Multiphase materials with lignin. IV. Blends of hydroxypropyl cellulose with lignin

Polymer blends of hydroxypropyl cellulose (HPC) and organosolv lignin (OSL) were prepared by mixing in solutions of both pyridine and dioxane, and casting as films, and by mixing in the melt followed by extrusion. All preparations exhibited partial miscibility as evidenced by a single Tg up to a composition of 40 wt% lignin above which phase separation was detected. Dioxane-cast and injection-molded blends were distinguished from the pyridine-cast materials by a positive Tg deviation from additivity, an approximation which adequately described the latter. This positive deviation in Tg is attributed to the formation of a liquid-crystal mesophase with a resultant reduction of amorphous HPC available for interaction with the lignin component. This explanation is supported by a rapid rise in modulus (approximately 150%) and tensile strength with very low lignin content, and by an associated sharp decline in ultimate elongation. The development of morphological features as observed by scanning electron microscopy provides further substantiation of this hypothesis.