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A Study of Ralex Membrane Morphology by SEM

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A Study of Ralex Membrane Morphology by SEM

Elmara M Akberova et al. Membranes (Basel).

Abstract

A comparative analysis of the effect of the manufacturing technology of heterogeneousion-exchange membranes Ralex CM Pes manufactured by MEGA a.s. (Czech Republic) on the structural properties of their surface and cross section by SEM was carried out. The CM Pes membrane is a composite of a sulfonated ion-exchanger with inert binder of polyethylene and reinforcing polyester fiber. In the manufacture of membranes Ralex the influence of two factors was investigated. First, the time of ion-exchange grain millingvaried at a constant resin/polyethylene ratio. Second, the ratio of the cation-exchanger and the inert binder of polyethylene varied. It has been found that the membrane surface becomes more electrically homogeneous with the growth of the ion-exchanger loading and a decrease in its particle size. With an increase in the milling time of resin grainsfrom 5 to 80 min a more than 1.5-fold decrease in their radius and in the distance between them was revealed.Besides, there is a 1.5-fold decrease in the fraction, as well as in the size of pores and structure defects. The fraction of the ion-exchange phase on the membrane surface decreases by 7%. With an increase in the resin loading from 45 to 70 wt %, the growth of the fraction of conducting regions on the surface is almost twofold, while their sizes remain practically unchanged. More significant changes in the surface structure of the studied membranes are established in comparison with the cross section.An increase in the resin content in the membranes from 45 to 70 wt % corresponds to a 43% increment of its fraction on the cross-section.The increase in the ion-exchanger content of Ralex membranes is accompanied by the growth of the fraction of macropores and structure defects on the membrane surface by 70% and a twofold decrease in the distance between conducting zones.

Keywords: Ralex ion-exchange membrane; microscopic analysis; structural inhomogeneity.

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Composite X-ray maps of the S and C elements distribution over the surface of Ralex membranes with resin content (a) 45 and (b) 70 wt % at ×200 magnification. Element S corresponds to the red color. Element C corresponds to the blue color.
Figure 2
Figure 2
Fraction (a) and weighted average radius (b) of ion-exchange particles (1), macropores and structure defects (2) on the surfaceof Ralex CM Pes membrane with resin loading 45 wt %.
Figure 3
Figure 3
Figure 3. Scanning electron microscope (SEM) image of the Ralex membrane surface with software-simulated ion-exchange sections of the circular shape.
Figure 4
Figure 4
SEM images of the surface of swollen CM Pes membrane samples at a magnification of 500. The time of resin particle milling: 5 (a), 40 (b), 60 (c) and 80 (d) min.
Figure 5
Figure 5
Fraction (a) andweighted average radius (b) of ion-exchange particles (1,1’), macropores and structure defects (2,2´) and the effective distance between ion-exchangers (3´)on the surface of heterogeneous membranes Ralex with different time of resin particlemilling.
Figure 6
Figure 6
Ion-exchange region (a) and macropore (b)radius distribution on the surface of swollen samples of CM Pes heterogeneous membranes with ion-exchanger milling time of 5 (1), 40 (2), 60 (3) and 80 (4) min.
Figure 7
Figure 7
Relative changes in physicochemical characteristics of Ralex membranes with different resin milling time. Relative changes ΔA% in physicochemical parametersАwere calculated according to the equation: ΔA% = 100(Аt-А5min)/А5min, where А5min—value of a physicochemical characteristic of the membrane with ion-exchanger after milling during 5 min. Qsw—total exchange capacity per gram of the swollen membrane, mmol/g; Qdr—total exchange capacity per gram of the dry membrane, mmol/g; W—water content, gH2O/gswoll.membr; b—swollen membrane thickness,μm.
Figure 8
Figure 8
SEM images of the surface (a,c,e) and cross-section (b,d,f) of swollen CM Pesmembrane at magnification of 500. Ion-exchanger content: 45 (a,b), 55 (c,d), and 70 (e,f) wt %.
Figure 9
Figure 9
Fraction (1,1´) and weighted average radius (2,2´) of ion-exchange particles (a), macropores and structure defects (b) on the surface (1,2) and cross-section (1´,2´) of Ralex CM Pes heterogeneous membranes with various resin loading.
Figure 10
Figure 10
Ion-exchanger radius distribution on the surface (a) and cross-section (b) of the swollen membranes CM Pes with resin content: 45 (1), 55 (2) and 70 (3) wt %.

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