Abstract

This paper describes the results obtained during an examination of the mechanical properties of chrome retan and semichrome fibres. The use of a large number of treatment combinations in two factorial arrangements has enabled a fairly comprehensive study of the problem to be made. Many of the variations possible with combination tannages, inside the limits of normal tannery practice, were investigated, and some of the methods of processing led to relatively large changes in the mechanical properties of the fibres. Thus it was found that the liming process can cause a loss of strength if it is prolonged, or if insufficient control is exercised at this stage when caustic soda is used. The use of concentrated chrome liquors in the semichrome process was also found to be undesir able if maximum fibre strength and extensibility is required. The mechanical properties of combination tanned fibres depend upon the humidity at which they are tested. The influence of humidity is much greater for combination tanned fibres than for raw, vegetable tanned, or chrome tanned fibres. Combination tanned fibres become steadily stronger and more extensible as the humidity is raised; this may be explained by assuming that water vapour absorption increases the lubrication between the fibril components within the fibre. Weight for weight, combination tanned fibres are weaker and have lower breaking extensions than raw fibres. The loss of strength as a result of processing depends on the fibre weight per unit length, and it is particularly marked for thin chrome retan fibres. The shape of the stress-strain curve for combination tanned fibres is independent of test conditions and method of processing. The curves can be adequately expressed in power law form, a method of expression found to be suitable also for raw fibres. There are close similarities between the broad pattern of physical and mechanical properties of raw collagen fibres and those fibres tanned in widely different ways. While tannage may introduce considerable changes in such properties as appearance, strength, and bieaking extension, the general pattern of fibre mechanical behaviour is largely unchanged.