A fully biodegradable plastic-grass composite material and a preparation method thereof

Abstract

The application discloses a kind of full biodegradable straw-plastic composite material and preparation method thereof.Full biodegradable straw-plastic composite material is composed of the following components by mass percentage: straw fiber 80-95% carbon dioxide-based polyester-polycarbonate staple fiber (PPC-P) 5-20%.The application finds through a large number of experiments that because there is physical cross between straw fiber and PPC-P fiber, so processing does not need to add compatilizer and coupling agent, and the use amount of PPC-P fiber can be greatly reduced, only 5%-20% of the use amount, thereby greatly reducing the cost of wood-plastic composite material.The resin used in the application is degradable carbon dioxide-based-polycarbonate, so that the composite material has full biodegradability.Carbon dioxide-based-polycarbonate is prepared from carbon dioxide, and the application reduces carbon dioxide emission.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high polymer composite materials, in particular to a full-fiber biodegradable straw-plastic composite material and a preparation method thereof. BACKGROUND

[0002] The straw-plastic composite material is a kind of fiber-like high-filled composite material obtained by compounding and modifying rice straw, straw, reed and other herbaceous plants and polyethylene, polypropylene, polyvinyl chloride and other thermoplastic resins through special mixing equipment. As a new type of wood-like material, the straw-plastic composite material combines the dual characteristics of plant fibers and synthetic resins, and has the excellent performance of wood and plastic, while overcoming some inherent shortcomings of wood and plastic. Developing the straw-plastic composite material industry can improve the utilization rate of agricultural and forestry solid waste. The straw-plastic composite material has a wide range of raw material sources and excellent performance. Compared with wood-plastic composite materials, the straw-plastic composite material has lower production cost and has the significance of turning waste into treasure. Using waste straw to prepare "straw-plastic" composite material can also solve the problem of large-scale burning of crop straw and turn waste into treasure.

[0003] However, the thermoplastic resins currently used are not biodegradable, so the disposal of the prepared straw-plastic composite material after the use cycle will have a great impact on the environment. Therefore, it is urgent to find a biodegradable thermoplastic resin to make straw-plastic composite material. Currently, the plant fibers or powders used in wood-plastic composite materials or straw-plastic composite materials mostly need to be chemically treated, and then mixed with synthetic resins through slurry mixing or melt co-extrusion process to prepare, which has the disadvantages of low efficiency, high energy consumption and large pollution.

[0004] A carbon dioxide-based polyester-polycarbonate (PPC-P) prepared by copolymerization of phthalic anhydride, propylene oxide and carbon dioxide (Chinese patent CN 111378101 A, J.CO2 Util.2021, 49, 101558) has complete biodegradability, and because the raw material uses low-cost phthalic anhydride, it realizes the production of low-cost biodegradable plastics. PPC-P has good light transmission performance, high barrier property, and the mechanical strength can reach 37MPa, and its Tg is 40-55℃, which is much higher than the Tg (30-40℃) of polymethyl ethylene carbonate (PPC), and has a wide range of applications.

[0005] Most of the synthetic resins in the related patents of the composite material prepared from straw fibers and synthetic resins on the market are provided in the form of granules. In order to achieve uniform mixing with straw, most patents process the straw into lignin or break it into powder for processing. This method cannot preserve the characteristics of straw. The straw-plastic composite material on the market is blended with resin and straw first, so it is easy to have voids and cavities after hot pressing, and a large amount of resin is needed, which has a high cost.

[0006] Common wood-plastic composites currently on the market often contain a high proportion of resin. For example, patent CN104212138A, "High-flowability Polylactic Acid-Based Wood-Plastic Injection Composite Material and Preparation Method thereof," uses 10-60 parts poplar fiber and 30-80 parts polylactic acid. However, the high resin content and high price of polylactic acid in the composite material increase the cost of the wood-plastic composite, limiting its application. Summary of the Invention

[0007] The present invention aims to overcome the shortcomings of existing technologies and provide a fully biodegradable straw-plastic composite material. This invention, for the first time, utilizes PPC-P fibers mixed with untreated straw fibers, reducing the amount of PPC-P resin required to less than 20%. PPC-P is a fully biodegradable, low-cost material, significantly reducing the overall cost of the straw-plastic composite material. This contributes to its widespread application and addresses the challenge of disposing of discarded straw in rural areas.

[0008] In order to achieve the above object, the present invention adopts the following scheme:

[0009] A fully biodegradable plastic composite material, consisting of the following components in percentage by mass:

[0010] Straw fiber 80-95%

[0011] Carbon dioxide based polyester-polycarbonate staple fiber (PPC-P) 5-20%.

[0012] Preferably, in the above-mentioned fully biodegradable plastic composite material, the carbon dioxide-based polyester-polycarbonate is a polymer copolymer obtained by terpolymerization of carbon dioxide, propylene oxide and phthalic anhydride, and has a number average molecular weight of 30,000-150,000; its structure is shown in formula (1); wherein m≥1, n≥1, k≥0, and m, n, and k are all integers;

[0013]

[0014] Preferably, in the above-mentioned fully biodegradable straw-plastic composite material, the straw fiber is straw fiber obtained by physically crushing wheat straw, corn straw or rice straw.

[0015] The method for preparing the above-mentioned fully biodegradable grass-plastic composite material comprises the following steps:

[0016] (1) Processing carbon dioxide-based polyester-polycarbonate into fibers through a spinning process, and cutting into PPC-P short fibers;

[0017] (2) drying the straw fibers and breaking them into short fibers;

[0018] (3) mixing the crushed straw fiber and PPC-P short fiber through a fiber mixer;

[0019] (4) placing the mixed straw fiber and PPC-P short fiber mixture into a mold for pre-pressing to obtain a pre-pressed sheet;

[0020] (5) The pre-pressed sheet is hot-pressed, and the PPC-P short fibers melt to bond the straw fibers together, and then a straw-plastic composite material is obtained by cooling.

[0021] Preferably, in the above-mentioned method for preparing the fully biodegradable grass-plastic composite material, the length of the PPC-P short fibers in step (1) is 10-20 mm, and the diameter of the PPC-P short fibers is 2-10 μm.

[0022] Preferably, in the above-mentioned method for preparing the fully biodegradable straw-plastic composite material, the drying in step (2) is vacuum drying, the vacuum drying temperature is 60-110° C., and the vacuum drying time is 3-12 h; the length of the crushed straw fibers is 1-20 mm.

[0023] Preferably, in the above-mentioned method for preparing the fully biodegradable grass-plastic composite material, the pre-pressing temperature in step (4) is 25-40°C.

[0024] Preferably, in the above-mentioned method for preparing the fully biodegradable grass-plastic composite material, the hot pressing temperature in step (5) is 150-200° C., the hot pressing time is 1-15 min, and the pressure is 1-10 MPa.

[0025] Compared with the existing technology, the present invention has the following beneficial effects:

[0026] (1) Most current wood-plastic materials use non-degradable resins such as polyethylene, polypropylene, and polyvinyl chloride. These resins are used to prepare most wood-plastic materials. Compatibilizers and coupling agents are required during processing, which increases costs. However, after extensive experiments, the present invention found that because there is a physical cross-link between straw fibers and PPC-P fibers, no compatibilizers or coupling agents are required during processing. Furthermore, the amount of PPC-P fibers used can be significantly reduced, requiring only 5% to 20%, thereby significantly reducing the cost of wood-plastic composite materials. Therefore, PPC-P fibers can be mixed with untreated straw fibers to prepare high-performance and inexpensive wood-plastic materials.

[0027] (2) The resin used in the present invention is a degradable carbon dioxide-based polycarbonate, making the composite material fully biodegradable. Carbon dioxide-based polycarbonate is prepared from carbon dioxide, and the present invention reduces carbon dioxide emissions.

[0028] (3) The present application uses a large amount of wheat straw, corn straw or rice straw, and turns waste into treasure.

[0029] (4) The current plastic material uses a double screw extruder to blend and process the raw materials, and the loss of the raw materials is large, and the present application does not need to blend the raw materials, and improves the processing efficiency.

[0030] (5) The straw plastic composite material prepared by the present application is waterproof and moistureproof, and fundamentally solves the problem that wooden products are easily rotted, expanded and deformed after absorbing water in a humid and water-rich environment, and can be used in environments where traditional wooden products cannot be applied.

[0031] (6) The present application does not need to chemically treat the straw during the preparation process, and does not produce any chemical acid and alkali waste liquid, and is friendly to the environment.

[0032] (7) The straw plastic composite material prepared by the present application has good color and no odor, has good mechanical properties, and can be used in outdoor products, packaging boxes, disposable products and other fields. DETAILED DESCRIPTION

[0033] Example 1

[0034] First, 80% of the mass percentage of the straw is crushed into 1-20mm length of straw short fibers, the straw short fibers are put into a hot press under the condition of no heating for 5-10min to flatten, and the pores and voids existing in the straw are excluded, then 20% of the mass percentage of the PPC-P fiber is cut into 1-20mm short fibers, then the straw short fibers and the PPC-P short fibers are mixed uniformly by a fiber mixing machine, because the Tg of PPC-P is 40-55℃, in order to prevent the PPC-P short fibers from curling or melting during the preheating process, thereby affecting the mixing of the two, so the mixture is covered with two layers of polyamide film on the top and bottom, and then put into the hot press version without preheating and directly hot pressed at 150-200℃, after hot pressing and cooling, the straw PPC-P straw plastic composite material is prepared. The tensile strength of the composite material is 60Mpa, the elongation at break is 83.5%, and the 24h water absorption rate is 3.8%.

[0035] Example 2

[0036] First, 85% by mass of straw was crushed into short straw fibers of 1-20 mm in length. The short straw fibers were then flattened in a hot press for 5-10 minutes without heating to remove any holes or voids in the straw. Then, 15% by mass of polypropylene (PPC)-polypropylene (PPC-P) fibers were sheared into short fibers of 1-20 mm in length. The straw and PPC-P short fibers were then mixed uniformly in a fiber mixer. Because the Tg of PPC-P is 40-55°C, to prevent curling or melting of the PPC-P short fibers during preheating, which would affect the mixing of the two, the mixture was covered with two layers of polyamide film and then placed in a hot press platen without preheating. Hot pressing was performed at 150-200°C, followed by cooling to produce a straw-PPC-polypropylene (PPC-P) plastic composite. The composite had a tensile strength of 68 MPa, an elongation at break of 87.2%, and a 24-hour water absorption rate of 4.3%.

[0037] Example 3

[0038] First, 90% by mass of straw was crushed into short straw fibers of 1-20 mm in length. The short straw fibers were then flattened in a hot press for 5-10 minutes without heating to remove any holes or voids in the straw. Then, 10% by mass of polypropylene (PPC)-polypropylene (PPC-P) fibers were sheared into short fibers of 1-20 mm in length. The straw and PPC-P short fibers were then mixed uniformly in a fiber mixer. Because the Tg of PPC-P is 40-55°C, the mixture was covered with two layers of polyamide film on top and bottom to prevent curling or melting of the PPC-P short fibers during preheating, which would affect the mixing of the two. The mixture was then placed on the hot press platen without preheating and hot-pressed at 150-200°C. After hot pressing, the mixture was cooled to produce a straw-PPC-P plastic composite. The composite exhibited a tensile strength of 73 MPa, an elongation at break of 89.1%, and a 24-hour water absorption rate of 4.7%.

[0039] Example 4

[0040] First, 95% by mass of straw was crushed into short straw fibers of 1-20 mm in length. The short straw fibers were then flattened in a hot press for 5-10 minutes without heating to remove any holes or voids in the straw. Then, 5% by mass of polypropylene (PPC)-polypropylene (PPC-P) fibers were sheared into short fibers of 1-20 mm in length. The straw and PPC-P short fibers were then mixed uniformly in a fiber mixer. Because the Tg of PPC-P is 40-55°C, to prevent curling or melting of the PPC-P short fibers during preheating, which would affect the mixing of the two, the mixture was covered with two layers of polyamide film and then placed in a hot press platen without preheating. Hot pressing was performed at 150-200°C, followed by cooling to produce a straw-PPC-polypropylene (PPC-P) plastic composite. The composite had a tensile strength of 80 MPa, an elongation at break of 91.6%, and a 24-hour water absorption rate of 4.9%.

[0041] Comparative Example 1 (preheating step added based on Example 1, composite material performance decreased)

[0042] First, 80% by mass of straw is crushed into short straw fibers of 1-20 mm in length. The short straw fibers are then flattened in a hot press for 5-10 minutes without heating to remove any holes or voids in the straw. Then, 20% by mass of polypropylene (PPC)-polypropylene (PPC) fibers are sheared into short fibers of 1-20 mm in length. The short straw fibers and PPC-polypropylene (PPC) fibers are then mixed uniformly in a fiber mixer. The mixture is covered with two layers of polyamide film and placed in a hot press platen for preheating at 150-200°C. After preheating, the mixture is hot-pressed at 150-200°C and cooled to produce a straw-PPC-polypropylene (PPC-P) plastic composite material. The composite material has a tensile strength of 40 MPa, an elongation at break of 63%, and a 24-hour water absorption rate of 4.7%.

[0043] Comparative Example 2 (Straw Fiber and PPC-P Pellets)

[0044] 80 parts by mass of straw were crushed into short straw fibers with a length of 1-20 mm. The short straw fibers were flattened in a hot press for 5-10 minutes without heating to remove any holes or voids in the straw. 20 parts by mass of polypropylene polycarbonate (PPC) pellets were then vacuum dried at 80°C. The short straw fibers and PPC-P pellets were then mixed evenly. The mixture was covered with two layers of polyamide film and then placed in a hot press. The hot press plate was directly hot-pressed at 150-200°C without preheating, and cooled after hot pressing to produce a straw-PPC-P plastic composite material. The composite material had a tensile strength of 47 MPa, an elongation at break of 51.6%, and a 24-hour water absorption rate of 4.8%.

[0045] Comparative Example 3 (Straw powder and PPC-P short fibers)

[0046] 80 parts by mass of straw were crushed into straw powder, and 20 parts by mass of polypropylene (PPC)-polypropylene (PPC) fibers were sheared into short fibers of 1-20 mm in diameter. The straw powder and PPC-P short fibers were then mixed evenly. Because the Tg of PPC-P is 40-55°C, to prevent the PPC-P short fibers from curling or melting during the preheating process, which would affect the mixing of the two, the mixture was covered with two layers of polyamide film on top and bottom. The mixture was then placed in a hot press at 150-200°C without preheating and then cooled to produce a straw-PPC-P composite material. Observation of the composite revealed that the two materials did not fuse well during the hot pressing process, resulting in poor performance. The composite material exhibited a tensile strength of 58 MPa, an elongation at break of 61.2%, and a 24-hour water absorption rate of 5.3%.

[0047] Comparative Example 3 (straw fiber and polypropylene (PP) short fiber)

[0048] First, 80% by mass of straw is crushed into short fibers 1-20 mm in length. The short fibers are then flattened in a hot press for 5-10 minutes without heating to remove any holes or voids in the straw. Then, 20% by mass of polypropylene (PP) fibers are sheared into short fibers 1-20 mm in length. The short fibers and PP fibers are then mixed in a fiber mixer. The mixture is covered with two layers of polyamide film and then hot-pressed at 150-200°C on the hot press platen without preheating. After hot pressing, the mixture is cooled to produce a straw-PP-plastic composite material. The composite material has a tensile strength of 45 MPa, an elongation at break of 53.5%, and a 24-hour water absorption rate of 4.6%. This composite material is not biodegradable.

Claims

1. A fully biodegradable plastic composite material, characterized in that It is composed of the following components in percentage by mass: Straw fiber 80-95% CO2-based polyester-polycarbonate staple fibers 5-20%; The carbon dioxide-based polyester-polycarbonate is a high molecular weight copolymer obtained by terpolymerization of carbon dioxide, propylene oxide and phthalic anhydride, and has a number average molecular weight of 30,000-150,000; its structure is shown in formula (1); wherein m≥1, n≥1, k≥0, and m, n, and k are all integers; The preparation method comprises the following steps: (1) Processing carbon dioxide-based polyester-polycarbonate into fibers through a spinning process, and cutting into PPC-P short fibers; (2) drying the straw fibers and breaking them into short fibers; (3) mixing the crushed straw fiber and PPC-P short fiber through a fiber mixer; (4) placing the mixed straw fiber and PPC-P short fiber mixture into a mold for pre-pressing to obtain a pre-pressed sheet; (5) hot pressing the pre-pressed sheet, melting the PPC-P short fibers to bond the straw fibers together, and then cooling to obtain a straw-plastic composite material; In step (4), the pre-pressing temperature is 25-40°C.

2. The fully biodegradable plastic composite material according to claim 1, characterized in that The straw fibers are straw fibers obtained by physically crushing wheat straw, corn straw or rice straw.

3. The fully biodegradable grass-plastic composite material according to claim 1, characterized in that In step (1), the length of the PPC-P short fibers is 10-20 mm, and the diameter of the PPC-P short fibers is 2-10 μm.

4. The fully biodegradable grass-plastic composite material according to claim 1, characterized in that In step (2), the drying is vacuum drying, the vacuum drying temperature is 60-110° C., and the vacuum drying time is 3-12 h; the length of the crushed straw fibers is 1-20 mm.

5. The fully biodegradable grass-plastic composite material according to claim 1, characterized in that In step (5), the hot pressing temperature is 150-200° C., the hot pressing time is 1-15 min, and the pressure is 1-10 MPa.

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