Abstract

Microfibrillated cellulose (MFC) is an important industrial nanocellulose product and material component. New MFC grades can widen the materials property range and improve product tailoring. Microfibrillated lignocellulose (MFLC) is investigated, with the hypothesis that there is an optimum in lignin content of unbleached wood pulp fibre with respect to nanofibril yield. A series of kraft fibres with falling Kappa numbers (lower lignin content) was prepared. Fibres were beaten and fibrillated into MFLC by high-pressure microfluidization. Nano-sized fractions of fibrils were separated using centrifugation. Lignin content and carbohydrate analysis, total charge, FE-SEM, TEM microscopy and suspension rheology characterization were carried out. Fibres with Kappa number 65 (11% lignin) combined high lignin content with ease of fibrillation. This confirms an optimum in nanofibril yield as a function of lignin content, and mechanisms are discussed. MFLC from these fibres contained a 40–60 wt% fraction of nano-sized fibrils with widths in the range of 2.5–70 nm. Despite the large size distribution, data for modulus and tensile strength of MFLC films with 11% lignin were as high as 14 GPa and 240 MPa. MFLC films showed improved water contact angle of 84–88°, compared to neat MFC films (< 50°). All MFLC films showed substantial optical transmittance, and the fraction of haze scattering strongly correlated with defect content in the form of coarse fibrils.

Graphic abstract

抽象的

微纤化纤维素（MFC）是重要的工业纳米纤维素产品和材料成分。新型MFC等级可以扩大材料性能范围并改善产品定制。对微纤化木质纤维素（MFLC）进行了研究，其假设是，相对于纳米原纤维产率，未漂白木浆纤维的木质素含量最佳。制备了一系列具有降低的κ值（较低的木质素含量）的牛皮纸纤维。通过高压微流化将纤维打浆并原纤化为MFLC。使用离心分离纳米级的原纤维级分。进行了木质素含量和碳水化合物分析，总电荷，FE-SEM，TEM显微镜和悬浮液流变学表征。Kappa值为65（11％木质素）的纤维结合了较高的木质素含量并易于原纤化。这证实了作为木质素含量的函数的最佳纳米原纤维产率，并讨论了机理。这些纤维的MFLC含有40-60％（重量）的纳米级原纤维，其宽度在2.5-70nm范围内。尽管尺寸分布很大，木质素含量为11％的MFLC薄膜的模量和拉伸强度数据仍高达14 GPa和240 MPa。与纯MFC膜（<50°）相比，MFLC膜的水接触角提高了84–88°。所有MFLC薄膜均显示出相当大的透光率，并且雾度散射的分数与粗纤维形式的缺陷含量密切相关。尽管尺寸分布很大，木质素含量为11％的MFLC薄膜的模量和拉伸强度数据仍高达14 GPa和240 MPa。与纯MFC膜（<50°）相比，MFLC膜的水接触角提高了84–88°。所有MFLC薄膜均显示出相当大的透光率，并且雾度散射的分数与粗纤维形式的缺陷含量密切相关。尽管尺寸分布很大，木质素含量为11％的MFLC薄膜的模量和拉伸强度数据仍高达14 GPa和240 MPa。与纯MFC膜（<50°）相比，MFLC膜的水接触角提高了84–88°。所有MFLC薄膜均显示出相当大的透光率，并且雾度散射的分数与粗纤维形式的缺陷含量密切相关。

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