Polymer pollution from nonbiodegradable polymer blends is a source of increasing environmental concern.  The obvious solution, the replacement of petroleum-based polymers with biodegradable polymers from renewable sources, is difficult, since these polymers are highly immiscible.  Here, we show how the addition of only a few percent of a tertiary phase can enable compatibilization and enhancement of the mechanical properties.  The tertiary phase can be selected for any binary polymer system using the spreading coefficient (λ_ij) and the work of adhesion (W_a) as guides.  We demonstrate this method using poly(lactic acid) as the continuous matrix phase, styrenic polymers, polystyrene (PS) or high-impact polystyrene (HIPS), as the discontinuous minority phase, and styrene acrylic copolymers [styrene methyl methacrylate (SMMA)] as the tertiary phase.  We show that a distinct maximum in the impact toughness, nearly 58 and 56% forPS and HIPS blends, respectively, occurs when 1.2 and 1.5% SMMA copolymers are added.

*Zuo X, Xue Y, Wang L, Zhou Y, Yin Y, Chuang YC, Chang C, Yin R, Rafailovich M, Guo Y. Macromolecules 2019; 52: 7547