Morphology and amorphous structure of blend membranes from cellulose and casein recovered from its cuprammonium solution

Abstract

Morphology, structure, and some properties of the blend membranes of cellulose/casein prepared from their cuprammonium hydroxide solution by alkali coagulation and subsequent acid neutralization were investigated in connection with the complex forms of cellulose in the mixed solutions and the change in complex forms developed by alkali coagulation. For this purpose, the cast solution was coagulated by either directly immersing the coagulation bath (W series) or after vaporization of ammonia in advance (D series). Circular dichroism (CD) measurements on the mixed solution and gel membranes revealed that the mixed solution with the fraction of casein fcas≧0.3 forms the independent casein/cuprammonium hydroxide complex, hence giving phase-separated state in an optical anisotropic sense, and this upper limit shifts towards lower fcas (= 0.2) during coagulation. Longest wavelength λ for the charge transfer excitation of cellulose/cuprammonium complex was seen for the gel membrane with fcas = 0.1, where highest tensile strength and crystalline orientation for the membranes are realized. Mechanical relaxation analysis suggests that the amorphous structural formation for D and W series membranes are quite different and that for the former is on the whole determined by the existing state of casein and cellulose in the mixed solution not by that in the gel membranes. Except for porosity Pra the swelling anisotropy parameter Lt was not correlated with (110) plane orientation parameter and most amorphous parameters, which control Lt of the regenerated cellulose membranes.