Fully reinforcing filler

The hydrated precipitated silica used with general-purpose elastomers in HRH adhesive systems (and also as fully reinforcing filler in rubber compounding) comes from water glass (sodium silicate). This is made from natural silica (sand) that is reacted either with sodium hydroxide or sodium carbonate at very high temperatures see Figure 8.6. 

Cotten and Boonstra (150) also investigated stress relaxation in swollen vulcanizates. In these experiments, very near elastic equilibrium, n was found to be of the order of 0.01 or less for unfilled vulcanizates and vulcanizates filled with graphitized black. For rubbers reinforced with fully reinforcing furnace black n was two to three times the value for the unfilled rubber. The additional relaxation appears to be due to slow desorption of polymer segments held relatively tightly at the filler surface. 

The situation is very different for elastomers the use of reinforcing fillers induces a simultaneous increase modulus and deformation at break. Curiously, the replacement of a part of the deformable matrix by solid objects doesn t reduce its deformability. The increase of these two antagonistic properties characterizes elastomer reinforcement. This fascinating paradox, despite not being fully understood, explains the ability of reinforced elastomers to provide... 

Hot-Applied Rubberized Asphalt. Hot-applied rubberized asphalts consist of proprietary blends of asphalt, mineral fillers, elastomers (natural, synthetic, or a blend of both), virgin or reclaimed oil, and a thermoplastic resin. It is applied hot in such a manner as to form an impermeable monolithic membrane over the surface to be waterproofed, which may be concrete, gypsum board or wood. Improved versions of this type of system consist of two coats of rubberized asphalt with a polyester mat in between, ealled the fully reinforced or two-ply system. 

The styrenic thermoplastic elastomers are the only type which are fully compounded in the manner of conventional elastomers. In this case, however, the addition of carbon black, or other fillers, does not give reinforcement. Additions of polystyrene, or high impact polystyrene, and oil are used to vary hardness and tear strength, and fillers can be used to cheapen the material. Other added polymers, e g., EVA, can be used to increase ozone resistance. These materials also require antioxidants for protection during processing and service life, and the poor UV stability restricts their use in outdoor applications. 

Figure 20.3. Comparison of the predicted Young s moduli of binary multiphase materials with morphologies best described by the aligned lamellar fiber-reinforced matrix model (Equation 20.1), the blend percolation model (Equation 20.2), and Davies model for materials with fully interpenetrating co-continuous phases (Equation 20.3). The filler Young s modulus in Equation 20.1 was assumed to be 100 times that of the matrix, and calculations were performed at Af=10, At-=100 and Af=l()00 to compare the effects of discrete filler particles with differing levels of anisotropy. It was assumed that E(hard phase)=100, pc=0.156 and (3=1.8 in Equation 20.2. For...

When properties are more of a concern, lower-cost fillers also can act as extenders that displace not resin, but rather higher-cost reinforcing additives. For example, wollastonite can sometimes partially or fully replace more expensive, milled glass filler, or partially replace chopped glass fibers, while providing similar mechanical properties [7-6, 7-13]. 

The gel coat is often made of the same primary resin as the molded part on which it is applied. A gel coat sometimes contains a pigment. The gel coat does not have the concentration of fillers or reinforcement that the molding compound has. Thus the gel coat provides an attractive resin-rich surface layer. The gel coat can be either applied to the surface of the mold and gelled before layup or applied as a coating after the part is fully processed. 

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