Cellulose acetate deterioration

This presentation will discuss the membrane performance and its physical and chemical changes under unfavourable conditions. This kind of studies will give us information on trouble-shooting counter-measures for unexpected membrane deteriorations, and on the durability of a cellulose acetate membrane under adverse conditions. 

The major chemical processes of membrane deteriorations are hydrolysis and oxidation. Cellulose acetate is most stable at the level of around pH 4.7, and at the pHs lower or higher than that value, membrane hydrolysis is accelerated. In practical applications of cellulose acetate membranes, feed water pH is usually controlled between 5 to 6. But it is Impossible to control the pH of demineralized pure water for electronic and pharmaceutical uses, i.e. for ultrapure water polishing. In such cases feed water pH 7 should be supplied to cellulose acetate material. Studies of membrane behaviour under such conditions will give good information for estimating the membrane life. 

Any biological deterioration of cellulose acetate membranes is always by "accidental". To prevent this kind of deteriorations, chlorine injection to feed water is common practice. Inadequate control of chlorine injection may result in the enzymic deterioration of cellulose acetate membrane. 

Figure 2. Rejection—flux pattern of deteriorated cellulose acetate membrane f p, permeate flux of new membrane Fp, permeate flux of deteriorated membrane.

Deterioration of Asymmetric Cellulose Acetate Membranes with NaOCl -------Structural and Chemical Change... 

Model of Deterioration Mechanisum, As acetyl content decreases due to hydrolysis or oxidation of ester bonding, solute permeability increases. Then concentration of solute( in this case sodium hypochlorite) in the membrane increases and the hydrolysis or oxidation rate increases and so on. It will be more reasonable to assume that hydrolysis or oxidation rate of cellulose acetate in the active surface layer may be accelerated by the action of the nascent oxygen generated from sodium hypochlorite. 

Prop Meet), but this method proved to be not very satisfactory on account of the appreciable migration of NG into the inhibitor, which resulted in its deterioration at elevated temp. Migration occurs also when using cellulose acetate inhibitors... 

The chemical sensitivity or life expectancy of reverse osmosis membranes is very important for manufacturing application. Thus chlorine is the most well known reagent for water disinfection. Glaster et al. 61 inspected the influence of halogens on the performance and durability of reverse osmosis membranes. Cellulose acetate was unresponsive to halogen agents but polyamide-type membranes deteriorated rapidly when exposed to halogens. 

Cellulose acetate products deteriorate by releasing acetic acid. Without air exchange, the acid vapor accumulates and is reabsorbed by the emission source... 

Chemistry, Physics, and Biology Laboratories. As a rule, before any artifact is subjected to treatment, the chemistry laboratory determines the causes of any alterations or deterioration. The nature and structure of the artifact, its pigments and inks, are identified to avoid negative reactions to prescribed treatment. Fixatives are recommended if required these may be cellulose acetate dissolved in acetone, soluble nylon, or acrylic resin sprays. Once stains are identified, several possible solvents are selected. For deacidification, either magnesium bicarbonate or barium hydroxide usually is recommended, depending on whether an aqueous or nonaqueous solution is called for. Bleaching is discouraged, but when necessary, hypochlorites are used with suitable antichlors. 

A survey of plastics-containing objects in the British Museum and the National Museum of Denmark showed that 1% of objects were actively deteriorating and were in immediate need of conservation, while 12% exhibited deterioration and required cleaning, stabilising and repair. All the acute objects contained cellulose nitrate, cellulose acetate, plasticised PVC or polyurethane foam. Most objects (60%) were defined as being of low conservation priority, that is, they were in a stable condition but needed some treatment such as cleaning. Only just over one quarter required no conservation treatment. In general, deterioration of plastic objects in museums is visible within 5-25 years of collection. 

USE An ultraviolet light absorber for stabilizing plastics and other organic materials against discoloration and deterioration. Effective in protecting polyesters, chlorinated polyesters, polystyrene, polyvinyls, polypropylene, alkyds, cellulose acetate, ethyl cellulose, acrylates, dyes, synthetic and natural fibers, waxes, detergent solns. cosmetic formulations. Ref Dunn, Fogg, J. Appl. Polymer Sci 2, 367 (1959). 

The majority of investigations on the degradation of cellulose acetate have been conducted on photographic film (cellulose triacetate) rather than moulded material. like cellulose nitrate, cellulose acetate (CA) is deteriorated by both physical and chemical factors and the physical cause of degradation is plasticizer loss. Three-dimensional objects moulded from cellulose acetate comprise 20-40 per cent by weight plasticizer. Typical plasticizers include triphenyl... 

A pile of transparent cellulose acetate tracing sheets from the 1980s illustrates typical physical deterioration. Sheets have shrunk and droplets of plasticizer can be seen at the surfaces. 

Two cellulose acetate spoon handles from the 1950s. Acid Detection (A-D) strips enclosed with the spoons indicate that the spoon handle in good condition (left) produces a high concentration of acetic acid, while the highly deteriorated example (right) produces none. The handle on the right is almost fully deacetylated and chemically similar to cellulose. 

Toxicology LD50 (oral, rat) 37 g/kg, (demtal, rabbit) 20 g/kg mildly toxic by ing., skin contact irritating to eyes, skin, respiratory system suspected carcinogen tumorigen TSCA listed Precaution Combustible exposed to heat or flame can react with oxidizing materials may soften or deteriorate certain plastics/elastomers incompat. with cellulose acetate, cellulose acetate butyrate... 

Precaution Combustible exposed to heat or flame can react with oxidizing materials may soften or deteriorate certain plastics/elastomers incompat. with cellulose acetate, cellulose... 

Membrane technology has often been mentioned as the next technological generation for the prtrification of natural gases. Indeed, membrane systems are operated successfully for gas sweetening for decades. The best known examples include CO2 selective membranes that are based on pure polymers, e.g., cellulose acetate (Cynara membranes by Natco or Separex membranes by UOP) and polyimide (Ube). Despite their popularity, their performance at high pressures deteriorates as a result of CO2 induced plasticization. 

The chemical reactivity of a polymer is, in large measure, the reactivity of its molecular components. Natural rubber, for example, undergoes deterioration when ozone attacks the double bonds of the polymer chain a saturated hydrocarbon chain, like polyethylene, is resistant to such attack. Celluloses offer their hydroxyl groups to a variety of reagents and thus make it possible to modify properties. Reaction with nitric acid produces NITROCELLULOSE, from which propellant (guncotton) and plastic (Celluloid) products are formed. Reaction with acetic acid produces cellulose acetate, which can be fabricated into films, sheets, and other useful forms ... 

Biofouling has been regarded as the most serious problem in the operation of SWRO plants. The usual method to prevent biofouling is continuous chlorine dosing to intake seawater with sodium bisulfate (SBS) dosing at the RO portion. However, membranes performance deterioration occurred by oxidation in case of both polyamide and cellulose acetate membranes, and biofouling has not been solved yet. Toray has developed a new method that is effective to prevent biofouling on SWRO membranes and verified its effectiveness at actual plants. 

It should be remembered that most museum objects have been used or displayed before they are collected. They have an unknown past, usually, which contributes greatly to the rate and type of deterioration. Instability of the earliest plastics, cellulose nitrate and acetate is expected due to their poorly stabilised formulations and because they are the oldest man-made plastics in museums. However, PVC was first developed in 1926 and is still in use, so its deterioration is rather unexpected. 

Polymers containing hydrolysable groups or which have hydrolysable groups introduced by oxidation are susceptible to water attack. Hydrolyzable groups such as esters, amides, nitriles, acetals, and certain ketones can react with water and cause deterioration of the polymer. The dielectric constant, power factor, insulation resistance, and water absorption are most affected by hydrolysis. For polyesters, polyamides, cellulose, and cellulose either and esters, the hydrolysable groups are weak links in the chain, and hydrolysis of such polymers can cause serious loss of strength. A summary of water absorption characteristics of common plastic and rubbers is presented in Table 1.15. 

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