Submitted to: Textile Research Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/16/2005
Publication Date: 2/1/2006
Citation: Cardamone, J.M., Nunez, A., Ashby, R.D., Dudley, R.L. 2006. Activated peroxide for enzymatic control of wool shrinkage part 1: elucidation. Textile Research Journal. 76(2):99-108.
Interpretive Summary: Conventional bleaching of wool with hydrogen peroxide requires high temperature (45°C to 60ºC) and relatively long exposure times (50 to 60 minutes). The new ARS process for making biopolished wool includes a pretreatment step utilizing activated hydrogen peroxide. Besides preparing the fibers for subsequent treatment by an enzyme to ultimately lead to itch-free, machine-washable wool, the peroxide pretreatment has a remarkable bleaching effect under relatively mild reaction conditions (30ºC for 30 minutes). Research was needed to determine the mechanism of this bleaching process to understand its advantages and limitations. Results showed that alkaline hydrogen peroxide reacts with dicyandiamide under pretreatment conditions to produce activated dicyandiamide peroxide, a more powerful agent than hydrogen peroxide. The activated peroxide was stabilized by including gluconic acid in the formulation of the pretreatment bath. The peroxide consumption of the stabilized bleaching bath during its contact with wool was approximately 10%; thus it could be recharged with a small amount of additional hydrogen peroxide for further use. A thorough understanding of the biopolishing process and its bleaching effect will enable an economic application to wool and thereby promote new markets for this commodity.
Technical Abstract: The ARS process combines activated peroxide for pretreatment and enzyme for subsequent treatment to provide bleached, biopolished, and shrinkage-resistant wool. The pretreatment step is of particular interest because it combines dicyandiamide (DD) with alkaline peroxide to form peroxycarboximidic acid, a stable and powerful bleaching agent that is stabilized by gluconic acid (GA)when applied at pH 11.5 for 30 minutes at 30°C. Analytical methods of analysis provided information showing that the active bleaching component, peroxycarboximidic acid, is formed immediately upon the combination of DD with alkaline H2O2 and that cyanamide forms concomitantly as a co-product. The peroxide pretreatment bath was stable at room temperature for up to 4.5 hours with only 10% peroxide consumed. It should therefore be possible to reconstitute the bleaching bath for further utilization. The eventual alkaline hydrolysis of cyanamide to form urea and the recombination of urea with peroxycarboximidic acid formed the end-product, guanylurea, shown by high performance liquid chromatography associated with electron impact mass spectrometry (LC/EI-MS), FTIR, and C13 NMR. Differential Scanning Calorimetry (DSC) and peroxide titration of pretreatment baths provided evidence that GA stabilizes the activated peroxide. Activated DD peroxide pretreatment is essential to the ARS process for it provides a high level of whiteness without loss in fabric properties and it prepares the wool fiber for enzymatic treatment designed to selectively modify the scales of wool to biopolish the fabric surface and provide itch-free, machine-washable wool.