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Study On The Selective Alkylation Of Bacterial Cellulose

Posted on:2014-12-31Degree:MasterType:Thesis
Country:ChinaCandidate:Y T LinFull Text:PDF
GTID:2181330467985077Subject:Applied Chemistry
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Bacterial cellulose (BC) is widely used in the fields of food, paper, biomedical sciences, and acoustic equipment because it has better properties than plant cellulose. Bacterial cellulose derivatives with different properties are getting more and more attention in recent years. Alkyl cellulose is an important cellulose derivative due to its special properties, such as good salt resistance, heat resistance, unique dissolution properties, thermal gelling properties and appropriate surface activity. Moreover, alkyl cellulose can be present in different forms such as powder, flake, film, fiber, and solution. It can be made into different types of water retention agents, emulsifier, thickener, filmogen and rheological modifier and has been widely applied in paints, building materials, detergents, cosmetics and medicine.In this paper, BC was produced with Hainan coconut juice as the fermentation broth. Regioselective etherification was carried out to bacterial cellulose to prepare6-O-(4,4’-dimethoxyphenyl)-trityl bacterial cellulose (6-O-DMT-BC),6-O-(4,4’-dimethoxyphenyl)-trity1-2,3-di-O-ethyl bacterial cellulose (6-O-DMT-2,3-Et-BC),2,3-two-O-ethyl bacterial cellulose (2,3-Et-BC) and2,3,6-O-alkyl bacterial cellulose (2,3,6-Al-BC). The structure of the products was characterized. The effects of reagent amount, reaction time, temperature and other conditions on the reaction were studied for each reaction system. The physical and chemical properties of the BC derivatives were investigated and the reaction laws are discussed.(1)6-O-DMT-BC was homogeneously prepared from BC in LiC1/DMAC, pyridine was used as acid binding agent and4,4’-dimethoxy-trityl chloride as the protective agent. The results show that the amounts of4,4’-dimethoxy-the trityl chloride (DMTC1) and Py have a significant effect on the degree of substitution (DS), while the DS does not simply increase with the amount of either substance. A proper molar ratio of DMTC1and Py is required. When n (anhydroglucose unit of bacterial cellulose, AGU):n (DMTC1) is1:5and the ratio of DMTC1and Py is1, the DS is about1. When the ratio of DMTC1and Py become1:10, more Py is required to reach DS1. Enlarging the reaction scale to lOg BC, the DS also decreases owing to mass and heat transfer efficiency reducing, and more Py is required to obtain6-O-DMT-BC with DS1. Extending reaction time is beneficial to increasing DS. FTIR, NMR measurements confirm the modification. XRD results indicate that the product has a more stable polymorph of cellulose II than raw BC with cellulose I structure. The thermal analysis results show that the thermal stability of BC derivatives decreases.6-O-DMT-BC with high DS dissolves in DMSO. The protecting group DMT can be removed through hydrolysis under acidic conditions.(2)6-O-DMT-BC was used to synthesize6-O-DMT-2,3-Et-BC.The results indicate that heterogeneous modification in THF can avoid complicate work-up in homogeneous reaction using solvents with high boiling point. Microwave assisted reaction or using KI as catalyst can obviously shorten reaction time from96h to5h or1.5h. Vacuum evaporation, followed by dialysis can reduce the loss of products. The solubility of the derivatives is improved.6-O-DMT-2,3-Et-BC can completely dissolve in DMSO, and partially dissolve in DMAC. FTIR indicates that BC has been partially ethylated, while accompanied with partial DMT depletion. XRD profiles show that polymorph of the products has no change, while with degree of crystallinity decreasing. TGA results reveal that thermal stability of the derivatives increases a little bit. DMT group can be completely removed, while with a slight depletion of ethyl.(3) The synthesis of2,3,6-tri-O-alkyl cellulose was carried out through a heterogeneous modification of BC in THF, with NaH as the base and KT as the catalyst. The results show that DS can be improved when the amounts of KI,NaH and alkylating agent are increased. When the molar ratio of AGU, KI, NaH, and C2H5Br was1:1:30:30, the reaction time being12h, BC derivatives with maximum DS2.36was prepared. FTIR spectra demonstrate that the products have been partially alkylated.EA results verify that the shorter the carbon chain of halon2,3,6-ABC substitution degree is higher, but overall low substitution degree.XRD results show that the derivatives have same polymorph with the raw BC, but the crystallinity decreased. TGA results indicate that the thermal stability of BC has no obvious change after modification. The solubility of the products is not good. And in the alkylation reaction, the reaction efficiency of Bacterial Cellulose is superior to Microcrystalline Cellulose.
Keywords/Search Tags:Bacterial cellulose, regioselective etherification, 6-O-(4,4’-dimethoxyphenyl)-tritylbacterial cellulose, 2,3-di-O-ethyl bacterial cellulose, 2,3,6-O-alkyl bacterial cellulose
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