Abstract:
The main goal of this work is to find a reasonable explanation for the frequently reported drastic deviations from the ‘‘rule of mixture’’ applied for calculation of the overall microhardness, H, of complex polymer systems comprising a soft, (with a glass transition, Tg, or melting, Tm, temperatures below room temperature) component and/or phase. According to the common practice, the contribution to H of the soft component and/or phase, Hs, is considered as Hs = 0, which results in extremely large differences between the measured and calculated H values for systems comprising more than 20–25 wt% soft component and/or phase. For such systems a different deformation mechanism during indentation process is postulated, namely ‘‘floating’’ of the solid particles in the soft component and/or phase, in addition to their plastic deformation. The contribution of the ‘‘floating effect’’ to the overall H is accounted for by the empirically derived relationship H = 1.97 Tg–571. Using the reported data on H and Tg for homopolymers, blockcopolymers and blends, the H values are recalculated and a good agreement with the experimentally measured values is found. A modified additivity law is suggested, which contains a term accounting for the contribution of the soft component and/or phase to the overall microhardness via the relationship between H and Tg; its application results in much smaller differences between the measured and calculated H values.
