Effect of the viscosity ratio on the PLA/PA10.10 bioblends morphology and mechanical properties

Abstract

PLA bio-blends with a predominantly biosourced PA10.10 in the composition range 10-50 wt% were prepared by melt blending in order to overcome the advanced brittleness of PLA. Due to the inherent immiscibility of the blends, 30 wt% of PA was needed to achieve a brittle-to-ductile transition and a co-continuous morphology was predicted at 58 wt% of PA. The initial enhancement of the PLA rheological behaviour through the environmentally friendly reactive extrusion process yielded a finer and more homogeneous microstructure and hence enhanced the mechanical properties of the bioblends at much lower PA contents. The brittle-to-ductile transition could be achieved with only 10 wt% and co-continuity was observed already at 44 wt% of PA. Results indicate the significant potential of modifying PLA flow behaviour as a promising green manufacturing method toward expanding PLA-based bio-blends applications.

Tuning gradient microstructures in immiscible polymer blends by viscosity ratio

“…Theoretically, a high viscosity ratio will result in large deformed droplets and a coarse morphology, whereas a low or matching viscosity ratio could result in fine fibrils and uniform morphology . In most experimental cases, the dispersed phase was found to be finer for viscosity ratios less than one ( p ≤ 1) than that for viscosity ratios larger than one ( p > 1) . In addition to the droplet deformation and breakup differences in low and high viscosity ratio polymer blends, the migration of components, which also depends on the viscosity ratio, is of significance for controlling the polymer morphology .…”

“…19 In most experimental cases, the dispersed phase was found to be finer for viscosity ratios less than one (p ≤ 1) than that for viscosity ratios larger than one (p > 1). [27][28][29][30] In addition to the droplet deformation and breakup differences in low and high viscosity ratio polymer blends, the migration of components, which also depends on the viscosity ratio, 31 is of significance for controlling the polymer morphology. 32,33 In a study on cellulose/aromatic polysulfonamide (PSA) alloy fibers with coresheath structures, the low viscosity PSA phase was found to migrate to the outer layer of a filament during spinning.…”

PLA/PA Bio-Blends: Induced Morphology by Extrusion

“…This situation would be expected as p is lower than 1 for these blends, which would promote the mechanisms of "End Pinching" and "Necking break-up" referenced in Table 1. On the other hand, it would lead to a lower probability of coalescence that could occur in the convergent flow zone in the head (see Figure 2), as a consequence of the increase in "surface energy" that the reactive modification causes in the PLA REx and that has been reported by Cailloux et al [18]. According to these authors, the surface energy of PLA is 46.4 mJ/m 2 vs. 51.5 mJ/m 2 for PLA REx .…”

“…This modification was obtained by a reactive extrusion (REx) process following the same procedure and conditions previously reported in [36], using as reagent a styrene-acrylic multifunctional-epoxide oligomeric agent (Joncryl-ADR-4400 ® , kindly supplied by BASF, Ludwigshafen, Germany), with an epoxy equivalent weight of 485 g/mol and a functionality of 14. Under these processing conditions, chain extension and sparsely three-arm star branching are promoted in PLA which results in a content of approximately 24% w/w of modified chains, causing an increase in its melt elasticity [18,37].…”

“…Among the strategies considered, melt blending of PLA with other polymers has been a practical and economic way for improving the properties of PLA [6,8,10,12,13]. Recently, blends with bio-sourced polyamides (PAs) have gained interest, regardless of their limited miscibility [14][15][16][17][18]. The control of the resulting morphology of these blends has proven to tailor their properties, such as mechanical, crystallization kinetics, and processability.…”