Study On The Patterns Of Pelt Swelling And Collagen Structure Changing In Different Salt-lime Solutions

In the leather industry,the purpose of liming is to properly disperse collagen fiber bundles and expose active groups for the tanning section,which may directly affect the structure,performance of collagen and even the quality of final finished leather.A large amount pollution of sulfur ions and solids containing calcium ions are generated due to the large number of chemical reagents used in liming,which is detrimental to the sustainable development of the leather industry.How to achieve the clean production in the leather industry has always been the direction of scientific researcher.However,it is still not very clear about the contribution of each component to the liming result and the discipline of interaction between the components with pelts in liming.Therefore,it is of great significance to explore the contribution of each component and the discipline of interaction between the components with collagen for the realization of clean production in leather making.The effects of calcium hydroxide and urea/2%calcium hydroxide solutions on pelts and structure of collagen were studied.The changes of pH value,swelling ratio of pelts during liming and the content of proteins,proteoglycans and hydroxyproline in the waste water after liming were investigated.The opening up of collagen fiber bundles before and after liming was analyzed by EVG staining and scanning electron microscopy.The structure of pelts before and after liming were analyzed by FT-IR,and the thermal properties of pelts were also analyzed by TG.The results show that 7%urea/2%calcium hydroxide liming solution is best for opening up of collagen fiber.The swelling ratio of pelts treated by urea/2%calcium hydroxide is higher than that treated by calcium hydroxide.Contents of protein and proteoglycan in the waste water is higher than that treated by calcium hydroxide,which indirectly proves that urea/2%calcium hydroxide has a better ability to remove the interfibrillar substance of collagen fibers.And urea/2%calcium hydroxide has a lower degree of hydrolysis of collagen than pure calcium hydroxide.Moreover,the fiber bundles treated byurea/2%calcium hydroxide have better opening up effect.The properties of different salts with urea/calcium hydroxide solution system were studied.The changes of conductivity,pH and viscosity of sodium sulfate,disodium hydrogen phosphate,calcium chloride and magnesium chloride/urea/calcium hydroxide solutions were investigated.The results show that the conductivity of calcium chloride increases with salt concentration increasing due to the particularity of calcium ions.Sodium sulfate is a strong acid and alkali salt,so the conductivity of sodium sulfate has an increased trend with the increase of salt solution.Disodium hydrogen phosphate and magnesium chloride are strong baseweak and acid salt and strong acid and weak base salt,so their conductivity has a decreased trend with the increase of salt solution.The results of the pH change of liming solution is the same as that of conductivity.Viscosity of the liming solution is more affected by disodium hydrogen phosphate and magnesium chloride concentration,compared to sodium sulfate and calcium chloride.So the change of its concentration may have a great influence on the liming effect.Finally,the pH value,conductivity of the salt/urea/calcium hydroxide solution,swelling ratio of pelts and liming mechanism during liming were further explored,based on the interaction mechanism between urea/calcium hydroxide with pelts and salt/urea/calcium hydroxide solution properties.The results show that the swelling ratio of pelts is positively correlated with liming time.Due to the large liquor ratio,the conductivity of liming solution is not significantly affected by the liming time.Compared to disodium hydrogen phosphate and sodium sulfate,calcium chloride and magnesium chloride have an inhibitory effect on pelts swelling,the ability to remove proteins and proteoglycans in the waste water is strong,and the hydrolysis of collagen is decreased.The swelling ratio of pelts is positively linearly related to the degree of hydrolysis of collagen.The SEM images and residual content of TG samples data show that collagen fiber bundles treated by calcium chloride had better opening up effect.