Study On Sisal Microfibrils/modified Gelatin Biomass Composites

In this study, we focus on the preparation and properties of sisal microfibers/gelatin biocomposites, which is a biodegradable, biocompatible material. This study is composed of three parts:the chemical modification of gelatin; the microfibrillation of sisal fiber; the preparation and properties of sisal microfibers/gelatin biocomposites.In terms of chemical modification of gelatin, cross-linked gelatin films were prepared with the crosslinking agent of basic chromium sulfate (Cr3+), dialdehyde starch (DAS) and quebracho tannin. The effects of the three crosslinking agents on the tensile strength, swelling behavior, water absorption, thermal degradation behavior, and the UV resistance of the cross-linked gelatin films were investigated. The results show that Cr3+ can crosslink the gelatin macromolecules effectively. At the Cr3+ content of 7%, the tensile strength of the Cr3+ modified gelatin increased from 5.2MPa to 16.2MPa. At the content of 3% of DAS and 6% of quebracho tannin, the tensile strength of the modified gelatin was increased to 7.7 MPa and 10.3 MPa, respectively. With respect to the swelling behavior, the equilibrium swelling degree of the modified gelatin film decreases, with the increasing amount of the modified agents. The water absorption behavior of modified gelatin was measured at the relative humidity (RH) was of 58% and 98%. The initial water absorption rate and the equilibrium water absorption ratio of gelatin films modified by Cr3+, DAS, quebracho tannin respectively have reduced significantly. At the 7% Cr3+,5% DAS,6% Quebracho tannin, the equilibrium water absorption ratio of the modified gelatin is the lowest. After UV radiation, the tensile strength of the modified gelatin films is reduced to different degrees. After radiation for 1h, the Cr3+ modified gelatin films exhibit the best resistance to UV irradiation, showing the minimium reduction of tensile strength. After 4 h radiation, the tensile strength of Cr3+, DAS, Quebracho tannin modified gelatin film decreased 44.9%,18.6%,19.5% respectively.According to SEM analyzing on sisal fibers, natural sisal fiber is bundles of tightly and tidily packed single fibers. There is crack section phenomenon on the surface of the fibers. The wax and other impurities attach to the fiber surface and the crack. The sisal fibers were microfibrillated by mechanical microfibrillation followed by alkaline treatment. The non-cellulose substances, such as wax, hemicellulose, lignin, were removed. The sisal microfibrils with diameters of about 5-10μm were obtained.The sisal microfibrils were mixed with water to make a mat. Sisal microfibrils/gelatin biomass composites were prepared by a solution impregnation technique. The influences of the sisal fibril on the mechanical properties, swelling properties, water absorption, enzymatic degradation, thermal degradation stability of the composites were investigated systematically. The addition of natural sisal fibers can not enhance the composites effectively. With the increase of sisal fibrils in the composite films, the tensile strength is increased; on the contrary, the elongation at break, equilibrium swelling degree, water absorption ratio, enzymatic degradation ratio have shown to be decreased.