MECHANICAL-PROPERTIES OF PET SHORT FIBER-POLYESTER THERMOPLASTIC ELASTOMER COMPOSITES

Presented in this paper is the investigation of the mechanical properties of PET short fiber-polyester thermoplastic elastomer (Hytrel) composites and the discussion of the short fiber reinforcement of the composites. Excellent adhesion of PET fiber to Hytrel elastomer was obtained by treating with isocyanate in toluene solution. The Hytrel composites filled with treated fiber showed a similar tensile behavior, with higher values, to that for the matrix elastomer when fiber loading was less than 5 vol %. The composites loading fibers more than 5 vol % displayed an obvious yield phenomenon, and their yield elongation (between 30-40%) was greater than the fiber's break elongation, which suggested that extensibility of the fiber was quite different from that of the matrix. It is considered that the reinforcement of the short fiber mainly depends on the difference of extensibility between the fiber and the matrix because the difference directly affects the effective transference of the stress from matrix to fiber. The modified parallel model for Young's modulus and yield strength of the composite can be given by the following equations: E(c0) = alphaV(f)E(f0) + beta(1 - Vf)E(m0), and sigma(cy) = V(f)sigma(f)(alphaepsilon(y)) + (1-V(f))sigma(m)(betaepsilon(y)), respectively, through introducing two effective deformation coefficients, alpha and beta, to represent the extensibility of the fiber and the matrix respectively. The alpha obtained from the experimental results did not depend on fiber loading but increased with increasing fiber length, and the alpha for Young's modulus was larger than the one for yield strength, which suggests that alpha is a function of the strain of the composite and may decrease with increasing the strain, namely, the deformation difference between the fiber and the matrix increases when the strain increases. On the other hand, beta is a function of a as: beta = 1 - alphaV(f)/1 - V(f) For the Hytrel elastomer, the maximum of each succeeding stress-strain cycle coincided with the original stress-strain curve for elongations under 600%, but for the Hytrel composites such coincidence was limited to elongations under 30%. This may be caused by the reforming of crystallites in the stress-softened Hytrel elastomer phase at high strain. (C) 1993 John Wiley & Sons, Inc.