Optimization Of Collagen Fiber Opening With Enzyme By Response Surface Methodology

In the traditional beamhouse,sodium sulfide and calcium hydroxide are used to dehair and disperse collagen fibers for tanning.However,the pollutants such as sulfide,ammonia nitrogen,and suspended solids are caused,which are the main sources of pollution in the tanning industry.Therefore,it is necessary to find a way reduce the pollution from the tanning industry.An efficient,clean and specific biological enzyme system was selected to replace traditional chemical materials.By establishing the response surface model（RSM）,the influence of different factors on the fiber opening in the process of dehairing/fiber opening and the relationship between each factor were studied.The physical properties,thermal stability and environmental benefits of the leather obtained by the traditional process and the enzyme process were studied.In the process of ammonium chloride（NH₄Cl）/dispase system for dehairing/fiber opening,the effects of NH₄Cl concentration,temperature,and time on the activity of dispase and the dissolution of interfibrillar substance were investigated.The dissolution of interfibrillar substance and the fiber opening were analyzed by EVG staining and SEM,and the RSM was established,which was compared with those of the traditional process.The results showed that the dehairing/fiber opening effect is the best with 1%NH₄Cl（base on the hide weight）at 32℃for 15h,.and environmental benefits is better than the traditional one.The effect of ammonium sulfate（（NH₄）₂SO₄）/dispase system for dehairing/fiber opening was investigated.The dehairing/fiber opening effect is the best with 1%（NH₄）₂SO₄ at 30℃for 15h,similar to the NH₄Cl/dispase system.The physical properties of tanned leather are better than those of the traditional process,and the tensile strength was increased by 18.22%,the elongation at break and elastic modulus were slightly improved,the thermal stability was comparable to the traditional process,and the pollutants were greatly reduced.Compared with NH₄Cl/dispase system,the contents of chemical oxygen demand（COD）,ammonia nitrogen（NH₃-N）and total solids（TS）were decreased slightly.Besides,the magnesium chloride（Mg Cl₂）/dispase system for dehairing/fiber opening was investigated.The dehairing/fiber opening effect is the best with 2%Mg Cl₂ at 35℃for 18h.Compared with those of the NH₄Cl/dispase system and（NH₄）₂SO₄/dispase system,the concentration of salt,temperature and time are increased,which might be because the better ability of NH₄⁺to combine with dispase than that of Mg²⁺,which could more effectively improve the solubility of dispase and accelerates the penetration rate of dispase.The physical properties of the leather obtained by the optimized Mg Cl₂/dispase system was better than those of the traditional process,with the tensile strength increased by 27.18%,with comparable elongation at break,elastic modulus,and thermal stability to those of the traditional one.The environmental benefits were significant.Further research on the effect ofα-amylase/neutral protease system on dehairing/fiber opening was done.The dehairing/fiber opening effect is the best with0.5 wt%neutral protease and 0.3 wt%α-amylase at 35℃for 20 h.Compared with the salt/dispase system,the temperature and time are increased.The physical properties of the leather by the optimizedα-amylase/dispase system were better than those by the traditional process,with the tensile strength increased by 27.85%,and comparable elongation at break and elastic modulus to the traditional one.The thermal stability of the leather and the environmental benefit are significantly better than those by the traditional process.