Correlation of Monomer Source and Structure to the Morphology and Properties of Lignin Based Polyurethanes

Lignin based polyurethanes (PU) have gained interest due to the possibility of using naturally available lignin as polyols to synthesize environmentally friendly PUs. The structural properties of the resultant PUs are dependent on the structure and type of polyol and isocyanate used during synthesis. Here, lignin based PUs were synthesized using lignin extracted from poplar wood with the novel CELF (Co-solvent Enhanced Lignocellulosic Fractionation) technology, as well as from soft wood, hard wood and wheat straw which react with the diisocyanates toluene diisocyanate-encapped PPG or hexamethylene diisocyanate. The morphology, mechanical and thermal properties of these PUs with various lignin fraction ranging from 30 to 60 wt% were studied. Independent of the type of the lignin used, increasing the fraction of lignin results in two-phase PUs. PUs synthesized from CELF lignin show that mechanical properties are highly reliant on the OH/NCO ratio used during synthesis. Dispersion of the lignin within PPG matrix depend on the fraction and origin of the lignin used, which dramatically impacted the measured mechanical properties.