Wollastonite mineral fiber fillings and its industrial application 

 

Currently used in plastic, rubber, adhesives, paint, printing ink and paper, inorganic non-metallic mineral fillers and pigments in many categories, according to their chemical composition can be divided into oxide, hydroxide, carbonate, sulfate, silicate, and several kinds of carbon. In recent years, wollastonite fiber is widely used. In addition, the application of kaolin, talc, mica, silica, aluminum hydroxide, magnesium hydroxide, such as titanium dioxide is also more common. The main effect of wollastonite non-metallic inorganic mineral filler is incremental, enhancement and gives the function, main properties of the filling effect of mineral filler is related to the chemical composition, particle size and particle size distribution, specific surface area, particle shape, packing density, and thermal properties, optical properties, electrical properties and surface properties and other factors.
　　(1) Increment
　　Low-price inorganic nonmetallic mineral fillings are added to reduce the cost of products. For example, calcium carbonate (both heavy and light calcium carbonates) is filled into plastics, rubber and rubber adhesives to reduce the amount of polymers, and calcium carbonate or talcum powder is filled into paper to reduce the amount of paper fiber. These inorganic nonmetallic mineral fillings are also called incremental agents.
　　(2) Reinforcement
　　This means the increase of the mechanical properties (including elastic modulus, tensile strength, rigidity, tear resistance, impact strength, compression strength, friction factor and wear resistance0 of high polymer-based composite materials like plastics, rubber and rubber adhesives. The reinforcement extent of inorganic nonmetallic mineral fillings typically depends on their size or specific surface area and particle shape. Superfine nonmetallic mineral fillings >5μm and acicular or flaky nonmetallic mineral fillings like wollastonite, mica, talc, kaoline and asbestos provide certain or different levels of reinforcement or stiffening properties. By reinforcement level the fillings are normally sequenced fiber fillings > flaky feelings > spherical fillings and by fluidity in base materials they are otherwise sequenced spherical fillings > flaky fillings > fiber feelings.
　　(3) Provision of functions
　　Wollastonite mineral fillings provide the filled materials with some special functions like dimensional stability, flame retardance or resistance, wear resistance, electric conductivity, heat insulation or conductivity, sound insulation, magnetism, generation of negative oxygen ions, bacteria resistance, optical properties (e.g. whitening) and sheltering, in which the chemical composition, light, heat, electricity and magnetism as well as specific area and particle shape of inorganic fillings play a critical role.

　　I. Application in rubber and plastics

　　Wollastonite powder has been used in sulfurized rubber, flooring asphalt ethylene tiles, ethylene resin, polyphenyl ether epoxy resin ethylene board and phenol moulds. To produce epoxy resin, 50% wollastonite powder is used as the color filling agent what provides low water absorption in non-consolidated state. Wollastonite improves the properties of polymers and reduces the price when used as fillings for elastic materials. This compound features high thermal stability, low dielectric index and water absorption and stable mechanical performance.

　　II. Application in papermaking industry

　　Fiber wollastonite is characterized by high whiteness and refraction rate and different shape and structure than conventional fillings. It is more suitably used in printing paper like news paper, coated paper and writing paper in replace of conventional fillings, which may represent a breakthrough into the papermaking industry. Besides, wollastonite fillings provide good dimensional stability, heat resistance, chemical resistance, flame retardance and electric insulation that are incomparable for plant fibers. Wollastonite added into paper pulp will provide the paper with some special properties and may be used to produce special purpose papers. Furthermore, as modified wollastonite fillings come in a special fiber structure, addition into paper pulp will not impair the mechanical strength of paper as much as conventional fillings. This also allows more addition into some papers requiring high mechanical strengths, which will become the major tendency for future research and development of fiber wollastonite.

　　III. Painting and coating industry

　　Use of high-grade wollastonite powder in some painting or coating products as a filling agent in replace of lithopone and some of titanium white or imported P820 improves the leveling of the coatings. The particle shape of wollastonite serves as a satisfactory suspending agent for coatings. Its soft and dispersed sediments can be used as reinforcing agent for clean coatings. Due to it low oil absorption, high filling rate and reduced consumption of bonding materials, the cost for the coatings is greatly reduced. The subalkaline nature of wollastonite makes it very suitable to be used in polyvinyl acetate coatings so that the coloring materials are evenly distributed. It links colors applicable for acid media as well as produces bright colored coatings with evenly distributed properties on the surface and good spraying performance. As a filling material, it improves the corrosion resistance of steel coatings. Besides water-based coatings and polyvinyl formal, it is also used in prime coat, intermediate coat, oil-based coatings, road sign coatings, sound insulation coatings and fireproof coatings. In asphalt coatings it can be used in replace of asbestos while in self-cleaning paints it can be used as a stiffener. Satisfactory performance has also been reported using wollastonite in oil ink industry in replace of titanium white and lithopone.