Cure kinetics of phenolic novolac resins

The cure kinetics and cure behavior of phenolic novolac resin with epoxy resin and with cyanate ester were compared with conventional hexamethylenetetramine (HMTA) curing agent, by means of DSC. Novolac-epoxy and novolac-cyanate systems offer volatile-free cure processes as well as higher thermo-oxidative stability. It was found that these two systems had higher reactivity, longer gel times and wider process windows than a conventional novolac-HMTA system.; The study revealed that the reaction rate expressions could be described as follows:(UNFORMATTED TABLE OR EQUATION FOLLOWS){dollar}{dollar}vbox{lcub}halign{lcub}#hfil&&quad #hfilcr Novolac-epoxy &{dollar}rm dalpha/dt=1.7times10sp6 exp ({lcub}-{rcub}59/RT)(1-alpha)sp{lcub}0.96{rcub}{dollar}cr Novolac-cyanate &{dollar}rm dalpha/dt=2.2times10sp8 exp ({lcub}-{rcub}76/RT)(1-alpha)sp{lcub}1.21{rcub}{dollar}cr Novolac-HMTA &{dollar}rm dalpha/dt=2.3times10sp{lcub}15{rcub} exp ({lcub}-{rcub}126/RT)(1-alpha)sp{lcub}1.66{rcub}{dollar}cr{rcub}{rcub}{dollar}{dollar}(TABLE/EQUATION ENDS)The results of the calculation correlated well with the experimental data obtained by dynamic temperature scans at constant rate.; The effect of HMTA concentration was also examined. There was an orderly increase in heat of reaction with HMTA/novolac molar ratio up to 1.0; above this value, heat of reaction decreased again.