Mid Sweden University

Predicting the modulus of short fiber-reinforced composites is complicated by simultaneous variations in fiber length, orientation, and volume fraction during processing. This work refines the classical modified rule of mixtures (MROM) by introducing two concentration-dependent weighting functions, and , which capture the evolution of effective fiber length, fiber-fiber interactions, fiber orientation, and loading-angle effects. A microstructural efficiency coefficient is further incorporated to describe reinforcement degradation from dilute to crowded fiber conditions. The model was validated using ethylene-vinyl acetate/short carbon fiber composites with fiber volume fractions of 1.37%-16.80%. Young's modulus measured at loading angles of 0 degrees, 45 degrees, and 90 degrees showed excellent agreement with predictions, with the refined formulation outperforming the classical MROM, particularly at higher loading angles. Overall, the refined framework provides a compact and physically grounded framework for accurately predicting stiffness and supports the design and optimization of short fiber-reinforced polymer systems.

Fibre properties significantly influence paper quality. This study investigates fibre property development along an industrial pulp production line, analysing morphological distributions and rheological behaviour to enhance refining performance indicators. Understanding these developments is critical for optimising resource efficiency and increasing industrial sustainability. Softwood thermomechanical pulp (TMP), from high-consistency (HC) and low-consistency (LC) refining, and bleached hardwood kraft pulp (BHKP) were examined. Fibre morphological properties were characterised using an optical fibre analyser, while suspension rheology was assessed using a pulp viscometer, supported by computational fluid dynamics (CFD) and discrete element method (DEM) simulations. Results demonstrate that fibre property distributions provide deeper insights into refining effects compared to average values alone. Systematic trends showed that HC-refined TMP from the first and second refining stage required significantly greater torque to break the fibrous network and fluidise the pulp compared to pulp that was also LC refined. This indicates that alterations in fibre properties, especially shortened fibre length resulting from different refining processes, govern fibre interactions in the three-dimensional network of the pulp suspensions and, therefore, their flow behaviour. In conclusion, combining morphological distribution analysis with specialised rheological measurements offers a robust tool for better understanding and monitoring mill-scale refining processes, enabling improved process optimisation in pulping and papermaking.

To address the global challenges of fossil fuel depletion and plastic pollution, promoting sustainable environmental development, we have explored the use of wheat gluten (WG) as a possible insulating material in electric applications. Inspired by previous work on whey protein foams, where a thermal treatment improved the mechanical integrity, WG was also here heat-treated at 150°C in air, and films were produced with and without a plasticiser (glycerol, GLY). The overall properties depended on the composition, processing conditions, environment, and whether a heat-treatment was used or not. At best, films exhibited an electric insulation competitive to fossil-based plastics (7.2 × 1014 Ω·m), oil resistance, and a comparatively low moisture uptake. Quite unexpectedly, these films, prepared with glycerol, remained flexible even after 4 weeks at 150°C. These results suggest that thermally treated WG/GLY materials have the potential to be used in e.g. low-voltage insulation parts in electric motors, achieving a balance between performance and sustainability in automotive applications.

The structural integrity of composite rocket propellants is critical for the reliability of rocket motors, as insufficient integrity can lead to failure or even motor explosion. However, the material properties of such propellants degrade over time. Ageing is typically monitored using tensile testing, a time-consuming and destructive method that requires substantial sample volumes. Consequently, alternative characterisation techniques are sought. One promising approach is dynamic mechanical analysis (DMA), which requires samples that are orders of magnitude smaller than those used for tensile testing. The aim of this study was to establish relationships between strain and elastic modulus (from tensile testing), storage modulus (from DMA), and hardness. Composite propellants based on hydroxyl-terminated polybutadiene, ammonium perchlorate, and aluminium were manufactured, subjected to accelerated ageing at 75–105 °C in an inert atmosphere for up to 190 days, and characterised by tensile testing, DMA, and hardness measurements. For each ageing temperature, the relative change of each property was plotted as a function of time. Empirical expressions linking strain, elastic modulus, storage modulus, and hardness were derived from the Arrhenius equation. These empirical models enable reliable conversion between, for example, storage modulus and strain for lifetime prediction, thereby demonstrating that DMA can serve as a viable alternative or complement to tensile testing. 

Achieving precise mechanical control in electrospun fibrous scaffolds remains a critical challenge for tissue engineering, where scaffold stiffness, strength, and extensibility must be tailored to diverse biological environments. Here, we establish a systematic framework for tuning the mechanical behavior of electrospun poly(epsilon-caprolactone) (PCL) fibers by integrating molecular-weight blending, polymer concentration control, fiber orientation, and environmental exposure within a single study. High-molecular-weight PCL (H-PCL) and blends with low-molecular-weight PCL (L-PCL) were electrospun to produce fibers with controlled diameters, morphologies, and orientations. Fiber alignment emerged as the dominant structural factor governing mechanical performance: oriented fibers exhibited substantially higher stiffness (similar to 90-140 MPa) and tensile strength (up to similar to 100 MPa), while randomly deposited fibers showed markedly greater extensibility (up to similar to 1000%). Polymer concentration and resulting fiber diameter further modulated stiffness, with optimal mechanical performance observed at intermediate concentrations (similar to 10-12% w/v). Molecular-weight blending provided an additional route to tailor fiber morphology and modulus, with oriented fibers reaching peak stiffness at similar to 50-60% H-PCL. Environmental exposure studies revealed that acidic treatments (formic and acetic acid solutions) reduce stiffness in a concentration- and temperature-dependent manner, whereas physiological soaking in phosphate-buffered saline (PBS, 37 degrees C) largely preserves scaffold integrity. Collectively, the electrospun scaffolds developed here span a broad mechanical window (similar to 5-140 MPa). When positioned against literature-reported electrospun PCL scaffolds for cardiac, bone, and muscle tissue engineering, this range bridges multiple application-relevant stiffness regimes. These results provide a unified structure-property framework for designing mechanically tunable PCL fibrous scaffolds across diverse biomedical applications.

This study introduces a ternary composite system based on silicone, carbon black (CB), and liquid metal (LM) gallium. Despite extensive studies on LM/elastomer systems, most have primarily focused on mechanical reinforcement or thermal conductivity, while a systematic understanding of their electrical modeling and electromagnetic shielding performance remains insufficient. Therefore, we utilized silicone as an elastomeric matrix, CB as conductive nanofillers, and gallium as a conductive metallic phase, a flexible composite with enhanced multifunctional performance is realized. Shear dispersion during fabrication induces a unique star-like architecture of gallium, which, together with the conductive CB network, facilitates the formation of efficient and continuous electrical pathways. The resulting composites exhibit notable improvements in mechanical strength, strain-dependent resistive response, and electromagnetic interference (EMI) shielding capabilities. In particular, the optimized composite achieves an EMI shielding effectiveness of similar to 35 dB in the X-band, while maintaining stable strain sensing performance over 1000 cycles at 30 % strain. A systematic investigation into the influence of gallium concentration elucidates the correlation between microstructural evolution and the composite's physical and electromagnetic behavior. This work not only deepens the understanding of LM-based ternary composites but also highlights their potential for advanced applications in flexible sensing, wearable electronics, and EMI attenuation technologies.

In this study, a two-stage, low-consistency (LC) refining process at the Holmen Braviken paper mill in Sweden was examined to evaluate the relationship between energy input, fibre distributions, and pulp properties, including handsheet properties. The LC refiners used thermo-mechanical pulp based on 100 % Norway spruce, with two specific energy levels: "low" (approximate to 80 kWh/adt) or "high" (approximate to 100 kWh/adt). All four permutations of these settings were examined. Overall, higher refining efficiency (measured by the increase in tensile index per applied energy) was observed in the first LC refiner stage than in the second. To further explore the impact of LC refining, pulp particle distributions were investigated. Samples from before, between and after the two LC stages were analysed using an optical fibre analyser, which provided detailed data on length-width-curl-fibrillation distributions. The impact of LC refining on these distributions was quantified using Kolmogorov-Smirnov statistics, highlighting statistically significant changes observed in the length and curl distributions. We investigated the correlation between energy input into the LC refiners and the impact on fibre distributions and handsheet properties. These insights underscore the effectiveness of our analytical approach and its potential for refining process control in mechanical pulping, offering a method for more targeted and efficient adjustments.

Water-soluble polymers are materials rapidly growing in volume and in number of materials and applications. Examples include synthetic plastics such as polyacrylamide, polyacrylic acid, polyethylene glycol, polyethylene oxide and polyvinyl alcohol, with applications ranging from cosmetics and paints to water purification, pharmaceutics and food packaging. Despite their abundance, their environmental concerns (e.g., bioaccumulation, toxicity, and persistence) are still not sufficiently assessed, especially since water soluble plastics are often not biodegradable, due to their chemical structure. This review aims to overview the most important water-soluble and biodegradable polymers, their applications, and their environmental impact. Degradation products from water-insoluble polymers designed for biodegradation can also be water soluble. Most water-soluble plastics are not immediately harmful for humans and the environment, but the degradation products are sometimes more hazardous, e.g. for polyacrylamide. An increased use of water-soluble plastics could also introduce unanticipated environmental hazards. Therefore, excessive use of water-soluble plastics in applications where they can enter the environment should be discouraged. Often the plastics can be omitted or replaced by natural polymers with lower risks. It is recommended to include non-biodegradable water-soluble plastics in regulations for microplastics, to make risk assessments for different water-soluble plastics and to develop labels for flushable materials. 

This study examined the high-temperature stability of polyether ether ketone (PEEK) and polyphenylene sulfide (PPS) in an oxygenated environment. Both polymers were extrusion-coated onto copper wires for electrical insulation in traction motors. Accelerated testing using thermogravimetry and calorimetry showed that copper catalyzed thermal oxidation of PEEK (at very high temperature), which was accelerated by a lower molar mass of the PEEK and an increased copper-polymer contact area. Both techniques indicated a complex thermal oxidation pattern for both polymers. Notably, the presence of copper seemed to reduce/retard the degradation of PPS. Overall, both polymers demonstrated high oxidation resistance at elevated temperature in an air environment, indicating long service life in electric motor, excluding factors like moisture, oil spray cooling and Joule heating.

Lignin is a major component of wood cell walls, and as such, contributes to the properties of pulp fibers and fiber materials. Despite the natural abundance of lignins, their structure-function relationships remain rather poorly understood. This is both due to the chemical heterogeneity of lignins and the difficulty of isolating them without altering their structure. Recent advances in the chemical analysis of lignins have enabled a statistical description of their complex molecular structure [1]. This, in turn, has enabled the use of molecular modelling to study their fundamental properties and behaviors. We report molecular simulations on the structure and physical properties of softwood lignin, including its role in the moisture behavior of wood cell wall structures and thermal response in the hot-pressing process for a fiber web. We have created a molecular model for native-like softwood lignin based on a statistical description of its chemical structure [1]. Using a molecular force field developed for lignins [2], we have carried out atomistic simulations to study the behavior of cellulose-lignin interfaces and neat lignin at different moisture contents and temperatures. We compare the predictions at ambient temperature with X-ray scattering experiments on native and delignified spruce samples to understand the role of lignin in the moisture response of wood microfibril structures [3]. We compare the predictions at elevated temperatures with hot-pressing experiments on fiber webs at varied temperatures, sample moisture contents and pressing times to determine the role of lignin softening and diffusion in the observed wet strengthening. Our work is an early step toward more systematic use of molecular modelling to understand lignin structure-function relationships. We anticipate that combined chemical analysis and simulation will find increasing use in the development of lignin-based materials, including the thermal and wet processing of lignin-containing fiber materials.