Research Of Surface Treatment And Application Of Wollastonite Products From Daye In Hubei Province

Wollastonite is a fibrillar dissociated metasilicate mineral with excellent physical and chemical properties,such as needle structure,high whiteness,thermal expansion low coefficient,high flame retardancy and electrical insulation,chemical stability.Wollastonite has broad application prospects with the development of deep processing technology,it has become a high-quality raw material in many industrial fields,including polymer rubber and plastics industry,paint and coating industry,building materials industry,ceramic metallurgy industry and paper industry.In this paper,for the wollastonite form Fengjiashan in Daye,hubei province,surface modification treatment of wollastonite and the application of the modified wollastonite were studied.Firstly,the dry modification process was used to modify the surface characteristics of wollastonite,and the effects of different agents on surface modification were investigated.Surface changes of modified wollastonite were analyzed by Fourier Transform Infrared Spectroscopy(FTIR).Secondly,the modified wollastonite was filled to natural rubber(NR)and PA66 called polymer matrix separately.Different effects of wollastonite and modified wollastonite on the mechanical properties of polymer matrix were compared.And the tensile fracture surfaces of the composite material were observed and analyzed by SEM.The results of the surface modification test were as follows Silicone oil agents have better effects on the modification of wollastonite than other modifiers.After being treated by silicone oil agents,the activation index reaches 99%～100%and the contact angle reaches up to 120°,through physical adsorption and hydrogen bond.For the long-chain organic amines,octadecylamine has better modification performance than dodecylamine.Treated by octadecylamine,the activation index is about 94%,and the contact angle is about 100°.Similar to silicone oil agents,through the same mode as silicone modification.Among the fatty acid agents,the activation index of modified wollastonite treated by stearic acid is 80%,and the contact angle is 110°,and by castor oil,the activation index is about 90%,andcthe contact angle is 60°.The main adsorption models of stearic acid on wollastonite surface include hydrogen bond and chemical adsorption.Moreover,the effects of silane coupling agents and aluminate coupling agent on wollastonite surface modification were investigated separately.After being treated by the silane coupling agent,activation index of the modified wollastonite is 99%～100%,and the contact angle is about 110°,90%and 95° for those treated by aluminate.Chemical adsorption and physical adsorption were verified to be the main adsorption models of coupling agents on wollastonite surface.The filling tests showed that wollastonite modified by agents have different effects on the mechanical properties of the composites,which consist of wollastonite and polymer matrix.When wollastonite or modified wollastonite was filled into NR,the tensile strength and hardness of the composite were improved by amine agents,and the tear strength and stretching strength were improved by silane coupling agents.For the wollastonite particles with size between 8 μm and 24 μm,the particle size of wollastonite has little effect on the mechanical properties of natural rubber.When 10 phr～70 phr of the wollastonite or modified wollastonite were added,the mechanical properties of composite decreased with the increasing addition amount of filler.For the composite composed of PA66 and wollastonite,the addition amount of wollastonite is less than 40%,and the tensile strength and flexural strength of the composite increased gradually with the increasing addition amount of wollastonite.When wollastonite with particle size of 8 μm～24 μm was added,the mechanical properties of PA66 increased firstly and then decreased with the increase of particle size.It was shown that the mechanical properties of composite were the best when wollastonite with the size of 14.79 μm was filled into PA66.Furthermore,different wollastonite modified by different chemical agents has different effects on the mechanical properties of PA66 composites.KH-592 performed well in improving the mechanical properties of composite composed of wollastonite and PA66.When wollastonite modified KH-592 were added,the effects of particle size and addition amount of wollastonite on the mechanical properties of the composite were similar to that of unmodified wollastonite.Based on the tensile fracture surface analysis of the composite by SEM,Si-69 could improve the interfacial adhesion of wollastonite and natural rubber matrix significantly.Additionally,the dodecyl group could improve the dispersibility of wollastonite in the rubber matrix effectively.The excessive addition amount of wollastonite was detrimental to the continuity of the rubber matrix.KH-592 improves the dispersibility of wollastonite in PA66 and the interfacial adhesion of wollastonite to PA66 significantly.