Evaluation of surface treatments for glass fibers in composite materials

Abstract

The thermomechanical stability of a number of organosilane surface treatments for glass fibers was evaluated for use in a fiber reinforced epoxy resin. All of the silane coatings were found to improve the tensile strength of E‐glass filaments, particularly at large gauge lengths. A phenylamino silane and an amino silane were particularly effective in this regard. The fiber/matrix interface was evaluated as a function of temperature and after exposure to boiling water using a single‐fiber composite test. All silane coatings transmitted a higher interfacial shear stress than obtained in composites with no coatings, and in all cases the shear stress transmission was considerably higher than would be expected from the yield properties of the resin. Measurements of the glass transition temperature of the epoxy resin, as well as Fourier‐Transform Infra‐Red analysis, indicated modification of resin properties in a zone around the glass fibers. Each of the silane coatings provided more stable thermomechanical properties than those obtained with uncoated glass, at least until the silanes were irreversibly degraded by boiling water. A phenylamino silane provided the most thermally stable properties. Finally, unidirectional E‐glass fiber reinforced laminae were fabricated and the measured values of longitudinal strength were compared favorably to theoretical predictions.

Effect of Glass Fiber Surface Treatments on Mechanical Strength of Epoxy Based Composite Materials

“…It is quite well known that, because of the chemical and structural differences of this coupling agent interface layer, the mechanical properties of composite materials change greatly (4,8,10,11). To investigate the effect of different treatments on interfacial reinforcement in glass fiber/epox composites, such single filamen tests as the fibe fragmentation test (4,12,13) and the fibe pull-out test (13,14), are commonly used, among others.…”

“…To investigate the effect of different treatments on interfacial reinforcement in glass fiber/epox composites, such single filamen tests as the fibe fragmentation test (4,12,13) and the fibe pull-out test (13,14), are commonly used, among others. However, although they yield conclusive results, these tests tend to hamper the interpretation of results and/or sample preparation.…”

Fibre/resin interaction in fragmentation tests: coaxial vs. simple specimens comparison

“…The demonstration was given as early as 1978 for glass fibres in epoxy or polyester resins tested up to 100-120 ЊC by Ohsawa et al (1978) who concluded that 'if the interfacial strength is greater than the matrix shear strength, the apparent strength calculated from the fragmentation test is merely the matrix shear strength'. Other authors conducted fragmentation tests on the (necessarily) same limited range of temperatures with glass (DiBenedetto & Lex, 1989;DiBenedetto, 1991) or carbon fibres (Wimolkiatisak & Bell, 1989;Skourlis & McCullough, 1993;Detassis et al, 1995) or with resin mixtures of variable stiffness associated with carbon (Rao & Drzal, 1991) or Nicalon SiC fibres (Ho et al, 1995); they all observed an increase of the fragment length with temperature or the reduction of the matrix modulus. In the last two studies, the authors point out that the extension of the fibre/matrix debonding process does not change very much from one resin system to the other and thus the comparison of the elastic reloading modes is quite relevant.…”

Fluorescent labels to study thermal transitions in epoxy/silica composites

“…They mainly depend on the ability of the interface to transfer stresses between the matrix and the re-inforcement [4]. In the case of polymer reinforced or fille with silica substrates (glass fibers silica particles, etc.…”