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Recently, we have demonstrated the initial process design of acid-catalyzed poly(ethylene glycol) (PEG) solvolysis of softwood Japanese cedar (JC) in a large-scale batch reactor (50 kg wood meal pe...

Microbial cellulose has proven to be a remarkably versatile biomaterial and can be used in a wide variety of fields, to produce for instance paper products, electronics, acoustics, and biomedical devices. Various biodegradable and biocompatible polymeric materials have recently been investigated to fabricate inorganic-organic hybrid composites by mimicking the mineralization system of natural bone, with some successful outcomes. However, the search for an ideal biomaterial with properties and functionalities similar to natural bone is a continuing process because no single material can satisfy all the requirements for creating optimal scaffolding properties, such as strength, toughness, osteoconductivity, osteoinductivity, controlled degradation, inflammatory response, and deformability. In this study, the ultrafine 3-D BC network structure with its native unique properties is exploited for the synthesis of materials analogous to natural bone. Our study showed that the formation of apatite is dependent on the presence and type of surface functional groups in the microfibrillar BC network. Degradation of BC has not been fully evaluated in in vitro and in vivo settings. Other cellulose-based materials have however shown limited degradation. Although the complete degradability of materials for tissue engineering applications is very attractive, it is difficult to practically optimize and synchronize the degradation time and mechanical properties of the materials. Modification of BC by incorporation of lysozyme (an enzyme with antibacterial action that is found in body fluids, saliva, sweat and tears) susceptible sugars such as analogues of N-acetylglucosamine (GlcNAc) was performed during microbial synthesis. In addition, GlcNAc shares the structure of some repeated disaccharide units of glycosaminoglycans, which are essential components of extracellular matrices. It is expected that the incorporation of GlcNAc will make BC more degradable and more relevant for end use, for instance in the biomedical area. Subtle changes were observed in the formation of apatite deposits on various BC-GlcNAc surfaces. However, the GlcNAc content of the BCGlcNAc produced was low (0.36 mole%) compared to other studies (4-18 mole%). The bacterial strain used in our study is different from those reported by others. It is possible that the type of cellulose producing strain influences the incorporation of GlcNAc in BC. This observation suggests that it is worth pursuing this type of investigations to tailor the surface properties of BC to meet the main criteria of mineralized collagen composites such as natural bone and teeth. Such investigations should be complemented by in vitro and in vivo degradation studies. Since BC is an environmentally friendly biopolymer, its use for materials fabrication for a broad range of applications can be envisaged as an alternative to forest resources. A limitation however is the large-scale production of BC-based composites.

Polyethylene glycol (PEG)-modified lignin (glycol lignin) can be produced through an acid-catalyzed reaction of Japanese cedar using PEG as a solvolysis reagent. Acid precipitation and the following solid–liquid separation steps are the rate-determining processes for glycol lignin production. The effect of temperature on the flocculation of glycol lignin suspensions, which is necessary for effective solid–liquid separation, was evaluated. The heat treatment of glycol lignin suspensions, at temperatures of ≥50 °C, improved flocculation and decreased the average filtration resistance values of the suspensions. However, alkaline lignins, such as those in soda and kraft lignins in black liquors, did not show significant improvements in flocculation following heat treatment at 50 °C. The heat-induced flocculation property depended on the type of glycol lignin. The degree of flocculation increased with the increase in the molecular weight of PEG used for glycol lignin production. The solid–liquid separation for the glycol lignin production was highly improved by a simple heat treatment.

Flexible clay polymer nanocomposite films with heat durability and high moisture-barrier property were prepared by using Li + -exchanged bentonite and polyethyleneglycol-modified lignin. Analyses revealed that the films comprised of laminated clay mineral layers and the lignin intercalated between the layers. The films retained their heat durability up to 350 °C, and their moisture vapor transmission rate (MVTR) at 40 °C a relative humidity (RH) of 90% was 1.64 g m − 2 day − 1 , which is lower than that of plastic films. The low MVTR originated from not only the water-resistant bentonite, owing to the migration of interlayer Li + ions into the octahedral sheets after annealing, but also the modified lignin. Consequently, the films have potential as a flexible substrate for electronic devices.

A potential alternative biorefinery platform, in which high quality lignin is the main product of the process, is demonstrated. The polyethylene glycol (PEG)-modified softwood lignin (glycol lignin, GL) was isolated from Japanese cedar by acid-catalyzed PEG solvolysis, where liquid PEG with varying polymer chain length was used as the solvolysis reagent with a small amount of acid catalyst. The isolated glycol lignin had the weight-average molecular weight of 4000–7000 and exhibited a viscous thermal flow property, which is impossible for industrial softwood lignin without further processing steps. Thermal analyses, such as thermomechanical analysis (TMA) and capillary flow tester rheometer (CFT), proved to be sensitive techniques for determination of thermal flow behavior. The lignin yield and solid residue (mostly cellulosic residue), respectively, of 28%–31% and 36%–38% (dry wood basis) were obtained from PEG200 solvolysis with 0.5%–0.7% acid catalyst. The results indicated the effectiveness of the one...

The acidic solvolysis of lignocellulose using a glycol solvent such as polyethylene glycol (PEG) is a promising process for separating its components and producing a valuable lignin product that can be used as thermoplastic and fusible materials. To decrease operational costs, a glycol solvent that is used as a solvolysis reagent must be recovered and reused. In the present study, PEG was recovered by the removal of water by evaporation from the supernatant after glycol lignin production by acidic solvolysis of Japanese cedar using PEG with an average molecular weight of 200 (PEG200). The recovered PEG200 worked as a solvolysis reagent and produced glycol lignin with appropriate yield. The thermomechanical analysis of glycol lignin from the fresh and recovered PEG200 systems exhibited two inflection points, which were assigned to a glass transition point (Tg) and a thermal softening point (Ts). The Ts of the glycol lignin from the recovered PEG200 system was higher than that from the fresh PEG200 system. These results suggest that the glycol lignin from the recovered PEG200 system had high thermostability as well as high thermal fusibility.

By adding 2 wt% multi-layer graphene oxide (MGO) to an epoxy resin, the thermal conductivity of the compos- ite reached a maximum, 2.03 times that of the epoxy. The presence of 2 wt%MGO percolating chains leads to an unprece- dentedly sharp rise in energy barrier at final curing stage, but an increased epoxy curing degree (!IR) is observed; however, this !IR difference nearly disappears after aging or thermal annealing. These results suggest that the steep concentration gra- dient of -OH, originated from the 2 wt%MGO percolating chains, exerts the vital driving force on the residual isolated/ trapped epoxy to conquer barrier for epoxy-MGO reaction. A modified Shrinking Core Model customized for the special layered-structure of MGO sheet was proposed to understand the resistance variation during the intercalative epoxy-MGO reaction. It shows that the promoted intercalative crosslinking is highly desirable for further improving the thermal conduc- tivity of the composite, but it meets with increased resistance. Guided by the kinetic studies, targeted optimization on the cure processing strategy was accordingly proposed to promote the intercalative crosslinking, a thermal conductivity, 2.96 times that of the epoxy, was got with only a small amount (30°C) increase of the post-heating temperature.

Multi-layer graphene oxide (MGO) has attracted considerable interest in conductive polymer composites. However, in most cases the optimal MGO content is determined using a complex procedure. Avoiding the complicated work of processing polymerized samples followed by testing various properties, here a facile strategy is proposed to directly identify the critical MGO content among formulations for epoxy composites with optimal thermal properties, simply by monitoring the “unusual” nonlinear MGO content-dependent cure behaviors, as well as the “unusual” pattern of double-peak curing curves. The formation mechanism of the double-peak pattern was explored, with emphasis on studying the epoxy/MGO reaction using a modified Shrinking Core Model. The optimal content determined in this work (2 wt% MGO) was verified by the thermal properties (thermal conductivity, structural thermal stability and coefficient of thermal expansion) of MGO/epoxy composites. Based on the inherent relationship between the effect of MGO percolating chains on the thermal polymerization behavior and the resulting thermal properties, this strategy can be easily extended to different kinds of conductive MGO/polymer composites.

Softwood lignin prepared by soda-anthraquinone (AQ) cooking does not have thermal melting characteristics. To improve the properties of softwood soda-AQ lignin, we have invented a new method of lignin modification using dried black liquor powder by a spray dryer system and polyethylene glycol (PEG). In this process, black liquor powder was directly treated with PEG under alkaline conditions to produce PEG-modified lignin (alkaline PEG treatment). Dried black liquor powder prepared by a spray dryer was dissolved into PEG and heated at either 120 or 160 °C at atmospheric pressure. The modified lignin (alkaline PEG-treated lignin) was precipitated with acid and recovered by filtration. The alkaline PEG-treated lignin showed adequate thermal melting characteristics. The treatment temperature and the molecular weights of PEG considerably affected the thermal properties of the alkaline PEG-treated lignin. There was an addition reaction of the PEG to the lignin hydroxyl group at the alpha- (-) carbon. However, in the acid precipitation step, if the mixture was allowed to set unfiltered for a long time, the PEG bonded with the lignin was hydrolyzed, which yielded the original soda-AQ lignin and PEG polymer.

In this paper, we prepared a novel organic–inorganic nanocomposite film with excellent insulation properties relative to the polyimide film in mild-processing conditions. The main component of the film is clay mineral and wood component, i.e., the layered silicate and poly(ethylene glycol)-modified lignin derivatives. In the nanocomposite film, an interlayer of silicate was bound by triethanolamine. Furthermore, the lignin derivatives filled the voids of the layered silicate, producing a defect-free densely packed nanocomposite film. This unique structure of the nanocomposite film provides high-thermal stability, a low thermal expansion coefficient of film consisting of clay and lignin derivatives, low gas transmittance rate, low volume/surface resistivity, and high dielectric breakdown voltage. The obtained nanocomposite film was installed in a planar-type transformer where it acted as an insulation film in the transformer coil with high dielectric breakdown voltage.

Graphite nanoplatelets (GNPs) were utilized to improve the electrical conductivity of pristine bacterial cellulose (BC) membranes. By physical and chemical methods, flake-shaped GNPs, weaving through the surface layer of web-like cellulose nanofibrils, were indeed fixed or trapped by the adjacent nanofibrils in the BC surface network, for comparison, rod-shaped multi-walled carbon nanotubes (MWCNTs) were homogeneously inserted into BC membrane through the pore structures and tunnels within the BC membrane. Strong physical and chemical interaction exists between the BC nanofibrils and the particles of GNP or MWCNT even after 15 h sonication. BC membrane with 8.7 wt% incorporated GNPs reached the maximum electrical conductivity of 4.5 S/cm, while 13.9 wt% MWCNT/BC composite membrane achieved the maximum electrical conductivity of 1.2 S/cm. Compared with one dimensional (1-D) MWCNTs, as long as GNPs inserted into BC membranes, the 2-D reinforcement of GNPs was proven to be more effective in improving the electrical conductivity of BC membranes thus not only break the bottleneck of further improvement of the electrical conductivity of BC-based composite membranes but also broaden the applications of BC and GNPs.

Rod-like cellulose nanowhiskers and spherical cellulose nanoparticles were prepared from wood-pulp-derived cellulose powder by mechanical refining processes such as high-pressure homogenization (HPH) and ball-milling (BM). The nanowhiskers obtained by the HPH method were found to be 200–500 nm long and 11–16 nm wide. The diameters of the nanoparticles were in the range 40–200 nm, depending on the BM time, and were reduced to 25–50 nm after extra HPH. By adjusting the BM time, cellulose nanoparticles having different polymorphs with similar morphologies were prepared. The X-ray diffraction patterns revealed the recrystallization of cellulose I (1 h of BM time) or cellulose II (4–8 h of BM time) in ball-milled nanoparticles after water washing and solvent exchange treatments. The nanowhisker widths derived from the specific surface areas (SSA) by adsorption methods such as Congo red dye, nitrogen, and water vapor, sorptions were in agreement with those obtained from transmission electron microscopy and atomic force microscopy images. Similar SSA values were obtained for micro- and nano-scale cellulose materials using water vapor adsorption methods, and the SSAs of nanoparticles obtained by different adsorption methods are also discussed.

Silver nanowires (AgNWs) surrounded by insulating poly(vinylpyrrolidone) have been synthesized by a polyol process and employed as transparent electrodes. The AgNW transparent electrodes can be fabricated by heat-treatment at about 200 °C which forms connecting junctions between AgNWs. Such a heating process is, however, one of the drawbacks of the fabrication of AgNW electrodes on heat-sensitive substrates. Here it has been demonstrated that the electrical conductivity of AgNW electrodes can be improved by mechanical pressing at 25 MPa for 5 s at room temperature. This simple process results in a low sheet resistance of 8.6 Ω/square and a transparency of 80.0%, equivalent to the properties of the AgNW electrodes heated at 200 °C. This technique makes it possible to fabricate AgNW transparent electrodes on heat-sensitive substrates. The AgNW electrodes on poly(ethylene terephthalate) films exhibited high stability of their electrical conductivities against the repeated bending test. In addition, the surface roughness of the pressed AgNW electrodes is one-third of that of the heat-treated electrode because the AgNW junctions are mechanically compressed. As a result, an organic solar cell fabricated on the pressed AgNW electrodes exhibited a power conversion as much as those fabricated on indium tin oxide electrodes. These findings enable continuous roll-to-roll processing at room temperature, resulting in relatively simple, inexpensive, and scalable processing that is suitable for forthcoming technologies such as organic solar cells, flexible displays, and touch screens. Open image in new window

A family of polysaccharide based scaffold materials, bacterial cellulose/chitosan (BC/CTS) porous scaffolds with various weight ratios (from 20/80 to 60/40 w/w%) were prepared by freezing (−30 and −80 °C) and lyophilization of a mixture of microfibrillated BC suspension and chitosan solution. The microfibrillated BC (MFC) was subjected to 2,2,6,6-tetramethylpyperidine-1-oxyl radical (TEMPO)-mediated oxidation to introduce surface carboxyl groups before mixing. The integration of MFC within chitosan matrix was performed by 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride (EDC)-mediated cross-linking. The covalent amide bond formation was determined by ATR-FTIR. Because of this covalent coupling, the scaffolds retain their original shapes during autoclave sterilization. The composite scaffolds are three-dimensional open pore microstructure with pore size ranging from 120 to 280 μm. The freezing temperature and mean pore size take less effect on scaffold mechanical properties. The compressive modulus and strength increased with increase in MFC content. The results show that the scaffolds of higher MFC content contribute to overall better mechanical properties.

The apatite forming ability of biopolymer bacterial cellulose (BC) has been investigated by soaking different BC specimens in a simulated body fluid (1.5 SBF) under physiological conditions, at 37°C and pH 7.4, mimicking the natural process of apatite formation. From ATR-FTIR spectra and ICP-AES analysis, the crystalline phase nucleated on the BC microfibrils surface was calcium deficient carbonated apatite through initial formation of octacalcium phosphate (OCP) or OCP like calcium phosphate phase regardless of the substrates. Morphology of the deposits from SEM, FE-SEM, and TEM observations revealed the fine structure of thin film plates uniting together to form apatite globules of various size (from

Optically transparent nanofiber paper containing silver nanowires showed high electrical conductivity and maintained the high transparency and low weight of the original transparent nanofiber paper. We demonstrated some procedures of optically transparent and electrically conductive cellulose nanofiber paper for lightweight and portable electronic devices. The nanofiber paper enhanced high conductivity without any post treatments such as heating or mechanical pressing, when cellulose nanofiber dispersions were dropped on a silver nanowire thin layer. The transparent conductive nanofiber paper showed high electrical durability in repeated folding tests, due to dual advantages of the hydrophilic affinity between cellulose and silver nanowires and the entanglement between cellulose nanofibers and silver nanowires. Their optical transparency and electrical conductivity were as high as those of ITO glass. Therefore, using this conductive transparent paper, organic solar cells were produced that achieved a power conversion of 3.2%, which was as high as that of ITO-based solar cells.

The 2,2,6,6-tetramethylpiperidine-1-oxy radial (TEMPO)-mediated oxidation was applied to aqueous suspensions of cotton linters, ramie and spruce holocellulose at pH 10.5, and water-insoluble fractions of the TEMPO-oxidized celluloses collected by filtration with water were analyzed by optical and transmission electron microscopy and others. The results showed that both fibrous forms and microfibrillar nature of the original native celluloses were maintained after the TEMPO-mediated oxidation, even though carboxylate and aldehyde groups of 0.67–1.16 and 0.09–0.21 mmol/g, respectively, were introduced into the water-insoluble fractions. Neither crystallinity nor crystal size of cellulose I of the original native celluloses was changed under the conditions adopted in this study. Carboxylate groups in the TEMPO-oxidized ramie were mapped by labeling with lead ions as their counter ions. The transmission electron micrographs indicated that some heterogeneous distribution of carboxylate groups along each cellulose microfibril or each bundle of cellulose microfibrils seemed to be present in the TEMPO-oxidized celluloses.

Two-dimensional FT-IR spectroscopy (2D FT-IR) was applied to the investigations of crystalline chitin structure. From this study, new information about spectral bands which are not observed in conventional 1D FT-IR was obtained. In 2D spectra, three specific bands were differentiated at 3482, 3421, and 3380 cm(-1) in the OH region. They could be assigned as C(6)OH groups which are hydrogen-bonded to the next C(6)OH; C(3)OH groups hydrogen-bonded to O(5); and C(6)OH groups bifurcated hydrogen-bonded to C(6)OH as well as C=O, respectively. Two pairs of bands appeared in the amide region, indicating the two types of hydrogen-bonded states of C=O groups. This is in good agreement with the results in the OH region; half of the C(6)OH groups are hydrogen-bonded to C=O as well as the next C(6)OH. The results accurately confirmed the Blackwell model which was established by an X-ray diffraction study. The temperature-dependency of hydrogen-bonds was also revealed by 2D FT-IR. Interchain hydrogen-bonds [C(6)OH...O(6)] first respond to a temperature followed by intrachain [C(6)OH...O=C] and [C(3)OH...O(5)] with increasing temperature. Interchain hydrogen-bonds [NH...O=C] are relatively stable in the temperature range of 40-180 degrees C.

This study investigates the improved swelling behavior of chitosan/poly(acrylic acid) complex by solvent (methanol, ethanol, and acetone) extraction. The complex is developed by photoinitiated free-radical polymerization of acrylic acid in the presence of chitosan. The swelling ratio of the complexes depends on the cosolvency effect of poly(acrylic acid) to the extracted solvent, which in turn affects the polymer network structure and ionic states characterized by dynamic force microscopy (DFM), Raman, and FT-IR spectroscopy. The DFM investigation displays the improved structural changes of the polymer network structure after solvent extraction and its relation to the improved swelling property of the chosen system in different environmental conditions (pH, solvent, and salt concentration) are discussed. A high swelling ratio of about 600 times its dry weight is observed in water as well as in low salt and solvent concentration after methanol extraction. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2930–2940, 2004

Liquid crystalline chitin/poly(acrylic acid) composite, with its unique optical properties, was fabricated by the free-radical photopolymerization of acrylic acid in an aligned mesophase. Alignment of the mesophase was achieved by unidirectional shearing. The developed composites, coated on calcium fluoride (CaF 2 ) substrate, were transparent, and the alignment was retained depending on the mesophase composition of the ternary dispersion (chitin microfibrils, water, acrylic acid). According to studies from polarized FTIR spectroscopy, both the degree of orientation and the molecular interactions were strongly affected by respective mesophase behavior. The average molecular chains of chitin microfibrils were oriented along the shear direction. A high dichroic ratio value of about 25, observed in composites of chitin/poly(acrylic acid) with a w/w ratio of 55:45, opens an interesting avenue to prepare a new chitin-based optically anisotropic composite.

A high magnetic field of 5 T was used to fabricate a magnetically aligned, optically anisotropic, liquid-crystalline chitin/poly(acrylic acid) composite. The aligned mesophase was fixed by photoinitiated free-radical polymerization. From an examination of polarized optical micrographs and an X-ray diffraction study, a high degree of orientation of 0.70 was observed for the composite with a higher liquid-crystalline chitin concentration (10.70 wt %); the orientation was reduced with a decreased chitin concentration at a given acrylic acid concentration. The X-ray data for the developed composite showed a uniplanar orientation for the chitin crystallites, with its molecular long axes perpendicular to the direction of the magnetic field. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 711–714, 2003

Phase behavior of a liquid crystalline chitin/acrylic acid liquid mixture was studied to fabricate a chitin-based composite with unique optical property. From a series of phase separation studies, we can evaluate the ternary phase diagram of a chitin microfibril, water, and acrylic acid monomer system. A suitable starting liquid crystalline chitin concentration to obtain anisotropic monophase over a range of acrylic acid concentration (up to 33 (w/w) %) was 14.62% (14−15%) by weight. At lower acrylic acid concentration range, crystalline microfibrillar fragments of chitin self-assembled to form upper isotropic phase and lower anisotropic liquid crystal phase at high enough concentration of chitin crystallites. The latter showed a characteristic chiral nematic order, a fingerprint-like texture. Above this chitin concentration and at higher acrylic acid concentration range, the system formed a monophasic stable flow-birefringence glassy phase, which displayed a nematic order. This phase occurred within a ve...

Requirements for flexible electronic substrate are successfully accomplished by green nanocomposite film fabricated with two natural components: glycol-modified biomass lignin and Li+ montmorillonite clay. In addition to these major components, a cross-linking polymer between the lignin is incorporated into montmorillonite. Multilayer-assembled structure is formed due to stacking nature of high aspect montmorillonite, resulting in thermal durability up to 573 K, low thermal expansion, and oxygen barrier property below measurable limit. Preannealing for montmorillonite and the cross-linking formation enhance moisture barrier property superior to that of industrial engineering plastics, polyimide. As a result, the film has advantages for electronic film substrate. Furthermore, these properties can be achieved at the drying temperature up to 503 K, while the polyimide films are difficult to fabricate by this temperature. In order to examine its applicability for substrate film, flexible electrodes are finely printed on it and touch sensor device can be constructed with rigid elements on the electrode. In consequence, this nanocomposite film is expected to contribute to production of functional materials, progresses in expansion of biomass usage with low energy consumption, and construction of environmental friendly flexible electronic devices.

Koga, H., Nogi, M., Komoda, N. et al. Uniformly connected conductive networks on cellulose nanofiber paper for transparent paper electronics. NPG Asia Mater 6, e93 (2014). https://doi.org/10.1038/am.2014.9., We demonstrate the fabrication of highly transparent conductive networks on a cellulose nanofiber paper, called cellulose nanopaper. Uniform coating of the conductive nanomaterials, such as silver nanowires (AgNWs) and carbon nanotubes, is achieved by simple filtration of their aqueous dispersions through the cellulose nanopaper, which acts as both filter and transparent flexible substrate. The as-prepared AgNW networks on the nanopaper offer sheet resistance of 12Xsq.Ω1 with optical transparency of 88%, which is up to 75 times lower than the sheet resistance on a polyethylene terephthalate film prepared by conventional coating processes. These results indicate that the 'filtration coating' provides uniformly connected conductive networks because of drainage in the perpendicular direction through paper-specific nanopores, whereas conventional coating processes inevitably cause self-aggregation and uneven distribution of the conductive nanomaterials because of the hard-to-control drying process, as indicated by the well-known coffee-ring effect. Furthermore, the conductive networks are embedded in the surface layer of the nanopaper, showing strong adhesion to the nanopaper substrate and providing foldability with negligible changes in electrical conductivity. This filtration process is thus expected to offer an effective coating approach for various conductive materials, and the resulting transparent conductive nanopaper is a promising material for future paper electronics.

In this study, we use nanostructured paper made from cellulose nanofibres (CNFs) as a flexible printable material for inkjet-printing of silver nanoparticle (AgNP) ink. The nanostructured paper is prepared by sheet casting of 10–40 nm wide mechanically fibrillated aqueous CNFs in suspension. The resulting nanostructured paper, in the form of densely packed laminar layers, has low surface roughness (40 ± 2.3 nm) and a nanoporous network structure. This unique surface feature helps the ink vehicles to permeate through the nanopores and also aids absorption along the fibril direction parallel to the surface while retaining the silver nanoparticles on the surface to compete with the initial spreading and final evaporation processes. As a result, well-defined inkjet-printed AgNP conductive tracks (∼400 μm wide) on nanostructured paper show lower electrical resistance (1.57 ± 0.09 Ω cm−1) than those on commonly used plastics, including polyimide (PI, 2.07 ± 0.17 Ω cm−1) and poly(ethylene naphthalate) (PEN, 2.10 ± 0.16 Ω cm−1), at a moderate curing temperature of 150 °C for 1 h. The inkjet-printed conductive tracks on nanostructured paper also show better electrical performance during and after folding than those printed on plastic substrates, such as PI, and exhibit stable electrical properties throughout a test period of 1000 h in a moisture resistance test (85 °C and 85% relative humidity). The better overall electrical performance compared with that of tracks on plastic substrates highlights the potential of genuinely nanostructured paper as a printing substrate for flexible printed electronics.