Highly toughened and heat resistant poly(l-lactide)/poly(ε-caprolactone) blends via engineering balance between kinetics and thermodynamics of phasic morphology with stereocomplex crystallite

Abstract

Enhancing matrix crystallization via forming stereocomplex (SC) crystallite has been considered as an effect way to improve the impact toughness and heat resistance of poly(l-lactide) (PLLA) when blending with other polymers. However, the roles of some of the key parameters, such as the kinetics of morphology evolution in blends, remain, yet, unclear, causing the troubles of the reproducibility of toughening PLLA by enhancing matrix crystallization and the stability in end-use applications (particularly in relative high temperature ranges). Herein, we provide a facile way to improve the toughness and heat resistance of PLLA via engineering the balance between the kinetics and thermodynamics of the dispersed phasic morphology in PLLA blends using PLLA/poly(ε-caprolactone) (PCL) (PLLA/PCL, 80/20 w/w) as an example, by adding a small amount of poly(d-lactide) (PDLA, ≤ 1% w/w). The few PDLA chains naturally interact with PLLA matrix chains, and co-crystallize to form SC crystallites, yielding high crystalline PPLA matrix but in controllable crystallization kinetics and increase of melting viscosity. As such, the coalescence or arrest of dispersed PCL phase is tailored via the tempo- and thermo-dimensional balance manipulation of thermal annealing (thermodynamics) and injecting moulding (quenching, dynamics), that relies on the PDLA content. The ease, with which highly impact toughened and heat-resistant PLLA materials were obtained by optimizing and matching the PDLA content and processing parameters including temperature and time, points to new directions in designing toughened PLLA with an economic manner.