Generalized Concept of the Reinforcement of Elastomers. Part 3: Self-Reinforcement by the Formation of Continuous Hard Phase in Segmented Polyurethane Elastomer

The author proposed the third concept in the reinforcement of elastomers for segmented polyurethane with the direct observation by microscopic techniques. The structure in segmented polyurethane elastomers fundamentally consists of three domains of different sizes, two kinds of micro-domain, cluster of 100 nm in diameter and spherulite of µm order. Of the micro-domains, one is the hard-segment (HS)-rich micro-domain consisting of hard segment (4 nm thickness) and soft segment (7 nm) and the other is the hard-segment (HS)-poor micro-domain of hard segment (4 nm) and soft segment (15∼20 nm). The HS cluster is constructed by the assembly of the HS-rich micro-domains. The spherulite seems to be composed of the dense packing of the HS cluster, growing up radially or circularly from the center to the outside surface. From physical and mechanical points of view, we can regard the above structures in the segmented polyurethane as bi-continuous structure of the HS clusters whose volume fraction is 0.2, and the matrix phase consisting of the HS-poor domains (0.8 in the volume fraction). The characteristic stress-strain relation of the segmented polyurethane is generated by the combination of both the continuous structures. That is, the initial very high stress (modulus) at small extension and the following gradual increase in stress at medium extension mainly result from the extension and the sliding of the HS cluster, respectively. The very large stress-upturn at large extension and the final great tensile strength are generated by the contribution of both the continuous structures. Thus, the third reinforcement is achieved by the formation of bicontinuous structure of the hard and strong cluster and also the strong matrix phase, in which the absolute structural defects seem not to be included.