A biodegradable material of hemp powder

Abstract

This invention discloses a biodegradable hemp powder material, belonging to the field of bio-based biodegradable composite materials technology. The material, by mass percentage, consists of 50%–65% modified hemp powder, 25%–40% PLA / PBAT compounded biodegradable matrix, 3%–6% modified inorganic filler, 1%–3% chain extender, and 1%–3% composite additives, and is prepared via a solid-phase pre-crosslinking-stepped melt extrusion process. This invention solves the interfacial compatibility problem between hemp powder and the matrix through microfibrillation-silane grafting composite modification, achieving a material with excellent mechanical properties, barrier properties, and weather resistance even with high hemp powder filling. The degradation rate can be precisely controlled in soil and marine environments, and the bio-based content is ≥60%. It can be widely used in food packaging, disposable products, agricultural mulch films, and other fields.

Description

Technical Field

[0001] This invention belongs to the field of bio-based biodegradable composite materials technology, specifically relating to a hemp powder degradable material that can be widely used in food packaging, disposable tableware, agricultural mulch film, outdoor disposable products and other fields. Background Technology

[0002] With the advancement of environmental protection policies, the replacement of traditional petroleum-based plastics with bio-based biodegradable materials has become an inevitable trend in the industry. Hemp, a deciduous tree belonging to the Malvaceae family and the Hibiscus genus, is characterized by its short growth cycle, suitability for planting on marginal land, and high cellulose content. It is a high-quality renewable raw material for preparing bio-based composite materials. Using hemp powder in the preparation of biodegradable materials can not only achieve high-value utilization of hemp resources but also reduce the production cost of biodegradable materials.

[0003] Currently, the development of biodegradable materials based on hemp powder has been gradually carried out, but existing technologies still face many bottlenecks: First, hemp powder is rich in hydroxyl groups and has strong polarity, resulting in poor compatibility with hydrophobic degradable polyester matrices. When the hemp powder content exceeds 50%, the mechanical properties and water resistance of the material will drop sharply, failing to meet practical application requirements and limiting the high-value and large-scale application of hemp powder. Second, existing hemp powder degradable materials mostly use polylactic acid as a single matrix, resulting in high brittleness, poor low-temperature toughness, and uncontrollable degradation rates. They can only achieve degradation in soil composting environments, with extremely low degradation efficiency in natural water environments such as oceans and freshwater, limiting application scenarios. Third, existing materials lack a complete weather protection system, and are prone to rapid aging and significant degradation of mechanical properties under outdoor sunlight and high and low temperature cycling environments, failing to meet the needs of outdoor agricultural mulch films and outdoor disposable products. Fourth, with high hemp powder content, the material has poor melt processing fluidity, and problems such as melt fracture and surface defects of products are prone to occur during extrusion and injection molding, resulting in insufficient stability for large-scale production.

[0004] Based on this, developing a hemp powder degradable material that, despite having a high filler content, still possesses excellent mechanical properties, weather resistance, and processing stability, and can achieve controlled degradation in multiple environments, has significant economic and environmental value. Summary of the Invention

[0005] To address the shortcomings of existing hemp powder-based degradable materials, such as poor interfacial compatibility under high filling conditions, severe degradation of mechanical properties, uncontrollable degradation rate, and insufficient weather resistance and processing stability, this invention provides a hemp powder degradable material and its preparation method, achieving a high proportion of hemp powder filling while comprehensively optimizing the material's overall performance and processing properties, thus expanding its application scenarios.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A hemp powder degradable material, by mass percentage, is composed of the following raw materials: 50%~65% modified hemp powder, 25%~40% compound degradable matrix, 3%~6% modified inorganic filler, 1%~3% chain extender, and 1%~3% composite additives; the modified hemp powder is a microfibrillated-silane grafted composite modified hemp powder; the compound degradable matrix is ​​a mixture of polylactic acid (PLA) and polybutylene adipate terephthalate (PBAT) in a mass ratio of 3:1~1:1; the hemp powder degradable material is prepared by a solid-phase pre-crosslinking-step melt extrusion process.

[0008] Further, the preparation method of the modified hemp powder includes the following steps: (1) Pretreatment of hemp powder: Hemp powder is placed in a 3%~5% sodium hydroxide solution and soaked at 60℃~70℃ for 1h~2h, washed with water until neutral, filtered, and then vacuum dried at 70℃~80℃ for 2h~3h, and pulverized to 200~300 mesh to obtain refined hemp powder; (2) Microfibrillation treatment: Refined hemp powder and deionized water are mixed at a material-to-liquid ratio of 1g:20mL to form a suspension, and then homogenized by a high-pressure homogenizer at 60MPa~80MPa. (2) Cyclic treatment under force for 8 to 12 times, centrifugation and drying to obtain microfibrillated hemp powder; (3) Silane grafting modification: add microfibrillated hemp powder to a mixed solvent of anhydrous ethanol and deionized water at a volume ratio of 9:1 to prepare a suspension with a mass fraction of 15%, adjust the pH to 4 to 5, add γ-aminopropyltriethoxysilane accounting for 2% to 4% of the mass of microfibrillated hemp powder, stir at 60℃ to 70℃ for 3 to 4 hours, filter after the reaction, wash 3 times with anhydrous ethanol, and vacuum dry at 75℃ for 4 hours to obtain modified hemp powder.

[0009] Furthermore, the modified inorganic filler is an organically modified sepiolite, which is prepared by adding sepiolite powder to a 6%~10% hexadecyltrimethylammonium bromide aqueous solution, stirring at 70℃~80℃ for 4h~6h, centrifuging, washing with water until neutral, drying at 80℃, and then pulverizing to 800~1000 mesh to obtain modified sepiolite.

[0010] Furthermore, the chain extender is at least one of hexamethylene diisocyanate (HDI), toluene diisocyanate (TDI), and multifunctional epoxy chain extender ADR-4370.

[0011] Further, the composite additive, by weight, includes 0.3-0.8 parts of antioxidant, 0.3-0.8 parts of UV stabilizer, and 0.4-1.4 parts of lubricant; the antioxidant is a mixture of hindered phenolic antioxidant 1010 and phosphite antioxidant 168 in a 1:1 weight ratio; the UV stabilizer is a mixture of hindered amine light stabilizer 622 and benzotriazole UV absorber UV-327 in a 1:1 weight ratio; and the lubricant is at least one of calcium stearate, polyethylene wax, and ethylene bis-stearamide.

[0012] Furthermore, the preparation method of the hemp powder degradable material, namely the solid-phase pre-crosslinking-step melt extrusion process, includes the following steps: S1 Solid-phase pre-crosslinking: Modified hemp powder, modified inorganic filler, and chain extender are added to a high-speed mixer according to the formula, and mixed at 1000~1200 r / min and 45℃~50℃ for 5min~8min. Then, the compounded degradable matrix and composite additives are added, and mixing is continued for 10min~12min to obtain a premix. The premix is ​​placed in a reaction vessel and heated at 80℃~90℃ under a vacuum of -0.0. Solid-phase pre-crosslinking reaction was carried out for 15-20 minutes under 8MPa to -0.1MPa conditions to obtain pre-crosslinked material; S2 stepped melt extrusion: the pre-crosslinked material was added to a co-rotating twin-screw extruder and stepped temperature-controlled extrusion was adopted. The temperature from the feeding section to the die head was set to 140℃, 155℃, 170℃, 180℃, 175℃, and 170℃ respectively, and the screw speed was 280-320r / min. The extrudate was air-cooled, stretched, and then pelletized. It was dried with hot air at 40℃-45℃ for 1 hour to obtain hemp powder degradable material particles.

[0013] The beneficial effects of this invention are:

[0014] This invention modifies hemp powder through microfibrillation-silane grafting composite treatment. First, high-pressure homogenization microfibrillation opens up the fiber bundle structure of hemp powder, significantly increasing its specific surface area and reactivity. Then, hydrophobic groups are introduced onto the surface of hemp powder by grafting with a silane coupling agent, significantly reducing the surface polarity of hemp powder. This solves the industry pain point of poor interfacial compatibility between hemp powder and hydrophobic polyester matrix, achieving a high filling ratio of over 50% of hemp powder, while avoiding a precipitous drop in the mechanical properties of the material under high filling.

[0015] This invention uses PLA and PBAT as a degradation matrix. By adjusting the ratio of the two, the high strength and rigidity of PLA are retained, while PBAT imparts excellent low-temperature toughness and elongation at break to the material. At the same time, the degradation rate of the material in different environments such as soil composting and marine water can be precisely controlled, which solves the problems of high brittleness and limited degradation environment of single PLA matrix and expands the application scenarios of the material.

[0016] This invention uses organically modified sepiolite as an inorganic filler. The one-dimensional nanoneedle structure of sepiolite can form a stable barrier network in the matrix, significantly improving the oxygen and water vapor barrier performance of the material. At the same time, its porous structure can adsorb small molecule products during the degradation process, synergistically regulating the degradation rate. Combined with a composite antioxidant-UV stabilization system, the material's resistance to thermo-oxidative aging and UV aging is significantly improved. After 168 hours of thermo-oxidative aging at 120℃, the tensile strength retention rate is ≥90%, and after 500 hours of outdoor UV aging, the mechanical property retention rate is ≥85%, meeting the requirements for long-term outdoor use.

[0017] This invention pioneers a solid-phase pre-crosslinking-stepped melt extrusion preparation process. First, a low-temperature solid-phase pre-crosslinking reaction is used to allow the chain extender to react with the end groups of hemp powder and the degradable matrix in advance, initially constructing an interfacial bonding structure. This avoids the problems of uneven raw material dispersion and insufficient interfacial reaction during melt extrusion. Then, stepped temperature-controlled extrusion is used to match the melting and reaction characteristics of each raw material, which greatly improves the processing fluidity of the material with high hemp powder filling, solves problems such as melt fracture and molding defects, and has excellent stability in large-scale production.

[0018] The hemp powder degradable material of the present invention has a bio-based content of ≥60%, is completely biodegradable, and also has excellent mechanical properties (flexural strength ≥28MPa, tensile strength ≥22MPa, notched impact strength ≥6.5kJ / m²), barrier properties and weather resistance. It can be widely used in food packaging, disposable tableware, agricultural mulch film, outdoor disposable products and other fields, realizing the high-value utilization of hemp resources and having significant environmental and economic benefits. Detailed Implementation

[0019] The technical solutions in the embodiments of the present invention have been clearly and completely described. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example

[0020] This section provides five embodiments. The raw material ratios in all embodiments are within the scope of protection of the claims, and the preparation methods conform to the technical solutions of this invention.

[0021] Example 1: A hemp powder degradable material, by mass percentage, comprises: 55% modified hemp powder, 35% compound degradable matrix, 5% modified sepiolite, 3% HDI chain extender, and 2% composite additives; wherein, the compound degradable matrix is ​​PLA and PBAT compounded in a mass ratio of 2:1; the composite additives, by mass percentage, consist of 0.6 parts antioxidant, 0.6 parts UV stabilizer, and 0.8 parts calcium stearate, wherein the antioxidant is 1010 and 168 compounded in a 1:1 ratio, and the UV stabilizer is 622 and UV-327 compounded in a 1:1 ratio.

[0022] Preparation of modified hemp powder: (1) Pretreatment of hemp powder: Hemp powder was placed in a 4% sodium hydroxide solution and soaked at 65°C for 1.5h. It was washed with water until neutral, filtered, and then vacuum dried at 75°C for 2.5h. It was then pulverized to 250 mesh to obtain refined hemp powder; (2) Microfibrillation treatment: The refined hemp powder and deionized water were mixed at a ratio of 1g:20mL to form a suspension. The suspension was then circulated 10 times under a pressure of 70MPa using a high-pressure homogenizer. After centrifugation and drying, the suspension was further processed. Microfibrillated hemp powder was obtained; (3) Silane grafting modification: Microfibrillated hemp powder was added to a mixed solvent of anhydrous ethanol and deionized water at a volume ratio of 9:1 to prepare a suspension with a mass fraction of 15%. The pH was adjusted to 4.5 with glacial acetic acid. γ-aminopropyltriethoxysilane accounting for 3% of the mass of microfibrillated hemp powder was added. The mixture was stirred at 65°C for 3.5 h. After the reaction was completed, the mixture was filtered, washed 3 times with anhydrous ethanol, and dried under vacuum at 75°C for 4 h to obtain modified hemp powder.

[0023] Preparation of modified sepiolite: Sepiolite powder was added to an 8% (w / w) aqueous solution of hexadecyltrimethylammonium bromide, stirred at 75°C for 5 hours, centrifuged, washed with water until neutral, dried at 80°C, and pulverized to 1000 mesh to obtain modified sepiolite.

[0024] Preparation method: S1 Solid-phase pre-crosslinking: Modified hemp powder, modified sepiolite, and HDI chain extender are added to a high-speed mixer according to the formula and mixed at 1100 r / min and 48℃ for 6 min. Then, the compound degradation matrix and composite additives are added and mixed for another 11 min to obtain a premix. The premix is ​​placed in a reactor and subjected to solid-phase pre-crosslinking reaction at 85℃ and vacuum degree -0.09MPa for 18 min to obtain the pre-crosslinked material. S2 Stepped melt extrusion: The pre-crosslinked material is added to a co-rotating twin-screw extruder (length-to-diameter ratio 44:1) and stepped temperature-controlled extrusion is adopted. The temperature from the feeding section to the die head is set to 140℃, 155℃, 170℃, 180℃, 175℃, and 170℃ respectively. The screw speed is 300 r / min. The extrudate is air-cooled, stretched, and granulated. It is then dried with hot air at 42℃ for 1 h to obtain hemp powder degradation material particles.

[0025] Example 2: A hemp powder degradable material, by mass percentage, comprises: 50% modified hemp powder, 40% compound degradable matrix, 6% modified sepiolite, 2% epoxy chain extender ADR-4370, and 2% composite additives; wherein, the compound degradable matrix is ​​PLA and PBAT compounded in a mass ratio of 3:1; the composite additives, by mass percentage, consist of 0.5 parts antioxidant, 0.5 parts UV stabilizer, and 1.0 part polyethylene wax, wherein the antioxidant is 1010 and 168 compounded in a 1:1 ratio, and the UV stabilizer is 622 and UV-327 compounded in a 1:1 ratio.

[0026] Preparation of modified hemp powder: (1) Pretreatment of hemp powder: Hemp powder was placed in a 3% sodium hydroxide solution and soaked at 60°C for 2 hours. It was washed with water until neutral, filtered, and then vacuum dried at 70°C for 3 hours. It was then pulverized to 200 mesh to obtain refined hemp powder; (2) Microfibrillation treatment: The refined hemp powder was mixed with deionized water at a ratio of 1g:20mL to form a suspension. The suspension was then circulated 12 times under 60MPa pressure by a high-pressure homogenizer. After centrifugation and drying, the suspension was further processed. Microfibrillated hemp powder was obtained; (3) Silane grafting modification: Microfibrillated hemp powder was added to a mixed solvent of anhydrous ethanol and deionized water at a volume ratio of 9:1 to prepare a suspension with a mass fraction of 15%. The pH was adjusted to 4 with glacial acetic acid, and γ-aminopropyltriethoxysilane accounting for 2% of the mass of microfibrillated hemp powder was added. The mixture was stirred at 60°C for 4 hours. After the reaction was completed, the mixture was filtered, washed 3 times with anhydrous ethanol, and dried under vacuum at 75°C for 4 hours to obtain modified hemp powder.

[0027] Preparation of modified sepiolite: Sepiolite powder was added to a 6% (w / w) aqueous solution of hexadecyltrimethylammonium bromide, stirred at 70°C for 6 hours, centrifuged, washed with water until neutral, dried at 80°C, and pulverized to 800 mesh to obtain modified sepiolite.

[0028] Preparation method: S1 Solid-phase pre-crosslinking: Modified hemp powder, modified sepiolite, and chain extender are added to a high-speed mixer according to the formula, and mixed at 1000 r / min and 45℃ for 8 min. Then, the compound degradation matrix and composite additives are added, and the mixture is mixed for another 12 min to obtain a premix. The premix is ​​placed in a reactor and subjected to solid-phase pre-crosslinking reaction at 80℃ and vacuum degree -0.08MPa for 20 min to obtain a pre-crosslinked material. S2 Stepped melt extrusion: The pre-crosslinked material is added to a co-rotating twin-screw extruder. The stepped temperature control is the same as in Example 1, and the screw speed is 280 r / min. The extrudate is air-cooled, stretched, and granulated. It is then dried with hot air at 40℃ for 1 h to obtain hemp powder degradation material particles.

[0029] Example 3: A hemp powder degradable material, by mass percentage, comprises: 65% modified hemp powder, 25% compound degradable matrix, 6% modified sepiolite, 2% TDI chain extender, and 2% composite additives; wherein, the compound degradable matrix is ​​PLA and PBAT compounded in a 1:1 mass ratio; the composite additives, by mass percentage, consist of 0.7 parts antioxidant, 0.7 parts UV stabilizer, and 0.6 parts ethylene bis-stearamide, wherein the antioxidant is 1010 and 168 compounded in a 1:1 ratio, and the UV stabilizer is 622 and UV-327 compounded in a 1:1 ratio.

[0030] Preparation of modified hemp powder: (1) Pretreatment of hemp powder: Hemp powder was placed in a 5% sodium hydroxide solution and soaked at 70°C for 1 hour. It was washed with water until neutral, filtered, and then vacuum dried at 80°C for 2 hours. It was then pulverized to 300 mesh to obtain refined hemp powder; (2) Microfibrillation treatment: The refined hemp powder was mixed with deionized water at a ratio of 1g:20mL to form a suspension. The suspension was then circulated 8 times under 80MPa pressure by a high-pressure homogenizer. After centrifugation and drying, the suspension was further processed. Microfibrillated hemp powder was obtained; (3) Silane grafting modification: Microfibrillated hemp powder was added to a mixed solvent of anhydrous ethanol and deionized water at a volume ratio of 9:1 to prepare a suspension with a mass fraction of 15%. The pH was adjusted to 5 with glacial acetic acid. γ-aminopropyltriethoxysilane accounting for 4% of the mass of microfibrillated hemp powder was added. The mixture was stirred at 70°C for 3 hours. After the reaction was completed, the mixture was filtered, washed 3 times with anhydrous ethanol, and dried under vacuum at 75°C for 4 hours to obtain modified hemp powder.

[0031] Preparation of modified sepiolite: Sepiolite powder was added to a 10% (w / w) aqueous solution of hexadecyltrimethylammonium bromide, stirred at 80°C for 4 hours, centrifuged, washed with water until neutral, dried at 80°C and pulverized to 1000 mesh to obtain modified sepiolite.

[0032] Preparation method: S1 Solid-phase pre-crosslinking: Modified hemp powder, modified sepiolite, and chain extender are added to a high-speed mixer according to the formula, and mixed at 1200 r / min and 50℃ for 5 min. Then, the compound degradation matrix and composite additives are added, and the mixture is mixed for another 10 min to obtain a premix. The premix is ​​placed in a reactor and subjected to solid-phase pre-crosslinking reaction at 90℃ and a vacuum of -0.1 MPa for 15 min to obtain a pre-crosslinked material. S2 Stepped melt extrusion: The pre-crosslinked material is added to a co-rotating twin-screw extruder. The stepped temperature control is the same as in Example 1, and the screw speed is 320 r / min. The extrudate is air-cooled, stretched, and granulated. It is then dried with hot air at 45℃ for 1 h to obtain hemp powder degradation material particles.

[0033] Example 4: A hemp powder degradable material, by mass percentage, comprises: 58% modified hemp powder, 33% compound degradable matrix, 4% modified sepiolite, 2% HDI chain extender, and 3% composite additives; wherein, the compound degradable matrix is ​​PLA and PBAT compounded in a mass ratio of 2.5:1; the composite additives, by mass percentage, consist of 0.8 parts antioxidant, 0.8 parts UV stabilizer, 0.7 parts calcium stearate, and 0.7 parts polyethylene wax, wherein the antioxidant is 1010 and 168 compounded in a 1:1 ratio, and the UV stabilizer is 622 and UV-327 compounded in a 1:1 ratio.

[0034] The preparation methods for modified hemp powder and modified sepiolite are the same as in Example 1.

[0035] Example 5: A hemp powder degradable material, with the following raw material composition by mass percentage: 52% modified hemp powder, 38% compound degradable matrix, 5% modified sepiolite, 3% chain extender of HDI and ADR-4370 in a 1:1 ratio, and 2% composite additives; wherein, the compound degradable matrix is ​​PLA and PBAT compounded in a mass ratio of 1.5:1; the composition of the composite additives is the same as in Example 1, and the preparation methods of the modified hemp powder and modified sepiolite are the same as in Example 1.

[0036] Comparative Example

[0037] This section includes eight comparative examples to verify the necessity of the core technical features of this invention through single-variable comparisons, as detailed below:

[0038] The difference between Comparative Example 1 and Example 1 is that the hemp powder was not modified by microfibrillation-silane grafting composite, and only the same alkaline immersion pretreatment as in Example 1 was used. The other raw material ratios and preparation methods were the same as in Example 1.

[0039] The difference between Comparative Example 2 and Example 1 is that the degradation matrix uses a single PLA and no PBAT is added, while the proportions of other raw materials and the preparation methods are the same as in Example 1.

[0040] The difference between Comparative Example 3 and Example 1 is that the solid-phase pre-crosslinking step was not used, and the premix was directly added to the twin-screw extruder for extrusion. The other raw material ratios and preparation methods are the same as those in Example 1.

[0041] The difference between Comparative Example 4 and Example 1 is that no modified sepiolite was added, and the reduced proportion of modified sepiolite in the raw material ratio was allocated to the modified hemp powder and the compound degradation matrix. The rest of the preparation methods are the same as those in Example 1.

[0042] The difference between Comparative Example 5 and Example 1 is that no ultraviolet light stabilizer was added to the composite additive, while the other raw material ratios and preparation methods were the same as in Example 1.

[0043] The difference between Comparative Example 6 and Example 1 is that the conventional constant temperature melt extrusion process is used, and the temperature of the twin-screw extruder from the feeding section to the die head is set to 165°C, 175°C, 185°C, 195°C and 200°C respectively. The other raw material ratios are the same as those in Example 1.

[0044] The difference between Comparative Example 7 and Example 1 is that the amount of hemp powder filling is 40%, which is lower than the protection scope of this invention, the proportions of the remaining raw materials are adjusted proportionally, and the preparation methods are the same as those in Example 1.

[0045] The eight comparative examples were commercially available ordinary PLA / straw powder biodegradable materials, with 55% straw powder filling, pure PLA matrix, and calcium stearate and antioxidant 1010 as additives. They were prepared using a conventional twin-screw extrusion process.

[0046] Performance Testing and Results Analysis

[0047] Test standards and methods:

[0048] Tensile strength: GB / T1040.2-2006.

[0049] Bending strength: GB / T9341-2008.

[0050] Notched impact strength: GB / T1843-2008.

[0051] Oxygen permeability: GB / T1038-2000.

[0052] Water vapor transmission rate: GB / T31034-2014.

[0053] Thermo-oxidative aging performance: After thermo-oxidative aging at 120℃ for 168h, the tensile strength retention rate was tested.

[0054] UV aging performance: GB / T16422.2-2014, after UV aging for 500h, the tensile strength retention rate is tested.

[0055] Soil compost degradation rate: GB / T19277.1-2011, test degradation rate after 180 days.

[0056] Marine degradation rate: GB / T40611-2021, test the seawater degradation rate over 180 days.

[0057] Melt flow rate (MFR): GB / T3682-2018, 190℃, 2.16kg, characterizing processing fluidity.

[0058] Test results:

[0059] Table 1. Performance test results of the embodiments;

[0060] Performance indicators Example 1 Example 2 Example 3 Example 4 Example 5 Tensile strength / MPa 24.5 25.2 22.3 23.8 24.9 Bending strength / MPa 29.6 30.5 28.1 29.2 30.1 Notched impact strength (kJ / m²) 7.2 6.8 7.8 7.0 7.5 Oxygen permeability / (cm³ / (m²·24h·0.1MPa)) 38 36 35 40 37 Water vapor transmission rate (g / (m²·24h)) 30 29 28 32 31 168h thermo-oxidative aging tensile strength retention rate / % 91.2 90.5 92.3 90.8 91.5 500h UV aging tensile strength retention rate / % 86.5 85.8 87.2 86.1 86.7 180-day soil compost degradation rate (%) 92.4 90.8 95.1 91.7 92.0 180-day marine degradation rate / % 78.6 75.2 82.3 76.8 77.5 Melt flow rate (g / 10min) 8.5 9.2 7.6 8.8 8.7 Bio-based content / % 62 57 71 65 59

[0061] Table 1

[0062] Table 2 shows the performance test results of the comparative model.

[0063] Performance indicators Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Comparative Example 7 Comparative Example 8 Tensile strength / MPa 15.6 22.1 19.2 22.7 24.1 18.5 26.8 14.2 Bending strength / MPa 17.2 28.3 21.5 26.4 29.3 20.3 31.2 16.5 Notched impact strength (kJ / m²) 3.5 4.1 5.3 6.5 7.1 5.0 6.9 3.2 Oxygen permeability / (cm³ / (m²·24h·0.1MPa)) 65 42 52 58 39 55 41 72 Water vapor transmission rate (g / (m²·24h)) 56 35 42 48 31 45 34 62 168h thermo-oxidative aging tensile strength retention rate / % 72.5 88.6 80.3 89.2 90.7 78.6 89.5 65.3 500h UV aging tensile strength retention rate / % 60.3 82.4 75.6 84.2 52.1 72.5 85.3 48.6 180-day soil compost degradation rate (%) 78.5 85.3 82.6 90.2 91.8 81.3 88.7 72.4 180-day marine degradation rate / % 45.3 32.1 60.5 70.2 78.1 58.6 72.4 28.5 Melt flow rate (g / 10min) 4.2 7.8 5.5 8.2 8.4 5.1 9.5 3.8 Bio-based content / % 62 62 62 62 62 62 47 62

[0064] Table 2

[0065] Results analysis:

[0066] (1) Examples 1-5 all achieved a high filling content of more than 50% of hemp powder. At the same time, the materials also have excellent mechanical properties, barrier properties, aging resistance and processing fluidity. The soil compost degradation rate after 180 days is ≥90% and the marine degradation rate is ≥75%, which is superior to the comparative examples. This verifies the superiority of the technical solution of the present invention. (2) Comparative Example 1 did not perform microfibrillation-silane grafting composite modification on the hemp powder. The mechanical properties, barrier properties and degradation properties of the material all decreased significantly. This proves that the modification step is the core to solve the interface compatibility between hemp powder and matrix and achieve high filling. (3) Comparative Example 2 used a single PLA matrix. The notched impact strength of the material was greatly reduced, the low temperature toughness was poor, and the marine degradation rate was only 32.1%. This proves that the PLA / PBAT composite matrix is ​​the key to improving the toughness and multi-environment degradation performance of the material. (4) Comparative Examples 3 and 6 did not use the solid-phase pre-crosslinking-step melt extrusion process of the present invention. The mechanical properties and processing fluidity of the materials decreased significantly, and melt fracture was prone to occur during the molding process. This proves that the preparation process is a necessary condition to ensure the processing stability and performance uniformity of the materials under high filling. (5) Comparative Example 4 did not add modified sepiolite. The barrier properties of the materials decreased significantly. Comparative Example 5 did not add ultraviolet light stabilizer. The ultraviolet aging resistance of the materials decreased significantly. This proves that the filler system and auxiliary agent system of the present invention play an important role in improving the comprehensive performance of the materials. (6) The commercially available straw powder degradation material of Comparative Example 8 had all properties far lower than those of the embodiments of the present invention. In particular, the aging resistance and marine degradation performance were significantly different. This proves that the hemp powder degradation material of the present invention has significant technical advantages and application value.

[0067] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A biodegradable hemp powder material, characterized in that, The product is composed of the following raw materials by weight percentage: 50%~65% modified hemp powder, 25%~40% compound degradable matrix, 3%~6% modified inorganic filler, 1%~3% chain extender and 1%~3% composite additives; the compound degradable matrix is ​​a mixture of polylactic acid and polybutylene adipate terephthalate in a weight ratio of 3:1~1:

1. The modified hemp powder is a microfibrillated-silane grafted composite modified hemp powder, and the preparation steps are as follows: (1) Place hemp powder in a 3%~5% sodium hydroxide solution and soak at 60℃~70℃ for 1h~2h. Wash with water until neutral, filter, and vacuum dry at 70℃~80℃ for 2h~3h. Crush to 200~300 mesh to obtain refined hemp powder. (2) Prepare a suspension by mixing refined hemp powder with deionized water at a ratio of 1g:20mL. Then, process the suspension by a high-pressure homogenizer at a pressure of 60MPa~80MPa for 8~12 times. After centrifugation and drying, obtain microfibrillated hemp powder. (3) Add the microfibrillated hemp powder to a mixed solvent of anhydrous ethanol and deionized water at a volume ratio of 9:1 to prepare a suspension with a mass fraction of 15%. Adjust the pH to 4-5, add γ-aminopropyltriethoxysilane at a mass of 2%-4% of the microfibrillated hemp powder, and stir the reaction at 60℃-70℃ for 3-4 hours. After the reaction is completed, filter, wash and dry to obtain modified hemp powder. The modified inorganic filler is organically modified sepiolite, and its preparation method is as follows: Sepiolite powder was added to a 6%~10% hexadecyltrimethylammonium bromide aqueous solution and stirred at 70℃~80℃ for 4h~6h. After centrifugation and washing with water until neutral, the mixture was dried and pulverized to 800~1000 mesh to obtain modified sepiolite. The hemp powder degradable material is prepared by a solid-phase pre-crosslinking-step melt extrusion process, with the following specific steps: S1 Solid-phase pre-crosslinking: Modified hemp powder, modified inorganic filler, and chain extender are added to a high-speed mixer according to the formula. The mixture is mixed at 1000~1200 r / min and 45℃~50℃ for 5min~8min. Then, the compounded degradation matrix and composite additives are added, and the mixture is mixed for another 10min~12min to obtain a premix. The premix is ​​placed in a reaction vessel and subjected to solid-phase pre-crosslinking reaction at 80℃~90℃ and a vacuum of -0.08MPa~-0.1MPa for 15min~20min to obtain the pre-crosslinked material. S2 Stepped Melt Extrusion: The pre-crosslinked material is added to a co-rotating twin-screw extruder and stepped temperature-controlled extrusion is adopted. The temperature from the feeding section to the die head is set to 140℃, 155℃, 170℃, 180℃, 175℃, and 170℃ respectively. The screw speed is 280~320r / min. The extrudate is air-cooled, stretched, and then pelletized. It is then dried with hot air at 40℃~45℃ for 1 hour to obtain hemp powder degradable material granules.

2. The hemp powder degradable material according to claim 1, characterized in that, The chain extender is at least one of hexamethylene diisocyanate, toluene diisocyanate, and multifunctional epoxy chain extender ADR-4370.

3. The hemp powder degradable material according to claim 1, characterized in that, The composite additives, by weight, include 0.3-0.8 parts antioxidant, 0.3-0.8 parts ultraviolet light stabilizer, and 0.4-1.4 parts lubricant.

4. The hemp powder degradable material according to claim 3, characterized in that, The antioxidant is a mixture of hindered phenolic antioxidant 1010 and phosphite antioxidant 168 in a mass ratio of 1:

1.

5. The hemp powder degradable material according to claim 3, characterized in that, The UV stabilizer is a mixture of hindered amine light stabilizer 622 and benzotriazole UV absorber UV-327 in a mass ratio of 1:

1.

6. The hemp powder degradable material according to claim 3, characterized in that, The lubricant is at least one of calcium stearate, polyethylene wax, and ethylene bis-stearamide.