Spinning and properties of isotactic polypropylene/hydrophobic silica nanocomposite fibers

Abstract

Silica particles filled polypropylene filament fibers were prepared. Firstly, melt mixing and solution (toluene) mixing were carried out to predisperse silica agglomerates, leading to composite resins. Then, the obtained composite resins were spun into multifilament fibers with various spinning speeds using the Fourne’s pilot plant fiber spinning machine (for melt mixed masterbatches) and free-fall monofilaments using ThermoHaake’s single screw extruder (for solution mixed resins). The characterizations of spun composite fibers including morphological analyses (SEM and AFM), crystallization temperature (DSC) and the fine structure (XRD) were studied. Properties evaluation included thermal property (TGA), tensile strength, shrinkage and surface hydrophobicity by contact angle measurement. SEM images of multifilament fibers demonstrated that shear stress applied during melt-mixing failed to overcome cohesion force among agglomerate particles. Successfully, AFM images revealed that solution mixing via autoclave treatment could disaggregate the silica agglomerates into nanoscale particles, producing an even distribution of nanoparticles within the bulk of the fiber or on the surface. As a consequence, the presence of the nanoparticles favorably induced heterogeneous nucleation process in the free-fall filament as evidenced by DSC analysis. Hot stage images further confirmed the nucleating effect of silica nanofiller. Well dispersion of nanoparticles in PP matrix resulted in an improvement in shrinkage properties of nanocomposite fibers. Furthermore, the surface hydrophobicity of the nanocomposite fibers was found higher than neat fiber thanks to an increase in surface roughness arising from the presence of nanoparticles on the surface.