热致相分离法iPP/nano-SiO2杂化中空纤维膜的结构与透过性能

通过熔融共混等规聚丙烯(iPP)/邻苯二甲酸二丁酯(DBP)/邻苯二甲酸二辛酯(DOP)/纳米二氧化硅(nano-SiO2)体系,采用热致相分离法(TIPS)制备了iPP中空纤维膜。对膜结构与透过性能进行了表征。用示差扫描量热仪(DSC)测定了体系的iPP动态结晶温度,融化峰值温度数值表明结晶只存在α晶型。X光电子能谱(XPS)表明nano-SiO2向膜表面发生了迁移,使得膜的亲水性有所提高,膜的接触角由120.05°降低到101.05°,降低了19.7%。随着nano-SiO2添加量的增加,膜的孔隙率和纯水通量均呈现先增大后减小的趋势。膜的孔隙率增加了20.2%,纯水通量增大了21.7%。经过拉伸后的杂化膜,孔隙率增大了27.4%,纯水通量增加了211%。研究表明:通过向铸膜液中添加nano-SiO2,可以优化膜结构,并改善膜的亲/疏水性以及透过性能。     

Effect of diluents on the crystallization behavior of poly(4‐methyl‐1‐pentene) and membrane morphology via thermally induced phase separation

The effect of diluents on polymer crystallization and membrane morphology via thermally induced phase separation(TIPS) were studied by changing the composition of the mixed‐diluents systematically, in the system of poly(4‐methyl‐1‐pentene) (TPX)/dibutyl‐phthalate (DBP)/di‐n‐octyl‐phthalate (D‐n‐OP) with TPX concentration of 30 wt %. The TPX crystallization was observed with differential scanning calorimetry (DSC) and wide angle X‐ray diffraction (WAXD). The membranes were characterized with scanning electron microscopy (SEM), porosity, and pore size measurement. As the content of D‐n‐OP increased in mixed‐diluents, the solubility with TPX increased, inducing the phase separation changing from liquid–liquid phase separation into solid–liquid phase separation, which changed the membrane morphology and structure. When the ratios of DBP to D‐n‐OP were 10 : 0, 7 : 3; 5 : 5, and 3 : 7, membranes were formed with cellular structure and well connected pores, while the ratio was 0 : 10, discernable spherulities were found with not well‐formed pore structure. The effect of composition of the mixed‐diluents on membrane morphology was more remarkable in TPX/dioctyl‐sebacate (DOS)/dimethyl‐phthalate (DMP) system, since good cellular structure was formed when the ratios of DOS to DMP were 10 : 0, 7 : 3, while spherulites were observed when 5 : 5. Dual endotherm peaks behavior on DSC melting curves emerged for all the samples in this study, which was attributed to the special polymer crystallization behavior, primary crystallization, and secondary crystallization occurred when quenching the samples. As the content of D‐n‐OP increased, the secondary crystallization enhanced which induced the first endotherm peak on DSC melting curves moving to a lower temperature and the broadening of the overall melting peak, as well as the increasing of the overall crystallinity. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Formation of porous poly(ethylene‐co‐vinyl alcohol) membrane via thermally induced phase separation

Crystalline poly(ethylene‐co‐vinyl alcohol) (EVOH) membranes were prepared by a thermally induced phase separation (TIPS) process. The diluents used were 1,3‐propanediol and 1,3‐butanediol. The dynamic crystallization temperature was determined by DSC measurement. No structure was detected by an optical microscope in the temperature region higher than the crystallization temperature. This means that porous membrane structures were formed by solid–liquid phase separation (polymer crystallization) rather than by liquid–liquid phase separation. The EVOH/butanediol system showed a higher dynamic crystallization temperature and equilibrium melting temperature than those of the EVOH/propanediol system. SEM observation showed that the sizes of the crystalline particles in the membranes depended on the polymer concentration, cooling rate, and kinds of diluents. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2449–2455, 2001     

Preparation and characterization of poly(ethylene‐co‐vinyl alcohol) membranes via thermally induced liquid–liquid phase separation

Porous membranes were prepared through the thermally induced phase separation of poly(ethylene‐co‐vinyl alcohol) (EVOH)/glycerol mixtures. The binodal temperature and dynamic crystallization temperature were determined by optical microscopy and differential scanning calorimetry measurements, respectively. It was determined experimentally that the liquid–liquid phase boundaries were shifted to higher temperatures when the ethylene content in EVOH increased. For EVOHs with ethylene contents of 32–44 mol %, liquid–liquid phase separation occurred before crystallization. Cellular pores were formed in these membranes. However, only polymer crystallization (solid–liquid phase separation) occurred for EVOH with a 27 mol % ethylene content, and the membrane morphology was the particulate structure. Scanning electron microscopy showed that the sizes of the cellular pores and crystalline particles in the membranes depended on the ethylene content in EVOH, the polymer concentration, and the cooling rate. Furthermore, the tendency of the pore and particle sizes was examined in terms of the solution thermodynamics of the binary mixture and the crystallization kinetics. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 853–860, 2003     

Porous polyphenylene sulfide membrane with high durability against solvents by the thermally induced phase‐separation method

Porous polyphenylene sulfide membranes were prepared as new solvent‐resistant membranes by the thermally induced phase‐separation (TIPS) method. Porous structures were either formed by solid–liquid phase separation (polymer crystallization) or liquid–liquid phase separation. The effects of solvents, cooling rates, and polymer concentrations on the porous structures were investigated. Various characteristics of pore structure can be obtained with suitable diluents and cooling rates using the TIPS method. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2959–2966, 2006     

热致相分离法iPP中空纤维微空膜结构与性能--稀释剂的作用

Isotactic polypropylene （iPP） hollow fiber microporous membranes were prepared using thermally induced phase separation （TIPS） method. Di-n-butyl phthalate （DBP）, dioctyl phthalate （DOP）, and the mixed solvent were used as diluents. The effect of α （DOP mass fraction in diluent） on the morphology and performance of the hollow fiber was investigated. With increasing α, the morphology of the resulting hollow fiber changes from typical cellular structure to mixed structure, and then to typical particulate structure. As a result, the permeability of the hollow fiber increases sharply, and the mechanical properties of the hollow fiber decrease obviously. It is suggested that the morphology and performances of iPP hollow fiber microporous membrane can be controlled via adjusting the compatibility between iPP and diluent.     

稀释剂对TIPS法等规聚丙烯中空纤维微孔膜孔径及其连通性的影响

热致相分离（TIPS）法制备等规聚丙烯（iPP）中空纤维微孔膜,邻苯二甲酸二丁酯（DBP）与邻苯二甲酸二辛酯（DOP）的混合溶剂作为制膜稀释剂。干/湿氮气流量法测定了α（稀释剂中DBP的质量分数）和β（铸膜液中聚合物的质量分数）对膜样品的平均孔径及其分布的影响,并采用膜孔曲折因子定量表达膜孔连通性。发现全部膜样品均体现窄孔径分布特征。对于相同的β, α增加导致平均孔径及膜孔连通性下降。α=0.20时,β增加,膜的平均孔径先增加后降低,膜孔曲折因子稍下降; α=0.35或0.50时,β增加,膜的平均孔径降低,膜孔曲折因子下降。膜孔连通性体现了膜内部的拓扑结构,共溶剂组成和铸膜液固含量能够调节iPP中空纤维微孔膜的孔径及其连通性。     

Kinetics-controlled compatibilization of immiscible polypropylene/polystyrene blends using nano-SiO2 particles

Rigid inorganic filler has been long time used as a reinforcement agent for polymer materials. Recently, more work is focused on the possibility that using filler as a compatibilizer for immiscible polymer blends. In this article, we reported our efforts on the change of phase morphology and properties of immiscible polypropylene(PP)/polystyrene(PS) blends compatibilized with nano-SiO₂ particles. The effects of filler content and mixing time on the phase morphology, crystallization behavior, rheology, and mechanical properties were investigated by SEM, DSC, ARES and mechanical test. A drastic reduction of PS phase size and a very homogeneous size distribution were observed by introducing nano-SiO₂ particles in the blends at short mixing time. However, at longer mixing time an increase of PS size was seen again, indicating a kinetics-controlled compatibilization. This conclusion was further supported by the unchanged glass transition temperature of PS and by increased viscosity in the blends after adding nano-SiO₂ particles. The compatibilization mechanism of nano-SiO₂ particles in PP/PS blends was proposed based on kinetics consideration.     

Porous cellulose acetate membrane prepared by thermally induced phase separation

Microporous cellulose acetate membranes were prepared by a thermally induced phase separation (TIPS) process. Two kinds of cellulose acetate with acetyl content of 51 and 55 mol % and two kinds of diluents, such as 2‐methyl‐2,4‐pentandiol and 2‐ethyl‐1,3‐hexanediol, were used. In all polymer‐diluent systems, cloud points were observed, which indicated that liquid–liquid phase separation occurred during the TIPS process. The growth of droplets formed after the phase separation was followed using three cooling conditions. The obtained pore structure was isotropic, that is, the pore size did not vary across the membrane. In addition, no macrovoids were formed. These pore structures were in contrast with those usually obtained by the immersion precipitation method. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3951–3955, 2003     

Fabrication and properties of PVDF and PVDF‐HFP microfiltration membranes

Poly(vinylidene fluoride) (PVDF) and poly(vinylidene fluoride)‐co‐hexafluoropropylene (PVDF‐HFP) were used to fabricate porous microfiltration membranes via a thermally induced phase separation (TIPS) method, and dibutyl phthalate (DBP) was used as diluent. The effects of polymer concentration on structure and performance were studied in detail. In addition, the effect of incorporation of hexafluoropropylene (HFP) groups on the membrane was also investigated. The formation mechanism was proposed with the assistance of a phase diagram. The results showed that the incorporation of HFP groups resulted in a lower crystallization temperature (T_c) of the polymer/DBP system. In addition, the porosity, pure water flux, and ink solution flux decreased with increasing polymer concentration. In contrast, the water contact angle, ink rejection ratio, and mechanical properties had an increasing tendency. When the polymer concentration was 30 wt %, the obtained membrane was most suitable for microfiltration. Furthermore, the incorporation of HFP groups improved the properties of the obtained membrane, including better hydrophobicity, mechanical properties, antifouling property, and chemical resistance. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46711.     

Membrane formation via thermally induced phase separation in polypropylene/polybutene/diluent system

Porous membranes were prepared from a polymer blend system by the thermally induced phase separation (TIPS) process. The polymer blend system was isotactic polypropylene (iPP)/polybutene (PB) and the diluent was diphenyl ether (DPE). Two types of porous membranes were prepared by the extractions of DPE alone and both DPE and PB after the phase separation. The effect of the addition of PB to the iPP solution on the phase diagram was investigated and the phase separation kinetics was measured by the light scattering method. The addition of PB resulted in the higher solute rejection property and lower water permeance. By the further extraction of PB from the porous iPP/PB membrane prepared by the extraction of DPE, the water permeance was approximately doubled, maintaining almost the same rejection property. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1701–1708, 2002; DOI 10.1002/app.10550     

Effect of diluent on poly(ethylene‐co‐vinyl alcohol) hollow‐fiber membrane formation via thermally induced phase separation

Poly(ethylene‐co‐vinyl alcohol) hollow‐fiber membranes with a 44 mol % ethylene content were prepared by thermally induced phase separation. A mixture of 1,3‐propanediol and glycerol was used as the diluent. The effects of the ratio of 1,3‐propanediol to glycerol in the diluent mixture on the phase diagram, membrane structure, and membrane performance were investigated. As the ratio increased, the cloud point shifted to lower temperatures, and the membrane structure changed from a cellular structure due to liquid–liquid phase separation to a particulate structure due to polymer crystallization. Better pore connectivity was obtained in the hollow‐fiber membrane when the ratio of 1,3‐propanediol to glycerol was 50:50, and the membrane showed about 100 times higher water permeability than the membrane prepared with pure glycerol. For the prepared hollow‐fiber membrane, the solute 20 nm in diameter was almost rejected. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 219–225, 2005     

Thermally induced phase separation in poly(lactic acid)/dialkyl phthalate systems

Thermally induced phase separation in poly(lactic acid)/dialkyl phthalate systems was investigated. Poly(DL ‐lactic acid) (PDLLA) and poly(L ‐lactic acid) (PLLA) with different molecular weights were used. A series of dialkyl phthalates, with different numbers of carbon atoms in the alkyl chain, were employed as solvents to control the interaction between polymer and solvent. The liquid–liquid phase‐separation temperature of the poly(lactic acid) solutions decreased systematically with a shorter alkyl chain in the phthalate. Based on the interaction between polymer and solvent and the molecular weight of polymer influencing liquid–liquid phase‐separation temperature significantly but crystallization temperature only slightly, proper thermal conditions were employed to investigate competitive phase separation and crystallization in PLLA solutions. Factors that can influence the final morphology of PLLA solutions were examined. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2224–2232, 2003     

Formation of microporous membrane of isotactic polypropylene in dibutyl phthalate‐soybean oil via thermally induced phase separation

Isotactic polypropylene (iPP) microporous membranes were prepared via the thermally induced phase separation (TIPS) process with the diluents being dibutyl phthalate (DBP) and soybean oil mixture. By changing the weight ratio of DBP to soybean oil systematically, it was determined experimentally that the cloud‐point curves were influenced to a great extent, while the crystallization curves showed much less dependence on the diluents composition. Scanning electron microscopy (SEM) showed that the resulting membrane morphologies changed significantly by varying the composition of the diluents, i.e., by changing the interaction parameter and other characteristics of diluents, the interwoven or celluar structure can be fabricated successfully at a fixed polymer concentration under the same cooling conditions. Different growth rates of iPP spherulite were obtained in the diluents with different composition. It is shown that the spherulites growth rates may be also attributed to the great variations of the final microporous morphology to a certain extent. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Effects of THF as cosolvent in the preparation of polydimethylsiloxane/polyethersulfone membrane for gas separation

Polydimethylsiloxane/polyethersulfone (PDMS/PES) asymmetric membranes are widely applied in gas separation. However, the effects of common cosolvent on these membranes remain unknown. In order to study the changes in membrane morphology and gas separation properties, asymmetric PDMS/PES membranes were prepared. The studied parameters were types of cosolvents, tetrahydrofuran (THF) concentration, evaporation time, and PDMS concentration. Membrane morphology was examined using scanning electron microscopy and gas separation was conducted using pure CO₂, N₂, CH₄, and Hat 25°C. The addition of cosolvent into the polymer solution decreased the dope viscosity and delayed liquid–liquid demixing during phase inversion. Macrovoids formation was observed in substructure layer after adding THF and these macrovoids elongated with the reduction in THF content. There were microvoids formed on top of macrovoids and microvoids layer became thicker due to the increasing evaporation time of solvents before coagulation in nonsolvent. The PDMS coating on the PES membrane formed a dense skin layer and exhibited higher selectivity compared to the uncoated membrane. Membrane contained THF cosolvent with 60 s evaporation time and 3 wt% coated PDMS is the optimum membrane among other membranes in this work. The CO₂/N₂ selectivity was enhanced by 73.3% with CO₂ permeance of 44.86 GPU. POLYM. ENG. SCI., 54:2177–2186, 2014. © 2013 Society of Plastics Engineers     

Crystallization and microporous membrane properties of ultrahigh molecular weight polyethylene with dibenzylidene sorbitol

Dibenzylidene sorbitol (DBS) was chosen as an in situ forming nucleating agent to study ultrahigh molecular weight polyethylene (UHMWPE) crystallization and microporous membrane. The experimental results indicated that DBS self‐assembled into fibrils first and the solution became a physical gel before UHMWPE crystallization during thermally induced phase separation (TIPS) of UHMWPE/liquid paraffin (LP)/DBS solution, and the temperature of DBS self‐assembly shows a strong dependence of DBS concentration. With decreasing temperature further, DBS fibrils as heterogeneous nucleating agent accelerated UHMWPE crystallization, which was showed more clearly in UHMWPE/LP/DBS phase diagram. UHMWPE microporous membranes were prepared through TIPS method with the control of DBS concentration. It was found that UHMWPE microporous membranes in the presence of DBS fibrils show small porous size and low water permeability, but relatively larger mechanical strength. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40706.     

Fabrication of cellulose acetate ultrafiltration membrane with diphenyl ketone via thermally induced phase separation

With diphenyl ketone as diluent, cellulose acetate (CA) ultrafiltration (UF) membrane with a bicontinuous structure was prepared via thermally induced phase separation (TIPS) method. The liquid–liquid phase separation region of CA/diphenyl ketone system was measured and the maximum corresponding polymer concentration was approximately 53 wt %. The effects of polymer concentration, coarsening time and coarsening temperature on the morphologies, and mechanical properties of CA membranes were investigated systematically. As the polymer concentration increased from 15 to 30 wt %, the bicontinuous structure could be obtained and the tensile strength of CA membranes increased from 3.92 to 30.17 MPa. With the increase of coarsening time, the thickness of dense skin layer and the asymmetry of cross‐section reduced. However, excess coarsening rendered the membrane morphology evolved from a bicontinuous structure to a cellular structure. When the coarsening time was 5 min, the bicontinuous structure in cross‐section showed good interconnectivity and the dense skin layer exhibited a thin thickness of 2 μm. The fabricated CA hollow fiber UF membrane exhibited a high tensile strength of 31.00 MPa and rejection of 96.10% for dextran 20 kDa. It is indicated that diphenyl ketone is a competitive diluent to prepare CA membranes with excellent performance via TIPS. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42669.     

Preparation of a poly(vinyl chloride) ultrafiltration membrane through the combination of thermally induced phase separation and non‐solvent‐induced phase separation

To regulate the polymer–diluent interaction and control the viscosity of the casting solution, diphenyl ketone (DPK) and a N,N‐dimethylacetamide/N,N‐dimethylformamide mixture were selected as a combined diluent. Poly(vinyl chloride) (PVC) utlrafiltration membranes, which had sufficient mechanical properties for their practical applications because of their bicontinuous spongy structure, were prepared by a combined process of thermally induced phase separation and non‐solvent‐induced phase separation. The phase‐separation mechanism was analyzed. In an air bath, the cast nascent solution immediately transformed into a transparent gel, and liquid–liquid phase separation was induced by a sudden drop in the temperature before crystallization. An ice–water bath was used to coagulate the membrane. The effects of the DPK and PVC concentrations on the membrane structures and performances were mainly investigated. The results show that an increase in the DPK content made the membrane pores change from fingerlike to spongy. Fully spongy pores formed, and the pores size decreased with increasing PVC concentration. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42953.     

Effect of the ethylene content of poly(ethylene-co-vinyl alcohol) on the formation of microporous membranes via thermally induced phase separation

Porous poly(ethylene-co-vinyl alcohol) (EVOH) membranes were prepared via thermally induced phase separation. The effect of the EVOH ethylene content on the membrane morphology and solute rejection property was investigated. For EVOHs with ethylene contents of 27–44 mol %, polymer crystallization (solid–liquid phase separation) occurred, and the membrane morphology was the particulate structure. However, the liquid–liquid phase separation occurred before crystallization for EVOH with a 60 mol % ethylene content. Cellular pores were formed in this membrane. For the particulate membranes, higher solute rejection and lower water permeance were obtained for EVOH with a lower ethylene content. The membrane formed by the liquid–liquid phase separation showed a sharper solute rejection change with a change in the solute radius than the particulate membranes did. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2583–2589, 2001     

Phase diagrams of thermally stable,polymer‐dispersed liquid crystals: Exploring the impact of chain length and chemical structure

Polymer‐dispersed liquid crystals (PDLCs) have garnered significant interest and motivated the investigation of the phase behavior of thermally stable smectic liquid crystals (LCs) via thermally induced phase separation (TIPS). In this study, we examined a series of two, biphenyl‐based smectic LCs suitable for high temperature polymer blend processing. Phase diagrams for LC/polystyrene (PS) blends at various compositions (0–60 wt%) were constructed. Less than 15 wt% of 8B8 (1,1′‐biphenyl‐4,4′‐diyl dioctanoate) LC in PS led to good polymer miscibility, while phase separation was induced at concentrations higher than 15 wt%. The LC concentration at saturation decreased with increasing aliphatic chain length. We also investigated the chain length (C6‐C16) effect on the PS glass transition temperature (T_g) at the LC saturation point. The T_g increased with increasing chain length due to reduced plasticization. We further examined the role of chemical structure (relatively less polar ether vs. more polar ester) on the phase diagram regions and the T_g of the nonpolar PS matrix, respectively. It is anticipated that these LC/PS phase diagrams will benefit elevated temperature processing for TIPS by highlighting the role of LC chemical structure and chain length on blend morphology. POLYM. ENG. SCI., 56:388–393, 2016. © 2016 Society of Plastics Engineers