Main > GASES > Gas Separation Membranes > Org.: USA. Uc. (Research) > Research Description
Author, points out that polymeric membranes used in gas separation applications often experience compaction--that is, a decrease in membrane thickness over time. "Compaction and plasticization are simultaneous and competing effects in these applications," he says. "Plasticization usually leads to swelling and an increase in the permeability of glassy polymers." Compaction, on the other hand, is due to mechanical deformation--that is, creep--when a large pressure drop is applied across the membrane.
Compaction, he adds, has been reported to cause a significant decrease in the performance of a membrane over time. This is possibly a result of a decrease in the free volume of the membrane skin layer or an increase in the thickness of the skin. Increased skin thickness occurs if the porous sublayer of the membrane in the region adjacent to the skin compacts and becomes as dense as the skin.
Author s group is currently developing a method for simultaneously measuring mechanical and transport properties of membranes made of cellulose acetate, polybenzimidazole, and other polymers in pressurized CO2/N2 feed streams. "We plan to use the results to develop a better understanding of the fundamental factors governing the relationship between creep and gas permeability in dense polymer films at elevated temperatures," he says.
Dense films have limited free volume for the transport of gas molecules through the materials. If the amount of free volume is increased so that it becomes interconnected, the material takes on the characteristics of a porous material.
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