THE EFFECT OF LIGNIN CONTENT ON THE CURE PROPERTIES OF PHENOL-FORMALDEHYDE RESIN AS DETERMINED BY DIFFERENTIAL SCANNING CALORIMETRY

The thermochemical behavior of lignin combined with phenol-formaldehyde (PF) thermosets has been investigated through Differential Scanning Calorimetry (DSC). The effect of the lignin type and content as well as of its methylolation effect have been investigated through the kinetic parameters of the curing reaction. The linearity of the Arrhenius plots of lnK vs 1/T justifies the use of the Borchardt and Daniel's nth order model to characterize the curing reactions of thermosets. The activation energy, the heat of the reaction and the order of the reaction have been used in order to evaluate the effect of lignin addition on the curing of phenolic resin. Results showed a decrease of the heat of the curing reaction of lignin-phenol-formaldehyde (LPF) resins as the lignin content increases but in a lesser extent for methylolated lignins containing thermosets. The smaller decrease of the heat of the curing reaction observed after the addition of the methylolated type of lignins compared to the non-methylolated lignin is an indication that the methylolation increases the reactivity of lignins.The heat of curing seems to give a better correlation with the amount of lignin content than does the activation energy. An increase of the order of the phenolic resin cure reaction after addition of methylolated or non-methylolated lignins by 50 to 100% was also observed.