A facile and clean strategy to manufacture functional polylactic acid bead foams

Expanded poly (lactic acid) (EPLA) is a promising bio-material with ultra-low density, thermal insulation, cushioning properties, as well as the ability to be fabricated products in complex shapes. However, the time consuming of inducing double melt peaks of PLA and the complex two-steps process of steam-sintering assisted supercritical CO2 foaming is inevitable since PLA belongs crystalline polymer. To develop a facile and simple method to produce EPLA foams with functions, we used the bulk polymerization of liquid reactants to form a sintering layer between PLA beads. Meanwhile, carbon nanotubes (CNT) were synchronously introduced and distributed in the sintering layer. And a unique EPLA foam with functional sintering layer was produced using supercritical CO2 foaming technology. The reported method could prepare EPLA foam with high expansion ratio of 8.5 times and high cell density of 8.25 × 108 cell/cm3. Compared with other methods, the novel EPLA foams exhibited excellent tensile strength and compressive strength, superior electrical conductivity of 0.12 S/m, electromagnetic shielding ability of 99% in the X-band at CNT content of 2.68 wt.%, as well as sensitive and accurate stress-sensing function. It facilitates the development of novel manufacturing technology and the expansion of applications fields of EPLA foam.