Cellulose acetate salt effect

The salt form of the polymer may also play a role in determining the performance of the formulation. Kane et al. [32] found that cellulose acetate phthalate was more effective than cellulose acetate trimellitate in controlling the dissolution of sulfothiazole-sodium tablets with cellulose acetate. The enteric properties of hydroxypropylmethylcellulose phthalate (HPMCP) were found to depend on the solubility of the drug that was coated. 

Deposition of polyelectrolytes Lajimi et al. [56] explored the surface modification of nanofiltration cellulose acetate (CA) membranes by alternating layer-by-layer deposition of acidic chitosan (CHI) and sodium alginate (AEG) as the cationic and anionic polyelectrolyte, respectively. The supporting CA membranes were obtained by a phase separation process from acetone/formamide. The permeation rate of salted solutions was found to be higher than that of pure water. The rejection of monovalent salt was decreased, while that of divalent salt remained constant so that the retention ratio increased. Increasing the concentration of feed solutions enhanced this selectivity effect. 

Membranes used for NF are made of cellulose acetate and aromatic polyamide with characteristics such as salt rejections from 95% for divalent salts to 40% for monovalent salts and an approximate MWCO of 300 for organics. An advantage of NF over RO is that NF can typically operate at higher recoveries, thereby conserving total water usage due to a lower concentrate stream flow rate. NF is not effective on small-molecular-weight organics, such as methanol. 

A continuous effect is the decrease in water content and void volume with Increasing temperature. Water is lost from the primary gel during annealing, both because of the formation of virtual crosslinks and because of the decrease in hydrogen bonding and cluster size in the water Itself. An example of a discontinuous effect is the dramatic increase in permselectivity (salt rejection) observed when cellulose acetate membranes are heated above the glass transition temperature 68.6 C. In fact, not one but two... 

A detailed study of SPSF desalination membranes was carried out by Brousse and coworkers43. Sulfonation was effected by chlorosulfonic acid on a commercial material (Polysulfone P 1700, Union Carbide), and the products as well as their sodium salts were cast from highly polar solvents. Their performance was compared to that of noncharged cellulose-acetate membranes, largely being used for desalination of brackish water. 

Types of membranes for reverse osmosis. One of the more important membranes for reverse-osmosis desalination and many other reverse-osmosis processes is the cellulose acetate membrane. The asymmetric membrane is made as a composite film in which a thin dense layer about 0.1 to 10 pm thick of extremely fine pores supported upon a much thicker (50 to 125 pm) layer of microporous sponge with little resistance to permeation. The thin, dense layer has the ability to block the passage of quite small solute molecules. In desalination the membrane rejects the salt solute and allows the solvent water to pass through. Solutes which are most effectively excluded by the cellulose acetate membrane are the salts NaCl, NaBr, CaClj, and NajSO sucrose and tetralkyl ammonium salts. The main limitations of the cellulose acetate membrane are that it can only be used mainly in aqueous solutions and that it must be used below about 60°C. 

Tendering Effects. Cellulosic materials dyed with sulfur black have been known to suffer degradation by acid tendering when stored under moist warm conditions. This effect may result from the liberation of small quantities of sulfuric acid which occurs when some of the polysulfide links of the sulfur dye are ruptured. A buffer, such as sodium acetate, or a dilute alkali in the final rinse, especially after oxidation in acidic conditions, may prevent this occurrence. Copper salts should never be used with sulfur black dyes because they catalyze sulfuric acid generation. Few instances of tendering with sulfur dyes other than black occur and the problem is largely confined to cotton. 

Marinading can also transform texture. In animal tissues, dilute acid (e.g., acetic or citric) or salt solution destroys collagen-collagen interactions and so softens the fibres. Presumably in plant material, for which this treatment is also effective, it is the pectins that are altered, since the cellulose crystallites are too tightly bonded to be affected. 

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