| Obtained from fermentation by bacteria, bacterial cellulose (BC) is a kind of novel biomaterial with an ultrafine-fibre network structure. Compared with the plant cellulose, BC displays unique properties including high purity, high crystallinity, high water holding capacity and high mechanical properties. Therefore, BC has been considered as one of the most promising renewable sources for various applications.In this work, BC was synthesized by Gluconacetobacter xylinum, and then introduced into the interface between glass fiber and epoxy resin. The fermentation conditions have been optimized. Otherwise, the application of BC has been explored by blending with gelatin, poly (lactic acid)(PLA) fiber and graphite oxide (GO) nanoplatelets. And the main results in this work are summed as follows:The optimal fermentation conditions, obtained by single factor and orthogonal experiments, were found as following:7.0%glucose,1.5%yeast extract,0.4%Na2HPO4,0.02%MgSO4,1.0%ethanol, pH6.8, inoculation amount7%, seed age24hour,30℃, static culture for10days.Surface modification of glass fiber with BC is synthesized during the process of fermentation. The network structure of BC provided glass fiber with more surface area and rougher surface to increase the effective contact area between the fiber and epoxy resin matrix; moreover, hydroxyl groups of BC could react with not only Si-OH on the surface of glass fiber but also epoxy resin to improve the interfacial adhesive strength. In this system, through changing the amount of BC or/and heat treatment temperature, we could effectively improve the interaction between BC and glass material. It was found that heat-treatment was able to1Microbond test results suggested that, when incubation time was1hour and temperature was140℃, the interfacial adhension achived optimal, and the IFSS value came up to the maximum value22.09±2.49MPa, increased by57.0%than that of the untreated ones.In order to improve the bioactivity and mechanical properties of BC, we combined BC and gelatin to a composite, and then the composite was treated with glutaraldehyde. The addition of gelatin affected the saturated solubility of oxygen in the medium and thus interfered with the growth of bacteria and the formation of BC pellicle structure. With increasing the addition level of gelatin, the width of cellulose ribbons became narrower than that of pure BC and the gelatin filled in the pores of BC to form a dense structure. Crosslinking could decrease the equilibrium water uptake of the composite, but increase thermal stability and mechanical properties. At a low degree of cross-linking, crosslinking reaction takes place mainly between the gelatin coated on the surface of BC which decrease the amount of free amino groups of gelatin. The anti-deformation ability of BC/GEL during tensile testing is weakened along with the decrease of bond strength between BC and gelatin, resulting from the decline of the number of BC-gelatin hydrogen bonds. As the degree of cross-linking increasing, covalent bonds between BC/gelatin even BC/BC formed. The increase of molecule junction density thus enhances the structure stability and mechanical strength of the composites. The most appropriate concentration of glutaraldehyde and crosslinking time were1.0wt%and24h, while the tensile and compressive strength of composite reached to128.14±8.56MPa and9.675±0.318kPa, respectivelyBC/PLA fiber composite is prepared in situ by adding PLA fiber mat into BC producing culture medium. The surface hydrophilicity and separation conditions of PLA fiber greatly affect the structure of the composite for the large fiber diameter. Modified with gelatin, the fiber had good surface hydrophilic property as well as its hydrothermal stability was improved. Good hydrophilicity, uniform dispersion and thinner fiber mat improved the impregnation properties of the fiber, therefore an interpenetrating network, due to the entwining of BC fibrils and PLA fibers, formed.GO, prepared from graphite by the improved Hummers method, was dispersed in water to create a GO nanoplatelets suspension by ultrasound of the dispersion. An electrically conductive composite of BC and GO nanoplatelets was prepared in situ by adding GO into BC producing culture medium. Black BC/GO composites couldn’t be in situ synthesized in static medium, but in agitated medium. With increasing GO concentration, the size and crystallinity index of composite particle decreased. Reduction by glucose, the electric conductivity of the composites increased with the increasing of GO concentration.The purified BC membranes were immersed into the GO nanoplatelets suspension and GO were absorbed into BC membrane, resulting in the BC/GO composites. Alkaline condition is preferred to neutral condition in the results of the exfoliation of GO. In addition, BC pellicle size reduction and ultrasonic treatment can help GO adhere to BC. When pH=9.0and GO concentration was2.0mg/mL, the conductivity value of reduced composites was6.26S/cm and the tensile strength was100.43±10.08MPa, while that of pure BC were1.17S/cm and38.46±2.18MPa, respectively. |
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