AbstractAn investigation was conducted to establish the viability of blending Kraft lignin (L), a naturally occuring, readily available polymer resource, with polyurethane‐(PU) based sealants. The sealants were tested in a detailed program where lignin‐sealant blends, having blend ratios varying between 0 and 20 pbw L, were prepared on substrates of aluminum, mortar, and wood, and subjected to laboratory control (C), artificial weathering (AW), and natural weathering (NW) conditions. Results of tension testing showed that generally, lignin acts as a reinforcing agent which adds rigidity to the polymeric matrix, as indicated by the increase in toughness and modulus of blended sealants with the addition of lignin. In addition, the curing mode of PU, as determined by sequence hardness testing, was modified with the addition of lig
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