughening fiber with specific proportions, and a special preparation process, the wet heat-oxidation double modified cassava powder improves the compatibility and degradation performance with polylactic acid, the toughening fiber obtained by steam explosion and purification of multiple plants can provide anchor points for the biodegradable heat-seal film, so that the biodegradable heat-seal film is not easy to have a long fracture when being pulled, and the components are uniformly dispersed by drying, dry mixing, multi-stage melt blending and casting forming, the obtained heat-seal film has high heat-seal strength, good sealing performance, 28d biodegradation rate reaches the standard, has good mechanical properties and complete biodegradation characteristics, can replace traditional non-degradable packaging film, and has outstanding environmental protection value and application prospect. DETAILED DESCRIPTION

[0023] It is necessary to point out here that the following detailed description is only used to further illustrate the application, and cannot be understood as limiting the protection scope of the application, and the skilled in the art can make some non-essential improvements and adjustments to the application according to the above application content.

[0024] The method used in the present application is a conventional method known to those skilled in the art, and the reagents and other materials used are commercially available products unless otherwise specified.

[0025] Example 1

[0026] The modified cassava powder is obtained by wet heat treatment and oxidation treatment of cassava starch;

[0027] The specific steps of the wet heat treatment are as follows: the moisture content of the cassava starch is controlled at 15%, and the cassava starch is heated at 70℃ for 5h; after the end of the heating, the moisture content of the cassava starch is adjusted to 25%, and the cassava starch is heated at 95℃ for 5h;

[0028] The specific steps of the oxidation treatment are as follows: deionized water is mixed with the cassava starch (the mass ratio of deionized water to cassava starch in the starch milk is 1:0.15), and the mixture is uniformly mixed to obtain starch milk; sodium hydroxide is used to adjust the pH of the starch milk to 9.0, and sodium hypochlorite is added dropwise into the starch milk under the condition of 25℃; the mixture is stirred at a speed of 350r / min for 1h; after the end of the stirring, 5% dilute hydrochloric acid is added to adjust the pH to 6.5; sodium sulfite is added, and the mixture is stirred at a speed of 120r / min for 15min to obtain modified cassava starch milk (the mass ratio of sodium hypochlorite, sodium sulfite to starch milk is 0.05:0.01:1); the modified cassava starch milk is washed with deionized water until it is neutral; the mixture is dried at 40℃, and is crushed to obtain modified cassava powder;

[0029] The toughening fiber is made from plants by explosion and purification treatment;

[0030] Explosion pretreatment: 5 parts of Zhijiang branches, 35 parts of just bamboo side branches, 6 parts of banana stems, and 25 parts of wheat straw are washed, dried, and cut into 2cm sections; the sections are placed in a sealed kettle, and are subjected to steam soaking under the condition of 180℃ and 1.0MPa for 6min; the pressure is instantaneously released at the 0.01 second level, and the mixture is sprayed out; after cooling, 1 part of vitamin C and 2 parts of citric acid are added, and the mixture is placed in the dark for 1d to obtain an explosion crude fiber material;

[0031] Purification: the crude fiber material is added into 50% ethanol aqueous solution, and the solid-liquid ratio is 1:10 (g:mL); the mixture is refluxed at 50℃ for 1.5h; the process is repeated once; the mixture is washed with water for 3 times; 10 parts of sodium hypochlorite is added, and the mixture is stirred at a speed of 220r / min for 1.5h; the mixture is washed with water for 3 times; the fiber is filtered out, and is dried to obtain toughening fiber (the length of the toughening fiber is 0.1mm, and the diameter is 5μm);

[0032] Drying of raw materials: 50 parts of polylactic acid (the number average molecular weight of the polylactic acid is 80000) is dried in a vacuum drying oven at 85℃ for 8h; 6 parts of modified cassava powder and 5 parts of toughening fiber are dried in a blast drying oven at 70℃ for 5h;

[0033] Dry mixing: the dried polylactic acid, modified cassava powder and toughening fiber were added into a high-speed mixer and dry mixed at a speed of 850 rpm for 6 min to obtain a mixture;

[0034] Preparation of pre-mixture: the mixture was stirred at a speed of 130 rpm, 4 parts of stearic acid, 8 parts of glycerol and 0.5 parts of sorbitol were added in sequence, and stirred for 8 min, and finally 3 parts of citric acid was added and stirred for 3 min to obtain a pre-mixture;

[0035] Granulation: the pre-mixture was added into a twin-screw extruder for melt blending, and the temperature gradient was set according to the section from the feeding port to the die head, in sequence: 145℃ for the feeding section, 155℃ for the melting section, and 160℃ for the die head section, and the screw speed was set to 200 rpm, and the extruded melt was granulated by a granulator to obtain hot-seal film granules with a diameter of 2 mm and a length of 3 mm;

[0036] The granules were added into a cast film extruder, the die head temperature was controlled at 160℃, the cooling roller temperature was 25℃, and the pulling rate was 3 m / min, and a biodegradable hot-seal film with a thickness of 20 μm was prepared by a casting method.

[0037] Example 2

[0038] The modified cassava powder was obtained by wet heat treatment and oxidation treatment of cassava starch;

[0039] The specific steps of the wet heat treatment were as follows: the moisture content of the cassava starch was controlled at 25%, and the cassava starch was heated at 100℃ for 6 h, and then the moisture content of the cassava starch was adjusted to 27%, and the cassava starch was heated at 96℃ for 6 h;

[0040] The specific steps of the oxidation treatment were as follows: deionized water and cassava starch were mixed (the mass ratio of deionized water to cassava starch in the starch milk was 1:0.15), and the mixture was uniformly mixed to obtain starch milk; sodium hydroxide was used to adjust the pH of the starch milk to 10.0, and sodium hypochlorite was added dropwise into the starch milk under the condition of 35℃, and the mixture was stirred at a speed of 350 r / min for 1.5 h; after the stirring was completed, 8% dilute hydrochloric acid was added to adjust the pH to 7.0, and sodium sulfite was added, and the mixture was stirred at a speed of 120 r / min for 20 min to obtain modified cassava starch milk (the mass ratio of sodium hypochlorite, sodium sulfite to starch milk was 0.06:0.02:1); the modified cassava starch milk was washed to neutral with deionized water, dried at 45℃, and pulverized to obtain modified cassava powder;

[0041] The toughening fiber was made from plants by explosion and purification treatment;

[0042] Explosion pretreatment: 8 parts of Lysal branches, 40 parts of Phyllostachys bambusoides lateral branches, 8 parts of banana stems, 27 parts of wheat straw were cleaned and dried, then cut into 3 cm sections, placed in a sealed kettle, and subjected to steam infiltration at 190℃ and 1.5 MPa for 7 min, then instantaneously released at 0.01 s, and then cooled. After that, 3 parts of vitamin C and 4 parts of citric acid were added, and the mixture was placed in the dark for 2 days to obtain an explosion crude fiber material;

[0043] Purification: the crude fiber material was added to 50% ethanol aqueous solution, the solid-liquid ratio was 1:10 (g:mL), and the mixture was refluxed at 50℃ for 1.8 h, repeated twice. The obtained product was washed with water for 4 times, 12 parts of sodium hypochlorite was added, and the mixture was stirred at 220 r / min for 1.8 h. The product was washed with water for 4 times, and then the fiber was filtered and dried to obtain the toughened fiber (the length of the toughened fiber was 0.2 mm, and the diameter was 10 μm);

[0044] Drying of raw materials: 50 parts of polylactic acid (the number average molecular weight of the polylactic acid was 100000) were dried in a vacuum drying oven at 90℃ for 9 h, and 8 parts of modified cassava powder and 7 parts of toughened fiber were dried in a blast drying oven at 75℃ for 5.5 h, respectively;

[0045] Dry mixing: the dried polylactic acid, modified cassava powder and toughened fiber were added into a high-speed mixer, and dry mixed at a speed of 900 rpm for 7 min to obtain a mixture;

[0046] Preparation of preformed material: the mixture was stirred at a speed of 140 rpm, 6 parts of stearic acid, 14 parts of glycerol and 1 part of sorbitol were added in sequence, and stirred for 9 min. Finally, 4 parts of citric acid was added, and the mixture was stirred for another 4 min to obtain a preformed material;

[0047] Granulation: the preformed material was added into a twin-screw extruder for melt blending. The temperature gradient was set from the feeding port to the die head as follows: 150℃ for the feeding section, 160℃ for the melting section, and 165℃ for the die head section. The screw rotation speed was set at 225 rpm. The extruded strip was granulated by a pelletizer to obtain hot-seal film granules with a diameter of 2 mm and a length of 3 mm;

[0048] The granules were added into a cast film extruder, the die head temperature was controlled at 162℃, the cooling roller temperature was 28℃, and the pulling rate was 4 m / min. A biodegradable hot-seal film with a thickness of 35 μm was prepared by a casting method.

[0049] Example 3

[0050] The modified cassava powder was obtained by wet heat treatment and oxidation treatment of cassava starch;

[0051] The specific steps of the wet heat treatment were as follows: the moisture content of the cassava starch was controlled at 35%, and the starch was heated at 130℃ for 7 h. After the treatment, the moisture content of the starch was adjusted to 30%, and the starch was heated at 100℃ for 8 h.

[0052] The specific steps of the oxidation treatment are as follows: mixing deionized water and cassava starch (the mass ratio of deionized water to cassava starch in the starch milk is 1:0.15), uniformly mixing to obtain starch milk; adjusting the pH of the starch milk to 11.0 by using sodium hydroxide, dropping sodium hypochlorite into the starch milk at 40℃, stirring at a speed of 350 r / min for 2 h, adding 10% dilute hydrochloric acid after the stirring is completed to adjust the pH to 7.0, adding sodium sulfite, and stirring at a speed of 120 r / min for 25 min to obtain modified cassava starch milk (the mass ratio of sodium hypochlorite, sodium sulfite to starch milk is 0.08:0.03:1); washing the modified cassava starch milk with deionized water until neutral, drying at 50℃, and crushing to obtain modified cassava powder;

[0053] The toughening fiber is made from plants by explosion and purification treatment;

[0054] Explosion pretreatment: 10 parts of dry branches of Jixiang, 45 parts of side branches of just bamboo, 12 parts of banana stems, and 30 parts of wheat straws are washed, dried, cut into 4 cm sections, placed in a sealed kettle, steam infiltrated at 200℃ and 2.0 MPa, and kept for 8 min, then instantaneously released at 0.01 second level, and cooled to add 5 parts of vitamin C and 6 parts of citric acid, and placed in dark for 3 days to obtain explosion crude fiber material;

[0055] Purification: the crude fiber material is added into 50% ethanol aqueous solution, the solid-liquid ratio is 1:10 (g:mL), reflux extraction is carried out at 50℃ for 2 h, repeated for 3 times, washed with water for 5 times, 15 parts of sodium hypochlorite is added, stirred at a speed of 220 r / min for 2 h, washed with water for 5 times, the fiber is filtered out, dried to obtain toughening fiber (the length of the toughening fiber is 0.3 mm, and the diameter is 15 μm);

[0056] Drying of raw materials: 55 parts of polylactic acid (the number average molecular weight of the polylactic acid is 120000) are dried in a vacuum drying box at 95℃ for 10 h, and reserved; 12 parts of modified cassava powder and 12 parts of toughening fiber are dried in a blowing drying box at 80℃ for 6 h, respectively, and reserved;

[0057] Dry mixing: the dried polylactic acid, modified cassava powder and toughening fiber are added into a high-speed mixer, dry mixed at a speed of 950 rpm for 8 min to obtain a mixture;

[0058] Preparation of preform: the mixture is stirred at a speed of 150 rpm, 8 parts of stearic acid, 18 parts of glycerol, 1.5 parts of sorbitol are added in sequence, stirred for 10 min, finally 5 parts of citric acid is added, and stirred for 5 min to obtain a preform;

[0059] Granulation: the pre-made material was added into a twin-screw extruder for melt blending, and a temperature gradient was set from the feeding port to the die head in sections as follows: 155℃ for the feeding section, 165℃ for the melting section, and 170℃ for the die head section, the screw rotation speed was set to 250 rpm, the extruded strip was granulated by a granulator to obtain hot-seal film granules with a diameter of 3 mm and a length of 5 mm;

[0060] The granules were added into a cast film extruder, the die head temperature was controlled at 165℃, the cooling roll temperature was 30℃, and the drawing speed was 5 m / min, and a biodegradable hot-seal film with a thickness of 50 μm was prepared by a casting method.

[0061] Comparative Example 1

[0062] The toughening fiber was prepared from plants by explosion and purification treatment;

[0063] Explosion pretreatment: 8 parts of dry branches of Lysidice rhodostegia, 40 parts of side branches of Phyllostachys pubescens, 8 parts of banana stems, and 27 parts of wheat straw were washed and dried, then cut into 3 cm sections, placed in a sealed kettle, and subjected to steam soaking at 190℃ and 1.5 MPa for 7 min, then instantaneously released at 0.01 second level, and cooled, then 3 parts of vitamin C and 4 parts of citric acid were added, and the mixture was placed in the dark for 2 days to obtain an explosion crude fiber material;

[0064] Purification: the crude fiber material was added into 50% ethanol aqueous solution, the solid-liquid ratio was 1:10 (g:mL), and the mixture was refluxed at 50℃ for 1.8 h, repeated twice, washed with water for 4 times, 12 parts of sodium hypochlorite was added, and the mixture was stirred at 220 r / min for 1.8 h, then washed with water for 4 times, the fiber was filtered out, and dried to obtain the toughening fiber (the length of the toughening fiber was 0.2 mm, and the diameter was 10 μm);

[0065] Drying of raw materials: 58 parts of polylactic acid (the number average molecular weight of the polylactic acid was 100000) were dried in a vacuum drying oven at 90℃ for 9 h, and 7 parts of toughening fiber were dried in a blast drying oven at 75℃ for 5.5 h;

[0066] Dry mixing: the dried polylactic acid and toughening fiber were added into a high-speed mixer, and dry mixed at a rotation speed of 900 rpm for 7 min to obtain a mixed material;

[0067] Preparation of pre-made material: the mixed material was stirred at a rotation speed of 140 rpm, 6 parts of stearic acid, 14 parts of glycerol, and 1 part of sorbitol were added in sequence, stirred for 9 min, and finally 4 parts of citric acid was added, and the mixture was stirred for another 4 min to obtain a pre-made material;

[0068] Granulation: the pre-material was added into a twin-screw extruder for melt blending, and a temperature gradient was set in sections from the feeding port to the die head, in the order of 150℃ for the feeding section, 160℃ for the melting section, and 165℃ for the die head section. The screw rotation speed was set at 225 rpm, the extruded strip melt was granulated by a granulator, and biodegradable heat-seal film granules with a diameter of 2 mm and a length of 3 mm were obtained;

[0069] The granules were added into a cast film extruder, the die head temperature was controlled at 162℃, the cooling roll temperature was 28℃, and the traction rate was 4 m / min. A biodegradable heat-seal film with a thickness of 35 μm was prepared by a casting method.

[0070] Comparative Example 2

[0071] The modified cassava powder was obtained by wet heat treatment and oxidation treatment of cassava starch;

[0072] The specific steps of the wet heat treatment were as follows: the moisture content of the cassava starch was controlled at 25%, and the cassava starch was heated at 100℃ for 6 h. After the end of the heating, the moisture content of the cassava starch was adjusted to 27%, and the cassava starch was heated at 96℃ for 6 h.

[0073] The specific steps of the oxidation treatment were as follows: deionized water and cassava starch were mixed (the mass ratio of deionized water to cassava starch in the starch milk was 1:0.15), and the mixture was uniformly mixed to obtain starch milk. Sodium hydroxide was used to adjust the pH of the starch milk to 10.0, and sodium hypochlorite was added dropwise into the starch milk under the condition of 35℃. The mixture was stirred at a speed of 350 r / min for 1.5 h. After the end of the stirring, 8% dilute hydrochloric acid was added to adjust the pH to 7.0, and sodium sulfite was added. The mixture was stirred at a speed of 120 r / min for 20 min to obtain modified cassava starch milk (the mass ratio of sodium hypochlorite, sodium sulfite to starch milk was 0.06:0.02:1). The modified cassava starch milk was washed to neutral with deionized water, dried at 45℃, and pulverized to obtain modified cassava powder.

[0074] Drying of raw materials: 57 parts of polylactic acid (the number average molecular weight of the polylactic acid was 100000) were dried in a vacuum drying oven at 90℃ for 9 h, and were ready for use. 8 parts of modified cassava powder were dried in a blast drying oven at 75℃ for 5.5 h, and were ready for use.

[0075] Dry mixing: the dried polylactic acid and modified cassava powder were added into a high-speed mixer, and were dry mixed at a rotation speed of 900 rpm for 7 min to obtain a mixture.

[0076] Preparation of pre-material: the mixture was stirred at a rotation speed of 140 rpm, 6 parts of stearic acid, 14 parts of glycerol, and 1 part of sorbitol were added in sequence, and were stirred for 9 min. Finally, 4 parts of citric acid were added, and were continuously stirred for 4 min to obtain a pre-material.

[0077] Granulation: The pre-made material was added to the twin-screw extruder for melt blending, and the temperature gradient was set in sections from the feeding port to the die head, in the order of: feeding section 150℃, melting section 160℃, die head section 165℃, the screw speed was set to 225rpm, the extruded strip melt was granulated by a pelletizer, and biodegradable heat-seal film granules with a diameter of 2mm and a length of 3mm were obtained;

[0078] The granules were added to the cast film extruder, the die head temperature was controlled at 162℃, the cooling roll temperature was 28℃, the pulling rate was 4m / min, and a biodegradable heat-seal film with a thickness of 35μm was prepared by the casting method.

[0079] Comparative Example 3

[0080] Drying of raw materials: 65 parts of polylactic acid (the number average molecular weight of polylactic acid is 100000) were dried in a vacuum drying oven at 90℃ for 9h, and were ready for use;

[0081] Dry mixing: The dried polylactic acid was added to a high-speed mixer and dry mixed at a speed of 900rpm for 7min to obtain a mixture;

[0082] Preparation of pre-made material: The mixture was stirred at a speed of 140rpm, 6 parts of stearic acid, 14 parts of glycerol, and 1 part of sorbitol were added in turn, and stirred for 9min, and finally 4 parts of citric acid was added and stirred for another 4min to obtain a pre-made material;

[0083] Granulation: The pre-made material was added to the twin-screw extruder for melt blending, and the temperature gradient was set in sections from the feeding port to the die head, in the order of: feeding section 150℃, melting section 160℃, die head section 165℃, the screw speed was set to 225rpm, the extruded strip melt was granulated by a pelletizer, and biodegradable heat-seal film granules with a diameter of 2mm and a length of 3mm were obtained;

[0084] The granules were added to the cast film extruder, the die head temperature was controlled at 162℃, the cooling roll temperature was 28℃, the pulling rate was 4m / min, and a biodegradable heat-seal film with a thickness of 35μm was prepared by the casting method.

[0085] Performance testing

[0086] (1) The biodegradable heat-seal films prepared by the methods of Examples 1-3 and Comparative Examples 1-3 were tested for performance according to the method in QB / T2358 "Plastic film packaging bag heat sealing strength test method";

[0087] Test conditions:

[0088] Sample: width: 15mm, length: 100mm;

[0089] Heat sealing: uniform temperature, pressure, and time for heat sealing;

[0090] Test: peel at 300 mm / min, record the maximum force;

[0091] Result: expressed in N / 15mm;

[0092] The test results are shown in Table 1.

[0093] Table 1

[0094]

[0095] As can be seen from Table 1, the heat seal strength of the biodegradable heat sealable film prepared in Examples 1-3 is not less than 1.8 N / 15mm. The heat seal strength of Comparative Examples 1-2 is significantly lower than that of the Examples, indicating that the biodegradable heat sealable film prepared in the application can effectively improve the heat seal strength, has better sealing performance, and meets the packaging use requirements.

[0096] (II) According to the method in GB / T 19277.1 "Determination of ultimate aerobic biodegradation of materials under controlled composting conditions - Method by determining released carbon dioxide - Part 1: General method", the biodegradable heat sealable films prepared in Examples 1-3 and Comparative Examples 1-3 were tested for performance.

[0097] Test conditions:

[0098] Environment: controlled composting conditions with temperature of 58±2℃ and humidity of 55±5%;

[0099] Period: 28d;

[0100] Principle: determine the amount of released CO2 and calculate the biodegradation rate.

[0101] The test results are shown in Table 2.

[0102] Table 2

[0103]

[0104] As can be seen from Table 2, the 28d biodegradation rate of the biodegradable heat sealable film prepared in Examples 1-3 meets the biodegradation requirement. The 28d biodegradation rate of Comparative Examples 1-3 is less than 60%, which is significantly lower than that of the Examples, indicating that the biodegradable heat sealable film prepared in the application has better biodegradation performance under controlled composting conditions.

[0105] The above examples only express several embodiments of the application, and the description is more specific and detailed, but it cannot be understood as limiting the scope of the patent of the application. It should be noted that for ordinary skilled in the art, without departing from the concept of the application, a number of modifications and improvements can be made, which are within the scope of protection of the application.

Claims

1. A biodegradable heat-sealing film, characterized in that, The biodegradable heat-sealing film is made from the following raw materials in parts by weight: 45-55 parts polylactic acid, 6-12 parts modified cassava flour, 5-12 parts toughening fiber, 8-18 parts glycerol, 0.5-1.5 parts sorbitol, 3-5 parts citric acid, and 4-8 parts stearic acid. The modified cassava flour is obtained from cassava starch through wet heat treatment and oxidation treatment, and the toughening fiber is made from plant raw materials through blasting and purification treatment.

2. The biodegradable heat-sealing film according to claim 1, characterized in that, The specific steps of the wet heat treatment are as follows: control the moisture content of the cassava starch to 15-35%, heat at 70-130℃ for 5-7 hours, and after the treatment, adjust the moisture content of the cassava starch to 25-30% and heat at 95-100℃ for 5-8 hours.

3. The biodegradable heat-sealing film according to claim 2, characterized in that, The specific steps of the oxidation treatment are as follows: Deionized water and cassava starch are mixed and stirred to obtain starch milk; the pH of the starch milk is adjusted to 9.0-11.0 using sodium hydroxide; sodium hypochlorite is added dropwise to the starch milk at 25-40℃ and stirred at 350r / min for 1-2h; after stirring, 5-10% dilute hydrochloric acid is added to adjust the pH to 6.5-7.0, sodium sulfite is added, and stirred at 120r / min for 15-25min to obtain modified cassava starch milk; the modified cassava starch milk is washed with deionized water until neutral, dried at 40-50℃, and pulverized to obtain modified cassava flour.

4. The biodegradable heat-sealing film according to claim 3, characterized in that, The mass ratio of deionized water to cassava starch in the starch milk is 1:0.15; the mass ratio of sodium hypochlorite, sodium sulfite to starch milk is 0.05-0.08:0.01-0.03:

1.

5. The biodegradable heat-sealing film according to claim 1, characterized in that, The toughening fiber is made from the following raw materials in parts by weight: 5-10 parts of Daphne odora branches, 35-45 parts of Phyllostachys edulis lateral branches, 6-12 parts of banana stems, 25-30 parts of wheat straw, 1-5 parts of vitamin C, 2-6 parts of citric acid and 10-15 parts of sodium hypochlorite.

6. The biodegradable heat-sealing film according to claim 5, characterized in that, The preparation process of the toughening fiber is as follows: (I) Blasting pretreatment: After washing and drying the branches of Daphne odora, the lateral branches of Phyllostachys edulis, the banana stems and wheat straw, cut them into 2-4cm sections and place them in a sealed autoclave. Steam-impregnate and keep them under pressure for 6-8 minutes at 180-200℃ and 1.0-2.0MPa. Release the pressure instantly in 0.01 seconds and spray them out. After cooling, add vitamin C and citric acid and let them stand in the dark for 1-3 days to obtain blasted coarse fiber material. (II) Purification: Add the crude fiber material to a 50% ethanol aqueous solution at a material-to-liquid ratio of 1:10 (g:mL), reflux at 50℃ for 1.5-2h, repeat 1-3 times, remove and wash with water 3-5 times, add sodium hypochlorite, stir at 220r / min for 1.5-2h, wash with water 3-5 times, filter out the fiber, and dry to obtain toughened fiber.

7. The biodegradable heat-sealing film according to claim 6, characterized in that, The polylactic acid has a number average molecular weight of 80,000-120,000; the toughening fiber has a length of 0.1-0.3 mm and a diameter of 5-15 μm.

8. A method for preparing a biodegradable heat-sealing film according to any one of claims 1-7, characterized in that, Includes the following steps: S1, Raw material drying: Dry polylactic acid in a vacuum drying oven at 85-95℃ for 8-10 hours, and set aside; dry modified cassava flour and toughening fiber in a forced-air drying oven at 70-80℃ for 5-6 hours, and set aside. S2, Dry Mixing: Add the dried polylactic acid, modified cassava flour and toughening fiber to a high-speed mixer and dry mix at 850-950 rpm for 6-8 minutes to obtain the mixture; S3, Pre-mix preparation: Stir the mixture at 130-150 rpm, add stearic acid, glycerin and sorbitol in sequence, stir for 8-10 min, finally add citric acid and continue stirring for 3-5 min to obtain the pre-mix. S4, Granulation: The pre-made material is added to a twin-screw extruder for melt blending. The temperature gradient is set in sections from the feed port to the die head, in the following order: feed section 145-155℃, melt section 155-165℃, die head section 160-170℃. The screw speed is set to 200-250 rpm. The strip melt is extruded and granulated by a pelletizer to obtain heat-sealing film granules with a diameter of 2-3 mm and a length of 3-5 mm. S5. Add the granules to the cast film extruder, control the die head temperature to 160-165℃, the cooling roller temperature to 25-30℃, and the traction speed to 3-5m / min, and obtain a biodegradable heat-sealable film with a thickness of 20-50μm by casting.

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