Fabrication And Performance Of Antimicrobial Casein-based Nano ZnO Composite For Leather Finishing

As one of the pillar parts in light industry,leather industry has a close relation with the national economy and people's livelihood.Leather finishing,used as surface coating of leather products,can not only beautify the products,but also improve their additional value.Casein has been widely used for leather finishing.It shows excellent film-forming performance,such as polishing resistance,high temperature resistance,resistant to ironing as well as superior bonding strength.However,casein contains different categories of amino acids and is easily affected by bacteria and finally become decayed.In this study we introduced inorganic antibacterial material,nano ZnO,to casein matrix via single in-situ and double in-situ method seperately.By changing pH of the system,we finally obtained antibacterial casein-based nano ZnO composite with different charge properties.Firstly,the commercial nano ZnO particles were introduced into caprolactam-modified casein(CA-CPL)matrix via single in-situ method and the casein-based nano-ZnO(CA-CPL/ZnO)composite was obtained.Effects of ZnO dosage,ZnO feeding stage,polyvinylpyrrolidone(PVP)and amount of silane coupling agent on the composite emulsion and films were investigated.When ZnO dosage was 1%,nano ZnO was added into the system before caprolactam,no PVP was used as the modifier,silane coupling agent KH570 dosage was 1%,CA-CPL/ZnO emulsion property and its film-forming performance were optimal.Transmission electron micrograph(TEM)result showed that CA-CPL/ZnO latexes had the core-shell structure and the size was about 400 nm.Dynamic laser light scattering(DLS)result showed that zeta potential of composite material was-35.6 mV and it belonged to an anionic material.Nano ZnO particles were evenly distributed on the surface of CA-CPL/ZnO film according to environmental scanning electron microscope(ESEM).Compared with those finished by pure CA-CPL,leather samples finished by CA-CPL/ZnO demonstrated superior tensile strength and dry rubbing fastness.The as-prepared CA-CPL/ZnO composite showed enhanced antibacterial property of emulsion and water resistance of film.To solve the above problem,double in-situ method was adopted.The optimal preparation process was explored by regarding stability and antibacterial propertiy of the emulsion and mechanical property and water resistance of films as indicators.The optimal process included 9.0 of pH,3%content of ZnO precursor,silane coupling agent KH560 as the surface modifier and 3.5%usage of KH560.TEM showed that the casein-based nano-ZnO composite presented multi-layerd core-shell structure and its size was about 259 nm.DLS result showed that zeta potential of composite material was-28.4 mV.ESEM showed nano ZnO were uniformly deposited through the CA-CPL/ZnO film.Compared with those finished by pure CA-CPL,leather samples finished by CA-CPL/ZnO demonstrated improved mechanical property,superior sanitation property and enhanced dry rubbing fastness.CA-CPL/ZnO composite via double in-situ method exhibited superior stability and impoved antibacterial property.The size was also reduced from 400 nm to 259 nm.To further improve antibacterial property and the binding ability between composite emulsion and leather substrate,cationic casein-based nano-ZnO composite was successfully prepared by regulating the pH value of casein solution.Effects of types of solvent,pH value,nano ZnO usage and CPL usage on the property of emulsion and films were also optimized.When formic acid was used to dissolve casein and pH value was 2.5,ZnO dosage was 2%and CPL dosage was 40%,the properties of as-prepared composite emulsion and film were optimal.Results showed that the zeta potential of cationic composite was 23.2mV,the morphology of emulsion was crossover-like net structure and nano ZnO were uniformly deposited among the CA-CPL/ZnO film.In addition,the introduction of nano ZnO was favorable for improving mechanical property,water vapor permeability and dry rub resistance of leather samples.Compared with leather sample finished with anionic composite,the samples finished with cationic CA-CPL/ZnO composite showed excellent sealing property.