Cure Characterization of Polyurethanes with Lignin and Cellulose Derivatives

Abstract

The cure kinetics of hydroxypropyl cellulose (HPC) and hydroxypropyl lignin (HPL)- based polyurethanes were studied by dynamic mechanical thermal analysis (DMTA) using the model proposed by Provder (1989). The biobased polymers were crosslinked with polymeric methylene diisocyanate (pMDI). The crosslinking reaction followed n th order kinetics with an order of reaction of 1.8 and an apparent activation energy of 13.40-14.7 kcal/mol. HPC lends itself less readily to crosslinking with pMD1 as compared to HPL. The optimum safe storage temperature was determined as -16°C for both resins. Vitrification and damping behavior of HPL-based polyurethanes were also studied as a function of resin stoichiometry (NCO:OH). The glass transition temperature (T g ) measured at the tan δ-peak maximum and its corresponding activation energy showed a positive linear increase with increasing NCO: OH. Increasing NCO: OH was observed to cause a broadening of the tan δ peak and a decline of the tan δ peak height. Using the vitrification model proposed by Wisarankkit and Gillham (1990) it was possible to construct a partial TTT-cure diagram of HPL-based polyurethanes. This followed the S-shaped pattern typical of thermosets.