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Additives: As wood flour has a strong water absorption, and very polar, but mostly non-polar thermoplastic, hydrophobic, so the poor compatibility between the two, the interfacial adhesion is small, often need to use suitable additives to modify the surface of polymers and wood flour, wood flour and resin to improve the interface between the affinity and capacity. Moreover, the high amount of wood flour filled with molten thermoplastics dispersed in poor, often in the form of a certain state of aggregation of presence, so that the melt flow is poor, extrusion processing difficulties must be added to the surface treatment agent to improve liquidity in order to facilitate extrusion. Meanwhile, the plastic substrate is also necessary to add various additives to improve the performance of its properties and processing of finished products, the bonding strength and mechanical properties of the composite wood flour and polymer. Common additives include the following categories:
Coupling agent: make produce strong interfacial bonding between the plastic and wood flour; wood flour while reducing water absorption, improve wood flour and plastic compatibility and dispersion, so that the mechanical properties of the composites increased significantly. Common coupling agents are: isocyanates, cumene peroxide, aluminum esters, phthalic acid esters, silane coupling agent, maleic anhydride-modified polypropylene agent (MAN-g-PP), ethylene - acrylate (EAA). 1wt% ~ 8wt% dosage of flour in general addition amount of the coupling agent, such as silane coupling agents can improve adhesion plastic and wood powder, wood powder to improve dispersibility, reduced water absorption, and with an alkaline treated wood meal can only improve the dispersibility of wood flour, wood flour does not improve its water-absorbing plastic adhesion. It should be noted that the maleate salt of stearic acid lubricant and coupling agent will react repulsion, when used with the lead product quality and yield.
Plasticizer: For some of the higher glass transition temperature and the viscosity of the melt flow resins such as hardness PVC, with the wood flour composite processing difficulties, often need to add a plasticizer to improve its workability. Plasticizer molecular structure contains a non-polar and non-polar gene, shear under high temperature, it can enter the polymer chains by genetic polarity attract each other forming a uniform stabilization system, and the longer it polar molecules inserted weakened mutual attraction of the polymer molecules, so that easy processing. In WPC often want to add plasticizers dibutyl phthalate (DOS) and the like. As PVC wood flour composite material, adding plasticizers DOP can reduce the processing temperature, decomposition of wood flour and fuming reduction, improved with the increase by agents DOP content, the tensile strength of the composite decline rate of increase in elongation at break .
Lubricant: WPC is often necessary to add a lubricant to improve the surface quality of the melt flow and extrusion products, lubricants used lubricant into inner and outer lubricant. Internal lubricant selection and matrix resin used in the relevant, it must have good compatibility with the resin at high temperatures and have some plasticizing effect, reduce the cohesive energy within the resin molecules, weakening the mutual intermolecular friction, to achieve lower melt viscosity of the resin, the purpose of improving the melt fluidity. External lubricant in the plastic molding process actually began to lubricate the interface between the resin and wood flour role, its main function is to promote the sliding resin particles. A lubricant generally tend to both internal and external lubricating properties of two kinds. Mold lubricants, barrel, screw life, the extruder capacity, production process energy consumption, low temperature impact properties of the article surface finish and profiles have a certain impact. Commonly used lubricants are: hard bile zinc ethylene bis-fatty acid amide, polyester wax, stearate, lead stearate, polyethylene wax, paraffin wax, oxidized polyethylene wax.
Coloring agent: In the course of wood plastic product, wood flour in a solvent material can easily migrate to the surface of the product so that the product bleaching, and eventually becomes gray, different products in a certain environment, will produce spots or rust . Therefore, the colorant in the production of wood-plastic composite material also has a relatively wide range of applications. It enables products are uniform and stable color and decolorization slow.
Foaming agent: WPC has many advantages, but because of the composite resin and wood flour to reduce the ductility and impact resistance, brittle materials, large density of nearly 200 times faster than conventional wood products, limiting its widespread use. The WPC foamed after because there is a good cell structure, can effectively prevent the passivation of the crack tip and crack expansion, which significantly improves the impact resistance and ductility of the material, and greatly reduces the density of the article . Many different types of foaming agents commonly used are mainly two: endothermic foaming agent (such as sodium bicarbonate NaHCO3) and exothermic foaming agent (azodicarbonamide AC), different thermal decomposition behavior of polymeric viscoelastic foam morphology and composition of the melt have different effects, and thus to select the appropriate blowing agent in accordance with the requirements of the article.
UV stabilizers and other: The UV stabilizers are as people and improve the quality of wood-plastic composites durability requirements of rapid development. It enables the composite polymer does not degrade or mechanical properties decrease. Commonly used are hindered amine light stabilizers and UV absorbers. In addition, in order to make the composite material to maintain a good appearance and perfect performance, often you need to add a fungicide, fungicide choice to consider the type of wood powder, containing added amount, the use of composite materials in the environment fungi, products water and other factors. Such as zinc borate preservative but can not prevent algae.
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