Biopolymer Blends Based on Poly (lactic acid): Shear and Elongation Rheology/Structure/Blowing Process Relationships

Abstract

This study was dedicated to the blown film extrusion of poly(lactic acid), which mainly presents poor shear and elongation viscosities, and its blends. In order to enhance its melt strength, two main routes were selected (i) a structural modification through chain extension and branching mechanisms by adding a reactive multifunctional epoxide (named Joncryl) and (ii) blending with poly(butylene adipate-co-terephtalate), named PBAT in presence (or not) of Joncryl. The effects of the reactive agent on the shear and elongation rheology, morphological, and interfacial properties of the blends were systematically investigated. A decrease of the interfacial tension has been also demonstrated according to the deformed drop retraction method (DDRM). Hence, the role of Joncryl as a compatibilizer was highlighted. Consequently, finer morphology of the dispersed phase was obtained. Furthermore, the impact of the two modification routes on the blown film extrusion ability of PLA has been studied. Based on the improved shear and elongational rheological properties, a great enlargement of the blowing processing window of PLA modified with Joncryl was demonstrated. Indeed, with the addition of Joncryl into OPEN ACCESSPolymers 2015, 7 940 PLA-PBAT blends, a reduction of the instability defects has been detected. Finally, the induced crystalline structure and the thermo-mechanical properties of blown films were shown to be improved.

Biosourced blends based on poly (lactic acid) and polyamide 11: Structure–properties relationships and enhancement of film blowing processability

“…When the temperature moved toward 100°C, E′ increased due to the cold crystallization of PLA. [21] The structural disorder introduced by these chain extenders decreased the chain mobility and thus reduced the crystallization ability of PLA. This increase was due to the significant crystallinity obtained upon annealing.…”

“…Such an evolution indicates that the development of the crystalline structure in the modified PLA/PA11 blends was effectively hindered by addition of the multifunctionalized epoxide as also confirmed by DSC data (Table 3). [21] The structural disorder introduced by these chain extenders decreased the chain mobility and thus reduced the crystallization ability of PLA. Moreover, the height and the sharpness of the tan δ peak were affected by the degree of crystallinity.…”

“…Different instability defects can be obtained as reported by Han et al [36,37] Draw resonance, bubble breathing, helical instability and frost line oscillation are the most common instabilities observed during processing. [21] In this study, the stability of the process was characterized by creating maps of stability (BUR vs. TUR). Hence, these two parameters of the blown films were varied and the stability or instability of the bubble was monitored.…”

“…In our previous works, Mallet et al [20] have studied the flow stability of modified PLA during reactive blown film extrusion. Al Itry et al [21] have discussed the effect of the film blowing process on the crystalline and thermomechanical properties of PLA/PBAT blends. In both of these two papers, the chemical modification was used and it was demonstrated that the balance of chain extension/branching was difficult to be controlled in parallel to compatibilization behavior.…”

The effect of the addition of poly(styrene‐co‐glycidyl methacrylate) copolymer on the properties of polylactide/poly(methyl methacrylate) blend

“…Therefore, to make PLA/PMMA blends suitable for engineering applications, toughness, and impact resistance should be improved. In this sense, reactive processing with epoxy groups has been reported to improve the compatibility of PLA containing systems . The reaction of the epoxy groups with PLA's carboxyl and hydroxyl end‐groups can lead to branching and consequently enhances melt strength and some mechanical properties .…”