Pittsburgh, Pennsylvania - Research at the Carnegie Mellon University indicates that the mechanical properties of lignin-based polyurethanes can be improved by treatment of lignin with Lewis acids.
The researchers conclude that chemical modification can lead tosignificant improvements in the properties of lignin-basedpolyurethanes, using "an inexpensive lignin monomer from renewableresources" and "an expensive, petroleum-derived isocyanate monomer toachieve the required material properties."
The team, Hoyong Chung of the Department of Chemistry, and Newell Washburn, of the Department of Biomedical Engineering, examined the possibility that the Lewis acid treatment would increase the concentration of hydroxyl groups available to react with diisocyanate monomers.
Their results are being published in the American Chemical Society's Appl. Mater. Interfaces journal.
Hydrogen bromide-catalysed modification of the lignin resulted in a 28 percent increase in hydroxyl group content, and the researchers measured associated increases in hydrophilicity
Polyurethanes were prepared by making a prepolymer based on mixtures of toluene diisocyanate (TDI) and unmodified or modified lignin, which was polymerised by adding polyethylene glycol (PEG).
Chung and Washburn found significant improvements in mechanical properties of modified lignin polyurethanes -- a 6.5-fold increase in modulus -- attributed to better integration of the modified lignin into the covalent polymer network, due to the higher concentration of hydroxyl groups.
See more at http://pubs.acs.org/doi/abs/10.1021/am300425x