Patent GB-986637-A (GB)
Title: Black organic fibres and fabrics and processes for making them from regenerated cellulose
IPC: D06M13/184
Filed: 1961-04-07
Abstract: Black, inert, heat-resistant, non-carbonized organic fibres and fabrics are made by a controlled thermochemical transformation of corresponding fibrous regenerated cellulose fibre, fabric, yarn or tow starting material without loss of fibre identity by impregnating the fibres of the starting material with a water-soluble salt of a strong acid and a nitrogenous base sufficient to bring about the transformation and heating the salt-impregnated material in a dry state at a temperature of 450-600 DEG  F. until it has passed beyond the point of lowest fibre strength and has regained a tensile strength equal to at least 20% of the original fibre strength.  The fibrous material may be held under tension during processing.  A nitrogenous phosphate salt may be used for the impregnation.  Salts suitable include amine and ammonium salts of strong acids, provided these have a solubility of at least 10% in water; e.g. salts of ammonium, mono-, di-, and tri-methyl- and ethyl-amines, hydrazine, aniline, morpholine, pyridine and ethylene diamine with sulphamic, sulphuric, phosphoric, hydrochloric, hydrofluoric, tri-chloroacetic and tri-fluoroacetic acids; ammonium sulphate and sulphamate, dibasic ammonium phosphate, ammonium chloride, and methyl- and ethyl-amine salts of phosphoric acids, and mixtures thereof, are preferred, 10-30% solutions being preferably used to give a salt pick-up of 5-20% on the dry basis.  Hot solutions may be used, e.g. at 140 DEG F.  A mixture which may be used consists of 10% ammonium sulphamate, 4% dibasic ammonium phosphate, 2% dicyandiamide, 4% boric acid and 80% water.  In a preferred method, the impregnated material is heated for 5-30 mins. at 550-500 DEG  F., conditions being so controlled as to produce a product having a tensile strength of at least 40% of the original tensile strength.  The black product is thereafter washed to remove soluble residues. The material may be impregnated with a phosphate salt and so treated as to yield a flexible flame-resistant product which is free from after-glow on intense heating and has a chemical composition comprising 54-61% carbon, 3.4-4.0% hydrogen and 3.1-5.8% nitrogen.  Phosphate salts are preferred owing to the flame- and fire-proofing thereby imparted and the freedom from glow or after-glow of the finished product when subjected to intense heat or flame.  Alternatively, where other salts are used for the treatment, the black product may be impregnated with a phosphate salt solution, e.g. 10% aqueous dibasic ammonium phosphate and dried.ALSO:Black, inert, heat-resistant, non-carbonised organic fibres and fabrics are made by a controlled thermochemical transformation of corresponding fibrous regenerated cellulose fibre, fabric, yarn or tow starting material without loss of fibre identity by impregnating the fibres of the starting material with a water-soluble salt of a strong acid and a nitrogenous base and heating the salt-impregnated material in a dry state at a temperature of 450-600 DEG F. unit it has passed beyond the point of lowest fibre strength and has regained a tensile strength equal to at least 20% of the original fibre strength.  The product is suitable for making heat-resistant insulative articles of wearing apparel, aprons and gloves, fire barrier drapes, fire-resistant insulating sleeves for electrical conductors and for piping and conduits, and fibrous insulating bats.  Fibres in flock form can be used as heat-resistant flocked coatings.  Fabrics, yarns and continuous filaments can be used in fibrereinforced plastics subject to high temperatures, including "ablation" types, and types which should not include any metal or metal atoms, or leave an ash residue upon decomposition or vapourization, as backings or reinforcing fibres in high-temperature types of adhesive tapes, including pressure-sensitive adhesive tapes, and as inert acid-resistant filter cloths for filtering very hot gases, liquids and even molten metals.  The yarns have better heat resistance than insulating properties than asbestos fabrics.  The fibrous material may be held under tension during processing.  A nitrogenous phosphate salt may be used for the impregnation. Salts suitable include amine and ammonium salts of strong acids, provided these have a solubility of at least 10% in water; e.g. salts of ammonium, mono-, di-, and tri-methyl- and ethyl-amines, hydrazine, aniline, morpholine, pyridine and ethylene diamine with sulphamic, sulphuric, phosphoric, hydrochloric, hydrofluoric, tri-chloroacetic and tri-fluoroacetic acids; ammonium sulphate and sulphamate, dibasic ammonium phosphate, ammonium chloride, and methyl- and ethyl amine salts of phosphoric acids, and mixtures thereof, are preferred, 10-30% solutions being preferably used to give a salt pickup of 5-20% on the dry basis.  Hot solutions may be used, e.g. at 140 DEG F.  A mixture which may be used consists of 10% ammonium sulphamate, 4% dibasic ammonium phosphate, 2% dicyandiamide, 4% boric acid and 80% water.  In a preferred method, the impregnated material is heated for 5-30 mins. at 550 DEG -500 DEG F., conditions being so controlled as to produce a product having a tensile strength of at least 40% of the original tensile strength.  The black product is thereafter washed to remove soluble residues.  The material may be impregnated with a phosphate salt and so treated as to yield a flexible flame-resistant product which is free from after-glow an intense heating and has a chemical composition comprising 54-61% carbon, 3.4-4.0% hydrogen and 3.1-5.8% nitrogen.  Phosphate salts are preferred owing to the flame- and fire-proofing thereby imparted and the freedom from glow or after-glow of the finished product when subjected to intense heat or flame.  Alternatively, where other salts are used for the treatment, the black product may be impregnated with a phosphate salt solution e.g. 10% aqueous dibasic ammonium phosphate and dried.