Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) nanocomposites with different contents of nanoclays were prepared by melt mixing. The clays used included unmodified clays, a commercially available hydrophilic nanoclay based on bentonite (nanoclay 1) and organically modified clay based on montmorillonite (nanoclay 2). The nanocomposites obtained were analyzed by x-ray diffraction, differential thermal and differential scanning calorimetry analyses and their basic tensile and other characteristics were determined. The distribution of the filler throughout the matrix was found to be good for both the types of nanocomposite materials. Nanoclay 1 induced slight increase in the b-phase and higher deviation of the main diffractions (2 ¼ 18.6 and 20.1 at 10 mass% filler). The degree of crystallinity of the materials containing nanoclay 2 decreased from 26.4 to 20.5% and from 23.9 to 18.7%, respectively, for the first and second heating. The tensile strength of the materials based on PVDF-HFP with nanoclays 1 and 2 was close to that of the initial copolymer or slightly increased with the addition of nanoclay 2. Young's modulus was in the range of 215-265 MPa. The heat resistance by Vicat increased by 7 C compared with the initial copolymer.
SYNOPSISSome properties of the ion-exchange membranes prepared by simultaneous and preirradiation techniques of grafting of acrylic acid onto tetrafluoroethylene-ethylene copolymer films, including porous microfilters, have been studied. The water content, electric resistance, transport number, distribution of grafting, thermal and chemical stability, and mechanical characteristics of the membranes were determined as a function of the grafting degree. Graft polymerization proceeds from both surfaces of the polymer film into the polymeric matrix depth. Cation-exchange membranes prepared possess good electrochemical and mechanical properties, high thermal and chemical stability a t grafting degrees from 30 to 50%, and can be successfully used in electrodialysis processes.
INTRODUCTIONThe interest toward synthetic membranes and membrane processes is growing rapidly nowadays. During the last 20 or 30 years, membranes have been increasingly employed in various fields as effective means for separation of molecular mixtures.Fluoro-containing polymers have drawn the attention of the researchers for their excellent mechanical properties and thermal and chemical stabilities. By using simultaneous and preirradiation techniques, the grafting of acrylic acid ( AAc ) mainly onto polytetrafluoroethylene ( PTFE ) and tetrafluoroethylene-hexafluoropropene copolymers (TFE-HFP ) was studied and cation-exchange membranes (CEM) were Although partly fluorinated polymers like tetrafluoroethyleneethylene copolymers (TFE-E) exhibit good properties similar to those of PTFE and offer some advantages in their p r o c e~s i n g ,~~~ grafting onto them to prepare ion-exchange membranes has not been studied thoroughly yet. Ellinghorst et al.lOsll used an electron-beam accelerator and preirradiation grafting method in vacuum to obtain ion-exchange membranes by grafting various hydrophilic monomers onto a substrate of partly fluorinated polymers and copolymers, including TFE-E copolymers. Based on TFE-E copolymer fibers, by using an electron-beam accelerator and preirradiation grafting method, acrylamide was grafted to prepare ion-exchange material possessing selectivity toward some metal cations.12In our previous work, the effect of AAc grafting conditions (monomer concentration, dose rate, film thickness, etc.) on the degree of grafting of TFE-E copolymers ( TFE-E-gAAc) at TFE content 52.8 mol ?& was ~tudied.'~ Both the simultaneous and the preirradiation grafting techniques were employed. In this paper, the water content and the electrochemical, mechanical, and other properties of the grafted TFE-E films were studied to examine the possibilities for their practical application as ionexchange membranes. The TFE-E-gAAc grafted films were prepared by a simultaneous method by using a 6oCo facility and 1269
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1270KOSTOV AND ATANASSOV repeated grafting (exposition 5 h and postpolymerization time 19 h each for 5 days). The preirradiation method in air, using a Cockroft-Walton electronbeam accelerator, was also employed. The degree of AAc ...
Nanocomposite materials based on vinylidene fluoride-hexafluoropropylene copolymer and organically modified montmorillonite Cloisite ® 15A were prepared by two different methods: melt mixing and co-precipitation. The changes taking place in crystalline structure, tensile strength, thermal behavior and the formation of piezoelectric β -phase as a result of the polymer system dissolution in dimethyl sulfoxide were studied. The technological specificity of each method has certain effect on the properties of the obtained nanocomposites. The highest content of β -phase -95 % was achieved by co-precipitation from the solution of vinylidene fluoride-hexafluoropropylene copolymer in dimethyl sulfoxide and 6 mass % content of Cloisite ® 15A. Despite the common view that the use of solvents and prolonged technological procedure lead to overall higher expenses, the obtained nanocomposites could be promising for the preparation of new piezo-materials.
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