Biodegradable plastic and preparation method thereof

Abstract

The invention discloses a biodegradable plastic and a preparation method thereof, belongs to the field of bioplastic preparation, and aims to solve the problem that the existing plastic is slow in degradation rate in a marine environment. The biodegradable plastic is prepared from the following components in percentage by weight: 50-80% of a biomass-based high polymer material; 10 to 35% of a degradable toughening agent; 1-5% of a photosensitizer; 2-10% of a microbial inducer; 1-5% of a processing aid; after the biomass degradable plastic is subjected to ultraviolet radiation for 7-15 days in a marine environment, initial cracks with the density being larger than or equal to 20 pieces / cm < 2 > appear on the surface, the initial cracks are broken into degradation units with the particle size being 5-20 mm after being subjected to mechanical impact of sea waves for 30-60 days, and the biological decomposition rate of the degradation units is larger than or equal to 90% within 6-12 months under the action of marine microorganisms; and no micro-plastic particles with the particle size of less than or equal to 1mm exist in the residual product. Through the synergistic effect of the photosensitizer and the microbial inducer, the degradation period in the marine environment is shortened, the degradation efficiency is improved, and the method is remarkably superior to the prior art.

Description

Technical Field

[0001] The present invention relates to the field of bioplastic preparation, and in particular to a biodegradable plastic and a preparation method thereof. Background Art

[0002] Plastics, as a polymeric synthetic material, are widely used in packaging, daily necessities, agriculture, fisheries, and other fields due to their lightweight, durable, low-cost, and easy processing properties. Traditional petroleum-based plastics, such as polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET), account for over 80% of this market. These plastics have a stable chemical structure and are difficult for microorganisms to decompose in the natural environment, with degradation cycles lasting decades to centuries. The resulting "white pollution" caused by large-scale waste has become a major challenge to global environmental governance.

[0003] The ocean, the largest garbage sink on Earth, receives more than 10 million tons of plastic waste each year, of which about 80% comes from land, such as coastal garbage and river wash, and 20% comes from marine activities such as fishing and maritime transportation. Among these marine plastic wastes, lightweight plastics such as plastic bags and plastic bottles account for more than 60%. They float on the sea surface or accumulate in the coastal zone for a long time under the influence of ocean currents. They not only directly threaten the survival of marine life such as turtles, whales, and seabirds through entanglement and accidental ingestion, but according to statistics, more than 1 million seabirds and 100,000 marine mammals die from plastic pollution every year worldwide, posing a potential risk to the ecosystem and human health.

[0004] To address the problem of plastic pollution, a variety of biodegradable plastics have been developed in existing technologies, such as polylactic acid (PLA), polybutylene adipate terephthalate (PBAT), and polycaprolactone (PCL). However, these materials have significant defects in the marine environment: First, degradation conditions are harsh, and most rely on industrial composting environments, such as high temperatures of 50-60°C and specific microbial communities. In the natural marine environment, with low temperatures, low salt levels, and low microbial diversity, the degradation rate is extremely slow, and may even be no different from traditional plastics. Second, they are prone to producing microplastics. Some materials only physically fragment under the impact of waves and cannot be completely decomposed by microorganisms, but instead accelerate the spread of microplastics. Third, the contradiction between performance and cost is prominent. If the focus is on improving marine degradability, they are prone to damage when used on land, such as insufficient water resistance and toughness. If the performance is enhanced, non-degradable ingredients need to be added, which goes against the original intention of environmental protection. Fourth, there is a lack of targeted design. Existing materials do not take into account special environmental factors such as strong ultraviolet rays, high salinity, and frequent mechanical impact in the ocean, making it difficult to achieve a dynamic balance of "stable use on land and rapid degradation in the ocean."

[0005] Therefore, developing a biodegradable material that can adapt to the marine environment and has high degradation efficiency has become the key to solving marine plastic pollution. Summary of the Invention

[0006] In order to overcome the above problems, the present invention aims to provide a biodegradable plastic and a preparation method, with the aim of solving the problem that current plastic products degrade slowly in the marine environment and pollute the ocean on a large scale.

[0007] To this end, the specific technical solutions adopted in the present invention are as follows:

[0008] According to one aspect of the present invention, there is provided a biodegradable plastic, which is made of the following components in percentage by weight:

[0009] Biomass-based polymer materials 50-80%;

[0010] Degradable toughening agent 10-35%;

[0011] Photosensitizer 1-5%;

[0012] Microbial inducer 2-10%;

[0013] Processing aids 1-5%;

[0014] After the biomass degradable plastic is exposed to ultraviolet radiation in the marine environment for 7-15 days, the surface of the biodegradable plastic will have a density of ≥20 / cm 2 The initial cracks in the plastic will break into degradation units with a particle size of 5-20 mm after 30-60 days of mechanical impact from waves. Under the action of marine microorganisms, the biodegradation rate of the degradation units is ≥90% within 6-12 months, and there are no microplastic particles with a particle size of ≤1 mm in the residual products.

[0015] Optionally, the biomass-based polymer material is a composite system, including 50-70 parts by weight of starch and 10-30 parts by weight of cellulose, wherein the starch is selected from at least two of corn starch, potato starch, and cassava starch and mixed in a ratio of 1:1-3:1, and the cellulose is alkali-treated straw cellulose with a degree of polymerization of 500-1000.

[0016] Optionally, the degradable toughening agent is a blend of polycaprolactone (PCL) and polybutylene succinate (PBS), with a weight ratio of 1:1-2:1, wherein the number average molecular weight of PCL is 80,000-150,000, and the melt index (190°C / 2.16kg) is 5-15g / 10min; the number average molecular weight of PBS is 100,000-200,000, and the melt index (190°C / 2.16kg) is 3-10g / 10min.

[0017] Optionally, the photosensitizer is a compound of anatase titanium dioxide (TiO2) and nano zinc oxide (ZnO) in a weight ratio of 3:1-5:1, wherein the TiO2 particle size is 200-300nm, the ZnO particle size is 100-200nm, and both are surface-modified with a silane coupling agent (KH550 or KH570), and the amount of the modifier is 2-5% of the total weight of the photosensitizer.

[0018] Optionally, the microbial inducer includes 60-80 parts by weight of trehalose and 20-40 parts by weight of chitosan oligosaccharide, wherein the trehalose is derived from brown algae extract, has a purity ≥98%, and a reducing sugar content ≤0.5%; the chitosan oligosaccharide has a molecular weight of 1000-5000Da, a deacetylation degree ≥90%, and has been verified by adaptive culture of marine Pseudomonas to promote the proliferation rate of such strains by 2-3 times.

[0019] Optionally, the processing aid is composed of the following components in parts by weight: 30-50 parts of lubricant, 20-40 parts of dispersant, and 10-30 parts of water resistance enhancer; the lubricant is a compound of calcium stearate and monoglyceride (weight ratio 2:1); the dispersant is polyethylene wax with a molecular weight of 2000-5000; the water resistance enhancer is sodium alginate with a viscosity (1% aqueous solution, 25°C) of 200-500 mPa·s.

[0020] A method for preparing biodegradable plastics, the method specifically comprising the following steps:

[0021] S1. Place the biomass-based polymer material in a hot air circulation dryer and dry it at 105-110°C for 3-4 hours, controlling the moisture content to ≤3%. Vacuum dry the degradable toughening agent at 80-90°C for 5-6 hours, with a vacuum degree of ≤-0.09MPa.

[0022] S2. Add the pretreated biomass-based polymer material, degradable toughening agent, photosensitizer, microbial inducer and processing aid into a high-speed mixer, and mix for 20-25 minutes at 70-75° C. and 800-1000 r / min to obtain a premix;

[0023] S3, adding the premix prepared in S2 to a twin-screw extruder, with the temperatures of the extruder zones being: 115-120° C. in zone 1, 125-130° C. in zone 2, 135-140° C. in zone 3, and 140-145° C. in zone 4, with a screw speed of 200-220 r / min and a feed rate of 6-7 kg / h, and pelletizing under water to obtain a degradation masterbatch with a particle size of 2.5-3 mm;

[0024] S4. The degradation masterbatch obtained in S3 is made into products through film blowing or injection molding process, wherein the die temperature during film blowing is 135-140° C., the traction ratio is 3.0-3.5, the injection pressure during injection molding is 90-100 MPa, the holding pressure is 60-70 MPa, and the cooling time is 18-22 seconds.

[0025] Optionally, in the blown film process, a continuous diamond grid pattern is pressed on the surface of the film by an embossing roller with a convex dot structure, wherein the diamond side length is 3-5 mm, the pattern depth is 0.2-0.3 mm, and circular pits with a diameter of 0.5-1 mm are formed at the intersection of the patterns, and the pit depth is 0.3-0.4 mm.

[0026] Optionally, in the injection molding process, for plastic bottle products, 3-4 circumferentially distributed easy-breaking marks are set at the connection between the bottle body and the bottle bottom. The easy-breaking marks are continuous serrated structures with a serration height of 0.1-0.15mm and a tooth pitch of 0.5-0.8mm. The wall thickness at the easy-breaking marks is 30-40% thinner than that of the adjacent areas.

[0027] Optionally, the product made of the biomass degradable plastic has a tensile strength ≥15 MPa and an elongation at break ≥200% under terrestrial conditions at 25°C and a relative humidity of 50-60%, and a weight loss rate ≤5% after being immersed in a 0.5% sodium chloride solution for 30 days, meeting the conventional use requirements of packaging or containers.

[0028] Compared with the existing technology, this application has the following beneficial effects:

[0029] The present invention adds anatase-type TiO2 and nano-ZnO to form a photosensitizer, which generates photogenerated electron-hole pairs under marine ultraviolet radiation, triggering a free radical chain reaction, destroying the plastic molecular chain structure, and causing initial cracks on the material surface. At the same time, the preparation process uses an embossing roller to press the diamond grid pattern and an injection molding easy-break mark design to significantly increase the material surface area and form stress concentration points. After mechanical impact from waves, the material breaks into small degradation units, increasing the crushing rate of the plastic in the marine environment, thereby facilitating rapid degradation.

[0030] While increasing the mechanical crushing rate, a microbial inducer is used to combine trehalose and chitosan oligosaccharides. Chitosan oligosaccharides can specifically promote the proliferation rate of strains such as marine Pseudomonas, and accelerate the oxidative decomposition of degradation units by activating the polysaccharide monooxygenase secreted by microorganisms, thereby further increasing the degradation rate of plastic products in the marine environment and improving the protection of the marine environment. Moreover, biomass-based polymer materials (corn starch, straw cellulose) and degradable toughening agents (PCL / PBS blends) are both biodegradable components, and the ester bonds in their molecular chains can be hydrolyzed by lipases secreted by microorganisms. Chitosan oligosaccharides, as a microbial carbon source, further promote the thoroughness of the decomposition process and avoid the residue problem caused by the addition of non-degradable components in traditional plastics.

[0031] Secondly, by optimizing the ratio of biomass-based polymer materials (50-70 parts by weight of starch + 10-30 parts by weight of cellulose) and degradable toughening agents (PCL / PBS weight ratio 1:1-2:1), the material can meet the impact and tear resistance requirements of plastic bags, plastic bottles and other products in terrestrial environments without affecting the use of plastic products on land.

[0032] In summary, the present invention improves materials, processes, and the structure of plastic products. Compared with traditional materials such as PLA and PBAT, which rely on industrial composting environments (50-60°C) for effective degradation and have a degradation cycle of several years or even decades in the marine environment, the present invention shortens the degradation cycle in the marine environment and improves the degradation efficiency through the synergistic effect of photosensitizers and microbial inducers, which is significantly superior to the existing technology. DETAILED DESCRIPTION

[0033] In order to help those skilled in the art better understand the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0034] Example 1

[0035] A biodegradable plastic is provided, which is made of the following components in percentage by weight:

[0036] Biomass-based polymer materials 50-80%;

[0037] Degradable toughening agent 10-35%;

[0038] Photosensitizer 1-5%;

[0039] Microbial inducer 2-10%;

[0040] Processing aids 1-5%;

[0041] After 7-15 days of ultraviolet radiation in the marine environment, biodegradable plastics will have a surface density of ≥20 / cm 2 The initial cracks in the plastic will break into degradation units with a particle size of 5-20 mm after 30-60 days of mechanical impact from waves. Under the action of marine microorganisms, the biodegradation rate of the degradation units is ≥90% within 6-12 months, and there are no microplastic particles with a particle size of ≤1 mm in the residual products.

[0042] The biomass-based polymer material is a composite system, including 50-70 parts by weight of starch and 10-30 parts by weight of cellulose, wherein the starch is selected from at least two of corn starch, potato starch, and cassava starch and mixed in a ratio of 1:1-3:1, and the cellulose is alkali-treated straw cellulose with a degree of polymerization of 500-1000.

[0043] The biodegradable toughening agent is a blend of polycaprolactone (PCL) and polybutylene succinate (PBS), with a weight ratio of 1:1-2:1. The number average molecular weight of PCL is 80,000-150,000, and the melt index (190°C / 2.16kg) is 5-15g / 10min; the number average molecular weight of PBS is 100,000-200,000, and the melt index (190°C / 2.16kg) is 3-10g / 10min.

[0044] The photosensitizer is a compound of anatase titanium dioxide (TiO2) and nano zinc oxide (ZnO) in a weight ratio of 3:1-5:1, wherein the TiO2 particle size is 200-300nm, the ZnO particle size is 100-200nm, and both are surface-modified with a silane coupling agent (KH550 or KH570). The amount of the modifier is 2-5% of the total weight of the photosensitizer.

[0045] The microbial inducer includes 60-80 parts by weight of trehalose and 20-40 parts by weight of chitosan oligosaccharide. The trehalose is derived from brown algae extract, has a purity of ≥98%, and a reducing sugar content of ≤0.5%. The chitosan oligosaccharide has a molecular weight of 1000-5000Da and a deacetylation degree of ≥90%. It has been verified by adaptive culture of marine Pseudomonas that it can promote the proliferation rate of this type of strain by 2-3 times.

[0046] The processing aid is composed of the following components in parts by weight: 30-50 parts of a lubricant, 20-40 parts of a dispersant, and 10-30 parts of a water resistance enhancer; the lubricant is a compound of calcium stearate and monoglyceride (weight ratio 2:1); the dispersant is polyethylene wax with a molecular weight of 2000-5000; and the water resistance enhancer is sodium alginate with a viscosity (1% aqueous solution, 25°C) of 200-500 mPa·s.

[0047] A method for preparing biodegradable plastics, the method specifically comprising the following steps:

[0048] S1. Place the biomass-based polymer material in a hot air circulation dryer and dry it at 105-110°C for 3-4 hours, controlling the moisture content to ≤3%. Vacuum dry the degradable toughening agent at 80-90°C for 5-6 hours, with a vacuum degree of ≤-0.09MPa.

[0049] S2. Add the pretreated biomass-based polymer material, degradable toughening agent, photosensitizer, microbial inducer and processing aid into a high-speed mixer, and mix for 20-25 minutes at 70-75° C. and 800-1000 r / min to obtain a premix;

[0050] S3, adding the premix prepared in S2 to a twin-screw extruder, with the temperatures of the extruder zones being: 115-120° C. in zone 1, 125-130° C. in zone 2, 135-140° C. in zone 3, and 140-145° C. in zone 4, with a screw speed of 200-220 r / min and a feed rate of 6-7 kg / h, and pelletizing under water to obtain a degradation masterbatch with a particle size of 2.5-3 mm;

[0051] S4. The degradation masterbatch obtained in S3 is made into products through film blowing or injection molding process, wherein the die temperature during film blowing is 135-140° C., the traction ratio is 3.0-3.5, the injection pressure during injection molding is 90-100 MPa, the holding pressure is 60-70 MPa, and the cooling time is 18-22 seconds.

[0052] In the blown film process, a continuous diamond grid pattern is pressed on the film surface by an embossing roller with a convex dot structure. The diamond side length is 3-5mm, the pattern depth is 0.2-0.3mm, and circular pits with a diameter of 0.5-1mm are formed at the intersection of the patterns, and the pit depth is 0.3-0.4mm.

[0053] In the injection molding process, for plastic bottle products, 3-4 circumferentially distributed easy-breaking marks are set at the connection between the bottle body and the bottle bottom. The easy-breaking marks are continuous serrated structures with a serration height of 0.1-0.15mm and a tooth pitch of 0.5-0.8mm. The wall thickness at the easy-breaking marks is 30-40% thinner than that of the adjacent areas.

[0054] Products made of biomass-degradable plastics have a tensile strength of ≥15MPa and an elongation at break of ≥200% under terrestrial conditions at 25°C and a relative humidity of 50-60%. After being immersed in a 0.5% sodium chloride solution for 30 days, the weight loss rate is ≤5%, meeting the normal use requirements of packaging or containers.

[0055] Example 2

[0056] A biodegradable plastic bag is made of the following components in percentage by weight:

[0057] Corn starch 60%;

[0058] Potato starch 10%;

[0059] PCL (number average molecular weight 120,000) 15%;

[0060] PBS (number average molecular weight 150,000) 10%;

[0061] Anatase TiO2 (200nm) 2.5%;

[0062] Nano ZnO (150nm) 0.5%;

[0063] Trehalose (brown algae extract) 6%;

[0064] Chitosan oligosaccharide (molecular weight 3000Da) 2%;

[0065] Calcium stearate 1%;

[0066] Monoglyceride 0.5%;

[0067] Polyethylene wax 1%;

[0068] Sodium alginate 1%;

[0069] A method for preparing a biodegradable plastic bag, the method specifically comprising the following steps:

[0070] S1, drying corn starch and potato starch at 105 ° C for 3.5 hours, reducing the moisture content to 2.8%;

[0071] S2, PCL, and PBS were dried under vacuum at 85 °C for 5 h;

[0072] S3. All raw materials were mixed at high speed at 70°C for 22 minutes. The temperatures of each zone of the twin-screw extruder were adjusted to 118°C, 128°C, 138°C, and 142°C, respectively, and the screw speed was 210 r / min. Granulation was performed to obtain masterbatch.

[0073] S4, film blowing process: die head temperature 138 ° C, blow-up ratio 3.2, diamond grid pattern (side length 4 mm, depth 0.25 mm, intersection circular pit diameter 0.8 mm, depth 0.35 mm) was pressed by embossing roller to produce a film with a thickness of 0.03 mm.

[0074] Test Example 1

[0075] Test method:

[0076] The plastic bag samples (5 cm×5 cm) prepared in Example 2 were hung in the offshore area (water depth 5 m, salinity 32‰, water temperature 18-22° C.), and samples were taken for testing every 30 days.

[0077] Comparison samples: ordinary PE plastic bags and PLA degradable plastic bags available on the market.

[0078] Test results:

[0079] As shown in Table 1:

[0080] Table 1: Test results of Example 2

[0081]

[0082] in conclusion:

[0083] Example 2: Dense cracks appeared on the surface after 60 days, and it broke into 5-15 mm fragments after 90 days. The edges of the fragments were blurred after 180 days, and only a small amount of fibrous residue remained after 360 days. No microplastics were detected (no particles ≤1 mm were seen under the scanning electron microscope).

[0084] PE: No obvious changes, only a small amount of algae attached to the surface.

[0085] PLA: After 90 days, the edges became slightly brittle, but the overall structure remained intact. A small amount of cracks appeared after 180 days.

[0086] Example 3

[0087] A biodegradable plastic bottle is made of the following components in percentage by weight:

[0088] Corn starch 50%;

[0089] Straw cellulose (DP 700, alkali treated) 20%;

[0090] PCL (number average molecular weight 100,000) 12%;

[0091] PBS (number average molecular weight 150,000) 8%;

[0092] Anatase TiO2 (250 nm, KH570 modified) 2%;

[0093] Nano ZnO (150 nm, KH550 modified) 1%;

[0094] Trehalose (brown algae extract, purity 99%) 4%;

[0095] Chitosan oligosaccharide (molecular weight 2000Da, degree of deacetylation 92%) 2%;

[0096] Calcium stearate 0.5%;

[0097] Polyethylene wax 0.5%;

[0098] Sodium alginate (viscosity 300 mPa·s) 1%;

[0099] A method for preparing a biodegradable plastic bottle, the method specifically comprising the following steps:

[0100] S1. After mixing straw cellulose and corn starch, dry them in hot air at 105°C for 4 hours (moisture content ≤ 3%);

[0101] S2, PCL, and PBS were vacuum dried at 85 °C for 5 h (vacuum degree −0.095 MPa);

[0102] S3. All raw materials were mixed at 75°C and 1000 r / min for 25 minutes. The temperatures of each zone of the twin-screw extruder were: 115°C (zone 1), 125°C (zone 2), 135°C (zone 3), and 140°C (zone 4). The screw speed was 210 r / min. Granulation was performed to obtain masterbatch with a diameter of 3 mm.

[0103] S4. Injection molding of a 500 ml plastic bottle: injection pressure 90 MPa, holding pressure 60 MPa, cooling time 20 seconds; four circumferential serrated break marks (serration height 0.1 mm, tooth pitch 0.7 mm, wall thickness 35% thinner than adjacent areas) are provided at the connection between the bottle body and the bottle bottom.

[0104] Test Example 2

[0105] Test purpose: To verify the degradation rate, morphological changes and microplastic production of plastic bottles in the marine environment.

[0106] Test method:

[0107] Sample: Plastic bottle prepared in Example 2 (cut into 5 cm × 5 cm sheets, 3 replicates per group);

[0108] Control samples: commercially available PE plastic bottle sheets, commercially available PBAT / PLA composite plastic bottle sheets;

[0109] Test environment: Sanya offshore (water depth 3m, salinity 33‰, water temperature 25-28℃, UV radiation intensity 40-60W / m 2 ), samples are hung on floating racks and samples are taken for testing every 30 days.

[0110] Test results:

[0111] As shown in Table 2

[0112] Table 2: Test results of Example 3

[0113]

[0114] Conclusion of Example 3:

[0115] 60 days: Cracks along the break marks appear on the surface, and the connection between the bottle body and the bottom begins to separate;

[0116] 120 days: fragmented into 10-20 mm fragments with fuzzy edges (scanning electron microscopy showed microbial attachment);

[0117] 270 days: The fragments degrade into 5-8mm flocculent residues without sharp edges;

[0118] 360 days: Only a small amount of fibrous residue remains, which can pass through a 20-mesh sieve (pore size 0.85 mm).

[0119] PE control: No significant changes were observed over 360 days, with only algae attached to the surface.

[0120] PBAT / PLA control: cracks appeared after 180 days and broke into 1-3 mm hard particles after 360 days (not completely degraded).

[0121] Table 3: Microplastics detection (particle content ≤ 1mm, mg / g residue)

[0122] time Example 3 PE control PBAT / PLA control 180 Not detected 35.6 18.2 360 Not detected 62.8 25.7

[0123] Microbial community analysis (bacteria attached to sample surface)

[0124] Example 3: After 30 days, the proportion of Pseudomonas reached 38% (initial 12%), which can secrete esterase to degrade polyester chains;

[0125] PBAT / PLA control: Pseudomonas accounted for only 22%, and degradation-resistant bacteria (such as Bacillus) appeared.

[0126] The plastic bottle of Example 3 loses 98.7% of its weight in a marine environment over 360 days, leaving no residual microplastics, which is significantly better than the control. The easy-break design accelerates the fragmentation process, meeting the degradation requirements of ocean wave impact.

[0127] Although the present invention has been disclosed above with reference to preferred embodiments, the embodiments are merely examples for the purpose of illustration and are not intended to limit the present invention. Those skilled in the art may make various modifications and alterations without departing from the spirit and scope of the present invention. The scope of protection claimed by the present invention shall be subject to the claims.

Claims

1. A biodegradable plastic, characterized in that: Made of the following components in weight percentage: Biomass-based polymer materials 50-80%; Degradable toughening agent 10-35%; Photosensitizer 1-5%; Microbial inducer 2-10%; Processing aids 1-5%; After the biomass degradable plastic is exposed to ultraviolet radiation in the marine environment for 7-15 days, the surface of the biodegradable plastic will have a density of ≥20 / cm 2 The initial cracks in the plastic will break into degradation units with a particle size of 5-20 mm after 30-60 days of mechanical impact from waves. Under the action of marine microorganisms, the biodegradation rate of the degradation units is ≥90% within 6-12 months, and there are no microplastic particles with a particle size of ≤1 mm in the residual products.

2. The biodegradable plastic according to claim 1, characterized in that The biomass-based polymer material is a composite system, including 50-70 parts by weight of starch and 10-30 parts by weight of cellulose, wherein the starch is selected from at least two of corn starch, potato starch, and cassava starch and mixed in a ratio of 1:1-3:1, and the cellulose is alkali-treated straw cellulose with a degree of polymerization of 500-1000.

3. The biodegradable plastic according to claim 1, characterized in that The degradable toughening agent is a blend of polycaprolactone (PCL) and polybutylene succinate (PBS), with a weight ratio of 1:1-2:

1. The number average molecular weight of PCL is 80,000-150,000, and the melt index (190°C / 2.16kg) is 5-15g / 10min; the number average molecular weight of PBS is 100,000-200,000, and the melt index (190°C / 2.16kg) is 3-10g / 10min.

4. The biodegradable plastic according to claim 1, characterized in that The photosensitizer is a compound of anatase titanium dioxide (TiO2) and nano zinc oxide (ZnO) in a weight ratio of 3:1-5:1, wherein the TiO2 particle size is 200-300nm, the ZnO particle size is 100-200nm, and both are surface-modified with a silane coupling agent (KH550 or KH570), and the amount of the modifier used is 2-5% of the total weight of the photosensitizer.

5. The biodegradable plastic according to claim 1, characterized in that The microbial inducer includes 60-80 parts by weight of trehalose and 20-40 parts by weight of chitosan oligosaccharide. The trehalose is derived from brown algae extract, has a purity of ≥98%, and a reducing sugar content of ≤0.5%. The chitosan oligosaccharide has a molecular weight of 1000-5000Da and a deacetylation degree of ≥90%. It has been verified by adaptive culture of marine pseudomonas that it can promote the proliferation rate of this type of strain by 2-3 times.

6. The biodegradable plastic according to claim 1, characterized in that The processing aid is composed of the following components in parts by weight: 30-50 parts of a lubricant, 20-40 parts of a dispersant, and 10-30 parts of a water resistance enhancer; the lubricant is a compound of calcium stearate and monoglyceride (weight ratio 2:1); the dispersant is polyethylene wax with a molecular weight of 2000-5000; and the water resistance enhancer is sodium alginate with a viscosity (1% aqueous solution, 25°C) of 200-500 mPa·s.

7. The method for preparing the biodegradable plastic according to any one of claims 1 to 6, characterized in that: The method specifically comprises the following steps: S1. Place the biomass-based polymer material in a hot air circulation dryer and dry it at 105-110°C for 3-4 hours, controlling the moisture content to ≤3%. Vacuum dry the degradable toughening agent at 80-90°C for 5-6 hours, with a vacuum degree of ≤-0.09MPa. S2. Add the pretreated biomass-based polymer material, degradable toughening agent, photosensitizer, microbial inducer and processing aid into a high-speed mixer, and mix for 20-25 minutes at 70-75° C. and 800-1000 r / min to obtain a premix; S3, adding the premix prepared in S2 to a twin-screw extruder, with the temperatures of the extruder zones being: 115-120° C. in zone 1, 125-130° C. in zone 2, 135-140° C. in zone 3, and 140-145° C. in zone 4, with a screw speed of 200-220 r / min and a feed rate of 6-7 kg / h, and pelletizing under water to obtain a degradation masterbatch with a particle size of 2.5-3 mm; S4. The degradation masterbatch obtained in S3 is made into products through film blowing or injection molding process, wherein the die temperature during film blowing is 135-140° C., the traction ratio is 3.0-3.5, the injection pressure during injection molding is 90-100 MPa, the holding pressure is 60-70 MPa, and the cooling time is 18-22 seconds.

8. The method for preparing biodegradable plastic according to claim 7, characterized in that: In the blown film process, a continuous diamond grid pattern is pressed on the film surface by an embossing roller with a convex dot structure. The diamond side length is 3-5 mm, the pattern depth is 0.2-0.3 mm, and circular pits with a diameter of 0.5-1 mm are formed at the intersection of the patterns, and the pit depth is 0.3-0.4 mm.

9. The method for preparing biodegradable plastic according to claim 7, characterized in that: In the injection molding process, for plastic bottle products, 3-4 circumferentially distributed easy-breaking marks are set at the connection between the bottle body and the bottle bottom. The easy-breaking marks are continuous serrated structures with a serration height of 0.1-0.15 mm and a tooth pitch of 0.5-0.8 mm. The wall thickness at the easy-breaking marks is 30-40% thinner than that of the adjacent areas.

10. The method for preparing biodegradable plastic according to claim 7, characterized in that: The product made of the biomass degradable plastic has a tensile strength of ≥15 MPa and an elongation at break of ≥200% under terrestrial conditions at 25°C and a relative humidity of 50-60%, and a weight loss rate of ≤5% after being immersed in a 0.5% sodium chloride solution for 30 days, thus meeting the conventional use requirements of packaging or containers.

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