The Action of Nitric and Hydrochloric Acids on Wool with Particular Reference to Supercontraction of the Fibers

Treatment of wool with 40% (wt./wt.) HNO₃ at 0-30° C. for periods up to 18 hr. causes a decrease in sulfhydryl, disulfide, and tyrosine contents and an increase in free amino groups. An equivalent concentration of HCl under similar conditions causes an increase in free amino groups and, with the more severe treatments, a decrease in tyrosine content and an increase in disulfide content as estimated by the Shinohara method. Alkali solubility and trypsin digestibility are greatly increased by the acid treatments; the solubility in urea/bisulfite solution first decreases, then increases with increasing time of treatment. Both acids cause loss of weight of the samples treated for 18 hr. at 30° C. Apart from a small increase in the initial rate, the kinetics of supercontraction of single fibers in solutions containing 1 N HCl and 4 M LiBr are not greatly changed by acid treatment, nor is the level of the final contraction greatly altered. In 6 M LiBr at pH ca. 6 the nitrated fibers contract very rapidly by 10-15% ; the contraction is then greatly retarded until a slow second stage of contraction develops. With HCl-treated fibers the contraction is again slightly accelerated initially and later retarded, but the changes are smaller and the division into two stages of contraction less apparent. Treat ment with HNO₃ causes the fibers to contract more rapidly at all levels of contraction in 4 M LiBr at pH ca. 8, and with the more severe treatments, the initial contraction is followed by a period of elongation and a second slow contraction. On the other hand, HCl-treated fibers contract rapidly to the final level of contraction, but this may be very small. With the more severe treatments in HCl, the initial contraction is followed by elongation to a length approximating the original. The kinetics of supercontraction are discussed in terms of chemical and configurational changes in the fibers.