Biodegradable heat-sealable film and method for its production

Abstract

The application relates to a biodegradable heat-seal film and a preparation method thereof, and belongs to the technical field of heat-seal films. The biodegradable heat-seal film is prepared from the following raw materials in parts 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. The modified cassava powder is obtained by wet heat treatment and oxidation treatment of cassava starch, and the toughening fiber is prepared by explosion and purification treatment of plants as raw materials. The biodegradable heat-seal film is prepared through the synergistic effect of polylactic acid, modified cassava powder and plant-based toughening fiber in a specific ratio. The wet heat-oxidation double-modified cassava powder improves the compatibility with polylactic acid and the degradation performance. 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 prone to long fracture when being pulled.

Description

Technical Field

[0001] This invention belongs to the field of heat-sealing film technology, specifically relating to a biodegradable heat-sealing film and its preparation method. Background Technology

[0002] Heat-sealable film is a functional film material widely used in the packaging industry. Its core function is to achieve adhesion and sealing between materials through heating. It is commonly used in the packaging of food, pharmaceuticals, and daily chemical products.

[0003] Most existing biodegradable heat-sealing films are made of materials such as polylactic acid. However, they have poor tear resistance in actual use. Due to the lack of effective stress anchors inside the film, it is easy to tear easily once a small tear occurs, resulting in a long tear. This seriously affects the sealing performance and reliability of the packaging, thus limiting its promotion and application in the packaging field. Summary of the Invention

[0004] The purpose of this invention is to provide a biodegradable heat-sealing film and its preparation method in order to solve the above-mentioned problems.

[0005] The present invention achieves the above objectives through the following technical solutions:

[0006] This invention provides a biodegradable heat-sealing film, which 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.

[0007] 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.

[0008] As a further optimization of the present invention, 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.

[0009] As a further optimization of the present invention, the specific steps of the oxidation treatment are as follows: Deionized water and cassava starch are mixed and stirred to obtain starch slurry; the pH of the starch slurry is adjusted to 9.0-11.0 using sodium hydroxide; sodium hypochlorite is added dropwise to the starch slurry at 25-40℃; the mixture is stirred at 350 r / min for 1-2 h; after stirring, 5-10% dilute hydrochloric acid is added to adjust the pH to 6.5-7.0; sodium sulfite is added; and the mixture is stirred at 120 r / min for 15-25 min to obtain modified cassava starch slurry; the modified cassava starch slurry is washed with deionized water until neutral; dried at 40-50℃ and pulverized to obtain modified cassava flour.

[0010] As a further optimization of the present invention, 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.

[0011] As a further optimization of the present invention, 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.

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

[0013] (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.

[0014] (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.

[0015] As a further optimization of the present invention, the number average molecular weight of polylactic acid is 80,000-120,000; the length of the toughening fiber is 0.1-0.3 mm and the diameter is 5-15 μm.

[0016] This invention also provides a method for preparing a biodegradable heat-sealing film, comprising the following steps:

[0017] 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.

[0018] 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;

[0019] 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.

[0020] 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.

[0021] 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.

[0022] The beneficial effects of this invention are as follows: This invention utilizes a specific ratio of polylactic acid, modified cassava flour, and plant-based toughening fibers in a synergistic effect, combined with a proprietary preparation process, to produce a biodegradable heat-sealable film. The wet-heat-oxidation dual-modification of cassava flour enhances its compatibility with polylactic acid and its degradation performance. The addition of toughening fibers obtained from various plants through steam explosion and purification provides anchor points for the biodegradable heat-sealable film, making it less prone to long tears when stretched. Through drying, dry mixing, multi-stage melt blending, and casting, the components are evenly dispersed, resulting in a heat-sealable film with high heat-sealing strength, good sealing performance, and a 28-day biodegradation rate that meets standards. It combines good mechanical properties with complete biodegradability, making it a viable alternative to traditional non-degradable packaging films, demonstrating significant environmental value and promising application prospects. Detailed Implementation

[0023] The present application will now be described in further detail. It should be noted that the following specific embodiments are only used to further illustrate the present application and should not be construed as limiting the scope of protection of the present application. Those skilled in the art can make some non-essential improvements and adjustments to the present application based on the above application content.

[0024] Unless otherwise specified, all methods used in this invention are conventional methods known to those skilled in the art, and all reagents and materials used are commercially available products.

[0025] Example 1

[0026] Modified cassava flour is obtained from cassava starch through wet heat treatment and oxidation treatment;

[0027] The specific steps of the wet heat treatment are as follows: control the moisture content of the cassava starch to 15%, heat it at 70℃ for 5 hours, and after the treatment, adjust the moisture content of the cassava starch to 25% and heat it at 95℃ for 5 hours.

[0028] The specific steps of the oxidation treatment are as follows: Deionized water and cassava starch are mixed (the mass ratio of deionized water to cassava starch in the starch slurry is 1:0.15), and the mixture is stirred until a starch slurry is obtained. The pH of the starch slurry is adjusted to 9.0 using sodium hydroxide. Sodium hypochlorite is added dropwise to the starch slurry at 25℃, and the mixture is stirred at 350 r / min for 1 hour. After stirring, 5% dilute hydrochloric acid is added to adjust the pH to 6.5, and sodium sulfite is added. The mixture is stirred at 120 r / min for 15 minutes to obtain modified cassava starch slurry (the mass ratio of sodium hypochlorite, sodium sulfite, and starch slurry is 0.05:0.01:1). The modified cassava starch slurry is washed with deionized water until neutral, dried at 40℃, and pulverized to obtain modified cassava flour.

[0029] The toughening fiber is made from plant materials through blasting and purification processes.

[0030] Explosion pretreatment: Wash and dry 5 parts of Daphne odora branches, 35 parts of Phyllostachys edulis lateral branches, 6 parts of banana stems and 25 parts of wheat straw, cut them into 2cm sections, place them in a sealed autoclave, steam immersion and pressure holding at 180℃ and 1.0MPa for 6 minutes, instantaneous pressure release at 0.01 seconds and spray out, add 1 part of vitamin C and 2 parts of citric acid after cooling, let stand in the dark for 1 day to obtain the blasted coarse fiber material;

[0031] Purification: Add the coarse fiber material to a 50% ethanol aqueous solution at a material-to-liquid ratio of 1:10 (g:mL), reflux at 50℃ for 1.5h, repeat once, remove and wash with water 3 times, add 10 parts of sodium hypochlorite, stir at 220r / min for 1.5h, wash with water 3 times, filter out the fiber, and dry to obtain toughened fiber (the toughened fiber has a length of 0.1mm and a diameter of 5μm).

[0032] Raw material drying: Dry 50 parts of polylactic acid (number average molecular weight of polylactic acid is 80,000) in a vacuum drying oven at 85℃ for 8 hours and set aside; dry 6 parts of modified cassava flour and 5 parts of toughening fiber in a forced-air drying oven at 70℃ for 5 hours and set aside.

[0033] Dry mixing: Add the dried polylactic acid, modified cassava flour and toughening fiber to a high-speed mixer and dry mix at 850 rpm for 6 minutes to obtain the mixture;

[0034] Pre-mix preparation: Stir the mixture at 130 rpm, then add 4 parts stearic acid, 8 parts glycerin, and 0.5 parts sorbitol in sequence, stir for 8 minutes, and finally add 3 parts citric acid and continue stirring for 3 minutes to obtain the pre-mix.

[0035] 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℃, melt section 155℃, die head section 160℃. The screw speed is set to 200 rpm. The strip melt is extruded and granulated by a pelletizer to obtain heat-sealing film granules with a diameter of 2 mm and a length of 3 mm.

[0036] The granules were added to a cast film extruder, and the die head temperature was controlled at 160℃, the cooling roller temperature at 25℃, and the traction speed at 3m / min. A biodegradable heat-sealable film with a thickness of 20μm was produced by the casting method.

[0037] Example 2

[0038] Modified cassava flour is obtained from cassava starch through wet heat treatment and oxidation treatment;

[0039] The specific steps of the wet heat treatment are as follows: control the moisture content of the cassava starch to 25%, heat it at 100℃ for 6 hours, and after the treatment, adjust the moisture content of the cassava starch to 27% and heat it at 96℃ for 6 hours.

[0040] The specific steps of the oxidation treatment are as follows: Deionized water and cassava starch are mixed (the mass ratio of deionized water to cassava starch in the starch slurry is 1:0.15), and the mixture is stirred until a starch slurry is obtained. The pH of the starch slurry is adjusted to 10.0 using sodium hydroxide. Sodium hypochlorite is added dropwise to the starch slurry at 35℃, and the mixture is stirred at 350 r / min for 1.5 h. After stirring, 8% dilute hydrochloric acid is added to adjust the pH to 7.0, and sodium sulfite is added. The mixture is stirred at 120 r / min for 20 min to obtain modified cassava starch slurry (the mass ratio of sodium hypochlorite, sodium sulfite, and starch slurry is 0.06:0.02:1). The modified cassava starch slurry is washed with deionized water until neutral, dried at 45℃, and pulverized to obtain modified cassava flour.

[0041] The toughening fiber is made from plant materials through blasting and purification processes.

[0042] Explosion pretreatment: Wash and dry 8 parts of Daphne odora branches, 40 parts of Phyllostachys edulis lateral branches, 8 parts of banana stems and 27 parts of wheat straw, cut them into 3cm sections, place them in a sealed autoclave, steam immersion and pressure holding at 190℃ and 1.5MPa for 7 minutes, instantaneous pressure release at 0.01 seconds and spray out, add 3 parts of vitamin C and 4 parts of citric acid after cooling, let stand in the dark for 2 days to obtain blasted coarse fiber material;

[0043] Purification: The coarse fiber material was added to a 50% ethanol aqueous solution at a material-to-liquid ratio of 1:10 (g:mL), and extracted by reflux at 50℃ for 1.8h. This process was repeated twice. The extracted material was washed with water four times, and 12 parts of sodium hypochlorite were added. The mixture was stirred at 220r / min for 1.8h, washed with water four times, and the fiber was filtered out. After drying, toughened fiber (the toughened fiber has a length of 0.2mm and a diameter of 10μm) was obtained.

[0044] Raw material drying: 50 parts of polylactic acid (number average molecular weight of polylactic acid is 100,000) were dried in a vacuum drying oven at 90℃ for 9 hours and set aside; 8 parts of modified cassava flour and 7 parts of toughening fiber were dried in a forced-air drying oven at 75℃ for 5.5 hours and set aside.

[0045] Dry mixing: Add the dried polylactic acid, modified cassava flour and toughening fiber to a high-speed mixer and dry mix at 900 rpm for 7 minutes to obtain the mixture;

[0046] Pre-mix preparation: Stir the mixture at 140 rpm, then add 6 parts stearic acid, 14 parts glycerol and 1 part sorbitol in sequence, stir for 9 min, and finally add 4 parts citric acid and continue stirring for 4 min to obtain the pre-mix.

[0047] 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 150℃, melt section 160℃, die head section 165℃. The screw speed is set to 225 rpm. The strip melt is extruded and granulated by a pelletizer to obtain heat-sealing film granules with a diameter of 2 mm and a length of 3 mm.

[0048] The granules were added to a cast film extruder, and the die head temperature was controlled at 162℃, the cooling roller temperature at 28℃, and the traction speed at 4m / min. A biodegradable heat-sealable film with a thickness of 35μm was produced by the casting method.

[0049] Example 3

[0050] Modified cassava flour is obtained from cassava starch through wet heat treatment and oxidation treatment;

[0051] The specific steps of the wet heat treatment are as follows: control the moisture content of the cassava starch to 35%, heat it at 130℃ for 7 hours, and after the treatment, adjust the moisture content of the cassava starch to 30% and heat it at 100℃ for 8 hours.

[0052] The specific steps of the oxidation treatment are as follows: Deionized water and cassava starch are mixed (the mass ratio of deionized water to cassava starch in the starch slurry is 1:0.15), and the starch slurry is obtained after mixing. The pH of the starch slurry is adjusted to 11.0 using sodium hydroxide. Sodium hypochlorite is added dropwise to the starch slurry at 40℃ and stirred at 350 r / min for 2 hours. After stirring, 10% dilute hydrochloric acid is added to adjust the pH to 7.0, and sodium sulfite is added. The mixture is stirred at 120 r / min for 25 minutes to obtain modified cassava starch slurry (the mass ratio of sodium hypochlorite, sodium sulfite, and starch slurry is 0.08:0.03:1). The modified cassava starch slurry is washed with deionized water until neutral, dried at 50℃, and pulverized to obtain modified cassava flour.

[0053] The toughening fiber is made from plant materials through blasting and purification processes.

[0054] Explosion pretreatment: Wash and dry 10 parts of Daphne odora branches, 45 parts of Phyllostachys edulis lateral branches, 12 parts of banana stems and 30 parts of wheat straw, cut them into 4cm sections, place them in a sealed autoclave, steam-moisten and keep them under pressure for 8 minutes at 200℃ and 2.0MPa, release the pressure instantly in 0.01 seconds and spray them out. After cooling, add 5 parts of vitamin C and 6 parts of citric acid, and let them stand in the dark for 3 days to obtain the blasted coarse fiber material.

[0055] Purification: Add the coarse fiber material to a 50% ethanol aqueous solution at a material-to-liquid ratio of 1:10 (g:mL), reflux at 50℃ for 2 hours, repeat 3 times, wash with water 5 times, add 15 parts of sodium hypochlorite, stir at 220r / min for 2 hours, wash with water 5 times, filter out the fiber, and dry to obtain toughened fiber (the length of the toughened fiber is 0.3mm and the diameter is 15μm).

[0056] Raw material drying: 55 parts of polylactic acid (number average molecular weight of polylactic acid is 120,000) were dried in a vacuum drying oven at 95℃ for 10 hours and set aside; 12 parts of modified cassava flour and 12 parts of toughening fiber were dried in a forced-air drying oven at 80℃ for 6 hours and set aside.

[0057] Dry mixing: Add the dried polylactic acid, modified cassava flour and toughening fiber to a high-speed mixer and dry mix at 950 rpm for 8 minutes to obtain the mixture;

[0058] Pre-mix preparation: Stir the mixture at 150 rpm, then add 8 parts stearic acid, 18 parts glycerol, and 1.5 parts sorbitol in sequence, stir for 10 min, and finally add 5 parts citric acid and continue stirring for 5 min to obtain the pre-mix.

[0059] 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, namely: 155℃ for the feed section, 165℃ for the melt section, and 170℃ for the die head section. The screw speed is set to 250 rpm. The strip melt is extruded and granulated by a pelletizer to obtain heat-sealing film granules with a diameter of 3 mm and a length of 5 mm.

[0060] The granules were added to a cast film extruder, and the die head temperature was controlled at 165℃, the cooling roller temperature at 30℃, and the traction speed at 5m / min. A biodegradable heat-sealable film with a thickness of 50μm was produced by the casting method.

[0061] Comparative Example 1

[0062] Toughening fibers are made from plant materials through a process of blasting and purification.

[0063] Explosion pretreatment: Wash and dry 8 parts of Daphne odora branches, 40 parts of Phyllostachys edulis lateral branches, 8 parts of banana stems and 27 parts of wheat straw, cut them into 3cm sections, place them in a sealed autoclave, steam immersion and pressure holding at 190℃ and 1.5MPa for 7 minutes, instantaneous pressure release at 0.01 seconds and spray out, add 3 parts of vitamin C and 4 parts of citric acid after cooling, let stand in the dark for 2 days to obtain blasted coarse fiber material;

[0064] Purification: The coarse fiber material was added to a 50% ethanol aqueous solution at a material-to-liquid ratio of 1:10 (g:mL), and extracted by reflux at 50℃ for 1.8h. This process was repeated twice. The extracted material was washed with water four times, and 12 parts of sodium hypochlorite were added. The mixture was stirred at 220r / min for 1.8h, washed with water four times, and the fiber was filtered out. After drying, toughened fiber (the toughened fiber has a length of 0.2mm and a diameter of 10μm) was obtained.

[0065] Raw material drying: 58 parts of polylactic acid (number average molecular weight of polylactic acid is 100,000) were dried in a vacuum drying oven at 90℃ for 9 hours and set aside; 7 parts of toughening fiber were dried in a forced-air drying oven at 75℃ for 5.5 hours and set aside.

[0066] Dry mixing: Add the dried polylactic acid and toughening fibers to a high-speed mixer and dry mix at 900 rpm for 7 minutes to obtain a mixture;

[0067] Pre-mix preparation: Stir the mixture at 140 rpm, then add 6 parts stearic acid, 14 parts glycerol and 1 part sorbitol in sequence, stir for 9 min, and finally add 4 parts citric acid and continue stirring for 4 min to obtain the pre-mix.

[0068] 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 150℃, melt section 160℃, die head section 165℃. The screw speed is set to 225 rpm. The strip melt is extruded and granulated by a pelletizer to obtain heat-sealing film granules with a diameter of 2 mm and a length of 3 mm.

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

[0070] Comparative Example 2

[0071] Modified cassava flour is obtained from cassava starch through wet heat treatment and oxidation treatment;

[0072] The specific steps of the wet heat treatment are as follows: control the moisture content of the cassava starch to 25%, heat it at 100℃ for 6 hours, and after the treatment, adjust the moisture content of the cassava starch to 27% and heat it at 96℃ for 6 hours.

[0073] The specific steps of the oxidation treatment are as follows: Deionized water and cassava starch are mixed (the mass ratio of deionized water to cassava starch in the starch slurry is 1:0.15), and the mixture is stirred until a starch slurry is obtained. The pH of the starch slurry is adjusted to 10.0 using sodium hydroxide. Sodium hypochlorite is added dropwise to the starch slurry at 35℃, and the mixture is stirred at 350 r / min for 1.5 h. After stirring, 8% dilute hydrochloric acid is added to adjust the pH to 7.0, and sodium sulfite is added. The mixture is stirred at 120 r / min for 20 min to obtain modified cassava starch slurry (the mass ratio of sodium hypochlorite, sodium sulfite, and starch slurry is 0.06:0.02:1). The modified cassava starch slurry is washed with deionized water until neutral, dried at 45℃, and pulverized to obtain modified cassava flour.

[0074] Raw material drying: 57 parts of polylactic acid (number average molecular weight of polylactic acid is 100,000) were dried in a vacuum drying oven at 90℃ for 9 hours and set aside; 8 parts of modified cassava flour were dried in a forced-air drying oven at 75℃ for 5.5 hours and set aside.

[0075] Dry mixing: Add the dried polylactic acid and modified cassava flour to a high-speed mixer and dry mix at 900 rpm for 7 minutes to obtain the mixture;

[0076] Pre-mix preparation: Stir the mixture at 140 rpm, then add 6 parts stearic acid, 14 parts glycerol and 1 part sorbitol in sequence, stir for 9 min, and finally add 4 parts citric acid and continue stirring for 4 min to obtain the pre-mix.

[0077] 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 150℃, melt section 160℃, die head section 165℃. The screw speed is set to 225 rpm. The strip melt is extruded and granulated by a pelletizer to obtain heat-sealing film granules with a diameter of 2 mm and a length of 3 mm.

[0078] The granules were added to a cast film extruder, and the die head temperature was controlled at 162℃, the cooling roller temperature at 28℃, and the traction speed at 4m / min. A biodegradable heat-sealable film with a thickness of 35μm was produced by the casting method.

[0079] Comparative Example 3

[0080] Raw material drying: Dry 65 parts of polylactic acid (number average molecular weight of polylactic acid is 100,000) in a vacuum drying oven at 90℃ for 9 hours, and set aside for later use;

[0081] Dry mixing: Add the dried polylactic acid to a high-speed mixer and dry mix at 900 rpm for 7 minutes to obtain a mixture;

[0082] Pre-mix preparation: Stir the mixture at 140 rpm, then add 6 parts stearic acid, 14 parts glycerol and 1 part sorbitol in sequence, stir for 9 min, and finally add 4 parts citric acid and continue stirring for 4 min to obtain the pre-mix.

[0083] 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 150℃, melt section 160℃, die head section 165℃. The screw speed is set to 225 rpm. The strip melt is extruded and granulated by a pelletizer to obtain heat-sealing film granules with a diameter of 2 mm and a length of 3 mm.

[0084] The granules were added to a cast film extruder, and the die head temperature was controlled at 162℃, the cooling roller temperature at 28℃, and the traction speed at 4m / min. A biodegradable heat-sealable film with a thickness of 35μm was produced by the casting method.

[0085] Performance testing

[0086] (i) The performance of the biodegradable heat-sealing films prepared by the methods in Examples 1-3 and Comparative Examples 1-3 was tested according to the methods in QB / T2358 "Test Method for Heat Seal Strength of Plastic Film Packaging Bags";

[0087] Test conditions:

[0088] Sample dimensions: Width: 15mm, Length: 100mm;

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

[0090] Test: The tensile testing machine was used to peel the material at a speed of 300 mm / min, and the maximum force was recorded;

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

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

[0093] Table 1

[0094]

[0095] As shown in Table 1, the heat-sealing strength of the biodegradable heat-sealing films prepared in Examples 1-3 of this invention is not less than 1.8 N / 15 mm. The heat-sealing strength of Comparative Examples 1-2 is significantly lower than that of the Examples, indicating that this invention can effectively improve the heat-sealing strength of the biodegradable heat-sealing film, resulting in better sealing performance and meeting packaging requirements.

[0096] (ii) The biodegradable heat-sealing films prepared by the methods in Examples 1-3 and Comparative Examples 1-3 were tested according to the methods in GB / T19277.1 "Determination of the final aerobic biodegradability of materials under controlled composting conditions by measuring carbon dioxide released - Part 1: General method".

[0097] Test conditions:

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

[0099] Period: 28 days;

[0100] Principle: Measure the amount of CO2 released and calculate the biodegradation rate;

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

[0102] Table 2

[0103]

[0104] As shown in Table 2, the 28-day biodegradability of Examples 1-3 of the present invention meets the biodegradability requirements. The 28-day biodegradability of Comparative Examples 1-3 is less than 60%, which is significantly lower than that of the Examples, indicating that the biodegradable heat-sealing film prepared by the present invention has superior biodegradability under controlled composting conditions.

[0105] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

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; The specific steps of the wet heat treatment are as follows: control the moisture content of cassava starch to 15-35%, heat at 70-130℃ for 5-7 hours, and after the treatment, adjust the moisture content of cassava starch to 25-30% and heat at 95-100℃ for 5-8 hours. 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 350 r / min for 1-2 h; 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 120 r / min for 15-25 min 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.

2. The biodegradable heat-sealing film according to claim 1, 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.

3. 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.

4. The biodegradable heat-sealing film according to claim 3, 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.

5. The biodegradable heat-sealing film according to claim 4, 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.

6. A method for preparing a biodegradable heat-sealing film according to any one of claims 1-5, 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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