WETTABILITY OF SURFACE OXYFLUORINATED POLYPROPYLENE FIBERS AND ITS EFFECT ON INTERFACIAL BONDING WITH CEMENTITIOUS MATRIX

The surface of high molecular weight polypropylene monofilament fibre was modified using a oxyfluorination method. The oxyfluorination treat ment level was varied and a hydrolysis post-treatment was also applied . Contact angles of oxyfluorinated, hydrolyzed oxyfluorinated and unmo dified polypropylene fibres were obtained by dynamic contact angle (DC A) measurement using three liquids of known dispersion, acid and base surface free energy components. The surface free energies were then ca lculated according to the acid-base theory developed by Good, van Oss and Chaudhury. Surface oxyfluorination largely increased the acid and base components of the fibres' surface free energy compared with unmod ified polypropylene fibres. The oxyfluorinated and unmodified polyprop ylene fibre surfaces were observed by Scanning Electronic Microscopy a nd Photoacoustic Infrared Spectroscopy. It was found that the surface oxyfluorination largely increases the roughness of the polypropylene s urfaces and the carbonyl group content increases as the treatment leve l increases. The interfacial shear bond strengths between the cementit ious matrix and the polypropylene fibres treated under various conditi ons were determined by embedded fibre pull-out tests. Results showed t hat the fibre surface oxyfluorination treatments increase the interfac ial bond strengths. The correlations between the shear bond strengths and surface free energy components were established. Results showed th at fibre/concrete interfacial bonding was best correlated with the aci d component of surface free energy of polypropylene fibres.