多元羧酸预处理制备木质纳米纤维素及其性能研究

Preparation and Properties of Lignocellulosic Nanofibrils Obtained by Polycarboxylic Acid Pretreatments

以芒草秸秆纤维为原料,采用草酸、顺丁烯二酸和柠檬酸预处理结合高压均质制得3种木质纳米纤维素(LCNF),并利用冷场发射扫描电子显微镜(FE-SEM)、透射扫描电子显微镜(TEM)、X射线衍射(XRD)分析仪和热重(TG)分析仪对LCNF性能进行表征分析。研究结果表明:多元羧酸预处理能促进纤维吸水润胀,削弱纤维之间结合力,有利于高压均质过程中的微纤丝解离。多元羧酸pKa值越小,酸性越强,预处理过程纤维水解越剧烈,制得的LCNF尺寸越均一。3种多元羧酸中草酸的pKa值最小为1.25,草酸制得的LCNF(O-LCNF)平均宽度最小为15.3 nm。与芒草秸秆纤维原料相比,高压均质会削弱微纤丝之间的氢键作用力,使得LCNF的部分结晶区遭到破坏,结晶度下降,草酸、顺丁烯二酸和柠檬酸体系制得的O-LCNF、M-LCNF和C-LCNF结晶度分别为50.4%、48.2%和50.0%。在草酸预处理体系下,所得的O-LCNF热稳定性最好,最大热失重速率温度为353.2℃。

Three kinds of lignocellulosic nanofibrils(LCNF)were prepared from miscanthus straw fiber with the treatment using oxalic acid,maleic acid and citric acid under the condition of high-pressure homogenization.The performances of LCNF were characterized by cold field emission scanning electron microscope(FE-SEM),transmission scanning electron microscope(TEM),X-ray diffraction(XRD)analyzer and thermogravimetric(TG)analyzer.The results showed that polycarboxylic acid pretreatment effectively promoted fiber swelling and weaken the bonding force between fibrils,which was beneficial for the dissociation of microfibrils during the high-pressure homogenization process.The acidity became stronger and the fiber hydrolyzed in the pretreatment process was more intensive when the pKa value of carboxylic acid was smaller,resulting in more uniform size of LCNF.Oxalic acid had the minimum pKa value of 1.25 among there polycarboxylic acids,and the minimum average width of the corresponding prepared LCNF was approximately 15.3 nm.Compared with the raw material of miscanthus straw fiber,high-pressure homogenization could weaken the hydrogen bond occurring in microfibrils,which destroyed partial crystalline area and decreased the crystallinity of LCNF.The crystallinity of O-LCNF,M-LCNF and C-LCNF prepared from oxalic acid,maleic acid and citric acid system was 50.4%,48.2% and 50.0%,respectively.Under the oxalic acid pretreatment system,the obtained(O-LCNF)exhibited the best thermal stability with the maximum weight loss rate temperature of 353.2℃.