As the market demand grows, the wood-plastic technology is quickly dig deep. The plastic wood is also commonly called wood-plastic. It is filled with wood fiber, mixed with PE, or PVC, and then modified accordingly. Materials, which are produced by extrusion or injection molding, include (profiles, plates, urban greening consumables, etc.) to functionally replace wood and plastic.
Wood-plastic products are much cheaper than pure plastic or pure wood. They can be used to recycle waste plant fibers, waste wood powder in wood processing and recycled plastics, which is beneficial to the full use of environment and resources. Advantages of wood and plastic, low density, low cost, water resistance, and sputum resistance; wood powder used for wood plastics is wood powder, bamboo powder, rice husk powder, wheat straw, peanut shell, sugar cane bagasse, etc. The resin has PVC, PE, PP, of which PE accounts for 70%, PVC accounts for 13%, and PP accounts for 17% [3]. Due to the rise in oil prices, the price of PE and PP, which are petroleum-based raw materials, rises, while PVC prices are stable. A development opportunity for plastic-wood composites for PVC base materials. Of course, it is not low cost, we can ignore these have a great impact on the mechanical properties of the products, we can analyze the actual production through actual production.
Wood-plastic products are much cheaper than pure plastic or pure wood. They can be used to recycle waste plant fibers, waste wood powder in wood processing and recycled plastics, which is beneficial to the full use of environment and resources. Advantages of wood and plastic, low density, low cost, water resistance, and sputum resistance; wood powder used for wood plastics is wood powder, bamboo powder, rice husk powder, wheat straw, peanut shell, sugar cane bagasse, etc. The resin has PVC, PE, PP, of which PE accounts for 70%, PVC accounts for 13%, and PP accounts for 17% [3]. Due to the rise in oil prices, the price of PE and PP, which are petroleum-based raw materials, rises, while PVC prices are stable. A development opportunity for plastic-wood composites for PVC base materials. Of course, it is not low cost, we can ignore these have a great impact on the mechanical properties of the product, we can analyze it through experiments.
First of all, we must know that the main components of wood flour are cellulose + lignin + hemicellulose, and other organic matter and water. In actual life, resin powder is added.
Mix the plant fiber mixture such as PVC+ wood powder, mix it on the double roll mill at 170 °C for 5 min, take the film, compress the film, prepare the sample, and the notched impact strength according to the GB1843-80 standard in the ZBC-25B pendulum impact test. The machine is carried out on the machine; the tensile properties are carried out on the CMT6104 universal electronic testing machine according to the GB/T1040-92 standard. Bending performance is tested according to GB1042-79 standard. The impact spline was cooled with liquid nitrogen, then brittle, vacuum-plated on the cross section, and scanned by scanning electron microscopy.
1. The influence variable of the moisture of wood flour in production
Through experiments, we found that when the wood powder is heated, the water first evaporates, and then the easily decomposed part of the lignin is decomposed, further heating the cellulose to oxidize and decompose, and finally the lignin is decomposed. When the modified plastic is filled with the wood powder which is not dried or dried, the residual water in the wood powder and the low-boiling volatile matter in the wood powder cause considerable bubbles in the sample. The mechanical properties of the material are significantly affected; at the same time, proper heat treatment can avoid the phenomenon of “burning†during the processing, and ensure smooth processing, bright products and normal color. Therefore, the wood flour must be dried before filling. In the initial stage of heating, the weight loss of wood bamboo powder is relatively large. Because of the evaporation of bamboo powder when heated, the amount of bamboo powder is basically unchanged after 1 hour. The weight loss of wood powder at 110 °C and 130 °C is mainly The water is volatilized. At the temperature of 150 °C, the bamboo powder in the initial stage of heating, the weight loss value is relatively large, mainly lost water, but as the heating time is extended, the bamboo powder reduction value becomes relatively flat, when the bamboo powder is mainly lost Low boiling point volatiles. When heating, if the temperature is low, the time is short, and the wood powder reduction is less than 3%. For example, if the temperature is high, the heating time is long, and the wood powder is infinitely reduced, it is meaningless and uneconomical. Considering the combination of performance and economy, the wood powder heating temperature is 110 ° C, 130 ° C, and the reduction range is 5-10%.
Second, the influence of resin selection on the mechanical properties of the product
The high filling of wood powder will affect the plasticizing performance and processing fluidity of PVC. The type of resin should be selected according to the melt flow rate (MFR) of the resin. MFR also has certain influence on the performance of the composite. Under the same processing conditions, The MFR of the resin is higher, the overall wettability of the wood powder is better, and the distribution of the wood powder is more uniform, and the wettability and distribution of the wood powder affect the mechanical properties of the composite material, especially the impact strength. The smaller the degree of polymerization of PVC, the higher the MFR of the resin. The parameters provided by the PVC resin manufacturer are not difficult to see. The viscosity of PVC SG-7 or PVC SG-8 is lower and the MFR is higher. Therefore, PVC SG -7 or PVC SG-8 is more suitable as a matrix resin for PVC/Wood Composites.
Third, the effect of wood powder selection on the mechanical properties of products
Wood flour is mechanically pulverized, and the wood powder of different particle sizes is subjected to different forces during the pulverization process. Therefore, wood powders of different particle sizes have different surface roughness and aspect ratio, and the wood itself " Microbubble structures suffer different degrees of damage. The larger the particle size of wood flour, the greater the surface roughness, and the effect of surface roughness of wood on performance is:
1 wood and plastic form a good impregnation;
2 deep interface diffusion and mechanical interlocking at the interface.
If deep interface diffusion and mechanical interlocking cannot be formed at the interface, it means that voids are formed at the interface, resulting in a decrease in material properties. We use 60 mesh, 100 mesh, 300 mesh wood powder to fill PVC, using the following formula
PVC powder SG-7 100
Stabilizer 3.5
Internal and external lubricants 0.5~2.0
aC foaming agent 0.3~0.5
aCR foam processing aid 5.0~8.0
Filler 4.0~6.0
Flame retardant 2.0~3.0
Nucleating agent 0.2~0.7
Plasticizer 5.0~10.0
Modified wood powder 20.0~30.0
Internal and external lubricants 0.5~2.0
aC foaming agent 0.3~0.5
aCR foam processing aid 5.0~8.0
Filler 4.0~6.0
Flame retardant 2.0~3.0
Nucleating agent 0.2~0.7
Plasticizer 5.0~10.0
Modified wood powder 20.0~30.0
We found that the impact strength and flexural strength of PVC/wood flour composites increased first and then decreased with the change of particle size of PVC powder. This trend was confirmed by electron microscopy of PVC/wood powder composites, 60 mesh wood. Powder, high surface roughness, loose structure, PVC resin failed to penetrate into wood powder, more exposed particles, more hollow around wood powder; 300 mesh wood powder, small particle size, easy to agglomerate wood powder; these defects are formed Stress concentration, easy to break under a small force. The 100 mesh wood powder has a moderate particle size, and the interface between the PVC resin and the wood powder has good compatibility, so the impact strength and the bending strength are maximized.
Through experiments, we conclude that: PVC SG-7 or PVC SG-8 is more suitable for base resin of PVC/wood-plastic composite; 100 mesh wood powder, moderate particle size, good compatibility with PVC resin, impact strength and flexural strength The maximum value appears; the pre-drying temperature of wood powder filled PVC is preferably 110 °C.
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