Preparation Of Bacterial Cellulose Fiber Composites And Their Applications

Bacterial cellulose(BC)is a kind of nano polysaccharides produced by bacteria with high purity,high crystallinity,high mechanical strength,high water binding capacity,high biocompatibility and biodegradable ability,in addition to the high efficiency and easy control of the bacterial cellulose synthesis process.However,its industrial application is restricted because of the few BC production strain,long cycle,low yield and high cost.In this work,the cellulose and cellulose-like structure producing microorganisms were screened and the bacterial cellulose composites were prepared to reduce its cost and further use as carriers to immobilize microorganisms(Cordyceps sinensis/Rhodotorula mucilaginosa/Rhodococcus qingshengii),and the decolorization performance were also studied.The main research contents and conclusions are as follows:The screening and identification of BC producing microorganisms from nature were conducted;while optimizing the key factors(carbon source,carbon source,nitrogen source,the nitrogen content of the source content,temperature,pH)to improve the BC production;and various testing methods were used for the BC characterization.The results showed that the six bacteria,screened with high BC yield,were named as Komagataeibacter rhaeticus ZL-1,K.rhaeticus ZL-2,K.xylinus ZL-3,K.rhaeticus ZL-4,K.rhaeticus ZL-5 and K.intermedius ZL-6 after identification;the effect of carbon source,carbon concentration,nitrogen source,nitrogen concentration and pH on the BC production of six bacteria was different,with the maximum yield up to 12 g/L;FTIR and XRD results confirmed that the membranes are cellulose and can be completely decomposed by cellulase,with good mechanical properties.The bacterial cellulose-like structure producing fungi was screened,the structure,characteristics,chemical composition,solubility of the membrane were analyzed,and the factors(incubation time,oxygen content,liquid volume)affecting the production were also studied,besides the formation of BC composite.The results showed that C.sinensis can produce the BC-like colorless gel film(CS),the fiber may consist of specialized hyphae,and the oxygen content greatly affected the synthesis of CS;FTIR,TGA,liquid chromatography and elemental analysis confirmed that CS contained polysaccharide and other components,and LiCL-DMac can be used to completely dissolve the membrane;BC/CS also had good biocompatibility and mechanical strength.The influence of various factors,such as bacteria,on the in vitro immoblization of microorganisms(Rhodotorula mucilaginosa /Rhodococcus qingshengii)was investigated by using BC as carriers,the optimum decolorization conditions and application properties of the composite were also determined.The results showed that the optimum pH of BC producing strains greatly affected the composites formation;confocal laser scanning microscopy(CLSM)confirmed that the two decolorizing microorganisms were totally wrapped by BC network;the optimum combination conditions with BC were similar for R.mucilaginosa and R.qingshengii,and the complex were both good at the pH,operational,and storage stability.The in situ static combination process and mechanism of BC with textile fibers,such as cotton fiber(CF),were studied.The composites were also evaluated in terms of structure and properties.The results showed that K.intermedius ZL-6 can attach to the cotton fiber toproduce BC and eventually wrap the fiber,with the formation of bacterial cellulose/Cotton(BC/CF)gradient composites from top to down;the optimal combination processes were:cotton fiber 0.1 g,inoculation amount 10 mL,bacteria age 5 d,culture time 6 d,temperature30 °C,with the young's modulus up to 4.32 GPa;BC can combine with a variety of textile fibers,but the effect will differ with the properties of textile fibers.Finally,the bacterial cellulose/textile fiber composites were used for microorganisms(R.mucilaginosa/R.qingshengii)immoblization and decolorization,the effects of different factors were investigated to get the optimum decolorization efficiency,and the second combination was also studied.The results showed that R.mucilaginosa and R.qingshengii can be completely fixed by BC/CF and restricted in the gradient network structure;both the two complexes can suspend in the reaction solution showing good decolorization efficiency;both the two complexes can maintain activity for a long time and be applied to a variety of bleaching system;the second combination was suitable for the decolorization of R.mucilaginosa.