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The adsorption of four cationic surfactants with different alkyl chain lengths on cellulose substrates was investigated. Cellulose fibers were used as model substrates, and primary alcohol groups of cellulose glycosyl units were oxidized into carboxylic groups to obtain substrates with different surface charges. The amount of surfactant adsorbed on the fiber surface, the fiber zeta-potential, and the amount of surfactant counterions (Cl(-)) released into solution were measured as a function of the surfactant bulk concentration, its molecular structure, the substrate surface charge, and the ionic strength. The contribution of each of these parameters to the shape of the adsorption isotherms was used to verify if surfactant adsorption and self-assembly models usually used to describe the behavior of surfactant/oxide systems can be applied, and with which limitations, to describe cationic surfactant adsorption onto oppositely charged cellulose substrates.

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The three-dimensional (3D) printed scaffolds were prepared by partial cross-linking of TEMPO-oxidized cellulose nanofibril/alginate hydrogel using calcium ions for printing the hydrogel while maintaining its shape, fidelity, and preventing the collapse of the filaments. The prepared scaffolds were fully cross-linked using calcium ions immediately after printing to provide the rigidity of the hydrogel and give it long-term stability. The composition of the prepared pastes was adjusted in view of the description of the hydrogel and 3D printing parameters. The rheological properties in terms of thixotropic behavior and viscosity recovery of hydrogels were investigated by performing steady shear rate experiments. The results show that the viscosity recovery for pure alginate hydrogel was only about 16% of the initial value, whereas it was 66% when adding cellulose nanofibrils to alginate. Consequently, the shape of the pure alginate scaffold was soft and easy to collapse contrarily to the composite scaffold. The biomimetic mineralization process of printed scaffolds using simulated body fluid, mimicking the inorganic composition of human blood plasma, was performed and the hydroxyapatite nucleation on the hydrogel was confirmed. The strength properties of the fabricated scaffolds in terms of compressive strength analysis were also investigated and discussed. The results show that the alginate/TEMPO-oxidized cellulose nanofibril system may be a promising 3D printing scaffold for bone tissue engineering.

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The aim of the present study was to investigate the rheological properties of microfibrillated cellulose/lignosulfonate hydrogels and to use them for the manufacturing of carbon objects by 3D printing and carbonization. To this purpose, both flow mode and thixotropic mode were used to characterize the hydrogel rheological behaviour which was subsequently used to search for formulation/processability correlations during 3D printing of square cuboids. At a concentration of 2%, microfibrillated cellulose (MFC) displayed excellent printability, i.e. a shear thinning behaviour with high yield stress and a viscoelastic response to a step-down shear rate variation. The addition of lignosulfonate (LS) induced a drop in the yield stress and, above a LS mass fraction of 30%, the MFC/LS hydrogel displayed an inelastic thixotropic response with a drop in printability (viz. the printed cuboids underwent a continuous deformation until hydrogel complete spreading). Above 50% of LS, the high viscosity slowed down the flow of MFC/LS hydrogels and printed cuboids had minor deformation. Freeze and air drying of cuboids printed with LS mass fraction lower than 20% and higher than 50%, respectively, allowed keeping the original shape and their carbonization under inert gas led to the production of highly conducting objects. In line with the high density of air dried samples, carbonized samples displayed an irregular structure with pores and crackles generated during drying and carbonization, whereas freeze dried samples had the typical lamellar structure of icetemplated materials.

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