Effect of Kraft Lignin from Hardwood on Viscoelastic, Thermal, Mechanical and Aging Performance of High Pressure Laminates

In this work, the synthesis and characterization of phenol-formaldehyde resols modified with 10, 20 and 30wt% of Kraft lignin (a waste from pulp industry) from hardwood were studied. In all cases, the Kraft lignin was activated by hydroxymethylation. The resols characterization involved industrial measurements of free formaldehyde, viscosity, total solids and density. The resins were used for the industrial impregnation of Kraft-type paper and the production of laboratory laminates. The mechanical and thermal properties of the laminates were determined. Mechanical measurements included tensile, flexural, impact and interlaminar tests. Thermogravimetric and dynamic mechanical analysis were used for the thermal characterization. In addition, the aging of materials in water was studied. No significant differences in mechanical and thermal properties between traditional and modified materials were found with replacement up to 20wt% of phenol. Modified laminates exhibited better water resistance due to the lignin hydrophobicity. This work was carried out in collaboration with Centro S.A., San Francisco, Cordoba, Argentina, a high pressure-laminates industry.