Commingled yarns and their use for composites

Abstract

Commingled yarns are one of the possible preforms used for continuous fiber reinforced thermoplastic composites in order to solve the problem of high melt viscosity during impregnation and consolidation as the required steps for manufacturing of technical components. The preforms can be considered as 'dry' prepregs, in which the solid resin is physically divided and more or less evenly distributed among the reinforcement fibers. Division of the polymer can be made using either powder or the fiber form. Glass fiber (GF) manufacturers (e.g. Vetrotex, France) especially took advantage of their expertise in fiber spinning to develop a commingling process for glass and thermoplastic filaments (Figure 1 (a» [1]. In their patented one-step process, Vetrotex succeeded in produc-ing commingled yarns with a rather uniform distribution of small glass and thermoplastic fiber bundles, a good consistency of the glass content, a wide range of the GF volume fraction (20-50vol.%), and the price level of industrial glass composites. Polypropylene (PP) has been their first choice for achieving a good balance between versatility of performance, ease of processing, and price (tradename Twintex®). More recently, a material with PET (polyethylene-terephthalate) fibers was developed for applications needing better thermal resistance and higher strength. Hoechst AG of Frankfurt am Main, Germany, has been granted a patent (WO 94/20658) for improvements to fiber yam intermingling which make it possible to produce filaments completely free from broken