Cellulose diacetate

The first reverse osmosis modules made from cellulose diacetate had a salt rejection of approximately 97—98%. This was enough to produce potable water (ie, water containing less than 500 ppm salt) from brackish water sources, but was not enough to desalinate seawater efficiently. In the 1970s, interfacial composite membranes with salt rejections greater than 99.5% were developed, making seawater desalination possible (29,30) a number of large plants are in operation worldwide. 

The price of cellulose ester flake has generally increased with inflation and as of mid-1987 was estimated at ca 3.64— 4.71/kg for cellulose diacetate molding resin and from ca 4.16— 4.71/kg for the mixed esters molding resins depending on purity and the number of propionyl or butyryl esters (4). 

Cellulose Diacetate. When preparing cellulose diacetate for dyeing, strong alkahes must be avoided in the scouring of acetate because the surface of the cellulose acetate would be saponified by such treatment. Many fabrics tend to crease and therefore requke open-width handling. Scouring is frequendy carried out on a jig or beam using 1.0 g/L of surfactant and 0.5—1.0 g/L tetrasodium pyrophosphate for 30 min at 70—80°C. 

Comparison of Table 5.4 and 5.7 allows the prediction that aromatic oils will be plasticisers for natural rubber, that dibutyl phthalate will plasticise poly(methyl methacrylate), that tritolyl phosphate will plasticise nitrile rubbers, that dibenzyl ether will plasticise poly(vinylidene chloride) and that dimethyl phthalate will plasticise cellulose diacetate. These predictions are found to be correct. What is not predictable is that camphor should be an effective plasticiser for cellulose nitrate. It would seem that this crystalline material, which has to be dispersed into the polymer with the aid of liquids such as ethyl alcohol, is only compatible with the polymer because of some specific interaction between the carbonyl group present in the camphor with some group in the cellulose nitrate. 

Although many plasticisers have been suggested for cellulose acetate very few have been used in practice. The most important of these are dimethyl phthalate (8 = 21.4), triacetin (8 = 20.3) and triphenyl phosphate (8 = 20.0), each of which have a solubility parameter within one unit of that of cellulose diacetate (-22.0). (All in units ofMPa. )... 

Because membrane filtration is the only currently acceptable method of sterilizing protein pharmaceuticals, the adsorption and inactivation of proteins on membranes is of particular concern during formulation development. Pitt [56] examined nonspecific protein binding of polymeric microporous membranes typically used in sterilization by membrane filtration. Nitrocellulose and nylon membranes had extremely high protein adsorption, followed by polysulfone, cellulose diacetate, and hydrophilic polyvinylidene fluoride membranes. In a subsequent study by Truskey et al. [46], protein conformational changes after filtration were observed by CD spectroscopy, particularly with nylon and polysulfone membrane filters. The conformational changes were related to the tendency of the membrane to adsorb the protein, although the precise mechanism was unclear. 

More than 90% of all plasticisers are used with PVC, the remainder being used with PVDC, cellulose diacetate, poly(vinyl acetate) (PVAC), nylons, urethanes and acrylates. 

The use of plasticisers, with other than PVC applications, is extensive. Many polar rubber sealants or caulking materials are plasticised in order to make them more pliable, e.g., polysulfides, polychloroprene (Neoprene ), nitrile rubber. Esters, similar to those employed with PVC, are used to render cellulose diacetate ("Acetate") overhead projection sheets more flexible. 

Polymeric pH indicators, phenolphthalein-formaldehyde (PPF) and o-cresolphthalein-formaldehyde (CPF) were synthesized with phenolphthalein and o-cresolphthalein reacted by formaldehyde under alkaline conditions, respectively. They can be immobilized in hydrolyzed cellulose diacetate membranes (HCDA) mainly due to macromolecular entrapment, and can be covalently bound to poly(vinyl alcohol) (PVA) via the considerable newly produced hydroxylmethyl groups [168,169], Phenol red (phenolsulfonphthalein) and its derivatives are commonly used for pH determination. 

Chlorine is the oldest and most widespread method of water disinfection. In reverse osmosis systems, chlorine may be added to feedwater for control of micro-organisms and, in addition, to prevent membrane fouling by microbiological growth. According to Vos et al. [i,2], chlorine will attack cellulose diacetate membranes at concentrations above 50 ppm. Membranes were found to show a sharp increase in salt permeability and a decrease in strength after one week of continuous exposure. Under milder conditions (10 ppm chlorine for 15 days) no detectable change in performance was observed. Spatz and Friedlander [3] have also found cellulose acetate membranes to be resistant to chlorine when exposed to 1.5 ppm for three weeks. 

The effect of casting solution composition on flux and rejection of formamide-modified cellulose acetate membranes is shown in Figure 1, illustrating the general capability of this membrane type as function of solvent concentration. Membranes of casting solution composition cellulose diacetate/acetone/ formamide 23/52/25 (solvent-to-polymer ratio 2.26) were used as reference membranes in this work. 

Figure 2. Effect of hydrophilic bentonite incorporation on the reverse osmosis performance of asymmetric cellulose diacetate membranes I, reference membrane III, with hydrophilic bentonite.

Figure 3. Effect of operating pressure on flux of cellulose diacetate membranes with hydrophilic bentonite incorporation at various annealing levels...

Figure 4. Flux and refection of cellulose diacetate membranes doped with organo-philic bentonite as a function of bentonite concentration...

Figure 6. Low-pressure reverse osmosis performance of ammonia-modified cellulose diacetate membranes (IV) compared with formamide-modified reference membranes (I)...

Membrane Preparation. Dried cellulose diacetate is dissolved in acetone in the weight ratio of 1 to 3 or 4. Gaseous ammonia is directed at room temperature over the solution surface in a rotary evaporator, the ammonia being readily absorbed by the polymer solution. Optimal ammonia concentration is 5 to 6 wt-%, a typical casting solution composition is cellulose diacetate/acetone/ ammonia 18.8/75.2/6.0 (solvent-to-polymer ratio 4). Casting is at room temperature. The precipitation bath is maintained at pH 4 through controlled addition of hydrochloric acid to compensate for the alkaline intake. 

Which is more polar (a) cellulose triacetate or (b) cellulose diacetate ... 

Figure 14.5 Chemical flowchart for the production of triacetate cellulosic diacetate and rayon materials.

Polymer Poly(D- propylene oxide) Cellulose triacetate Cellulose diacetate Polyfy-methyl L-glutamate) (a-helix)... 

Disperse dyes are nonionic and have very low water solubility. They are applied as a dispersion to polyester, nylon, cellulose diacetate, triacetate, and acrylics. 

Figure 5.6 The effect of annealing temperatures on the flux and rejection of cellulose acetate membranes. The anealing temperature is shown on the figure. (Cellulose diacetate membranes tested at 1500 psig with 0.5 M NaCl) [22]. Reprinted with permission from Elsevier...

Plasma fractionators (secondary membranes) Dideco, Italy Albusave Cellulose diacetate 1.00 0.02 350... 

Asahi, Japan BT902 Cascadeflo Cellulose diacetate 1.7 106b 210... 

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