Tailoring foaming behavior of poly(lactic acid) by different geometric sizes of bio-based polyamide

Naturally derived materials have attracted much attention owing to the demand of sustainability. In this work, bio-based polyamide was used to tailor the foaming behavior of poly(lactic acid) by dispersing into different geometric sizes. The results showed that both micro-sized spherical and fibrillar polyamide markedly shortened the half-crystallization time of poly(lactic acid) in isothermal crystallization process, while nanofibrils played a better role on promoting crystallization than submicron spheres. When the polyamide was in a fibrillar state, the blends exhibited a higher complex viscosity in low frequency region. With increasing frequency, the blend containing nanofibrils displayed an obvious disentanglement phenomenon. Regarding foaming, the micro-sized polyamide particles with larger diameter were more conducive to cell nucleation than that with smaller size. The nanofibrils led to the highest cell density of 1.46 x 109 cells/cm3 and smallest cell size of 22.5 mu m in foams, and promoted the formation of open-cell structures. Owing to the reduced cell size, the collapse stress of foams containing polyamide was higher than that of poly(lactic acid) foam. This work provides a method for regulating cellular structure of polymers by controlling the geometric size of the second phase.