The Dissolution And Regeneration Of Native Collagen Fibers In Ionic Liquid And The Preparation Of Collagen-based Composites

In this paper, ionic liquid,1-butyl-3-methylimidazolium chloride ([BMIM]Cl), was applied to resolve natural collagen fibers. Deionized water, ethanol, methanol and acetone were then employed as precipitants to regenerate collagen films. Polarized optical microscopy (POM) was used to observe the resolution condition of collagen fiber in the [BMIM]Cl. Scanning electron microscope (SEM), X-ray diffraction (XRD), Fourier transform infrared(FTIR), Temperature-dependence IR, Thermogravimetry (TG), were employed to analyze and compare the structure, thermal stability and morphology of collagen films before and after regeneration. Collagen/cellulose composites were also made with [BMIM]Cl. The morphology, thermal stability and swelling property of these composites with different ratio were studied. The mechanisms of collagen dissolving in ionic liquid were proposed. The destruction of hydrogen bond and the salt bond were believed to be the main driving forces to dissolve the collagen fibers. The mechanism of the regeneration of collagen in precipitants was discussed as well. The results of POM show that the bright zone of cellulose decreases as temperature rises. When the temperature comes to120℃, the bright zone of cellulose disappears, presenting completely black under the field of view of polarizing microscope, which indicates that the crystalline portion of collagen fiber was destroyed completely and collagen fiber was completely dissolved in ionic liquid.The regeneration effects of different kinds of precipitants to collagen film were also studied. Deionized water, ethanol, methanol and acetone were used as precipitants. The results turned out that property of film forming of collagen films regenerated from deionized water and ethanol is better and their thickness is quite even. Collagen films regenerated from methanol turned pale and had rough surface. Collagen films regenerated from acetone turned yellow and shrank to some degree, resulting in an uneven surface. It can be concluded that precipitants have great effect on the morphology of collagen after regeneration. The morphology, structure and thermal stability of collagen before and after regeneration were studied. SEM pictures shows that the morphology of collagen films regenerated from different precipitants display marked differences and no obvious fiber exists on the surface of regenerated films, which implies that collagen fiber was dissolved completely. XRD results shows that the gap between molecule chains of regenerated collagen becomes larger, which may be caused by the dispersion of molecules during dissolution. Besides, the peak that represents triple helix disappears, which implies that the triple helical structure of collagen is partly broken into random coil form during the dissolution and regeneration. In this paper, deconvolution of the amide regions is required to understand the qualitative and quantitative contributions of different structural components of collagen to the peaks in amide regions. The results show that the helical structure and regularity of collagen was destroyed and decreased, respectively. The results of Temperature-dependence IR show that as temperature increases, the hydrogen bonds in collagen were destroyed by ionic liquid. Coats-Redfern method was employed to calculate the thermal degradation activation energy of collagen before and after regeneration. It turns out that the thermal degradation activation energy of collagen after regeneration is lower than that of native collagen fibers, which indicates that collagen degraded to some degree during the dissolving and regeneration.Cellulose and collagen were used to make collagen/cellulose composite films, fiber and gel with good properties. According to the dissolution condition of cellulose, white nontransparent half-soluble cellulose films and transparent completely-soluble cellulose film were obtained. As the loading of cellulose decreased, the toughness of composite fiber decreased and fiberizability decreased as well. Swelling experiment found that the swelling ratio of collagen/cellulose with completely-dissolved cellulose increased while that of collagen/cellulose with half-dissolved cellulose increased but then decreased as the loading of collagen increased. TG analysis showed that when cellulose dissolved completely, the thermal stability of samples increased as the content of cellulose increased; when cellulose dissolved partly, the thermal stability of samples was optimal when the ratio of collagen/cellulose is1:1.