Interfacial shear strength and durability improvement by monomeric and polymeric silanes in basalt fiber/epoxy single-filament composite specimens

Silane coupling agent effects in basalt fiber-epoxy systems have been investigated through measurement of the interfacial shear strength (IFSS) in single-fiber composite (SFC) specimens. Three silane were studied: 3-aminopropyltriethoxysilane (APS) and two polymeric silanes in which dimethoxy- or trimethoxysilane groups are attached via side chains to a polyethyleneimine backbone. Optimal conditions for silane application were standardized. Crosslinking of the deposited silanes is shown to result in decreased interpenetration by the matrix epoxy resin and lower values of IFSS. The polymeric silane with trimethoxy groups was found, as expected, to be inferior to the other two. APS and the polymeric dimethoxysilane gave similar results in improvement of IFSS and its retention after 1 h boiling in water. Monitoring of acoustic emission (AE) during straining of SFC specimens established a one-to-one correspondence between the number of AE events and fiber breaks. Measurement of AE pulse energies provided evidence for the sizing effect of polymeric silane coatings, through healing of surface flaws, as well as for moisture attack at severe surface flaws on the fiber during silane treatment.