Cellulose film composites

Water barriers are also an important application of regenerated cellulose films composites. In the same smdy, the water absorption (%) of RC and RC/HNT nanocomposites for 2 and 24 h was investigated by Soheilmoghaddam et al. (2013) (Fig. 5). It was reported that the incorporation of HNT improved the water resistance of RC. Water absorption of the nanocomposite films decreased from 87.5 to 77 % as HNT content increased from 0 to 8 wt% after 24 h. This was attributed to the potential of hydrogen bond formation between HNT and RC matrix which can result in the formation of a strong stmcture which in turn reduces the diffusion of water molecules in the material. 

Cellulose acetate, the earhest reverse osmosis membrane, is still widely used. Asymmetric polyamide and thin-film composites of polyamide and several other polymers have also made gains in recent years whereas polysulfone is the most practical membrane material in ultrafiltration appHcations. 

Commercial interest in RO began with the first high-flux, high-NaCl-retention Loeb-Sourirajan anisotropic cellulose acetate membrane. Practical application began with the thin film composite (TFC) membrane and implementation for seawater desalination at Jeddah, Saudi Arabia [Muhurji et ak. Desalination, 76, 75 (1975)]. 

The objective of this work is to determine the surface concentration of the hydroxyl groups of cellulose and PVA films utilizing their chemical modification. We chose these polymers mainly because the hydroxyl group is their sole functional group. Recently we have reported that a cellulose film is more excellent in wettability towards water than PVA, though cellulose is insoluble in water, in contrast to PVA(4). Since only the chemical composition of the surface must be responsible for water... 

The origin of thin-film-composite reverse osmosis membranes began with a newly formed research institute and one of its first employees, Peter S. Francis. North Star Research and Development Institute was formed in Minneapolis during 1963 to fill a need for a nonprofit contract research institute in the Upper Midwest. Francis was given the mission of developing the chemistry division through support, in part, by federal research contracts. At this time the Initial discoveries by Reid and Breton ( ) on the desalination capability of dense cellulose acetate membranes and by Loeb and Sourlrajan (,2) on asymmetric cellulose acetate membranes had recently been published. Francis speculated that improved membrane performance could be achieved, if the ultrathin, dense barrier layer and the porous substructure of the asymmetric... 

Fig. 1. Water flux and NaCl rejection of several membrane types (10), where (D) represents seawater membranes, which operate at 5.5 MPa and 25°C ( ), brackish water membranes, which operate at 1500 mg/L NaCl feed, 1.5 MPa, and 25°C and (SSI) nanofiltration membranes, which operate at 500 mg/L NaCl feed, 0.74 MPa, and 25°C. A represents cellulose acetate—cellulose triacetate B, linear aromatic polyamide C, cross-linked polyether D, cross-linked fully aromatic polyamide E, other thin-film composite membranes F, asymmetric membranes G, BW-30 (FilmTec) H, SU-700 (Toray) I, A-15 (Du Pont) J, NTR-739HF (Nitto-Denko) K, NTR-729HF (Nitto-Denko) L, NTR-7250 (Nitto-Denko) M, NF40 (FilmTec) N, NF40HF (FilmTec) O, UTC-40HF (Toray) P, NF70 (FilmTec) Q, UTC-60 (Toray) R, UTC-20HF (Toray) and S, NF50 (FilmTec). To convert MPa to psi,...

Two different RO membrane types were evaluated in this study. The first was a standard cellulose acetate based asymmetric membrane. The second type, a proprietary cross-linked polyamine thin-film composite membrane supported on polysulfone backing, was selected to represent potentially improved (especially for organic rejection) membranes. Manufacturer specifications for these membranes are provided in Table III. Important considerations in the selection of both membranes were commercial availability, high rejection (sodium chloride), and purported tolerance for levels of chlorine typically found in drinking water supplies. Other membrane types having excellent potential for organic recovery were not evaluated either because they were not commercially... 

The importance of proper RO membrane selection has already been discussed. A review of commercially available RO membranes revealed five different basic membranes that could provide organic recovery. Cellulose acetate and cellulose acetate blends, aromatic polyamide, polyamide thin-film composite, cross-linked polyimine thin-film composite (FT-30), and polybenzimidazole were available when this work was performed. Only the first four types were commercially available. All membranes were available with excellent salt rejection (>97 sodium chloride). Two types of membranes, cellulose acetate and FT-30, have shown short-term (<2-months intermittent use) resistance... 

Cellulose acetate membrane was studied because of its past use in concentrate preparation and the need to better define its performance for specific organic recovery. Cellulose acetate continues to be widely used for a variety of industrial and commercial water purification applications. Cellulose acetate was not expected to perform at the level of the more highly cross-linked and inert thin-film composite membrane. 

Salts rejected by the membrane stay in the concentrating stream but are continuously disposed from the membrane module by fresh feed to maintain the separation. Continuous removal of the permeate product enables the production of freshwater. RO membrane-building materials are usually polymers, such as cellulose acetates, polyamides or polyimides. The membranes are semipermeable, made of thin 30-200 nanometer thick layers adhering to a thicker porous support layer. Several types exist, such as symmetric, asymmetric, and thin-film composite membranes, depending on the membrane structure. They are usually built as envelopes made of pairs of long sheets separated by spacers, and are spirally wound around the product tube. In some cases, tubular, capillary, and even hollow-fiber membranes are used. 

Photo 1. Cellulose sample used. Top A part of molded film from the cellulose— PMMA composite, PC—3. Molding conditions temperature 300°C time, 2 min pressure, 50 kg/cm . Bottom under a microscope. 

Almost all RO membranes are made of polymers, cellulosic acetate and matic polyamide types, and are rated at 96-99% NaCl rejection. RO membranes are generally of two types, asymmetric or skinned membranes and thin film composite membranes. The support material is commonly polysulfones, while the thin film is made from various types of polyamines and polyureas. 

In studies to remove organic fouling on RO membranes, it has been reported that several commercial cleaners developed by Pfizer gave excellent results. Differential pressure of the membrane system could be reduced by 42% using a neutral pH liquid formulation (Floclean 107) designed to remove organics, silt, and other particulates from cellulose acetate RO membranes. For polyamide, polysulfone, and thin-film-composite... 

Permeate flux 0.001 to 0.1 L/s m for cellulose acetate 0.006 to 0.0075 L/s m for hollow fiber 0.001 to 0.002 L/s m for thin film composite 0.007 to 0.009 L/s m. Permeate flux increases about 3% for every 1°C increase. Permeate flux decreases by 10 to 50%, depending on the concentration polarization. Permeate flux is reduced because of particulates and bacterial adhesion so that flux for tubular < spiral wound < hollow fiber. 

While the cellulose acetate membranes are compacted at the moderate pressures required for brackish water desalination, the thin film composite membranes exhibit bo compaction at these pressures and a very low compaction rate at pressures of 1,000 psig. 

The superior flux and rejection capabilities of the thin film composite membrane has been demonstrated at the municipal wastewater reclamation facility of the Orange County Water District in California. Both asymmetric cellulose acetate and thin film composite membranes were tested on lime clarified secondary effluent. The pilot plants were operated at 85% recovery and the rejections reported in Table 4.5 are the percent rejection of the constituents in the feed-water and not the rejection of the average concentration of the specific constituents in the feed/reject stream. Use of the average concentration would give a higher rejection in both cases. 

The thin film composite membrane exhibited superior overall rejection performance in these tests, with ammonia and nitrate rejection showing an outstanding improvement. It has also been reported that silica rejection by the thin film composite membranes is superior to that of cellulose acetate. While the above data indicates a marginal improvement in the rejection of chemical oxygen demand (COD), which is an indication of organic content, other tests conducted by membrane manufacturers show that the polyurea and polyamide membrane barrier layers exhibit an organic rejection that is clearly superior to that of cellulose acetate. Reverse osmosis element manufacturers should be contacted for rejection data on specific organic compounds. ... 

Early examples of cellulose acetate composite membranes used cellulose ester sheet materials as the porous underpinnings for the float-cast films. These sheet materials included (a) Loeb-Sourirajan asymmetric cellulose acetate mem-... 

Nanofiltrarion membranes were received from Fluid Systems in San Diego, USA (now Koch Membrane Systems). Thin film composite membranes were chosen due to their low fouling characteristics compared to poly sulphone membranes used in other studies. The CA-UF membrane is, as the name suggests, classed as a UF membrane and the material is cellulose acetate. However, it is treated as a NF membrane here as it is often used for similar applications according to the manufacturer, and also because it exhibits some salt rejection. Membrane characteristics as given from... 

GagHatdo P., Adham S., Tmssell R. (1997), Water purification using reverse osmosis thin film composite versus cellulose acetate membranes, Proc. AWW A Membrane Technolog Conference, New Orleans, Feb. 97, 597-608. 

Zhu, X. (1996), Colloidal fouling of thin film composite and cellulose acetate reverse osmosis membranes, Dissertation, University of California, Civil Engineering, Los Angeles. 

Curcumin-loaded CS/cellulose microcrystal composite films can be prepared by the vapour induced phase inversion method and show good antimicrobial action against bacteria and fungi. Cellulose fibres made of CS/lignosulfonate (LS) multilayers exhibit... 

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