Rheological study of quaternary ammonium-containing star-shaped polylactic acid

Quaternary ammonium-containing star-shaped polylactic acid (PLA-Q) is analyzed in melt rheology and found to follow a clustering behavior. The viscosity of this polymer is largely higher than its analog, of the same structure, without ammonium ions. This difference is attributed to physical interactions taking place between the ammoniums and hindering the flow of the melt polymer. The frequency sweeps of the storage (G ') and loss (G '') modulus of the melt PLA-Q are achieved at different temperatures and different shearing times. The iso-temperature and iso-time superposition of the resulting curves were achieved using, respectively, a temperature and a time shift factors, this superposition allowed the determination of the flow activation energy; its value corresponds to an ionic process confirming the ionic interactions. When the two shift factors are used simultaneously, a unique master curve of both G ' and G '' is obtained; this curve follows the Rouse model indicating the presence of two types of ionic associations within the melt polymer: a large number of multiplets having small size and a small number of clusters of larger size. (c) 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 48337.