Spinning of fibers from polypropylene/silica composite resins

Isotactic polypropylene (iPP)/silica (SiO₂) composites were prepared by solution (toluene) mixing followed by either sonication or autoclaving to disaggregate the silica agglomerates. The obtained composite resins were then spun into monofilament fibers using a ThermoHaake's single screw extruder. The obtained fibers were characterized by morphological analyses (scanning electron microscope, atomic force microscopy (AFM), and Raman), crystallization profile (differential scanning calorimetry), and hot-stage microscopy. AFM images and Raman analysis maps revealed that silica particles of a submicron size range were present on the surface. The inclusion of silica particles into the resins resulted in a higher crystallization temperature (T_c) and shrinkage resistance of the composite fiber when compared to those of the neat or toluene-prepared PP fibers, which were attributed to the nucleating effect of the silica filler with an effective reinforcement. In addition, the silica loadings (0.25–1 wt%) increased the tensile strength attributable to its change in shape from round to elongated and flattened after spinning process, except that the greatest increase (1.4-fold) was seen at 0.25 wt% silica. However, the variances were large, resulting from diameter variation arising from free-fall fibers obtained by gravitational force only. Interestingly, the surface hydrophobicity of the composite fibers was found to be higher than the neat fibers due to the increase in the surface roughness arising from the presence of particles on the surface.