Preparation And Performance Of Chicken Keratin-based Biofilm

In recent years,the "white waste"produced by the use of a large number of plastic products has caused increasingly serious environmental problems and harm to life.Therefore,it has become a hot topic to find natural degradable polymers instead of petroleum-based polymers to prepare plastics.Protein and cellulose,which are abundant in nature,are of great social and environmental significance and economic value for their effective functional utilization,especially for the replacement of petroleum-based polymers for high-quality applications.As a by-product of the poultry industry,chicken feathers are often used in low-value applications such as landfills,incineration,or as animal feed.However,chicken feathers are rich in keratin,which is renewable,biocompatible and biodegradable.Moreover,due to the existence of many disulfide bond crosslinking structures in both intramolecular and intermolecular,it has high strength and rigidity,so it has good mechanical stability and structural stability,and has a broad prospect in the construction of functional materials such as biofilms.Cellulose also has excellent renewable,biocompatible and biodegradable properties.The preparation of biofilms based on keratin and cellulose instead of traditional petroleum-based films can alleviate environmental and ecological problems.However,at present,the preparation of keratin-based films is in the explorative stage,and the methods are not perfect,the mechanism is not clear,and the performance of the films is far from meeting the requirements.In this thesis,keratin was extracted from chicken feathers from different sources,the structure and other properties of keratin were compared,and the keratin-based biofilm was prepared by blending and cross-linking,and the main properties of the film were studied,such as water solubility,mechanical properties,etc.This thesis provides a reference for the preparation and performance research of keratin-based biomaterials.The research content of this thesis mainly includes three parts:Firstly,the structure and other properties of the extracted chicken feather keratin were analyzed.L-cysteine was used as a reducing agent to extract keratin from two breeds of Chai chicken and Hailan white chicken,and the feather shaft and fiber of Hailan white chicken,and their structure and performance were analyzed.The extracted keratin retains the chemical structure of the original chicken feathers.Structures and molecular weights of chicken feather keratin and keratin at different parts of chicken feather are similar,but have subtle difference.Compared with red feather keratin,white feather keratin has more ?-helical structure,and the crystal structure is destroyed more thoroughly during extraction,so the molecular weight range of white feather keratin is smaller.Compared with the keratin extracted from the pinna,it is found that the stalk keratin contains a smaller amount of ?-helical structure,so the feather is harder to the touch,but the molecular weight range of the two is similar.This comparison provides a theoretical basis for the selection of raw materials for the preparation of keratin-based biomaterials.Then,a keratin-based water-soluble film was prepared.Keratin and cellulose nanocrystals extracted from filter paper were blended to prepare a film that can be dissolved in water within 2 minutes,and its mechanical properties were characterized.Through ultrasound,the intermolecular hydrogen bonds of cellulose are opened,and the structure of keratin will be further opened at the same time,exposing more hydrophilic groups,forming hydrogen bonds between the two to prepare a film.After the film enters the water,cellulose with a large number of hydroxyl groups and keratin rich in a variety of hydrophilic groups quickly dissolve in water,so that the film dissolves quickly in water.Because the isoelectric point of keratin is about 4.3 and the pKa of cellulose is 7,if the ratio of keratin to cellulose is different,or the pH of the water is different,the dissolution time of the film is different.In addition,a large number of hydrogen bonds can be formed between keratin and cellulose,so that the two molecular chains are entangled with each other,so that the mechanical properties of the film are better;adding small molecule glycerol to the macromolecular chain improves the water solubility and mechanical properties of the film performance.Finally,a keratin-based biofilm was prepared.Keratin and modified cellulose were cross-linked through Maillard reaction to prepare a biofilm with good water retention and mechanical properties.Through the cross-linking of the amino groups of keratin and the aldehyde groups of the modified cellulose,not only the cross-linking network inside the film is constructed,but the macromolecular chains are more uniformly dispersed,which slows down the degree of aggregation of the macromolecular chains,which is beneficial to improve the film's performance.When the ratio of keratin to modified cellulose is 4:1,The cross-linking sites on the modified cellulose are completely occupied by keratin,and the cross-linking network is the tightest,so the water retention of the film is the best,which can be used to prepare daily chemical products with special purposes;when the film is stretched,adding glycerin will improve the mechanical properties of the film.This is because the small glycerol molecules slip between the large molecular chains.However,further research is needed for the performance of other aspects of the composite film.