Patent GB-552129-A (GB)
Title: Manufacture of cellular products
IPC: C08J9/00
Filed: 1941-09-19
Abstract: 552,129. Cellulose derivative compositions and articles; moulding plastic substances. BRITISH CELANESE, Ltd. Sept. 19, 1941, Nos. 12075 and 12076. Convention dates, April 26, and June 18. [Class 2 (ii)] [Also in Group V] Moulded cellular products of materials having a basis of cellulose esters or ethers are obtained by treating the cellulose derivative material in finely divided form with a liquid, capable of softening or dissolving the material, in an amount of 1-40 per cent. of the weight of the cellulose derivative so that the material retains its finely divided form, subjecting the finely divided material containing the absorbed liquid to elevated temperature and to a pressure of at least 1,000 pounds per square inch, and thereafter releasing the pressure quickly to permit rapid vaporization of the absorbed liquid and at the same time moulding the material to the desired form or shape. Cellular products of cellulose esters may be partially or completely de-esterified to form cellular products suitable as substitutes for sponges. Products suitable for heat insulating material for refrigerators or pipes or for insulation or coverings for electrical equipment may be made. Thin sheets or discs may be used for filtration purposes. The pores may be sealed by treatment of the surface of the expanded material with a solvent or by heating, or by inserting thin sheets of unplasticized cellulose derivatives above and below the charge before closing the mould and then allowing the material to expand. Such products may be used in making life-belts and rafts. The solvent or softening liquid may be acetone, ethyl alcohol, water, chloroform, ethylene dichloride, acetone and ethyl or methyl alcohol, ethylene dichloride and ethyl or methyl alcohol, butyl alcohol, diacetone alcohol or gasoline hydrocarbons. The desired quantity of liquid may be applied to the finely divided cellulose derivative which may be in the form of fibres or small particles, by spraying, and the mixture may be tumbled until the liquid is uniformly distributed. Alternatively, the cellulose derivative may be exposed to the vapours of the solvent or swelling liquid until the desired quantity is absorbed. The impregnated material may be subjected to heat and pressure in a mould provided with a piston or plunger shaped to conform to the mould. Upon sudden release of the pressure the rapid vaporization of the liquid causes the cellulose derivative to expand to a firm cellular structure which fills the mould. The cellulose derivative mass may be extruded into moulds through orifices so that the pressure is suddenly released as the material passes the orifices. The moulds or pressure chambers may be heated by oil, gas, or electricity. The heating should be such that at the time when the pressure is released the cellulose derivative has been at least partially converted, i.e. softened or gelled by the liquid. The cellulose derivative may be cellulose acetate, nitrate, or other ester or methyl or benzyl cellulose. The products may be strengthened or modified in appearance by incorporating in the composition, fibrous fillers such as cotton, flax, or hemp, or other fillers such as cork, sawdust, shavings, clay, or asbestos. Pigments, fire retardants, and plasticizers may be incorporated. If the porous bodies are to be saponified, there may be used caustic soda, caustic potash, sodium silicate, ammonium hydroxide, or sodium carbonate. Alcoholic solutions of alkali may be used. Water-soluble fillers such as sodium bicarbonate, sodium chloride, sodium borate, sodium citrate, and sodium potassium tartrate may be incorporated in the composition. These fillers are removed when the porous bodies are subjected to the saponification and washing treatments. The saponified products may be used for surgical or sanitary dressings, pads, tampons and the like.