The leather industry, world over, has adopted several new practices as a part of their green initiative. In this study the chrome tanning process, one of the most important steps in leather making, was evaluated for its ‘greenness’. The prominent tool employed for assessing greenness for an industrial process, atom economy (the conversion efficiency of a chemical process in terms of all atoms involved) was studied for the first time for four types of chrome tanning processes: direct chrome liquor recycle (DCLR), ethanolamine-assisted, pickleless chrome tanning, and conventional chrome tanning. All chemicals involved in the reaction with skin protein were taken into consideration for the computation of overall atom economy. An atom economy of only 29% was obtained for the conventional chrome tanning system. Among the four improved methods of chrome tanning evaluated, the pickleless chrome tanning method provides the maximum atom economy of about 57% followed by ethanolamine and DCLR, having atom economies of 42 and 32%, respectively.
Part I. Preparation of Four Natural Iridoids and Their Dyeing/Cross-Linking (Tanning) Property to Hide Powder. Four iridoid compounds, genipin, loganin aglycone, oleuropein aglycone and E-6-O-methoxycinnamoyl scandoside methyl ester aglycone were prepared from Gardenia jasminoides Ellis, Lonicera japonica Thunb, Olea europaea Linn and Hedyotis diffusa (Willd) Roxb respectively, their structures were identified by electron spray ionization mass spectrometry (ESI-MS), 1H NMR and 13C NMR. Their dyeing/tanning properties on hide powder was investigated, the relationship between dyeing/cross-linking (tanning) property and the chemical structures were discussed. The results showed that these four natural iridoids could react with hide powder under mild conditions (35°, pH=7.5-8.0), within a short time (about 6 h) and at a low dosage (5% (w/w) of hide powder). The hydrothermal stability of the reacted hide powder was 20-25°? higher than the control sample, and different colors, such as dark blue, brown-yellow, yellow and mauve, were imparted to hide powder. The mechanism might be that cross-linking reaction took place between iridoids and –NH2 groups of collagen molecular chains. These results implied that natural iridoids might act as completely novel “natural reactive dyes”, especially for protein fibers and offering environmental-friendly simultaneous tanning-dyeing agents for leather manufacture.
A “clean” leather dyeing was designed with wringing (8-10kg/cm2), ultrasound (28kHz, 2.4W/cm2) and microwave (2450MHz, 10W/L). Twenty leathers were successively colored with this method in lab scale. The dye exhaustion (%), the color values and the color rub fastnesses were determined respectively. Also, the grain surface and the cross-section of the leathers were analyzed before and after dyeing. As presented, it only needed 5min to color with this method and the dye exhaustion averages 2.3% a leather, which were helpful for the recycle of the dye solution. The color for the first ten leathers just varied within a small range (ΔΕ<1), when the solution was directly recycled without dye replenishment. The color fastnesses reached up to 4-5 scale (dry rub) and 3 scale (wet rub) after the leathers were coated as a common shoe upper finishing formula. Furthermore, the grain and the collagen fibers were not damaged during the dyeing process, which were proved by Scanning Electron Microscope and X-ray diffraction analysis. In short, this clean and quick dyeing is a potential choice for leather dyeing.
Leather handle strongly relates to leather quality, and in the leather industries it is still manually assessed by experts. In this paper a new approach, Descriptive Sensory Analysis, was applied when subjectively measure leather handle and thus a comprehensive handle profile was established. Ten attributes of leather samples were identified and quantified by a trained expert panel according to agreed procedures. Principal Component Analysis was used to reduce data dimensionalities and a conception 3D handle space was proposed and demonstrated to exhibit the handle attributes of leather.