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SynopsisThe crystallization behavior of poly(ethy1ene) terephthalate (PET) melt spun into fiber monofilaments was examined using a laboratory set-up. The wind-up speeds ranged from free fall under gravity to 1500 m/min. The major additional variables that were manipulated included the mass flow rate and the filament temperature profile. The structure of the as-spun fibers was probed using tensile tests, differential scanning calorimetry, optical birefringence, and x-ray diffraction. It was found that while the filaments that had been spun nonisothermally were essentially amorphous, those that had been made under isothermal conditions at temperatures ranging from 180°C to 240°C were oriented and crystalline. In addition, the rate of oriented crystallization was much greater than that under quiescent conditions at the same temperature. This is perhaps the first published study which shows that highly crystalline (up to 40% crystallinity) PET fibers can be obtained at low spinning speeds merely by altering the fiber temperature profile while the material is still above the polymer glass transition temperature.

The increase in the rate of polymer crystallization brought about by mechanical deformation above the polymer glass-transition temperature is examined. For flexible macromolecules, this deformation results in alignment and extension of polymer chains. By hypothesizing that the instantaneous growth rate at a given constant temperature depends uniquely on the polymer chain orientation in the surrounding melt, a n explicit expression is obtained for the growth rate of a spherulite in terms of experimentally measurable quantities. Isothermal meltspinning experiments were conducted with poly(ethy1ene terephthalate) (PET) using a laboratory setup. Very large values of the total crystallinity and significantly enhanced values of the crystallization rate were generated by operating at different temperatures that straddle the temperature of maximum crystallization rate for the quiescent melt. Measured rates of crystallization do, indeed, correlate with the instantaneous amorphous orientation. Furthermore, a masterplot, independent of temperature, is obtained by normalizing the crystallization rate under spinning conditions with that under quiescent conditions. This is the first time that such data have become available, and, given the processing history, such a master plot should be of use in predicting the crystallinity levels in actual nonisothermal industrial experiments.

The concentrated solution and melt rheology of poly(vinylidene fluoride) [PVDF] were studied by using a falling needle solution viscometer, a Brookfield viscometer, and a Kayeness capillary rheometer. It was found that the concentrated solution (15 wt% in N‐dimethyl acetamide) rheology exhibited a different behavior for various grades of PVDF produced by different types of polymerization. While Newtonian behavior was found in one type of PVDF, shear thinning was found in another type. The power law model was used to describe the general solution behavior of these materials. Zero shear rate viscosity correlated well with the molecular weight (Mw) of the material. Melt viscosity of PVDF exhibited continuous shear thinning behavior throughout the whole range of shear rates. The data were best fitted by a second‐degree polynomial curve. Correlations were established between the molecular weight, molecular weight distribution, and the parameters of the polynomial curve. These correlations are useful for the prediction of various grades of PVDF designated for specific engineering applications. The correlations obtained from solution provided better and more accurate correlations to Mw parameters than those of melt rheology.