Effect of the simultaneous biaxial stretching on the structural and mechanical properties of PLA, PBAT and their blends at rubbery state

• The issues of stretchability of biopolymers and their blend were addressed.
• Stretching of PBAT induces less microstructural modification than PLA.
• Chain extension and branching mechanisms do not modify the crystallization and mechanical properties of PBAT polymer in comparison to PLA.
• The compatibilized PLA/PBAT blends show a lower stretchability according to their higher strain hardening.

This works deals with the study of the strain-induced structural changes of PLA, PBAT and their blends with/without multi-functional styrene-acrylic oligomers (Joncryl ADR®-4368). The films were prepared through a single-screw extrusion. Uni and bi-axially simultaneous stretching, at a temperature above the glass transition temperature, were performed. The experimental conditions were chosen so as not to generate significant thermal crystallization during tests duration. Stretching induced semi-crystalline films with a supposed in-plane mechanical isotropy. Their structural, morphological and thermo-mechanical properties were characterized using dynamic mechanical and thermal analysis (DMTA), differential scanning calorimetry (DSC), wide-angle X-ray scattering (WAXS), and transmission electron microscopy (TEM). The strain-induced crystals of PLA combined mesophase and α′-form crystals. Besides, the stretched PBAT was found to be composed of mixed-crystal structure of BT and BA units in a PBT-like crystal form. The Joncryl addition promoted significant changes on the crystallization kinetics of PLA without affecting the crystallization kinetic of PBAT. In fact, Joncryl acted as a nucleating agent making thus faster the thermal crystallisation of PLA. In parallel, the strain induced crystallisation in PLA was accelerated and stresses increased. The same effect was still observed in the PLA_PBAT blends.

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