FLAX FIBRE

Evening Post, Volume CXI, Issue 138, 13 June 1931, Page 15

FLAX FIBRE

BLEACHING METHODS

CHEMICAL , EXPERIMENTS

Although prevented by his recent illness from carying on the work, Dr. J. S. Maclaurin, at tho behest of tho Department of Scientific and Industrial Research, has been experimenting to determine whether it is possible to find a cheaper and more satisfactory method of bleaching flax (phonnium tenax) than the present one of sun bleaching or "paddocking" a-s it is called.

Early in tho investigation, experiments showed that fresh fibre straight from tho stripper is very much more readily bleached • by artificial means than the same fibre after'drying. 1"1S fact precluded the - employment iot a large sample of dry fibre of uniform quality for all experiments and necessitated the use of a considerable number of samples of moist fibre direct from the stripper. These were obtained from time to time as required and were kept moist by wrapping m damp cloths and keeping in a closed box. As was to be expected, the samples were irregular in quality of leaf and in com-: pleteness of stripping and even, m the same hank there was seldom anything approaching uniformity. This flack of uniformity increased tho difficulties or the research very cousidorably, as it necessitated the careful mixing of the fibres in each hank and made necessary many determinations whore a few would have sufficed had the fibre been uniform. . The principal bleaching agents tried were hydrogen peroxide, ozone, sodium hypochlorite, and potassium permanganate. Hydrogen peroxide gave excelrent results, but its cost precludes its use. for tho commercial bleaching of flax. Several experiments on the, action of ozone on moist flax fibre showed that the bleaching action is slow and not very marked, and that the cost is prohibitive. Experiments with sodium hypochlorite showed that very good results could be obtained with, this substance, but as tho results were not better than those obtained, at a smaller cost, and apparently with less danger of damage to the fibre, with potassium permanganate, it was decided to postpone research on hypochlorite until that on permanganate had been completed. A very largo number of experiments was made on bleaching with potassium permanganate under very varied conditions. Very good results we/o obtained by treating the fibre with one per cent, of its dry weight of potassium permanganate and one of sulphuric acid,''dissolved in about thirty parts of water to one of fibre, .followed by treatment with sufficient sulphurous acicl in dilute solution to remove the precipitated manganese oxide, with final washing in water and drying. By this treatment, bleaching is more rapid and rather more thorough 'than in the absence of sulphuric acid. Still greater speed of action can be obtained by using hot solutions, but in this case the extra cost of, heating will have to be considered.

A very important point in connection with the bleaching with permangpnate is that, samples so treated do; not appear to s.uffer any reduction in tensile strength. In all the samples examined, portions of tho untreated fibre have been kept for comparison purposes, and their tonsilo strength can be compared at any time with that of tho corresponding bleached portion. Such tests, made after keeping for two months, showed no difference between the bleached arid the unbleached fibre. Further tests will bo made after longer periods of keoping. , '■...' \ A large number of experiments was made .to determine the effect of a preliminary treatment '." of the fibro with various substances in reducing1 the amount of permanganate required for satisfactory bleaching. Among the substances tried were sodium hydrosulphite, hot water, and cold water. Treatment with sodium hydrosulphite gives excellent results and very considerably reduces tho amount of permanganate required but at a cost that is much too great: Very much more promising results, from an economic standpoint, were obtained by washing with hojt water, or even with cold water followed by thorough wringing. Three washings with cold water, each follow,ed by officient wringing, reduced the amount .of permanganate required by 50 per cent. ■ It is along these lines that the artificial bleaching of flax on a commercial sealo is likely to bo most successful, says Dr. Maclaurin, in his report. Ho adds that there is no doubt that, if greater care in stripping were exercised and the stripped fibre artificially bleached and dried, the product would be increased in quantity owing to the elimination of "paddocking" losses, and'would be so much improved in. quality as to command a considerable advance in price. In view of theso facts it seems highly probable that artificial bleaching by tho permanganate method, efficiently carried out, would prove distinctly profitable. ' ■ ■' .-•■•;