用反应量热仪研究棉短绒纤维素的乙酰化反应

用反应量热仪(RCle)对棉短绒纤维素的乙酰化反应进行了研究。研究发现:该反应放热速率图基本由3～4个放热峰构成;初期第一或第二个放热峰的峰值较大,主要为醋酐的水解反应;往后峰值依次变小,直至缓慢放热,主要为纤维素乙酰化反应。研究中还测量了不同反应温度及水分含量对反应放热速率的影响,并与木浆粕的反应过程进行了对比。结果表明,棉短绒纤维素乙酰化过程具有非均相表面反应的特点。放热速率随温度的升高而加快。提高水分含量,使醋酐水解放热量变大,并能破坏反应区结构,提高反应速率,缩短总反应时间。与木浆粕相比,棉短绒纤维素具有结晶度高及α-纤维素含量高的特点,反应放热表现为:初期放热速率低,中后期高,总体反应时间较长。

Study on the Acetylation Reaction of Cotton Linters by Reaction Calorimeter

The acetylation reaction of cotton linters was studied by reaction calorimeter（RCle）.It was found that the reaction exothermic rate map consisted of three to four exothermic peaks.The first or second peak value was larger due mainly to the hydrolysis of acetic anhydride,and the subsequent prak values became gradually smaller due to the acetylation of cotton linters.The effects of reaction temperature and moisture content on the exothermic rates were also studied.Experimental results showed that the acetylation of cotton linters reflected the characteristics of heterogeneous surface reaction.The exothermic rates increased with the increase of reaction temperature.Increasing moisture content in the cotton linters led to higher reaction rate and shorter total reaction time.Compared with wood pulp,cotton linters have lower moisture content,higher crystallinity and higher cellulose content.Its reaction exothermic characters showed the lower heat release rate in the initial stage than wood pulp,higher in the middle and later,and the longer total reaction time.