Composite material based on biological straw powder and polypropylene and preparation method thereof
By preparing modified straw powder and polypropylene composite materials, the problems of insufficient mechanical properties and compatibility of bio-based materials have been solved, achieving a combination of high performance and environmental protection, and meeting the performance and appearance requirements of demanding application scenarios.
Patent Information
- Application Number
- CN202511334703.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-18
- Publication Date
- 2025-11-11
AI Technical Summary
Existing bio-based materials have shortcomings in terms of mechanical properties and compatibility, making it difficult to meet the performance requirements of demanding application scenarios. At the same time, traditional methods increase the difficulty of material processing and result in uneven appearance.
Modified straw powder and polypropylene composite material were used. Through chitosan coating, phosphate starch crosslinking and modified silane coupling agent grafting processes, combined with multi-level synergistic interface modification of functional fillers, the interfacial compatibility between straw powder and PP substrate was optimized. Uniform dispersion was achieved by pre-dilution of PE powder and control of main/side feeding speed.
It significantly improves the impact toughness and mechanical property stability of composite materials, forms a clear and uniform dotted decorative effect, and combines aesthetic value with environmental protection characteristics, achieving a combination of high performance and environmental protection.
Smart Images
Figure CN120923923A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of bio-based composite material preparation technology, specifically relating to a composite material based on bio-straw powder and polypropylene and its preparation method. Background Technology
[0002] With the increasing global awareness of environmental protection, bio-based materials have become a research hotspot in the field of polymer materials due to their advantages such as renewability and biodegradability. Currently, traditional bio-based materials are mostly prepared by blending biodegradable polymers such as polylactic acid (PLA) and polybutylene adipate / terephthalate (PBAT) with biological fillers (such as straw powder and wood flour). However, these traditional bio-based materials have significant drawbacks: on the one hand, the mechanical properties (such as impact strength and heat resistance) of PLA and PBAT substrates are poor, making it difficult to meet the high performance requirements of applications such as refrigerator drawers and small appliance casings; on the other hand, in pursuit of better biodegradability, traditional bio-based materials typically add a large amount (generally more than 10%) of biological fillers, which not only easily leads to decreased processing fluidity and increased surface roughness, but also makes it impossible to accurately control the dotted effect on the material surface, making it difficult to meet the aesthetic and decorative requirements of products. In addition, existing technologies also include methods for preparing composite materials by blending polypropylene (PP) with biological fillers. However, such methods either add a high proportion (usually 20-50%) of biological fillers to improve the rigidity of the material, resulting in a significant reduction in the toughness of the material and an increase in processing difficulty; or they simply use biological fillers as fillers without optimizing the interfacial compatibility between the biological fillers and the PP substrate, and without establishing an effective method for controlling the amount added, resulting in uneven surface effects and poor mechanical property stability of the material, failing to balance the material's performance, appearance, and environmental friendliness. Therefore, improving the mechanical properties of bio-stalks and enhancing the compatibility between corn stalks and polymers are key to preparing high-performance straw / polymer composites and promoting straw recycling. Summary of the Invention
[0003] The purpose of this invention is to address existing problems by providing a composite material based on bio-straw powder and polypropylene, and a method for preparing the same.
[0004] This invention is achieved through the following technical solution: A composite material based on bio-straw powder and polypropylene, comprising the following components in parts by weight: 85-95 parts of polypropylene (PP) substrate, 0.8-1.2 parts of modified straw powder, 3-12 parts of low-density polyethylene, 0.5-0.7 parts of functional filler, 0.2-0.5 parts of antioxidant, and 0.3-0.8 parts of lubricant.
[0005] Furthermore, the preparation of the modified straw powder includes the following steps: (1) After drying and crushing the crop straw through an 80-mesh sieve, the straw is transferred to a planetary ball mill and ball-milled for 1.5 to 2.5 hours at a speed of 300 to 400 r / min with ethanol as the dispersion medium (solid-liquid ratio 1:5) to obtain crude straw powder. (2) Place the crude straw powder in a 0.5% citric acid aqueous solution (solid-liquid ratio 1:10), stir at 60~70℃ for 1~2h, filter, wash with deionized water until neutral, and vacuum dry at 60~70℃ for 6~8h to obtain pretreated straw powder. (3) Add the pretreated straw powder to a high-speed mixer, add chitosan aqueous solution (2% by mass) at 5-8% of the mass of the pretreated straw powder, stir at 60-70℃ for 30-40 min, then add phosphate starch at 3-5% of the pretreated straw powder, heat to 70-80℃, and stir at 800-900 r / min for 40-50 min; (4) Add 1% of the total mass of modified silane coupling agent, continue stirring for 20-30 minutes and then spray dry. After drying, classify by air classifier and select 120-150 mesh particles as modified straw powder.
[0006] Furthermore, the modified silane coupling agent is prepared by mixing epoxy fatty acid methyl ester with silane coupling agent (γ-aminopropyltriethoxysilane, KH550) at a mass ratio of 3:1, adding 0.5~0.6% of dibutyltin dilaurate by mass of the mixture, and stirring the mixture at 70~80℃ for 1.5~2h to obtain the modified silane coupling agent.
[0007] Furthermore, the preparation of the functional filler includes the following steps: 1) Take the waste residue from edible fungi cultivation, wash it to remove the culture medium residue, dry it at 80~90℃ for 4~5 hours, then crush it through a 100-mesh sieve to obtain fungi residue powder; 2) Take agricultural waste rice husks, burn them in an air atmosphere in a muffle furnace at 500~550℃ for 2~3 hours, cool them and crush them through a 120-mesh sieve to obtain porous rice husk ash; 3) Mix the above-mentioned mushroom residue powder and porous rice husk ash evenly at a mass ratio of (2~3):1, add deionized water at a solid-liquid ratio of 1:(6~8), stir at 60~70℃ for 30~40min, then add 2~3% citric acid by weight of the mixed powder, continue stirring for 1~1.5h, filter, and dry at 70~80℃ and -0.08~-0.09MPa for 3~4h to obtain mushroom residue-rice husk composite matrix; 4) Add the fungal residue-rice husk composite matrix to a phosphate starch solution with a mass concentration of 5-10wt% at a mass ratio of 1:(3~4), stir at 50-60℃ for 1-1.5h, and then spray dry with an inlet air temperature of 180-200℃ and an outlet air temperature of 80-90℃ to obtain the functional filler.
[0008] Furthermore, the edible fungi cultivation waste residue mentioned in step 1) is shiitake mushroom residue, specifically the cultivation substrate residue produced after the completion of industrialized shiitake mushroom production.
[0009] Furthermore, the antioxidant is a compound of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1.
[0010] Furthermore, the lubricant is calcium stearate or ethylene bis-stearamide.
[0011] A method for preparing a composite material based on bio-straw powder and polypropylene includes the following steps: S1. Weigh out the corresponding weight parts of PP substrate, modified straw powder, low-density polyethylene, functional filler, antioxidant, and lubricant for later use. S2. Add the modified straw powder and PE powder to a high-speed mixer and mix for 5 to 10 minutes at 60~80℃ and 800~1200r / min to obtain straw powder-PE premix. S3. After mixing the PP substrate, antioxidant and lubricant evenly according to the mass proportions, add them to the twin-screw extruder through the main feed port. Add the straw powder-PE premix obtained in step S2 to the twin-screw extruder through the side feed port for co-extrusion. Then, it can be injection molded by an injection molding machine.
[0012] Furthermore, the main feeding speed mentioned in step S3 is controlled at 20~30 kg / h; The side feeding speed should be controlled at 1~3 kg / h.
[0013] Furthermore, the screw speed of the twin-screw extruder described in step S3 is 200~300 r / min; The extrusion temperature is divided into the following zones: Zone 1 160~170℃, Zone 2 170~180℃, Zone 3 180~190℃, Zone 4 180~190℃, and the die head temperature 180~190℃.
[0014] The present invention has the following advantages over the prior art: 1. Compared to the problems of high brittleness, low heat distortion temperature, and insufficient mechanical properties of traditional biodegradable materials such as PLA / PBAT substrates, this invention uses polypropylene (PP) as the substrate, fully leveraging its superior comprehensive mechanical properties, low cost, and ease of processing. This invention employs a unique multi-level synergistic interface modification process involving chitosan coating, phosphate ester starch crosslinking, and modified silane coupling agent grafting. This significantly improves the interfacial compatibility between straw powder and the PP substrate, avoiding mechanical property fluctuations caused by low-proportion filler additions. It ensures that the straw powder is uniformly dispersed in the PP matrix and forms a strong interfacial bond. Even with only 1% filler, the impact toughness of the composite material is significantly improved, while completely avoiding mechanical property degradation caused by filler introduction, ensuring long-term performance stability and reliability of the product during use.
[0015] 2. This invention firstly solves the process problem of lightweight biomass raw materials being easy to fly and difficult to disperse by pre-dilution of PE powder. Then, through the coordinated control of the main / side feeding speed, the bio-straw powder and functional fillers are optimally dispersed in the polymer melt, and finally a clear and uniform dotted decorative effect is formed on the material surface, which has both aesthetic value and biomass texture, and meets the market's demand for upgrading the appearance of environmentally friendly materials.
[0016] 3. This invention uses crop straw as raw material to prepare modified straw powder, while the functional filler uses solid waste such as shiitake mushroom residue and agricultural waste rice husks, realizing the high-value utilization of agricultural waste. It has outstanding green and environmentally friendly characteristics and provides the microplastics industry with a new material path that combines high performance and environmental protection characteristics, with broad application prospects. Attached Figure Description
[0017] Figure 1 The tensile strength of the composite material of bio-straw powder and polypropylene; Figure 2 The flexural strength of the composite material of bio-straw powder and polypropylene; Figure 3 The impact strength of the composite material of biological straw powder and polypropylene. Detailed Implementation
[0018] To further explain the present invention, the following specific embodiments are described. Example 1
[0019] A method for preparing a composite material based on bio-straw powder and polypropylene includes the following steps: S1. Weigh out the corresponding weight parts of 85 parts of PP substrate, 0.8 parts of modified straw powder, 3 parts of low-density polyethylene, 0.5 parts of functional filler, 0.2 parts of antioxidant, and 0.3 parts of calcium stearate for later use. The antioxidant is a compound of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1; S2. Add the modified straw powder and PE powder to a high-speed mixer and mix for 5 minutes at 60℃ and 800r / min to obtain straw powder-PE premix. S3. After mixing the PP substrate, antioxidant and calcium stearate evenly according to the mass fraction, add it into the twin-screw extruder through the main feed port, and control the main feed speed at 20kg / h. The straw powder-PE premix obtained in step S2 is added to a twin-screw extruder through a side feed port. The side feed speed is controlled at 1 kg / h for co-extrusion. The screw speed is 200 r / min. The extrusion temperature is set in the following sections: Zone 1 160℃, Zone 2 170℃, Zone 3 180℃, Zone 4 180℃, and the die head temperature is 180℃. Then, it is injection molded by an injection molding machine. The preparation of the modified straw powder includes the following steps: (1) After drying and crushing the wheat straw through an 80-mesh sieve, it was transferred into a planetary ball mill and ball milled for 1.5 hours at 300 r / min with ethanol as the dispersion medium (solid-liquid ratio 1:5) to obtain crude straw powder. (2) Place the crude straw powder in a 0.5% citric acid aqueous solution (solid-liquid ratio 1:10), stir at 60°C for 1 hour, filter, wash with deionized water until neutral, and vacuum dry at 60°C for 6 hours to obtain pretreated straw powder. (3) Add the pretreated straw powder to a high-speed mixer, add chitosan aqueous solution (2% by mass) at 5% of the mass of the pretreated straw powder, stir at 60°C for 30 min, then add phosphate starch at 3% of the pretreated straw powder, heat to 70°C, and stir at 800 r / min for 40 min. (4) Add 1% of the total mass of modified silane coupling agent, continue stirring for 20 minutes and then spray dry. After drying, classify by air classifier and select 120 mesh particles as modified straw powder. The modified silane coupling agent is prepared by mixing epoxy fatty acid methyl ester and KH550 at a mass ratio of 3:1, adding 0.5% of dibutyltin dilaurate by mass of the mixture, and stirring at 70°C for 1.5 h to obtain the modified silane coupling agent. The preparation of the functional filler includes the following steps: 1) Take shiitake mushroom residue, specifically the cultivation substrate residue produced after the completion of industrialized shiitake mushroom production. Wash to remove culture medium residue, dry at 80℃ for 4 hours, and then crush through a 100-mesh sieve to obtain mushroom residue powder. 2) Take agricultural waste rice husks, burn them in an air atmosphere in a muffle furnace at 500℃ for 2 hours, cool them and crush them through a 120-mesh sieve to obtain porous rice husk ash; 3) Mix the above-mentioned mushroom residue powder and porous rice husk ash evenly at a mass ratio of 2:1, add deionized water at a solid-liquid ratio of 1:6, stir at 60℃ for 30 min, then add 2% citric acid by weight of the mixed powder, continue stirring for 1 h, filter, and dry at 70℃ and -0.08 MPa for 3 h to obtain mushroom residue-rice husk composite matrix. 4) The fungal residue-rice husk composite matrix was added to a 5wt% phosphate starch solution at a mass ratio of 1:3, stirred at 50℃ for 1 hour, and then spray-dried with an inlet air temperature of 180℃ and an outlet air temperature of 80℃ to obtain the functional filler. Example 2
[0020] A method for preparing a composite material based on bio-straw powder and polypropylene includes the following steps: S1. Weigh out the corresponding weight parts of 90 parts of PP substrate, 1 part of modified straw powder, 8 parts of low-density polyethylene, 0.6 parts of functional filler, 0.3 parts of antioxidant, and 0.5 parts of calcium stearate for later use. The antioxidant is a compound of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1; S2. Add the modified straw powder and PE powder to a high-speed mixer and mix for 7 minutes at 70℃ and 1000r / min to obtain straw powder-PE premix. S3. After mixing the PP substrate, antioxidant and calcium stearate evenly according to the mass fraction, add it into the twin-screw extruder through the main feed port, and control the main feed speed at 25kg / h. The straw powder-PE premix obtained in step S2 is added to a twin-screw extruder through a side feed port. The side feed speed is controlled at 2 kg / h for co-extrusion. The screw speed is 250 r / min. The extrusion temperature is set in the following sections: Zone 1 165℃, Zone 2 175℃, Zone 3 185℃, Zone 4 185℃, and the die head temperature is 185℃. Then, it is injection molded by an injection molding machine. The preparation of the modified straw powder includes the following steps: (1) After drying and crushing the wheat straw through an 80-mesh sieve, it was transferred into a planetary ball mill and ball-milled for 2 hours at 350 r / min with ethanol as the dispersion medium (solid-liquid ratio 1:5) to obtain crude straw powder. (2) Place the crude straw powder in a 0.5% citric acid aqueous solution (solid-liquid ratio 1:10), stir at 65°C for 1.5h, filter, wash with deionized water until neutral, and vacuum dry at 65°C for 7h to obtain pretreated straw powder. (3) Add the pretreated straw powder to a high-speed mixer, add chitosan aqueous solution (2% by mass) at 6.5% of the mass of the pretreated straw powder, stir at 65°C for 35 min, then add phosphate starch accounting for 4% of the pretreated straw powder, heat to 75°C, and stir at 850 r / min for 45 min; (4) Add 1% of the total mass of modified silane coupling agent, continue stirring for 25 minutes and then spray dry. After drying, classify by air classifier and select 140 mesh particles as modified straw powder. The modified silane coupling agent is prepared by mixing epoxy fatty acid methyl ester and KH550 at a mass ratio of 3:1, adding 0.55% of dibutyltin dilaurate by mass of the mixture, and stirring at 75°C for 1.7 h to obtain the modified silane coupling agent. The preparation of the functional filler includes the following steps: 1) Take shiitake mushroom residue, specifically the cultivation substrate residue produced after the completion of industrialized shiitake mushroom production. Wash to remove culture medium residue, dry at 85℃ for 4.5 hours, and then crush through a 100-mesh sieve to obtain mushroom residue powder. 2) Take agricultural waste rice husks, burn them in an air atmosphere in a muffle furnace at 525℃ for 2.5 hours, cool them and crush them through a 120-mesh sieve to obtain porous rice husk ash; 3) After mixing the above-mentioned mushroom residue powder and porous rice husk ash evenly at a mass ratio of 2.5:1, deionized water is added at a solid-liquid ratio of 1:7. The mixture is stirred at 65℃ for 35 minutes, and then 2.5% citric acid by weight of the mixed powder is added. The mixture is stirred for another 1.2 hours. After filtration, the mixture is dried at 75℃ and -0.085 MPa for 3.5 hours to obtain the mushroom residue-rice husk composite matrix. 4) The fungal residue-rice husk composite matrix was added to a 7.5wt% phosphate starch solution at a mass ratio of 1:3.5, stirred at 55℃ for 1.2h, and then spray-dried with an inlet air temperature of 190℃ and an outlet air temperature of 85℃ to obtain the functional filler. Example 3
[0021] A method for preparing a composite material based on bio-straw powder and polypropylene includes the following steps: S1. Weigh out the corresponding weight parts of 95 parts of PP substrate, 1.2 parts of modified straw powder, 12 parts of low-density polyethylene, 0.7 parts of functional filler, 0.4 parts of antioxidant, and 0.6 parts of calcium stearate for later use. The antioxidant is a compound of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1; S2. Add the modified straw powder and PE powder to a high-speed mixer and mix for 10 minutes at 80℃ and 1200r / min to obtain straw powder-PE premix. S3. After mixing the PP substrate, antioxidant and calcium stearate evenly according to the mass fraction, add it into the twin-screw extruder through the main feed port, and control the main feed speed at 30kg / h. The straw powder-PE premix obtained in step S2 is added to a twin-screw extruder through a side feed port. The side feed speed is controlled at 3 kg / h for co-extrusion. The screw speed is 300 r / min. The extrusion temperature is set in the following sections: Zone 1 170℃, Zone 2 180℃, Zone 3 190℃, Zone 4 190℃, and the die head temperature is 190℃. Then, it is injection molded by an injection molding machine. The preparation of the modified straw powder includes the following steps: (1) After drying and crushing the wheat straw through an 80-mesh sieve, it was transferred into a planetary ball mill and ball milled for 2.5 hours at 400 r / min with ethanol as the dispersion medium (solid-liquid ratio 1:5) to obtain crude straw powder. (2) Place the crude straw powder in a 0.5% citric acid aqueous solution (solid-liquid ratio 1:10), stir at 70°C for 2 hours, filter, wash with deionized water until neutral, and vacuum dry at 70°C for 8 hours to obtain pretreated straw powder. (3) Add the pretreated straw powder to a high-speed mixer, add chitosan aqueous solution (2% by mass) at 8% of the mass of the pretreated straw powder, stir at 70°C for 40 min, then add phosphate starch at 5% of the pretreated straw powder, heat to 80°C, and stir at 900 r / min for 50 min. (4) Add 1% of the total mass of modified silane coupling agent, continue stirring for 30 minutes and then spray dry. After drying, classify by air classifier and select 150 mesh particles as modified powder. The modified silane coupling agent is prepared by mixing epoxy fatty acid methyl ester and KH550 at a mass ratio of 3:1, adding 0.6% of dibutyltin dilaurate by mass of the mixture, and stirring at 80°C for 2 hours to obtain the modified silane coupling agent. The preparation of the functional filler includes the following steps: 1) Take shiitake mushroom residue, specifically the cultivation substrate residue produced after the completion of industrialized shiitake mushroom production. Wash to remove culture medium residue, dry at 90℃ for 5 hours, and then crush and pass through a 100-mesh sieve to obtain mushroom residue powder. 2) Take agricultural waste rice husks, burn them in an air atmosphere in a muffle furnace at 550℃ for 3 hours, cool them and crush them through a 120-mesh sieve to obtain porous rice husk ash; 3) After mixing the above-mentioned mushroom residue powder and porous rice husk ash evenly at a mass ratio of 3:1, add deionized water at a solid-liquid ratio of 1:8, stir at 70℃ for 40 min, then add 3% citric acid by weight of the mixed powder, continue stirring for 1.5 h, filter, and dry at 80℃ and -0.09 MPa for 4 h to obtain mushroom residue-rice husk composite matrix; 4) The fungal residue-rice husk composite matrix was added to a 10wt% phosphate starch solution at a mass ratio of 1:4, stirred at 60℃ for 1.5h, and then spray-dried with an inlet air temperature of 200℃ and an outlet air temperature of 90℃ to obtain the functional filler.
[0022] Comparative Example 1 Compared with Example 2, Comparative Example 1 replaced the modified straw powder with an equal amount of untreated wheat straw powder, while the other steps were the same as in Example 2.
[0023] Comparative Example 2 Compared with Example 2, Comparative Example 2 does not add functional fillers, but the other steps are the same as in Example 2.
[0024] Comparative Example 3 Compared with Example 2, Comparative Example 3 replaces the modified silane coupling agent in step (4) with an equal amount of unmodified KH550 silane coupling agent, while the other steps are the same as in Example 2.
[0025] Comparative Example 4 Compared with Example 2, Comparative Example 4 replaces the modified straw powder with an equal amount of unmodified wheat straw powder and omits the use of functional fillers. The other steps are the same as in Example 2.
[0026] Performance testing Tensile strength was determined using an electronic universal testing machine (CMT4104, MITES Industrial Systems (China) Co., Ltd.) according to GB / T1040, with a tensile rate of 50 mm / min. Five specimens were tested per group, and the average value was taken. Bending strength was determined according to GB / T9341, with a bending rate of 2 mm / min and a span of 64 mm. Five specimens were tested per group, and the average value was taken. Notched impact strength of cantilever beams was determined using a pendulum impact testing machine (XJUD-5.5, Chengde Jinjian Testing Instruments Co., Ltd.) according to GB / T 1043, with an impact energy of 5.5 J. Five specimens were tested per group, and the average value was taken.
[0027] Test results are as follows Figure 1-3 As shown, the tensile strength of Comparative Example 1 is 21 MPa, the flexural strength is 28 MPa, and the impact strength is 3.2 KJ / m. 2 Compared to Example 2 (tensile strength 33.5 MPa, flexural strength 32.3 MPa, impact strength 6.8 KJ / m),2 The percentages decreased by 37.3%, 13.3%, and 52.9% respectively, indicating that compared to unmodified crop straw, the addition of the modified straw powder of this invention to the preparation of composite materials of bio-straw powder and polypropylene helps to improve the mechanical properties of the composite materials.
[0028] Comparative Example 2 has a tensile strength of 26.5 MPa, a flexural strength of 27.8 MPa, and an impact strength of 6.4 KJ / m. 2 Compared with Example 2, the values decreased by 20.9%, 13.9%, and 5.9% respectively, indicating that the functional filler of the present invention can not only effectively utilize waste materials, but also improve the mechanical properties of composite materials.
[0029] Comparative Example 3 has a tensile strength of 28 MPa, a flexural strength of 30.5 MPa, and an impact strength of 5.5 KJ / m. 2 Compared with Example 2, the performance decreased by 16.4%, 5.6%, and 19.1% respectively, indicating that the modified silane coupling agent of the present invention has better performance than the traditional coupling agent.
[0030] Comparative Example 4 has a tensile strength of 18.5 MPa, a flexural strength of 25.2 MPa, and an impact strength of 2.9 KJ / m. 2 Compared with Example 2, the performance decreased by 44.8%, 22.0%, and 57.4% respectively, indicating that the modified straw powder and functional filler of the present invention have a synergistic effect, and the absence of any link will lead to a decrease in performance.
[0031] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. A composite material based on bio-straw powder and polypropylene, characterized in that, It is composed of the following components in parts by weight: 85-95 parts polypropylene base material, 0.8-1.2 parts modified straw powder, 3-12 parts low-density polyethylene, 0.5-0.7 parts functional filler, 0.2-0.5 parts antioxidant, and 0.3-0.8 parts lubricant.
2. The composite material based on bio-straw powder and polypropylene according to claim 1, characterized in that, The preparation of the modified straw powder includes the following steps: (1) After drying and crushing the crop straw through an 80-mesh sieve, the straw is transferred to a planetary ball mill and ball-milled for 1.5 to 2.5 hours at a speed of 300 to 400 r / min with ethanol as the dispersion medium to obtain crude straw powder. (2) Place the crude straw powder in a 0.5% citric acid aqueous solution, stir at 60~70℃ for 1~2h, filter, wash with deionized water until neutral, and vacuum dry at 60~70℃ for 6~8h to obtain pretreated straw powder; (3) Add the pretreated straw powder to a high-speed mixer, add chitosan aqueous solution at 5-8% of the mass of the pretreated straw powder, stir at 60-70℃ for 30-40 min, then add phosphate starch at 3-5% of the pretreated straw powder, heat to 70-80℃, and stir at 800-900 r / min for 40-50 min; (4) Add 1% of the total mass of modified silane coupling agent, continue stirring for 20-30 minutes and then spray dry. After drying, classify by air classifier and select 120-150 mesh particles as modified straw powder.
3. The composite material based on bio-straw powder and polypropylene according to claim 2, characterized in that, The modified silane coupling agent is prepared by mixing epoxy fatty acid methyl ester and KH550 at a mass ratio of 3:1, adding 0.5~0.6% of dibutyltin dilaurate by mass of the mixture, and stirring at 70~80℃ for 1.5~2h to obtain the modified silane coupling agent.
4. The composite material based on bio-straw powder and polypropylene according to claim 1, characterized in that, The preparation of the functional filler includes the following steps: 1) Take the waste residue from edible fungi cultivation, wash it to remove the culture medium residue, dry it at 80~90℃ for 4~5 hours, then crush it through a 100-mesh sieve to obtain fungi residue powder; 2) Take agricultural waste rice husks, burn them in an air atmosphere in a muffle furnace at 500~550℃ for 2~3 hours, cool them and crush them through a 120-mesh sieve to obtain porous rice husk ash; 3) Mix the above-mentioned mushroom residue powder and porous rice husk ash evenly at a mass ratio of (2~3):1, add deionized water at a solid-liquid ratio of 1:(6~8), stir at 60~70℃ for 30~40min, then add 2~3% citric acid by weight of the mixed powder, continue stirring for 1~1.5h, filter, and dry at 70~80℃ and -0.08~-0.09MPa for 3~4h to obtain mushroom residue-rice husk composite matrix; 4) Add the fungal residue-rice husk composite matrix to a phosphate starch solution with a mass concentration of 5-10wt% at a mass ratio of 1:(3~4), stir at 50-60℃ for 1-1.5h, and then spray dry with an inlet air temperature of 180-200℃ and an outlet air temperature of 80-90℃ to obtain the functional filler.
5. The composite material based on bio-straw powder and polypropylene according to claim 4, characterized in that, The edible fungi cultivation waste residue mentioned in step 1) is shiitake mushroom residue, specifically the cultivation substrate residue produced after the completion of industrialized shiitake mushroom production.
6. The composite material based on bio-straw powder and polypropylene according to claim 1, characterized in that, The antioxidant is a compound of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:
1.
7. The composite material based on bio-straw powder and polypropylene according to claim 1, characterized in that, The lubricant is calcium stearate or ethylene bis-stearamide.
8. A method for preparing a composite material based on bio-straw powder and polypropylene as described in any one of claims 1 to 7, characterized in that, Includes the following steps: S1. Weigh out the corresponding weight parts of PP substrate, modified straw powder, low-density polyethylene, functional filler, antioxidant, and lubricant for later use. S2. Add the modified straw powder and PE powder to a high-speed mixer and mix for 5 to 10 minutes at 60~80℃ and 800~1200r / min to obtain straw powder-PE premix. S3. After mixing the PP substrate, antioxidant and lubricant evenly according to the mass proportions, add them to the twin-screw extruder through the main feed port. Add the straw powder-PE premix obtained in step S2 to the twin-screw extruder through the side feed port for co-extrusion. Then, it can be injection molded by an injection molding machine.
9. The composite material based on bio-straw powder and polypropylene according to claim 8, characterized in that, The main feeding speed mentioned in step S3 is controlled at 20~30 kg / h; The side feeding speed should be controlled at 1~3 kg / h.
10. The composite material based on bio-straw powder and polypropylene according to claim 8, characterized in that, The screw speed of the twin-screw extruder mentioned in step S3 is 200~300 r / min; The extrusion temperature is divided into the following zones: Zone 1 160~170℃, Zone 2 170~180℃, Zone 3 180~190℃, Zone 4 180~190℃, and the die head temperature 180~190℃.