The effect of low T g polybutadiene (PBD) rubbery polymer as a part of polysiloxane/PBD E-glass fibers sizing on mechanical properties of a corresponding epoxy composite material has been evaluated by the punch shear test technique. The results show that the use of hydroxyl terminated PBD led to significant increase in interface shear strength, energy absorption, as well as dynamic modulus and T g in a corresponding composite material. The sizing composition and fiber morphology were characterized by FTIR spectroscopy and AFM microscopy, respectively. Possible rational for such sizing composition/material property relationship is discussed.

Hybrid polysiloxane-based sizings with embedded silica and silica/latex nanoparticles were studied to improve Interfacial Shear Strength (IFSS) and energy absorption using the micro-droplet test method. The sizing mixture comprised of mixed polysiloxane with silica nanoparticles has been screened by varying one parameter at a time. The best mechanical performance was observed in the following concentration range: 1.0–2.0 wt% tetraethoxysilane (TES)/3-glycidoxypropyltrimethoxy silane (GPS) mixture, and 1.0–3.0 wt% Ludox® silica nanoparticles; 1.0–1.5 TES/GPS ratio, and 20 nm silica nanoparticles size. Increase of nanoparticles size leads to a decline in both strength and energy absorption, whereas chemical modification of nanoparticles surface has no significant effect compared to the baseline. The study also shows that the combination of hard (silica) and soft (latex) nanoparticles works best to maximize the strength and energy absorption. Hard particles increase surface roughness that increases interfacial strength and energy absorption during debonding whereas rubber particles contribute to improved energy absorption. Possible rational for such sizing composition/material property relationship will be discussed.