Understanding the effect of chain entanglement state on melt crystallization of the polymer freeze-extracted from solution: The role of critical overlap concentration

Publication date: Available online 18 June 2019Source: PolymerAuthor(s): Yingxiong Wang, Jiaxin Fu, Mingjin Liu, Qiang Fu, Jie ZhangAbstractFreeze-drying of dilute polymer solution is a widely accepted method to yield disentangled polymer. By this method, it has been pointed out that samples recovered from dilute solution possess a better crystallization ability than the bulk polymer. Here, the important role of the critical overlap concentration c* in polymer solution is firstly stressed to give a more quantitative understanding in the relation between entanglement state and melt crystallization behavior. Crystallization kinetics of poly (lactic acid) freeze-extracted from dichloromethane solution with various concentration below and above c*, as well as the crystalline structure after isothermal crystallization at 110 °C, were investigated by means of differential scanning calorimetry (DSC) and small-angle X-ray scattering (SAXS). Results indicated that crystallization kinetics and lamellar thickness (Lc) show a strong dependence on precursor solution concentration only when the concentration is lower than the critical value (c*), while above c* the crystallization behavior changes a little. Besides, a more rational method to characterize the chain entanglement state in polymer solution and to select concentrations accordingly was suggested, that is, using a dimensionless variable [η]c which is the product of intrinsic viscosity [η] and solution concentration c.Graphica...

Source: Polymer - June 18, 2019 Category: Chemistry Source Type: research