Bamboo-based wood-plastic composite material manufacturing process based on thermoplastic material forming technology

Abstract

The invention discloses a bamboo-based wood-plastic composite material manufacturing process based on a thermoplastic material forming technology, and belongs to the technical field of wood-plastic composite material preparation. EPDM and PP are added into an internal mixer to be premixed, and a premix is obtained; preparing a composite mildew preventive; adding the pretreated bamboo fibers and the composite mildew preventive into a melting section of a double-screw extruder, adding the premix into a feeding section of the double-screw extruder, adding a vulcanizing agent into an inlet of a vulcanizing section of the double-screw extruder, mixing, extruding and granulating; and carrying out hot press molding on the granules, and then cooling and cutting to prepare the bamboo-based wood-plastic composite material. According to the bamboo-based wood-plastic composite material manufacturing process based on the thermoplastic material forming technology, interface bonding is enhanced through bamboo fiber pretreatment, the proportion of EPDM and PP and vulcanization parameters are optimized, rigidity and toughness balance is achieved, and the long-acting mildew resistance is improved through the synergistic effect of multiple components of the composite mildew preventive.

Description

Technical Field

[0001] The invention relates to the technical field of preparation of wood-plastic composite materials, in particular to a manufacturing process of bamboo-based wood-plastic composite materials based on thermoplastic material molding technology. Background Art

[0002] With rising global environmental awareness and the advancement of policies such as the "plastic ban," wood-plastic composites (WPCs), made from natural plant fibers and thermoplastics, have become an important alternative to traditional wood and pure plastics because they combine the advantages of both wood and plastic (such as recyclability, ease of processing, and corrosion resistance). Bamboo fiber, a natural fiber with abundant reserves and excellent mechanical properties (cellulose content exceeding 70% and tensile strength up to 1000 MPa), is widely used in the preparation of WPCs. However, its application still faces the following technical bottlenecks: The surface of bamboo fiber is rich in hydroxyl groups and is highly polar, while thermoplastics (such as PP) are non-polar. The interfacial bonding between the two is weak, resulting in low mechanical properties of the composite material (such as impact strength and tensile strength); the starch, protein and other components contained in bamboo fiber are prone to mold growth, especially in humid environments (such as outdoors and bathroom scenes), the material is prone to mildew, affecting its service life; the toughness of the PP matrix alone is insufficient, and adding EPDM (ethylene propylene diene monomer rubber) can improve the toughness, but EPDM and PP have poor compatibility, and the traditional blending process is prone to phase separation, and the vulcanization process is difficult to control, and "over-vulcanization" or "under-vulcanization" is prone to occur, affecting the processing fluidity and final performance of the material. Summary of the Invention

[0003] The purpose of the present invention is to provide a bamboo-based wood-plastic composite material manufacturing process based on thermoplastic material molding technology. By pre-treating bamboo fibers to enhance interface bonding, optimizing the EPDM and PP ratio and vulcanization parameters to achieve a balance between rigidity and toughness, and synergistically enhancing the long-term mildew resistance of the composite mildew inhibitor through the multi-component synergistic effect, the present invention comprehensively solves the problems of poor interface compatibility, insufficient mildew resistance, and difficulty in balancing processing and performance of traditional bamboo-based wood-plastic composite materials, and has significant practical value.

[0004] To achieve the above object, the present invention provides a bamboo-based wood-plastic composite material manufacturing process based on thermoplastic material molding technology, comprising the following steps: S1, pre-treating bamboo fiber; S2, adding EPDM and PP into an internal mixer and premixing to obtain a premix; S3, preparing a composite mildew inhibitor; S4, adding the pretreated bamboo fiber obtained in S1 and the composite mildew inhibitor obtained in S3 to the melting section of a twin-screw extruder, adding the premix obtained in S2 to the feeding section of the twin-screw extruder, adding the vulcanizing agent to the inlet of the vulcanizing section of the twin-screw extruder for mixing, and extruding and granulating; S5, forming the granules through hot pressing, cooling, and cutting to prepare a bamboo-based wood-plastic composite material.

[0005] Preferably, the specific operation of S1 is: placing the bamboo fiber in a drying oven for drying, and crushing and sieving it through a grinder, then placing the dried and crushed bamboo fiber in a high-speed mixer, and spraying the coupling agent solution for mixing, so that the coupling agent and the bamboo fiber fully react, and then placing the reacted bamboo fiber in a drying oven for drying to obtain pretreated bamboo fiber.

[0006] Preferably, in S1, the primary drying temperature is 80-100°C, the drying time is 4-6 hours, the sieve aperture is 80-100 mesh, the secondary drying temperature is 60-80°C, the drying time is 2-3 hours, and the moisture content of the pretreated bamboo fiber is <2%.

[0007] Preferably, in S1, the coupling agent solution is prepared by weighing 1-2% of the weight of the bamboo fiber coupling agent KH-550, adding anhydrous ethanol to dilute it, and adding glacial acetic acid to adjust the pH to 4-5, stirring evenly and letting it stand for 5-10 minutes to obtain a coupling agent solution.

[0008] Preferably, in S2, the mass ratio of EPDM to PP is (1-3):(7-9), the temperature in the internal mixer is 160-180°C, the rotation speed is 80-100 r / min, and the blending time is 10-12 min.

[0009] Preferably, the specific operation of S3 is: adding hydrophobic silica, quaternary ammonium salt and nano zinc oxide into a high-speed mixer and mixing them, and adding zinc stearate dispersant to obtain a composite mildew inhibitor.

[0010] Preferably, in S3, the amount of hydrophobic silica is 5-10% of the mass of the bamboo fiber, the quaternary ammonium salt accounts for 20-40% of the total mass of the composite mildew inhibitor, the nano zinc oxide accounts for 60-80% of the total mass of the composite mildew inhibitor, the amount of zinc stearate is 1-2% of the mass of the nano zinc oxide, the temperature in the high-speed mixer is 60-70°C, the speed is 1000-1500 r / min, and the mixing time is 15-20 min.

[0011] Preferably, in S4, the twin-screw extruder includes a feeding section, a melting section, a vulcanization section, a homogenization section and an extrusion section, the feeding section temperature is 160-170°C, the melting section temperature is 170-190°C, nitrogen is passed into the melting section for protection, the vulcanization section temperature is 190-200°C, the time is 3-5min, the homogenization section temperature is 180-190°C, the extrusion section temperature is 170-180°C, and the speed of the twin-screw extruder is 150-200r / min.

[0012] Preferably, in S4, the vulcanizing agent is dicumyl peroxide, the amount of the vulcanizing agent is 1-2.5% of the mass of EPDM, the pretreated bamboo fiber accounts for 40-50% of the total material mass, the total mass of the premix and the vulcanizing agent accounts for 45-55% of the total material mass, and the composite mildew inhibitor accounts for 2-5% of the total material mass.

[0013] Preferably, in S5, the hot pressing molding temperature is 150-170°C, the hot pressing pressure is 10-20 MPa, the hot pressing time is 10-15 min, and step cooling is adopted during cooling, first cooling at 40°C for 10 min, and then cooling at 25°C for 10 min.

[0014] Therefore, the present invention adopts the above-mentioned bamboo-based wood-plastic composite material manufacturing process based on thermoplastic material molding technology, which has the following beneficial effects: (1) By pre-treating bamboo fiber with a coupling agent solution, the siloxane group in the coupling agent is hydrolyzed and reacts with the hydroxyl group on the surface of the bamboo fiber to form a covalent bond. The organic group at the other end is compatible with the PP / EPDM group, forming a bridging structure and significantly reducing interface defects. (2) The hydrophobic silica in the composite mildew inhibitor forms a barrier on the surface of the material, reducing water penetration. The quaternary ammonium salt achieves rapid sterilization by destroying the mold cell membrane. Nano zinc oxide inhibits mold reproduction by slowly releasing zinc ions. The addition of zinc stearate can prevent nano zinc oxide from agglomerating, ensuring that the mildew inhibitory ingredients are evenly dispersed. (3) The parameter range of each step is clear and adjustable. The segmented feeding design of twin-screw extrusion avoids material agglomeration and local overheating. The hot pressing step cooling reduces the internal stress and deformation of the product. The qualified rate of the finished product is high, which is suitable for large-scale continuous production.

[0015] The technical solution of the present invention is further described in detail below through examples. DETAILED DESCRIPTION

[0016] Unless otherwise defined, technical or scientific terms used in the present invention shall have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs.

[0017] In the present invention, unless otherwise specified, other test materials and instruments and equipment are conventional test materials in this field and can be purchased through commercial channels.

[0018] Example 1 The present invention provides a manufacturing process for bamboo-based wood-plastic composite materials based on thermoplastic material molding technology, comprising the following steps: S1 bamboo fiber pretreatment: 100 kg of bamboo fiber was placed in a drying oven at 80°C for 6 hours. After drying, it was crushed by a grinder and then passed through an 80-mesh sieve. Weigh 1 kg of coupling agent KH-550 (1% of the mass of bamboo fiber), add an appropriate amount of anhydrous ethanol to dilute, adjust the pH to 4 with glacial acetic acid, stir evenly and let it stand for 5 minutes to prepare a coupling agent solution. The dried and crushed bamboo fibers were placed in a high-speed mixer, sprayed with a coupling agent solution, and mixed for 30 minutes to allow the coupling agent and the bamboo fibers to fully react. Subsequently, the reacted bamboo fibers were placed in a drying oven and dried at 60°C for 3 hours to obtain pretreated bamboo fibers with a moisture content of 1.8%.

[0019] S2 premix preparation: Weigh 10 kg of EPDM and 90 kg of PP in a 1:9 EPDM to PP mass ratio and add them to an internal mixer. Set the mixer temperature to 160°C and the speed to 80 rpm for 12 minutes to obtain a premix.

[0020] Preparation of S3 composite mildew inhibitor: Weigh 5 kg of hydrophobic silica (5% of the weight of the bamboo fiber), 4 kg of quaternary ammonium salt, and 16 kg of nano-zinc oxide and add them to a high-speed mixer. Weigh 0.16 kg of zinc stearate (1% of the weight of the nano-zinc oxide) and add them to the high-speed mixer. Set the mixer to 60°C and 1000 rpm for 20 minutes to obtain a composite mildew inhibitor.

[0021] S4 extrusion granulation: Add the pretreated bamboo fiber and the composite mildew inhibitor to the melting section of a twin-screw extruder. Add the premix to the feed section of the twin-screw extruder. Weigh 0.1 kg of dicumyl peroxide (1% of the mass of the EPDM) as a vulcanizing agent and add it to the inlet of the vulcanizing section of the twin-screw extruder.

[0022] The temperature settings of each section of the twin-screw extruder are: feeding section 160℃, melting section 170℃ (nitrogen protection), vulcanization section 190℃, time 3min, homogenization section 180℃, extrusion section 170℃, speed 150r / min, extrusion granulation.

[0023] S5 thermoforming: The granulated material was placed into a mold and hot-pressed in a hot press. The temperature was set at 150°C, the pressure was 10 MPa, and the time was 10 minutes. After hot pressing, a step-cooling process was adopted: first cooling at 40°C for 10 minutes, then cooling at 25°C for 10 minutes, and finally cutting to obtain the bamboo-based wood-plastic composite material.

[0024] Example 2 The difference between this embodiment and embodiment 1 is that the mass ratio of EPDM to PP is 2:8, and the other conditions are the same.

[0025] Example 3 The difference between this embodiment and embodiment 1 is that the quaternary ammonium salt accounts for 30% of the total mass of the composite mildew inhibitor, and the other conditions are the same.

[0026] Comparative Example 1 The difference between this comparative example and Example 1 is that the bamboo fiber is not pretreated, and the other conditions are the same.

[0027] Comparative Example 2 This comparative example differs from Example 1 in that no composite mildew inhibitor is added, and other conditions are the same.

[0028] Comparative Example 3 The difference between this comparative example and Example 1 is that the vulcanization time is 1 min, and the other conditions are the same.

[0029] Comparative Example 4 The difference between this comparative example and Example 1 is that the pretreated bamboo fiber accounts for 60% of the total material mass, the total mass of the premix and the vulcanizing agent accounts for 35% of the total material mass, and the composite mildew inhibitor accounts for 5% of the total material mass. The other conditions are the same.

[0030] The mechanical properties of Examples 1-3 and Comparative Examples 1-4 were tested according to ISO 527-2. The test results are shown in Table 1.

[0031] Table 1 Mechanical properties test results

[0032] As can be seen from Table 1, when comparing Example 1 and Example 2, the impact strength is improved as the amount of EPDM is increased. This is because EPDM as an elastomer can increase the toughness of the material, while an increase in the proportion of the elastomer will reduce the rigidity, thereby reducing the tensile strength.

[0033] By comparing Example 1 and Comparative Example 1, it can be seen that when the bamboo fiber is put into use without pretreatment, due to the poor interface bonding between the bamboo fiber and the matrix, the bamboo fiber is easily pulled out of the matrix when subjected to force, resulting in a decrease in tensile strength and impact strength, which proves the key role of coupling agent pretreatment in interface enhancement.

[0034] By comparing Example 1 and Comparative Example 3, it can be seen that insufficient vulcanization time leads to insufficient cross-linking of EPDM, unstable structure of the elastomer dispersed phase, and decreased impact strength, which proves that vulcanization is an important step to ensure toughness.

[0035] By comparing Example 1 and Comparative Example 4, it can be seen that when the proportion of bamboo fiber is high, the tensile strength and impact strength of the product will also be affected. The reason is that the high fiber ratio leads to uneven melt mixing, fiber agglomeration, and internal defects, which leads to a decrease in tensile strength and impact strength.

[0036] The mildew resistance performance of Examples 1-3 and Comparative Examples 1-4 was tested according to GB / T 18261-2013, and the results were expressed by mildew resistance time and mildew resistance grade. The results are shown in Table 2.

[0037] Table 2 Anti-mildew performance test results

[0038] As shown in Table 2, by comparing Example 1 and Example 3, the ratio of quaternary ammonium salt in Example 3 is increased, and the first mildew time is prolonged. The reason is that the rapid bactericidal effect of quaternary ammonium salt is enhanced, which verifies the improvement effect of the ratio of quaternary ammonium salt in the composite mildew inhibitor on the mildew resistance.

[0039] Comparing Example 1 and Comparative Example 2, mildew appeared in Comparative Example 2 on the 30th day and reached level 4 after 6 months, which shows the importance of the composite mildew inhibitor in the mildew prevention effect.

[0040] Comparing Example 1 and Comparative Example 4, the first mildew time in Comparative Example 4 is shortened because the excessive bamboo fiber increases the water absorption channel, which leads to the occurrence of mildew. This also proves that the proportion of bamboo fiber must match the composite mildew inhibitor.

[0041] The processing performance tests were performed on Examples 1-3 and Comparative Examples 1-4, and the results are shown in Table 3.

[0042] Table 3 Processing performance test results

[0043] As shown in Table 3, compared with Example 1 and Example 2, the extrusion torque fluctuation increases slightly due to the increase of EPDM, but is still within a stable range, and the hot pressing molding qualification rate remains basically unchanged.

[0044] By comparing Example 1 and Comparative Example 1, it can be seen that due to the poor compatibility between bamboo fiber and the matrix, the melt fluidity is uneven, the extrusion torque fluctuation is greatly increased, the interface delamination is easy to occur during hot pressing, and the qualified rate is reduced to 90%.

[0045] By comparing Example 1 and Comparative Example 3, it can be seen that due to insufficient vulcanization time, the EPDM is insufficiently cross-linked, which in turn leads to melt phase separation, increased extrusion torque fluctuations, and large differences in local fluidity during hot pressing, and the final qualified rate is reduced to 92%.

[0046] By comparing Example 1 and Comparative Example 4, it can be seen that the excessive amount of bamboo fiber leads to increased melt viscosity, which results in unsmooth extrusion during extrusion, a sharp increase in extrusion torque fluctuations, difficulty in filling the mold during hot pressing, and a significant decrease in the qualified rate.

[0047] In summary, by optimizing parameters such as the EPDM ratio and the mildew inhibitor composition, Examples 1-3 exhibited excellent mechanical properties (high strength and high toughness), mildew resistance (long-term mildew resistance), and processing performance (stable and controllable), verifying the rationality of the process of the present invention. The comparative example, by comparison, highlighted the key roles of bamboo fiber pretreatment, sufficient vulcanization, reasonable material ratio, and the addition of the composite mildew inhibitor. These factors together ensure the comprehensive performance advantages of bamboo-based wood-plastic composite materials.

[0048] Therefore, the present invention adopts the above-mentioned bamboo-based wood-plastic composite material manufacturing process based on thermoplastic material molding technology, enhances interface bonding through bamboo fiber pretreatment, optimizes the EPDM and PP ratio and vulcanization parameters to achieve a balance between rigidity and toughness, and the synergistic effect of multiple components of the composite mildew inhibitor improves long-term mildew resistance. It comprehensively solves the problems of poor interface compatibility, insufficient mildew resistance, and difficult balance between processing and performance of traditional bamboo-based wood-plastic composite materials, and has significant practical value.

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A bamboo-based wood-plastic composite material manufacturing process based on thermoplastic material molding technology, characterized by: The following steps are involved: S1, pre-treating bamboo fiber; S2, adding EPDM and PP into an internal mixer and premixing to obtain a premix; S3, preparing a composite mildew inhibitor; S4, adding the pretreated bamboo fiber obtained in S1 and the composite mildew inhibitor obtained in S3 to the melting section of a twin-screw extruder, adding the premix obtained in S2 to the feeding section of the twin-screw extruder, adding the vulcanizing agent to the inlet of the vulcanizing section of the twin-screw extruder for mixing, and extruding and granulating; S5, forming the granules through hot pressing, cooling, and cutting to prepare a bamboo-based wood-plastic composite material.

2. The manufacturing process of bamboo-based wood-plastic composite material based on thermoplastic material forming technology according to claim 1, characterized in that: The specific operation of S1 is: placing the bamboo fiber in a drying oven for drying, and crushing and sieving it through a grinder, then placing the dried and crushed bamboo fiber in a high-speed mixer, and spraying the coupling agent solution for mixing, so that the coupling agent and the bamboo fiber fully react, and then placing the reacted bamboo fiber in a drying oven for drying to obtain pretreated bamboo fiber.

3. The manufacturing process of bamboo-based wood-plastic composite material based on thermoplastic material forming technology according to claim 2, characterized in that: In S1, the primary drying temperature is 80-100°C, the drying time is 4-6 hours, the sieve aperture is 80-100 mesh, the secondary drying temperature is 60-80°C, the drying time is 2-3 hours, and the moisture content of the pretreated bamboo fiber is <2%.

4. The manufacturing process of bamboo-based wood-plastic composite material based on thermoplastic material forming technology according to claim 2, characterized in that: In S1, the coupling agent solution is prepared by weighing 1-2% of the weight of the bamboo fiber coupling agent KH-550, adding anhydrous ethanol to dilute it, and adding glacial acetic acid to adjust the pH to 4-5, stirring evenly and then standing for 5-10 minutes to obtain a coupling agent solution.

5. The manufacturing process of bamboo-based wood-plastic composite material based on thermoplastic material forming technology according to claim 1, characterized in that: In S2, the mass ratio of EPDM to PP is (1-3):(7-9), the temperature in the internal mixer is 160-180°C, the speed is 80-100 r / min, and the blending time is 10-12 min.

6. The manufacturing process of bamboo-based wood-plastic composite material based on thermoplastic material forming technology according to claim 1, characterized in that: The specific operation of S3 is: adding hydrophobic silica, quaternary ammonium salt and nano zinc oxide into a high-speed mixer and mixing, and adding zinc stearate dispersant to obtain a composite mildew inhibitor.

7. The manufacturing process of bamboo-based wood-plastic composite material based on thermoplastic material forming technology according to claim 6, characterized in that: In S3, the amount of hydrophobic silica is 5-10% of the mass of the bamboo fiber, the quaternary ammonium salt accounts for 20-40% of the total mass of the composite mildew inhibitor, the nano zinc oxide accounts for 60-80% of the total mass of the composite mildew inhibitor, the amount of zinc stearate is 1-2% of the mass of the nano zinc oxide, the temperature in the high-speed mixer is 60-70° C., the speed is 1000-1500 r / min, and the mixing time is 15-20 min.

8. The manufacturing process of bamboo-based wood-plastic composite material based on thermoplastic material forming technology according to claim 1, characterized in that: In S4, the twin-screw extruder includes a feeding section, a melting section, a vulcanization section, a homogenization section and an extrusion section. The temperature of the feeding section is 160-170°C, the temperature of the melting section is 170-190°C, nitrogen is passed into the melting section for protection, the temperature of the vulcanization section is 190-200°C, the time is 3-5min, the temperature of the homogenization section is 180-190°C, the temperature of the extrusion section is 170-180°C, and the speed of the twin-screw extruder is 150-200r / min.

9. The manufacturing process of bamboo-based wood-plastic composite material based on thermoplastic material forming technology according to claim 1, characterized in that: In S4, the vulcanizing agent is dicumyl peroxide, and the amount of the vulcanizing agent is 1-2.5% of the mass of EPDM. The pretreated bamboo fiber accounts for 40-50% of the total material mass. The total mass of the premix and the vulcanizing agent accounts for 45-55% of the total material mass. The composite mildew inhibitor accounts for 2-5% of the total material mass.

10. The manufacturing process of bamboo-based wood-plastic composite material based on thermoplastic material forming technology according to claim 1, characterized in that: In S5, the hot pressing molding temperature is 150-170°C, the hot pressing pressure is 10-20 MPa, the hot pressing time is 10-15 min, and step cooling is adopted during cooling, first cooling at 40°C for 10 min, and then cooling at 25°C for 10 min.

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