Extrusion assisted by supercritical CO 2 : A review on its application to biopolymers

Abstract

Extrusion assisted by supercritical CO 2 (sc-CO 2) is an emerging method for the microcellular foaming of polymer. Instead of batch foaming, which requires formation of single-phase polymer/CO 2 solution in long cycle times, the extrusion assisted by supercritical fluids overcomes this issue by providing rapid mixing and dissolution of CO 2 in the polymer melt. Because the sc-CO 2 is soluble in many molten polymers and acts as a removable plasticizer, its introduction in an extruder will permit a decrease of the processing temperature. This technic allows the use of fragile component like active molecule or starchy and proteinaceous materials. At the end of the extruder, the pressure drop will create instability and phase separation with the creation of porosity. This review is dedicated to the extrusion assisted by sc-CO 2 with different types of biopolymer. Industrial application domains include agro-food, biomedical, pharmaceutical, packaging and many others.

Biocomposite films based on poly(lactic acid) and chitosan nanoparticles: Elaboration, microstructural and thermal characterization

“…Structuring polymeric systems at micro‐ and nano‐scales to control their physical properties is considered as a key issue in various domains such as packaging, construction, transportation, and biomedicine including tissue engineering. Research on the development of structured bio‐based materials for these applications is very active as discussed in a recent review . In this regard, poly(lactic acid) (PLA) experiences a great interest as matrix materials in packaging, pharmaceutical and biomedical applications .…”

Foaming of poly(ethylene‐co‐vinyl acetate) and poly(ethylene‐co‐vinyl acetate‐co‐carbon monoxide) and their blends with carbon dioxide

“…The densities of EVACO-2410 foams were in the range from 0.13 to 0.41 g/cm 3 , with the majority of the foams displaying densities around 0.2 g/cm 3 . Foaming at 100 and 200 bar at 60 8C led to the foams with the higher densities of about 0.4 g/ cm 3 . Table I further shows that foaming at 300 bar led to foams with lower densities in EVACO-2410 at all temperatures, while low density foams were obtained only at 50 and 60 8C with EVA-25.…”

“…The densities of EVA-25 foams were found to range from 0.11 to 0.94 g/cm 3 . With this polymer, foam densities were observed to decrease with increasing temperature at a given pressure.…”

“…Foaming of polymers with carbon dioxide is of growing interest as an environmentally benign, tunable process to generate porous materials. Several review articles have already appeared on the topic which discuss the foaming behavior of glassy as well as semicrystalline polymers, copolymers, and blends . Among the factors that influence the outcomes in terms of pore size and morphology are (a) the solubility and diffusivity of carbon dioxide in the polymer at a given pressure and temperature, (b) the extent of the lowering of the glass transition or melting temperatures in the presence of carbon dioxide, (c) how the melt strength of the polymer is affected in the presence of carbon dioxide, (d) how the decompression is carried out, and (e) how the accompanying vitrification or crystallization processes proceed.…”

“…Several review articles have already appeared on the topic which discuss the foaming behavior of glassy as well as semicrystalline polymers, copolymers, and blends. [1][2][3][4][5] Among the factors that influence the outcomes in terms of pore size and morphology are (a) the solubility and diffusivity of carbon dioxide in the polymer at a given pressure and temperature, (b) the extent of the lowering of the glass transition or melting temperatures in the presence of carbon dioxide, (c) how the melt strength of the polymer is affected in the presence of carbon dioxide, (d) how the decompression is carried out, and (e) how the accompanying vitrification or crystallization processes proceed. These factors also influence other features of foams such as (a) pores being closed or interconnected, (b) pores being uniform or displaying a bimodal or gradient distribution, or (c) foams displaying a skin layer or not.…”