Preparation Of Collagen-based Composites And Application In Cleaner Tanning Process

Chrome-containing leather scraps have become an important available resource because of containing large amount of collagen and chromium salt.How to extract and reuse these effective components to cleaner tanning process is the primary research hotspot.In this thesis,three kinds of collagen-based composites were prepared by modifying collagen hydrolysate(CH)extracted from chrome-containing leather scraps by alkali hydrolysis with polymers,which were subsequently used in low-salt pickling,less-chrome tanning/retanning and "compact" process.The main contents and conclusions were as follows:1)Preparation and characterization of collagen-based composites.Amino resins,acrylic resins and aromatic resin prepolymers were used to modify CH to prepare collagen-based composites,namely collagen-based amino resin(MCL),collagen-based acrylic resin(NCL)and collagen-based aromatic resin(ACL).These three composites were characterized using Fourier Transform-Infrared Spectroscopy(FT-IR),Differential Scanning Calorimetry(DSC),Thermal Gravimetric analysis(TG/DTG),X-ray Diffraction(XRD),laser particle size analyzer and Scanning Electron Microscope(SEM),respectively.The results showed that the modification of CH occurred in the amorphous region of collagen polypeptide.For MCL,a certain amount of triazine cross-linked structural unit was introduced.NCL was linear molecular structure and contained larger amount of carboxyl groups.Polar aromatic groups were introduced into the molecular structure of ACL.Besides,the molecular arrangement of MCL and ACL was more orderly due to the introduction of triazine and aromatic polar units.Moreover,due to the cross-linking density of three collagen-based composites is different,the three composites showed different thermal stability,the thermal stability of ACL was better than MCL and NCL.2)Application in low-salt pickling and less-chrome tanning/retanning process.The collagen-based composites were applicated in pickling,chrome tanning and chrome retanning,in order to realize cleaner tanning technology such as low-salt pickling and less chrome tanning/retanning.The amounts of collagen-based composites,salt in pickling and chrome powder in chrome tanning,the physical and mechanical properties of crust leather,absorption rate and distribution of chrome were investigated and evaluated.For the application in pickling process,the deliming and softening skin was pre-tanned by 6% collagen-based composites,pickling using 5% salt,the mechanical property of crust leather can achieve the requirement of crust leather obtained by conventional pickling methods.Besides,the usage of composites can effectively control the acid swelling of pickled skin and reduce the amount of salt by 25%?30%.Among these three composites,MCL showed the best inhibition effect.The study on the application of less chrome tanning / retanning process showed that the pretanning of three kinds of collagen-based composite materials can effectively increase the chrome of coordination binding points,to improve the absorption and binding rate of chrome powder.For the application in chrome tanning process,the deliming and softening skin was pre-tanned by 6% collagen-based composites,pickling using 5% salt,chrome tanning using 5% basic chromium sulphate(BCS),The results showed that the tensile strength and tear strength of crust leather increased 7%?17% and 6%?9%,respectively.The value of shrinkage temperature and chrome absorption rate were higher than than 96?and 73%.Moreover,compared with conventional chrome tanning,the amount of BCS decreased 15%?19%.For the application in chrome retanning process,the wet blue leather was treated by using 6% collagen-based composites and 3% BCS.The results showed that the tensile strength and tear strength of crust leather increased 8%?14% and 2%?4% respectively.The chrome absorption rate was higher than 71%.Compared with conventional chrome retanning,the amount of BCS reduced 23%?27%.3)Application in the filling process.These three collagen-based composites were used in the filling process,to make filling,dyeing and fatliquoring in the same bath.The results showed that the absorption rate of anionic fillers,dyestuffs and oils significantly increased by using collagen based composite materials in filling process,and the value of total organic carbon(TOC)in comprehensive wastewater reduced by 11.2%?29.5%.Meanwhile,the physical and mechanical properties of crust leather were significantly improved,such as,the tensile strength and tear strength increased by 14.2%?33.1% and 33.2%?40.6% respectively.Attributed to the different polymer molecular structure of these three collagen-based composites,leather can be more compact by using MCL and ACL,more soft by using NCL.