Fabrication of poly (lactic acid) foams using supercritical nitrogen

Abstract

<jats:p> In this article, poly (lactic acid) (PLA) was foamed via batch foaming using supercritical nitrogen as a physical blowing agent by two methods, conventional foaming process (CFP) and low-temperature foaming process (LTFP). The fabrication processes, cell morphologies, thermal properties, crystallization behavior, and electrical resistance of resulted foams were studied to investigate the effect of foaming on these properties of PLA. It was found that the foams resulted from CFP method have micrometric cell sizes, while LTFP method led to nanometric cell structure and high cell density. Also scanning electron microscopy showed that the PLA foams have a heterogeneous cellular structure. The results showed that the foaming process increased the melting point and degree of crystallinity of PLA, which led to decrease in the electrical resistance of samples. </jats:p>

Forefront Research of Foaming Strategies on Biodegradable Polymers and Their Composites by Thermal or Melt-Based Processing Technologies: Advances and Perspectives

“…PBAs can be added to the polymer in liquid, gaseous, or supercritical form. Examples of gaseous PBAs include carbon dioxide (CO 2 ) and nitrogen (N 2 ) gas [39], while liquid PBAs include hydrocarbons such as isopentane [40]. CO 2 has much higher solubility and lower diffusivity in molten polymers than N 2 and is mostly used in the extrusion foaming of low-density foams.…”

“…Polymer foams can be obtained by different processing technologies, namely foam extrusion, foam injection moulding, batch processing (i.e., in an autoclave), bead foaming, microwave foaming, or additive manufacturing. Several published review papers have reviewed several polymer foam production processes [39,41,[50][51][52]95,96]. This review will provide an overview of these main processes of foaming commonly applied to biodegradable thermoplastic polymers to obtain lightweight parts.…”

“…Particularly, the dissolved gas used in foaming has great influence on the crystallization and melting behaviours of PLA [239,240]. Among the gases commonly used in PLA foaming, CO 2 is much more soluble in PLA compared to N 2 [39,76]. Dissolved CO 2 increases PLA's crystallization rate, while N 2 has a neutral impact on PLA's crystallization rate due to its low solubility in PLA [117].…”