Preparation Of Bacterial Cellulose Acetate With Low Degree Of Substituent And Bacterial Cellulose-ferulic Acid Antioxidant Composite Membrane

Bacterial cellulose?BC?is a natural renewable polymer with unique physical and chemical properties,such as 3D nanofiber network structure,high purity,high Young's modulus,good biocompatibility and biodegradability.BC has superior application potential in food and medical fields than plant cellulose.In this study,N-methylimidazole?NMIM?was used as catalyst in the synthesis of low-substituted bacterial cellulose acetate,the antioxidant bacterial cellulose-ferulic acid functional composite membrane was prepared with adsorption-laccase catalytic crosslinking.This study is mainly composed of three parts as follows:1.In the first section,Gluconacetobacter xylinus ATCC5382 was used to product bacterial cellulose with NMIM as the catalyst,acetic anhydride as the acetyl reagent,and bacterial cellulose acetate with DS range from 0.3 to 0.9 was prepared in heterogeneous system?BCA-HE?.BCA-HE with a maximum DS of 0.95 was obtained under the condition of 10 mL acetic anhydride,0.3 mmol NMIM,and reaction at 70^oC for 5 hours.Scanning electron microscopy analysis showed that BCA-HE has a fiber structure similar to BC.X-ray diffraction analysis showed that BCA-HE has a much lower crystallinity.Fourier infrared spectroscopy and ¹³C CP/MAS NMR spectroscopy indicated that partial hydroxyl group of BCA-HE was replaced by acetyl.Thermogravimetric analysis demonstrated that the thermal stability of BCA-HE was decreased to a certain degree.The solubility analysis illustrated that BCA-HE has good water solubility and a certain solubility in dimethylsulfoxide?DMSO?.2.In the second section,bacterial cellulose was used as raw material,dimethylacetamide/lithium chloride?DMAc/LiCl?as solvent,NMIM as catalyst,acetic anhydride as acetyl reagent,and bacterial cellulose acetate with DS range from0.4 to 1.4 was prepared in homogeneous system?BCA-HO?,BCA-HO with a maximum DS of 1.5 was obtained under the condition of 3 mL acetic anhydride,0.4mmol NMIM,and reaction at 40^oC for 1.5 hours.Scanning electron microscopy analysis showed that the fiber structure of BCA-HO changed greatly after regeneration,which was significantly different from BC.X-ray diffraction analysis showed that the crystallinity and crystal structure of BCA-HO changed a lot compared with BC.Fourier transform infrared spectroscopy and ¹³C CP/MAS NMR spectroscopy analysis indicated that some of the hydroxyl groups of BCA-HO fibers were replaced by acetyl agents,and BCA-HO has a high acetyl content compared to BCA-HE.Thermogravimetric analysis demonstrated that the thermal stability of BCA-HO decreased delightly.The solubility analysis illustrated that BCA-HO has certain solubility properties in water,DMSO and acetone.The cellulose acetate is prepared by using NMIM as a catalyst.The reaction under homogeneous contion takes less time than heterogeneous,and also the process is milder,the DS obtained is higher.3.In the third section,the bacterial cellulose-ferulic acid?BC-FA?composite membrane was prepared with two steps:the bacterial cellulose membrane was used as raw material to adsorb ferulic acid,and then the ferulic acid was polymerized inside cellulose by catalysis of laccase.The results of antioxidant analysis showed that the BC-FA had good antioxidant activity,and the inhibition of DPPH·and ABTS·⁺were67.25%and 96.81%,respectively.The desorption rate of composite membrane with laccase-catalyzed in different time and temperature decreased 57%and 60.3%compare with that without laccase-catalyzed.Scanning electron microscopy analysis showed that the BC-FA retained the three-dimensional network fiber structure of BC,but the microfibers were interconnected to form a larger diameter fiber bundle.Fourier infrared spectroscopy analysis indicated that FA was successfully combined with BC.X-ray diffraction analysis showed that BC-FA has similar crystal structure to BC,but the crystallinity decreased.Thermogravimetric analysis demonstrated that the thermal decomposition behavior of BC-FA has significantly changed compared with bacterial cellulose.The combination of BC and FA imparted fine antioxidant activity to BC and also the crystallinity and thermal stability was changed.