INTERFACIAL SHEAR-STRENGTH AND DURABILITY IMPROVEMENT BY SILANES IN SINGLE-FILAMENT COMPOSITE SPECIMENS OF BASALT FIBER IN BRITTLE PHENOLICAND ISOCYANATE RESINS

In connection with a study of the fiber reinforcement of wood, a numbe r of silane coupling agents were evaluated in the bonding of basalt fi bers to phenolic and isocyanate resins most commonly used in wood bond ing. Interfacial shear strength improvement before and after 1 h boili ng in water was determined, utilizing a modified single-filament compo site specimen in which the fiber was first coated by a thin layer of b rittle phenolic or isocyanate resin before being embedded in a flexibl e epoxy resin matrix. In the case of the phenolic resin, the most impr ovement was obtained with 3-(4-methoxyphenyl)propylmethyldichlorosilan e, which provides more reactive aromatic sites for substitution than p henethyltrimethoxysilane. Similarly, for the isocyanate resin, 3-amino propyltriethoxysilane gave the best results. In this case, the reactio n of the amino group with the isocyanate resin through successive form ation of carbamic acid and urea bonds was confirmed by FT-IR spectral data. Monitoring of acoustic emission during straining of the specimen s revealed the sequential occurrence of three failure processes, namel y fiber fracture, brittle resin microcracking, and propagation of the microcracks into the epoxy resin. By setting the appropriate threshold during measurement, low-energy resin fracture events could be filtere d off to obtain the high-energy emission data from fiber fracture.