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.
Highlights
In many industrial fields, the development of porous and light polymer structures is of great interest
The cell sizes continuously increased with increasing pressure, contrary to the tendency found by the precedent authors
The decreased with higheroffiller contents could be explained by a good indicated that the optimal conditionscell for size the processing nanocomposite foams were different from interface between the two components, which favored the presence of in the polymer matrix
Summary
The development of porous and light polymer structures is of great interest. Physical blowing agents (PBAs) are compounds that expand quickly because of a phase change such as the vaporization of liquids or supercritical fluids (SCFs) at the foaming temperature and pressure [7,8]. They have high foaming efficiency, they should not be toxic, and must have high heat stability. PLA withapproaches different types of fillers appears to be alternative or complementary option These macromolecular proved to be efficient in an improving foamability thanks to Potential fillers can vary in origin from lignocellulosic fibers from different sources enhanced crystallization rate and melt strength [13]. The effects of operating conditions; fillers in terms of size, shape, content, and surface treatment; as well as the effect of chain extenders are reviewed and discussed
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