Plasma polymers used for controlled interphase in polymer composites

Abstract

The performance of fiber-reinforced composites is strongly influenced by the functionality of composite interphases. Sizing, i.e. functional coating (interlayer), is therefore tailored to improve the transfer of stress from the polymer matrix to the fiber reinforcement by enhancing fiber wettability, adhesion, compatibility, etc. The world market is dominated by glass reinforcement in unsaturated polyester. However, commercially produced sizing (wet chemical process) is heterogeneous with respect to the thickness and uniformity, and hydrolytically unstable. Companies search for new ways of solving the above problems. One of the alternative technologies is plasma polymerization. Plasma polymer films of hexamethyldisiloxane, vinyltriethoxysilane, and tetravinylsilane, pure and in a mixture with oxygen gas, were engineered as compatible interlayers for the glass fiber/polyester composite. The interlayers of controlled physicochemical properties were tailored using the deposition conditions with regard to the elemental composition, chemical structure, and Young’s modulus in order to improve adhesion bonding at the interlayer/glass and polyester/interlayer interfaces and tune the cross-linking of the plasma polymer. The optimized interlayer enabled a 6.5-fold increase of the short-beam strength compared to the untreated fibers. The short-beam strength of GF/polyester composite with the plasma polymer interlayer was 32% higher than that with commercial sizing developed for fiber-reinforced composites with a polyester matrix. The progress in plasmachemical processing of composite reinforcements enabled us to release a new conception of composites without interfaces.