Body temperature-responsive gels derived from hydroxypropylcellulose bearing lignin

Hydroxypropylcellulose bearing lignin (HPC-L) prepared from softwood by the atmospheric acetic acid pulping followed by derivatization showed the lower critical solution temperature (LCST) of approximate 38 °C in 2% aqueous solution, which were 5° lower than that of pure HPC with a similar molecular mass to HPC-L. Two types, urethane and epoxy, of chemical gels were prepared from HPC-L and HPC using hexamethylene diisocyanate and polyethylene glycol diglycidyl ether as crosslinkers, respectively. The urethane-type gels from both HPCʹs have undergone shrinking at less than 20 °C. This thermoresponse of the gels did not reflect LCST of the sources. Such low temperature shrinking was brought about by the hydrophobicity of crosslinker. On the other hand, the epoxy-type gels showed a very similar volume transition temperature (VTT) upon shrinking to LCST; the epoxy-type HPC-L gel showed VTT at 38 °C, while the corresponding HPC gel had VTT at 46 °C. This difference in VTT as well as LCST was attributable to hydrophobicity of lignin dangled to HPC. Thus, the body temperature-responsive gel can be prepared from HPC-L with the water-soluble crosslinker.