Three-Dimensional Printed Shape Memory Gels Based on a Structured Disperse System with Hydrophobic Cellulose Nanofibers.

Inks for 3D printing were prepared by dispersing bacterial cellulose nanofibers (CNF) functionalized with methacrylate groups in a polymerizable deep eutectic solvent (DES) based on choline chloride and acrylic acid with water as a cosolvent. After 3D printing and UV-curing, the double-network composite gel consisting of chemically and physically crosslinked structures composed from sub-networks of modified CNF and polymerized DES, respectively, was formed. The rheological properties of inks, as well as mechanical and shape memory properties of the 3D-printed gels, were investigated in dynamic and static modes. It was shown that the optimal amount of water allows improvement of the mechanical properties of the composite gel due to the formation of closer contacts between the modified CNF. The addition of 12 wt% water results in an increase in strength and ultimate elongation to 11.9 MPa and 300%, respectively, in comparison with 5.5 MPa and 100% for an anhydrous system. At the same time, the best shape memory properties were found for an anhydrous system: shape fixation and recovery coefficients were 80.0 and 95.8%, respectively.

A Polyelectrolyte Colloidal Brush Based on Cellulose: Perspectives for Future Applications.

This feature article is devoted to the evaluation of different techniques for producing colloidal polyelectrolyte brushes (CPEBs) based on cellulose nanofibers modified with grafted polyacrylates. The paper also reviews the potential applications of these CPEBs in designing electrode materials and as reinforcing additives. Additionally, we discuss our own perspectives on investigating composites with CPEBs. Herein, polyacrylic acid (PAA) was grafted onto the surface of cellulose nanofibers (CNFs) employing a "grafting from" approach. The effect of the PAA shell on the morphological structure of a composite with polypyrrole (PPy) was investigated. The performance of as-obtained CNF-PAA/PPy as organic electrode material for supercapacitors was examined. Furthermore, this research highlights the ability of CNF-PAA filler to act as an additional crosslinker forming a physical sub-network due to the hydrogen bond interaction inside chemically crosslinked polyacrylamide (PAAm) hydrogels. The enhancement of the mechanical properties of the material with a concomitant decrease in its swelling ratio compared to a pristine PAAm hydrogel was observed. The findings were compared with the recent theoretical foundation pertaining to other similar materials.

Rheological properties and 3D-printability of cellulose nanocrystals/deep eutectic solvent electroactive ion gels.

3D-printing of stimuli-responsible electroactive gels containing biopolymers, such as cellulose nanocrystals (CNC), is a prospective area of material science. Deep eutectic solvents (DES) have shown a potential interest for applications in electroactive materials as well as for processing of cellulose. In this work, CNC obtained by two methods of processing microcrystalline cellulose were used for preparation of inks containing 6-15 wt% of CNC in polymerizable DES based on choline chloride/acrylic acid. The impact of rheological properties of the inks on 3D-printability was evaluated. The effect of CNC content on the morphology and ionic conductivity of 3D-printed electroactive composite gels was investigated using atomic force microscopy and impedance spectroscopy measurements. The potential application of the obtained materials for designing of a 3D-printed tactile sensor have been demonstrated.

Plasticizing of chitosan films with deep eutectic mixture of malonic acid and choline chloride.

Chitosan (CS) films containing deep eutectic solvent (DES) based on malonic acid (MA) and choline chloride (ChCl) were successfully prepared by solution casting method by using DES content ranging from 0 to 82 wt%. A strong interaction of CS with the components of DES was demonstrated by analyses of water sorption isotherms, atomic force microscopy and FTIR results. The plasticizing effect of the MA and ChCl mixture on the CS matrix was shown by static bulk mechanical measurements, thermal analysis and quantitative nanomechanical mapping (QNM). Elongation at break increased from 3 to 62% at increase of DES content from 0 to 67 wt%, while further increase of DES content led to the decreasing of maximal elongation. Introduction of DES into CS films led to the appearance of glass transition temperature in the region +2 - -2.3 °C. QNM results indicated homogeneity of the films containing up to 75 wt% of DES.