TEMPO氧化法制备五节芒纤维素纳米纤丝及其悬浮液稳定性和流变行为表征

五节芒Miscanthus floridulus的纤维素含量高。为高效利用五节芒,采用2,2,6,6-四甲基哌啶-1-氧自由基(TEMPO)氧化处理五节芒纤维素,再通过高压均质制备了五节芒纤维素纳米纤丝(CNF)。透射电镜(TEM)观察发现,五节芒纤维素纳米纤丝为纤维状结构,直径为(10.0±2.3) nm,长度在微米级,表面羧基质量摩尔浓度为1.98 mmol·g-1;Zeta电位结果表明:五节芒纤维素纳米纤丝悬浮液具有极好的储存稳定性。稳态流变测试表明:纤维素纳米纤丝悬浮液随着固含量提高,黏度升高,剪切变稀行为增强;动态流变测试表明,由于五节芒纤维素纳米纤丝的高长径比,其悬浮液在固含量为0.56%时,即表现出明显的凝胶行为;Cox-Merz规则在纤维素纳米纤丝固含量较低时适用,而当纤维素纳米纤丝固含量为0.56%时不适用。

Stabilization and rheological behavior of Miscanthus floridulus cellulose nanofibril prepared by TEMPO-mediated oxidation

To better use the stalk of Miscanthus floridulus, a species of perennial grass with high cellulose content, a M. floridulus cellulose nanofibril (CNF) was prepared by 2, 2, 6, 6-tetramethylpiperidine 1-oxyl (TEMPO)-mediated oxidation and successively isolated by high pressure homogenization. Analysis consisted of using a transmission electron microscopy (TEM), NaOH conductometric titration, zeta potential, steady and dynamic rheology tests, and the Cox-Merz rule. Results of TEM observations showed that M. floridulus CNF had a fibril structure (10.0±2.3) nm in diameter and several micrometers in length; its surface carboxyl content was 1.98 mmol·g-1 measured by NaOH conductometric titration. Zeta potential results revealed that M. floridulus CNF suspensions were very stable. The steady rheology test found that M. floridulus CNF suspensions performed shear thinning behavior--the higher the CNF content, the higher the viscosity with a stronger shear thinning behavior. The dynamic rheology test showed that M. floridulus CNF suspensions exhibited a storage and loss modulus platform with low frequencies at a content of 0.56%, which indicated a gel structure had formed. Furthermore, the Cox-Merz rule applied in M. floridulus CNF suspensions at low CNF content but did not apply at CNF content of 0.56%. Therefore, the M. floridulus CNF can be prepared successfully by TEMPO-mediated oxidation method, and perform good storage stability. The M. floridulus CNF suspension can form gel at low concentration suggests its potential in thickener and flocculant applications.