1. The effect of PVC/HIPS/ABS blend ratio on the properties of heterogeneous cation exchange membrane
Marzieh Namdari1, Tavan Kikhavani*2, Seyed Nezammeddin Ashrafizadeh1
1Department of Chemical Engineering, Iran University of Science and Technology, Iran
2Department of Chemical Engineering, Ilam University, Iran
The areal electrical resistance of prepared membranes decreased with increasing the PVC content in the casting solution. This may be attributed to the better distribution of functional groups on the membrane surface.
The effects of polymer ratio (PVC to HIPS to ABS) on the mechanical resistance of the synthesized membranes are shown in table 1.
Table 1: The effect of blend ratio of polymers binder on mechanical property of prepared membranes(PVC:HIPS:ABS)
Polyvinylchloride (PVC) /high impact polystyrene (HIPS) /acrylonitrile-butadiene-styrene (ABS) blend heterogeneous cation exchange membranes were made by solution casting method using tetrahydrofuran as solvent and cation exchange resin powder as functional group agents. Scanning electron microscopy was used to study the membrane structure and distribution of functional groups. The amount of ABS in all membranes kept the same and the effect of different ratio of PVC to HIPS on membrane properties was studied. By varying the blend ratio of polymer binder from 0:80:20 to 80:0:20 (PVC: HIPS: ABS) the electrical resistance of membranes was decreased and the conductivity was increased. Membranes with 40:40:20 blend ratio of polymer binder (PVC to HIPS to ABS) had the lowest water content and the most fixed ion concentration.
The SEM images of the prepared membranes are presented in Fig. 1. With increasing the PVC-HIPS ratio, the membrane surface becomes more uniform.
0:80: :60: :40:20
60:20: :0:20
Figure 1. SEM images of synthesized membranes with various polymers blend ratio binder (PVC:HIPS:ABS)
The obtained results shows that by increasing the PVC percentage in the casting solution, the water content is initially increased, because of the addition of polar chloride groups into the polymer matrix. By increasing the PVC percentage to 40% the membrane water content decreased due to the uniform distribution of resin particles and decreasing the number of free spaces. However, the more presence of polar chloride groups, improve the hydrophilicity of polymer matrix and increased the membrane water content.
The IEC in the membrane with the most HIPS percentage is higher than that of other ones, as can be seen in Fig. 2, despite the presence of polar nitrile and chloride groups in them.
The membrane transport number enhance with increasing PVC: HIPS ratio due to the uniform distribution of functional groups on the membrane surface (Fig. 3).
Figure 2. The effect of blend ratio on IEC (PVC:HIPS:ABS): (1) 0:80:20; (2) 20:60:20; (3) 40:40:20; (4) 60:20:20; (5) 80:0:20
Figure 3. The effect of blend ratio on transport number (PVC:HIPS:ABS): (1) 0:80:20; (2) 20:60:20; (3) 40:40:20; (4) 60:20:20; (5) 80:0:20
The effect of polymers ratio on properties of heterogeneous cation exchange membrane were investigated in this study. It was found that adding PVC into the casting solution has a significant effect on the distribution of resin particles in the surface of synthesized membranes. The existence of polar groups increase the polymer-particle interactions and improve the compatibility of particles with the binder. This makes more uniform distribution of functional groups in the membranes an enhance membrane potential and transport number. The IEC can be decreased by decreasing the HIPS percentage in the casting solution. The mechanical strength of the membranes can be enhanced with increasing the PVC content. Furthermore, it was found that the water uptake of prepared membranes is negligible.
Today, separation membranes have become vital materials in industries and also day-to-day life. Among these membranes, ion exchange membrane (IEM) is one of the most advanced and promising separation membranes. Ion exchange membranes have been extensively investigated and utilized as separators in electrically driven processes such as electrodialysis (ED) for desalting of brackish water, reconcentrating brine from seawater, production of table salt, nitrate removal from drinking water, production of pure and ultra-pure water, and other applications. In IEMs, charged groups attached to polymer backbone are freely permeable to opposite sign ions under an electrical field influence.
According to the membrane structure and its preparation method, ion exchange membranes can be heterogeneous or homogeneous. Heterogeneous ion exchange membranes can be prepared through mechanical incorporation of ion exchange resin particles in polymer film. The most desirable ion exchange membrane has high selectivity, low electrical resistance and good mechanical, chemical, and thermal stabilities.
Preparation of heterogeneous cation exchange membranes with reasonable properties, good mechanical strength, and lower cost was the primary target of this research. For this purpose, PVC/HIPS/ABS blend heterogeneous cation exchange membranes were prepared via solution casting method. Polymers blending in membrane preparation process would improve the properties of synthesized membranes such as enhancing the mechanical strength and also the separation properties of them. The use of PVC, HIPS and ABS blend as polymer binder would satisfy this purpose by combining of good mechanical support (strength and rigidity) of glassy polymers with toughness and high permeability of flexible rubbery ones.
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Tear Resistance (grf/mic)
Membrane (PVC:HIPS:ABS)
10/44
Sample1 (0:80:20)
11/75
Sample2 (20:60:20)
14/29
Sample3 (40:40:20)
17/70
Sample4 (60:20:20)
20/57
Sample5 (80:0:20)