Study On Polymer Modified Rice Husk-Cement Composites

Plant fiber-cement composite is a kind of compound material that is made after a series of procedure. Cement is taken as the substrate, straw fiber is taken as reinforcement, and chemical agent and water is added in the composites. Research and development of the plant fiber-cement composites are based on the research and development of cement-bonded particleboard. However the timber resource of our country is comparatively in short supply. The development of cement-bonded particleboard is restricted in raw material. Most crops straw probably is annual and produces quickly. But trees can be used after being planted many years. Compared with the timber, crops straw is cheap and is not used in industry. Plant fiber used as the construction materials can enhance its value, which has significant economic benefits. It can save resources and protect the environment.In this paper, Styrene-Acrylic emulsion (SAE), vinyl acetate-ethylene copolymer emulsion (EVA) and Polyacrylate emulsion (PAE) at different contents were selected as modifying rice husk-cement composites. rice husk-cement composites are manufactured by the way of treating rice husk with sodium silicate solution and adding polyvinyl alcohol(PVA) fiber. The mechanical properties were tested. The composites were characterized using FT-IR, XRD, SEM and the modification mechanism was explored. Through the above study the following conclusions were obtained: SAE, EVA and PAE all can improve the mechanical properties of rice husk-cement composites, rice husk-cement composites modified by EVA had the best performance. A sotong adhesion film which can block the gaps in the cement composites, was formed between cement and rice husk when adding polymer; chemical reaction was occurred on the polymer with active groups and the surface of Ca(OH)2formed during cement hydration process or the silicate in cement composites; cement hydration and polymer film occurred simultaneously, cement hydration products and polymer film interleaved together. An cross-linked network structure was formed. all these chemical reactions can promote matrix phase and enhanced phase in the cement composite with good combination, thereby mechanical properties of cement composites were improved.Treated by5%sodium silicate solution, chemical reaction happened on the rice husk surface, the original structure of it has exfoliated. The waxy layer had hydrolyzed so the rice husk surface becomes rough and plastic nails formed, the dissolution of the carbohydrate in the rice husk can benefit for combining with cement paste in alkaline conditions. Mechanical properties in the styrene-acrylic emulsion and polyacrylate latex modified cement composites were not improved obviously after adding PVA fiber, Maybe PVA fiber had the tendency to conglobation, it had poor dispersion in the cement composites. Mechanical properties in the vinyl acetate-ethylene copolymer emulsion modified cement composites had been greatly enhanced adding PVA fibers EVA copolymer reduced the calcium hydroxide in the cement paste due to the chemical interaction between Ca2+ions and were released in the EVA alkaline hydrolysis. The acetate anions released by the alkaline hydrolysis of EVA can form organ metallic compounds with Ca2+ions in solution and increase the C-S-H interface. Furthermore, the anions CH3COO-can be incorporated between the layers of C-S-H, thereby increasing the space between them. The presence of PVA may lead to the adsorption or incorporation of-OH group between the layers.