Study On Modification Of Bacterial Cellulose And Its Dry Milling Process

In recent years,Bacterial Cellulose(BC)had been the research focus of new biomaterials due to its characteristics of ultrastructure,high purity,high Young's modulus and high water holding capacity,good biocompatibility and biodegradability.At present,many problems with low production and high fermentation costs limited its application.In particular,it was difficult to dry for BC membranes,and presented the poor rehydration after drying.Therefore,on the basis of increasing the BC of production,in order to prepare high rehydration rate of BC powder,firstly in situ and non in situ modification were used in the project through the modified anddry mode.The response surface process was optimized for the modifier with high rehydration rate.And the modified BC films were characterized to explore the mechanism of rehydration.Secondly,different drying methods were adopted to dry the modified BC,and drying characteristic were characterized and analyzed.The results provide a theoretical basis for the production of BC powder.The main research contents and results were as follows:(1)The production of BC by potato starch wastewater researched in laboratory was adopted to research the optimal fermentation conditions,comparing with the coconut culture.The single factor experiment was applied on the fermentation method,temperature,inoculation quantity,bottling volume and fermentation period.In addition,the pH value,acidity and reducing sugar in the fermentation process was monitored.The results showed as follows: static culture at 29?,inoculum size was 7%,bottling volume of 125/250 mL and the fermentation period was 7 days.The results showed that the change trend of parameter in the potato starch wastewater culture was similar to that of coconut juice culture,and the change range of pH in coconut juice medium was less.Coconut juice may have a larger buffer capacity.(2)In situ bioremediation,polysaccharides and two carbohydrates were added to the fermentation medium to change the property of BC to participate in the biosynthetic pathway of BC.The results showed that the addition of polysaccharide and trehalose could improve the rehydration rate and yield of the BC membrane compared with the unmodified BC membrane.And adding 1.0g/L of HA could significantly improve the rehydration rate of composite membrane.The modified BC membranes showed good physical properties which high porosity,decreasing fiber density,and a light transmittance increasing.The micrographs of infrared spectrum(FTIR)and field emission scanning electron microscope(SEM)showed that the modifier agents were successfully embedded in the structure of BC with dif-ferent forms.Further,characterization of the HABC composite membrane showed that the addition of HA could produce the HABC membrane that exhibit a better thermal stability,low crystallinity.It was speculated that the addition of modifier may changes the structure of BC and causing the degree of crystallinety decreasing.It was the cause of the change of re-hydratetion rate.(3)Different modified BC was prepared by non in situ modification by solution impregnation method.And the lactic acid,sucrose,chitosan were selected from different modifying agents.Preparation of lactic acid modified BC membrane was adopted to the response surface method,The result was as follows: lactic acid concentrateon 14.67%,impregnate time of 151.48 min,impregnate temperature of 89.22?.The optimized modified BC membrane of rehydration rate achieved 107.34%,an increase of 9.4 times.At the same time,the sucrose and chitosan modification process were tested by single factor test: the sucrose concentration of 6%,vacuum impregnation of 2h,the impregnation temperature of 60?.the preparation processs of chitosan modified BC is the chitosan concentration of 1%,impregnate temperature of 80?,impregnate time of 4h.The FTIR and SEM showed that the characteristic absorption peaks of the three modifier agents appeared in the infrared spectrum and affected the hydrogen bond content in the BC molecules.Due to the difference of the modified reaction,the lactic acid modified BC and the original BC of fiber arrangement and pore size was closed,presented better physical properties.(4)Based on the process of preparing modified BC with lactic acid,sucrose and chitosan,the BC suspension was modified by lactic acid,sucrose and chitosan.Then the BC powder was employed four drying methods which was hot air drying,microwave drying,vacuum freeze drying and freeze drying by gradient heating respectively.Moreover,it was compared the rehydration differences of BC after drying.The results showed that the rehydration rate of modified BC treated with hot air and microwave was lower than those of vacuum freeze drying,gradient freeze drying.And the highest BC rehydration rate was obtained by gradient freeze drying.The rehydration rate of BC modified by chitosan was higher than that of modified BC by lactic acid and sucrose.The SEM,XRD and contact angle measurements showed that the drying process could change the degree of crystallinity which affected the BC structure.Nevertheless,the modified agents may protect the BC structure at the pretreatment.The BC powder appeared a better surface wetting capability.