Research status and development direction of modified wollastonite for plastics

Industrial wollastonite products can be divided into two categories: finely ground wollastonite and needle-like wollastonite. The former is mainly used in ceramics and metallurgical industry; the latter is mainly used for its fibrous physical and mechanical properties are widely used in plastics, rubber, paints, coatings, papermaking and other fields, especially in plastics is particularly notable.

Wollastonite is a new type of functional filler, the chemical molecular formula for CaSiO3. Natural wollastonite is often white to grey, density 2.78 ~ 2.91g/cm3, hardness 4.5 ~ 5.0, mostly acicular, radial, fibrous aggregates, even if it is a tiny particles still maintain the fibrous structure.
Industrial wollastonite products can be divided into two categories: finely ground wollastonite and acicular wollastonite. The former is mainly used in ceramics and metallurgical industry; the latter is mainly the use of its fibrous physical and mechanical properties are widely used in plastics, rubber, paints, coatings, paper and other fields, especially in plastics is particularly notable.
Wollastonite in different plastics has many special advantages, but there are also wollastonite surface hydrophilic and oleophobic and plastic compatibility is not good, wollastonite's high hardness will wear the processing equipment and so on, so wollastonite for plastics must do a reasonable surface modification in order to give better play to the advantages of its application in plastics. At present, wollastonite surface modification methods mainly include: coupling agent surface modification method, mechanical force surface chemical modification method, surface inorganic coating method.
Coupling agent surface modification method
This is a traditional commonly used surface modification method, simple process, convenient operation. According to the coupling method, coupling agent surface modification method is divided into general coupling system and reaction coupling system, the former only add coupling agent, the latter at the same time add coupling agent and reactive assistant coupling agent. Commonly used coupling agents include silane coupling agent, stearic acid, aluminate, titanate, zirconate, methacrylic acid, polyethylene glycol, aluminium-titanium composite and other composite coupling agents.
The action mechanism of this method is that one end of the coupling agent molecule can react with the surface of wollastonite, hydrophilicity becomes lipophilicity, forming a strong solid chemical bonding, and the other end of the nature of the organic matter can be physically entangled with the polymer molecules, improving the compatibility with the polymer matrix, so as to firmly combine the two kinds of materials with different properties.

There are more specific examples of general coupling system applications. Yang Qi et al. found that the coupling treatment of ultrafine wollastonite has a toughening and strengthening effect on PP/POE system with good results.
Liu Xinhai and other experiments show that fatty acid and titanate compound treatment of wollastonite chemisorption or chemical reaction, wollastonite modified product surface properties have changed from hydrophilic to hydrophobic; infrared spectroscopy analysis results proved the formation of new grafts on the surface of wollastonite powder, that is, the product of surface modification.
The results of the filling reinforcement application tests showed that the modified wollastonite powder has good reinforcement properties and excellent electrical insulation properties.
Wei et al. found that the optimal process parameters for stearic acid modified wollastonite are: modifier dosage of 2%, modification time of 15-20min, and modification temperature of 70℃. The mechanical properties of the vulcanised film prepared by ultrafine modified wollastonite filled with natural rubber worked relatively well, with tensile strength up to 21.93 MPa (generally up to 19-20 MPa), elongation up to 642.0%, and hardness 57 Shore, which was higher than those of the silica-filled vulcanised film.
Yang Yunbo et al. confirmed that coupling agent-treated ultrafine wollastonite and EPDM synergistically can play a good toughening effect on PP, although the tensile strength of the system is slightly decreased, while the elongation at break is significantly increased.
Li Fumei et al. found that the surface treatment of wollastonite with coupling agent can improve the interfacial bonding between wollastonite and nylon, thus improving the mechanical properties of wollastonite/glass fibre reinforced nylon 6.
Hu Shan et al. showed that wollastonite modified with silane coupling agent can achieve a good activation effect, added to the unsaturated polyester resin, with the increase of wollastonite dosage, the tensile strength, bending strength of the material increases, but there is a great value.
Wu Xueming et al. studied two kinds of wollastonite rigid particles (one by polymethyl methacrylate surface modification, the other is not modified) filled with hard PVC found that, in a certain range of filling amount, the two kinds of wollastonite can improve the impact strength of PVC; the surface of the surface of a layer of PMMA coated with a layer of rigid particles of the second crushed wollastonite in the filling amount of 50, the optimum value of the impact strength of 9.1kJ/m2, tensile strength of 31.8MPa, the impact strength is the best value, and the impact strength is the best value, and the impact strength is the best value. strength was 31.8 MPa, which was 128% and 9% higher than the unfilled one, respectively.
Jia Juanhua et al. showed that the surface treatment of wollastonite by coupling agent can improve the interfacial bonding properties of wollastonite and nylon, and the notched impact strength, tensile strength and flexural strength of wollastonite-reinforced nylon 66 increased, and the overall performance of the material was significantly improved.
Xie Gang and other experiments found that the tensile strength, elongation at break, bending strength and flexural modulus of the blended materials filled with activated wollastonite have a substantial increase in the filling of activated wollastonite, the smaller the particle size of the blended materials filled with activated wollastonite, the better the mechanical properties of the blended materials.
Zhou et al. showed that wollastonite can significantly improve the tensile modulus and flexural modulus of the composite material, and the appropriate amount of wollastonite makes the tensile strength and flexural strength of the material have a certain degree of improvement, but after the content of wollastonite is increased to 20%, the tensile and flexural strength of the material are decreased. Moreover, the reason that silane coupling agent treated wollastonite improves the mechanical properties of the combined reinforced materials is explained as follows: the coupling agent coated on the surface of wollastonite through strong interactions, such as chemical bonding, on the one hand, it reduces the surface energy of the filler, which is conducive to reducing the agglomeration of filler particles and improving the dispersion of the system; on the other hand, it can increase the hydrophobicity of the filler and improve the affinity between filler and the base polypropylene, which can increase the wettability and improve the mechanical properties of wollastonite. On the other hand, it can improve the hydrophobicity of the filler, improve the affinity between the filler and the base polypropylene, thus improving the wettability and the interfacial bonding between wollastonite and polypropylene.