Preparation Of Cellulose Acetate With Transesterification Reaction

With the consumption of non-renewable fossil energy and the concerns of deteriaratingenvironment, lignocellulosic biomass using as a renewable resource has attracted more andmore attention. However, the utilization of cellulose, which occupied more than40%oflignocellulosic biomass, was limited by its strong hydrophilicity, thermal instability anddissolution problem in common solvents. Therefore, the functionalization of cellulose toimprove its performance has become a foundation of its integrated application. The studyfound that, the polarity of cellulose can be significantly reduced after acetylation, on the otherhand, the mechanical properties, hydrophobicity, flame resistance, dimensional stability andthermal stability of cellulose can be enhanced at the same time. In addition, the fullyacetylated cellulose can play a very important role and be a alternative choice in many fields,such as the base material, aerospace material and membrane material. In this study,transesterification reactions of cellulose were handled in separated systems, dimethylsulfoxide (DMSO) and ionic liquid, which were chosen as solvents for acetylated celluloseand cellulose, respectively. Through research, the primary results are described as follows:1. Cellulose acetylation was investigated in DMSO with isopropenyl acetate (IPA) asacetylating reagent and1,8-diazabicyclo [5,4,0] undec-7-ene (DBU) as catalyst at70-130oCfor3-12h. The degree of substitution (DS) of acetylated cellulose was determined bytitrationand1H NMR, and confirmed by FTIR analysis. The results indicated that per-O-acetylationwas achievedat over90oC for relatively long duration (9h). The three well resolved peaks ofcarbonyl carbons in13C NMR spectra also provided evidences of per-O-acetylation.2. The solubility of cellulose acetates in common organic solvents was examined, and theresult showed that chloroform can be an alternative choice as a solvent for fully acetylatedcellulose formed in this study besides DMSO. Meanwhile, the solubility of cellulose acetateassociated with DS, DS distribution and molecular weight. The intrinsic viscosity ofacetylated cellulose solution implied almost no degradation of cellulose during acetylation inDMSO except at higher temperature (130oC) for long time. The results of X ray diffractionanalysis showed that, CTA II-type diffraction pattern was generated after per-O-acetylation of α-cellulose in DMSO/IPA/DBU system, whereas this kind of diffraction pattern was alwaysgenerated in acidic heterogeneous system using regenerated cellulose as material inpreviously reports. TG/DTG analysis was also studied in this literature, it demonstrated that,the themal stability of celluose was improved after acetylation and has a positive correlationwith DS of acetylated cellulose.3. Cellulose acetylation in ionic liquid [Amim]Cl with IPA as acetylating reagent andDBU as catalyst was proposed. The result showed that, the maximum DS of acetylatedcellulose was reached in less than half hour at120oC, and the cellulose acetate with DS＞2.0was successfully achieved under selected conditions in [Amim]Cl. The effect of reactiontemperature, reaction time, molar ratio of IPA to sugar ring of cellulose, and the amount ofcatalyst on DS of acetylated cellulose were studied in this study, the results showed thattemperature is the most important factor to improve the DS of cellulose acetate.4. DS distribution of acetylated cellulose produced in [Amim]Cl was confirmed by13CNMR in quantitative model and Peakfit software. The results indicated that, at the beginningof reaction, hydroxyl group of C-6exhibited a much better activity than C-2and C-3. In theintermediate stage, DS of C-6hydroxyl group stabilized and DS of C-3hydroxyl groupincreased rapidly. When reaching the maximum total DS, DS distribution of acetylatedcellulose was displayed as C3-OH＞C6-OH＞C2-OH.5. Cellulose acetate membranes were prepared using acetylated cellulose produced inDMSO/IPA/DBU system and the optical and physical properties of the membranes werestudied. The study found that, the physical property of cellulose acetate membranes waspositively associated with DS, whereas the optical property was negatively correlated with DS,which means the improvement of optical property is obtained at the expense of certainphysical property. The X ray diffraction analysis showed that, the crystalline form changed inthe membrane-forming process using volatile chloroform to dissolve cellulose acetate.Meanwhile, the influence of “vinegar syndrome” phenomenon on surface morphology ofcellulose acetate membranes was also studied.