All-cellulose nanocomposites film from sisal fiber

In this work, self-reinforced cellulose nanocomposite films were produced using cellulose and nanofiber from sisal fiber as matrix and reinforcement, respectively. Cellulose nanofiber was prepared via catalytic oxidation using TEMPO/ NaClO/ NaClO2 system. By mild mechanical treatment in water, oxidized celluloses could be disintegrated into individual cellulose nanofiber and utilized as nanofiller. A morphology of TEMPO-oxidized cellulose nanofiber was characterized through transmission electron microscopy (TEM), which revealed nanosized fibrils with diameters in the range of 10–20 nm and at least 1 µm in length. These cellulosic nanofibers were subsequently impregnated in dissolved cellulose matrix which was prepared by dissolving sisal fiber in lithium chloride/N,N-dimethylacetamide solvent. The effects of reinforcement content in all-cellulose nanocomposite films were examined in terms of morphology, mechanical properties, physical properties, and thermal properties. The crystallinity of the nanocomposite films was increased as the cellulose nanofiber content went up. Even though tensile strength of 0.5% composite film was reduced from 40 to 29 MPa, elongation at break was greatly increased from 11% to 37%. These results mean that the nanocomposite films were tougher than the neat cellulose film. In addition, the cellulose nanofiber led to an improvement in the thermal stability of the nanocomposite films, as evidenced by an increment of the onset of the degradation temperature. The hydrophilicity of the nanocomposite film was decreased with an increasing amount of cellulose nanofiber. The % water absorption of the nanocomposite film was reduced from 202% to 150% with the addition of 2% nanofiber.

本研究以剑麻纤维提取的纤维素与纳米纤维分别作为基体与增强相，制备了自增强型纤维素纳米复合薄膜。纤维素纳米纤维通过TEMPO/次氯酸钠（NaClO）/亚氯酸钠（NaClO₂）催化氧化体系制备得到。通过水中温和机械处理，氧化纤维素可被解离为单根纤维素纳米纤维，用作纳米填料。采用透射电子显微镜（Transmission Electron Microscopy，TEM）对TEMPO氧化纤维素纳米纤维的形貌进行表征，结果显示其为直径10~20 nm、长度至少1 μm的纳米级原纤。将上述纤维素纳米纤维浸渍于溶解态纤维素基体中，该基体通过将剑麻纤维溶解于氯化锂/N,N-二甲基乙酰胺溶剂体系制备得到。本研究考察了增强相含量对全纤维素纳米复合薄膜形貌、力学性能、物理性能及热性能的影响。随着纤维素纳米纤维含量提升，复合薄膜的结晶度随之升高。尽管0.5%含量的复合薄膜拉伸强度从40 MPa降至29 MPa，但其断裂伸长率从11%大幅提升至37%。上述结果表明，该纳米复合薄膜相较于纯纤维素薄膜具有更高的韧性。此外，纤维素纳米纤维可提升复合薄膜的热稳定性，表现为降解起始温度升高。随着纤维素纳米纤维添加量增加，纳米复合薄膜的亲水性降低；当添加2%纳米纤维时，复合薄膜的吸水率从202%降至150%。