On polymer-polymer miscibility and cellulose ester blends: A case study

Abstract

Differential Scanning Calorimetry (DSC) and micro-Raman Spectroscopy were used to study blends of cellulose acetate (CA) with cellulose acetate butyrate (CAB) prepared by solution blending. It is shown that these blends combine two characteristics: (a) values of enthalpy of mixing (ΔHmix) and Gibbs free energy of mixing (ΔGmix) close to zero, due to similar molecular interactions and (b) multiple, more or less equivalent, minimum values of ΔGmix leading to non-equilibrium structures, mainly due to the inherent microheterogeneity of pure polymers. New interpretations are provided for the observed thermal behavior (e.g. existence of multiple thermal transitions) of the blends. None of the terms miscible, partially miscible or immiscible is truly appropriate to characterize these blends. The thermal behavior of pure polymers, blends and chemically synthesized copolymers of similar degree of substitution is pretty much alike, thus, development of copolymers by physical blending of cellulose esters seems to be feasible.