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 Affect the composite life and raw materials, products, anti-environment capacity, the production process.
 : The water absorption of wood plastic composites.
Wood-plastic composites (WPC) is a class of green materials, the rise in recent years, the main raw material for production of wood-plastic composite materials of agricultural and forestry wastes (wood powder, bamboo powder, chaff powder plant fiber) and waste plastic PE / PP, substitute for natural wood, plant fiber there is the drawback of the high water absorption, and how to reduce the water absorption of wood-plastic composite materials has become a very important technical issues. In this wood-plastic composite absorbent causes, hazards, and water absorption factor.
  The WPC absorbent reasons:
 The main raw material of wood plastic composite materials, agricultural and forestry wastes, the main ingredients of plant fiber. The plant fiber is mainly composed of cellulose, hemicellulose, lignin and cellulose content up to each of the base ring of the repeating unit of cellulose macromolecules containing three hydroxyl cellulose has a high water absorption. In addition, cellulose is linked together by the crystalline and amorphous staggered two-phase system, of which there are many gaps system, which enhances cellulose absorbent. Hemicellulose is a polymer composed of polysaccharide-based, also contain more hydroxyl obviousness absorbent, hemicellulose can not form a crystalline, water molecules easily enter the water absorption is even higher than cellulose. Lignin also contain polar groups, and therefore has certain absorbent, but because of the natural lignin molecular weight hydrophilic groups relative to the cellulose less, so the lower water absorption.
 Wood-plastic composite material filled with a large number of plant fiber, inevitably has a certain amount of water absorption. Although the plant fiber in the wood-plastic composites have been plastic coated, and the surface hydroxyl groups of plant fiber in the production process is compatible with some of the coupling agent or the agent role of esterification or etherification. Therefore, the water absorption of wood plastic composites is much lower than the water absorption of the wood. Studies have shown that wood-plastic composite materials for a long time after immersion in water absorption is not low, especially polyolefin wood-plastic composite materials as wood substitutes for outdoor architectural and outdoor decoration, long-term exposure in the natural environment, exacerbated by a wood-plastic composite absorbent.
 The hazards of the WPC absorbent
mechanical properties: wood-plastic composite materials absorb water and its performance are many reasons. Absorption of water molecules will significantly reduce the mechanical strength of plant fibers, plant fibers will swell, and the surrounding plastic matrix have a tiny crack, these tiny cracks exacerbated by the water absorption of wood-plastic composite materials, making the stress transfer efficiency is greatly reduced, the result that the mechanical strength of wood-plastic composite materials to reduce resistance to freeze-thaw performance variation.
 Wood-plastic composites after water absorption into the free water in the wood-plastic composite materials and plant fiber intermolecular hydrogen bonds, leading to further reduce wood / plastic interface affinity, and these free water will dissolve some of the plant fiber soluble substances, changed the compatibility of wood and plastic interface, the results also reduces the strength of wood plastic composite wpc materials.
  Wood flour content of 50% of MAPE content of 8% of the wood-plastic composite materials, after soaking 40d at room temperature, can make the material tensile strength decreased by 20%, the bending strength decreased by 13%, impact strength decreased by 8%.
   After water absorption of wood plastic composites, the modulus was also significantly reduced. The tensile modulus decreased by 39% wood fiber content of 40% of HDPE based wood plastic composites in water and soak 2000h; wood flour content of 65% of HDPE based wood plastic composites in the saturated absorbent state, the tensile modulus the loss of 40%. After 50h of boiling water, wood fiber content of 30% of HDPE based wood plastic composites, the flexural modulus decreased by approximately 25%; wood fiber content of 40% PP-based wood-plastic composites soaked in water for 2000h, the flexural modulus the loss of 39%.
b Deformation: wood-plastic composites will occur significantly deformed after absorbing water. This is because plant fiber absorbent expansion of the force imposed on the surrounding plastic matrix, in this force, the macromolecular chains of the plastic substrate is prone to molecular relaxation creep, and thus easily lead to wood-plastic composite material deformation. Water exists destruction of the wood / plastic interface, the result will make the relaxation of the plastic molecules more likely to occur, so with the increase of water weight, the total deformation of the wood-plastic composite materials under constant external force increased significantly, dropping the constant external force, permanent deformation of the wood-plastic composite materials also increased significantly.
  Absorbent effect of plant fiber expansion, but also the size of the wood-plastic composite materials change and to intensify their deformation. With the extension of the immersion time, the thickness of the expansion of wood-plastic composites gradually increased, and directly related to the expansion of the thickness of the plant fiber content.
C, moldy materials:
 Fungi of wood-plastic composite materials corrosion problems. Wood-plastic composite materials due to the filling of a large number of plant fiber, plant fiber plastic coated as well as coupling agent or compatibilizer role, therefore no pure plant fiber is so easy to mold rot fungi (mold and wood rot fungi) infection, but water absorption to a certain content can provide a good living environment for the fungus, wood-plastic composite materials to mildew, and even decay, greatly reducing its life. Meanwhile, the mildew will make wood-plastic composite material surface to produce the visible mold spots, affect its appearance.
  3 WPC water absorption factors
 a, the interface compatibility
 As mentioned above, the root causes of wood-plastic composites absorbent plant fiber containing polar hydroxyl group, therefore, reduce the polarity of the reaction of wood plastic composites plant fiber hydroxyl groups and some groups, good interface compatibility reduce the content of plant fibers in wood-plastic composite materials will affect the water absorption of wood-plastic composite materials. Between the fiber and plastic matrix to produce affinity, can reduce the water absorption of wood plastic composites, the better the interface affinity, the lower water absorption. Water absorption of 5% of the MAPP-modified wood-plastic composite materials than the unmodified low of about 2%, such as wood-plastic composite materials with a higher graft rate of MAPP modified with lower water absorption.
 With different coupling agent modified wood composites, water absorption different. Maleic anhydride modified wood plastic composite water absorption of less than silane and titanate, because of the modification effect of the former is better, better closed the hydroxyl of the plant fiber, wood / plastic interface compatibility excellent the latter two.
 The same wood flour content, the higher the maleic anhydride and the role of plant fiber, the more the lower the water absorption of wood plastic composites. MAPE content of 30% wood flour content of 70% of wood-plastic composites, water absorption and MAPE content of 8%, the plastic content of 42%, the water absorption of wood flour content of 50% of wood-plastic composites. This suggests that the water absorption of wood plastic composites plant fiber content is not simply proportional to the interfacial interaction has a significant impact, plant fiber filled with high wood-plastic composite materials, If you have a good interface compatibility , the water absorption can be less than the lower plant fiber content of the wood-plastic composite materials.
 a wood flour content
 The water absorption of wood flour content, wood flour processing the same conditions, higher wood flour content, wood-plastic composite water absorption of the higher, because in the same preparation conditions, the more wood flour, The surface hydroxyl groups more, resulting in higher wood flour content, the higher the water absorption of wood-plastic composite materials; the water absorption of wood plastic composites is much smaller than the timber, absorbent slowed considerably faster than wood.
   Cellulose content in the water absorption in composite materials and plant fiber, plant fiber content increased, the cellulose content is also a corresponding increase in the water absorption of wood plastic composites also increased. In other words, the water absorption of wood-plastic composite material is a cellulose absorbent.
 C, the water temperature has a great impact on the water absorption of wood plastic composites. The higher the temperature, the water absorption of wood plastic composites reach saturation the time required for the shorter.
 d, forming methods
  Molding method there is a certain influence on the water absorption of wood plastic composites. The transfer molding this new method of preparation of wood-plastic composites, compared with low water absorption pressure molding. The reason is that the transfer molding press forming with better wood / plastic interface compatibility and less porosity.
   Wood-plastic composite materials prepared by the same formula, extrusion molding materials with high water absorption, pressure molding, followed by injection molding the minimum, because of repression and injection molding material is relatively dense texture. In addition, the use of wood-plastic composite materials to suppress molding and injection molding, high plastic content of the surface pores less, and thus low water absorption.
 e, the types of fibers
   Different fiber WPC final water absorption is not the same possible reason is the different composition of fiber, water absorption will affect the types and proportions of the basic chemical composition (cellulose, hemicellulose, lignin) fiber.
 These are the water absorption of PP / PE Wood Plastic, PVC wood-plastic absorbent such as above the basic nearly Fortunately, pvc wood products for indoor more, but also for outdoor flower boxes, fence and related outdoor decoration, pvc wood-plastic foam and foam of two kinds, much less the amount of foaming of wood flour than foam, not foam and wood flour added to the resin twice, pvc the water absorption of wood plastic composites also to arouse our attention.
 How to reduce the water absorption of wood-plastic composite materials in addition to the above include the following.
 a process of wood flour moisture excluded as much as possible of wood flour moisture content is controlled below 1%, so have improved the stability of production and product dense. The compactness of such products for the presence of PP / PE / pvc wood plastic foam products, water will play the role of the blowing agent will be noon by shadow, so that the water absorption of the products and reduce the mechanical properties but also to the fungal the growth of the soil.
 b equipment and manufacturing process selection, equipment (extruder and die) is important to choose the structural design for the twin-screw screw, how to ensure good material plasticization. Mold compression ratio and flow channel design help to improve the density and dimensional stability of the products.
 c wood flour mesh size and wood choice of substrate and coupling treatment of wood flour (how to improve compatibility) of wood flour and resin and wood flour and the inorganic filler with a reasonable and rational added.
  d wood plastic production can not be separated from the lubricant quality of lubricants and lubricant and lubricant between the type and amount of match is to ensure normal production and product quality. Such as the type of lubricant, good or bad quality, the level of the melting point, the level of acid value, the size of the molecular weight, liquid and solid. For PP / PE Wood Plastic in basic with the use of stearic acid, paraffin wax, PE wax, stearic acid salt. Lubricant melting point of about 50-60 degrees, including stearic acid, paraffin, bad PE wax will shadow seems that the thermal deformation of the product and will be dissolved in the resin and reduce the infiltration of the fiber. In this way it will shadow noon to wood powder and the inorganic filler and resin compatibility and coupling, and reduce product mechanical properties.
 Ya Yang Composite Materials Technology Co., Ltd. R & D of the PA Series lubricants are the amine class of compounds and complexes of maleic anhydride grafted by the corresponding proportion of PP / PE Wood Plastic special additives, maleic anhydride grafted complexes will dissolve in the resin and wood powder and the inorganic filler has a strong coupling effect, thus greatly improving the wood flour and inorganic filler and resin compatibility, reduce the water absorption of composite materials, the mechanical properties of composite materials not only not reduced instead of increased. With adding a small amount, apply to wood-plastic PP / PE extrusion, injection molding, molding and other processes, and dispersion, lubrication, coupling compatibility versatility.
 Second, the weather resistance of the composite materials.
  1, the composite weather is good or bad for the life of the material and appearance of the shadow noon.
 Two wood-plastic composites weathering objective factors (external environment such as ultraviolet light, water, oxygen, acid, alkali, temperature, etc.) and composite additives (Toner, lubricants, stabilizers, foaming objective factors, etc.) is no solution, only as far as possible in the selection, do not add to or less plus shadow seems that wood-plastic composites weathering of additives.
  3, how to improve the weather resistance of wood-plastic composite materials. In addition to the two mentioned in the shadow noon weathering additives less with or without added need to add to improve the composite weatherability additives such as antioxidants, UV absorbers. But it is difficult to meet the use requirements of this co-extrusion process in the weather and good about the surface of the composite co-extruded 0.1mm thick material such as ASA physical status, but the PP / PE wood-plastic co-extrusion difficult PVC wood.
 Third, the choice of lubricant. The lubricant has been done above some talk, to do some of the following supplement. Good or bad of the lubricant film to noon the following properties of wood-plastic composite materials.
 Products apparent deterioration of (lubricant precipitation surface spots, discoloration, etc.).
 The two products Vicat drop products deformation: Once the products in the course of the deformation will shadow noon product appearance, mechanical properties, weather resistance, decreased water absorption increased fungi more susceptible.
 3, the dimensional stability.
 4, for the PVC wood in addition to products related to the performance of the lubricant will shadow noon with the following additives: plasticizers conducive to the production and processing, but will reduce the product Vicat. The flexibilizer CPE help to improve the toughness of the product, but will reduce the material strength, stiffness and modulus. CPE will lead to decreased thermal stability and light stability, weather resistance variation. PA-48 Ya Yang Technology Co., Ltd. R & D flexibilizer in the toughening of PVC thermal stability and light stability can be greatly improved, greatly improved the weather resistance of PVC products. An equivalent amount of the PA-48 PVC products, PVC products than the CPE in the tensile strength, yield strength, room temperature shock, low temperature impact, elastic modulus and other mechanical properties by 30-40%.
  Ya Yang Technology Co., Ltd. to provide customers with the PVC wood-plastic formulations on the choice of lubricants and additives:
 a, stearic acid in 100 kg of resin added in about 0.2 kg, and never add paraffin.
 b, without the little plus DOP and soybean oil.
 c, without CPE or similar to the CPE elastomer toughening agent.
 d, the foaming agent to the powerful foaming agent of the Division CCR-10, mainly to add 20-40% of the total blowing agent, a CCR-20 with a basic system will not be blowing agent remains in the product can improve The surface of the product rigidity and weathering shadow noon. CCR-10 is a Division I after years of hard work a modified blowing agent used in the development of thermal deformation, weathering resistance, environmental protection and higher sheet, profiles, pipes, gas evolution, slightly smaller than a CCR-20 decompose completely, improve the rigidity of products, Vicat have help. Its decomposition is slow so that the extrudate leaving the die surface quickly cooling, contribute to the formation of dense surface of the foam structure, for Sai Luka crust foam. Products produced small is small: in the course of deformation, strength, high modulus, good weather resistance.