Mechanical properties of polymers containing fillers

The addition of fillers can significantly change the mechanical characteris tics of a material. In this paper, a general, mechanistic model is establis hed to determine the moduli, relaxation moduli, break strengths, and break strains for polymer films containing liquid and solid micro fillers. Based on rigorous continuum mechanics principles, this model considers the filler /filler interactions, incorporates the nonlinear synergistic effects of fil lers, and provides accurate predictions in comparison with experimental dat a. The analytical model developed provides information that is not availabl e or extremely difficult to obtain experimentally. The model can be applied to determine the filler/matrix adhesion and filler modulus using measured modulus of a filled polymer film (a filled polymer is a polymer containing fillers). It is found that the compression moduli of polymer films containi ng liquid fillers differ significantly from the tension moduli, especially when the volume fraction of the filler is high. The difference in compressi on and tension Young's moduli normalized by the tension Young's modulus is as high as 35%. The relative error in maximum pressure calculation during H ertzian contact caused by using the tension moduli is as high as 48%. The r elaxation modulus of a filled polymer him is determined through inverse Lap lace transforms of its composite modulus in the s-space. For a filled polym er film containing liquid phase fillers, a closed form solution for its rel axation modulus has been obtained. It is found that the composite relaxatio n modulus of the filled polymer is proportional to the relaxation modulus o f the matrix polymer multiplied by a factor related to the volume fraction of the liquid filler. The break strength of the filled polymer is found to be proportional to the break strength of the polymer matrix material multip lied by a power function of the modulus ratio of filled polymer to polymer matrix, R. The break strain of the filled polymer is proportional to the br eak strain of the polymer matrix multiplied by a power function of VR. (C) 1999 John Wiley & Sons, Inc.