Rana Md Sohel, Rahim Md Abdur, Mosharraf Md Pervez, Tipu Md Fazlul Karim, Chowdhury Jakir Ahmed, Haque Mohammad Rashedul, Kabir Shaila, Amran Md Shah, Chowdhury Abu Asad
Department of Pharmaceutical Chemistry, Faculty of Pharmacy, University of Dhaka, Dhaka 1000, Bangladesh.
Department of Pharmacy, Faculty of Pharmacy, University of Dhaka, Dhaka 1000, Bangladesh.
Polymers (Basel). 2023 Mar 20;15(6):1530. doi: 10.3390/polym15061530.
Natural cellulose, a sustainable bioresource, is highly abundant in nature. Cellulosic materials, particularly those that explore and employ such materials for industrial use, have recently attracted significant global attention in the field of material science because of the unique properties of cellulose. The hydroxyl groups enable the formation of intra- and inter-molecular hydrogen bonding and the arrangement of cellulose chains in a highly ordered crystalline zone, with the remaining disordered structure referred to as an amorphous region. The crystalline areas of cellulose are well-known as cellulose nanocrystals (CNCs). In the present study, we extracted CNCs from pure cellulose isolated from waste jute fibers by sulfuric acid hydrolysis, followed by characterization. Pure cellulose was isolated from jute fibers by treating with sodium hydroxide (20% /) and anthraquinone (0.5%) solution at 170 °C for 2 h, followed by bleaching with chlorine dioxide and hydrogen peroxide solution. CNCs were isolated from pure cellulose by treating with different concentrations (58% to 62%) of sulfuric acid at different time intervals (20 min to 45 min). The FTIR study of the CNCs reveals no peak at 1738 cm, which confirms the absence of hemicellulose in the samples. The CNCs obtained after 45 min of acid hydrolysis are rod-shaped, having an average length of 800 ± 100 nm and width of 55 ± 10 nm, with a high crystallinity index (90%). Zeta potential significantly increased due to the attachment of SO ions on the surface of CNC from -1.0 mV to about -30 mV, with the increment of the reaction time from 20 min to 45 min, which proved the higher stability of CNC suspension. Crystallinity increased from 80% to 90% when the reaction time was increased from 20 to 45 min, respectively, while a crystallite size from 2.705 to 4.56 nm was obtained with an increment of the acid concentration. Acid hydrolysis enhanced crystallinity but attenuated the temperature corresponding to major decomposition (Tmax) at 260 °C and the beginning of degradation (Ti) at 200 °C due to the attachment of SO ions on the surface, which decreased the thermal stability of CNC. The second degradation at 360 °C indicated the stable crystal structure of CNC. The endothermic peak at 255 °C in the DTA study provided evidence of sulfated nanocrystal decomposition and the recrystallization of cellulose I to cellulose II, the most stable structure among the other four celluloses. The proposed easy-to-reproduce method can successfully and efficiently produce CNCs from waste jute fibers in a straightforward way.
天然纤维素作为一种可持续的生物资源，在自然界中含量极为丰富。纤维素材料，尤其是那些探索并将此类材料用于工业用途的材料，由于纤维素的独特性质，最近在材料科学领域引起了全球的广泛关注。羟基能够形成分子内和分子间氢键，并使纤维素链在高度有序的结晶区排列，其余无序结构称为无定形区。纤维素的结晶区域就是众所周知的纤维素纳米晶体（CNCs）。在本研究中，我们通过硫酸水解从废弃黄麻纤维中分离出的纯纤维素中提取了CNCs，随后进行了表征。通过在170℃下用氢氧化钠（20%/）和蒽醌（0.5%）溶液处理2小时，从黄麻纤维中分离出纯纤维素，随后用二氧化氯和过氧化氢溶液进行漂白。通过在不同时间间隔（20分钟至45分钟）用不同浓度（58%至62%）的硫酸处理从纯纤维素中分离出CNCs。对CNCs的FTIR研究表明，在1738cm处没有峰值，这证实了样品中不存在半纤维素。酸水解45分钟后得到的CNCs呈棒状，平均长度为800±100nm，宽度为55±10nm，具有高结晶度指数（90%）。随着反应时间从20分钟增加到45分钟，由于SO离子附着在CNC表面，ζ电位从-1.0mV显著增加到约-30mV，这证明了CNC悬浮液具有更高的稳定性。当反应时间分别从20分钟增加到45分钟时，结晶度从80%增加到90%，而随着酸浓度的增加，微晶尺寸从2.705nm增加到4.56nm。酸水解提高了结晶度，但由于SO离子附着在表面，使对应于主要分解的温度（Tmax）在260℃和降解起始温度（Ti）在200℃时降低，这降低了CNC的热稳定性。在360℃的第二次降解表明了CNC的晶体结构稳定。DTA研究中255℃的吸热峰提供了硫酸化纳米晶体分解以及纤维素I重结晶为纤维素II的证据，纤维素II是其他四种纤维素中最稳定的结构。所提出的易于重现的方法能够以直接的方式成功且高效地从废弃黄麻纤维中生产出CNCs。
