Due to increased demand for more sustainable products, producers of rigid polyurethane (PUR) and polyurethane/polyisocyanurate (PUR/PIR) foams are searching for ways to use more renewable materials. One way to increase sustainability of foams is to incorporate lignin, an abundant natural polymer, to replace fossil-fuel based polyol. The incorporation of lignin as a polyol substitute in rigid PUR foam has been reported to improve mechanical performance, oil sorption capacity, and biodegradability, but this is the first study to investigate the impacts lignin incorporation on the performance of rigid polyurethane/polyisocyanurate. The focus of this study was to expand the application of lignin in low-density rigid PUR and PUR/PIR foams, while ensuring that the developed foams met standard requirements for insulation applications. Another aspect was to find the most suitable lignins for this application by evaluating the performance of foams made with a wide range of unmodified commercial lignins. Lastly, the maximum loading percentage of lignin as polyol replacement in rigid PUR and PUR/PIR foams was elucidated using a commercial kraft lignin. The results showed that the corn stover lignin isolated through enzymatic hydrolysis process was the best for rigid PUR/PIR foam applications. Additionally, replacing 30 wt.% of polyols with lignins showed that lignins with higher hydroxyl and metal contents, and more neutral pH resulted in foams with higher compression strengths and closed cell contents. Moreover, the incorporation of lignin with decreased molecular weight (via ALPHA processes developed at Clemson University) enhanced PUR/PIR foam compression strength and closed cell content compared to control formulations with no lignin. We were also able to formulate rigid PUR and PUR/PIR foams where 50 and 100% of commercial polyol (respectively) was replaced with unmodified lignin, while meeting standard requirements for insulative foam applications.
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