Rheological and foaming behavior of linear and branched polylactides

In this work, a chain extender (CE), Joncryl © ADR, was added to a polylactide (PLA) at two concentrations, 0.4 and 0.7 wt%, using two different strategies. The rheological properties and foamability of the neat PLA and PLA containing the CE were studied. The steady and transient rheological properties of the neat PLA and CE-treated PLAs revealed that the introduction of the CE profoundly affected the melt viscosity and elasticity. The linear viscoelastic properties of CE-enriched PLAs suggested that a long chain branching (LCB) structure was formed from the reaction with the CE. LCB-PLAs exhibited an increased viscosity, more shear sensitivity, and longer relaxation time in comparison with the linear PLA. The LCB structure was also found to affect the transient shear stress growth and elongational flow behavior. LCB-PLAs exhibited a pronounced strain hardening, whereas no strain hardening was observed for the linear PLA. Batch foaming of the linear and LCB-PLAs was also examined at foaming temperatures of 130, 140, and 155 ᵒC. The LCB structure significantly increased the integrity of the cells, cell density and void fraction.