Degradation of Cellulose Acetate

Shrinkage, tackiness and increased brittleness due to the migration and subsequent evaporation of plasticiser from between the cellulose acetate chains, is also a frequent cause of degradation. The degradation of some plasticisers has been shown to increase acidity of cellulose acetate-containing materials. Triphenyl phosphate, used as a plasticiser for cellulose acetate since the 1940s, decomposes to form diphenyl phosphate and phenol. Diphenyl phosphate is a strong acid so it is likely to accelerate the deacetylation of cellulose acetate. 

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Wilson, W. K., Forshee, B. W., Degradation of Cellulose Acetate Films, ... 

Ramachandhran, V. and Misra, B.M., Studies on the radiolytic degradation of cellulose acetate membranes, 7. Appl. Polym. Sci. 30, 35, 1985. 

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... 

Table 1. Some products of the thermal degradation of cellulose acetate analysed by TGA/MS/MS...

Figure 5. Proposed scheme for the thermal degradation of cellulose acetate based on TGA/MS/MS analysis...

The thermal degradation of cellulose acetate hydrogen phthalate (CAP) and its blends with PMMA has been investigated by thermogravimetry [a.l75]. The TG/DTG curves showed two decomposition stages for pure CAP. The decomposition behaviour was changed with the addition of PMMA. For 90/10 and 70/30 CAP/PMMA blends, there were three... 

The earliest preparation of cellulose acetate is credited to Schiitzenberger in 1865. The method used was to heat the cotton with acetic anhydride in sealed tubes at 130-140°C. The severe reaction conditions led to a white amorphous polymer but the product would have been severely degraded and the process difficult to control. Subsequent studies made by Liebermann, Francimont, Miles, the Bayer Company and by other workers led to techniques for controlled acetylation under less severe conditions. 

UV absorbers have been found to be quite effective for stabilization of polymers and are very much in demand. They function by the absorption and harmless dissipation of the sunlight or UV-rich artificial radiation, which would have otherwise initiated degradation of a polymer material. Meyer and Geurhart reported, for the first time in 1945 [10], the use of UV absorber in a polymer. They found that the outdoor life of cellulose acetate film was greatly prolonged by adding phenyl salicylate (salol) [10]. After that, resorcinol monobenzoate, a much more effective absorber, was introduced in 1951 [11] for stabilization of PP, but salol continued to be the only important commercial stabilizer for several years. The 2,4-dihydroxybenzophenone was marketed in 1953, followed shortly by 2-hydroxy-4-methoxybenzophenone and other derivatives. Of the more commonly known UV absorbers, the 2-hydroxybenzophenones, 2-hy-droxy-phenyl-triazines, derivatives of phenol salicylates, its metal chelates, and hindered amine light stabilizers (HALS) are widely used in the polymer industry. 

Cellulose acetate was the first high-performance reverse osmosis membrane material discovered. The flux and rejection of cellulose acetate membranes have now been surpassed by interfacial composite membranes. However, cellulose acetate membranes still maintain a small fraction of the market because they are easy to make, mechanically tough, and resistant to degradation by chlorine and other oxidants, a problem with interfacial composite membranes. Cellulose acetate membranes can tolerate up to 1 ppm chlorine, so chlorination can be used to sterilize the feed water, a major advantage with feed streams having significant bacterial loading. 

The degradation of cellulose to the compound now known to be -cello-biose octaacetate by acetic anhydride-acetic acid-sulfuric acid was first reported almost ninety years ago. Assignments of structure to the various products from this reaction caused much controversy in the period during which the structure of cellulose and of starch was being established. However, no useful purpose is served by reviewing these controversies in this Series, their place now being in the domain of the chemical historian. 

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