Silica/Perfluoropolymer Nanocomposites Fabricated by Direct Melt-Compounding: A Novel Method without Surface Modification on Nano-Silica

Abstract

A novel method for the fabrication of silica/perfluoropolymer nanocomposites was investigated, whereby nano-sized silica particles without surface modification were dispersed uniformly through mechanical 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, poly(tetrafluoroethyleneco-perfluoropropylvinylether), with the loose silica agglomerates prepared in the first stage. In the first stage, the packing structure and the fracture strength of the silica agglomerate were controlled by destabilizing an aqueous colloidal silica solution with a mean primary diameter of 190 nm via pH control and salt addition. In the next stage, the silica/perfluoropolymer nanocomposite was fabricated by breaking down the prepared loose silica agglomerates with low fracture strength by means of a shear force inside the polymer melt during melt-compounding.

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

“…11 For the direct melt-compounding process, in addition to the shear stress induced in the kneaded polymer, the critical threshold value necessary for breaking down the agglomerates of nanofillers are the main factors that control the dispersion state of the fillers. Therefore, in the authors' method, loosely packed agglomerates of silica nanoparticles with low fracture strength (loose silica agglomerates) were prepared intentionally by destabilizing an aqueous solution of nano-sized colloidal silica via pH control and KBr addition.…”

“…However, the characteristics of the fabricated silica/PFA nanocomposites were not discussed in the previous study. 11 The present study was aimed at elucidating the formability and the mechanical properties of the silica/PFA composites filled with unmodified silica nanoparticles fabricated by the authors' method. First, using aqueous solutions of nano-sized colloidal silica as starting materials, silica agglomerates with different strength were prepared from the destabilized colloidal silica dispersion systems via pH control and KBr addition.…”

“…As examples of silica/PFA nanocomposites exhibiting "good" dispersion of nano-silica (see Fig. 3(a)), composites A, A-2 and A-3, wherein silica particles with a diameter, d p, Silica , of 190 nm were dispersed uniformly, fabricated with varying silica volume fractions, V f, Silica , from 2.8 to 14.4% in the authors' previous study 11 were subjected to MFR measurement and tensile testing. As negative controls of the silica dispersion state, composites B and C exhibiting "poor" dispersion of silica (see Figs.…”

“…The procedure for the fabrication of composites A, A-1 and A-2, including the preparation of loose silica agglomerates with d p, Silica = 190 nm, was described in the previous paper. 11 In this paper, the procedure for the fabrication of composites B and C will be described in the following Sections 2.2 and 2.3. Co.) was conducted to evaluate the fracture strength of the agglomerates.…”

“…The fabrication of both composites B and C follows the procedures described in the previous paper. 11 Composite C was fabricated by melt-compounding the PFA with the 873 K-sintered silica agglomerates in an intensive twin-rotor batch mixer (Labo Plastomill, KF70 model, Toyo Seiki Seisaku-sho, Ltd.). On the other hand, fumed nano-silica in powder form was added into the same mixer and mixed with the kneaded PFA melt to obtain composite B.…”