| During the last decade, there has been a considerable attention in wood-plastic composites (WPC) by dispersion of wood flour (WF) in a polymer matrix. However poor interface compatibility and flame retardancy restrain the application of WPC. There are some effective methods have been used to optimize the interfacial adhesion properties, such as silane or maleic anhydride, but brought fire danger at same time. Halogen-containing flame retardants show high efficiency but large amount of smoke and toxic gas were released during combustion. An intumescent flame retardant system was friendly to environment. However, the high addition will result in worsen on mechanical performance. Three parts of research work were contained in this paper.Two kinds of ethylene-acrylic acid (EAA) and ethylene vinyl acetate (EVA), were introduced to high density polyethylene-wood flour composites (HDPE/WPC) in order to improve the interface adhesion. The acrylic acid content was different for EAA-5990 and EAA-3340. Compared to EAA-3340, EAA-5990 greatly improved the interface adhension at the same cotent addition. But EVA had a negative effect on the WPC interface modification. Compared to unmodified WPC, the tensile strength and flexural strength of WPC were increased to 30.7MPa and 53.5MPa, which were improved 111.7% and 85.8% with the content of 7% EAA-5990, respectively. And the water absorption and thickness swelling also were decreased greatly for WPC containing EAA-5990 and EAA-3340, but increased for WPC containing EVA. FTIR analysis indicated that hydrogen bond did occur between hydroxyl group of WF and carboxyl group of EAA-5990 or EAA-3340. The morphology of fracture surface of WPC was characterized by Scanning electron microscope (SEM); and it suggested that voids hardly presented in WPC containing 7% EAA. The results clearly proved that good interface adhesion between HDPE and WF was obtained by the formation of hydrogen bond.The effects of ammonium polyphosphate (APP) and WF content on the flame retardant and mechanical properties of WPC were investigated. The flammability of WPC was characterized by limiting oxygen index (LOI), vertical burning (UL-94) and cone calorimeter (CONE) tests. The results indicated 22%APP/40%WF addition enhanced LOI to 30.5 and achieved UL-94 V-0 level. CONE data revealed that heat release rate (HRR) and total heat release (THR) were significantly decreased from 530 to 228 kW/m2.113 to 75 MJ/m2 respectively. Thermogravimetic analysis (TG) and FTIR demonstrated that thermal stability of WPC was improved due to that some chemical reaction did occur between wood flour and APP to form strong protective char. The tensile strength and flexural strength of WPC were also improved due to the presence of WF as reinforced materials.A novel flame retardant was prepared by ion exchange reaction. APP was grafted on the nano SiO2 by silane coupling KH-550, the product was called APP-K-nano SiO2. The LOI continue increased to 32.1 and UL-94 V-0 rating at the loading of 22% APP-K-nano SiO2. Cone results revealed that PHRR, THR, TSP also greatly decreased to 141 kWm-2,44 MJm-2,and 10 m2 respectively. TG results shown that APP-K-nano SiO2 promoted the char forming and improved the heat stability of WPC sample. The FTIR and element energy spectrum (EDS) were used to analyze the fire retardant mechanism. It was revealed that the Si-O-P-N crosslinking structure was formed to improve flame retardancy of WPC. |
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