Silica fillers reinforcement

Zinc salt of maleated EPDM rubber in the presence of stearic acid and zinc stearate behaves as a thermoplastic elastomer, which can be reinforced by the incorporation of precipitated silica filler. It is believed that besides the dispersive type of forces operative in the interaction between the backbone chains and the filler particles, the ionic domains in the polymer interact strongly with the polar sites on the filler surface through formation of hydrogen bonded structures. 

Mark and his co-workers reported the reinforcement of poly(dimethylsiloxane) networks by silica gel particles [1-6]. For example, bis(silanol)-terminated poly-(dimethylsiloxane) was reacted with tetraethoxysilane in the presence of acid-catalyst to produce the reinforced siloxane networks. The reaction proceeded homogeneously. The content of the silica filler can be controlled by the feed ratio of polysiloxane and tetraethoxysilane. 

Generally speaking, commercial rubber products are manufactured as a composite from a rubber and a nano-filler, which is in a group of fillers of nanometer size (mainly, carbon black and particulate silica). For an example, a pneumatic tire for heavy-duty usages such as aircrafts and heavyweight tracks is made from natural rubber (NR) and carbon black and/or silica. Their reinforcing ability onto rubbers makes them an indispensable component in the rubber products [1,2]. 

Silica fillers are generally used to reinforce these materials, carbon black being less reinforcing, and its use being somewhat specialised. 

Silica fillers also react with the rubber causing an increase in viscosity and dry and unmanageable processing behaviour. Filler activators need to be added to silica-reinforced compounds to overcome these problems. The usual filler activators used are diethylene glycol, polyethylene glycol and amines such as triethanolamine. Some of these activators not only overcome the problems of processing and accelerator absorption, but depending on the cure system used, will also act as vulcanisation activators. 

Nitrile mbber is much like SBR in its physical properties. It can be compounded for physical strength and abrasion resistance using traditional fillers such as carbon black, silica, and reinforcing clays. The primary benefit of the polymer is its oil and solvent resistance. At a medium ACN content of 34% the swell in IRM 903 oil at 70°C is typically 25—30%. Nitrile mbber processes on conventional mbber equipment and can be compression, transfer, or injection molded. It can also be extmded easily. 

Fig. 5. shows the technology progress of the extension fatigue durability of silicone rubber. At present, silicone rubber achieves a fatigue durability of about 50 million cycles by using improved dispersion uniformity of the reinforcing silica filler [12]... 

In semicrystalline polymers, fillers may act as reinforcement, as well as nucle-ation agents. For example in PP, nanoscale silica fillers may nucleate the crystallization resulting in spherulites that show enrichment in particles in the center of the spherulite (Fig. 3.64). For a quantitative analysis of, e.g., filler sizes and filler size distributions, high resolution imaging is necessary and tip convolution effects [137-140] must be corrected for. The particles shown below are likely aggregates of filler particles considering the mean filler size of 7 nm [136]. 

Silica fillers play a prominent role in the paste rheology of polyurethane and rubber coating mixtures. Silica fillers are also used for surface matting. In polyurethanes, the layer thickness is even thinner than is used with PVC. Dispersion is enhanced by dispersion aids. Fillers are used at relatively low concentrations in PU formulation. But in rubber coatings, large quantities of calcium carbonate are used to decrease cost. Rheology and reinforcement are adjusted with carbon black. 

Experiments were performed on DC745U and M97 silica-filled silicone polymers as described elsewhere [1-5]. The gum stocks for all formulations were co-block polymers of dimethylsiloxane, diphenylsiloxane, methylphenylsiloxane, and/or methylvinyl siloxane. The gum stock was reinforced with high surface area silica filler and crosslinked with peroxide curing agents. These materials were tested in both new as well as service return conditions. 

---