Gradient modified plant fiber-based full-biodegradable composite film and preparation method thereof

Abstract

The invention relates to the technical field of full-biodegradable films, and discloses a gradient modified plant fiber-based full-biodegradable composite film and a preparation method thereof.The preparation method comprises the following steps that 1, gradient modification of the surface of plant fiber powder is conducted, specifically, the plant fiber powder and a modifier are mixed, modification treatment is conducted for 1-8 h at the temperature of 80-150 DEG C, and then the plant fiber powder is obtained; after the reaction is finished, washing residues with distilled water until the residues are neutral, and then drying; step 2, master batch preparation: uniformly mixing the plant fiber powder modified in the step 1 with a biodegradable high polymer material, and preparing the master batch in a twin-screw machine; step 3, hot-pressing to form a film; and step 4, performing blow molding to form the film. According to the gradient modified plant fiber-based full-biodegradable composite film and the preparation method thereof, the modified plant fibers and the biodegradable high polymer material are blended, the plant fiber-based full-biodegradable composite film is prepared, the comprehensive performance of the film is excellent, and meanwhile the preparation process is low in cost and small in pollution.

Description

Technical Field

[0001] The invention relates to the technical field of biodegradable films, and in particular to a gradient-modified plant fiber-based fully biodegradable composite film and a preparation method thereof. Background Art

[0002] my country's agricultural production covers 300 million mu of land and consumes 2 million tons of land film every year, both of which are the highest in the world. Land film can increase temperature, retain moisture, prevent insects, suppress salt, suppress weeds, improve the crop growth environment, and thus increase crop yields. However, the white pollution problem caused by land film is becoming more and more prominent, and it may become a potential hidden danger affecting my country's regional food security. The main component of traditional land film is polyethylene, which is not biodegradable. Years of land film covering will accumulate a large amount of residual film in the soil, causing soil compaction, which in turn reduces crop yields. Therefore, it is urgent to solve agricultural land film pollution and develop fully biodegradable land film.

[0003] At present, fully biodegradable membranes are mainly made of biodegradable polymers such as PBAT, PLA, PHA, PCL, and PBS. However, these biodegradable polymers have disadvantages such as high cost and poor film coating performance in actual application. Plant fiber is abundant in my country, and it is used as a filler and composited with biodegradable polymers to reduce the cost of membrane materials. At present, plant fiber-based fully biodegradable membranes have problems such as uneven filler dispersion and poor mechanical properties of composite membranes during the preparation process. Therefore, developing an efficient strategy to improve the compatibility between plant fiber materials and biodegradable polymer materials is crucial for the production of low-cost, high-performance, green and degradable fully biodegradable composite membranes.

[0004] The purpose of the present invention is to provide a gradient modification method to adjust the surface properties of plant fiber powder, and to prepare a plant fiber-based fully biodegradable film with excellent mechanical properties by compounding it with a biodegradable polymer material, so as to solve the problem of poor compatibility between plant fiber raw materials and biodegradable polymer materials. The present invention uses a modifier to perform different degrees of surface treatment on plant fiber powder, effectively increasing the compatibility between plant fiber powder and biodegradable polymers, and improving the mechanical properties, barrier properties and degradation properties of the composite film. Summary of the invention

[0005] The purpose of the present invention is to provide a gradient modified plant fiber-based fully biodegradable composite film and a preparation method thereof. The modified plant fiber is blended with a biodegradable polymer to prepare a plant fiber-based fully biodegradable composite film. The film has excellent comprehensive performance, and the preparation process is low in cost and less in pollution.

[0006] To achieve the above object, the present invention provides a method for preparing a gradient modified plant fiber-based fully biodegradable composite film, comprising the following steps: Step 1, gradient modification of the surface of plant fiber powder: the plant fiber powder and the modifier are mixed, and the modification treatment is performed at 80-150° C. for 1-8 h. After the reaction is completed, the plant fiber after the reaction is washed with distilled water until it is neutral, and then dried; Step 2, masterbatch preparation: the modified plant fiber powder and the biodegradable polymer obtained in step 1 are mixed evenly to prepare masterbatch in a twin-screw machine; Step 3, hot pressing film forming: taking the master batch of plant fiber powder composite biodegradable polymer material in step 2, hot pressing at 130-180° C. and 1-25 MPa to obtain a composite film; Step 4, film blowing: take the masterbatch of plant fiber powder and biodegradable polymer in step 2, and blow it into film in a film blowing machine at 125-180°C.

[0007] Furthermore, the raw material of the plant fiber powder in step 1 is one or more of rice straw, corn straw, wheat straw, cotton straw, rape straw, tobacco stalk, corn cob, bamboo powder, wood powder, dead branches and leaves or sugarcane bagasse, and the particle size of the plant fiber powder is 500-2000 mesh.

[0008] Furthermore, in step 1, the modifier is one or more of sodium chlorite, acetic acid, formic acid, sodium hydroxide, sodium sulfite, DES, sodium hypochlorite, ionic liquid, sodium hydroxide / polyethylene glycol, and acetic acid / glycerol.

[0009] Furthermore, in step 1, the solid-liquid ratio of the plant fiber powder and the modifier is 1g:7-30ml.

[0010] Furthermore, the number of modification treatments in step 1 is 1-5 times, the drying temperature is 30-105° C., and the time is 8-96 hours.

[0011] Furthermore, in step 2, the plant fiber powder accounts for 30-70% of the total mass of the plant fiber powder and the biodegradable polymer.

[0012] Furthermore, in step 2, the biodegradable polymer material is one or more of PBAT, PHA, PLA, PCL, and PBS.

[0013] Furthermore, when preparing the masterbatch in step 2, the temperature of the twin-screw machine is set to 120-180°C.

[0014] The present invention also provides a gradient-modified plant fiber-based fully biodegradable composite film, which is prepared according to the above-mentioned preparation method.

[0015] The present invention also provides a gradient modified plant fiber-based fully biodegradable composite film for use in ground film, packaging film and vest bag.

[0016] The advantages and positive effects of the gradient modified plant fiber-based fully biodegradable composite film and the preparation method thereof described in the present invention are: 1. The present invention effectively improves the compatibility between plant fibers and biodegradable polymers through a low-cost gradient modification method. Under the condition of high plant fiber content, the composite film still maintains ideal mechanical properties. The prepared plant fiber-based biodegradable composite film can be used for ground film, packaging film, and vest bag.

[0017] 2. The present invention achieves regulation of plant fiber structure on a micrometer scale by modifying plant fibers. The production process is low in energy consumption and low in cost, and can realize industrial large-scale preparation.

[0018] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a macroscopic picture of the modified plant fiber in the embodiment of the present invention, A is the plant fiber powder before modification; B is the plant fiber powder after modification. DETAILED DESCRIPTION

[0020] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0021] Unless otherwise defined, technical or scientific terms used in the present invention shall have the common meanings understood by one having ordinary skills in the field to which the present invention belongs.

[0022] Unless otherwise defined, the instruments, equipment and reagents used in the present invention are conventionally commercially available.

[0023] Example 1 A gradient modified plant fiber-based biodegradable composite film, wherein the composite film material comprises 47 parts of PBAT, 3 parts of PLA and 50 parts of modified bamboo powder in terms of mass percentage. That is: (1) 50 parts by weight of modified bamboo powder; (2) PBAT 47 parts by weight; (3) PLA: 3 parts by weight.

[0024] The method for preparing a modified plant fiber-based fully biodegradable composite film comprises the following steps: 1. Gradient treatment method is used to obtain bamboo powder with structure control: Treat 500-2000 mesh bamboo powder with sodium hydroxide / sodium sulfite at a solid-liquid ratio (g / mL) of 1:20 at 80-150℃ for 1-2 h. After the reaction, wash with distilled water to neutrality and dry at 45-70℃ for 24 h.

[0025] 2. Take 50 parts of modified bamboo powder, 47 parts of PBAT and 3 parts of PLA particles and blend them through a twin-screw extruder to obtain a composite masterbatch. The processing parameters of the twin-screw extruder are as follows: the heating temperature is set to 130~175℃, the roller speed is set to 20~35r / min, and the number of times is 1-5 times.

[0026] 3. The composite masterbatch is hot pressed into a film in a hot press to obtain a modified plant fiber / PBAT / PLA composite film. The hot press processing parameters are as follows: the heating temperature is set to 140-170°C, the pressure is set to 1-25 MPa, the preheating time is set to the running time, and the running time is set to 1-5min.

[0027] 4. Blow the composite material masterbatch into film in a film blowing machine to obtain a modified plant fiber / PBAT / PLA composite film material. The processing parameters of the film blowing machine are as follows: the heating temperature is set to 125-180°C, and the preheating time is set to 35-60 minutes.

[0028] Example 2 A gradient modified plant fiber-based fully biodegradable composite film, wherein the composite film material comprises 47 parts of PBAT, 3 parts of PLA and 50 parts of modified bamboo powder in terms of mass percentage. That is: (1) 50 parts by weight of modified bamboo powder; (2) PBAT 47 parts by weight; (3) PLA: 3 parts by weight.

[0029] The method for preparing the modified plant fiber and the fully biodegradable composite film comprises the following steps: 1. Gradient treatment method is used to obtain bamboo powder with structure control: Treat 500-1000 mesh bamboo powder with sodium chlorite / acetic acid solution at a solid-liquid ratio (g / mL) of 1:25 at 80-150℃ for 3h-5h. After the reaction, wash with distilled water until neutral and dry at 45-70℃ for 8-48h.

[0030] The remaining steps are the same as those in Example 1.

[0031] Example 3 A gradient modified plant fiber-based fully biodegradable composite film, wherein the composite film material comprises 47 parts of PBAT, 50 parts of modified bamboo powder, and 3 parts of PLA in terms of mass percentage. That is: (1) 50 parts by weight of modified bamboo powder; (2) PBAT 47 parts by weight; (3) PLA: 3 parts by weight.

[0032] The method for preparing a modified plant fiber-based fully biodegradable composite film comprises the following steps: 1. Gradient treatment method is used to obtain bamboo powder with structure control: Treat 500-1000 mesh bamboo powder with acetic acid solution at a solid-liquid ratio (g / mL) of 1:15 at 110-130℃ for 6-8 h. After the reaction, wash with distilled water until neutral and dry at 45-70℃ for 8-48 h.

[0033] The remaining steps are the same as those in Example 1.

[0034] Comparative Example 1 A plant fiber-based fully biodegradable composite film, the composite film material comprises 50 parts of bamboo powder, 47 parts of PBAT, and 3 parts of PLA in terms of mass percentage. That is: (1) 50 parts by weight of bamboo powder; (2) PBAT 47 parts by weight; (3) PLA: 3 parts by weight.

[0035] The method for preparing a bamboo powder-based biodegradable composite film comprises the following steps: 1. Take 50 parts of dry bamboo powder, 47 parts of dry PBAT, and 3 parts of PLA, mix them evenly through a high-speed mixer, and then put them into a twin-screw to prepare masterbatch. Twin-screw processing parameters: temperature is 120-180℃.

[0036] 2. The composite masterbatch is hot pressed into film in a hot press to obtain a plant fiber-based fully biodegradable composite film material. The hot press processing parameters are as follows: the heating temperature is set to 130~180℃, the pressure is set to 1-25 MPa, the preheating time is set to the running time, and the running time is set to 1~5min.

[0037] 3. The composite material masterbatch is blown into film in a film blowing machine to obtain a plant fiber-based fully biodegradable composite film material. The processing parameters of the film blowing machine are as follows: the heating temperature is set to 125~180℃, and the preheating time is set to 35~60min.

[0038] Performance Testing The performance tests were conducted on the composite films obtained in Examples 1-3 and Comparative Example 1. The tensile strength, elastic modulus and elongation at break of the plant fiber-based fully biodegradable composite films are shown in Table 1.

[0039] Table 1

[0040] It can be seen from the test data in Table 1 that compared with the pure PBAT film, the tensile strength of the fully biodegradable composite film compounded with bamboo powder is reduced, but compared with Examples 1-3 and Comparative Example 1, the tensile strength of the modified plant fiber composite film is higher than that of the unmodified plant fiber fully biodegradable composite film, and compared with the pure PBAT film, the tensile strength of the modified plant fiber fully biodegradable composite film does not decrease significantly (maximum 16%). In addition, considering the high cost of biodegradable polymers, the modified plant fiber fully biodegradable composite film is preferred under the demand for cost reduction.

[0041] Compared with the pure PBAT film, the elastic modulus of the composite film prepared in Examples 1-3 is higher. Although the elastic modulus of the composite film prepared in Comparative Example 1 is better than that in Examples 1-3, the tensile strength and elongation at break of the composite film prepared in Comparative Example 1 are poor. Considering comprehensively, the modified plant fiber fully biodegradable composite film will be preferred. Compared with the pure PBAT film, the elongation at break of the modified plant fiber fully biodegradable composite film prepared in Examples 1-3 is reduced, but considering the cost, the modified plant fiber fully biodegradable composite film has better comprehensive performance.

[0042] Therefore, the present invention adopts the above-mentioned gradient modified plant fiber-based fully biodegradable composite film and its preparation method, blends the modified plant fiber with biodegradable polymer materials, and prepares a plant fiber-based fully biodegradable composite film. The composite film has excellent comprehensive performance, and the preparation process is low-cost and less polluting.

[0043] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for preparing a gradient modified plant fiber-based fully biodegradable composite film, characterized in that: The following steps are involved: Step 1, gradient modification of the plant fiber surface: the plant fiber powder and the modifier are mixed, and the modification treatment is performed at 80-150° C. for 1-8 h. After the reaction is completed, the plant fiber is washed with distilled water until it is neutral, and then dried; Step 2, masterbatch preparation: the modified plant fiber powder in step 1 and the biodegradable polymer material are mixed evenly to prepare masterbatch in a twin-screw machine; Step 3, hot pressing film forming: take the masterbatch in step 2, and hot press at 130-180°C and 1-25 MPa to obtain a composite film; Step 4, film blowing: Take the masterbatch in step 2 and blow it into a film in a film blowing machine at 125-180°C.

2. The preparation method according to claim 1, characterized in that: The raw material of the plant fiber powder in step 1 is one or more of rice straw, corn straw, wheat straw, cotton straw, rape straw, tobacco stalk, corn cob, bamboo powder, wood powder, dead branches and leaves or sugarcane bagasse, and the particle size of the plant fiber powder is 500-2000 mesh.

3. The preparation method according to claim 1, characterized in that: In step 1, the modifier is one or more of sodium chlorite, acetic acid, formic acid, sodium hydroxide, sodium sulfite, DES, sodium hypochlorite, ionic liquid, sodium hydroxide / polyethylene glycol, and acetic acid / glycerol.

4. The preparation method according to claim 1, characterized in that: In step 1, the solid-liquid ratio of the plant fiber powder and the modifier is 1g:7-30ml.

5. The preparation method according to claim 1, characterized in that: The conditions for drying the modified plant fiber in step 1 are a temperature of 30-105° C. and a time of 8-96 hours.

6. The preparation method according to claim 1, characterized in that: In step 2, the plant fiber powder accounts for 30-70% of the total mass of the plant fiber powder and the biodegradable polymer material.

7. The method for preparing a modified lignin composite film according to claim 1, characterized in that: In step 2, the biodegradable polymer material is one or more of PBAT, PHA, PLA, PCL, and PBS.

8. The preparation method according to claim 1, characterized in that: When preparing the masterbatch in step 2, the temperature of the twin-screw machine is set to 120-180°C.

9. A gradient modified plant fiber-based biodegradable composite film, characterized in that: The preparation method is obtained according to any one of claims 1 to 8.

10. Use of the gradient modified plant fiber-based biodegradable composite film according to claim 9 in ground film, packaging film, vest bag or cling film.

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