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

In connection with a study of the fiber reinforcement of wood, a number of silane coupling agents were evaluated in the bonding of basalt fibers to phenolic and isocyanate resins most commonly used in wood bonding. Interfacial shear strength improvement before and after 1 h boiling in water was determined, utilizing a modified single-filament composite specimen in which the fiber was first coated by a thin layer of brittle phenolic or isocyanate resin before being embedded in a flexible epoxy resin matrix. In the case of the phenolic resin, the most improvement was obtained with 3-(4-methoxyphenyl)propylmethyldichlorosilane, which provides more reactive aromatic sites for substitution than phenethyltrimethoxysilane. Similarly, for the isocyanate resin, 3-aminopropyltriethoxysilane gave the best results. In this case, the reaction of the amino group with the isocyanate resin through successive formation of carbamic acid and urea bonds was confirmed by FT-IR spectral data. Monitoring of acoustic emission during straining of the specimens revealed the sequential occurrence of three failure processes, namely 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 filtered off to obtain the high-energy emission data from fiber fracture.