E. Andreassen et al., MELTING BEHAVIOR OF POLYPROPYLENE FIBERS STUDIED BY DIFFERENTIAL SCANNING CALORIMETRY, Journal of applied polymer science, 57(9), 1995, pp. 1075-1084
Polypropylene fibers produced in a compact-spinning process were studi
ed by differential scanning calorimetry (DSC). With unrestrained fiber
s, the onset of melting increases with decreasing draw ratio, increasi
ng M(w)/M(n), decreasing extrusion temperature, increasing annealing r
atio, and increasing draw-down ratio. These trends are discussed in te
rms of restraints and reorganization. The onset of melting is shifted
to lower temperatures as the heating rate increases for all combinatio
ns of material and processing parameters, indicating suppressed reorga
nization. At low draw ratios, the height and width of the endotherm ar
e affected by the spinline stress, and a secondary peak or shoulder is
observed on the high temperature side of the main peak. The magnitude
of the secondary peak increases with decreasing M(w)/M(n), increasing
draw ratio, decreasing draw-down ratio, and decreasing heating rate,
but its position mainly depends on the heating rate. This indicates th
at the secondary peak may be due to the melting of structures that hav
e been reorganized during the heating scan. As the draw ratio increase
s, the melting regime broadens, especially towards lower temperatures,
and several maxima emerge on the DSC curve. Reorganization and shrink
age during heating may explain these observations. (C) 1995 John Wiley
& Sons, Inc.