Study On Preparation And Properties Of Polypropylene Composites Filled With Wollastonite

Polypropylene(PP) is a thermoplastic base resin which is widely used in automobile industry, building materials, household appliances, agricultural application, etc. Using natural mineral filled polypropylene can effectively improve its mechanical properties and reduce the cost. We respectively used silane coupling agent(KH-570), stearic acid(SA), silane coupling agent and stearic acid compound modifier to modify wollastonite, and then successfully used the modified wollastonite as a filler to prepare wollastonite/polypropylene composite material with excellent mechanical property. The main research work is as follows:Firstly, optimized the reaction conditions of silane coupling agent modifying wollastonite, The experimental results show that when the dosage of silane coupling agent was 4% of the quality of wollastonite, pH of the reaction system was 5, stirring speed was 600 r/min, reaction time was 2 h and reaction temperature was 80 ℃, the modification effects of wollastonite is the best. The water contact angle of modified wollastonite could reach 120.79 °. FTIR and TG analysis showed that wollastonite was successful modified by silane coupling agent, modification mechanism was that silane coupling agent first hydrolyzed forming silanol, then reacted with hydroxyl groups on the surface of the wollastonite, formed a layer on the surface of wollastonite in molecular membrane, making wollastonite surface changed from hydrophilic to hydrophilic.Secondly, optimized the reaction conditions of stearic acid modifying wollastonite, Experimental results show that the best modification effect achieved when the stearic acid dosage was 2% of the quality of wollastonite, the reaction time for 1 h, the reaction temperature was 80 ℃, stirring speed of 600 r/min, best modification result was gained and the water contact angle could be 131.35 °. Compared with silane coupling agent the modification effect had got improved. FTIR and TG analysis showed that stearic acid had successfully modified wollastonite. Stearic acid was coated on the surface of wollastonite by chemically bonded moiety.Thirdly, silane coupling agent and stearic acid were used as compound modifier to modify wollastonite, the best modification effect achieved when the ratio of KH-570 was 50%, the addition of two modifiers was 4%, 80 ℃ for 2 h, and stirring speed of 600 r/min, the water contact angle reached 143.25 °. Wollastonite’s lipophilicity was obviously improved. FTIR showed that both silane coupling agent and stearic acid on modifying wollastonite were effective, composite modified wollastonite had both silane coupling agent and stearic acid modified wollastonite’s characteristics.Lastly, through comparing, we got that when the dosage of filler was 20%, the wollastonite modified with compound modifier /polypropylene composites had the best mechanical properties: impact strength was 9.38 kJ?m-2, tensile strength was 33.67 MPa, bending strength was 45 MPa. They were 86.11%, 7.43% and 22.88% higher than that of neat PP. At the same time the wollastonite modified with compound modifier /polypropylene composite had the highest vicat softening point, reaching 155.4 ℃. Compared with neat PP the composite had a better thermostability.SEM of composites analysis showed that adding modifier can improve the dispersion of wollastonite in polypropylene. Compound modification is superior to the single modification.