Supertough Polylactide Blend Foams with Controlled Cell Size

The mechanical properties of polymeric foams are strongly associated with their cellular structure. However, the relationship between the cellular structure and the mechanical behavior of polymeric foams is complicated by the interdependence of cell size and expansion ratio. Herein, we explored the relationship between cell size and impact strength in poly(lactic acid) (PLA)/rubber blend foams by controlling the cell size while maintaining a constant expansion ratio. Surprisingly, a cell size-induced brittle-to-tough transition was observed at a critical cell size. Foams exhibited brittleness when the cell size exceeded this critical threshold, whereas smaller cell sizes led to improved toughness. The increased toughness was attributed to the robust interaction of stress fields generated by adjacent cells and rubber particles, which could hinder the progression of cell-induced crazes into cracks, resulting in greater energy absorption. This study provides a universal strategy for enhancing the resilience of polymer/rubber blend foams.