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

Presented in this paper is the investigation of the mechanical propert ies of PET short fiber-polyester thermoplastic elastomer (Hytrel) comp osites and the discussion of the short fiber reinforcement of the comp osites. Excellent adhesion of PET fiber to Hytrel elastomer was obtain ed by treating with isocyanate in toluene solution. The Hytrel composi tes 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 % di splayed an obvious yield phenomenon, and their yield elongation (betwe en 30-40%) was greater than the fiber's break elongation, which sugges ted that extensibility of the fiber was quite different from that of t he matrix. It is considered that the reinforcement of the short fiber mainly depends on the difference of extensibility between the fiber an d the matrix because the difference directly affects the effective tra nsference of the stress from matrix to fiber. The modified parallel mo del for Young's modulus and yield strength of the composite can be giv en 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 defor mation coefficients, alpha and beta, to represent the extensibility of the fiber and the matrix respectively. The alpha obtained from the ex perimental 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 functi on 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 elas tomer, the maximum of each succeeding stress-strain cycle coincided wi th the original stress-strain curve for elongations under 600%, but fo r the Hytrel composites such coincidence was limited to elongations un der 30%. This may be caused by the reforming of crystallites in the st ress-softened Hytrel elastomer phase at high strain. (C) 1993 John Wil ey & Sons, Inc.