New challenges in polymer foaming: A review of extrusion processes assisted by supercritical carbon dioxide

Abstract

International audienceIt is well known that supercritical carbon dioxide (sc-CO 2) is soluble in molten polymers and acts as a plasticizer. The dissolution of sc-CO 2 leads to a decrease in the viscosity of the liquid polymer, the melting point and the glass transition temperature. These properties have been used in several particle generation processes such as PGSS (particles from gas saturated solutions). It is therefore highly likely that extrusion processes would benefit from the use of sc-CO 2 since the rationale of the extrusion processes is to formulate, texture and shape molten polymers by forcing them through a die. Combining these two technologies, extrusion and supercritical fluids, could open up new applications in extrusion. The main advantage of introducing sc-CO 2 in the barrel of an extruder is its function as a plasticizer, which allows the processing of molecules which would otherwise be too fragile to withstand the mechanical stresses and the operating temperatures of a standard extrusion process. In addition, the dissolved CO 2 acts as a foaming agent during expansion through the die. It is therefore possible to control pore generation and growth by controlling the operating conditions. This review focuses on experimental work carried out using continuous extrusion. A continuous process is more economically favourable than batch foaming processes because it is easier to control, has a higher throughput and is very versatile in the properties and shapes of the products obtained. The coupling of extrusion and supercritical CO 2 technologies has already broadened the range of application of extrusion processes. The first applications were developed for the agro-food industry twenty years ago. However, most thermoplastics could potentially be submitted to sc-CO 2-assisted extrusion, opening new challenging opportunities, particularly in the field of pharmaceutical applications. This coupled technology is however still very new and further developments of both experimental and modelling studies will be necessary to gain better theoretical understanding and technical expertise prior to industrial use, especially in the pharmaceutical field

Challenges and Strategies in Thermal Processing of Amorphous Solid Dispersions: A Review

“…A temporary plasticizer generally refers to the injection of supercritical carbon dioxide (sc-CO 2 ) into the extrusion process (82). sc-CO 2 exhibits high plasticization efficiency in polymers that have high CO 2 solubility (83), with the added benefit that expansion of sc-CO 2 upon exiting the extrusion process results in the complete removal of CO 2 from the final product (82). Thus, the composite T g of the final product is not depressed and molecular mobility is not Adapted with permission from (31) increased within the matrix.…”

Thermoplastic Foams: Processing, Manufacturing, and Characterization

“…As the polymer exists from the die, foam cells are generated by the sudden pressure drop. The inal step is cooling, calibration, and cuting of the extruded foams [11,12].…”

Characterisation of natural fibre reinforced PLA foams prepared by supercritical CO2 assisted extrusion

“…In the industry more cost-effective continuous processing technologies such as extrusion foaming and foam injection moulding are preferred. Recently, many studies have focused on extrusion foaming using supercritical CO 2 (scCO 2 ) as physical blowing agent [11]. When CO 2 is supercritical, its solubility and diffusivity in PLA increases significantly.…”