Preparation, Characterization And Performance Study Of Natural Silk Fibroin Materials

Silk is a kind of natural polymer material,which has been widely used in many fields,such as food,medicine and biotechnology.It has excellent properties,such as mechanical property,bio-compatibility and degradability.However,it is difficult for silk fibroin to dissolve into silk fibroin solutions.Preparing these silk fibroin solutions is very slow and time-consuming.What is more,the silk protein materials are soluble in water and the mechanical properties of silk fibroin films are very poor.Thus,these factors will affect and restrict the application of silk fibroin in the biotechnology and medicine field.This paper used 1.0?6.0 wt%calcium chloride-formic acid(CaCl2-FA)soultion to dissolve silk into silk fibroin solutoin,and prepared a series of silk fibroin films,such as Mori silk films,Thai silk films and Mori-Thai silk-silk blending films.At the same time,these films were tested by differential scanning calorimetry(conventional DSC,Stepscan DSC and Flash DSC),thermogravimetric analysis and dynamic thermomechanical analysis,combined with scanning electron microscopy,Fourier transform infrared spectroscopy and X-ray diffraction.We explore the effects of preparation conditions(different concentrations of CaCl2,blending and solvent induction)on the structure,secondary conformation and glass transition temperature,melting point of the silk fibroin films.What's more,we also studied on thermal stability and mechanical properties of the silk fibroin films.At last,the thermodynamic parameters,kinetic parameters,and formation mechanism of the silk fibroin films were investigated using thermogravimetry techniques and the models of Kissinger,Ozawa,and Vyazovkin.The main results are as follows:1.The CaCl2-FA solution can dissolve the silk quickly at room temperature,and when the concentration of CaCl2 increases from 1.00 wt%to 6.00 wt%,the three-dimensional pore structure of silk fibroin fibers are gradually disintegrated,and the fibrous structure of the silk fibroin fibers are gradually dissolved into small fibers.In addition,we also find that the surface of the blending film after water treatment changed from smooth to staggered pile of fibers and the surface of the film will form a network structure after ethanol treatment.This is due to the effect of polar solvent water and ethanol.2.The secondary conformation of the silk fibroin is changed from the ?-sheet structure to the random coil structure,when the increase of the concentration of CaCl2.Howevre,with the increase of the concentration of calcium chloride,the using lifetime and activation energy of the silk fibroin films become decreased.The results of Stepscan DSC(SSDSC)and Flash DSC(FDSC)show that the glass transition temperature of silk protein is also decreased with the increase of the concentration of CaCl2.The result of thermogravimetric analysis shows that different kinds of silk fibroin materials have different thermal decomposition mechanisms.The thermal decomposition mechanism of Mori silk fibroin film is in accordance with the chemical reaction process(Chermical reaction).The Thai silk fibroin film follows two dimensional diffusion mechanism.The blending silk fibroin film conforms to the contracting cylinder model.3.These silk fibroin films are prepared by low concentration(?2.0wt%)CaCl2-FA solution have better rigidity.however,the silk fibroin films which are made by high concentration(>2.0 wt%)CaCl2-FA solution has better ductility.The results show that the elasticity modulus of Mori silk fibroin films are higher than those of Thai silk fibroin films,and it's stiffness is better than that of Thai silk fibroin.The blending silk fibroin film,which are blended by two kinds of silk fibroin solutions,have a higher tensile strength.