Lignocellulosic nanofibrils (LCNF) are produced from a single source of unbleached, oxidized wood fibers by serial disintegration, high‐pressure microfluidization, and homogenization. Sequential centrifugation enables fractionation by fibril width (≈5, ≈9, and ≈18 nm). LCNF residual lignin of high molecular mass reports together with the finest fraction (LCNF‐fine), whereas the more strongly cellulose‐bound lignin, of relatively lower molecular mass, associates with the coarsest fraction (LCNF‐coarse). Hot pressing softens the amorphous lignin, which fills the interstices between fibrils and acts as an in‐built interfacial cross‐linker. Thus, going from the LCNF‐fine to the LCNF‐course films, it is possible to obtain a range of values for the structural consolidation (density from 0.9 to 1.2 g cm−3 and porosity from 19% to 40%), surface roughness (RMS from ≈6 to 13 nm), and strength (elastic modulus from 8 to ≈12 GPa). The concentration of free hydroxyl groups controls effectively the direct surface interactions with liquids. The apparent surface energy dispersive component tracks with the total surface free energy and appears to be strongly influenced by the higher porosity as the fibril lateral size increases. The results demonstrate the possibility to tailor nanofibril cross‐linking and associated optical and thermo‐mechanical performance of LCNF films.

No abstract

No abstract

No abstract

Nano-lignocellulose (NLC) and lignin-free nanocellulose (nano-holocellulose, NHC) were used in paper coating to investigate their effect on coating layer quality and offset printing. The NLC was produced by microfluidisation of unbleached secondary fibres while the reference NHC was obtained from the same fibre source after lignin removal (OHEPH bleaching), following the same mechanical process. TEMPO-mediated oxidation of the fibres prior to microfluidisation was applied to increase the electrostatic charge and hydrophilicity of the nanofibrils. The coatings, displaying given surface morphology and energy, were applied on Kraft, printing-grade papers at three grammage levels. The structure of the coated and uncoated (reference) papers were accessed (SEM and AFM) and IGT printing was carried out to determine the print density, print gloss, rub-off resistance, surface energy, roughness, ink transfer, dry pick resistance, water interference and set-off. The results highlight the important effect of residual lignin or type of nanocellulose on the coating layer and the development of offset printing properties. It was observed that roughness was a key factor leading to a deterioration of the print properties, predominantly affecting the NLC coating. Considering the lower hydrophilicity of NLC, an alternative dispersion with water-alcohol mixtures is proposed. By using this dispersing medium, tailorable surface coverage, surface smoothness, ink acceptance and improved printability was achieved. We show that under these conditions and compared to NHC, NLC is equally effective as a coating layer.