Rheological Characterization of Sulfuric Acid Solutions of Poly(p-phenyleneterephthalamide)

Abstract

Several grades of poly(p-phenyleneterephthalamide) (PPD-T) with different molecular weights were prepared. The rheological properties of sulfuric acid solutions of PPD-T were measured. In the vicinity of the critical concentration tan <5 and eta'/G' exhibited a minimum value, but G'/2G '' and eta* showed a maximum value. High concentrations produce an anisotropic phase. Tendencies of yield behavior were observed for these solutions in the anisotropic phase. Above the saturated concentration the solution system showed gel-like properties, i.e., with increasing concentration abrupt reduction of G'/2G '' and abrupt increases of eta*, eta'/G' and tan delta were observed. With increasing temperature the viscosity of isotropic and anisotropic phases was decreased but that of biphase was increased. The critical concentration was reduced with increasing molecular weight, but increased with increasing temperature. Use of reduced variables seemed to eliminate molecular weight dependency on the critical concentration curve. The shear viscosity appeared to be proportional to (<(M)over bar>w)(6.7).