Corrêa Ana Carolina, Carmona Vitor Brait, Simão José Alexandre, Galvani Fabio, Marconcini José Manoel, Mattoso Luiz Henrique Capparelli
Nanotechnology National Laboratory for Agriculture (LNNA), Embrapa Instrumentation, P.O. Box 741, 13560-970 São Carlos, SP, Brazil.
Graduate Program in Materials Science and Engineering (PPGCEM), Federal University of São Carlos (UFSCar), Rod. Washington Luiz, Km 235, 13565-905 São Carlos, SP, Brazil.
Polymers (Basel). 2019 Nov 1;11(11):1785. doi: 10.3390/polym11111785.
Cellulose nanocrystals (CNC) were obtained from macauba and gravata fibers. Macauba (or Bocaiuva) is a palm tree found throughout most of Brazil and Gravata is an abundant kind of bromelia with 1-2m long leaves, found in Brazilian Pantanal and Cerrado. The raw fibers of both fibers were mercerized with NaOH solutions and bleached; they were then submitted to acid hydrolysis using HSO at 45 °C, varying the hydrolysis time from 15 up to 75 min. The fibers were analyzed by X-ray diffraction (XRD), FTIR Spectroscopy, scanning electron microscopy (SEM) and thermal stability by thermogravimetric analysis (TG). XRD patterns did not present changes in the crystal structure of cellulose after mercerization, but it was observed a decrease of hemicellulose and lignin contents, and consequently an increase of cellulose content with the increase of NaOH solution concentration in the mercerization. After acid hydrolysis, the cellulose nanocrystals (CNC) were also analyzed by transmission electron microscopy (TEM) which showed an acicular or rod-like aspect and nanometric dimensions of CNC from both fibers, but the higher values of aspect ratio (L/D) were found on CNC obtained from gravata after 45 min of acid hydrolysis. The mercerization and subsequent bleaching of fibers influenced the crystallinity index and thermal stability of the resulting CNC, but their properties are mainly influenced by the hydrolysis time, i. e., there is an increase in crystallinity and thermal stability up to 45 min of hydrolysis, after this time, both properties decrease, probably due to the cellulose degradation by the sulfuric acid.
纤维素纳米晶体（CNC）由马卡巴纤维和格拉瓦塔纤维制得。马卡巴（或博卡尤瓦）是一种遍布巴西大部分地区的棕榈树，格拉瓦塔是一种常见的凤梨科植物，叶子长1 - 2米，生长在巴西潘塔纳尔湿地和塞拉多地区。两种纤维的原纤维均用氢氧化钠溶液进行丝光处理并漂白；然后在45℃下用硫酸进行酸水解，水解时间从15分钟到75分钟不等。通过X射线衍射（XRD）、傅里叶变换红外光谱（FTIR）、扫描电子显微镜（SEM）以及热重分析（TG）对纤维进行热稳定性分析。XRD图谱显示丝光处理后纤维素的晶体结构没有变化，但观察到半纤维素和木质素含量降低，因此随着丝光处理中氢氧化钠溶液浓度的增加，纤维素含量增加。酸水解后，还通过透射电子显微镜（TEM）对纤维素纳米晶体（CNC）进行了分析，结果表明两种纤维的CNC均呈针状或棒状，且尺寸为纳米级，但酸水解45分钟后，从格拉瓦塔纤维获得的CNC的长径比（L/D）值更高。纤维的丝光处理及随后的漂白影响了所得CNC的结晶度指数和热稳定性，但其性能主要受水解时间的影响，即水解45分钟前结晶度和热稳定性增加，此后这两种性能均下降，这可能是由于硫酸导致纤维素降解所致。
