Paper is an attractive substrate for sustainable and scalable organic electronics; however, its intrinsically insulating nature, the absence of continuous electronic pathways, and the lack of control over mixed ionic–electronic transport have limited its use in electrochemical devices. Here, we nanoengineer cellulose fibers by introducing cationic charges to facilitate a high specific surface area accessible for the adsorption of functional components. We further speed up the diffusion-controlled adsorption through controlled partial fibrillation of the fibers. The combined cationic charge and high surface area enabled high adsorption of the conducting polymer PEDOT:PSS (poly(3,4-ethylenedioxythiophene):polystyrene sulfonate) throughout the internal nanostructure of the fiber wall. The modified fibers were then rapidly transformed to mechanically robust, electrically conductive papers using a conventional papermaking methodology. Post-treatment of papers containing 30 wt% PEDOT:PSS resulted in excellent charge transport and a conductivity as high as 13 S cm−1. Furthermore, electrochemical impedance spectroscopy of wet papers confirmed effective mixed ionic–electronic transport. Finally, to demonstrate the possibilities of the electroactive paper, we integrated the paper as channel materials in organic electrochemical transistors and evaluated them as enzyme-free hydrogen peroxide sensors, achieving a limit of detection of 0.79 µM and a sensitivity of 8.5% per decade, highlighting the potential of combining fiber-wall engineering with scalable processing and device integration.

The long-term reliability of power transformers is critically dependent on the chemical and mechanical integrity of their lignocellulose-based insulation systems. Despite decades of research, the complex physicochemical mechanisms governing cellulose degradation under thermal, oxidative, hydrolytic, and mechanical stresses remain only partially understood at the molecular level. This review consolidates the current understanding of cellulose degradation in transformer insulation, emphasizing the chemical pathways that drive depolymerization and the formation of key degradation products. Analytical and diagnostic techniques, including direct polymer characterization and indirect oil-based monitoring methods, are evaluated in terms of sensitivity, applicability, and limitations. Recent developments in advanced spectroscopic and scattering methods are discussed as tools for elucidating degradation at the molecular scale. The review also highlights mitigation strategies such as thermally upgraded papers, nanoparticle-enhanced composites, and antioxidant additives. Finally, emerging research directions are proposed, focusing on real-time, non-invasive monitoring, integration of multi-sensor diagnostics with AI, and interdisciplinary approaches to design more durable insulation systems.

The surface composition of softwood Kraft fiber materials, particularly the relative contributions of cellulose, hemicelluloses, and lignin at fiber surfaces, strongly influences interfacial properties relevant to paper performance and surface modification. Because these properties are governed by the outermost fiber surface rather than by bulk composition alone, methods capable of resolving chemically heterogeneous lignocellulosic surfaces are needed. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is attractive for this purpose because it provides surface-sensitive and chemically resolved information, but its spectra are complicated by fragment overlap, adduct formation, matrix effects, and contamination. Here, a semi-quantitative ToF-SIMS workflow was developed using compacted reference samples, total-ion-count normalization, pairwise principal component analysis, and conservative marker-ion validation. Unbleached and bleached handsheets were used to assess whether the workflow could detect bleaching-induced chemical differences at softwood Kraft fiber surfaces. The analysis reproducibly differentiated lignin- and polysaccharide-associated ion patterns. Unbleached handsheets showed higher relative contributions from guaiacyl lignin-associated fragments, whereas bleached handsheets showed enhanced polysaccharide-associated signals. Two-dimensional chemical imaging supported these trends by visualizing the spatial distribution of assigned marker ions across the handsheet surfaces. The workflow provides a practical, semi-quantitative surface-characterization method for pulp fibers surfaces, fiber modification, adhesive and coating interfaces, and related bio-based material surfaces.

Extrusion-based 3D-printing is a promising manufacturing method because it can integrate various nanomaterials, including highly conductive MXenes. Nevertheless, the fabrication of both wet and dry stable 3D-printed structures with MXene has remained challenging due to the difficulty in forming mechanically stable, crosslinked networks with the required rheological properties. In this work, a MXene ink formulation incorporating cellulose nanofibers (CNFs) as rheology modifiers is developed, enhancing structural integrity and enabling a one-step freeze-induced crosslinking process to produce lightweight, porous structures. The 3D-printed structures exhibit remarkable mechanical strength, supporting up to 10,000 times their own weight, while maintaining a conductivity of over 195 S m⁻¹. Additionally, they demonstrate a specific capacitance of 240 F g⁻¹ at 5 mV s⁻¹, highlighting their potential for applications in advanced iontronic devices. A fully 3D-printed supercapacitor concept is showcased in two distinct configurations: in-plane and stacked; demonstrating their structural integrity and electrochemical stability in aqueous environments.

Quaternized cellulose fibers and cellulose nanofibrils (CNFs) are attractive candidates for the development of new renewable and biodegradable materials. However, the etherification reaction, through which functionalization is commonly achieved, provides low efficiencies, limiting industrial interest in the modification. This work primarily aims to increase the efficiency for the quaternization of cellulosic fibers while keeping the fiber-structure intact. This was achieved using high-consistency kneading to mix and modify the fibers at far higher solids contents than previously reported, efficiently limiting the alkaline hydrolysis of the reagent. Increasing the solids content from 5 to 45 wt% improved the reaction efficiency from 2 % to unprecedented 38 %. Characterization of the fibers showed that high-consistency quaternization affected the wet dimensions of the fibers, with enhanced swelling and fibrillation being obtained. Based on the tensile testing of handsheets made, it was concluded that quaternizing the fibers enhanced the strainability of the material, from 1.8 to 6.7 %, and that kneading achieved a concomitant increase in stress-at-break, from 15 to 103 MPa. CNFs produced from fluidized high-consistency-quaternized fibers had dimensions comparable to those produced from hand-mixed fibers, having aspect ratios above 200, the CNF films produced were transparent, tough, and with a high propensity to sorb water.

This study investigates how partial modification of softwood Kraft fibres into dialcohol cellulose affects fibre wall integrity and swelling behaviour across a modification range of similar to 25- similar to 50%. Structural transformations within the fibre wall and the roles of the secondary cell wall layers in generating balloon-like morphologies during heterogeneous swelling were examined. A combination of optical microscopy techniques including polarised light, differential interference contrast and confocal laser scanning microscopy with dual fluorescent labelling was employed to visualise morphological changes. Results show that swelling intensified with increasing modification. At 51% modification, fibres exhibited uniform swelling, and the characteristic balloon-collar-like structures disappeared. Mild ballooning was observed in "never-dried" fibres with similar to 25% modification. Fibre width increased with modification, ranging from 35 +/- 9 mu m (unmodified) to 58 +/- 24 mu m (similar to 50% modification), with greater variability at higher modification levels. Water retention values also rose, from 1.7 to 6.3 g water per gram of fibre. Finally, the modification-induced swelling introduced inelastic strain in the fibre wall, preserving balloon-collar morphology in air-dried fibres.

Cellulose and its derivatives are considered sustainable alternatives to non-biodegradable fossil-based plastics. Chemically modified cellulose fibres to dialcohol cellulose (DAC) fibres demonstrated a melt processing window between the glass transition and degradation temperatures which enabled their extrusion by using only water as a temporary plasticizer. With the aim of supporting an industrial upscale of DAC fibres, this study investigates the processing design and the feasibility of melt processing, minimizing the moisture. Melt processes-structure-properties relationships were studied by varying the sequence of primary and secondary melt processes, i.e., extrusion and injection moulding, and by changing the moisture content. The effect of moisture and processing design on the fibre structural properties, such as molecular weight, crystallinity, fibre morphology and fibre suspensions rheology, was assessed. Then, the thermomechanical behaviour of the 3D-shaped DAC injected materials was correlated with DAC fibres structural features obtained by the different processing design and moisture content. Our results identified the injection moulding as a milder process for achieving the preparation of 3D-shaped material with enhanced mechanical properties. Moreover, we disclosed the relevance of controlled moisture in the extrusion process for enabling a secondary shaping directly after compounding and the possibility of 3D-shaping DAC fibres after a rehydration step.

To replace petroleum-derived polymers with cellulose fibres, it is desirable to have the option of melt processing. However, upon heating, cellulose degradation typically starts before the material reaches its softening temperature. Alternatives to plastics should also, ideally, be recyclable via existing recycling streams. Here, we address the problem of melt processing cellulose as fibres while preserving recyclability. Native cellulose fibres were partially modified to dialcohol cellulose to impart thermoplastic characteristics. We demonstrate melt processing of these modified fibres with only water as plasticiser. Processability was investigated at selected processing temperatures and initial moisture content by monitoring the axial force of the extruder screws as a rheological indicator. The effects on molecular structure, fibre morphology and material properties were characterised by NMR spectroscopy, microscopy, tensile testing, fibre morphology analysis and X-ray diffraction. When comparing the melt-processed extrudate with handsheets, the already exceptional ductility was further increased. Moderate losses in tensile strength and stiffness were observed and are attributable to a loss of crystallinity and fibre shortening. This is the first report of strong and durable extrudates using cellulosic fibres as the only feedstock. Finally, the potential for recycling the processed material with unmodified fibres by paper recycling procedures was demonstrated.

Research interest in quaternization of cellulose fibres has increased considerably over the past decades. However, there is little or no consensus regarding how to characterize the material in terms of degree of substitution (DS), and the literature suggests a range of different methods focusing on charge determination as well as nitrogen content quantification. This work aims to fill the knowledge gap regarding how the different methods perform in relation to each other, and for what cellulosic systems each method has advantages, disadvantages and even potential pitfalls. FT-IR and NMR measurements are used to establish successful modification and determine the relative number of substituent groups. Another six methods are compared for the determination of the DS of cellulosic fibres and nanofibrils. The methods include Kjeldahl measurements, nitrogen determination by chemiluminescence, determination of molecular nitrogen by the Dumas method, colloidal titration, conductometric titration and polyelectrolyte adsorption. It can be concluded that most techniques investigated are reliable within certain ranges of DS and/or when using appropriate post-treatment of the quaternized material and suitable sample preparation techniques. The results from the present work hence provide recommendations to make an educated choice of method, and experimental protocol, based on the technique at hand.

Dialcohol cellulose can be prepared by periodate-mediated oxidation of cellulose followed by reduction with borohydride. The two-step reaction creates a modified cellulose polymer which is ring-opened between the C2 and C3 carbons in the glucose unit. This material has attracted both scientific and commercial interest, due to its potential role in the transition towards a fossil-fuel-free society. In order to become a reliable component in the materials of tomorrow, chemical properties such as degree of modification must be accurately quantified. In this work we describe how solid-state NMR spectroscopy, enhanced by dynamic nuclear polarization (DNP), can be used for this purpose. Our results illustrate that it is possible to obtain high sensitivity enhancements in dialcohol cellulose with the DNP enhanced solid-state NMR technique. Enhancements above a factor of fifty, on a 400 MHz/263 GHz DNP system in the presence of 12 mM AMUPol radical were achieved. This allows us to quantify the degree of modification in dialcohol cellulose samples in time spans as short as 20 min using DNP enhanced multiple-contact cross polarization experiments. We also exemplify how DNP enhanced, ¹³C-¹³C dipolar recoupling experiments can be used for the same purpose and for studying chemical shift correlations in dialcohol cellulose. Graphical abstract: (Figure presented.)