We propose a theory for the appearance of two‐phase structures during the formation of polymer membranes from a casting solution immersed in a coagulant bath. Our model is based on diffusion induced phase separation at the spinodal in the ternary nonsolvent‐solvent‐polymer system. A simplified treatment of the interdiffusion process by the diffusion layer method permits the formulation of criteria for the formation of two‐phase structures in the course of the solvent‐coagulant exchange. Our criteria are expressed in terms of the composition dependence of the chemical potentials in the stable and metastable region of the ternary phase diagram. Comparison with experimental results shows qualitative similarities with theoretical predictions.

SynopsisThe proton magnetic resonance relaxation times and heat capacity of water in perfluoroethylene sulfonic acid (Nafion), chlorosulfonated polyethylene (SPE), and sulfonated polysulfone (SPS) were measured as a function of temperature. Only the relaxation data for water present in Nafion conformed to the BPP model. The data indicate that the presence of fine pores, -12 in diameter, causes water-surface interactions to play a significant role. For materials with the same pore size, a difference in spin-lattice relaxation time T I may be correlated to the Flory-Huggins parameter x calculated for the interaction of water with the neutral portion of the polymer backbone. Only a part of the water present in Nafion and SPE undergoes freezing, while no transition was observed for water in SPS for temperatures down to -60°C. For Nafion and SPE, the heat of fusion AH/ calculated from combined FID data and the DSC study was -20 cal/g.

SUMMARYA new technique is described for the microfiltration of cheese brine. Soft cheese brine with viable counts/ml of up to 1·2 × 106bacteria and 2·2 × 104yeasts and moulds was filtered using a pleated tangential flow filtration cartridge of 0·2 εm pore size membrane. This filtration resulted in a 3–4 orders of magnitude reduction of bacteria and the complete rejection of yeast and mould from the permeate. Hard cheese brine with similar bacterial loads was treated with a 1·2 εm pore size membrane cartridge and the resulting permeate contained 2–3 orders of magnitude fewer bacteria and no yeasts or moulds. Flux decline during the filtration was a function of the number of microorganisms and the amount of N in the brine. A cleaning procedure using enzyme and acid washes was established in order to prolong membrane performance.

No abstract

No abstract