Influence of wool and thermo-binder fibers relative fractions on the adhesion of non-woven Alfa fibers reinforced unsaturated polyester hybrid composites

Alfa/wool/thermo-binder fibers hybrid composites were investigated in order to analyze adhesion state. Bearing in mind the chemical structure of wool and thermo-binder fibers, this study revealed a good compatibility between the reinforcement and the matrix. Dielectric measurements revealed the presence of two dielectric relaxations in the composite. The first relaxation was attributed to the α mode relaxation and the second one was associated with the conductivity noted for high temperature. This study allowed the analysis of the interfacial polarization effect using the Havrilliak–Negami model in the electric modulus formalism. The lowness of this relaxation intensity revealed a good adhesion of the fibers in the matrix. Differential Scanning Calorimetry (DSC) showed a slow decrease of the Tg glass transition temperature compared to the matrix, which could be explained by the existence of interactions between the fibers and the matrix. Vibrational analysis, based on FTIR measurements, showed a less hydrophilic character of Alfa fibers owing to a basic dissociation that occurs between the wool fibers and the water molecules associated with Alfa fibers. Furthermore, adhesion mechanism in the composite material was established by covalent and hydrogen bonds. Tensile testing performed on this composite confirmed that such adhesion was improved by increasing the thermo-binder fibers relative fraction.