GB799715A - Process for the preparation of cellulose powder - Google Patents

Abstract

A process for the preparation of cellulose powder from cellulose obtained in known manner from cellulosic raw material comprises separating from a suspension of the cellulose a portion containing at least 50 per cent cellulose of fibre length less than 0.2 mm., preferably less than 0.1 mm., and converting said portion to a cellulose powder by dehydration, drying and breaking up any fibre aggregates resulting. The process is applicable to the waste product called "save-all stuff" resulting from the decomposition of cellulosic raw materials, e.g. hardwood, softwood, and animal plants, portions containing at least 50 per cent cellulose of fibre length less than 0.2 mm., preferably less than 0.1 mm., being separated by either a wet sieving, or a flotation or sedimentation process. Decomposition of cellulosic raw material may be achieved by any known process, e.g. the sulphate or soda-sulphate process, and subsequent bleaching may be done by use of calcium hypochlorite. Dehydration, drying and breaking up any fibre aggregrates present may likewise be effected in known manner. Examples are given.ALSO:A process for the preparation of cellulose powder from cellulose obtained in known manner from cellulose raw material comprises separating from a suspension of the cellulose a portion containing at least 50 per cent cellulose of fibre length less than 0,2 mm., preferably less than 0,1 mm., and converting said portion to a cellulose powder by dehydration, drying and breaking up any fibre aggregates resulting. In example 1 an aqueous cellulose suspension is thickened in a screening drum to about 4 per cent consistency. Filtration through a sieve having an inner mesh width of about 0,3 mm. results in a filtrate containing 0,4-015 g. per litre of fibres, 60 per cent of which are smaller than 0,2 mm. The short fibres are enriched by flotation to 2-3 per cent stuff consistency and further thickened on a cell filter to a content of 20 per cent dry substance. In example 2 an aqueous cellulose suspension is placed in a rotating sieve having an inner mesh width of 0,4-0,8 mm. The filtrate therefrom containing fibres less than 0,2 mm. long is conveyed to a settling funnel, the short fibres being enriched therein by sedimentation, with subsequent dehydration on a cell filter with attached press. In example 3 "save-all stuff" is conveyed to a thickener having a sieve of about 0,4 mm. inner mesh width and the filtrate containing 0,5-0,7 g. per litre of short fibres, as defined above, is treated as described in example 2. A cylindrical sieve of inner mesh width from 0,3-0,4 mm. and a cell filter of less than 2 mm. inner mesh are employed in example 4.