Interface Behavior And Properties Research Of Novel PVDF/wood Flour Composites System

Wood plastic composites(WPC) are extensively applied to several realm instead of timber, which embodied the valid application of rebirth resources. Comparing with timber, wood plastic composites have less hot flexibility and water absorbability, excellent size stability, anti-bacteria corrosion, convenient usage and maintainability. At present, WPC are mainly composed of wood flour and thermoplastic including polypropylene, polyethylene and poly(vinyl chloride). There are some technique difficulties for these WPC that stil could not generally present the high-durability of ultraviolet ray, the high efficiency of flame retardance and water resistance. Therefore, in this research, polyvinylidene fluoride (PVDF) was chosen to manufactured the WPC, and a technique was put forward. To improve the compatibility of wood flour and PVDF, the surface modification of wood flour was carried out using four different silane. The interface structure of composites, interface response behavior under surroundings action outside which affected the mechnical properties, water resistance and flame retardance were studied systematically. The mechanism of reinforced mechnical properties, high-durability of ultraviolet ray, water resistance and condensed phase synergistic flame retardance were concluded. Finally, PVDF/wood flour composites presenting high properties composed of anti-ultraviolet, water resistance and flame retardance was invented successfully. The main researches are summarized below:(1) To aim at the interface structure and characteristic of PVDF/wood flour composites, the surface modification of wood flour was carried out using vinyltriethoxysilane (A-151), gamma-aminopropyltriethoxysilane (KH-550), Trifluoropropyl-trimethoxysilane (TF3) and (Heptadecafluoro-1,1,2,2- tetradecyl) trimethoxysilane (TF17). The results showed that the wood flour surface acquired hydrophobic modification with different degree by forming Si-O-Cellulose on wood flour surface. Because of the steric hindrance of fluorinated long-chain, the sum of Si-O-Cellulose covalent bonding on the wood flour surface decreased.(2) The effects of interface characteristic on the reinforced mechanical properties of composites were investigated systematically. The results showed that the mechanical of composites were reinforced while the wood flour being modified by appropriate silane. When the concentration of TF3 was 2.0 wt% with respect to the wood flour content, flextual and IZOD impact strength increased to 53.7 MPa and 3.576 KJ/m² respectively. The mechanism of reinforced properties is high van der waals force between organic functional group on wood flour surface and PVDF, and mechanical combinative force. The analysis of interface between wood and PVDF indicated that the fracture surface of reinforced composites presented lengthways-truncation of wood flour. The clear fracture surface were observed.(3) The interface, aggregate structure and anti-aging mechnism of PVDF/wood flour composites exposure to ultraviolet radiation were investigated for the first time. The analysis indicated that there were crosslinking and chain scission at the interface and continuous phase of composites while exposure to ultraviolet radiation. Van der waals force at the interface was affected. The movement ability of polymer chains and mechnical properties of composites were changed accordingly, KH-550,TF3 and TF17 facilitated crystallization in solid amorphous phase of composites interface.(4) The effects of silane on water transmission of composites were investigated. The results showed that interface between silane-modified wood flour and polymer were improved, interface gap shorten and water absorption of composites decreased. Total water absorption of composites exposure to ultraviolet increased, indicating that ultraviolet radiation degradation initiated the increasing amounts of hydroxy group on wood flour surface; multiple hole gererated at the interface and the inside of wood floor cellulose increased the initial water absorption of composites.(5) Synergistic flame-retarded effects between silane and PVDF/wood flour composites were studied. The study showed that synergistic flame-retarded effects were enhanced by silane. H₂O, CO₂ etc generated from materials pyrolytic decomposition form the gas obstruction, which prohibite penetration of oxygen and heat; Wood flour modified by A-151, TF3 and TF17 facilitate the formation of combustion char particles, which effectively obstruct the dispersion of flame and heat. The LOI of PVDF/wood flour composites treated by 2.0 wt%TF3 was 38.7%, 0.8mm sample could be passed by UL94-V0 flame-retarded rating.