Additives: because wood powder has strong water absorption, and strong polar, and thermoplastic most nonpolar, hydrophobic, so between the poor compatibility of bonding interface is very small, often need to use the appropriate additive to the modified polymer and wood powder surface. In order to improve the interface between wood powder and resin affinity. Moreover, high filled plastic wood flour in the melt in the heat dispersion effect is poor, often exist in some form of aggregation, the melt flow is poor, extrusion molding difficult, need to add surface treatment agent to improve liquidity for extrusion molding at the same time, the plastic substrate also need to add all kinds of help The utility model can improve the processing performance and the performance of the finished product, improve the bonding force between the wood flour and the polymer and the mechanical properties of the composite material:
The coupling agent can produce strong interfacial adhesion between plastic and wood powder surface; at the same time to reduce the water absorption of wood powder, improve the dispersibility and compatibility of wood powder and plastic, so the mechanical properties of the composites increased obviously. The coupling agent commonly used are: isocyanate, dicumyl peroxide, aluminate phthalic acid, esters, silane coupling agent, maleic anhydride modified polypropylene agent (MAN-g-PP), ethylene acrylate (EAA). The general content of coupling agent was added to 8wt% 1wt% wood powder, such as silane coupling agent can improve the bonding strength of plastic and wood powder, good dispersibility of wood powder, reduce water absorption, and Treatment of wood powder can improve the dispersion of wood powder with alkali, adhesive and plastic and wood powder can improve water absorbency. It should be noted that the maleic acid salt, coupling agent and stearic acid salt lubricant will happen repulsion reaction when used together leads to the decrease of the quantity and quality of the products.
Plasticizer for glass transition temperature and the melt flow of high viscosity resin such as the hardness of PVC composite, difficult processing and wood powder, often need to add plasticizers to improve its processability. Plasticizer molecular structure containing polar and non polar two genes, in the high temperature shear under the action of it can enter the polymer molecular chain, the polarity genes attract each other to form a uniform and stable system, and nonpolar molecules it long into the reduced attraction of polymer molecules, so that the processing is easy. To often added plasticizer dibutyl phthalate in WPC (DOS) such as in. PVC wood powder In the composites, the addition of plasticizer DOP can reduce the processing temperature, reduce the decomposition of wood powder and smoke, and improve the tensile strength and elongation at break with the increase of DOP content.
The surface quality of lubricant wood composite liquidity often need to add lubricant to improve the melt and extrusion products, the lubricant is divided into internal and external lubricant lubricant. In the selection of lubricants and related matrix resin used, it must be with the resin has good compatibility in high temperature, and have a certain increase plastic resin, reduce the intermolecular cohesive energy, weaken the mutual friction between molecules, in order to reduce the viscosity of the molten resin, improve melt flowability. External lubricant in the plastic molding processing actually played the role of lubrication between the interface of resin and wood powder, its main function is to promote the sliding of the resin particles Usually a lubricant and often two, lubricating performance. Lubricant to the mold, the barrel life of screw extruder, production capacity, energy consumption in the production process, are affected by low temperature impact properties of surface finish products and profiles. Commonly used lubricants: hard acid zinc ethylene bis, fatty acid amide, polyester wax, stearic acid, lead stearate, polyethylene wax, paraffin wax, oxidized polyethylene wax.
The use of colorants in wood plastic composite materials in the process of wood powder in the solvent material easy to migrate to the surface of the product, make the product decolorization, and eventually become gray, different products in a certain environment, will produce dark spots or rust. Therefore, colorants in wood plastic composite materials production also has been widely used. The products have uniform and stable color, and was slow.
The foaming agent composite material has many advantages, but because of composite resin and wood flour, the ductility and impact resistance reducing material, brittle, density is higher than the traditional wood products is nearly 2 times as large as, limited its widespread use. The wood plastic composite materials after foaming due to good foam structure is good the crack tip can be passivated and stop the expansion of the crack, which significantly improves the material impact resistance and ductility, and the density of the products greatly reduced. Many types of foaming agent, commonly used mainly has two kinds: endothermic blowing agent (such as sodium bicarbonate NaHCO3) and exothermic foaming agent (azo two AC), the hot formamide The decomposition behavior is different, which has different effects on the viscoelasticity of polymer melt and the foam form, so it is necessary to choose the appropriate foaming agent according to the use of the product.
Application of ultraviolet stabilizers and other UV stabilizers also along with the people to the wood plastic composite material quality and durability requirements increase rapidly. It can make the composite polymer degradation or mechanical properties decrease. Used a hindered amine light stabilizer and ultraviolet absorber. In addition, in order to make the composite material can keep good appearance and perfect performance, often need to add antibacterial agent, antibacterial agent to the selection of species, the amount of wood powder, composite materials using fungi in the environment, water content and other factors of products. Such as the zinc borate corrosion but not anti algae.