Nondestructive testing of defects in adhesive joints

of 125±2 ºC. Desalting performance of such membranes was studied in continuous mode for a period of
24 hours. It is observed (Figure 5) that membranes cured for all selected cure time except the lowest one
(10 minutes) show almost constant flux and rejection with time. It is seen from Figure 5B that the
rejection for membranes cured for 30 and 40 minutes are almost the same, whereas there is an average
15% rejection enhancement by varying the cure time from 20 to 30 minutes without much sacrifice in the
flux. Hence 30 minutes cure time was selected as optimum.
Molecular weight cut off: The separation profile of different organic compounds (varying molecular
weight from 90 to 600 gm/mole) with the variation of curative dose and cure time for different PVA TFC
membranes are shown in Figure 6. It is seen that more the cross-link density of the barrier layer (due to
higher cross-linker dose) higher the rejection of any selected organic compound. The lowest selected
cross-linker dose of 2% produces membrane with no specific molecular weight cut off in the selected
range i.e. 90-600 Dalton. The higher range of cross-linker doses i.e. 20-50% MA, produce membranes
with MWCO in the range of 200-300 Dalton. For membranes with MA dose of 10%, MWCO values are
between 350-450 Dalton.
Membranes performance with different inorganic salt solution: The desalting performances of the
membranes were tested with different electrolyte solutions. The performances of the membranes (flux and
rejection) varying in their curative dose are presented graphically in Figure 7. The % rejections of
sulphate salts (MgSO4 and Na2SO4) are almost same for all the selected membranes irrespective of their
curative dose. The rejection of the chloride salts are much lesser than the sulfate salts, which may be due
to higher repulsion of sulfate than chloride by the charged surface of the membranes. Although the
variation of curative dose (2-50%) has negligible effect on the % rejection of sulphate salts but there is a
gradual increase in rejection of chloride salts with increase in MA concentration which may be due to a
synchronization of charge enhancement and membranes tightening.
Conclusions:
The overall trend of rejection by such membranes is > > R
2 4 SO Na R RMgSO NaCl > R ≅ (R =
4
MgCl R
2 CaCl2
Rejection). The average MWCO of the membranes varies between 350-450 Dalton. As for such
membranes 65% difference is observed between the rejection of MgSO4
(R 70-90%) and NaCl (R15-
35%), hence, they may be useful for the removal of dissolved sulphate hardness and partial desalination
of brackish water.
Acknowledgement: Financial assistance from CSIR, India is highly acknowledged.
References:
[1] Amjad Z. Ed.; Reverse Osmosis: Membrane Technology, Water Chemistry, and Industrial
Applications, Van Nostrand Reinhold: New York, 1993.
[2] Ahn KH, Cha HY, Yeom IT, Song KG. Desalination 1998; 119(1-3):169-176.
[3] Ikeda K, Kimura S, Ueyama K. Maku 1998; 23:266-272.
[4] Krumova M, Lopez D, Benavente R, Mijangos C, Perena JM. Polymer 2000; 41(26):9265-9272.
[5] Suzuki M, Yoshida T, Koyama T, Kobayashi S, Kimura M, Hanabusa K, Shirai H. Polymer 2000;
41(12):4531-4536.
[6] Radovanovic P, Thiel SW, Hwang ST. Journal of Membrane Science 1992; 65(3):213-229.
[7] Kesting RE. A structure perspective' in: Synthetic Polymeric membranes, 2 nd . ed. Wiley, 1985.
Biomaterial membrane
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