Preparation and Physico-Chemical Study of Glass—Sisal (Treated—Untreated) Hybrid Composites of Bisphenol-C based Mixed Epoxy—Phenolic Resins

Abstract

Glass—sisal (treated and untreated) composites of mixed matrix material (25 wt% epoxy resin of bisphenol-C (EBC) and 25 wt% bisphenol-C-formaldehyde (BCF) of glass—sisal fibers) were prepared by hand lay-up technique at 150°C under 7.6 MPa pressure for 2 h. Hydrophilic character of the sisal fibers was reduced by acrylation of alkali-treated fibers with acrylic acid. Tensile strength, flexural strength, electric strength, and volume resistivity were increased from 26.4 to 35.3 MPa (33.7%), 46.7—64.1 MPa (37.3%), 1.41—1.93 kV/mm (36.9%), and 1.27 × 10¹²—1.81 × 10¹² Ω-cm (42.5%), respectively, on alkali treatment and acrylation. The edges of 5 × 5 cm² specimens were sealed with matrix material and subjected to distilled water and 10% each of aq. HCl and aq. NaCl solutions at room temperature for water uptake study. The equilibrium water uptake is reduced from 10.07—8.47% in water, 7.91—6.4% in 10% aq. NaCl and 12.13—11.00% in 10% aq. HCl on acrylation. Diffusivity was found to increase from 0.71— 0.82 × 10^{− 11} in water, 1.02—1.73 × 10⁻¹¹ in 10% aq. NaCl and 0.4—0.59 × 10⁻¹¹ m ²/s in 10% aq. HCl. Drastic reduction in water uptake is due to replacement of hydrophobic vinyl ester groups. No effect of boiling water is observed on stability of composites. Saturation time in boiling water reduced 24 times without any damage to the untreated and treated sisal—glass fiber composites, respectively. Composites may be useful for low load bearing applications and also in harsh acidic and saline environments.