Cellulose nitrate plasticisers

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 originally a trade name the term celluloid has come into general use to describe camphor-plasticised cellulose nitrate compositions. 

Nitration of cellulose followed by plasticisation of the product with camphor has the effect of reducing the orderly close packing of the cellulose molecules. Hence whereas cellulose is insoluble in solvents, except in certain cases where there is chemical reaction, celluloid is soluble in solvents such as acetone and amyl acetate. In addition the camphor present may be dissolved out by chloroform and similar solvents which do not dissolve the cellulose nitrate. 

Plasticised amorphous thermoplastics Certain plastics may be mixed with high-boiling low-volatility liquids to give products of lower T. The most important example occurs with p.v.c. which is often mixed with liquids such as di-iso-octyl phthalate, tritolyl phosphate or other diesters to bring the below room temperature. The resultant plasticised p.v.c. is flexible and to some degree quite rubbery. Other commonly plasticised materials are cellulose acetate and cellulose nitrate. 

Non-drying oil resins are soluble only in Aromatic hydrocarbons. They are used with amino resins for stoving finishes for appliances. Medium resins are used as plasticisers for cellulose nitrate. Along with natural oils several natural occurring and synthetic acid like resin (abiotic acid) pelargonic acid and isooctanoic acid are added to modify alkye resins. The alkyd resins are obtained by two processes, i.e., (1) Fatty Acid Process and (2) Alcoholysis process. 

During roller-blending to disperse iron red pigment (iron(III) oxide) into plasticised cellulose nitrate, the mixture became a gel after 15 passes and tended to self-ignite. 

Cellulose nitrate is a semi-synthetic plastic based on cellulose from wood or cotton. It is mixed with nitric and sulphuric acids, and uses camphor as a plasticiser. It is another compound that was being developed by various people in different places at the same time, but was launched in England in 1862 as Parkesine . It was later called Xylonite . Cellulose nitrate was finally patented in America in 1870 under the name celluloid , but has been known by over 60 different trade names during the years it has been in production. 

Since the properties and degradation reactions of plastics are usually influenced by their formulations and manufacturing processes, this chapter will first discuss those areas. Four plastics have been identified as being more vulnerable to degradation than others in museum collections cellulose nitrate, cellulose acetate, plasticised PVC and polyurethane foam. The most frequently seen... 

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. 

Figure 2 Poster made from cellulose nitrate in 1960s showing shrinkage due to loss of camphor plasticiser and cracking...

Details DIBP is one of the rare odourless plasticisers with excellent heat/light stabilities, and it is inexpensive. DIBP is a commonly used as a plasticiser for cellulose nitrate production. DIBP has not yet undergone an EU classification and labelling assessment and it is very unlikely that it has any toxicological effects. Since it is not known for sure, its toxicology information is not given here (http //w w w. dibp-facts.com/index.asp page=3). 

Certain triesters can be incorporated into plastics where they act as plasticisers by reducing the amount of cross-linking which would otherwise take place in the polymerisation process. Triaryl phosphates were first used to plasticise cellulose nitrate and cellulose acetate. Trioctyl phosphate and octyl diphenyl phosphate are particularly suitable for plasticising PVC [21],... 

Tricresyl phosphate (Table 12.28) (originally used to reduce the inflammability of cellulose nitrate) and other triaryl phosphates are used as flame retardants and plasticisers with PVC. Triethyl... 

Plasticisers are also used in products such as lacquers and adhesives that fall outside the definition of the plastics industry. Dicyclohexyl phthalate is used in nitrocellulose lacquers polyethylene glycol and its monostearate are compatible with cellulose nitrate. Dibutyl maleate is compatible with polyvinyl acetate, and di- -hexyl adipate, diethylene glycol di-2-ethyl butyrate or dibutyl sebacate can be used in polyvinyl butyral. Benzoates are recommended for... 

Polyvinyl acetate (PVAc) (adhesives), as well as cellulose acetate (CA) compounds and sheets, cellulose nitrate pigment binders and polyvinyl butyral (PVB) sheets (used mainly for safety glass interlayers) are other main users of plasticisers. 

The first plastic material to be made from non-plastic precursors was cellulose nitrate. This was obtained by Alexander Parkes (1813-1890) by treating cellulose fibres with nitric acid, and was first displayed at the Great International Exhibition in Ijondon in 1862 under the name Parkesine. Parkes moulded his new material into small decorative articles, as well as utilitarian objects such as knife handles. Parkesine was the first semi-synthetic plastic, so called because one of the starting materials was polymeric. The applications of cellulose nitrate were much extended by J. W. Hyatt (1837-1920) in the United States, who found that camphor was effective as a plasticiser, and the resulting mixture was known as celluloid. Another semi-synthetic plastic, cellulose acetate, was introduced around the end of the nineteenth century, and had the advantage over cellulose nitrate of being less flammable. 

Cellulose acetate cellulose ester used with plasticiser as an injection moulding and extruding material. Not so highly flammable as cellulose nitrate. Used as sheet for packaging, also to produce pens, combs, knife-handles, etc. 

---