Preparation And Characterization Of Homogeneous Composite Membranes Reinforced By Wool Keratin Fibrils

This paper carried out a series of exploratory research work about bio-inspired designing composites, in which the wool fibrils at micro to sub-micro scales used as reinforcement to blend with keratin matrix, and then characterized the distribution and arrangement structure, as well as the effects of composites mechanical properties. It can successfully resolved the low strength and low modulus of neat keratin membranes. Additional, the branched fibrils, like plant roots, were also used to strengthen and toughening the composite membranes.In this paper, it realized the properties comparison between homogeneous and heterogeneous composites, namely wool fibrils reinforced composites compared to inorganic K2Ti6O13whisker reinforced composites. The result of UV-Vis-NIR absorption spectrum analysis showed that the light transmission in homogeneous composites is superior to in heterogeneous composites, which indicating that the wool fibrils and keratin matrix has good interface. FT-IR spectrum and X-ray diffraction were employed to investigate the molecular structural changes of fibrils and membranes, and the results showed the fibrils almost maintained the characteristics of wool, both many disulphide bonds and a-helix molecules. Characteristic absorption peaks and crystallinity of composite membranes mainly depended on the keratin matrix, and almost have no influence of the reinforcements. The mechanical testing results of keratin composites showed that when fibrils quality percentage is5%, whiskers quality percentage is3%, and also uniformly dispersed and highly oriented, the composite membranes have optimal mechanical properties. However, the strength of homogeneous composites is higher than heterogeneous ones by42%.Then, branched fibrils were prepared, and the strengthen efficiency of different types fibrils were analyzed. The modulus and strength of plain fibrils reinforced membranes increased70.2%and48.8%respectively than those of neat keratin membranes, only strain at break decreased7.8%. Compared with the neat keratin membranes, ultrasonic processed one-step and two-step branched fibrils reinforced membranes have better mechanical properties, the stress increased92.4%and94.9%respectively, and strain at break increased7.4%and7.7%respectively.With the aid of corrected law of mixtures and the mechanics experimental results of composite membranes, here calculated the stress of plain fibrils is206.12Mpa, modules is278.28Mpa, strain at break is0.74, and shear stress is6.87Mpa. However, the stress of one-and two-step branched fibrils are1.81and1.86times as many as plain fibrils respectively, and modules are1.28and0.95times, and strain at break are1.42and1.96times, and shear strengths are1.81and1.86times. It confirmed that the branched structure has a better effect on strengthen and toughen, but the number of branched ends has little impact on the properties of composites, not only because the long time ultrasonic processing easily decrease the properties of fibrils, as well as the incomplete branching.In addition, this paper also took fracture mechanics and micromechanics to analysis the damage characteristics of heterogeneous and homogeneous composite membranes, as well as the branched fibrils reinforced membranes. Firstly, the micrographs of cross-sections shown that whiskers performed bridging fibre fracture model and fibrils performed breaking fibres fracture model. The analysis results revealed that the branched fibrils could achieve both reinforcement and toughness simultaneously, not only because fibrils ends deformation, which can effectively reduce the stress concentration, but also because the additional friction and deforming force of fibrils ends. On the basis of modified shear lag model, the axial load transfer model equations of single fibril among multi-fibrils were established, in which found that when fibril modulus Ef/matrix modulus Em is2～50, the value of longitudinal spacing/the length of fibrils equal to0.053～0.667, and the ratio (df/d) of fibril diameter (df) to the space (d) of between the fibrils is larger (namely d smaller, or V%larger), the axial load transfer efficiency higher. In experiment, the first item have reached the theory range, to enhance the mechanical properties of homogeneous composite membrane just can by improving the value of longitudinal spacing/the length of fibrils and df/d value.Through the establishment of finite element model, it defined that the stress distribution of fibrils and whiskers reinforced composite membranes. The researches include the fracture pattens of heterogeneous composites, and based on the structural bionics, the plain, one-and two-step branched fibrils were prepared to reinforce homogeneous membranes, the influence of fibrils ends shapes on the mechanical properties were also discussed. Finally, it revealed the fracture process of homogeneous composite membranes, large matrix deformation and interfacial shear stress around fibrils fracture easy to product matrix crack and interfacial debonding, however, due to the good interfacial interaction, made the interfacial debonding too difficult to continue, instead by the existing or new matrix crack.The present thesis researched the inorganic whisker and wool fibrils reinforced keratin composite membranes systemically, especially including structure, properties and preparation technology. The achievements with research play a beneficial role in the development and application of keratin regeneration composites and provide a theoretical basis for related field.