Surface modification of glass fibers by oxidized plasma coatings to improve interfacial shear strength in GF/polyester composites

Plasma‐polymerized films (interlayers) of tetravinylsilane in mixture with oxygen gas (oxygen fraction 0‐0.71) were coated on glass fibers (GF) used as reinforcements in GF/polyester composite. Oxygen atoms of increased concentration (0‐18 at.%) were partly incorporated into the plasma polymer network, forming SiOC/COC bonding species and partly forming side polar (hydroxyl, carbonyl) groups with enhanced oxygen fraction. The amount of oxygen in plasma coatings influenced the Young's modulus, interfacial adhesion, and surface free energy of the interlayer. To determine the interfacial shear strength, a microindentation test was implemented for individual glass fibers on a cross‐section of GF/polyester composite. The interfacial shear strength for oxidized plasma coatings was up to 21% higher than that for the non‐oxidized interlayer, indicating a direct chemical effect of oxygen atoms on interphase properties. The interphase shear failure was controlled by the shear strength at the interlayer/fiber interface as follows from experimental and model data. POLYM. COMPOS., 40:E186–E193, 2019. © 2017 Society of Plastics Engineers