Radiation-induced Grafting Of Styrene Research Articles

Radiation-Induced Grafting of Styrene onto Polyvinylfluoride (PVF) Films: Impact of Grafting Conditions on Grafted Film Properties

Radiation-Induced Grafting of Styrene onto Polyvinylfluoride (PVF) Films: Impact of Grafting Conditions on Grafted Film Properties

Radiation-induced Grafting of Styrene onto Polyethylene Films for Preparation of Cation Exchange Membranes: Effect of Crosslinking+

Crosslinked cation exchange membranes bearing sulfonic acid groups (PE-g-PSSA/DVB) were prepared by radiationinduced grafting of styrene/divinylbenzene (DVB) mixtures onto low density polyethylene (PE) films followed by sulfonation reactions. The effect of addition of DVB (2 and 4%) on the grafting behavior and the physico-chemical properties of the membranes such as ion exchange capacity, swelling and ionic conductivity were evaluated incorrelation with grafting yield (Y%). The structural and thermal properties of the membranes were also studied using differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA), respectively. Crosslinking with DVB was found to considerably affect the properties of the membranes in a way that reduces the swelling properties and enhances the chemical stability. The ion conductivity of the crosslinked membranes recorded a level of 10–2 S/cm at sufficient grafting yield (28%) despite the reduction caused by the formation of crosslinking structure. The results of this work suggest that membranes prepared in this study are potential alternatives for various electrochemical applications.

Pulse radiolysis investigation of · OH and · H radicals initiated degradation reaction of sulfonated aromatics as model compounds for proton exchange membrane

In order to predict ·OH and ·H radicals initiated degradation of proton exchange membrane (PEM) based on polymers obtained by radiation-induced grafting of styrene or α-methylstyrene on different polyolefin, isopropyl benzene sulfonic acid (IPBS) and tert-butyl benzene sulfonic acid (TBBS) were taken as model compounds for PEM with and without α-H, respectively. Results indicated that ·OH radicals played a vital role in PEM degradation. Eighty-nine percent of ·OH radicals reacted with IPBS to form benzylic radicals by electron transfer and subsequent deprotonation reactions. Benzylic radicals can react with O2 to form peroxyl radicals, which leads to PEM degradation. TBBS, without α-H, reacted with ·OH or ·H radicals, benzylic radicals would not be generated, and only adducts were formed. Adducts have less influence on the stability of TBBS than benzylic radicals. In this work, we elucidated that PEM, without α-H, with similar structures to TBBS, had a stronger resistance to oxidative degradation than PEM with α-H, with similar structures to IPBS.

Solvent effect on post-irradiation grafting of styrene onto poly(ethylene-alt-tetrafluoroethylene) (ETFE) films

Radiation-induced grafting of styrene onto ETFE films in different solvent was investigated after simultaneous irradiation (in post-irradiation condition) using a 60Co source. Grafting of styrene followed by sulfonation onto poly(ethylene-alt-tetrafluoroethylene) (ETFE) are currently studied for synthesis of ion exchange membranes. The ETFE films were immersed in styrene/toluene, styrene/methanol and styrene/isopropyl alcohol and irradiated at 20 and 100kGy doses at room temperature. The post-irradiation time was established at 14day and the grafting degree was evaluated. The grafted films were sulfonated using chlorosulfonic acid and 1,2-dichloroethane 20:80 (v/v) at room temperature for 5h. The degree of grafting (DOG) was determined gravimetrically and physical or chemical changes were evaluated by differential scanning calorimeter analysis (DSC), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The ion exchange capacity (IEC) values showed the best performance of sulfonation for ETFE membranes grafted in toluene solvent. Surface images of the grafted films by SEM technique have presented a strong effect of the solvents on the films morphology.

Radiation-induced grafting of styrene into poly(vinylidene fluoride) film by simultaneous method with two different solvents

Radiation-induced grafting of styrene into poly(vinylidene fluoride) (PVDF) films with 0.125mm thickness at doses of 1 and 2.5kGy in the presence of a styrene/N,N-dimethylformamide (DMF) solution (1:1, v/v) and at doses of 20, 40 and 80kGy in presence of a styrene/toluene solution (1:1, v/v) at dose rate of 5kGyh−1 was carried out by the simultaneous method under nitrogen atmosphere and room temperature, using gamma rays from a Co-60. The films were characterized before and after modification by calculated grafting yield (GY %), infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and thermogravimetry (TG/DTG). GY results shows that grafting increases with dose, and the grafting of styrene was confirm by FT-IR due to the new characteristic peaks and by the TG and DSC attributed to changes in thermal behavior of the grafted material. Results showed that the system allows the controlled grafting of styrene into PVDF using gamma rays at doses as low as 1kGy in DMF.

Radiation synthesis and Cr(VI) removal of cellulose microsphere adsorbent

A novel cellulose-based adsorbent was prepared by radiation-induced grafting of styrene onto the surface of cellulose microspheres, followed by acetylation and amination processes. The grafting yield was adjusted by the total absorbed dose, dose rate and the concentration of styrene. The structure of the adsorbent was characterized by micro-FTIR, XPS and SEM. The adsorption of Cr(VI) ions has been investigated as a function of contact time, adsorbent feed, pH, Cr(VI) and NaCl concentration. It was found that adsorption equilibrium could be achieved within 30 min for initial Cr(VI) of 100 mg L−1. The adsorption kinetics was well described by the pseudo-second order model equation, and the adsorption isotherm was better fitted by the Langmuir mode. The maximum theoretical Cr(VI) uptake of the adsorbent was 123.4 mg g−1. The influence of NaCl concentration on Cr(VI) uptake and XPS analysis revealed that Cr(VI) ions were adsorbed through ion-exchange mechanism.

Post-irradiation time effects on the graft of poly(ethylene-alt-tetrafluoroethylene) (ETFE) films for ion exchange membrane application

Grafting of styrene followed by sulfonation onto poly(ethylene-alt-tetrafluoroethylene) (ETFE) was studied for synthesis of ion exchange membranes. Radiation-induced grafting of styrene onto ETFE films was investigated after simultaneous irradiation (in post-irradiation condition) using a 60Co source. The ETFE films were irradiated at 20 kGy dose at room temperature and chemical changes were monitored after contact with styrene for grafting. The post-irradiation time was established at 14 days when the films were remained in styrene/toluene 1:1 v/v. After this period the grafting degree was evaluated in the samples. The grafted films were sulfonated using chlorosulfonic acid and 1, 2-dichloroethane 20:80 (v/v) at room temperature for 5 h. The membranes were analyzed by infrared spectroscopy (FTIR), differential scanning calorimeter (DSC), thermogravimetric measurements (TG) and degree of grafting (DOG). The ion exchange capacity (IEC) of membranes was determined by acid–base titration and the values for ETFE membranes were achieved higher than Nafion ® films. Preliminary single cell performance was made using pure H 2 and O 2 as reactants at a cell temperature of 80 °C and atmospheric gas pressure. The fuel cell performance of ETFE films was satisfactory when compared to state-of-art Nafion ® membranes.

Radiation-induced grafting of styrene onto ultra-high molecular weight polyethylene powder for polymer electrolyte fuel cell application: II. Sulfonation and characterization

Post-sulfonation of selective styrene-grafted ultra-high molecular weight polyethylene (UHMWPE-g-PS) films was carried out by chlorosulfonic acid and the properties of the membranes were investigated. The UHMWPE-g-PS films were previously prepared by initial γ-irradiation of polyethylene powder, grafting with styrene, followed by hot-pressing to process into films. The range of ion exchange capacities ( IECs) obtained with different degrees of grafting ( DG) of styrene was in the range of 0.97–2.77 mequiv./g. The water and methanol uptake of sulfonated films were studied on a weight and volume basis. FTIR spectroscopy and thermal gravimetric analysis (TGA) of control UHMWPE, UHMWPE-g-PS, and UHMWPE-g-PSSA were compared. The methanol permeability values at 30 °C for the series of UHMWPE-g-PSSA membranes were in the range 4.86 × 10 −8 to 1.67 × 10 −6 cm 2/s, with corresponding proton conductivities of 0.025–0.29 S/cm at 90 °C. The methanol permeability values of UHMWPE-g-PSSA were generally lower than that of Nafion 117 for comparable or even higher proton conductivity. Transmission electron microscopy (TEM) analysis was used to observe microstructure for evidence of nanophase separation of hydrophilic and hydrophobic domains. Owing to its low cost and the results of the current study, UHMWPE-g-PSSA is suggested as a viable proton exchange membrane for low temperature hydrogen and direct methanol fuel cell applications.

Thermal stability of proton exchange fuel-cell membranes based on crosslinked-polytetrafluoroethylene for membrane-electrode assembly preparation

We investigated thermal properties of proton exchange membranes (PEMs) prepared by the radiation-induced grafting of styrene into crosslinked-polytetrafluoroethylene films and the subsequent sulfonation for fuel-cell applications. A conventional thermogravimetric analysis was found to be unreliable because the resulting curve varied greatly with the heating rate. Thus, in order to obtain accurate information, we performed an ex-situ heat-treatment analysis, which involved heating of the PEMs at fixed temperatures of 200–350 °C and measurement of their remaining weight, ion exchange capacity (IEC) and proton conductivity ( σ) after washing in pure water. The IEC and σ did not change at any temperature up to 200 °C, indicating high thermal stability. At 250 °C, however, the PEM properties deteriorated probably via radical cleavage of the C–S bond between a sulfonic acid group and an aromatic ring, and condensation of two sulfonic acid groups. Finally, the PEM was hot-pressed with two electrodes at 200 °C to produce a good membrane-electrode assembly for a fuel cell.

Radiation-induced grafting of styrene onto ultra-high molecular weight polyethylene powder and subsequent film fabrication for application as polymer electrolyte membranes: I. Influence of grafting conditions

Ultra-high molecular weight polyethylene (UHMWPE) powder was irradiated by gamma rays using a 60Co source. Simultaneous and pre-irradiation grafting was performed in air and in inert atmosphere at room temperature. The monomer selected for grafting was styrene, since the styrene-grafted UHMWPE could be readily post-sulfonated to afford proton exchange membranes (PEMs). The effect of absorbed radiation dose and monomer concentration in methanol on the degree of grafting (DG) is discussed. It was found that the DG increases linearly with increase in the absorbed dose, grafting time and monomer concentration, reaching a maximum at a certain level. The order of rate dependence of grafting on monomer concentration was found to be 2.32. Furthermore, the apparent activation energy, calculated by plotting the Arrhenius curve, was 11.5 kJ/mole. Lower activation energy and high rate dependence on monomer concentration shows the facilitation of grafting onto powder substrate compared with film. The particle size of UHMWPE powder was measured before and after grafting and found to increase linearly with increase in level of grafting. FTIR-ATR analysis confirmed the styrene grafting. The grafted UHMWPE powder was then fabricated into film and post-sulfonated using chlorosulfonic acid for the purposes of evaluating the products as inexpensive PEM materials for fuel cells. The relationship of DG with degree of substitution (DS) of styrene per UHMWPE repeat unit and ion exchange capacity (IEC) is also presented.

Improvement of polymer electrolyte membrane by radiation-induced grafting of styrene onto FEP film with subsequent sulfonation

Poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) film was homogeneously and highly grafted by styrene monomer under simultaneous irradiation with an electron beam, whereas preirradiation with an electron beam was insufficient to accomplish a high degree of grafting without activation of the styrene monomer. Following its subsequent sulfonation, the styrene-grafted FEP film exhibited considerably higher values of both the IEC and IC and less methanol crossover than the Nafion membrane. The grafting of styrene onto the FEP polymer is thought to be initiated by the abstraction of F atoms from the CF3 groups in the polymeric structure. It was estimated that two sulfonic acid groups can be attached to the benzene ring of one styrene molecule. The profile of sulfur across the FEP film, which is related to the concentration profile of sulfonic acid groups inside the styrene-grafted FEP film, became more and more homogeneous over a period of several hours, due to the step by step diffusion of monomers into the film, eventually showing a high IC value of 0.25 S/cm in the case of the 125 μm thick FEP film, whereas Nafion 117 (125 μm thickness) exhibited an IC value of 0.12 S/cm.

Preparation and characterization of a strong basic anion exchanger by radiation-induced grafting of styrene onto poly(tetrafluoroethylene) fiber

A novel anion-exchange fiber with strong basic groups has been prepared by grafting styrene onto poly(tetrafluoroethylene) fibers via irradiation. Experiments were carried out to analyze the effects of synthesis conditions on the grafting degree and to characterize the physicochemical properties of the anion-exchange fibers. The experimental results showed that preirradiation grafting styrene onto poly(tetrafluoroethylene) fiber could significantly reduce the waste of raw material and the formation of homopolymer, although the grafting degree was relatively low. The grafting reaction could be effectively enhanced through the addition of magnesium powder into the reaction system. The optimal temperature and time for preirradiation grafting were 80 °C and 6 h, respectively. The experimental results also showed that the anion-exchange fibers had excellent mechanical properties and thermal stability at a temperature up to 420 °C. The fibers were stable in acidic, alkali, and oxidative solutions. The static ion-exchange capacity of the fibers was as high as 6.08 mmol/g. The static adsorption capacities for Cr 2O 2− 7 and MnO − 4 ions were 214.08 and 290.98 mg/g, respectively.

The influence of crosslinker on the properties of radiation-grafted films and membranes based on ETFE

Crosslinked proton-exchange membranes were prepared by radiation-induced grafting of styrene into poly(ethylene- alt-tetrafluoroethylene) (ETFE) and subsequent sulfonation. The influence of the crosslinker, divinylbenzene (DVB), on various film and membrane properties was investigated in detail. A series of grafted films and membranes were prepared at varying DVB concentrations at a fixed graft level (∼25%) for this purpose. Grafting kinetics and kinetic parameters, including initial polymerization rate ( r po), radical recombination rate ( γ) and delay time ( t 0) at different DVB concentrations were evaluated. Moreover, resultant grafted films and membranes have been characterized with respect to their dimensional stability, chemical composition, thermal stability, crystallinity and fuel cell relevant properties. The concentration of crosslinker in the initial grafting solution was found to influence crucially the grafting reaction and graft levels. Dimensional increase, considerable especially after sulfonation, can be controlled by the introduction of DVB. Furthermore, the FTIR-ATR measurements exhibited that the grafted films were highly crosslinked within the surface near as compared to the entire bulk region. The influence of DVB on the crystallinity and thermal stability was not significant. On the contrary, the water uptake and proton conductivity of the membranes decreased substantially, while the IEC decreased slightly with increasing DVB concentration.

Influence of reaction parameters on grafting of styrene into poly(ethylene- alt-tetrafluoroethylene) films

This study concerns the investigation of the effect of reaction conditions on the radiation-induced grafting of styrene into poly(ethylene- alt-tetrafluoroethylene) base film. Grafting was obtained by the pre-irradiation method, using styrene in isopropanol/water mixture. The influence of irradiation and reaction conditions, such as irradiation dose, monomer concentration, water content of the grafting solution and reaction temperature on the grafting yield was investigated. The grafting kinetics in terms of initial polymerization rate ( r p0), radical recombination rate ( γ) and delay time ( t 0) was evaluated. It was found that the rate and the extent of grafting were strongly dependent on the grafting conditions. The order of dependence of the rate of grafting was found to be 0.46, 1.5 and 0.62 for pre-irradiation dose, monomer concentration and water content in the grafting mixture, respectively. The activation energy was determined to be 98.4 kJ/mol for the temperature range of 50–80 °C. The use of kinetic equations for the polymerization gives a useful description of the grafting process. It was determined that the initial polymerization rate and the radical recombination rate vary significantly with reaction conditions. The delay time is dependent mainly on irradiation dose and to some extent on monomer concentration.

Radiation synthesis and characteristics of PTFE- g-PSSA ion exchange membrane applied in vanadium redox battery

Radiation-induced grafting of styrene onto polytetrafluoroethylene (PTFE) membranes was studied by a simultaneous irradiation technique. Grafting was carried out using γ - radiation from a 60Co source at room temperature. Effects of absorbed dose, atmosphere, dose rate, and the concentration of initial monomer on the degree of grafting ( DOG) were investigated and the most appropriate grafting condition was obtained. Subsequently, sulphonation of the grafted PTFE membrane (PTFE- g-PS) was carried out and a series of ion exchange membranes (PTFE- g-PSSA) was prepared. Further characterizations of FTIR, TGA, and SEM testified that grafting and sulphonation of the membranes were successfully processed; moreover, grafting of styrene not only occurred in the surface of PTFE membrane, but also in the micropores of the membrane. Ion exchange capacity ( IEC) and conductivity were found increase with the grafting yield. The results suggest that at a low dose, such as 17 kGy, the ion exchange membrane (IEM) which will be suitable for vanadium redox battery (VRB) use can be obtained.

Copolymerization of Styrene onto Polyethersulfone Films Induced By Gamma Ray Irradiation

Radiation-induced grafting of styrene into polyethersulfone (PES) films were investigated by simultaneous method in solution using gamma-ray from a radio nuclide 60Co source. The starting materials were prepared via casting method of the polymeric solution. The grafted membranes have side chains of polystyrene which may be sulfonated to become proton conductive to be used as polymer electrolyte membrane in fuel cell. The localized energy of high intensity gamma-ray induced breaking of chemical bonds leads to free radical formation, a reactive species having a single unpaired electron. The radical start a conventional polymerization sequence comparable with that obtained with a chemical catalyst acting as initiator. The effects of grafting conditions include monomer concentration, irradiation total dose, dose rate and addition of cross linking agent, were studied by means of the techniques of structure analysis, morphology, thermal degradation and crystallinity. The degree of grafting (DOG) was analyzed by percentage of the weight increase. As a result, the reaction always follows the same pattern: DOG increases rapidly initially whilst propagation is the main reaction, then more slowly as termination becomes more frequent.

Structural, thermal and ion transport properties of radiation grafted lithium conductive polymer electrolytes

Structural, thermal and ion transport properties of lithium conductive polymer electrolytes prepared by radiation-induced grafting of styrene onto poly(vinylidene fluoride) (PVDF) films and subsequent activation with LiPH 6/EC/DEC liquid electrolyte were investigated in correlation with the content of the grafted polystyrene ( Y%). The changes in the structure were studied using Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). Thermal gravimetric analysis (TGA) was used to evaluate the thermal stability. The ionic conductivity was measured by means of ac impedance spectroscopy at various temperatures. The polymer electrolytes were found to undergo considerable structural and morphological changes that resulted in a noticeable increase in their ionic conductivity with the increase in Y% at various temperatures (25–65 °C). The ionic conductivity achieved a value of 1.61 × 10 −3 S cm −1 when Y of the polymer electrolyte reached 50% and at 25 °C. The polymer electrolytes also showed a multi-step degradation behaviour and thermal stability up to 120 °C, which suits normal lithium battery operation temperature range. The overall results of this work suggest that the structural changes took place in PVDF matrix during the preparation of these polymer electrolytes have a strong impact on their various properties.

Preparation of PFA-g-polystyrene sulfonic acid membranes by the γ-radiation grafting of styrene onto PFA films

Poly(tetrafluoroethylene-co-perfluorovinylether)-g-polystyrene sulfonic acid (PFA-g-PSSA) membranes were prepared by radiation-induced grafting of styrene onto PFA films using a simultaneous irradiation technique and a subsequent sulfonation in a chlorosulfonic acid/dichloroethane mixture. The PFA films were exposed to γ irradiation doses of 50–200 kGy at a dose rate of 10 kGy/h. The physico-chemical properties of the PFA-g-PSSA membranes such as the degree of grafting, ion exchange capacity, water uptake and tensile strength were evaluated. The structure variations after the grafting and sulfonation were investigated using FTIR-ATR spectroscopy. Differential scanning calorimetry and thermogravimetric analysis have been used to study the thermal decomposition and the melting behavior of the grafted PFA films. The as-prepared PFA-g-PSSA membranes in this work showed a good combination of a high ion exchange capacity (1.8–3.25 meq/g), acceptable water uptake (40–70 wt%), low thickness and volume expansion and/or contraction.

Structure-property Relationships in Radiation Grafted Poly(tetrafluoroethylene)-graft-polystyrene Sulfonic Acid Membranes

Structure-property relationships in poly(tetrafluoroethylene)-graft-polystyrene sulfonic acid (PTFE-g-PSSA) membranes prepared by radiation-induced grafting of styrene onto poly(tetrafluoroethylene) (PTFE) films using simultaneous radiation-induced grafting followed by sulfonation reaction were established. The physico-chemical properties of the membranes such as ion exchange capacity, swelling and ionic conductivity were correlated with the degree of grafting and the structural changes taking place in the membrane matrix during the preparation procedure. The variation in the crystallinity of membranes was studied by differential scanning calorimetry (DSC). The membranes thermal stability was evaluated using thermogravimetric analysis (TGA) and the effect of the heat treatment on the ion exchange capacity and the water uptake was investigated. The membranes were found to undergo substantial structural changes in the form of ionic sites increase, hydrophilicity enhancement, hydrophobicity reduction and crystallinity decrease with the increase in the degree of grafting. These structural changes were found to have a collective effect on the physico-chemical properties of the membranes but their relative contribution depends on the degree of grafting.

Radiation-induced grafting of styrene into radiation-modified fluoropolymer films

Poly(tetrafluoroethylene) (PTFE), poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) and poly(tetrafluoroethylene-co-perfluoropropylvinyl ether) (PFA) films were modified by electron beam irradiation in the molten state. These radiation-modified films and original films were irradiated in vacuum at room temperature to initiate the grafting of styrene in the subsequent step. The grafting of styrene into the fluoropolymer films was proved by FT-IR spectroscopy. The influence of cross-linking dose, grafting dose and grafting time on the yield of grafting was studied. The yield of grafting can be enhanced by the pre-irradiation of the films in the molten state. The change in the geometric dimension of the films caused by grafting was also measured and discussed. The grafted PTFE films were sulfonated by chlorosulfonic acid. The molar ratio of sulfonic acid groups to styrene units was found to be close to unity.