Study On Key Basic Issues Of TanningChemistry

Leather is a kind of collagen based natural high molecular weight material with multi-scale structure, and it is the core task of tanning chemistry to establish the relationship between leather processing, leather structure and leather properties. Collagen fibers have two kinds of different scale motion forms under stress, one is collagen molecular motion, the other is collagen fiber motion. Molecular motion is the bridge to establish the relationship between structure and properties of materials. Therefore, to establish the relationship between the structure and properties of leather, there are two key scientific issues need to be clear:what are collagen molecules motion law and collagen fibers motion law, and which are their influence factors. My thesis is mainly focusing on these two issues and several conclusions are drawn as followings.The analysis of the structure of the collagen based tissues showed that homogeneous system collagen fiber have sparse stacking, orientation and reticulate polymer crystallization etc. condensed state structure characteristics and fibers morphology(coiled shapes), fibers orientation(arrangement of collagen fibers), physical property of interstitial fibers and interface interaction between fibers and fibers interstitial of heterogeneous system are the main factors affecting fibers motion.The study on the heat shrinkage transition behavior of collagen fibers show that heat shrinkage transition followed the mechanism of Nâ†'D1â†'D2â†'M (N orientation crystalline state collagen, D1 orientation amorphous collagen, D2 non-orientation amorphous collagen, M melting non -reticulate collagen).The heat contraction process of collagen fibers was characterized by TEM, SEM, XRD, DMA, DSC and FTIR. The TEM and SEM analysis showed that collagen fibers have sparse stacking, orientation and reticulate polymer crystallization etc. structure characteristics; The TEM, SEM and XRD analysis showed that the shrinkage of collagen molecular is "in situ" shrinkage; The force field analysis of collagen molecular showed that lateral balance covalent bond force and axial non-equilibrium entropy force is the physical essence of "in situ" heat shrinkage; The DMA analysis showed that there are two stages of disorientation and one viscous flow transition. The first disorientation process is the transition of orientation crystallization collagen to orientation amorphous collagen, the second disorientation process is the transition of orientation amorphous collagen to non-orientation amorphous collagen, the viscous flow process is the transition of reticulate collagen to non-reticulate collagen.Analysis of interaction process between PAA and collagen fibers, and mechanical properties of wet and dry leather retanned by PAA showed that PAA mainly influenced and regulated collagen fibers texture in wet-dry transition process of leather. The wet-dry transition of collagen fibers texture was investigated from fibers kinematics and the result showed there are two stages in wet-dry transition, one is the moving closer to each other of collagen fibers, the other is the binding of collagen fibers. There are two kinds of aggregation tendency of collagen fibers, ordered and disordered aggregation.The wet-dry transition behavior of leather texture retanned by PAA was characterized by SEM,XRD,TEM and stress-strain analysis. The influence of capillary pressure difference force, hydrogen bond and adhesion force of capillary flow to texture was investigated, the results showed that:(a)collagen fibers tends to be ordered aggregation under capillary pressure difference force and keep the state of separation in the absence of capillary pressure difference force;(b) hydrogen bond force is an important factor affecting the fiber aggregation. In the absence of hydrogen bond force, collagen fibers tends to keep the state of separation;(c)A new combination mode, the adhesion of solidification capillary flow, was formed between fibers after leather retanned by PAA, (d) with the increasing of adhesion force of solidification capillary flow, the tendency of disordered aggregation increases.