Chapter 2
Separation and Concentration of Anionic Organic Electrolytes by Electrotransport through Polyethylene Films Grafted with Cationic Polymers Kazunori Yamada, Koki Sasaki, and Mitsuo Hirata
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Department of Industrial Chemistry, College of Industrial Technology, Nihon University, Narashino, Chiba 275-8575, Japan
Electrotransport of anionic and neutral phenyl compounds such as benzoic acid (BA), benzenesulfonic acid (BSA), and phenyl-1,2ethanediol (PhED) was studied using polyethylene films photografted with 2-(dimethylamino)ethyl methacrylate (DMAEMA). The BA and BSA permeabilities of DMAEMA-grafted PE (PE-g-PDMAEMA) films were considerably increased by the application of the direct current at pH 6. On the other hand, the permeability of phenyl-1,2-ethanediol (PhED) increased slightly. BA and BSA could be selectively permeated from the respective binary BA/PhED and BSA/PhED mixtures by making use of the difference in the permeabilities between the anionic and neutral phenyl compounds. In addition, anionic phenyl compounds could be concentrated by 1.8 to 1.9 times the initial concentrations by the continuous application of the direct current in the aqueous BA and BSA solution systems.
It is possible to add new properties to polymer substrates by grafting various monomers onto the surfaces or throughout the bulk of the polymeric substrates such as polyethylene (PE) (1-5), polypropylene (PP) (6-9), or poly(tetrafluoroethylene) (PTFE) (10-13) by using U V radiation (1-5), Co y rays (7,10), plasma (6), or electron beam (8,9) as an energy source or by the combined use of the plasma treatment and photografting (11-13). We reported in previous papers (2,3) that the wettabilities and adhesivities of polyethylene (PE) plates were enhanced without affecting any bulk properties by the photograftings of hydrophilic monomers. Furthermore, it was found that the grafted layers formed on the PE substrates could absorb a significant amount of water. When the photograftings of hydrophilic monomers were carried out throughout the bulk of P E films used in place of PE plates, the grafted P E films possessed reasonable mechanical properties in the swollen state (4,14). They are suitable for use in hydrogel systems or functional membranes (5). Among these grafted PE films, 2-(dimethylamino)ethyl methacrylate (DMAEMA) grafted PE (PE-gPDMAEMA) films showed good electrical conductivities and water-absorptivities even at lower grafted amounts (4,14). Generally, polyelectrolytes undergo conformational changes with a change in the environmental conditions such as pH, ionic strength, and electric field of the medium (15,16). Therefore, if such polyelectrolytes are covalently bonded to polymeric films as grafted polymer chains,
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© 1999 American Chemical Society Khan and Harrison; Field Responsive Polymers ACS Symposium Series; American Chemical Society: Washington, DC, 1999.
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17 their permeabilities to neutral and ionic small molecules can be controlled in response to one or more of the above mentioned environmental changes. Our work has been geared toward studying the application of grafted PE films as functional membranes for the separation, concentration, and recovery of anionic and cationic compounds. In fact, many kinds of ionic membranes have been designed for the concentration and selective separation of anionic and canonic compounds by several researchers (17-19). We reported in previous papers that ionic phenyl compounds such as benzoic acid (BA), benzenesulfonic acid (BSA), and paminobenzoic acid could be uphill transported against the concentration gradient by the use of the pH difference across the PE-g-PDMAEMA films. The concentration of each ionic phenyl compound in the acidic side increased by about 1.8 times the initial concentration (20,21). However, it took much longer time to concentrated the concentration of the ionic phenyl compounds against the concentration gradient. Thus, we tried to examine electrotransport properties of PE-g-PDMAEMA films to some anionic phenyl compounds. In this study, the control of permeation of anionic phenyl compounds and their selective separation and concentration by electrotransport were examined using PE-gPDMAEMA films with the aim of applying them to various types of functional membranes. Experimental Section 3
Photografting. A film of P E (thickness = 30 ^m, density = 0.924 g/cm ) supplied from Tamapoly Co., Ltd., in Japan was used as a polymer substrate. D M A E M A was purified by distillation under reduced pressure. Other chemicals were used as supplied. The PE films, cut strips of 6.0 cm length and 3.0 cm width, were dipped for 1 min in a 50 ml of an acetone solution containing 0.25 g benzophenone (BP) as a sensitizer to coat the PE surfaces with BP (1-3). Next, the pH value of an aqueous DMAEMA monomer solution at 1.0 mol/dm was adjusted to 8.0 with concentrated HC1 to prepare PE-g-PDMAEMA films. Photografting of D M A E M A onto the BP-coated PE films was carried out by applying U V rays emitted from a 400 W high pressure mercury lamp to the aqueous D M A E M A monomer solutions adjusted to pH 8 in the Pyrex glass tubes at 60 ^ using a Riko RH400-10W rotary photochemical reactor (4). The grafted amount was calculated from the weight increase of the samples in mmol/g. 3
Permeation Control in Response to the Direct Current. Two platinum mesh electrodes and PE-g-PDMAEMA films swollen in NH4C1/HC1 or NH4Cl/NaOH buffer solutions of pH 4 to 10 housed in the permeation cells were arranged in order of one platinum electrode, the PE-g-PDMAEMA film, and another platinum electrode (22,23). A 100 ml of buffer solution containing BA, BSA. or PhED (concentration = 2.0 mrnoVdm ) was put in one side of the cell and a 100 cnr of the buffer solution in the other side of the cell, and then the direct current was turned on and off in a stepwise manner with stirring. During applying the direct current, 0 . 5 - 2 mol/dm HC1 or NaOH was added to the feed and permeate solutions to keep their initial pH values. The amounts of permeated B A , BSA, and PhED were determined by measuring the absorbance of the aliquots (X = 219 nm for B A and B S A and X = 205 nm for PhED), and then each aliquot was immediately returned to the permeate solution. 3
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Selective Permeation by Electrotransport. The binary mixtures of BA/PhED and BSA/PhED in a NH4C1/HC1 buffer solution of pH 6 (100 cm ) were put in the feed side, and the direct current of 10 mA was applied with stirring. The amounts of two phenyl compounds, designating one phenyl compound as A and another as B, 3
Khan and Harrison; Field Responsive Polymers ACS Symposium Series; American Chemical Society: Washington, DC, 1999.
18 Table I. Determination of the amount of permeated phenyl compounds for the binary BA/PhED and BSA/PhED mixture systems. Binary component
Downloaded by TUFTS UNIV on June 3, 2018 | https://pubs.acs.org Publication Date: August 19, 1999 | doi: 10.1021/bk-1999-0726.ch002
(nm)
loge (dm /molcm)
Xi (nm)
loge (dm /molcm)
3
3
BA/PhED
212
3.76 3.76
219
3.87 3.10
BSA/PhED
