Aquivion membrane displays improved properties as compared to Nafion membrane, partly due to shorter side chains. However, some improvements are still necessary for proton exchange membrane fuel cell to operate at low relative humidity. To overcome this drawback, the addition of clay nanoparticle into the Aquivion matrix can be considered. In this study, different composite membranes have been prepared mixing short-side-chain PFSA (perfluorosulfonic acid) Aquivion and selectively modified halloysite nanotubes for PEMFC low relative humidity operation. Halloysites were grafted with fluorinated groups, sulfonated groups, or perfluoro-sulfonated groups on inner or outer surface of the tubes. The obtained composite membranes showed improved properties, especially higher water uptake associated with reduced swelling and better mechanical strength compared to pristine Aquivion membrane and commercially available Nafion HP used as reference. The best performance in this study was obtained with Aquivion loaded with 5 wt% of pretreated perfluoro-sulfonated halloysite. The composite membrane, referred to as Aq/pHNT-SF5, displayed the largest water uptake and proton conductivity among the panel of membranes tested. The chemical stability was not affected by the presence of halloysite in the Aquivion matrix.
The grafting of phosphorus compounds onto natural fibers has been investigated as a strategy for improving poly(1,4‐butanediol succinate)/flax biocomposite fire behavior. Three phosphorus compounds ? dihydrogen ammonium phosphate, poly(methacryloyloxy)methyl phosphonic acid homopolymer and poly(methacryloyloxy)methyl phosphonic acid methylmethacrylate copolymer ? were selected. The aim of this work was to compare the fire performance conferred by the grafted compounds depending on whether phosphorus is brought by a molecule or a macromolecule. TGA, pyrolysis combustion flow calorimetry and cone calorimetry were used to characterize the thermal stability and fire behavior of the samples. The pyrolysis combustion flow calorimetry results showed that in all cases the presence of phosphorus changes the degradation pathway and thus the flammability properties of flax. The ability of the grafted flame retardant to promote char formation and residue formation was found to be dependent on the nature and quantity of phosphorus covalently bonded to flax. Conversely, cone calorimeter tests revealed similar fire behavior whatever the grafting agent. A significant increase of the char amount and a global enhancement of fire parameters were observed with increasing grafting rate. Moreover, phosphonated polymers promoted a charred sheath around the fibers which acts in addition to their charring, conferring a fire performance close to that of dihydrogen ammonium phosphate for the biocomposite. 相似文献
The present work is based on the Van Krevelen’s approach proposed by Lyon et al. [1] to determine the relationships between the molecular structure and the flammability of molecules using Microscale Combustion Calorimeter (MCC). Via this approach, the contributions to Heat Release Capacity (HRC) and Total Heat Release (THR) were successfully calculated for two phosphorus-containing groups: phosphonate and dioxaphosphorinane. We showed that the Van Krevelen’s approach was invalid when the molecules contain both phosphorus and ester or acid groups. We hypothesized that these functions interact between them during the thermal decomposition. In this study we propose to calculate “Interaction Indexes” to estimate the level of interactions according to the chemical structure. The results enable to draw first conclusions about the best chemical architecture for lowering flammability. 相似文献
The synthesis of isocyanate free polyurethanes is a major concern. This paper first reports the synthesis of new biobased isosorbide dicyclocarbonates from isosorbide. Then polyhydroxyurethanes (PHUs) were synthesized by a cyclocarbonate–amine step growth polyaddition with four commercial diamines (e.g. jeffamine D-400, 1,10 diaminodecane, diethylenetriamine and isophoronediamine). These unprecedented products, obtained with high yield, were characterized by 1H NMR, FTIR, DSC, SEC and TGA analyses. PHUs exhibited glass transition temperatures from ?8 °C to 59 °C, and degradation temperatures (Td 5%) between 234 °C and 255 °C. Last but not least, the compounds produced during the degradation of these PHUs were analyzed by ATG-IR technique and showed that carbon dioxide and secondary amines are released. 相似文献