Microcellular foaming of polylactide and poly(butylene adipate‐co‐terphathalate) blends and their CaCO₃ reinforced nanocomposites using supercritical carbon dioxide

Abstract

Foamed polylactide (PLA), PLA–PBAT (poly (butylene adipate‐co‐terphathalate)) blend and their composites with CaCO 3 were prepared in a batch process using supercritical carbon dioxide (CO 2 ) at 12 MPa and 45°C. The solubility of CO 2 and its diffusion patterns in different PLA samples was investigated. PLA systems had a relatively high CO 2 solubility related to the carboxyl groups. CO 2 desorption behaviors in PLA systems first followed the Fickian diffusion mechanism in short time and then decreased slowly to a plateau. The addition of both PBAT and CaCO 3 into PLA impeded the desorption of CO 2 . In the presence of second phase PBAT, nanoparticles CaCO 3 and dissolved CO 2 , the PLA crystallization behavior investigated by DSC technique was greatly changed. As the desorption time increased, the gas induced crystallinity slightly decreased in consequence of less CO 2 content in each system and thus less plasticization effect. The cell morphology of foamed PLA and PLA composites showed interesting microstructure patterns. The prepared pure PLA foam exhibits a typical bimodal structure because of the foaming in both the amorphous and crystalline zones. With PBAT and CaCO 3 into PLA, the composite foam presented significant increase in cell uniformity and cell density. With less CO 2 content in each PLA sample, the cell structure showed interesting variation. Pure PLA foam presented transition from bimodal structure to more uniform cell structure with decreased cell density. In contract, PLA–PBAT foam show unfoamed regions because of none CO 2 left in the separated PBAT phase. Copyright © 2016 John Wiley & Sons, Ltd.