Mechanical and morphological properties of injection molded linear and branched-polylactide (PLA) nanocomposite foams

• Linear and branched polylactide/clay nanocomposites were foamed in an injection molding machine.
• LCB-PLA based nanocomposites provided a more uniform, finer and denser cellular structure.
• The mechanical properties of the foamed specimens were remarkably affected by cellular structure.
• A significant improvement of the mechanical properties was obtained at 0.5 wt% clay loading.

Linear and long chain branched (LCB) polylactide (PLA)–clay nanocomposites were prepared via melt compounding using a twin-screw extruder. An organo-modified clay, Cloisite 30B, and a chain extender, Joncryl, were employed in this study. The resulting systems were also foamed in a conventional injection molding machine using a chemical blowing agent, namely activated azodicarbonamide. The PLA crystallinity, clay dispersion, and foam cellular morphology were characterized. Unlike the linear PLA, the addition of nanoclay markedly reduced the crystallinity of the LCB-PLA. The clay inclusion as well as the LCB structure generally decreased the cell size and foam density, while increasing the cell density. The mechanical properties of the unfoamed and foamed linear and LCB-PLA samples and their corresponding nanocomposites were also characterized by tensile and Izod impact testing. The corresponding results revealed that the LCB-PLA nanocomposite with 0.5 wt% clay loading exhibited a significantly improved cellular structure in comparison with other foamed samples, leading to increased values of the specific modulus, tensile and impact strength.

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