Synergy of supercritical CO₂ and superheated H₂O for enhanced processability of polyethersulfone towards open cell foams

Abstract

Processing of a high glass transition (Tg) polymer such as polyethersulfone (PES; Tg = 225°C) poses a challenge as it requires high processing temperatures or sometimes toxic solvents. In this work, we report of a facile process using superheated water (shH2O) and supercritical carbon dioxide (scCO2) co‐media. PES solids were foamed in the scCO2/shH2O co‐media or scCO2 alone in a batch process at different temperatures. The scCO2/shH2O produced a synergistic effect and achieved PES foams even at processing temperatures as low as 85°C below the nominal Tg; whereas, scCO2 alone required higher processing temperatures. Moreover, the scCO2/shH2O co‐media produced highly porous PES foams that were at least 23% higher in porosity than what was obtained using scCO2 alone. In addition, the scCO2/shH2O produced open cell foams at some processing conditions; whereas, scCO2 produced closed cell morphologies. Since both CO2 and H2O are innocuous, this approach has potential for use in the preparation of ultrafiltration membranes, which currently require the use of toxic solvents for their fabrication by way of the phase inversion process. Moreover, the use of scCO2/shH2O is a cost‐effective approach for the processing of high Tg polymers at significantly lower temperatures. POLYM. ENG. SCI., 58:1108–1114, 2018. © 2017 Society of Plastics Engineers

Open-Celled Foams of Polyethersulfone/Poly(N-vinylpyrrolidone) Blends for Ultrafiltration Applications

“…Owusu-Nkwantabisah et al [ 29 ] analysed the effects of using H 2 O along with CO 2 as a foaming agent for foaming of polyethersulfone and found that using scCO 2 + shH 2 O as foaming agent delivered an increased porosity and in some cases, open pores. As the structure found in foams H-8 and L-8 previously could develop open pores if the overall porosity is increased, scCO 2 + shH 2 O was used as foaming agent.…”

“…The expansion ratio and the foaming temperature window of the foams were significantly increased due to the use of co-blowing agent. Owusu-Nkwantabisah et al [ 29 ] used a combination of supercritical CO 2 and superheated H 2 O to produce PESU foams and found a significantly increased level of porosity and interconnectivity between pores as compared to a PESU foam that was foamed by using only supercritical CO 2 . Schulze et al [ 30 ] also achieved open-celled foams using block copolymers and CO 2 as foaming agent in the presence of water during the loading process.…”

“…Polyarylsulfones such as polyethersulfone (PESU), polysulfone (PSU) and polyphenylsulfone (PPSU) have been widely studied for obtaining permeable foams [ 17 , 18 , 20 , 21 , 22 , 29 ]. PESU is widely used for membranes as it provides high thermal stability due to its high glass transition temperature, good chemical stability due to the presence of sulfonyl groups and ether linkages, and favorable structural stability due to the presence of two aromatic groups in the repeating unit [ 32 ].…”

“…Therefore, the cell size is also desired to be similar to the cell size of the selective layer such that flaws occurring on the surface during foaming can be easily compensated by the internal structure. We focus on manufacturing completely open nanocellular foams, which the previous studies [ 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 41 , 42 , 43 ] did not fully realize. In recent years, the research on polymer foams has shifted towards composites involving graphene and other nanoparticles to deliver highly porous microcellular and nanocellular foams [ 44 , 45 , 46 , 47 , 48 , 49 ].…”

Preparation of fast‐degrading poly(lactic acid)/soy protein concentrate biocomposite foams via supercritical CO2 foaming

“…They have been used in many fields, including as biological tissue scaffolds, food packaging, and thermal insulation . There are several methods of fabricating polymeric foams, including gas foaming, emulsion freeze drying, thermally induced phase separation, particulate leaching/solvent casting, and 3D printing . Among them, foaming using a supercritical blowing agent has been recognized as the most environmental friendly, economic, and easiest‐to‐be‐industrialized method to produce polymer foams.…”