Cellulose acetate etching

Relationship Between Nodular and Rejecting Layers. Nodular formation was conceived by Maler and Scheuerman (14) and was shown to exist in the skin structure of anisotropic cellulose acetate membranes by Schultz and Asunmaa ( ), who ion etched the skin to discover an assembly of close-packed, 188 A in diameter spheres. Resting (15) has identified this kind of micellar structure in dry cellulose ester reverse osmosis membranes, and Panar, et al. (16) has identified their existence in the polyamide derivatives. Our work has shown that nodules exist in most polymeric membranes cast into a nonsolvent bath, where gelation at the interface is caused by initial depletion of solvent, as shown in Case B, which follows restricted Inward contraction of the interfacial zone. This leads to a dispersed phase of micelles within a continuous phase (designated as "polymer-poor phase") composed of a mixture of solvents, coagulant, and a dissolved fraction of the polymer. The formation of such a skin is delineated in the scheme shown in Figure 11. 

Phosgene has been employed in the modification of the surfaces of cellulose-acetate membranes used for water desalination and waste water treatment [1450]. Similarly, phosgene has been used to surface-modify porous diaphragms for electrolytic cells [324]. Aluminium and aluminium-based alloys can be etched at a high rate when COClj is used in a mixed gas plasma [1004], as can semiconductors (see Section 9.12). 

Polymeric membranes are prepared from a variety of materials using several different production techniques. Table 5 summarizes a partial list of the various polymer materials used in the manufacture of cross-flow filters for both MF and UF applications. For microfiltration applications, typically symmetric membranes are used. Examples include polyethylene, polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE) membrane. These can be produced by stretching, molding and sintering finegrained and partially crystalline polymers. Polyester and polycarbonate membranes are made using irradiation and etching processes and polymers such as polypropylene, polyamide, cellulose acetate and polysulfone membranes are produced by the phase inversion process.f Jf f ... 

In the woik of Olde Riekerink et al. (2002), one type of UF (cellulose triacetate, CTA) membrane and one type of RO (cellulose acetate blend, CAB) membrane were selected for CO2 plasma modification. CTA ultrafilters are well known for their low fouling properties and CAB membranes are widely used for desalination. CO2 plasma treatment resulted in the gradual etching of the membrane s dense top layer. 

Olde Riekerink, M.B., Engbers, G.H.M., WessUng, M. and Feijen, J. 2002. Tailoring the properties of asymmetric cellulose acetate membranes by gas plasma etching. faterfacg Sci. 245 338-348. 

Peck and Kaye [240] immersed cellulose acetate specimens in acetone, at —50°C, and then flooded the surfaces with cold absolute alcohol, followed by replication which showed the skin, orientation, voids and pigment. Reding and Walter [21] etched PE with hot carbon tetrachloride (high density PE), benzene (low density PE) or toluene, which removed the amorphous material. Bailey [241] used a rapid xylene etch to reveal spher-ulites in PE and PP, while Li and Kargin [242] etched with benzene. A method was developed for obtaining PE for TEM. Melt crystallized PE, backed with carbon and gelatin, was exposed to xylene and dissolved to a thin layer and examined directly by TEM [243, 244]. 

Specimen surface was polished electrochemically by mixed solution of sulfuric acid and ethyl alcohol (1 3). After polishing, the surface of the specimen was adhered by a film of nitric acid cellulose using acetic acid methyl solution. Specimens were then sealed in the polyethylene sheet and irradiated for 43.2 Ks (12 h) by the atomic reactor in Rikkyo University (thermal neutron = 1.1 x 1010 n/cm2 s) or JRR-4 in JAERI (1.5 x 109 n/cm2 s). After cooling down for 0.61 Ms (7days), the film of nitric acid cellulose was striped off from specimen. Boron distribution in the specimen corresponds to particle-tracks produced on the film of nitric acid cellulose by the interaction between thermal neutron and boron (10B (n,a) 7Li). Using 2.5N-NaOH solution at 303 K, particle-tracks by a-rays produced by thermal neutron with boron were etched for 2.7 ks. Then etched films were washed for 10.8 ks in flowing water. We observed microstructure by optical microscopy and SEM. 

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