Mohamed Mahmoud Nasef

Radiation-induced grafting of styrene onto poly(tetrafluoroethylene) (PTFE) films. I. Effect of grafting conditions and properties of the grafted films

Radiation-induced grafting of styrene onto poly(tetrafluoroethylene) (PTFE) films was studied by a simultaneous irradiation technique. Grafting was carried out using g-radiation from a 60 Co source at dose rates of 1.32-15.0 kGy h ˇ1 at room temperature. The effects of type of diluent, dose rate, irradiation dose, and the initial monomer concentration in the grafting solution on the degree of grafting were investigated. The degree of grafting was found to be strongly dependent upon the grafting conditions. The dependence of the initial rate of grafting on the dose rate and the initial monomer concentration in the grafting solution was found to be in the order of 0.6 and 1.7, respectively. The chemical structure and the crystallinity of the grafted PTFE films were studied by means of Fourier- transform infrared, (FTIR), electron spectroscopy for chemical analysis (ESCA) and X-ray diffractometry (XRD). # 2000 Society of Chemical Industry

Preparation of crosslinked cation exchange membranes by radiation grafting of styrene/divinylbenzene mixtures onto PFA films

Crosslinked cation exchange membranes bearing sulfonic acid groups were prepared by radiation-induced grafting of styrene containing 2 and 4% divinylbenzene (DVB) onto poly(tetrafluoroethylene-co-perfluorovinyl ether) (PFA) films followed by sulfonation reactions. The degree of grafting was found to be dependent on the grafting parameters including irradiation time and DVB concentration in the bulk solution. The physico-chemical properties of the membranes such as ion exchange capacity, water uptake and ionic conductivity were evaluated in correlation with the degree of grafting and the level of crosslinking. All the properties of the membranes were found to be functions of the degree of grafting. However, crosslinking of polystyrene grafts with DVB was found to considerably reduce the water uptake and the ionic conductivity of the membranes while showing no effect on the ion exchange capacity. The thermal stability of the membranes represented by desulfonation temperature was found to be independent of crosslinking. Membranes having degrees of grafting of 24% (0% DVB), 24% (2% DVB) and 17% (4% DVB) possess good combinations of physico-chemical properties and can be of practical interest.

Cation exchange membranes by radiation‐induced graft copolymerization of styrene onto PFA copolymer films. II. Characterization of sulfonated graft copolymer membranes

PFA-g-polystyrene sulfonic acid membranes were prepared by simultaneous radiation-induced graft copolymerization of styrene onto poly(tetrafluoroethylene- co-perfluorovinyl ether) (PFA) film followed by sulfonation. The membrane physicochemical properties such as swelling behavior, ion exchange capacity, hydration number, and ionic conductivity were studied as a function of the degree of grafting. Thermal as well as chemical stability of the membranes was also investigated. The membrane properties were found to be mainly dependent upon the degree of grafting. The water uptake, ion exchange capacity, hydration number, and ionic conductivity of the membranes were increased, whereas the chemical stability decreased as the degree of grafting increased. The membranes showed reasonable physico-chemical properties compared to Nafion 117 membranes. However, their chemical stability has to be further improved to make them acceptable for practical use in electrochemical applications.

Proton exchange membranes prepared by simultaneous radiation grafting of styrene onto poly(tetrafluoroethylene-co-hexafluoropropylene) films. I. Effect of grafting conditions

The simultaneous radiation grafting of styrene onto poly(tetrafluoroethylene- co-hexafluoropropylene) (FEP) films was studied at room temperature. The effects of grafting conditions (type of solvent, irradiation dose, dose rate, and monomer concentration) were investigated. The degree of grafting was found to be dependent on the investigated grafting conditions. The dependence of the initial rate of grafting on the dose rate and the monomer concentration was found to be of 0.5 and 1.3 orders, respectively. The results suggest that grafting proceeds by the so-called front mechanism in which the grafting front starts at the surface of the film and moves internally toward the middle of the film by successive diffusion of styrene through the grafted layers. Some selected properties of the grafted films were evaluated in correlation with the degree of grafting. We found that the grafted FEP films possess good mechanical stability, which encourages their use for the preparation of proton exchange membranes.

Cation exchange membranes by radiation-induced graft copolymerization of styrene onto PFA copolymer films. I. Preparation and characterization of the graft copolymer

PFA-g-polystyrene graft copolymers were prepared by simultaneous radiation- induced graft copolymerization of styrene onto poly(tetrafluoroethylene-co-perfluorovinyl ether) (PFA) films. The effects of grafting conditions such as monomer concentration, dose, and dose rate were investigated. Three solvents, i.e., methanol, benzene, and dichloromethane, were used as diluents in this grafting system. Of the three solvents employed, dichloromethane was found to greatly enhance the grafting process, and the degree of grafting increased with the increase of monomer concentration until it reached its highest value at a styrene concentration of 60 (vol %). The dependence of the initial rate of grafting on the monomer concentration was found to be of the order of 1.2. The degree of grafting was found to increase with the increase in irradiation dose, while it considerably decreased with the increase in dose rate. The formation of graft copolymers was confirmed by FTIR analysis. The structural investigation by X-ray diffraction (XRD) shows that the degree of crystallinity content of such graft copolymers decreases with the increase in grafting, and consequently, the mechanical properties of the graft copolymers were influenced to some extent. Both tensile strength and elongation percent decreased with the increase in the degree of grafting.

Proton exchange membranes prepared by simultaneous radiation grafting of styrene onto poly(tetrafluoroethylene-co-hexafluoropropylene) films. II. Properties of sulfonated membranes

Proton exchange membranes were prepared by radiation-induced grafting of styrene onto commercial poly(tetrafluoroethylene-co-hexafluoropropylene) films using a simultaneous irradiation technique followed by a sulfonation reaction. The resulting membranes were characterized by measuring their physicochemical properties such as water uptake, ion exchange capacity, hydration number, and proton conductivity as a function of the degree of grafting. The thermal properties (melting and glass transition temperatures) and thermal stability of the membrane were also investigated using differential scanning calorimetry and thermal gravimetric analysis, respectively. Membranes having degrees of grafting of 16%and above showed proton conductivity of the magnitude of 1022 V21 cm21 at room temperature, as well as thermal stability at up to 290°C under an oxygen atmosphere.

XPS studies of radiation grafted PTFE-g-polystyrene sulfonic acid membranes

Structural investigations of PTFE-g-polystyrene sulfonic acid membranes prepared by radiation grafting of styrene onto PTFE were conducted by X-ray photoelectron spectroscopy (XPS). The analyzed materials included original PTFE film as a reference material, grafted film, and sulfonated membrane samples having various degrees of grafting. Interest is focused on C1s, F1s, O1s, and S2p of narrow XPS spectra as the basic elemental components of the membrane. The original PTFE film was found to undergo structural changes in terms of chemical composition and shifting in binding energy induced by incorporation of sulfonated polystyrene grafts, and the amount of such changes depends on the degree of grafting. The atomic ratio of F/C was found to decrease with the increase in the degree of grafting, while that for S/C and O/C were found to increase.

Thermal stability of radiation grafted PTFE-g-polystyrene sulfonic acid membranes

The thermal stability of radiation grafted PTFE-g-polystyrene sulfonic acid obtained by grafting of styrene onto PTFE films followed by sulfonation was studied using thermal gravimetric analysis (TGA) and oven heat treatment under nitrogen atmosphere. The TGA results were analyzed in correlation with the membrane two-step preparation procedure and the variation of the degree of grafting. The membranes were found to undergo a three-step degradation pattern due to dehydration, desulfonation, and decomposition of the PTFE matrix. The effect of desulfonation on some physico-chemical properties of the membranes such as ion exchange capacity and water uptake was investigated with respect to the degree of grafting , the temperature and the time of heat treatment.

Thermal degradation behaviour of radiation grafted FEP-g-polystyrene sulfonic acid membranes

The thermal degradation behaviour and the gaseous products of FEP-g-polystyrene sulfonic acid membranes prepared by radiation-induced grafting of styrene onto poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) films and the subsequent sulfonation were studied using thermal gravimetric analysis coupled with Fourier transform infrared spectrometry (TGA/FTIR). The membranes were found to have a three-step degradation behaviour due to water removal, elimination of sulfonic acid groups and decomposition of the FEP matrix. The evolving gaseous products were identified using FTIR analysis. The degree of grafting was found to have a strong effect on the weight loss in the membranes, whilst the degradation temperatures of the individual membrane components were shown to be independent of the degree of grafting.

The Preparation and Characterization of Chitosan / Poly (Vinyl Alcohol) Blended Films

In this study, chitosan and PVA were blended at different proportions (considering chitosan as the main component) in solution forms. The chemical structure and the morphology of the obtained blend films were investigated using FTIR and field emission scanning electron microscope (FESEM). The thermal stability of the blend films were also studied using thermal gravimetric analysis (TGA). Our results showed that chitosan and PVA form a compatible blend and their films displayed homogenous and smooth surface properties compared to their individual pure components. The blending of PVA with chitosan at all proportions was found to highly enhance the swelling of the obtained films compared to that of pure chitosan one.