Foaming of PLA Composites by Supercritical Fluid-Assisted Processes: A Review

Abstract

Polylactic acid (PLA) is a well-known and commercially available biopolymer that can be produced from different sources. Its different characteristics generated a great deal of interest in various industrial fields. Besides, its use as a polymer matrix for foam production has increased in recent years. With the rise of technologies that seek to reduce the negative environmental impact of processes, chemical foaming agents are being substituted by physical agents, primarily supercritical fluids (SCFs). Currently, the mass production of low-density PLA foams with a uniform cell morphology using SCFs as blowing agents is a challenge. This is mainly due to the low melt strength of PLA and its slow crystallization kinetics. Among the different options to improve the PLA characteristics, compounding it with different types of fillers has great potential. This strategy does not only have foaming advantages, but can also improve the performances of the final composites, regardless of the implemented foaming process, i.e., batch, injection molding, and extrusion. In addition, the operating conditions and the characteristics of the fillers, such as their size, shape factor, and surface chemistry, play an important role in the final foam morphology. This article proposes a critical review on the different SCF-assisted processes and effects of operating conditions and fillers on foaming of PLA composites.

Self-foaming polymers: Opportunities for the next generation of personal protective equipment

“…A critical point is the synchronization of the decomposition and/or vaporization of the blowing agent with the initiation of the viscosification of the polymer material. [56,71,[79][80][81][82][83][84][85][86][87][88][89][90] It is indeed essential that the bubbles nucleate and grow in a certain viscosity window sometimes called the viscosity foaming window. [71,80] If the gas is released before the viscosity enter the foaming window, it will quickly diffuse through the polymer.…”

“…[86] If the gas is released once the viscosity exceeds the foaming window, no nucleation will occur due to the large elastic modulus of the polymer matrix that completely precludes any deformation. [89][90][91] No cavities will be formed.…”

Preparation of Microcellular Foams by Supercritical Carbon Dioxide: A Case Study of Thermoplastic Polyurethane 70A

“…Polymer foams can be produced by two approaches depending on either the chemical or physical blowing agent used. Chemical blowing agents such as azodicarbonamide, sodium bicarbonate and zinc carbonate are the molecules that decompose into gases at a high temperature condition in a polymer matrix to generate the porous structure [4]. On the other hand, physical blowing agents are gaseous substances which can be dissolved into the polymer matrix at an elevated pressure, then generate bubbles in the matrix through depressurization afterward.…”

Blending and foaming thermoplastic starch with poly (lactic acid) by CO2‐aided hot melt extrusion

“…Foams of PLA or its composites may have applications in many industrial fields including biomedicine as controlled drug delivery systems or scaffolds in implant for living tissues. 7,8 Our group studied the process of hot extrusion assisted by supercritical CO 2 to optimize the foaming of several polymers. [9][10][11] In a previous publication, 12 we explored the influence of the die temperature and the addition of a static mixer on the properties of PLA foams.…”

“…Foams of PLA or its composites may have applications in many industrial fields including biomedicine as controlled drug delivery systems or scaffolds in implant for living tissues 7,8 . Our group studied the process of hot extrusion assisted by supercritical CO 2 to optimize the foaming of several polymers 9–11 .…”