SUM!HARY
A time-temperature equivalence exists for the uftimate elongation and bireftingence of 2.5 acetyl celJuiose acetate. This equivalence can be extended beJow the gJass transition temperature. TJIE experimentally obtained shift factors agree with tJte WilIiam~~ndei-Fen equation over a very narrow temperatrlrr: range only.
An empirical method has been developed to obtain a master curve of reduced birefringence as a furtdon of reduced elongation, independent of elongation ratio, rate and temperature of stretching. i _ INTRODUCTtON Cellulose acetate membranes are important for desalination (Z-6) by reverse osmosis because of their high salt rejection at relatively high flow rates. The efficiency of the reverse osmosis process can be improved by two approaches: the casting solution formulations can be improved in order to increase the flow rate per unit area (I, 3-6) or, on the other hand, the surface area of the membranes per unit volume of apparatus can be increased by membrane geometry (I, 7, 8). Spiral modules or hollow fibers permit this increase in relative surface area. The hollow fibers offer the advantage that they are mechanically self-supporting and do not require, therefore, extensive support grids. They are quite difficult to manufacture, however, and many technological problems have to be solved for their melt or solution extrusion (8). Most hollow fibers are of the low flux type, i.e. without a microscopic structure, even though attempts have been made to produce hi& flux fibers (9, IO). During the extrusion process the flow in the die and the subsequent stretching of the fiber result in molecular orientation along the fiber a& Even though the inftuence of molecular orientation on the transport properties in dastomers has been investigated (I&13), little is known about the effkct of molecular orierltation on the performance of cellulose acetate membranes.