Natural rubber Thermal expansion coefficient

At (ft—> 0 equation [7.2.37] gives a linear dependence of the relative vapor pressure, P°v(/Pvo on the solvent volume concentration with the angle coefficient exp(l+x). At 1 solution obeys the Raul s law. Note that the value of < )i in [7.2.37] is temperature-dependent due to difference in thermal expansion coefficients of components. The % value for a given solvent depends on the concentration and molar mass of a polymer as well as on temperature. However, to a first approximation, these features may be ignored. Usually % varies within the range 0.2 - 0.5. For example, for solutions of polyethylene, natural rubber, and polystyrene in toluene % = 0.28,0.393 and 0.456, correspondingly. 

Temperatures do not depend on the amount or size of filler. The values of the bulk moduli and the thermal expansion coefficients are independent of filler size, but depend considerably on the volume fraction of filler. All filled and unfilled materials show a glass-rubber transition, at which temperature the thermal expansion coefficient increases considerably and the bulk modulus decreases sharply [84]. The mineral fillers seem to modify mechanical properties on three levels [85, 86] in terms of their nature, their size, shape and distribution, and in terms of the changes they bring about in the microstructure of the matrix. 

Fig. Linear thermal expansion coefficients of natural rubber (cured with 0o5> 1.0 2.0 3 0. 0, 10.0 and 20.0 parts of di-cumyl peroxide per hundred parts of rubber) plotted against (X=-l)/(X +2).

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