Emulsifying Behavior Of Modified Collagen Peptides And Its Regulation On The Properties Of Collagen Fibers

Amphoteric polymers are widely used in many fields such as drug delivery,antifouling coating,and tanning,because of their excellent chemical,biocompatibility,and controllable charge properties.The application in the green chrome-free tanning can adjust the charge properties of leather and the state of fiber network,which is effectively to improving the problems of low chemical absorption,poor quality and functionality in resulted leather,complex operation,and low production efficiency.At present,most of the amphoteric leather chemicals are prepared from petrochemical materials,which are limited by resources and environmental protection.The research often focuses on the development of new products,rather than the systematic research on the influence law and structure-activity relationship.Based on these,a series of amphoteric peptide based leather chemicals were prepared,which were applied to the fatliquoring process and the adsorption of functional chemicals in different tanned leather.The effect on the properties evolution of chrome-free tanned leather and the mechanism of action with collagen fibers were discussed.It provides some theoretical guidance for the green chrome-free tanning chemicals research.The main research work includes the following contents.The collagen peptides（CP）with different relative molecular weights were extracted from leather collagen by enzyme-alkali method,which reacted with C^12～14 alkyl glycidyl ether（AGE）to prepare amphoteric peptide based polymers（AAPP）with different hydrophilic and lipophilic properties.Then amphoteric peptide based fatliquors（APF）were prepared by emulsifying castor oil with AAPP.The properties of surfactants are the key factors affecting the properties of fatliquor.Firstly,combined with single factor and response surface experiment,the optimal synthesis conditions of AAPP were obtained.Their structures were determined by FT-IR,XPS,GPC and Zeta potential.The surface activity,micelle performance,and interfacial properties were characterized by surface tension tester,fluorescence spectrometer,conductivity meter,dynamic contact angle measuring instrument,and nanoparticle analyzer.The structure-activity relationship were elucidated.The results showed that the surface activity and micelle properties of AAPP were mainly affected by the relative molecular weight,charge properties,hydrophilicity and lipophilicity.The larger the relative molecular weight of AAPP was,the thicker the interfacial film was,and the stronger the ability to reduce surface tension was.The increase of alkyl long chain could improve the efficiency of AAPP in reducing surface tension by increasing the adsorption rate of molecules at the interface.When the concentration of AAPP in solution exceeded the critical micelle concentration（CMC）,the molecules began to agglomerate.The polar groups between molecules were conducive to their combination to form larger micelle,and the close arrangement of molecules reduced the polarity inside the micelle.Furthermore,the effects of particle size,interfacial film state and strength on the stability of APF were studied by polarizing microscope and rheometer.The results showed that the good emulsifying power,small droplet particle size,uniform distribution,and strong interfacial film strength were favorable to the stability of APF.The main role of maintaining the emulsion stability lied in the charge interaction,hydrogen bond,and hydrophobic interaction between AAPP and castor oil.Finally,through the characterization of degradability,environmental risk,and biosafety,it is confirmed that APF were easy degradation,low biological risk,low cytotoxicity,and no sensitization.The above results show that the APF belonged to environment-friendly tanning chemicals and meet the development needs of green and sustainable tanning,which were prepared by the modification of green biomass collagen peptide.APF were applied to the fatliquoring process of chrome-free tanning.The fatliquoring properties of leather were investigated by TOC,softness instrument,tensile machine,ultra-depth field microscope,SEM,XRD,and TG.The influence of APF structures on the evolution of softness,hygienic properties,mechanical properties,microstructure,and thermal properties of fatliquored leather were further explored.It was shown that the relative molecular weight of AAPP was less than 5000,which was conducive to the penetration of APF into leather.The low isoelectric point（pI）of AAPP decreased the absorption of APF.When the relative molecular weight of AAPP was 1500～7000,APF had good filling property in the leather,which was conducive to improve the softness and the grain surface flatness of leather,and the looseness of collagen fibers.The decrease in relative molecular weight and alkyl long chain content of AAPP improved the hygienic properties of fatliquored leather.Furthermore,APF was applied to the fatliquoring process of F-90,TWS,and chrome tanned leather.The influence of APF on the dispersion and surface charge distribution of collagen fibers in different microenvironments was explored.The research showed that the absorption rate of APF increased by 14.65%,6.68%,and 4.86%than that of commercial anionic representative fatliquor（CF）in F-90,TWS,and chrome tanned leather.All kinds of leather with APF were improved on softness,fiber looseness,and mechanical properties.It proved that APF could penetrate into the leather,reduce the resistance of relative sliding,increase the spacing and disorder of arrangement among collagen fibers,to improve the compliance effect of collagen fibers.Simultaneously,there is a certain bridging effect among APF,tan,and collagen fibers.The good crosslinking made the APF absorption and softness of TWS tanned leather comparable to that of chrome tanned leather,and even higher than that in mechanical property.Finally,through Zeta potentiometer and two-dimensional infrared spectroscopy,it is found that APF could regulate the internal charge properties and density of leather by changing its pI.When the pI of leather was higher than that of APF,the addition of APF reduced the positive charge content of leather.The greater the difference in pI was,the higher the amount of positive charge reduction was.When the pI of leather was close to that of APF,the addition of APF increased its charge density and positive charge content.Additionally,the study shows that the N-H and O-H of APF binds to C=O of the amide I band in collagen fibers by the form of hydrogen bond.The above results provide a theoretical basis of the interaction mechanism between chrome-free tanning supporting chemicals and collagen fibers.Based on APF fatliquored TWS tanned leather,various functional leather materials,including colored leather,responsive discoloration,and conductive leather materials,were prepared by adding dyes,thermal responsive pigments,light responsive pigments,and PEDOT:PSS.The color characteristic value,color difference（ΔE）,chroma,and conductivity of functional leather materials were studied by the methods,including UV-vis spectrophotometer,spectrograph,leather color fastness instrument,thermal infrared imager,chromaticity analysis software,electrochemical workstation.It was found that APF can improve the poor absorption of chemicals in chrome-free tanned green leather.Compared with the functional leather materials with CF,the dye uptake of dyed leather with APF increased by 3.8%and the K/S value increased by 7.487.The ΔE of the thermal and light response functional leather materials were increased by 10.98 and 12.19 respectively.The conductivity of conductive leather materials increased to 3.68 × 10^-4 S/m.Therefore,APF could make functional leather materials show more excellent color,response sensitivity,and conductivity.This research provides a certain theoretical basis and practice for developing of green chrome-free tanned leather functional materials.