聚乙烯醇（PVA）／纳米TiO2杂化膜的研究与应用

主要介绍了水溶性聚乙烯醇（PVA）／TiO2杂化膜作为包装材料具有的一些优异性能和用途,从发展现状、制备方法和用途三方面对PVA／TiO2杂化膜进行了归纳总结,并分析了PVA／TiO2杂化膜现阶段所存在的问题。PVA材料的亲水性、环保性、生物相容性及纳米TiO2的亲水性、光照后不发生光腐蚀、耐酸碱性、化学稳定性和对生物无毒性等特点将赋予PVA／TiO2杂化膜广泛的应用前景。     

Dialysis membranes from polyethylene films grafted with acrylic acid

Low‐density polyethylene‐g‐poly(acrylic acid) membranes were prepared by the direct radiation grafting of aqueous acrylic acid solutions (containing Mohr's salt) onto low‐density polyethylene films and were irradiated at two different irradiation doses (2 and 3 Mrad) at a dose rate of 0.02 Mrad/h. Two series of polyethylene‐g‐poly(acrylic acid) membranes with 100 and 150% grafting were obtained. The free carboxylic acid groups in the grafted films were converted into the corresponding acrylates by reactions with different metal salts. The swelling (water uptake) and dialysis permeability of glucose and urea through the grafted membranes in different metal‐ion forms were investigated. The prepared membranes showed good permeability to both solutes, which increased as the hydrophilicity of the membrane increased. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 10–14, 2004     

Monovalent cation perm-selective membranes (MCPMs):New developments and perspectives

As one of the most typical and promising membrane processes, electrodialysis (ED) technique plays a more and more significant role in industrial separation. Especially, the separation of monovalent cations and multivalent cations is currently a hot topic, which is not only desirable for many industries but also challenging for academic explorations. The main aim of the present contribution is to view the advances of a wide variety of monovalent cation perm-selective membranes (MCPMs) and their preparation technologies including (1) covalent crosslinking,(2) surface modification, (3) polymer blending, (4) electrospinning, (5) nanofiltration alike membrane, and (6) organic–inorganic hybrid. The relevant advantages and disadvantageswith respect to some specific cases have been discussed and compared in detail. Furthermore, we elaborately discuss the opportunities and challenges of MCPMs, the fabricating strategies to take and the future perspectives.     

Analysis of compaction and life‐time prediction of porous polymer membranes: influence of morphology,diffusion and creep behaviour

In membrane applications, large values of permeability and selectivity are generally desired during the whole period of application. The permeability of porous polymer membranes often is reduced by the effect of compaction. Compaction of polymer membranes is a time‐dependent process which is strongly determined by the viscoelastic properties of the polymer and its plasticisation caused by the feed medium (e.g. a liquid medium or a process gas in the case of porous support structures). In this study, the time‐dependent compaction of porous polymer membranes under pressure is modelled. The influence of viscoelastic and diffusion properties of the polymer material on the permeability of the membrane is analysed for different types of membrane morphologies. The life‐time of a porous polymer membrane is associated with the time at which the glass transition is achieved in a creep experiment. Equations are derived in order to estimate the maximum life‐time of polymer membranes based on compaction. The analysis reveals that the diffusion coefficient, the average retardation time in creep, the magnitude of creep compliance and the time–temperature–pressure shift factor strongly influence compaction of microporous membranes. Generally, a larger tortuosity at constant porosity yields a lower life‐time of the membrane. Buckling of cell struts is the dominant failure mechanism in porous membranes with a very high porosity and allows an estimation of life‐time. © 2016 Society of Chemical Industry     

刮刀厚度对聚酰胺正渗透复合膜性能的影响

为考察正渗透过程基膜厚度对膜水通量的作用,有效地提高膜的综合性能,采用浓度2 mol/L的NaCl作为汲取液、去离子水为原料液作为评价系统,考察了刮刀厚度不同对正渗透复合膜性能的影响。结果表明,以筛孔80μm的筛网作为支撑材料,当采用厚度为45μm的刮刀所制备的超滤膜作为支撑材料时,制备所得的正渗透复合膜性能为佳,结构参数S可低至1.086 mm;并具有最好的稳定性以及最佳的污染冲洗恢复效果。     

Surface‐Initiated Atom Transfer Radical Polymerization from Electrospun Mats: An Alternative to Nafion

Proton exchange membranes for fuel cell applications are synthesized by surface‐initiated (SI) atom transfer radical polymerization (ATRP). Poly(vinylidene fluoride‐co‐chlorotrifluoroethylene) is electrospun into 50 µm thick mat, which is then employed as multifunctional initiator for copper‐mediated SI ATRP of 4‐styrene sulfonic acid sodium salt. Fine‐tuning of the ATRP conditions allows adjustment of the membrane's ion exchange capacity by varying the loading of the grafted ionomer. Structure and composition of the membranes are investigated by spectroscopic means and thermogravimetric analysis, respectively. The membrane morphology is probed by scanning electron microscopy. A membrane with proton conductivity as high as 100 mS cm⁻¹ is obtained. Long‐term durability study in direct methanol fuel cells is conducted for over 1500 h demonstrating the viability of this novel facile approach.

     

Pre‐Oxidized Acrylic Fiber Reinforced Ferric Sulfophenyl Phosphate‐Doped Polybenzimidazole‐Based High‐Temperature Proton Exchange Membrane

Pre‐oxidized acrylic fiber (POAF) and ferric sulfophenyl phosphate (FeSPP) are incorporated into polybenzimidazole (PBI) membrane for the first time to prepare high‐temperature proton exchange membranes (PEMs). The strong hydrogen bonds formed between PBI/POAF and FeSPP lead to good dispersion of POAF and FeSPP, facilitate the construction of proton channels, and enhance the dimensional and mechanical stability of the membranes. PBI/FeSPP (30 wt%) shows good proton conductivity (5.43 × 10⁻² and 4.13 × 10⁻² S cm⁻¹ at 180 °C at 50% and 0 relative humidity (RH), respectively) and improved dimensional and mechanical stability compared with pristine PBI. By incorporating 5 wt% POAF into PBI/FeSPP (30 wt%), the swelling ratios are halved and the mechanical strength is enhanced by almost 30% while the proton conductivity is slightly affected (3.84 × 10⁻² and 2.97 × 10⁻² S cm⁻¹ at 180 °C at 50% and 0 RH for PBI/FeSPP (30 wt%)/POAF (5 wt%), respectively). This work offers a new route in the preparation of high‐temperature PEMs with enhanced properties.

     

Novel Proton Conducting Membranes from the Combination of Sulfonated Polymers of Polyetheretherketones and Polyphosphazenes Doped with Sulfonated Single‐Walled Carbon Nanotubes

Intent on developing efficient proton exchange membranes used for direct methanol fuel cells as well as hydrogen fuel cells, a series of membranes based on sulfonated polyetheretherketone and sulfonated polyphosphazene‐graft copolymers is prepared by cross‐linking reaction because the former material has good enough mechanical property, while the latter is excellent in the proton transfer. The cross‐linked membranes combine the advantages of the two kinds of polymers. Among them, the membrane poly[(4‐trifluoromethylphenoxy)(4‐methylphenoxy)phosphazene]‐g‐poly {(styrene)₁₁‐r‐[4‐(4‐sulfobutyloxy)styrene]₃₃‐sulfonated poly(ether ether ketone)75 (CF₃‐PS₁₁‐PSBOS₃₃‐SPEEK75) shows a proton conductivity at 0.143 S cm⁻¹ under fully hydrated conditions at 80 °C and performs tensile strength about five times as much as did the sulfonated polyphosphazene membrane CF₃‐PS₁₁‐PSBOS₃₃. Further doping of sulfonated single‐walled carbon nanotubes (S‐SWCNTs) into the cross‐linked membranes on the screening of additives gives composite membrane CF₃‐PS₁₁‐PSBOS₃₃‐SPEEK75‐SWCNT possessing proton conductivity of 0.196 S cm⁻¹, even higher than that of Nafion 117 and a tensile strength comparable to that of Nafion 117. However, this significance of the composite membrane in the proton conduction is not observed in the test with a H₂/air fuel cell when it shows a maximal power density of 280 mW cm⁻² at 80 °C, whereas 294 mW cm⁻² is observed for CF₃‐PS₁₁‐PSBOS₃₃‐SPEEK75.

     

Separation of water–isopropyl alcohol mixtures with novel hybrid composite membranes

New‐fangled hybrid composite membranes were prepared by the incorporation of 5, 10, and 15 mass % NaY–zeolite particles into blend membranes of carboxymethyl cellulose (CMC)‐g‐acrylamide/sodium alginate (NaAlg) and crosslinked with glutaraldehyde. The pervaporation (PV) separation performance of the hybrid composite membranes was explored for the dehydration of isopropyl alcohol from their aqueous solutions at 30°C. The effect of NaY–zeolite in these blend membranes was investigated in PV dehydration. From the experimental results, we found that NaY particles could be intercalated in the aqueous polymer solution. The obtained results show that both the flux and selectivity increased simultaneously with increasing zeolite content in the membrane. This was explained on the basis of an enhancement of the hydrophilicity, selective adsorption, and molecular sieving action by the creation of pores in the membrane matrix. The membranes were characterized by differential scanning calorimetry, scanning electron microscopy, and Fourier transform infrared spectroscopy. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2012     

Effects of water vapor on gas permeation and separation properties of MFI zeolite membranes at high temperatures

Understanding the effects of water vapor on gas permeation and separation properties of MFI zeolite membranes, especially at high temperatures, is important to the applications of these zeolite membranes for chemical reactions and separation involving water vapor. The effects of water vapor on H₂ and CO₂ permeation and separation properties of ZSM‐5 (Si/Al ～ 80) zeolite and aluminum‐free silicalite membranes were studied by comparing permeation properties of H₂ and CO₂ with the feed of equimolar H₂/CO₂ binary and H₂/CO₂/H₂O ternary mixtures in 300–550°C. For both membranes, the presence of water vapor lowers H₂ and CO₂ permeance to the same extent, resulting in negligible effect on the H₂/CO₂ separation factor. The suppression effect of water vapor on H₂ and CO₂ permeation is larger for the less hydrophobic ZSM‐5 zeolite membrane than for the hydrophobic silicalite membrane, and, for both membranes, is stronger at lower temperatures and higher water vapor partial pressures. © 2011 American Institute of Chemical Engineers AIChE J, 2012