Application of 7 categories of nano-powder materials in liquid silicone rubber
Liquid silicone rubber is mainly composed of basic polymers, reinforcing fillers, cross-linking agents and various auxiliaries in a certain proportion to prepare a base rubber with self-leveling and thixotropy, and then mix it with air at room temperature or under heating conditions. Elastomers formed by contact with moisture in or with cross-linking agents.
Because the physical and mechanical properties of pure liquid silicone rubber are very poor, it generally needs to be reinforced and modified to meet the needs of practical applications. Among them, adding reinforcing fillers is undoubtedly the most concise and convenient method. Commonly used nano-fillers are nano-silica, nano-calcium carbonate, organic montmorillonite, carbon nanotubes and graphene, nano-zinc oxide, nano-titanium dioxide, silicon carbide, aluminum oxide and nano-silver wires.
1. Nano silica
The synthesis methods of nano-silica are mainly based on gas phase method and precipitation method. Nano-silica prepared by gas phase method has few surface hydroxyl groups, uniform particle size and good dispersibility. Zhu Zhimin et al. used fumed silica as a reinforcing filler and found that after adding 10 parts of silica, the physical and mechanical properties of liquid silicone rubber were significantly improved, and the Shore A hardness, tensile strength and shear strength could reach 40, respectively. , 1.6MPa, 1.4MPa; there is no significant change in shear strength after aging.
Due to the higher cost of fumed silica, the lower cost precipitated silica is of interest. The water content of the precipitated silica is higher, and the surface hydroxyl number is much higher than that of the fumed silica, which makes the surface activity of the precipitated silica very high, and it is easy to agglomerate, which is not conducive to dispersion in the rubber matrix. In order to solve this problem, physical or chemical methods are usually used to modify its surface to prevent the occurrence of agglomeration and improve its dispersibility.
2. Nano calcium carbonate
Nano calcium carbonate has the advantages of small particle size, high specific surface area, high surface activity, large filling amount and convenient processing. , Nano calcium carbonate is widely used in liquid silicone rubber as a common reinforcing filler.
3. Organic Montmorillonite (OMMT)
Montmorillonite (MMT) is a typical layered silicate and is a relatively common reinforcing filler in the rubber industry. In order to improve the compatibility of MMT with silicone rubber, it is usually organically modified to obtain OMMT. The study found that OMMT can be well dispersed in the silicone rubber matrix, thereby greatly improving the physical and mechanical properties of the silicone rubber.
4. Carbon Nanotubes (CNTs)
Due to the large aspect ratio, high modulus, extremely high toughness and low density of CNTs, they have always attracted attention, so the research of CNTs in the field of liquid silicone rubber reinforcement has become more and more extensive.
5. Graphene
Graphene is a kind of two-dimensional nanomaterial with hexagonal lattice arrangement formed by sp2 carbon atom hybridization. It has excellent electrical, thermal and physical and mechanical properties, and has stable performance, wide sources and simple preparation. , is a very ideal functional filler.
6. Nano zinc oxide
ZnO is a commonly used vulcanization activator in the rubber industry, and can also be used as a filler to improve the physical and mechanical properties and thermal conductivity of materials.
In theory, reducing the particle size of ZnO and increasing the specific surface area are beneficial to improve the reactivity, so nano-ZnO can be used as a functional reinforcing filler for liquid silicone rubber. In addition, ZnO is also a good UV shielding agent with anti-aging properties. The modified ZnO can also impart new properties to silicone rubber such as self-cleaning properties.
7. Nano titanium dioxide
Nano-titanium dioxide has the characteristics of less surface defects, more unpaired atoms, and large specific surface area. When it is used to strengthen rubber, it is prone to physical or chemical bonding and increases cross-linking sites, which is beneficial to improve the physical and mechanical properties of rubber materials. After being subjected to external force in the stress field, nano-titanium dioxide produces micro-domain deformation in the matrix to absorb energy, and the rubber material exhibits good radiation resistance.
Other functional reinforcing fillers In addition to the above-mentioned functional nano-reinforced fillers, there are many other types of reinforcing fillers, such as silicon carbide, alumina, nano-silver wires, etc. These reinforcing fillers can not only effectively improve the physical properties of liquid silicone rubber. Mechanical properties can also impart some special properties.