Abstract

Novel polyurethane based two-component self-leveling sealant formulations, incorporating various types of kraft processed lignins including softwood, hardwood, and eucalyptus wood lignin, were produced and their performance properties established in a research program which sought to develop more durable cost effective sealants as well as cultivate a market for lignin, a highly underutilized by-product of the pulp and paper industry. The tensile and compressive performance characteristics of lignin and kaolin filled sealant formulations, compounded at different volumetric filler loadings, were compared and the results indicated that both types of filler increase the modulus of the base elastomer in relation to the semi-empirical relation of Nielsen. This suggests that the mechanical properties are dependent on the maximum packing fraction of the respective fillers which in turn, is a function of their particle size and size distribution. The relationship between the modulus and the volumetric filler loading was useful in the preparation of sealant formulations having optimum filler contents. Finally, these optimum formulations were prepared for a subsequent testing program in which the tensile strength and cyclic performance of the sealants was compared to that of existing two-component self-leveling sealant compounds currently available on the market. Results of these performance tests indicate that lignin filled elastomeric sealants, in most instances, have adequate tensile strength and perform adequately if subjected to a moderate cyclic strain program. Further improvements in performance properties may be obtained if adjustments to the particle size are made and this is warranted considering six to ten times cost advantage these fillers possess in relation to conventional fillers.