Dramatic Swelling of Copolymer Membrane Induced by Polyol-Based Antifoam Agent

Polymer membranes represent a low cost, low energy solution to separating biologically derived chemicals from fermentation. However, the performance of these membranes is commonly limited by fouling caused by biological components, but additives are also included in typical fermentation broths that can interact with the polymer membrane. Here, we examine how a common polyol antifoam agent (Antifoam 204) dramatically swells and plasticizes a high performing biobutanol membrane copolymer of hydroxyhexafluoroisopropyl and n-butyl substituted norbornene. When equilibrated against 1 wt % (aq) butanol, the solvent in the copolymer increases from <10 vol % without the antifoam to >40 vol % at 1 ppm of antifoam and >80 vol % at 100 ppm of antifoam. The effect of the antifoam on the properties of the copolymer as determined by QCM-D is much more significant than that of the butanol concentration. Even with 4 wt % butanol (greater than typically viable for biobutanol), the copolymer swells <25 vol % without the antifoam. The rheological properties of the copolymer are also influenced with a phase angle of <15° (viscoelastic solid) with a nearly GPa modulus when swollen with aqueous butanol solution, while the phase angle increases to >50° (viscoelastic liquid) with an MPa modulus with the addition of ppm of antifoam. These results demonstrate the striking effect of solution additives on the properties of advanced polymers for membranes and illustrate the importance of considering the potential interactions of all components with a membrane beyond those of interest for the separation.