A systematic study of air gap distance effects on the structure and properties of poly(vinyl butyral)hollow fiber membrane via thermally induced phase separation(TIPS)has been carried out.The results show that the hollow fiber membrane prepared at air gap zero has no skin layer; the pore size near the outer surface is larger than that near the inner surface; and the special pore channel-like structure near the outer surface is formed,which is quite different with the typical sponge-like structure caused by TIPS and the finger-like structure caused by non-solvent induced phase separation(NIPS),because of the synergistic action of non-solvent induced phase separation at air gap zero.The pore size gradually decreases from outer surface layer to the intermediate layer,but increases gradually from intermediate layer to the inner surface layer.With the increase of air gap distance,the pore size near the outer surface gets smaller and a dense skin layer is formed,and the pore size gradually increases from the outer surface layer to the inner surface layer.Water permeability of the hollow fiber membrane decreases with air gap distance,the water permeability decreases sharply from 45.50×10-7 to 4.52×10-7 m3/(m2·s·kPa)as air gap increases from 0 to 10 mm at take-up speed of 0.236 m/s,further decreases from 4.52×10-7 to 1.00×10-8 m3/(m2·s·kPa)as the air gap increases from 10 to 40 mm.Both the breaking strength and the elongation increase with the increase of air gap distance.The breaking strength increases from 2.25 MPa to 4.19 MPa and the elongation increases from 33.9% to 132.6% as air gap increases from 0 mm to 40 mm at take-up speed 0.236 m/s.
The production of environmental friendly emulsion paint is of great significance. Vacuum steam stripping of methyl isobutyl ketone (MIBK) and methyl ethyl ketone (MEK) from cathodic electrophoretic emulsion was studied. The effects of mass ratio of vapor to feed (V/F), vacuum degree and feed temperature on removal rate of MIBK and MEK, emulsion size and solid volume fraction of the emulsion were investigated, and the removal of MIBK and MEK from cathodic electrophoretic emulsion by vacuum desorption was also studied. The results show that removal rates of both MIBK and MEK increase with the increase of V/F, vacuum degree and feed temperature. Removal rates of MIBK and MEK are 98.3% and 93.6%, respectively, at the operating condition V/F of 0.7, feed temperature of 27 °C and vacuum degree of 90 kPa. The emulsion size of cathodic electrophoretic emulsion increases slightly with feed temperature when temperature is below 42 °C, and increases rapidly with feed temperature when temperature is above 42 °C. Solid volume fraction increases by 10% as vacuum degree increases from 0 to 90 kPa at V/F of 0.7 and feed temperature of 27 °C. Compared with vacuum desorption, vacuum steam stripping can get a higher removal rate of MIBK and MEK under the same feed flow, vacuum degree and feed temperature.
Poly(vinyl butyral)(PVB) hollow fiber membranes were fabricated via thermally induced phase separation(TIPS).The effects of coagulation bath temperature(CBT) on the structure and performance of membranes were investigated in detail.The morphologies of the membranes were studied by scanning electron microscopy(SEM),the performances of water permeability,rejection,breaking strength and elongation were measured,respectively.The results indicate that all the membranes have the asymmetric morphology and the thickness of the skin layer decreases and the pore size of the outer layer increases with the increase of CBT.The permeability of membranes prepared at air gap 1.0 cm and take-up speed 0.253 m/s increases from 1.047×10-7 to 5.909×10-7 m3/(m2·s·kPa) with the CBT increasing from 20 °C to 40 °C,and sharply increases to 35.226×10-7 m3/(m2·s·kPa) once the CBT arrives at 50 °C.While the carbonic ink rejections have no significant decrease,totally exceed 98%,but that of acid-maleic acid copolymer greatly decreases with the increase of CBT.Both the breaking strength and elongation decrease with the increase of CBT.
The streaming potential of poly(vinyl butyral) (PVB) hollow fiber membrane was studied in different electrolyte solutions (including NaCl,KCl,CaCl2 and MgCl2),the effects of ionic strength,ion valence and pH value on the streaming potential (SP) of the membrane were investigated.The zeta potentials and surface charge densities of the membrane were estimated on the basis of Helmholtz-Smoluchowski equation and Gouy-Chapmann theory.The results show that the PVB membrane has a weak negative charge due to the specific adsorption of ions.Moreover,the streaming potential,the zeta potential and the surface charge density of the membrane depend strongly on the salt concentration and the type and valence of ions.The iso-electric point (IEP) of the PVB membrane is around 3.0 in the monovalent media (NaCl and KCl) and 3.5 in divalent electrolytes (CaCl2 and MgCl2).A few retentions were obtained for PVB membrane in low concentration solutions.This result verifies that the negative charged membrane surface can reject inorganic solutes by means of electrostatic repulsion effect even though the size of membrane pores is much larger than the size of salts.
