A quantitative study has been made of the effects on the membrane gel structure of parameters w h m significance with respect to desalination performance had previously been empirically established. The composition of the polymer solutions, the fabrication temperatuws, and the preasure employed during desalination are shown to be related, in that they all influence the swelling behavior of the gel structure. The relationship which has been found between the water content and the rate of water transport across semipermeable membranes of cellulose acetate is explained on the basis of a solution transport mechanism., INTRODUCTION Semipermeable membranes of cellulose acetate have been developed which are highly effective in the removal of dissolved salts from water by reverse osmosis. In this study the effects of the membrane fabrication variables on its operation were examined. As a result of this study a model for the structure of the membrane was developed which explains the effects of each step in the fabrication and is consistent with the observed transport phenomena.Although comparatively little attention has been given to problems involving the structure of semipermeable membranes of cellulose acetate, a copious amount of work in the related fields of cellulose chemistry and ultrafiltration has been reported. Manegold' and Elford2 have investigated the structure of collodion membranes, and Maier and Scheuermanna have treated the sequence of events in the casting solution immediately preceding gelation.Baker, Fuller, and Pape' have studied the structure of cellulose acetate and concluded that ordered amorphous regions are present. With respect to the disposition of water in the gel structure, it has long been believed that water in cellulosic materials concentrates in the amorphous regions6* and in

The surface degradation of both linear and crosslinked polymethylmethacrylate (PMM) has been studied over the surface temperature range of 550° to 910°K by means of a hot-plate pyrolysis technique. It was demonstrated that surface gasification due to the high heat flux at the decomposing PMM surface involves a depolymerization process and surface desorption of methylmethacrylate monomer. The apparent activation energy for the linear rate of regression of the solid PMM surface (linear pyrolysis rate) was found to decrease with increasing surface temperature, approaching a limiting constant value of 11.2±0.6 kcal/mole at ∼650°K for linear PMM and at ∼770°K for crosslinked PMM. The mechanism for the surface degradation is depicted as (1) formation of monomer in the surface substrate, (2) diffusion of monomer to the surface, and (3) desorption of monomer from the surface. The linear pyrolysis rate data are correlated by means of an absolute rate theory treatment of surface decomposition. The experimental results are in good agreement with the theory.

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SynopsisThe mechanism by which water and dissolved salts permeate selectively through membranes has been investigated. It has been demonstrated that the predominant mechanism of permeation involves the interaction of the various species with specific sites and their associated bound water molecules. The extent of the bound water held by the cellulosic membranes of interest has been determined. Correlation haa been found between the permeation characteristics demonstrated by membranes at various steps in their preparation and its bound water content. The mechnism of rejection of salts haa been shown to be related to the relative inability of their ions to become solvated by bound water. A model haa been hypothesized which correctly describes the behavior of the desalination membrane with reference to water and soluble inorganic salts.

An improved instrument has been designed and constructed for the measurement of the linear decomposition and sublimation rates of solid substances. This instrument, which is provided with automatic recording devices, eliminates many of the shortcomings of the earlier prototypes and makes possible the determination of linear rates with a precision of 1%. Important new features include (1) an integral heating element and thermocouple assembly; (2) stainless-steel and Plexiglas construction throughout; (3) heavy, solid-copper electrical-conductor supports for the heating element; and (4) a precision position-sensing potentiometer. The use of cut strands of Plexiglas 55 is recommended for periodic standardization and calibration of the instrument.