Constrained shrinkage of highly oriented poly(methyl methacrylate) fibers

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Department of Biomedical Engineering


Constrained shrinkage of fibers is the primary method used to examine orientation in amorphous materials. During the test, fibers are constrained, heated, and the stress that develops is measured as a function of time and temperature. This article describes an apparatus developed to measure that stress and a series of experiments for melt-spun poly(methyl methacrylate) fibers fabricated under three conditions: (1) constant viscosity, (2) increasing temperature, and (3) increasing draw velocity. Results show that both the rates of rise and the decay of the fiber shrinkage stress have an Arrhenius relationship with temperature. Fibers fabricated at a constant viscosity have the same maximum shrinkage stress and rate of stress decay. As the processing temperature decreases or as draw velocity increases, for other parameters held constant, the maximum shrinkage stress increases. The rate of stress rise increases with decreasing processing temperature or increasing draw velocity. Maximum shrinkage stress also increases with increasing molecular orientation when measured by a different test, free heat-induced shrinkage of the fibers. However, it was not possible to correlate both of these results to rubber elasticity theory attributed to the high degree of orientation present in the fibers and high polydispersity in the starting material.

Publication Title

Journal of Applied Polymer Science