Compatibility in biobased poly(L‐lactide)/polyamide binary blends: From melt‐state interfacial tensions to (thermo)mechanical properties

Abstract

The melt compatibility between poly(L-lactide) (PLA) and polyamides (PAs) with related thermomechanical properties is addressed. A particular attention is paid to four commercial PAs with extrusion processing temperatures close to PLA (PA10-10 to PA12). PLA/PA blend morphologies without a compatibilizer are first revealed by scanning electron microscopy. PA12 displays the best droplet dispersion into PLA (D n 700 nm), whereas a poor interfacial adhesion is attested for PLA/PA10-10 blends. Interfacial tensions corroborate the PLA/PA10-10 incompatibility (γ 12 9 mN/m, 240 C) with decreasing γ 12 in the order PLA/PA10-10 > PLA/PA11 > PLA/PA12 (γ 12 2 mN/m). Surface tensions confirm the highest compatibility between PLA and PA12. Ductilities, toughnesses, and thermal resistances of PLA/PA blends are evaluated up to 40-wt % PA. Brittle-to-ductile transitions are observed for PA content higher than 30-wt % with the highest ductility for PLA/PA12, in accordance with their enhanced compatibility. Impact strengths display similar trends with a twofold increase for PLA/PA12. An outstanding synergy between PLA and PA is highlighted by dynamic mechanical analyses with heat deflection up to 130 C for PLA/PA blends. The synergy arises from a peculiar crystallization of PLA in the presence of PA. PLA/PA morphologies/interfaces can be consequently tuned by an appropriate PA choice with interesting improvements of thermomechanical properties for high-performance/durable applications.

Role of Compatibilizer in Improving the Properties of PLA/PA12 Blends

“…The values of stress at yield, elongation at break, and Young's modulus evaluated by tensile tests are tabulated in Table 1. The poor ductility of PLA (3.4%) drastically improved by the addition of 30 wt.% PA12 (153%), indicating good compatibility as confirmed in our previous studies (Raj et al, 2019). PLA-g-MA was incorporated in the blends to observe the potential evolution of compatibility and its effect on mechanical properties.…”

“…It can be clearly seen that the droplet diameter decreases linearly up to 2 wt.% and an increment in the droplet size was noticed with a further increase in PLA-g-MA concentration. The lower droplet diameters, better interfacial adhesion, and stronger interface between the blend components of injection molded samples (Figure 6) when compared to compression molded samples (Figure 4) could be the reason for higher ductility in blends (Stoclet et al, 2011;Walha et al, 2016;Raj et al, 2019). It is interesting to observe that for injection molded samples, the droplet size of 5 wt.% PLAg-MA (0.96 µm) is lower than PLA/PA12 (70/30) (1.1 µm); this fine dispersion of PA12 droplets even at higher concentration of PLA-g-MA could be the reason for the ductility behavior of the blends at 5 wt.% of PLA-g-MA (260%).…”

“…Blending PLA with engineering polymers is an efficient way to overcome a majority of the limitations of PLA. Over recent years, intensive research is being carried on PLA based blends with engineering polymers such as polycarbonates (Bouzouita et al, 2016), poly(methylmethacrylate) (Samuel and Jean-Marie Raquez, 2013), polyesters (Jiang et al, 2014), and polyamides (Stoclet et al, 2011;Raj et al, 2019). Among the engineering polymers, polyamides stand out, as the blending would enhance the targeted properties of PLA such as low ductility, poor impact strength, and low heat resistance.…”

“…In general, PLA/PA blends are immiscible but compatible in nature. Different types of polyamides have been blended with PLA including PA6 (Wang et al, 2010), PA11 (Stoclet et al, 2011), PA6-10 (Pai et al, 2013), PA10-10 (Cailloux et al, 2018), PA10-12 (Raj et al, 2019), and PA12 (Raj et al, 2019). In order to achieve better final properties, it is necessary to improve the compatibility further.…”

“…In our previous work, we have reported various PLA blends with long-chain aliphatic polyamides. It was found that PA12 showed the best compatibility with PLA with low interfacial tensions, good dispersion, and exceptional mechanical properties (ductility>170% for 40 wt.% PA12), good impact properties, and thermal resistance (Raj et al, 2019). Hence, in an attempt to obtain further improvement thermal resistance and mechanical properties we present the effect of PLA-g-MA as a compatibilizer on the properties of PLA/PA12 blends.…”