Thermal properties and micromorphology of polyurethane resins based on liquefied benzylated wood

Abstract

Liquefied benzylated wood based Polyurethanes (PUs) are synthesized with excess toluene diisocyanate (TDI), isophorone diisocyanate (IPDI) and hexamethylene diisocyanate (HDI). Four polyethylene glycols (PEG) of molecular weight 400, 600, 1000 and 2000 are mixed with liquefied wood using dibasic ester (DBE) as liquefaction reagent to incorporate different proportions of soft segment into the network prior to crosslinking with TDI. By differential scanning calorimetry, thermogravimetry, wide angle X-ray diffraction and SEM analysis, thermal properties and micromorphology of PU samples are investigated. Results indicated that molecular weight of the PEG had only a minor effect on glass transition temperature (<i style="">T_g</i>) of PU samples, but diisocyanates had major effects. The <i style="">T_g</i> of HDI-based PU network was –25°C lower than that of TDI (40°C) and IPDI (28.6°C). From SEM analysis, TDI, IPDI-based films have better phase-mixing properties than HDI-based PU. All the films had greater thermal stability than conventional PU films based on polyether or polyester alone.