Research On The Development Of Test Methods For Key Parameters, The Behaviors Of Mass Transfer And Chemical Reaction During The Purification And Dissolution Processes Of Cellulosic Fibers

Recently,the production capacity of viscose fiber is also the largest among all regenerated cellulosic fibers in the word,which could account for more than 65% of the total production capacity of regenerated cellulosic fibers.However,in the preparation process,there exists a large amount of exhaust,wastewater and solid waste emissions,which will cause many serious environmental problems.To solve this problem,many researchers have taken a lot of effort to studty on development of emission-reduction technology for viscose industry.In this study,in order ro reduce the usage of carbon disulfide and thus develop a cleaner preparation process of viscose dope,the main focus are on the development of some rapid and accurate test methods for the key parameters during viscose industry.Simultaneously,some on-line monitoring and in-time controlling methods for viscose preparation process have been also developed.Besides,an economically feasible process has been developed for purification of the bamboo viscose fiber.Lastly,the relationship between some key parameters of cellulosic fibers and its reactivity during xanthation process has been also investigated by chemometrics analytic techniques.Specifically as follows:Since the test methods of the cellulosic fibers' purity are old,complicated and time-consuming,it is very essential to develop some rapid and simple methods to meet the requirements of the modern viscose manufacturing process.In this paper,based on UV/Vis spectrometry coupled with chemometrics analysis,a simple and rapid method has been built for indirectly determination of the alpha-cellulose's content in cellulosic fibers.Besides,a headspace gas chromatographic(HS-GC)technique has been also used for batch analysis of the alpha-,beta-,and gamma-cellulose's content in cellulosic fibers.Since the detection technology of the reactivity of cellulosic fibers was defective in rayon industry,such as poor accuracy,time-consuming,complicated,etc.,a rapid method for determination of the reactivity has been established based on light scattering technique.Comparing with the improved Fock method,the relative deviation of this method is less than 11%,which proved that it is reliable for rapid analysis the reactivity of cellulosic fibers using the present method.However,a disadvantage,i.e.,emission some toxic odors,should be overcome during measurement process.In order to solve this problem,in this study,a semi-automatic efficient method has been established based on HS-GC technique,which can achieve the batch measurement of fiber samples.Then,the relationship between the key parameters of cellulosic fibers and its reactivity has been inverstageted by chemometrics analysis.The results showed that as the ash content and crystallinity of fibers kept within reasonable bounds,the influence capacity of the other key parameters from high to low are intrinsic viscosity,alpha-cellulose content,and carboxyl content.Base on partial least squares regression analysis,the influence degree of each pararemeter can be quantified,which can be better for providing guidance on the process of improving the cellulosic fibers' reactivity.Coupling with the flow injection analysis,an in-line monitoring UV/Vis spectroscopy technique has been built for the dissolution of hemicellulose from cellulosic fibers during cold caustic extraction(CCE)process.Then,based on this technique,the dissolution kinetics of hemicellulose during CCE process has been established,which can achieve the accurate controlling of the CCE process for purification the cellulose fibers.Due to the low utilization problem of alkali during signle CCE process,a new purification process for cellulosic fibers has been developed in this paper.The advantage of this process has been demonstrated from both the mass transfer theory and experiment.And the optimal process has been found subsequently.Lastly,the reactivity of the CCE-treated fibers has been improved and the utilization paths of hemicellulose separated from CCE-lye has been also introduced basically.Lastly,a novel method for on-line determination of the content of dissolved cellulose during pulp xanthation by ATR-UV/Vis spectroscopy assisted with multivariate data analysis has been reported in this paper.The results showed that with the application of orthogonal signal correction(OSC)and partial least square regression(PLSR)techniques,a good-robustness and accurate calibration model has been developed,in which the R2,root mean squared error cross validation(RMSECV),and relative prediction errors(RPE)are 0.9985,0.2203,and 0.34%,respectively.Based on this robust method,the dissolution kenitics of cellulosic fiber during xanthation process has been also invesgated.Furthermore,based on the ATR-UV/Vis spectroscopy,an accuracy method for judging the end-point of xanthation reaction process has been also established,which is very important for precise controlling the xanthation process.