Improvement of creep resistance of polytetrafluoroethylene films by nano-inclusions

To improve creep resistance of directional polytetrafluoroethylene (PTFE) films, epoxy grafted nano-SiO₂ is mixed with PTFE powder before sintering and calender rolling. The aligned macromolecular chains (especially those in amorphous region) of the composite films can be bundled up by the nanoparticles to share the applied stress together. In addition, incorporation of silica nanoparticles increases crystallinity of PTFE and favors microfibrillation of PTFE in the course of large deformation. As result, PTFE films exhibit lower creep strain and creep rate, and higher tensile strength and hardness. The work is believed to open an avenue for manufacturing high performance fluoropolymers by nano-inclusions.     

Fluoride ions at the Cu–fluoropolymer interface

Nanometer thick films of sputtered and evaporated Cu were deposited on the surfaces of the fluoropolymers poly(tetrafluoroethylene) (PTFE), poly(tetrafluoroethylene‐co‐hexafluoropropylene) (FEP) and poly(tetrafluoroethylene‐co‐perfluoropropyl vinyl ether) (PFA) and studied by both angle‐resolved XPS at takeoff angles of 10°, 45° and 80° and in situ argon ion etching. Higher yields of the fluoride ion to fluoropolymer ratio were detected for sputtered than evaporated Cu. PFA and FEP show enhanced interaction with sputtered Cu to produce fluoride ions relative to the more polycrystalline PTFE. At intermediate depths (takeoff angle of 45°), PFA and FEP exhibit the strongest fluoride F 1s signals compared with the fluoropolymer peaks. The amount of fluoride ion detected reaches a maximum after brief Ar ion etching and then decreases with prolonged etching. Compared with untreated fluoropolymers, improved adhesion of evaporated Cu was observed on the fluoropolymer surfaces that were argon ion etched to expose fluoride ions. Copyright © 2013 John Wiley & Sons, Ltd.     

Electroless Ni-plating on PTFE fine particles

A Ni electroless plating process was used with polytetrafluoroethylene (PTFE) fine particles (25–500 μm). Using nonionic hydrocarbon surfactant, PTFE particles were dispersed in the plating bath. The PTFE hydrophobicity was sufficiently high that Ni was deposited partly on the PTFE surface in the initial step. The Ni-PTFE particles were formed into the Ni-PTFE plate by heat treatment at 350 °C after pressing. The Ni-PTFE plate had electrical conductivity and gas permeability, which were influenced by the pore distribution in the plate. Pores with 1 μm diameter might be especially important to impart high gas permeability to the Ni-PTFE plate.     

A sheath flow gating interface for the on-line coupling of solid-phase extraction with capillary electrophoresis

A sheath flow gating interface (SFGI) is presented for the on-line coupling of solid-phase extraction (SPE) with capillary electrophoresis (CE). The design, construction and operation of the SFGI are described in detail. After operating conditions were investigated and selected, the SFGI was evaluated on a SPE–CE–UV setup using hydroxylated poly(glycidyl methacrylate-co-ethylene dimethacrylate) monolith as the absorbent and using three phenols as the test analytes. The preconcentration factors obtained with the SPE–CE–UV system and the SPE–UV part are 530 and 550, respectively. The plate numbers obtained using the SPE–CE–UV system are slightly better than or comparable to those with the CE–UV part. The precisions (RSDs) of 100 consecutive injections are 2.43%, 3.86%, and 4.25% for peak height, peak area and migration time, respectively. The measured recoveries for the river water samples spiked at three different levels are in the range of 93.6–102.8% with the interday RSD values ranging from 2.0 to 4.5% (n = 3). These data collectively demonstrate that the SFGI has the ability to exactly and reproducibly transfer nanoliters of fractions from SPE onto CE with no degradation of the efficiencies of SPE and CE, suggesting a great potential to be routinely used for the coupling of SPE, microcolumn LC or FIA with CE.     

高压消解-ICP-AES法测定燃料油中钒铁镍硅铝钙钠硫

利用超声波处理制备样品,采用方差分析法进行均匀性检验。以HNO3和H2O2为溶剂,使用钢衬聚四氟乙烯罐高压消解样品,建立了以无机标准溶液制作校准曲线测定燃料油中元素的ICP-AES方法,实现了燃料油中V、Fe、Ni、Si、Al、Ca、Na、S等元素的同时测定。相应各元素的检出限为0.4、0.3、1.4、0.9、1.0、0.7、0.8、150 mg/kg;线性范围为1.3~500、0.9~500、4.1~500、2.8~500、3.0~500、2.1~500、2.4~500、450~45000 mg/kg。方法的相对标准偏差为0.1%~7.5%,回收率为96%~107%。本方法可以推广到其它相关石油产品中的元素分析。     

The oxidation‐treated interface on tribological properties of carbon fibers‐reinforced PTFE composite under oil‐lubricated condition

The effect of air oxidation and ozone surface treatment of carbon fibers (CF) on tribological properties of CF reinforced polytetrafluoroethylene (PTFE) composites under oil‐lubricated condition was investigated. Experimental results revealed that ozone treated CF reinforced PTFE (CF–PTFE) composite had the lowest friction coefficient and wear under various applied loads and sliding speeds compared with untreated and air‐oxidated composites. X‐ray photoelectron spectroscopy (XPS) study of carbon fiber surface showed that, after ozone treatment, oxygen concentration was obviously increased, and the amount of oxygen‐containing groups on CF surfaces was largely increased. The increase in the amount of oxygen‐containing groups enhanced interfacial adhesion between CF and PTFE matrix. With strong interfacial adhesion of the composite, stress could be effectively transmitted to carbon fibers; carbon fibers were strongly bonded with PTFE matrix and large scale rubbing‐off of PTFE was prevented, therefore, the tribological properties of the composite were improved. Copyright © 2009 John Wiley & Sons, Ltd.     

Sm2O3增强聚四氟乙烯／混杂纤维复合材料的摩擦磨损性能研究

采用冷压烧结方法制备Sm2O3增强聚四氟乙烯／混杂纤维复合材料，用AG-1型电子万能试验机和MM-200型摩擦磨损试验机分别评价了Sm2O3增强聚四氟乙烯／混杂纤维复合材料的力学性能和摩擦磨损性能，采用扫描电子显微镜观察其磨损表面形貌．结果表明：添加少量Sm2O3可以提高炭纤维和玻璃纤维混杂填充PTFE复合材料的力学性能和摩擦磨损性能，尤其对改善减摩效果尤为显著；加入1％Sm2O3可以使PTFE／15％CF／10％GF复合材料的拉伸强度、弯曲强度和硬度分别提高9．0％、5．1％和49．1％，摩擦系数降低22％，磨痕宽度降低5．4％，得到性能较为优良的耐磨材料．这是由于Sm2O3起到了润滑及阻止纤维和基体磨损作用的缘故．     

Preparation and Thermal Characterization of PTFE/PES Nanocomposites

Summary: PTFE/PES composites were prepared by precipitation of Radel A® into a PTFE latex containing nanoparticles with average diameters of 48 nm and spherical shape. Several samples were prepared by varying the relative ratio between the Radel A® and PTFE content. The combination of SEM and AFM analysis indicates that the precipitation of Radel A in the presence of PTFE leads mainly, if not exclusively, to a bimodal mixture of the two homoparticles. The fractionated crystallization behaviour of these samples is revealing of the PTFE dispersion degree within the Radel A® matrix. When the PTFE amount is lower than 2%, a perfect PTFE nanoparticle dispersion is obtained. When the amount of PTFE is comprised between 5 and 30%, larger PTFE clusters are obtained that, after melting, coalesce and crystallize at higher temperatures depending on the crystallization propensity of their individual heterogeneous nuclei. Finally, in case of samples 40%, only one crystallization exotherm is observed at 310 °C indicating the formation of very large clusters that after melting coalesce into wide domains.     

Tailored surface free energy of membrane diffusers to minimize microbial adhesion

Biofouling is considered to be the limiting factor of the majority of membrane processes. Since microbial adhesion is a prerequisite for membrane biofouling, prevention of microbial adhesion and colonization on the membrane surfaces will have a major impact in preventing biofouling. In this paper the effects of surface free energies on bacterial adhesion were investigated and the optimum surface free energy of membranes on which bacterial adhesion force is minimal was obtained. A graded nickel–polytetrafluoroethylene (PTFE) composite coating technique was used to tailor the surface free energy of membrane diffusers to the optimum value. Initial experimental results showed that these coatings reduced microbial adhesion by 68–94%.     

Complementary DSC and dilatometric investigation of M-PTFE pyrotechnic compositions

Results of high thermal resolution microcalorimetric and dilatometric measurements performed on reducer — polytetrafluoroethylene (M-PTFE) pyrotechnic compositions have been discussed. The materials were selected for the study because of their behaviour in combustion tests. Two complementary thermal properties, i.e. the specific heat and coefficient of linear thermal expansion (CLTE), have been analysed in detail. The specific heat was obtained from DSC measurements performed from −20 to 375°C. Measurements of CLTE and linear expansion were carried out from −40 to 270°C. In both cases the measurements were performed on thermocycling with the high thermal resolution preserved. A special attention has been paid to a two-stage phase transition occurring just below the room temperature. This revised version was published online in July 2006 with corrections to the Cover Date.