HDPE预辐照接枝SSS与AA体系的反应动力学研究

采用电子束引发预辐照接枝方法在高密度聚乙烯(HDPE)上接枝丙烯酸(AA)与对苯乙烯磺酸钠(SSS)两种单体,以制备含磺酸和羧酸基团的双功能基阳离子交换膜。研究发现,接枝速率与辐照剂量、单体总浓度及反应温度密切相关。接枝反应的活化能为22．2kJ／mol。傅立叶变换红外光谱(FTIR)测试表明,接枝膜上引入了磺酸基团和羧酸基团。     

Radiolytic preparation of poly(styrene sulfonic acid) - grafted poly(tetrafluoroethylene-co-perfluorovinyl vinyl ether) membranes with highly cross-linked networks

In this study, various amounts of a divinylbenzene (DVB) cross-linking agent (5∼30%) were introduced during a simultaneous irradiation grafting of styrene onto a PFA film of a 25 μm thickness in order to prepare a series of poly(styrene sulfonic acid)-grafted poly(tetrafluoroethylene-co-perfluorovinyl vinyl ether) (PFA) membranes with various degrees of cross-linking and grafting (29∼74%). The effects of the DVB cross-linking agent on the properties of the prepared membranes, such as water uptake, proton conductivity, methanol permeability, and chemical stability, were also investigated in this study. The results indicated that the ion exchange capacity (IEC) slightly decreased with increasing DVB content, whereas the water uptake, proton conductivity, and methanol permeability of the membrane greatly decreased. The chemical stability of the prepared membranes was found to be significantly improved with increasing DVB content. The results indicated that the cross-linked network membranes are promising for application in a direct methanol fuel cell.     

聚乙烯辐照接枝体系改变pH对接枝率的影响

采用γ射线辐照引发接枝的方法，在高密度聚乙烯（HDPE）上接枝丙烯酸（AA）和对接枝苯乙烯磺酸钠（SSS），制备了一种含羧酸基团和磺酸基团的阳离子交换膜，详细研究了反应体系在不同pH值下的接枝率变化规律。实验表明，在共辐照接枝方法中，当AA与SSS一步法接枝HDPE或接枝上AA的HDPE膜再共辐照接枝SSS时，总接枝率（Gt）及对苯乙烯磺酸钠的接枝率（Gs）随体系的pH的降低而升高，在预辐照一步法接枝中，Gt与Gs随体系pH的降低先升高后又有所降低，综合分析认为，改变pH值使体系粘度发生变化，从而影响了单体向基体的扩散速率。     

Preparation and characterization of proton exchange membranes from polystyrene grafted poly（vinylidene fluoride） powder

Proton exchange membranes(PEMs) were prepared in three steps:graRing of polystyrene onto PVDF powder using pre-irradiation graft polymerization technique, processing the grafted PVDF powder into membranes of around 50-μm thickness, and sulfonating them with cholorosulfonic acid to form poly(vinylidene fluoride)-g-poly(styrene sulfonic acid) membranes. Kinetics of the graft polymerization was studied. The existing of polystyrene side-chains in the grafted PVDF powders, and PSSA groups in PEMs, were proved by FT-IR. Properties of the PEMs, i.e. the ion exchange capacity, water uptake, proton conductivity, thermal property and oxidative stability,were characterized. Dependence of properties on the degree of grafting was investigated, too.     

过氟化聚合物的苯乙烯接枝研究--辐照条件与反应条件的影响

Fuel cell is in focus as a very low exhaust new dynamo system. Especially polymer electrolyte fuel cells (PEFC) using proton exchange membranes (PEM) have attracted much attention for the electrical vehicle and other mobile applications such as cellar phone and personal computer. Conventional perfluoro-sulfonic acid membranes such as Nation() (DuPont de Nemours LTD.) have been the popular PEM used in PFEC. However, there are still several problems such as insufficient gas barrier properties, low thermal resistance, and their high costs.In this study, hawse have studied the partially fluorinated PEM for PEFC by radiation grafting onto per-fluorinated polymers such as PFA, FEP and ETFE with reactive styrene monomers using pre-irradiation grafting method in gas and in liquid phase, respectively, and successive sulfonation. Characteristic properties of the grafted and sulfonated materials have been discussed and optimized fabricating conditions were determined.Characteristic properties of the obtained materials have been measured by differential scanning calorimetry,thermogravimetric analysis and FT-IR spectroscopy, etc.In the case of irradiation in air, glass transition temperatures (Tg) of the grafted materials depend on the yields of styrene grafting onto the materials. That is higher yields of grafting give lower thermal stability. On the other hand, when the peroxy radicals were converted trapped radicals by exposure in air after irradiation under oxygen-free atmosphere, Tg of the grafted materials hardly depends on the grafting yields.Moreover, the yields of grafting in gas phase were higher than that of liquid phase. However, the sample form of grafting in gas phase has been greatly changed, whereas the sample form of grafting in liquid phase has kept its original feature.Therefore, it is suggested that the fabricating conditions for PEFC membranes were preferred to irradiation under oxygen-free atmosphere and grafting in liquid phase.Ion exchange capacities of the sulfonated-materials could be 3.0meq/g. Other properties of the obtained membranes such as chemical structure were also discussed.     

γ射线辐照聚偏氟乙烯接枝苯乙烯磺酸乙酯

以聚偏氟乙烯(Polyvinylidene fluoride,PVDF)树脂为基材,采用γ射线预辐射接枝法在PVDF树脂上接枝苯乙烯磺酸乙酯(Ethyl styrenesulfonate,ETSS),探讨吸收剂量、接枝温度、接枝反应时间及单体浓度对接枝率的影响。之后在95℃水解PVDF-g-PETSS聚合物得到PVDF接枝苯乙烯磺酸(PVDF-g-PSSA)离子交换树脂。红外光谱、X射线光电子能谱、热重分析证明PVDF-g-PETSS及PVDF-g-PSSA被成功制备。当接枝率为120%时,PVDF-g-PSSA的离子交换容量达到2.05 mmol/g。这种将带有磺酸基团的单体通过辐照接枝引入PVDF基材然后水解的方法简单、高效、污染小,有望在离子交换树脂及离子交换膜的制备中得到应用。     

Study of radiation-induced grafting of acrylic acid-sodium styrene sulfonate onto poly （tetrafluoroethylene-cohexafluoropropylene） film

Poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) films were immersed in aqueous solution of acrylic acid (AA) and sodium styrene sulfonate (SSS), then irradiated by ^60Co γ-rays at 25℃. The effects o| reaction time, absorbed dose, dose-rate, inhibitor and monomer concentration on the grafting yield were studied. Grafting yields of both AA and SSS onto FEP, respectively, increase with irradiation dose, but some saturation will appear at high dose and monomer concentration. The grafting yield increases with reaction time and then levels off. The grafting of SSS onto FEP is more difficult than the grafting of AA. The analysis of grafted membranes using DSC and FT-IR have been done.     

Graft Polymerization of Acrylic Acid on a Polytetrafluoroethylene Panel by an Inductively Coupled Plasma

Surface modification on a polytetrafluoroethylene (PTFE) panel was performed with sequential nitrogen plasma treatments and surface-initiated polymerization. By introducing COO– groups to the surface of the PTFE panel through grafting polymerization of acrylic acid (AA), a transparent poly (acrylic acid) (PAA) membrane was achieved from acrylic acid solution. Grafting polymerization initiating from the active groups was achieved on the PTFE panel surface after the nitrogen plasma treatment. Utilizing the acrylic acid as monomers, with COO– groups as cross link sites to form reticulation structure, a transparent poly (acrylic acid) membrane with arborescent macromolecular structure was formed on the PTFE panel surface. Analysis methods, such as FTIRmicroscopy and XPS were utilized to characterize the structures of the macromolecule membrane on the PTFE panel surface. A contact angle measurement was performed to characterize the modified PTFE panels. The surface hydrophilicities of modified PTFE panels were significantly enhanced after the plasma treatment. It was shown that the grafting rate is related to the treating time and the power of plasma.     

聚醚砜微孔膜电子辐照接枝改性及过滤性能研究

利用电子束辐照技术对聚醚砜（PES）微孔膜进行接枝丙烯酸（AA）改性。用称重法测量接枝率,分析辐照剂量及气氛对膜接枝率的影响规律,用红外光谱分析膜接枝后官能团的变化,用扫描电镜观察样品的表面形貌;并分析了接枝率对水通量及牛血清白蛋白（BSA）溶液通量的影响。研究结果表明,对浓度为1mol/L的单体丙烯酸,在氮气或空气的氛围下辐照,接枝率随辐照剂量的增加先增大而后降低,并在整个辐照剂量范围内,氮气氛围下辐照的接枝率均高于空气氛围的接枝率。当接枝率较小时,水通量及BSA溶液通量均随接枝率的增大而增大,并当接枝率为11%时,二者同时达到最大值,随着接枝率的进一步增大,其值反而降低。     

Radiation-chemical synthesis of polypropylene fabrics with sulfonic acid functional groups

A sorption-active material carrying sulfonic acid groups was synthesized by the radiation-induced graft polymerization of styrene monomer onto the surface of non-woven polypropylene fabric, followed by sulfonation of the grafted polystyrene chains. The effect of the main experimental parameters (absorbed dose, monomer concentration, reaction time) on the styrene degree of grafting was investigated. The sulfonation process with 5% chlorosulfonic acid at room temperature was investigated in detail and the optimal sulfonation conditions for the samples with a medium degree of grafting (70-140%) were determined. Densities of 3.5-5 meq/g were obtained by applying those sorption-active PP fabrics with a sulfonic acid group.     

用辐射接枝法对HDPE膜进行功能化改性

利用预辐射接枝技术,在聚乙烯膜上接枝苯乙烯磺酸钠（ＳＳＳ）、苯乙烯三甲基氯化铵（ＶＢＴＡＣ）等具有离子交换性能的单体,研制出具有抗菌性能的离子交换膜,并且使得原先增水性的基膜转变为亲水性较好的膜。通过实验,掌握了膜的接枝工艺,并对膜接枝过程、结构特征、经性能有较多的了解。从各个角度对膜的亲水性能作了定量研究,提出了水合数与表面自由能的计算方法。对几种膜的抗菌性能进行了评价。确定了ＶＢＴＡＣ膜作为抗     

电子束引发双功能基阳离子交换膜的制备研究

在所有的离子交换膜中,最引人注目的当数20世纪70年代已商品化的Nation系列膜。具有磺酸功能基的Nation膜电阻低,但用在氯碱工业时电流效率低。1974年Seko发明了全氟羧酸阳离子交换膜,使电流效率有实质性提高,并推动了复合膜的发展。复合膜具有磺酸膜的低电阻性能和羧酸膜的高电流效率。本工作采用辐射接枝法制备含羧酸基团和磺酸基团的双功能基阳离子交换膜,目的主要是以低成本且简单可行的辐射接枝法代替共聚法,制备稳定性好、低电阻、高电流效率的阳离子交换膜。     

Solid polymer electrolyte water electrolysis systems for hydrogen production based on our newly developed membranes, Part I: Analysis of voltage–current characteristics

A new solid polymer electrolyte water electrolysis system was constructed using an original proton exchange membrane (PEM). The highly proton-conductive PEM was prepared by the γ-ray-induced post-grafting of styrene into a crosslinked-polytetrafluoroethylene (PTFE) film and subsequent sulfonation. The water vapor to be electrolyzed was controlled at a constant relative humidity and introduced into the cell at different temperatures up to 80 °C. As the cell voltage was increased, the current became higher; the maximum current was 50 mA/cm² at 2.5 V at a temperature of 80 °C, corresponding to a hydrogen production rate of 0.38 mL/min cm² in the normal state (25 °C, 1 atm). The voltage–current characteristics were analyzed with a theoretical model based on Butler–Volmer kinetics for electrodes and transport resistance through the PEM. This analysis revealed that the anode exchange current density and interfacial resistance determined the electrolysis performance.     

Synthesis and characterization of PEFC membranes based on fluorinated-polymer-alloy using pre-soft-EB grafting method

Polymer electrolyte fuel cell (PEFC) membranes based on thin film of crosslinked perfluorinated polymer-alloys (RX-FA) have been fabricated by soft electron beam (soft-EB) grafting with styrene monomers using soft-EB irradiation under nitrogen atmosphere at room temperature (RT). The characteristic properties of styrene-grafted materials (GRX-FA) and sulfonated materials (SRX-FA) have been measured by differential scanning calorimetry (DSC) and FT-IR spectroscopy, ionic conductivity and so on. The glass transition temperatures (dry state) of all obtained SRX-FA were about 105 ± 1 °C, which are higher than Nafion^®. The ion exchange capacities of SRX-FA have been achieved about 3.3 meq/g (dry). The ionic conductivity of obtained SRX-FA has showed about 0.17 S/cm at 60 °C with relative humidity (RH) of ∼95%. The ionic conductivities of the obtained SRX-FA were higher than that of conventional perfluoro-sulfonic acid membranes (PFSA). Fabricated membrane electrode assemblies (MEAs) based on the obtained SRX-FA have shown encouraging performance in the PEFC, compared with the conventional PFSA. The power density of obtained MEAs based on the SRX-FA was about 330-340 mW/cm² under 500 mA/cm² at 60 °C operation. Moreover, the maximum power densities of obtained MEAs based on the SRX-FA shows about 630 mW/cm² at 60 °C. On the other hand, the power density at 500 mA/cm² and maximum power density of MEA based on Nafion^®112 were about 320 and 590 mW/cm² at 60 °C. Thus, the power density of the obtained SRX-FA was higher than that of conventional PFSA.     

A study on the distribution of polystyrene sulfonic acid grafts over the cross-section of a PFA film

In this study, the distribution behaviors of polystyrene sulfonic acid (PSSA) grafts over the cross-section of grafted PFA membranes (PFA-g-PSSA) were investigated by using SEM-EDX analysis. Membranes with various degrees of grafting (DOG) and thicknesses were prepared by a simultaneous radiation grafting of styrene and a subsequent sulfonation with chlorosulfonic acid. A SEM-EDX instrument was utilized to directly observe that the distribution behaviors of the PSSA grafts over the cross-section of grafted PFA membranes and the results showed that the distribution behaviors were largely affected by the grafting conditions such as the degree of grafting, monomer concentration, and film thickness.     

Proton exchange membranes prepared by radiation-induced graft copolymerization from binary monomer mixtures onto poly(tetrafluoroethylene-co-hexafluoropropylene) film

Sulfonic acid proton exchange membranes based on a poly(tetrafluoroethylene-co-hexafluoropropylene) film were synthesized through the single-step graft copolymerization of sodium styrenesulfonate and acrylic acid monomers from binary monomer aqueous solutions using the electron beam pre-irradiation method in air. The effects of the various polymerization parameters (absorbed dose, reaction time, and monomer ratio) on the degree of grafting were studied.A correlation between the degree of grafting and some of the physical-chemical properties (water uptake and ion-exchange capacity) of the synthesized copolymers was established. The distribution of the sulfonic acid groups was investigated across the thickness of several membranes in order to gain a better understanding of the graft copolymerization process from binary monomer aqueous solutions onto the fluorinated film and to synthesize membranes with optimal physical-chemical properties.     

Gamma-radiation-induced grafting of binary mixture of methacrylic acid and 4-vinyl pyridine onto Teflon-FEP film as an effective polar membrane for separation processes

Ionic bifunctional membranes have been synthesized by grafting binary mixture of methacrylic acid (MAAc) and 4-vinyl pyridine (4-VP) onto Teflon-FEP film by pre-irradiation method. Optimum conditions pertaining to maximum percentage of grafting were evaluated as a function of different reaction parameters. Maximum percentage of grafting of binary mixture (MAAc-co-4-VP) (71.29%) was obtained at an optimum total dose of 54.48 kGy and the total concentration was 9.49 mol/L ([4-VP] = 0.07 mol/L and [MAAc ] = 9.42 mol/L) in 5 ml of water. The effect of alcohols as additives to the reaction medium on percent grafting of the binary mixture has also been studied. The membranes were characterized by FTIR spectroscopy, scanning electron microscopy and thermogravimetric analysis. Swelling studies of the membranes were performed in different solvents such as water, benzene, carbon tetrachloride and dimethyl formamide (DMF). Maximum swelling was observed in DMF with minimum swelling in benzene. Metal ion (Cu²⁺, Ni²⁺ and Fe²⁺) uptake studies show better affinity for Fe²⁺ ions. Conductance measurements in different aqueous salt solution showed that these membranes have affinity for Na⁺/K⁺ ions and Cl⁻ ions and hence can be used in desalination/separation processes for the separation of both type of cationic and anionic ions.     

Anisotropic proton-conducting membranes prepared from swift heavy ion-beam irradiated ETFE films

Poly(ethylene-co-tetrafluoroethylene) (ETFE) films were irradiated by swift heavy ion-beams of ¹²⁹Xe²³⁺ with fluences of 0, 3 × 10⁶, 3 × 10⁷, 3 × 10⁸ and 3 × 10⁹ ions/cm², followed by γ-ray pre-irradiation for radiation grafting of styrene onto the ETFE films and sulfonation of the grafted ETFE films to prepare highly anisotropic proton-conducting membranes. The fluence of Xe ions and the addition of water in the grafting solvent were examined to determine their effect on the proton conductivity of the resultant membranes. It was found that the polymer electrolyte membrane prepared by grafting the styrene monomer in a mixture of 67% isopropanol and 33% water to the ETFE film with an ion-beam irradiation fluence of 3.0 × 10⁶ ions/cm² was a highly anisotropic proton-conducting material, as the proton conductivity was three or more times higher in the thickness direction than in the surface direction of the membrane.     

聚四氟乙烯膜辐射接枝反应条件的研究

采用了共辐射接枝技术，在室温下将苯乙烯接枝到聚四氟乙烯薄膜上，合成了辐射接枝膜。研究了溶剂种类、单体浓度、辐射剂量以及剂量率等因素对接枝反应的影响。结果表明，单体浓度和辐射剂量率是反应的主要影响因素，两者对接枝反应速率的影响指数分别为1．2和0．4。