(302b) Enhanced Degradation and Toughness in Blends of Polylactide and Poly(ethylene oxide)-b-Poly(butylene oxide)

The accumulation of fossil fuel-derived and non-degradable plastics represents a major threat to both ecosystems and human health worldwide. In the United States, nearly half of all plastic waste is mismanaged, meaning that at present any serious attempt to combat the plastic crisis must consider the development of biodegradable alternatives. Polylactide (PLA) is a bio-sourced and compostable alternative to conventional plastics, but lacks the toughness required for many applications. Moreover, due to its glass transition well above room temperature and low water permeability, it can only be composted under industrial conditions (high temperature and pH) and takes decades to degrade under most environmental conditions. Recently, we reported a PLA-immiscible poly(ethylene oxide)-b-poly(butylene oxide) diblock polymer additive (PEO-PBO) that imparts a roughly 20-fold increase in toughness to PLA when blended at loadings as low as 1.8 wt%. Herein, we report that this same PEO-PBO additive accelerates degradation of PLA when aged at ambient conditions without sacrificing the enhancement in toughness. The molecular weight of PLA in 5 wt% PEO-PBO/PLA blends was found to begin decreasing after 10 months of aging at ambient conditions, while identical films aged under dry, inert atmosphere remained intact. The molecular weight of PLA in these blends decreased to roughly 80%, 50% and 25% of original after 10 months, 1.5 years, and 3 years of aging, respectively. Aged films exhibited no significant loss in toughness compared to unaged films for up to 9 months, and films aged for as long as 1.5 years retained a roughly 5-fold increase in toughness over neat PLA, despite the loss in molecular weight. In accelerated model-environmental degradation studies conducted in deionized water at 50 °C, 1.5 year-aged PEO-PBO/PLA blends disintegrated within 43 days, as compared to 111 days for unaged PEO-PBO/PLA blends and 150 days for neat PLA under the same conditions. These results demonstrate that blending with small quantities of PEO-PBO can both increase toughness in PLA in the short term while accelerating degradation in the long term, simultaneously widening its range of commercial viability and reducing its environmental impact.