Radical scavenging efficiencies of silane-grafted carbon nanotubes and their effects on crosslinking reaction of vinyl ester/styrene resin

Abstract

Carbon nanotubes (CNTs) that were first grafted with vinyl trimethoxysilane (VTMS) and then with methacryloxypropyl trimethoxysilane (MATMS) could result in well dispersion in thermosetting vinyl ester/styrene resin and exhibit significant enhancement in storage modulus of the composite. If the VTMS-grafted CNTs were grafted with VTMS, rather than MATMS, in the second step of grafting, significant phase separation was found in the composite. The scavenging efficiencies of the silane-grafted CNTs for hydroxyl (OH.) radicals measured by electron paramagnetic resonance (EPR) were investigated as a function of the step and degree of grafting. The EPR data revealed that the radical scavenging efficiency of a given CNTs exhibited a significant decrease after the first step of grafting with VTMS but exhibited insignificantly further decrease after the second step of grafting with MATMS. The radical scavenging efficiency of a given silane-grafted CNTs was decreased with increasing degree of the silane grafting, an indication that the radical scavenging mechanism involved the reactions of radicals with the CNTs, rather than with the silane grafts. The radical-initiated crosslinking of the vinyl ester/styrene composite was significantly retarded by the silane-grafted CNTs; this should be taken into consideration when producing thermoset polymer/CNT composites having highly enhanced moduli.