The elastic extension of polymer fibers in the glassy state: Experimental results

The results of the continuous chain model for the elastic deformation of polymer fibers in the glassy state, which has been presented in the previous article, are compared to the results from experiments on poly(p-phenylene terephthalamide) (PpPTA), poly(ethylene terephthalate) (PET), cellulose, and PE fibers, and PpPTA and PET sheets. The calculated elastic stress versus strain curve is compared to the experimental curve of PpPTA fibers. The predicted relation between the elastic modulus versus strain curve and the orientation of the fiber during extension are compared to the results obtained by x-ray diffraction. The effect of plastic deformation on the experimental modulus versus strain curve is considered, and a new method for the experimental determination of the shear modulus g from the elastic modulus versus strain curve is presented. The calculated elastic modulus versus strain curves are compared to the experimental curves of PpPTA, PET, cellulose, and PE fibers with widely divergent values for their orientation parameter. The shear moduli for these fibers have been determined and are compared with literature values, the relation between the experimentally determined shear modulus and the structure of the fiber is discussed. The shear moduli of a series of PET fibers are compared to the values obtained by birefringence. The modulus of PpPTA and PET sheets are compared to the calculated values. Good agreement between the experimental and calculated results has been obtained. (C) 1997 The Society of Rheology.