UHMWPE微孔膜的制备及其性能研究

用热致相分离法制备超高相对分子质R聚乙烯(UHMWPE)微孔膜,并通过调节成型条件(UHMWPE的含量及其相对分子质量、冷却速率)实现了UHMWPE微孔膜微观结构的可控化,研究了成型条件对微孔膜的结晶性能和力学性能的影响.结果表明,在UHMWPE含量和相对分子质量增大,冷却速率加快时,微孔膜的结晶度降低,平均孔径和孔隙...     

聚偏氟乙烯管式微孔膜的工艺研究

对聚偏氟乙烯(PVDF)管式微孔膜生产工艺进行了研究。系统地讨论了相转化法制备管式微孔膜过程中各个因素的影响。研究发现,铸膜液温度对PVDF管式膜截留率和纯水通量影响不明显;铸膜液中加入NH4Cl后,膜的纯水通量增加,截留率减小,孔径增大;不同凝固浴制得的PVDF管式微孔膜不同,膜的纯水通量和截留率也不同。     

热致相分离法制备扩链PET微孔膜及其表征

采用热致相分离法制备扩链聚对苯二甲酸乙二醇酯(PET)微孔膜,研究了三(环氧丙基)异氰尿酸酯(TGIC)用量及铸膜液N-甲基吡咯烷酮(NMP)初始浓度对PET微孔膜结构的影响.结果表明:随着TGIC用量增加,PET膜孔径减小,孔分布变得密集;TGIC1.2质量份时扩链PET膜的孔径最小(0.5μm左右),孔的分布最密集...     

熔融物挤压拉伸法制备UHMWPE微孔膜微观结构及性能研究

利用液体石蜡作溶剂,根据热致相分离的原理,通过双螺杆制备了超高摩尔质量聚乙烯( UHMWPE)微孔膜;并研究了不同聚合物初始浓度及助剂对微孔膜的结构和性能的影响.通过扫描电子显微镜(SEM)和水通量,孔隙率等测试表征方法得出,随着聚合物初始浓度的增加,膜的孔隙率、水通量都逐渐降低,而拉伸强度和断裂伸长率则逐渐增强;助剂SiO2和聚乙烯吡咯烷酮(PVP)能使孔隙率、水通量增大.     

热致相分离法(TIPS)制备PVDF微孔膜微观结构及性能的研究

采用热致相分离法( TIPS)制备聚偏氟乙烯(PVDF)微孔膜.探索PVDF微孔膜结构和性能,选择邻苯二甲酸二甲酯DMP、邻苯二甲酸二丁酯(DBP)作为溶剂,考察了溶剂浓度对PVDF膜性能的影响,冷却速度和助剂对膜性能的影响.通过SEM照片,纯水通量以及孔隙率等表征和测试,得出在单一溶剂体系中,选用DBP作为溶剂,PVDF质量分数为40％,空气冷却,加入5％的聚乙烯吡咯烷酮(PVP),得到的微孔膜性能最优.     

聚偏氟乙烯管式微孔膜的工艺研究

对聚偏氟乙烯(PVDF)管式微孔膜生产工艺进行了研究。系统地讨论了相转化法制备管式微孔膜过程中各个因素的影响。研究发现，铸膜液温度对PVDF管式膜截留率和纯水通量影响不明显；铸膜液中加入NH4Cl后，膜的纯水通量增加，截留率减小，孔径增大；不同凝固浴制得的PVDF管式傲孔膜不同，膜的纯水通量和截留中也不同。     

逆向热致相分离法(RTIPS)制备PES/DMAc/DEG体系微孔膜及其性能表征

以PES/DMAc/DEG低临界共溶温度(LCST)体系为铸膜液,利用低临界共溶温度(LCST)的热致相分离(LCST-TIPS,简称RTIPS)法制备PES微孔膜。探究影响PES微孔膜理化性能及其结构的2个主要因素:凝胶浴温度、非溶剂(DEG)/溶剂(DMAc)的质量比。运用扫描电镜(SEM)﹑纯水通量﹑BSA截留率和机械强度表征微孔膜的结构和性能。试验结果表明:随DEG∶DMAc质量比增加,PES/DMAc/DEG体系的相分离温度降低;SEM结果显示,RTIPS法制备的PES微孔膜表面有明显的微孔,断面呈现双连续海绵状结构;当DEG∶DMAc质量比为0.9∶1、凝胶浴温度为80℃时,PES/DMAc/DEG体系制得的PES膜的渗透性能和机械性能最优:纯水通量为1 230 L/(m^2·h),断裂强度为1.95 MPa。PES/DMAc/DEG体系制得的最优性能的PES平板膜MSWDEG-2-80的应用结果显示,其对膜进水中的UV254具有较好的去除效果,且膜出水浊度稳定,为(0.23±0.01) NTU。     

稀释剂对热致相分离法制备聚偏氟乙烯膜结构的影响

以聚偏氟乙烯(PVDF)和一种在常温下为固态的水溶性潜溶剂己内酰胺(CPL)为膜材料和稀释剂,基于热致相分离原理,制备了PVDF微孔膜,通过差示扫描量热仪对不同条件下二元共混物的结晶性能进行了分析,利用扫描电镜研究了稀释剂含量对膜微观结构的影响。结果表明,PVDF质量分数小于25%,PVDF/CPL高温溶液体系在降温过程中发生液-液相分离,主要形成了双连续网络孔结构。研究了PVDF浓度对膜水通量、BSA截留率、膜强度等的影响,该研究为用单一水溶性稀释剂制备PVDF微孔膜定了基础。     

聚偏氟乙烯有机膜的共混改性及性能研究

将聚偏氟乙烯和高分子聚合物共混,通过溶胶-凝胶相转化法研制综合性能良好的微孔膜,考察了铸膜液浓度、PVDF与共混添加剂的配比、凝胶浴温度、溶剂挥发时间和酸、碱、氧化处理对共混膜性能的影响.结果表明,随着铸膜液中聚合物总含量、膜液的黏度增加,纯水通量总体呈下降趋势,孔隙率先增加后减小,最后趋近平衡;随着共混添加剂在铸膜液中相对含量的增加,纯水通量先增加后减小,孔隙率可得到有效提高,平均孔径变化不大;凝胶浴温度对纯水通量没有较大影响;延长溶剂的挥发时间,使平均孔径减小;找到合适的共混添加剂并选择适当的膜液组成,能够使共混改性膜的纯水通量、孔隙率、抗酸、碱、氧化性能较改性前得到有效提高.其中纯水通量较改性前提高10％左右,孔隙率提高15％左右,说明共混化是一种改善PVDF膜性能的有效方法,具有极好的实用开发价值.     

混合稀释剂制备PVDF微孔膜的结构与性能研究

以邻苯二甲酸二甲酯(DMP)和N,N-二甲基乙酰胺(DMAc)作为混合稀释剂,采用复合热致相分离法制备聚偏氟乙烯(PVDF)微孔膜,并用扫描电镜、差示扫描量热分析仪、拉伸压缩材料试验机等测试仪器对微孔膜结构和性能进行了研究。结果表明:随着PVDF含量增加,体系的结晶度下降;随着混合稀释剂中DMP含量增加,膜强度先增大后减小,而水通量增加,截留率减小;冷却速率对孔隙率影响不大,但冷却速率减小,水通量增加,而截留率下降;DMAc与DMP质量比为1/2时,膜强度以及水通量均比单纯采用DMP做稀释剂时的好,前者的水通量达247 L/h.m2,比后者的增加了28%。     

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     

Preparation and membrane performance of poly(ethylene-co-vinyl alcohol) hollow fiber membrane via thermally induced phase separation

Poly(ethylene-co-vinyl alcohol) (EVOH) hollow fiber membranes with ultrafiltration performance were prepared from EVOH/glycerol systems via thermally induced phase separation (TIPS). The diluent glycerol was used as bore liquid to make a lumen of the hollow fiber for the purpose of prevention of the diluent evaporation and the larger pores formation at the inner surface of the hollow fiber. The obtained hollow fiber membranes showed asymmetric structures with skin layer near the outer surface, the larger pores just below the skin layer and the smaller pores near the inner surface. The formation of the larger pores near the outer surface was due to the enhanced pore growth by the water penetration. Some primary factors affecting the structure and performance of the membranes such as ethylene content (EC) in EVOH, cooling water bath temperature and take-up speed were studied extensively. The water permeability can be improved by increasing the water bath temperature and the take-up speed and by decreasing the EC. Both the pore size at the outer surface and the connectivity between the pores have to be considered together to understand the experimental result of the water permeability and the solute rejection.     

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     

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     

Optimization of structure and properties of polyphenylene sulfide porous membrane by controlling the process of thermally induced phase separation

Polyphenylene sulfide (PPS) porous membranes were successfully prepared from miscible blends of PPS and polyethersulfone (PES) via thermally induced phase separation followed by subsequent extraction of the PES diluent. The morphologies, crystalline structures, mechanical properties, pore structures and permeate fluxes of the PPS porous membranes obtained from different phase separation processes were characterized and are discussed. During the phase separation in the heating process, PPS and PES mainly underwent liquid–liquid phase separation, and then a nonhomogeneous porous structure with a mean pore size of 100 μm and a honeycomb‐like internal structure formed on the membrane surface. The phase separation of PPS/PES occurring in the cooling process was easier to control and the related pore diameter distribution was more regular. In the process of direct annealing, as the phase separation temperature decreased, the pore size distribution became more homogeneous and the mean diameter of the pores also decreased gradually. When the phase separation temperature decreased to 200 °C, PPS membranes with a network structure and a uniform as well as well‐interconnected porous structure could be obtained. In addition, the maximum permeation flux reached 1718.03 L m^–2 h^–1 when the phase separation temperature was 230 °C. The most probable pore diameter was 6.665 nm, and the permeate flux of this membrane was 2.00 L m^–2 h^–1; its tensile strength was 17.07 MPa. Finally, these PPS porous membranes with controllable pore structure as well as size can be widely used in the chemical industry and energy field for liquid purification. © 2020 Society of Chemical Industry     

Estimation of phase diagrams for copolymer‐diluent systems in thermally induced phase separation

The binary interaction model was introduced to estimate phase diagrams of copolymer‐diluent systems in thermally induced phase separation. The crystallization curves and cloud points of poly(ethylene‐co‐vinyl alcohol) (EVOH) with 1,4‐butanediol, EVOH/1,3‐propanediol, and EVOH/glycerol were calculated and compared with experimental value or literature data. Fair agreement was obtained. To confirm the importance of incorporating intramolecular interactions, calculations with and without the consideration of intramolecular interactions were performed and compared. It was found that better results can be obtained if intramolecular interaction was introduced. The reason for the small differences between the calculated value and the experimental data of the liquid–liquid phase separation is discussed. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

冷却条件对HDPE微孔膜微观结构影响

采用DSC和光学显微镜绘制了HDPE/矿物油共混体系的相图,采用带热台的偏光显微镜和扫描电镜研究了HDPE含量、冷却速率和冷却温度对微孔膜微观结构的影响。研究发现:随着共混体系中HDPE含量的减少,体系晶间孔和晶体内孔增多增大;随着冷却速率的增加,体系晶体内孔增多增大,晶间孔尺寸降低;冷却温度对微孔结构的影响较低。     

Biodegradable composites based on starch/EVOH/glycerol blends and coconut fibers

Unripe coconut fibers were used as fillers in a biodegradable polymer matrix of starch/ethylene vinyl alcohol (EVOH)/glycerol. The effects of fiber content on the mechanical, thermal, and structural properties were evaluated. The addition of coconut fiber into starch/EVOH/glycerol blends reduced the ductile behavior of the matrix by making the composites more brittle. At low fiber content, blends were more flexible, with higher tensile strength than at higher fiber levels. The temperature at the maximum degradation rate slightly shifted to lower values as fiber content increased. Comparing blends with and without fibers, there was no drastic change in melt temperature of the matrix with increase of fiber content, indicating that fibers did not lead to significant changes in crystalline structure. The micrographs of the tensile fractured specimens showed a large number of holes resulting from fiber pull‐out from the matrix, indicating poor adhesion between fiber and matrix. Although starch alone degraded readily, starch/EVOH/glycerol blends exhibited much slower degradation in compost. Composites produced 24.4–28.8% less CO₂ compared with starch in a closed‐circuit respirometer. Addition of increasing amount of fiber in starch/EVOH/glycerol composite had no impact on its biodegradation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of electrospun ethylene vinyl alcohol copolymer (EVOH) fibres on the structure,morphology, and properties of poly(lactic acid) (PLA)

The effect of ethylene content and of the concentration of the solution used for electrospinning on the morphology of electrospun poly ethylene vinyl alcohol (EVOH) fibre was studied. Also, poly(lactic acid) (PLA) filled with electrospun EVOH fibres was investigated. Good interfacial adhesion between PLA and EVOH fibres was obtained with smaller diameter fibres. The effect of electrospun fibres resulted in disrupted lamellar morphology and also decreased the degree of crystallinity related to the semicrystalline framework. Surface roughness was calculated using atomic force microscopy (AFM). Surface roughness increased with the increase in fibre diameters. The rheology experiments revealed that electrospun EVOH fibres enhance the storage modulus of PLA composites while having low crystallinity. EVOH fibres showed the capacity of tuning the degradation behaviour. The good interfacial morphology between PLA and smaller diameter fibres slowed down the degradation rate, whereas composites with larger diameter fibres, due to poor interfacial adhesion showed faster degradation rate than the other compositions, because large EVOH fibres afford channels by which NaOH solution can easily penetrate throughout the composite material. The incorporation of EVOH fibres into PLA matrix allowed obtaining materials with increased storage modulus and also showed viability to tune the degradation behaviour of PLA based products.     

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