Mittuniversitetet

Chitosan films with potential application in triboelectric nanogenerators (TENGs) represent a promising approach to replace non-biobased materials in these innovative devices. In the present work, chitosan with varying molecular weights (MW) and degrees of deacetylation was dissolved in aqueous acetic acid (AA) at different acid concentrations. It was observed that the MW had a greater influence on the viscosity of the solution compared to either the acid concentration or deacetylation degree. Gel formation occurred in high-MW chitosan solutions prepared with low AA concentration. Films prepared from chitosan solutions, through solvent-casting, were used to prepare TENGs. The power output of the TENGs increased with higher concentrations of AA used in the chitosan dissolution process. Similarly, the residual AA content in the dried films also increased with higher initial AA concentrations. Additionally, hot-pressing of the films significantly improves the TENG power output due to the decrease in morphological defects of the films. It was demonstrated that a good selection of the acid concentration not only facilitates the dissolution of chitosan but also plays a key role in defining the properties of the resulting solutions and films, thereby directly impacting the performance of the TENGs. 

Triboelectric nanogenerators (TENGs) represent a promising technology for energy harvesting and self-powered sensing with a wide range of applications. Despite their potential, challenges such as the need for cost-effective, large-area electrodes and engineering sustainable triboelectric materials remain, especially given the impending restrictions on single-use engineering plastics in Europe. To address these challenges, engineering nano-graphite-coated paper is presented as a sustainable and high-performance alternative for triboelectric layers. Moreover, this material, which can be produced on an industrial scale, offers a viable replacement for metal electrodes. The combination of nano-graphite and paper, with its large contact area and inherent surface roughness, enables ultra-high power densities exceeding 14 kW m−2, driven by electrostatic discharge at the surface. Beyond energy harvesting, smart sensors are developed for floors and walls that detect movements for security purposes and smart sheets that monitor body movements and physiological activities during sleep. The findings highlight the potential of this engineering paper to serve as an eco-friendly alternative to engineering plastics in TENGs and electrodes, opening new avenues for future applications. 

Cellulose regeneration is a critical step in the production of textiles, cellulose derivates, edible films for packaging or biomedical products because the regeneration process alters the cellulose properties. Cellulose regeneration involves complex intermolecular interactions and kinetics that determine the structure and properties of the regenerated cellulose products. Homogeneous quality is crucial for meeting market demands, but it is challenging due to variations in raw materials, process conditions, and other factors. On-line real-time monitoring of the cellulose regeneration process will allow researchers to optimize the process and producers to assess and control the key parameters involved during the regeneration process, ensuring both optimal product quality and process efficiency. This paper describes for the first time the potential of using focused beam reflectance measurements (FBRM) to monitor the evolution of cellulose regeneration under different conditions. The analysis of the evolution of the cellulose particle growth under different conditions allow us to confirm that the mechanism of cellulose aggregation is initiated by hydrophobic interactions and to understand the contribution of the different processes involved during the regeneration such as nucleation, particle growing, cellulose flocculation and floc break down. The results indicate that hydrolysis of urea in alkaline conditions, accelerated by elevated temperatures, has a major impact on the regeneration process confirming the idea that urea prevents hydrophobic interactions. The effects of temperature, initial cellulose concentration, seeding and aging have been quantified. FBRM analysis offers crucial insights that enhance understanding of the regeneration process, enabling its optimization and facilitates the creation of customized cellulose-based materials tailored for specific applications. 

Cellulose has shown great potential in the development of green triboelectric nanogenerators. Particularly, regenerated cellulose (R-cellulose) has shown remarkably high output power density but the structural features and key parameters that explain such superior performance remain unexplored. In this work, wood cellulose fibers were dissolved in a LiOH(aq)-based solvent to produce a series of R-cellulose films. Regeneration in different alcohols (from methanol to n-pentanol) was performed and the films’ structural features and triboelectric performance were assessed. Nonsolvents of increased hydrophobicity led to R-cellulose films with a more pronounced (1–10) diffraction peak. An open-circuit voltage (VOC) of up to ca. 260 V and a short-circuit current (ISC) of up to ca. 150 µA were measured for R-cellulose against polytetrafluoroethylene (as negative counter-layer). However, R-cellulose showed an increased VOC of 175% (from 88.1 V) against polydimethylsiloxane when increasing the alcohol hydrocarbon chain length from methanol to n-pentanol. The corresponding ISC and output power also increased by 76% (from 89.9 µA) and by 382% (from 8.8 W m–2), respectively. The higher R-cellulose hydrophilicity, combined with soft counter-tribolayer that follow the surface structures increasing the effective contact area, are the leading reasons for a superior triboelectric performance.

Cellulose laminates represent a remarkable convergence of natural materials and modern engineering, offering a wide range of versatile applications in sustainable packaging, construction, and advanced materials. In this study, novel all-cellulose laminates are developed using an environmentally friendly approach, where freshly regenerated cellulose II films are stacked without the need for solvents (for impregnation and/or partial dissolution), chemical modifications, or resins. The structural and mechanical properties of these all-cellulose laminates were thoroughly investigated. This simple and scalable procedure results in transparent laminates with exceptional mechanical properties comparable to or even superior to common plastics, with E-modulus higher than 9 GPa for a single layer and 7 GPa for the laminates. These laminates are malleable and can be easily patterned. Depending on the number of layers, they can be thin and flexible (with just one layer) or thick and rigid (with three layers). Laminates were also doped with 10 wt% undissolved fibers without compromising their characteristics. These innovative all-cellulose laminates present a robust, eco-friendly alternative to traditional synthetic materials, thus bridging the gap between environmental responsibility and high-performance functionality. 

Inks and toners used for printing contain materials, such as polyester, with strong triboelectric properties to enhance the binding effects, making wastepaper, such as magazines and newspapers, good candidates for triboelectric materials. Herein, high-output power triboelectric nanogenerators (TENGs) that utilize wastepaper as triboelectric layers (wastepaper-based triboelectric nanogenerators (WP–TENGs)) are reported. Journal paper and office copy paper wastes are investigated. The results show that the maximum power densities of the WP–TENGs reach 43.5 W m−2, which is approximately 250 times the previously reported output of the TENG with a recycled triboelectric layer made from wastepaper. The maximum open circuit voltage (V OC) and short circuit current (I SC) are 774 V and 3.92 mA (784 mA m−2), respectively. These findings can be applied to extend the life cycle of printed papers for energy harvesting, and they can later be applied for materials recycling to enhance the sustainable development of our society. 

In the history of cellulose chemistry, hydrogen bonding has been the predominant explanation when discussing intermolecular interactions between cellulose polymers. This is the general consensus in scholarly textbooks and in many research articles, and it applies to several other biomacromolecules’ interactions as well. This rather unbalanced description of cellulose has likely impacted the development of materials based on the processing of cellulose—for example, via dissolution in various solvent systems and regeneration into solid materials, such as films and fibers, and even traditional wood fiber handling and papermaking. In this review, we take as a starting point the questioning of the general description of the nature of cellulose and cellulose interactions initiated by Professor Björn Lindman, based on generic physicochemical reasoning about surfactants and polymers. This dispute, which became known as “the Lindman hypothesis”, highlights the importance of hydrophobic interactions in cellulose systems and that cellulose is an amphiphilic polymer. This paper elaborates on Björn Lindman’s contribution to the subject, which has caused the scientific community to revisit cellulose and reconsider certain phenomena from other perspectives. 

Triboelectric nanogenerators (TENGs) are ideal to meet the increasing need for green and efficient energy solutions, e.g., in small wireless and/or wearable applications. Regenerated cellulose is an exemplary material regarding both power output and mechanical performance, and it is environmentally friendly and economically favourable. To further improve the triboelectric performance of the cellulose, colour printing was done on the surface with conventional laser printing. Printer toners commonly contain substances with different triboelectric properties. [1] In this work, cellulose fibres were dissolved using a LiOH/urea solvent and regenerated in an ethanol bath and eventually dried under controlled conditions. Thereafter the resulting transparent cellulose films were run through a conventional laser paper printer to apply toners of different colour and patterns on the surface. Cyan, magenta, yellow and black was printed in one layer. In addition, black was printed in certain patterns from low to high coverage and in several layers to evaluate the effect of applied amount. The samples were analysed using SEM, AFM, XRD, FTIR and a TENG was assembled in the contact-separation mode to investigate the triboelectric performance. The printed cellulose films were found to give enhanced triboelectric output. The results show an interesting and simple processing route to enhance the performance of cellulose- based TENG materials that can be useful in the development of cheap and sustainable small wireless electrical generators or sensors.

[1] Zhang, R.; Hummelgård, M.; Örtegren, J.; Andersson, H.; Olsen, M.; Chen, W.; Wang, P.; Eivazi, A.; Dahlström, C.; Norgren, M., Adv. Engin. Mater., 2023, in press, https://doi.org/10.1002/adem.202300107

The triboelectric properties of the tribolayers are essential factors affecting the current density of triboelectric nanogenerators (TENGs). To enhance the current density, composites have been developed to tune their triboelectric properties. Previous studies have reported enhanced TENG performance with composite materials, primarily based on their composition, while chemical interactions between the components have been less analyzed. In this study, we report a novel approach to improve the current density of a TENG by introducing dipole-dipole interactions between a nylon filter membrane and graphene oxide (GO) through hydrogen bonds. The Raman spectroscopy confirmed the occurrence of the interactions resulting from hydrogen bonding. The enhancing mechanisms of hydrogen bonds were further analyzed by Kelvin probe force microscope (KPFM) measurement, which demonstrated that hydrogen bonding could influence the surface potential of the coated GO, leading to increased output of the nylon/GO@NFM TENG (NGN-TENG). Our results show that an ultrahigh current density of 1757 mA·m−2 was obtained with a 2 × 2 cm2 NGN-TENG. Additionally, we demonstrated the feasibility of using the NGN-TENG as a motion sensor to sense finger motions. These findings suggest that the introduction of hydrogen bonds in TENG composites can provide a promising route for improving their performance. 

Cellulose has shown great potential in the development of green triboelectric nanogenerators (TENG) [1]. Particularly, regenerated cellulose (R-cellulose) has shown remarkably high output power density but the structural features and key parameters that explain such superior performance remain unexplored. In this work, wood cellulose fibers were dissolved in a LiOH(aq)-based solvent to produce a series of R-cellulose films. Regeneration in different alcohols (from methanol to n-pentanol) was performed and the films’ structural features and triboelectric performance were assessed. Nonsolvents of increased hydrophobicity led to R-cellulose films with higher hydrophilic character; the films showed a (1- 10) diffraction peak of larger amplitude and higher apparent crystallinity. An open-circuit voltage (VOC) of up to ca. 260 V and a short-circuit current (ISC) of up to ca. 150 μA were measured for R-cellulose against polytetrafluoroethylene (as negative counter-layer). However, R-cellulose showed an increased VOC of 175% (from 88.1 V) against polydimethylsiloxane from methanol to n-pentanol. The corresponding ISC and output power also increased by 76% (from 89.9 μA) and by 382% (from 8.8 W m–2), respectively. The higher R-cellulose hydrophilicity, combined with soft counter-layer that follow the surface structures increasing the effective contact area, are the leading reasons for a superior triboelectric performance.

[1] Zhang, R., Dahlström, C., Zou, H., Jonzon, J., Hummelgård, M., Örtegren, J., Blomquist, N., Yang, Y., Andersson, H., Olsen, M., Norgren, M., Olin, H. & Wang, Z.L. Adv. Mater. 32, 2002824, 2020; https://doi.org/10.1002/adma.202002824