Studies On The Thermal Properties Of Skin And Fibers And Gelatin Production Technology

The dry and wet heat properties of fibers on dechroming processes including soaking, liming, oxalic acid and sodium citrate are studied by determining the shrinkage temperature, shrinkage ratio and curve using thermal platform microscope and the collagen hydrolyzing in solution and content of chromium in leather, and moreover, the thermal properties of skin graft and fibers on different layers of skin after dechroming processes are analyzed. The results showed that:(1) It plays different effects on dry heat properties with different materials. The space between fibers becomes big by soaking, and a part of the hydrogen bond and electrovalent bond is destroyed, the shrinkage curve is crawling too long and the turning point is indistinct. The changing trends of shrinkage curves are similar after using lime, oxalic acid, sodium citrate, and the turning point is distinct. The sequence of shrinkage ratios and shrinkage temperatures after different processes from big to small is: oxalic acid>soaking>wet blue>sodium citrate>liming, wet blue>sodium citrate>liming>soaking>oxalic acid. The dry heat properties can be enhanced by liming and the shrinkage ratio is lower, shrinkage temperature is higher with the time of liming becoming long. The shrinkage ratio is higher and shrinkage temperature is lower with the time of oxalic acid dechroming becoming long. The changing trends of shrinkage curves are similar after dechroming different time. The dry heat properties can be enhanced using sodium citrate, and the shrinkage ratio is reduced, shrinkage temperature is increased with the time going on, and the turning point is distinct.(2) The content of chromium reduces on dechroming processes, the stability of collagen structure is decreased, and the collagen hydrolyzing is enhanced. The hydrothermal properties (Ts) of wet blue were different as dechroming materials. The quantity of dechroming and collagen hydrolyzing are enhanced with the oxalic acid and lime dechroming time going on, the stability of collagen structure is destroyed. The hydrothermal properties of wet blue are reduced. The sodium citrate plays effects on dechroming and cross-link among collagen fibers, so the content of chromium reduces, collagen hydrolyzing is enhanced, but shrinkage temperature rises with dechroming time becoming longer.(3) The thermal stability of skin graft relates to cross bonding, but the fibers relates to amorphism and crystal regions. The cross bonding is more, the thermal stability is higher, and the shrinkage temperature is higher, the shrinkage ratio is lower.The wet blue and being liming, the thermal stability of skin graft is higher than fibers, and, the thermal stability on both sides of the skins is higher than middle, the flesh layer is higher than grain layer. After dealing with oxalic acid, the thermal stability of fibers are higher than skin graft on grain layer, but lower on both flesh and middle layers, and, the thermal stability on both sides of the skins are higher than middle, the flesh layer is higher than grain layer. Sodium citrate can make the thermal stability of skin graft higher than fibers, and, the middle is higher than other sides, the flesh layer is higher than grain layer.The dry heat shrinkage behaviors of wool fibers are studied by the thermal platform microscope during the processing of sheepskin as well as the effects of different tanning agents, fatliquors, enzyme on the wool fibers. The results showed that both pickling and fatliquoring can improve the dry heat shrinkage behaviors of wool fibers, but the tanning can not. The kinds and numbers of fatliquors play important effects on the dry heat shrinkage behaviors. The enzyme can also reduce the final contraction percentage.The changing rules of effect factors of gel strength and quantity of gelatin are studied by orthogonal design and range analysis, and moreover, the spray-drier technology of jelly powder is optimized. The results showed that the effect sequence of every factor to gel strength and quantity is: temperature> time> pH, temperature> pH> time; the optimum conditions of cooking the pig raw material are: 4 hours at the temperature of 62℃and the pH=5.28; the effect sequence of every factor to gel strength and viscosity of jelly powder is: pump> solution concentration> aspirator> inlet temperature, aspirator> pump> solution concentration> inlet temperature, the yield and the moisture both are: solution concentration> pump> aspirator> inlet temperature; The optimum conditions of spray-drier preparation are: solution concentration 5%～6%, pump 18ml/min, inlet 170～175℃and the aspirator 35～37m3/h.