SUMMARY

Casting of highly viscous and non-Newtonian membrane solution in a defect-free manner is not trivial. If proper processing conditions are not set and maintained for the membrane solution, air entrainment, pinholes, etc. will form in the deposited layer. As the membrane hydrolyzes (solidifies), residual stresses will be induced, which may further augment the defects formed during the fluid casting stage. Durability issues have been studied; however they are limited to only the solid phase. Although studies suggest that slot die casting is the best manufacturing process to mass produce thin films/membranes, these studies do not address the defects that arise while casting such highly viscous (>5 Pa-s) and temperature dependent non-Newtonian solutions. The objective of this research is to understand the underlying phenomena that cause the inception and propagation of defects in the membrane film during the manufacturing stage. A casting window will be generated within which defect free casting can be obtained. Mathematical modeling and experimental techniques will be used for this study, which is anticipated to minimize or eliminate such defects. Preliminary results have shown four types of casting defects; pinholes, holes, air bubbles and break lines. Outside the casting window, all four defects are seen at low flow rates/pressures, while air bubbles caused by dripping are the only defects noticed at high flow rates/pressures.