Selection criteria for solvent and coagulation medium in view of macrovoid formation in the wet phase inversion process
✍ Scribed by Ruoh-Chyu Ruaan; Terry Chang; Da-Ming Wang
- Book ID
- 101273291
- Publisher
- John Wiley and Sons
- Year
- 1999
- Tongue
- English
- Weight
- 104 KB
- Volume
- 37
- Category
- Article
- ISSN
- 0887-6266
No coin nor oath required. For personal study only.
✦ Synopsis
Sponge-like and finger-like structures are two distinct membrane structures commonly observed in membranes produced by the wet immersion process. An index ⌽ calculated solely from solubility parameters was defined as an indicator of the membrane structure. The ⌽ values of four polymers, poly(methyl metharylate), polysulfone, cellulose acetate, and poly(vinylidene fluoride), in various solvent-nonsolvent pairs were calculated and compared with the corresponding membrane structures. It was found that the finger-like structure often occurred at higher ⌽ values. Although the ⌽ value represents mostly the thermodynamics nature of a system, as an index for prior selection of solvent-nonsolvent pairs for a particular polymer, a general rule of thumb was developed. Taking 15% polymer concentration and 300 m casting thickness as a referential casting condition, selecting solvent-nonsolvent pairs with ⌽ values higher than 0.25 is suggested, when a finger-like structure is desired. The polymer concentration in the casting solution and the casting thickness will also affect the membrane structure. If a higher polymer concentration needs to be used, selection of a polymersolvent-nonsolvent system with a ⌽ value much higher than 0.25 is suggested, or keeping the casting thickness lower than 300 m to obtain a finger-like membrane structure.