NaClO添加量对TEMPO氧化纳米微纤丝结构与性能的影响

以毛竹粉为原料,采用TEMPO催化氧化联合超声处理制备纳米微纤丝,通过改变Na Cl O与纤维素的质量比,研究了Na Cl O添加量对纳米纤维素的长径比、纤维形态以及羧基含量等特性的影响。结果表明:随着Na Cl O添加量的增加,纳米纤维素羧基含量逐渐提高,长径比增大;当Na Cl O添加量为15 mmol/g时,纳米纤维素羧基含量可高达1.646 mmol/g,横截面直径可达6～10 nm,长径比为273～455;随着纳米纤维素羧基含量的增加,纳米纤维素悬浮液的透光率和剪切黏度不断增大。虽然TEMPO催化氧化程度不断加深,但纳米纤维素的晶型并未遭到破坏,仍然呈现出典型的纤维素I晶体结构,而随着羧基含量的增加,纳米纤维素的结晶度和热稳定性有一定程度的下降。

Effect of NaClO addition on structure and properties of TEMPO oxidized cellulose nanofibrils

Cellulose nanofibrils were isolated from bamboo powder by the combination of the 2,2,6,6-tetramethylpiperidin-1-oxyl radical (TEMPO) catalytic oxidation and ultrasonic treatment.By changing the mass ratio of NaClO to cellulose,the effects of the NaClO addition on the aspect ratio of cellulose nanofibrils,the morphology and the carboxyl content of cellulose nanofibrils were investigated.The TEMPO oxidation method was used to selectively oxidize the primary alcohol hydroxyl group on cellulose C 6 into carboxyl group and aldehyde group in aqueous solution by TEMPO/NaBr/NaClO system.The solution was then mechanically stirred and made the oxidized cellulose to be uniformly and efficiently dispersed into deionized water to form cellulose nanofibrils suspension liquid.The TEMPO oxidation method had the advantages of low energy consumption and little pollution,and the prepared cellulose nanofibrils had large aspect ratio,small cross-sectional area and narrow diameter distribution range.The results showed that both the carboxyl content and the aspect ratio of cellulose nanofibrils increased gradually with the increase of NaClO content.When the addition amount of the NaClO was 15 mmol/g,the carboxyl group content of cellulose nanofibrils could be as high as 1.646 mmol/g,the cross-sectional diameter could reach 6-10 nm and the aspect ratio was 273-455.With the increase of the carboxyl group content of cellulose nanofibrils,the light transmittance and shear viscosity of the cellulose nanofibrils suspension also increased.When the carboxyl content of cellulose nanofibrils was 1.646 mmol/g,the transmittance of cellulose nanofibrils suspension in the wavelength range of 400-800 nm could reach 97.8%,and the initial shear viscosity and final equilibrium shear viscosity of cellulose nanofibrils suspension reached 56.41 mPa ·s and 5.53 mPa ·s,respectively.The results of this study also showed that,as the amount of NaClO increased,the degree of catalytic oxidation of the TEMPO continued to deepen,while the crystalline form of cellulose nanofibril was not destroyed and still presented typical crystal structure of cellulose I.However,the cellulose nanofibril had slight decreases in crystallinity and thermal stability.