Dilatometric investigation of deformation mechanisms in polystyrene-polyethylene block copolymer blends. Correlation between Poisson ratio and adhesion

The deformation behavior of blends contg. polystyrene (I) [9003-53-6], low-d. polyethylene (II) [9002-88-4], and a hydrogenated butadiene-styrene diblock copolymer (III) was examd. by tensile testing with simultaneous vol. measurements. Assuming that shearing causes no vol. changes, crazing, after yielding, was the only deformation mechanism in blends with low I and III contents. Shearing became important in blends with high I concns. due to formation of a semicontinuous low modulus phase. The decrease in the Poisson ratio with increasing II content in I-II blends, as opposed to an increase in the presence of III, shows the Poisson ratio to be very sensitive to adhesion between the components. The toughness of I-II blends is discussed in terms of concns. of craze nuclei. Too few craze nuclei give rise to brittle failure because the resulting low no. of crazes cannot accommodate much deformation of the matrix whereas too many craze nuclei also cause brittle failure because of the high probability of combination of the crazes to form a crack. The concn. of craze nuclei depends on the no. of dispersed particles and their adhesion to the matrix. [on SciFinder (R)

The influence of shrinkage on drying behaviour of clays

A correct description of the evolution of moisture concn. profiles in shrinking materials is complicated by the influence of shrinkage on mass transfer. Shrinkage has to be accounted for in the diffusion equation. Simulations have been performed for three types of shrinkage: isotropic, unidirectional and no shrinkage. Since many materials show isotropic shrinkage behavior, unidirectional and no shrinkage should be considered as approxns. of the actual material behavior. Various numerical simulations show that for clays the influence of the type of shrinkage on drying curves is smal