Modification of perfluorinated polymers by high-energy irradiation

This review surveys about the possibilities for the modification of perfluorinated polymers using high-energy irradiation: degradation, functionalization, branching, and cross-linking. The reaction mechanisms for the different reaction conditions are discussed. Electron irradiation of polytetrafluoroethylene (PTFE) with a very high dose leads to a complete degradation of the macromolecules to low-molecular products. In the presence of oxygen perfluorocarboxylic acids and in an inert atmosphere, mixtures of perfluorinated olefins and paraffins can be obtained. Virgin PTFE is disintegrated by high-energy irradiation in air with a lower dose into a micropowder modified with COOH groups. This powder can be homogeneously incorporated in other polymers. So, the special properties of PTFE can be made effective in these polymers. Micropowders functionalized with COOH groups and polyamides (PA) form by reactive extrusion PTFE-PA blockcopolymers which can be used as slide bearing materials. The copolymers poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) and poly(tetrafluoroethylene-co-perfluoropropyl vinyl ether) (PFA) irradiated in air show a significantly higher degree of COOH functionalization compared with PTFE. Irradiation of molten PTFE in an inert atmosphere leads to formation of different kinds of double bonds, CF₃ side groups, long-chain branches as well as cross-links. Irradiation of PFA in vacuum results in the generation of COF and COOH groups; in molten state also branches and cross-links are formed.The focus of the present paper is on the work that has been carried out at the Institute of Polymer Research Dresden.     

Effect of electron irradiation on nitrofurans and their metabolites

Research on the degradation of aqueous furazolidone, nitrofurantoine and semicarbazide (SC) solutions, and 3-amino-2-oxazolidinone (AOZ) residues in tissues of chicken and crucian under electron beam irradiation have been carried out. Results showed that about 75% furazolidone and 70% nitrofurantoine degraded at 6 kGy dose, and SC with the initial concentration of 667 μg/L degraded by 94% at 12 kGy dose. While AOZ in the crucian and chicken degraded by 22.5% and 20.7%, respectively, after being irradiated at 12 kGy. The degradation conditions were investigated to provide a reference to improve irradiation techniques.     

The degradation of DGEBA/DICY under 100 keV proton irradiation

The degradation process of diglycidyl ether of bisphenol A (DGEBA)/ dicyandimide (DICY) solidified system under 100 keV proton irradiation was investigated. It was found that the proton irradiation results in mass loss, which the maximum is approximately 15.5 μg/cm², and change in surface morphology of DGEBA/DICY. The analyses of FT-IR and XPS showed that, the proton irradiation induces the debonding of the weak groups such as -CH₃, C-O, leading to formation of stable carbon-rich structure by recombination of the occurred free radicals, and chemical reaction between the free radicals with participation of proton. The degradation of DGEBA/DICY exhibits exponential variation with the proton fluence, which the degradation rate is high at the initial stage of irradiation, and becomes slow trending to constant after the proton fluence reaches 6 × 10¹⁵ /cm².     

丙烯酸水溶液聚合法制备PTFE/PAA/Nafion膜及其性能

采用廉价的多孔聚四氟乙烯(PTFE)膜作为基底, 用少量的Nafion与PTFE膜复合可制备低成本的质子膜. 但疏水性的PTFE膜与亲水性的Nafion膜结合性不佳. 基于此, 本文对疏水性的PTFE膜材料表面进行设计, 先采用丙烯酸对疏水性的PTFE膜表面进行亲水性改性, 再喷涂亲水性Nafion膜, 完成低成本PTFE/PAA/Nafion膜的制备. 实验结果表明, 改性前的PTFE膜材料水接触角为150°, 改性后的膜接触角变为55.6°, 亲水性大幅上升, 膜的机械强度和尺寸稳定性(断裂强度为25.2 MPa, 80 ℃下的溶胀率为11.9%)均优于Nafion117膜, 而 Nafion用量则节省了60%. PTFE/PAA/Nafion膜具有高质子导通率(80 ℃下达到131.9 mS/cm), 接近于Nafion117膜, 最大功率密度可以达到404.2 mW/cm².     

Friction and wear properties of combined surface modified carbon fabric reinforced phenolic composites

Carbon fabric (CF) was surface treated with silane-coupling agent modification, HNO₃ oxidation, combined surface treatment, respectively. The friction and wear properties of the carbon fabric reinforced phenolic composites (CFP), sliding against GCr15 steel rings, were investigated on an M-2000 model ring-on-block test rig. Experimental results revealed that combined surface treatment largely reduced the friction and wear of the CFP composites. Scanning electron microscope (SEM) investigation of the worn surfaces of the CFP composites showed that combined surface modified CFP composite had the strongest interfacial adhesion and the smoothest worn surface under given load and sliding rate. SEM and X-ray photoelectron spectroscopy (XPS) study of carbon fiber surface showed that the fiber surface became rougher and the oxygen concentration increased greatly after combined surface treatment, which improved the adhesion between the fiber and the phenolic resin matrix and hence to improve the friction-reduction and anti-wear properties of the CFP composite.     

Toward developing accelerated stress tests for proton exchange membrane electrolyzers

Proton exchange membrane water electrolysis is technically the most suitable technology for the production of green hydrogen on a large scale. Although it is still more expensive than hydrogen produced from fossil sources, it has already been commercialized. Novel components with cost-effective materials and efficient manufacturing processes are being rapidly developed. However, these components must endure durability tests that can guarantee a lifetime of at least 50,000 operation hours. Consequently, there is an urgent need to develop accelerated stress test protocols based on a deep understanding of degradation mechanisms of stack components. Recent reports show that the main degradation mechanisms are associated to anode catalyst dissolution, membrane chemical decomposition, and formation of semiconducting oxides on the metal components. These mechanisms can be accelerated by stressors such as high current density, dynamic operation, and shutdown modes. On the basis of these reports and knowledge of the operational requirements for large-scale proton exchange membrane water electrolysis, we propose an accelerated stress test protocol for the fast evaluation of newly developed cost efficient and durable components.     

The reciprocal influence between ion transport and degradation of PA66 in acid solution

Transport behavior of acid solution through polyamide was studied by measuring element distribution in cross section, pH, and ion concentration. Degree of degradation that related to the decreasing of molecular weight and flexural strength was observed in order to study the influence of acid solution on the polyamide 66 (PA66) degradation. The permeation mechanism of acid solution can be explained: at first water penetrates into polyamide and it is followed by acid. In this process, water does not affect the molecular weight at 50 °C but only reduces the polyamide strength by plasticization. Moreover, proton (H⁺) has contributed to the anion transport and degradation of polyamide by the hydrolytic reaction. Proton attacks the polyamide chain, and scission of chain occurs, and reacts with anion to form other material substance. This process affects the decrease of molecular weight and the significant loss of polyamide strength. Analysis results from ion concentration measurement shows that the amount of proton and anion transport into deionized waterside was imbalance, which probably due to the different mobility between proton and anion or formation of other material substance by reaction of anion and PA66 bond. Such information is not only necessary for the investigation of hydrolytic degradation of polymer and prediction of lifetimes for a protective polymer lining/coating to chemical attack, but may also be helpful towards gaining a deeper insight into the processes of degradation of other polymer.     

多杀菌素及其光照降解产物分析

采用五级质谱研究了多杀菌素的质谱断裂规律, 应用串联质谱选择反应检测技术考察了光照条件下多杀菌素的降解程度, 利用液相色谱-质谱联用手段分析了多杀菌素降解产物, 并推断了主要降解产物的结构. 结果表明, 多杀菌素17碳上的福乐糖胺容易失去, 三氧甲基鼠李糖很稳定; 多杀菌素浓度随紫外光照射时间的增加而降低, 在照射484 min后, 降解率达到70%左右, 形成11种降解产物, 这些降解产物是多杀菌素A或D经氧化、还原及水解等反应形成.     

车用燃料电池启停工况性能衰减

车用燃料电池(质子交换膜燃料电池)技术经过二十余年的持续研发和不断突破,使得燃料电池汽车性能基本满足了商业化指标,并成为当前备受瞩目的新能源汽车。然而,质子交换膜燃料电池伴随实际车况变化会经历燃料供应、湿度、温度、电流、电压等复杂循环过程,造成燃料电池的关键材料衰减加速,并且车用燃料电池的耐久性问题棘手且涉及面广。本文针对车用燃料电池的启停工况,归纳分析了启停工况下燃料电池的研究过程、衰减机理、实验论证、建模分析,并从燃料电池系统管理角度分析了启停衰减的缓解策略。通过对已有启停工况下质子交换膜燃料电池性能衰减失效的梳理,提出了本文的观点、分析和解释。     

Effects of adjacent groups of benzimidazole on antioxidation of polybenzimidazoles

The chemical oxidative stabilities of poly(2,2-(m-phenylene)-5,5-bibenzimidazole) (PBI-ph), poly(2,5-benzimidazole) (ABPBI), poly(2,2′-hexyl-5,5′-bibenzimidazole) (PBI-hex), and poly(2,2′-imidazole-5,5′-bibenzimidazole) (PBI-imi) are studied. By means of FTIR and ¹HNMR analysis, more information about the degradation process of PBI-ph is found as: CH₂ groups are left in the residual polymers; after the N-H bond and the trisubstituted benzene ring are oxidized by oxidative free radicals, the meta-phenylene is relatively stable. Through Fenton tests, the chemical oxidative stabilities of these PBIs are compared and results show that PBI-ph is the stablest material while PBI-imi is the unstablest one. Through FTIR analysis, the structure changes to those degraded PBIs are compared. The conjugated structure formed between meta-phenyl and benzimidazole can protect the main chain of PBI-ph from the attack of oxidative free radicals. Additionally, effects of acid on PBI-ph degradation rate are evaluated and the results show that phosphoric acid can slow down the chemical oxidative degradation.     

Microwave-assisted degradation of acid orange using a conjugated polymer,polyaniline, as catalyst

Microwave-assisted photocatalytic degradation of dyes is one of the emerging technologies for waste water remediation. Microwave effectively accelerates photocatalytic degradation, when microwave electrodeless lamp (MEL) substitutes traditional UV lamp as light source. This setup can be extremely simplified if MEL and photocatalyst can be replaced by a catalyst which can work under microwave irradiation in the absence of any light source. The present work reports for the first time degradation of acid orange 7 (AO) under microwave irradiation using polyaniline (PANI) as catalyst in the absence of any UV lamp as light source. The degradation/decolourization was carried out in neutral acidic and basic media and was monitored spectrophotometrically to evaluate the ability of microwave irradiation to degrade AO. Microwave irradiation showed excellent performance as it completely decolourizes AO dye solution in 10 min. With the advantages of low cost and rapid processing, this novel catalyst is expected to gain promising application in the treatment of various dyestuff wastewaters on a large scale.     

质子辐照对有机硅树脂增强甲基硅橡胶的性能损伤及机理

硅橡胶具有优良的电绝缘性以及耐高低温、耐电晕、耐化学腐蚀、耐大气老化、耐臭氧和耐辐射等性能,近年来在航天领域得到了广泛应用．在宇宙空间的带电粒子如质子、电子等的辐照作用下,硅橡胶会发生性能退化,其质损率上升,产生析气现象,从而直接影响航天器的可靠性和寿命．自80年代以来,人们就对不同辐照源及不同粒子注量对硅橡胶材料的影响进行了研究,但直到近几年才将研究热点转向辐照场中硅橡胶的性能退化及微观结构的演变规律,其辐照环境大多集中于γ射线、Si^＋和F^＋离子、He^2＋离子等．对于空间环境下带电粒子辐照对硅橡胶材料的影响,国外由于相应的研究工作保密性强,报道甚少;国内哈尔滨工业大学则对我国自行研制的白炭黑增强空间级甲基硅橡胶质子辐照作用后的性能与微观结构的变化做了较为深入的研究。     

Effect of pyrolytic carbon content on microstructure and tribological properties of C/C-SiC brake composites fabricated by isothermal chemical vapor infiltration

Four types of C/C-SiC composites were prepared by isothermal chemical vapor infiltration (ICVI) of SiC on C/C preforms of different densities. Tribological properties of the composites were evaluated by using MM-1000 testing machine. The results indicated that the friction behaviors of the composites are a strong function of the content of pyrolytic carbon (in matrix). Moreover, friction film was formed on the surface and increased with pyrolytic carbon content. Debris originated of particulate and film-type have been observed after friction testing with ratio and size determined by the content of pyrolytic carbon.     

Studies of the degradation of organotin stabilizers in poly(vinyl chloride) during gamma irradiation

Organotin stabilizers of the type Bu₂SnX₂ (X = SCH₂CO₂C₈H₁₇ or O₂CCH?CHCO₂C₈H₁₇) present in poly(vinyl chloride) (PVC) and subjected to varying doses of gamma irradiation in the range 1–200 kGy (0.1–20 Mrad) are shown to suffer degradation with dealkylation to form monobutyltin trichloride and tin(IV) chloride, which have been characterized by a subsequent alkylation procedure followed by gas chromatographic analysis. The extent of degradation of the stabilizers on prolonged gamma irradiation is much more severe than during thermal degradation leading to comparable blackening of the polymer.