[Effect of sodium chloride on elasticity of silicone matrices]

An increase in the availability of the active ingredient from silicone matrices can be achieved by using sodium chloride as the filler. An addition of sodium chloride also influences the mechanical properties of silicone systems. The temperature dependence of real Young's model E' of addition silicone systems with sodium chloride was measured. With increasing NaCl concentration in the silicone system, the values of Young's module E are increased. The increase is also influenced by the particle size of NaCl. The values of the module are moderately increased also with increasing temperature, which corresponds to the kinetic theory of caoutchouc elasticity. A significant increase in E takes place at NaCl concentrations higher than 20%. With a 50% NaCl content in the system, E is increased approximately 3.5 times in comparison with an unfilled sample. Various theories of elastic behaviour of composites can be employed for the description of the effect of the filler on the mechanical properties of silicone systems under small deformations. The effect of chloride is best described by the relation proposed by Nielsen. The value of the constant A in Nielsen's relation, dependent on the shape of the filler particles and Poisson's constant of the unfilled matrix, decreases with increasing particle size. With a change in particle size, a certain change in particle shape takes place. Hydrodynamic theory provides good results for sodium chloride particle size of 102.5 microns, but for particle sizes of 20 microns and 60 microns it is less successful than Nielsen's relation.