GB1114273A - Treatment of animal hides and skins using alkali metal phosphorus compositions - Google Patents

Abstract

Alkali metal-phosphorus-sulphur compounds used in aqueous slurries or solutions for unhairing hides and skins are prepared by reacting a phosphorus sulphide with excess alkali metal hydroxide and/or sulphide. If the hair is to be recovered, at least half the alkali metal in the product should be provided by hydroxide; vice-versa if the hair is to be destroyed. The compounds may be used in a lime system using a slurry containing 6% lime - in this case the hydroxide: P4S10 ratio should be above 12 to 20:1, or the sulphide: P4S10 ratio above 8 to 14:1. Alternatively a non-lime system may be used, containing 0.5-50% alkali metal or ammonium hydroxide, amines, urea, or ammonia, 0.1-10% CaCl2, Ca(NO3)2, alkali metal carbonates, Zn hydrosulphite, or Ba or Sr chloride, nitrate or sulphate as "sharpening agents", and 0.5-50% alkali metal halides, e.g. NaCl, nitrates, or sulphates as buffering agents; the alkalinity may also be provided by using higher alkali metal hydroxide: P4S10 ratios e.g. 55 to 60:1. In either case, alkali metal sulphides or sulphydrates, or sulphur may be added as sharpening agents, and the additives may be dry blended with the alkali-metal-P-S compound or added to the solution. The amount of alkali-metal-P-S compound used may be 0.1-10%, and the unhairing solution preferably has a pH of at least 12, e.g. 12.2-12.8. (All % are by wt. of the hides). The hides may first be soaked in water containing up to 2% alkali metal sulphides, tetrasulphides or sulphydrates. The alkali metal in the P-S compounds may be Na, K, Li, Rb or Cs.ALSO:Alkali metal-phosphorus-sulphur compounds are prepared by reacting a phosphorus sulphide with an aqueous solution or melt of an alkali metal hydroxide or sulphide, using more than 12 moles of hydroxide or 8 moles of sulphide per mole of P sulphide expressed as P4S10. A mixture of alkali metal hydroxide and sulphide may be used, replacing 2 moles of hydroxide with one of sulphide, or vice versa. The alkali metal may be Na, K, Li, Rb, or Cs. The solution of alkali metal compound may be at least 10%, preferably 70% for hydroxide and 60-65% for sulphide; with dilute solutions, water is evaporated during or after reaction to give a solid product. The P sulphide may be P4S10 to P4S24, and is preferably added to the alkali metal compound to maintain alkalinity. The products are used for unhairing hides; other active materials e.g. sulphur, and alkali metal sulphydrates, may be mixed with the reactants.