Abstract
This work reports the effect of the addition of an oligomer of lactic acid (OLA), in the 5–20 wt% range, on the processing and properties of polylactide (PLA) pieces prepared by injection molding. The obtained results suggested that the here-tested OLA mainly performs as an impact modifier for PLA, showing a percentage increase in the impact strength of approximately 171% for the injection-molded pieces containing 15 wt% OLA. A slight plasticization was observed by the decrease of the glass transition temperature (Tg) of PLA of up to 12.5 °C. The OLA addition also promoted a reduction of the cold crystallization temperature (Tcc) of more than 10 °C due to an increased motion of the biopolymer chains and the potential nucleating effect of the short oligomer chains. Moreover, the shape memory behavior of the PLA samples was characterized by flexural tests with different deformation angles, that is, 15°, 30°, 60°, and 90°. The obtained results confirmed the extraordinary effect of OLA on the shape memory recovery (Rr) of PLA, which increased linearly as the OLA loading increased. In particular, the OLA-containing PLA samples were able to successfully recover over 95% of their original shape for low deformation angles, while they still reached nearly 70% of recovery for the highest angles. Therefore, the present OLA can be successfully used as a novel additive to improve the toughness and shape memory behavior of compostable packaging articles based on PLA in the new frame of the Circular Economy.
Highlights
Polylactide (PLA) is a linear thermoplastic biodegradable polyester that can be obtained from starch-rich materials by fermentation to give lactide, which is polymerized at the industrial scale by ring-opening polymerization (ROP) [1]
PLA was supplied by NatureWorks LLC (Minnetonka, MN, USA) as IngeoTM Biopolymer 6201D. This PLA grade contains 2 mol% D -lactic acid. It was supplied in pellet form and it had a density of 1.24 g cm−3 whereas its melt flow index (MFI) was 20 g/10 min, measured at 210 ◦ C and 2.16 kg
The addition of 15 wt% OLA provided an increase in the impact strength from 25.7 kJ m−2 to almost 70 kJ m−2
Summary
Polylactide (PLA) is a linear thermoplastic biodegradable polyester that can be obtained from starch-rich materials by fermentation to give lactide, which is polymerized at the industrial scale by ring-opening polymerization (ROP) [1]. Su et al [29] and Zhang et al [30] have reported different approaches to overcome the intrinsic brittleness of PLA by adding different contents of PBS using reactive compatibilizers. The work carried out by Gonzalez-Ausejo et al [34] reported a clear improvement in toughness by using sepiolite nanoclays as gas barrier and compatibilizer in PLA/poly(butylene adipate-co-terephthalate) (PBAT) blends. Tsou et al [35] improved toughness of PLA by using an adipate ester plasticizer It has been reported the positive effect of combining two plasticizers: one solid plasticizer, namely poly(ethylene glycol). Many research works have been focused on using environmentally friendly plasticizers, which can contribute to improving toughness without compromising the overall biodegradability of PLA. The shape memory behavior of the pieces was analyzed and related to the OLA dispersion within the PLA matrix
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