(527g) Characterization of Polymer Fibers with Nanocalorimetry

The thermophysical properties of isotactic polypropylene (iPP) fiber is investigated with rapid scanning nanocalorimetry, namely using a Mettler Toledo Flash differential scanning calorimeter (DSC). This technique facilitates the ability to obtain properties in the absence of viscous flow, fiber deformation, polymer degradation, and reorganization due to its very rapid scanning (as high as 50,000 K/s) and short-time measurements (< 0.01 s). For a melt-spun iPP fiber drawn lightly in the solid state, we find that upon heating at 1000 K/s, we first observe beta melting followed by alpha crystallization and then alpha melting. The fiber, as-received, is found to have relatively low crystallinity (~ 25 %) and a very high fraction of the rigid amorphous phase (nearly 50 %). The same type of characterization is performed using conventional DSC, but it gives very different results due to the ability of the beta phase to transform to the alpha phase on the time scale of conventional DSC measurements made at 10 K/min. Thus, in contrast to conventional DSC, we show that using the Flash DSC, one can obtain the thermal signature of as-received fiber because the measurements are made over fractions of seconds and reorganization during cooling below T_g does not occur during the measurement. The influence of various thermal treatments on this same iPP will be also discussed, as well as the relationship between the rigid amorphous fraction and crystallinity. This is important because the rigid amorphous phase in semi-crystalline polymers impacts dielectric, mechanical, and thermophysical properties and governs the rate of crystallization, reorganization, crystal perfection, and melting.