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Plastic wood composite products have been widely used in various outdoor and indoor applications. Such as: plastic wood composite doors, door covers, shutters, cabinets, wardrobes, exterior wall hanging panels, ceilings, decorative wall panels, skirting lines, floors, floor keels, guardrail columns, pavilions, gallery frames, fences, leisure chairs, flower stands, flower boxes, tree ponds, tree enclosures, air conditioners, air conditioner covers, road signs, transportation trays, etc. In particular, plastic wood composite materials have excellent waterproof, moisture-proof, acid and alkali resistance, and corrosion resistance. The advantages are particularly significant when used in high-salt areas at the seaside. Plastic wood composite profiles are easy to use and flexible in application. They can not only replace the use of wood, but also are a new type of environmentally friendly material with excellent performance. The market prospect is very broad.
Plastic wood composite materials have excellent comprehensive performance, and there are more and more varieties and quantities of plastic wood composite used in outdoor construction and landscape. With the continuous progress of manufacturing technology and process, the appearance quality of products has greatly improved. However, many plastic wood composite companies, and even many large brand companies, have inherent defects in material design due to lack of targeted research. These deficiencies often only gradually exposed the problems after two or three years of construction. At this time, it is too late to solve the problems. When tracking down issues, material design defects are often difficult to find. After a period of use in outdoor plastic wood composite buildings and landscapes, some longer-scale plastic wood composite will gradually bend and sag. This is a common defect in outdoor plastic wood composite buildings and landscapes. The plastic wood composite material is beautifully straight when it is built, and gradually bends and deforms after several cold and heat.
Temperature stress and creep
The temperature rises in summer, and the plastic wood composite material produces thermal expansion. Longer plastic wood composite has greater thermal expansion. Because the two ends are fixed, the temperature stress is also large (the stress and expansion are proportional to the deformation). When the expansion reaches a certain value, the plastic wood composite will become unstable and bend and bend with the increase of thermal expansion. Degree (bending deformation) increases. If the installation is in the hot season, the temperature difference from the maximum temperature is small, so there is basically no bending and deformation due to thermal expansion. However, in the low temperature season, the toughness and strength of plastic wood composite decrease with temperature; because the two ends are fixed, the temperature stress caused by the cooling and shrinkage of plastic wood composite reaches the maximum value, which often leads to the damage of the fixed place.
Water swelling and creep
During the rainy season, the plastic wood composite material absorbs water and expands, and the plastic wood composite material produces a small amount of creep elongation, which cannot be recovered; and with the alternating cycle of dry and wet, it periodically generates creep elongation and superimposes. As the wood inside the plastic wood composite reaches the possible water swelling limit and the binding force of the polymer material, the increase in water swelling creep elongation gradually decreases to zero, reaching the creep limit. The creep of plastic wood composite material is the combined result of temperature stress creep superposition and water-absorbing expansion creep. When both ends of plastic wood composite material are fixed and restrained, with the superposition of various creeps of plastic wood composite material, it is a beautiful linear material when built , gradually appearing obvious bending; and alternating between several cold and heat.
Design scheme of plastic wood composite material deformation
The moisture absorption of the polymer base in the plastic wood composite material is very small, and the moisture absorption of the plant fiber is large. In formula design and process design of wood plastic materials, the water absorption of wood plastic materials must be reduced as much as possible, and the strict water absorption rate shall be used as the quality index for assessment; temperature stress and creep are determined by the characteristics of the material, and must be determined from the polymer material itself finds an improvement plan. Controlling and reducing the linear expansion coefficient of plastic wood composite materials can effectively control and reduce temperature stress.