Celluloid

CELLULOID. This artificial substance, known also as arti ficial ivory and xylonite, is a compressed, solid solution of nitrated cellulose in camphor or a camphor substitute. It is colourless or slightly yellow, transparent in thin sheets, and capable of being stained with the most delicate colours, which permeate its entire mass. Celluloid is of uniform composition and its specific gravity is about 1.35; it is insoluble in water or dilute acid, usually emits a faint smell of camphor and is inflammable.

Celluloid becomes plastic when immersed in water at or near boiling-point and can then be moulded into any desired form. At ordinary temperatures it can be cut, turned, sawn, drilled and otherwise worked to form numerous useful and ornamental articles. Having a tensile strength of 10,000-12,000 lb. per sq. in., it is one of the strongest of artificial materials. Celluloid is elastic, and can be produced in very thin sheets and films; cellu loid films o•0000039 ( in. thick were made in 1924 by the U.S. Bureau of Standards, for use in X-ray researches.

The solubility of nitrated cellulose in camphor is the important property on which the success of making ordinary celluloid de pends. Tissue paper, cotton, wood or other cellulose material is nitrated by means of a mixture of strong nitric and sulphuric acids. The product, which is of the nature of, but less highly nitrated than, gun-cotton, is bleached, washed and dried; it is then incorporated in a mixing-machine, with natural or synthetic camphor and volatile solvents. At this stage softeners, e.g., oils, colouring matter and filling material, selected according to the kind of celluloid required, may be added. The gelatinous mass ob tained is transferred to heated adjustable rollers by which it is kneaded and rolled into sheets of any desired thickness. After re moval from the rollers, the sheets are pressed and dried or sea soned to eliminate the volatile solvents.

Numerous modifications of the process thus briefly described have been proposed, some having for their objects the production of so-called "non-inflammable celluloid" and the use of a substi tute for camphor, the price of which is usually high.

Making Celluloid Safe.

The attempts to make a celluloid which is less inflammable than ordinary celluloid have been to some extent successful. To achieve this result, a chloride has been added to the celluloid-making materials, or a bromate or other substance capable of liberating flame-extinguishing gases, or the celluloid mass has been very highly compressed. Acetyl cellulose or cellulose ethers have also been used instead of the nitrated cellulose; this use, however, leads to a consideration of processes, outside the scope of this article, in which acetyl cellu lose, cellulose ethers, and synthetic resins and not nitrated cellu lose are used.

There have been very many attempts, mostly unsuccessful, to obtain a suitable camphor substitute. The most commonly used substitutes for camphor are the cresyl phosphates dibutylphthal ate ; these also render the celluloid less inflammable. Recently cel luloid manufacture has been very much modified. Celluloid is pre cipitated, in the form of powder, by gradually adding water to its solutions. After separation, the powder is dried, filled into moulds and heated until plastic under pressure. Such processes have the advantage of considerably shortening the seasoning step and facilitating addition of colouring matter.

The term celluloid was first applied by Messrs. J. W. and I. S. Hyatt, who began the manufacture of the material in the United States in 1869. Their work was based on that of A. Parkes and D. Spill, who, in 1855 and 1868 respectively, succeeded in England in making similar plastic materials. The advance of J. W. and I. S. Hyatt was due to their investigations into the action of cam phor upon cellulose and to their improved mechanical methods. The industry has become established in the United States, Great Britain, France, Germany, Austria, Switzerland and Japan.

Not only ivory but also horn, tortoise-shell, amber, agate, ebony and many other natural substances may be imitated by means of celluloid, and it is used in making numerous useful and ornamental articles. These include cutlery handles, billiard balls, collars, auto mobile windows, piano keys, buttons, combs, brush and mirror backs, fancy boxes, dolls, hollow balls and other toys, dental plates, accumulator cases, telephone mouthpieces, transparent screens and parts of drawing and optical instruments. During the War the demand for celluloid articles such as accumulator cases and transparent screens, was great.

In obtaining irregular colour effects in celluloid, e.g., for pro ducing imitation tortoise-shell, colouring matters are dropped very carefully and in small quantities upon a sheet of celluloid before seasoning, as the sheet passes between rollers ; the colouring matter sinks into the sheet.

See F. Boeekmann, Celluloid (1921) ; H. H. Hodgson, Celluloid (T. E. L.)