JOURNAL OF COMPOSITE MATERIALS Article Spinning of fibers from polypropylene/ silica composite resins Natee Srisawat 1 , Manit Nithitanakul 2 and Kawee Srikulkit 1,3 Abstract Isotactic polypropylene (iPP)/silica (SiO 2 ) 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 morpho- logical 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 0.25wt% 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. Keywords Silica/polypropylene composite fibers, nucleating agent, shrinkage resistance, surface roughness, hydrophobicity Introduction Isotactic polypropylene (iPP) fibers are commonly found in many end-use products due to their advanta- geous properties, including their lightweight, resistance to moisture and chemicals, low cost, sufficient strength- to-weight ratio, and their ease in processing. Furthermore, the properties of iPP fibers can be enhanced by melt mixing with particulates and fibrous materials as well as by melt blending with other poly- mers. 1–5 The resultant particulate fillers can be found in a wide size, ranging from nanometers to microns. However, polymer composites which contain nano- sized particles at a much lower loading ratio than con- ventional fillers have recently attracted a great deal of attention because they offer enhanced mechanical and thermal properties when compared to the conventional composites. Nano-sized particles, and particularly carbon nanotubes (CNTs) 6,7 and montmorillonite (MMNT) 8,9 particles, have taken the lead as the novel nanofillers for plastics, as well as for fibers, thanks to their high aspect ratio. Even though fillers with a high aspect ratio are ideal for plastic reinforcement, recently silica has been widely investigated for use in polymeric materials. For instance, the use of silica as a filler to enhance the mechanical properties of PP fibers has been reported, 10,11 while the addition of silica to polyester and polyamide improved the properties of the resultant polymer composite. 12–17 In particular, fumed silica (amorphous SiO 2 ) has received considerable interest 1 Department of Materials Science, Faculty of Science, Chulalongkorn University, Bangkok, Thailand 2 Petroleum and Petrochemical College, Chulalongkorn University, Bangkok, Thailand 3 National Center of Excellence for Petroleum, Petrochemicals and Advanced Materials, Bangkok, Thailand Corresponding author: Kawee Srikulkit, Department of Materials Science, Faculty of Science, Chulalongkorn University, Bangkok, 10330, Thailand Email: kawee@sc.chula.ac.th Journal of Composite Materials 46(1) 99–110 ! The Author(s) 2011 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0021998311410477 jcm.sagepub.com at PENNSYLVANIA STATE UNIV on May 17, 2016 jcm.sagepub.com Downloaded from