Polyurethane/conducting carbon black composites: Structure, electric conductivity, strain recovery behavior; and their relationships

The polyurethane composites with conducting carbon black (CB) were prepared by a solution-precipitation process, which was followed by melt compressio n molding. The polyurethane used has good shape memory effect. The morpholo gy of CB fillers in polyurethane matrix and the resulting conductivity of t he composites were investigated. It has been found that CB fillers exist in the forms of aggregates. The percolation threshold is achieved at the CB c oncentration of 20 wt %. The presence of CB fillers decreases the degree of crystallinity of polycaprolactone (PCL) soft segments of the polyurethane. However, the composites still have enough soft-segment crystals of polyure thane to fulfil the necessary condition far the shape memory properties. Dy namic mechanical data show that CB is an effective filler for the reinforce ment of the polyurethane matrix, but does not deteriorate the stable physic al cross-link structure of the polyurethane, which is necessary to store th e elastic energy in the service process of the shape memory materials. Addi tion of CB reinforcement in the polyurethane has influenced the strain reco very properties, especially for those samples with CB concentrations above the percolation threshold. The response temperature of the shape memory eff ect T-r has not been affected too much. Strain fixation S-f, which expresse s the ability of the specimens to fix their strain, has been improved in th e presence of the CB fillers. The final recovery rates R-f and strain recov ery speeds V-r of the shape memory measurements, however, have decreased ev idently. It is expectedly ascribed to the increased bulk viscosity as well as the impeding effect of the inter-connective structure of CB fillers in t he polymer matrix. (C) 2000 John Wiley & Sons, Inc.