Studies On The Method And Principle Of Hydrogen Peroxide Unhairing

In this paper, the factors influencing hydrogen peroxide unhairing of cattle hide and the mechanism of the process were studied. The effects of hydrogen peroxide offer, pH value, temperature, float and added rate of hydrogen peroxide on efficiency of unhairing were investigated. Contents of hydroxy-proline and nitrogen in waste water were determined by colorimetry and Kjeldahl procedures so that the relationship between hydrolytic degree of hide protein and unhairing condition could be observed. The comparison of hydrogen peroxide unhairing and conventional sodium sulfide unhairing was made based component analysis of waste water, effectiveness of chrome tanning and physical properties of resultant leather. Meanwhile the influence of two unhairing techniques on microstructure of hide or leather in processing was researched by histological observation and the histological mechanism of hydrogen peroxide unhairing was elucidated.To obtain further information of chemical mechanism, a series of typical ammo acids existing in hide collagen were treated with alkali hydrogen peroxide solution in the condition similar to unhairing process, and the change of their structure was determined by IR. Furthermore, the influences of alkali hydrogen peroxide solution on isoelectric point (IP) and shrinkage temperature (Ts) of hide and glass transition temperature (Tg) of gelatine were studied.The trials above indicated that the offer of hydrogen peroxide and the pH value of float were the main factors affecting unhairing result. When pH value was 12.5-13.0 and hydrogen peroxide offer was more than 7.5% based on hide weight, hair could be easily removed. But when hydrogen peroxide offer was more than 9.5%, hide collagen would be damaged evidently. Suitable temperature of float was 25C; incomplete unhairing would be observed when lower temperature was used. A short float and a faster added rate of hydrogen peroxide were favourable to unhairing.Compared with sodium sulfide unhairing, the unhairing with hydrogen peroxide could produce decreased contents of COD, S2", NH3-N2 and suspended solid in waste water; the content of S2- was particularly elimitated. It was also found that unhairing with hydrogen peroxide could increase content of Cr2O3 in leather after chrome tanning and improve tensile strength of crust. During unhairing, hair root was dissolved at the first, then hair was completely removed. At the same time, collagen fibers of hide were effectively dispersed. A distinct advantage of using hydrogen peroxide was that the connection of grain and reticular layers could be enhanced which could reduce loose grain of resultant leather.Reacted with hydrogen peroxide, some of cystines in hiar were derived into sulfide or sulfonate, leading to hair removing. Alcoholic hydroxyl of serine in hide collagen was oxidized into carboxyl group, and that of threouine was oxidized into acetaldehyde which could link with free amino group of protein. The linkage between protein fibers was verified by increased Ts of hide and raised Tg of gelatine. Both the derivation of alcoholic hydroxyl into carboxyl group and the linkage interaction of free amino group led to lower IP of hide, as observed.