Effect of six technical lignins on thermo-mechanical properties of novolac type phenolic resins

Lignin has been studied as an alternative to phenol in phenolic resins, due to economic and environmental reasons. The possibility of partially replacing phenol in phenol-formaldehyde (PF) resins by different types of lignins and analyze the lignin functional groups influence on the thermo-mechanical properties of the resins, has been explored. Novolac phenolic resins were prepared with six lignins: five lignins from black liquor of soda pulping bagasse and a commercial ammonium lignosulphonate from pinus taeda (LSA). These lignins have different percentages of functional groups (OH aromatic carbonyls and methoxyl) and polysaccharides. The kinetic study found that modified resins elaborated with lignin LSA exhibit the highest values of activation energy (148.66 and 148.92 kJ mol^-1 in models of Flynn-Wall-Osawa and Friedman respectively), resulting to be the most stable of modified resins. Finally, this same resin has the highest value of the modulus of elasticity (MOE) of 8.02 GPa, even higher than unmodified phenolic resins. Therefore, LSA lignin, showed the best results in friction phenolic resins, this would imply the stability is within the bio-polymer and attributable to the linkage between PF and lignin.