The Preparation Of A New Type Of Solvent And Its Dissolution Behavior To Cellulose

Cellulose is considered as the most abundant renewable biopolymer with excellent biocompatiblity and biodegradability in nature.It can be used to prepare various useful cellulose products,and can be derivatized to prepare cellulose derivative,and replace oil resources partly.Cellulose molecules have many hydroxyls,which can form complex inter- and intra- molecular hydrogen bonds. So cellulose cannot be dissolved in common solvents and cannot be melt,which limits its applications.On the theory that urea and thiourea can improve the performance of NaOH long ago,Professor Lina Zhang in Wu Han University of China has applied it into cellulose area,which proved to be much cheaper and environment friendly than viscose and cuprammonium method.Professor Lixia Gu of Donghua University invented another aquous system by assembling the three material in a defmate proportion,which proved to be much effective by dissoluting more cellulose and with more stable solution.In this study,the function of each component in the new solvent was analyzed by dissolving cellulose separately,and the mechanism was put forward furtherly.The influence factors to dissolving process were studied systemly and the best preparation conditon was obtained.As for the stability of acquired solution and solvent applicability to other materials were also discussed in this paper,the main results were as follows:1.Analyzed the function of each component in the green new type of solvent separately by polarized optical microscopy,optical microscope and solubility degree measurement,which showed that NaOH would swell cellulose and result in its dissolution in solvent.As for urea and thiourea,it showed no dissolution ability without NaOH.However,the assembleness of NaOH with either urea or thiourea or its conbination has much better dissolution power,where our new type of solvent proved to be the best.The mechanism was that the hydrogen bond in cellulose was destroyed and a more stable bond was formed because of the stronger polar of C=O,C=S and -NH₂,synergetic affection accelerated the final dissolution.2.All kinds of factores to dissolution ability were studies systemly,they were: smash degree,solvent pre-cool temperature,water containing ratio,adding sequence,ratio of churning,temperature and time of churning and pre-treatment. So the best technics was as followes:Smash the cellulose pulp into an average diameter of 0.01cm,then dry it to a water containing ratio of less than 1%,add the cellulose into solvent by sequence one,that is firstly pre-cool the sovent into about -10℃,where long needle like crystal came our with an average length of 1.0cm,then add cellulose pulp,churn dramaticly for 3 minutes,after that use an iced brine bath of -2 to 0℃for another dramatic churning of 27 minutes.If pre-treated,the dissolution degree would get another increase,in this paper,a 7% cellulose solution was obtained by the method above.3.Storage length was used to test the stablity,and it showed that in a temperature of 0℃environment,the cellulose solution was the most constant. Any lower or higher of this temperature would result in unreversible gelation and the fluctuation of environment temperature would reduce cellulose constancy,too. The granule diameter would also affect the constancy,so,after a filtration by sieve net,storage time would increase significantly.It was also found that different cellulose had different constancy,the greater the degree of polymerization,the less constancy.When comes to the same degree of polymerization,wood pulp was less than cotton.4.The new solvent was also applied to other material like wood pulp, bamboo pulp and straw.Comparing to cotton pulp of 6.1%,the dissolution degree was different,4.2%,2.1%and 4.3%respectively,which showed that this green solvent was applicable to wood pulp and straw,no bamboo pulp recently because of its low degree of dissolving.By testing the rheological performance,it was found that all the four solution had gelation phenomenon in the tempature range of 20℃-70℃,and gelation module G_gelgrows with the concentration,while gelation temperature T_gelshowed an oposite trend。Rheological result showed that the bamboo solution was the best,followed by wood solution,straw solution,then cotton linter solution,where the trend is reverse to the dissolution solubility.So it could be deduced that the content of pulp had direct influence to viscosity,the more content,the higher viscosity,but the less rhelogical ability.