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Plasma Coating of Glass Fibers to Improve the Interfacial Shear Strength in GF/Polyester Composites



The fiber coating method is essential for improving the interfacial adhesion in glass fiber reinforced polyester composites. In our study, plasma polymer interlayers of pure tetravinylsilane monomer and monomer in a mixture with oxygen gas (0-71%) were used to surface modify glass fibers at an effective power of 2.5 W. We demonstrate that elemental composition and chemical structure of plasma polymer can be influenced by an amount of oxygen atoms (0-19 at.%) partly incorporated into plasma polymer network and partly forming side hydroxyl and carbonyl groups eliminating cross-linking of the network. Thus, the chemical properties result in reduced mechanical properties at enhanced oxygen concentration. The adhesion at the interlayer/glass interface can be optimized as the result of sufficient concentration of Si-O-C bonding species and adequate crosslinking of the network. The vinyl groups at the interlayer surface are responsible for chemical bonding to the polyester resin and their concentration was approximately constant. The polar groups (hydroxyl, carbonyl) at the interlayer surface are favorable for wetting the surface by the resin. A fiber bundle (unsized fibers) coated by plasma coatings was embedded in polyester resin and cured to fabricate composite specimen that was cut and polished using conventional metallographic techniques to form composite cross-sections. The microindentation test (Interfacial Testing System) was carried out on the individually selected glass fibers (GF) on a cross-section of GF/polyester composite to determine the interfacial shear strength. The shear strength for plasma coated fibers depends on oxygen amount in mixture and varied from 0 to 32% above the strength of industrially sized fibers. Nonlinear finite element analysis was used to correctly interpret the microindentation data. The plasma polymer interlayers with high shear yield strength (0.6-1.5 GPa) may be effectively applied to improve the interfacial shear strength in GF/polyester composites.

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