Fabrication and Mechanical Properties of Silica/Perfluoropolymer Nanocomposites by Direct Melt-Compounding without Surface Modification on Nano-Silica

The authors’ research group has previously developed a novel method for the fabrication of silica/perfluoropolymer nanocomposites, wherein nano-sized silica particles without surface modification were dispersed uniformly through breakdown of loosely packed agglomerates of silica nanoparticles with low fracture strength in a polymer melt during direct melt-compounding. The method consists of two stages: the first stage involves preparation of the loose silica agglomerate, and the second stage involves melt-compounding of a completely hydrophobic perfluoropolymer, PFA (poly(tetrafluoroethylene-coperfluoropropylvinylether)), with the loose silica agglomerates. By using this simple method without any lipophilic treatment of silica surfaces, silica nanoparticles with a primary diameter of 190 nm could be dispersed uniformly into the PFA matrix. The main purpose of the present study is to evaluate the tensile properties of silica/PFA nanocomposites fabricated by the above method. In order to elucidate the effects of the size of the dispersed silica in the PFA matrix on the properties of the composites, silica/PFA composite samples exhibiting the dispersion of larger-sized silica particle-clusters were fabricated as negative controls exhibiting poor dispersion state of the silica additives. The results obtained under the present experimental conditions showed that the size of the dispersed silica in the PFA matrix exerts a strong influence on the ultimate properties, such as tensile strength and elongation at break, of the composite materials. Furthermore, uniform dispersion of isolated silica nanoparticles was found to improve not only the Young’s modulus but also the ultimate tensile properties of the composite.