Interfacial Phenomena in Glass Fiber Composites

Surface interactions between fibers and polymer matrix are known to affect the properties of the composite materials. Glass reinforced polymer composite materials have long been used in the industry for making roofing shingles. The interfacial properties of these composites are governed by the chemical nature and physical compatibility between glass fibers and polymer matrix. There are different surface modification techniques applied to the glass fiber surfaces which aid processing and achieving of optimum composite properties. In this study, we enhanced our understanding of these complex surface interactions by elucidating the effect of different surface modification techniques used on glass fibers during processing and their effect on composite properties.;The effect of different sizing components on the interfacial properties of glass fibers has been studied by varying the gamma-aminopropyltrimethoxysilane and 1-hydroxyethyl-2-cocoimidazoline concentrations in the sizing to form sized glass fibers containing different amounts of silane and imidazoline components and their corresponding glass composite properties are also studied. We found that the sizing chemistry has a strong influence on the mechanical performance of these composites. The isoelectric point, the pH where the zeta potential of the surface is zero, is useful in predicting the dispersion properties of sized glass fibers in polyelectrolyte. The imidazoline component changes the isoelectric point to neutral pH which is good for fiber dispersion and leads to good composite structure making imidazoline a key component contributing to the mechanical performance. The silane component changes the isoelectric point to high basic pH which leads to poor fiber dispersion and leads to decrease in the mechanical performance. The silane component distributes uniformly on the sized glass fiber interface while the imidazoline component shows nonuniform distribution with agglomeration at specific locations. Increasing homogeneity of the imidazoline component distribution is a desired outcome that was not recognized.;We also explored the effect of sizing, polyelectrolyte and binder surface treatments on the surface properties of glass fibers and their synergistic interactions. It was observed that the polyelectrolyte treatment covers the sizing chemistry and the corresponding binder treatment covers the polyelectrolyte treatment. The water dynamic contact angle of sized, polyelectrolyte and binder treated glass fibers shows that the sized and binder treated glass fibers show slightly hydrophilic interactions while the polyelectrolyte treated glass fibers show hydrophobic interactions. We also demonstrated that the polyelectrolyte solution wets the sized glass fiber surface during dispersion and the polyelectrolyte completely covers the sized glass surface by non-specific physical adsorption after multiple wetting cycles.;The distribution of urea-formaldehyde modified acrylic polymeric binders on glass mats was also studied. We found out that the binder deposits at the cross points between the glass fibers as well as coats on the single glass fiber surface. The binder deposition is non-uniform throughout the mat surface with little control on the distribution. Also, the binder by itself is hydrophilic in nature but the glass mat coated with binder shows hydrophobic interactions due to the mat structure. With time, wetting of the water droplet on the glass mat demonstrates the hydrophilic nature of the binder present on glass mat.