Tailoring flame-retardancy and strength of papers via layer-by-layer treatment of cellulose fibers

The layer-by-layer (LbL) technology was used to adsorb polyelectrolyte multilayers consisting of cationic polyethylenimine (PEI) and anionic sodium hexametaphosphate (SHMP) onto cellulose fibers in order to enhance the flame-retardancy and tensile strength of paper sheets made from these fibers. The fundamental effect of PEI molecular mass on the build-up of the multilayer film was investigated using model cellulose surfaces and a quartz crystal microbalance technique. The adsorption of a low (LMw) and a high molecular weight (HMw) PEI onto cellulose fibers and carboxymethylated (CM) cellulose fibers was investigated using polyelectrolyte titration. The fibers were consecutively treated with PEI and SHMP to deposit 3.5 bilayers (BL) on the fiber surfaces, and the treated fibers were then used to prepare sheets. In addition, a wet-strength paper sheet was prepared and treated with the same LbL coatings. Thermal gravimetric analysis of LbL-treated fibers showed that the onset temperature for cellulose degradation was lowered and that the amount of residue at 800 °C increased. A horizontal flame test and a vertical flame test were used to evaluate the combustion behavior of the paper sheets. Papers prepared from both cellulose fibers and CM-cellulose fibers treated with HMw-PEI/SHMP LbL-combination self-extinguished in a horizontal configuration despite the rather low amounts of adsorbed polymer which form very thin films (wet thickness of ca. 17 nm). The tensile properties of handsheets showed that 3.5 BL of HMw-PEI and SHMP increased the stress at break by 100% compared to sheets prepared from untreated cellulose fibers

All-natural and highly flame-resistant freeze-cast foams based on phosphorylated cellulose nanofibrils

Pure cellulosic foams suffer from low thermal stability and high flammability, limiting their fields of application

The use of model cellulose gel beads to clarify flame-retardant characteristics of layer-by-layer nanocoatings.

Layer-by-Layer (LbL) assembled nanocoatings are exploited to impart flame-retardant properties to cellulosic substrates. A model cellulose material can make it possible to investigate an optimal bilayer (BL) range for the deposition of coating while elucidating the main flame-retardant action thus allowing for an efficient design of optimized LbL formulations. Model cellulose gel beads were prepared by dissolving cellulose-rich fibers followed by precipitation. The beads were LbL-treated with chitosan (CH) and sodium hexametaphosphate (SHMP). The char forming properties were studied using thermal gravimetric analysis. The coating increased the char yield in nitrogen to up to 29 % and showed a distinct pattern of micro intumescent behavior upon heating. An optimal range of 10-20 BL is observed. The well-defined model cellulose gel beads hence introduce a new scientific route both to clarify the fundamental effects of different film components and to optimize the composition of the films

Вплив попиту на процес ціноутворення

The creep behavior of nanocellulose films and aerogels are studied in a dynamic moisture environment, which is crucial to their performance in packaging applications. For these materials, the creep rate under cyclic humidity conditions exceeds any constant humidity creep rate within the cycling range, a phenomenon known as mechanosorptive creep. By varying the sample thickness and relative humidity ramp rate, it is shown that mechanosorptive creep is not significantly affected by the through-thickness moisture gradient. It is also shown that cellulose nanofibril aerogels with high porosity display the same accelerated creep as films. Microstructures larger than the fibril diameter thus appear to be of secondary importance to mechanosorptive creep in nanocellulose materials, suggesting that the governing mechanism is found between molecular scales and the length-scales of the fibril diameter.funding agencies|BiMaC Innovation|

Hard and transparent films formed by nanocellulose-TiO2 nanoparticle hybrids

T he formation of hybrids of nanofibrillated cellulose and titania nanoparticles in aqueous media has been studied. Their transparency and mechanical behavior have been assessed by spectrophotometry and nanoindentation. The results show that limiting the titania nanoparticle concentration below 16 vol% yields homogeneous hybrids with a very high Young's modulus and hardness, of up to 44 GPa and 3.4 GPa, respectively, and an optical transmittance above 80%. Electron microscopy shows that higher nanoparticle contents result in agglomeration and an inhomogeneous hybrid nanostructure with a concomitant reduction of hardness and optical transmittance. Infrared spectroscopy suggests that the nanostructure of the hybrids is controlled by electrostatic adsorption of the titania nanoparticles on the negatively charged nanocellulose surfaces

Rapidly Prepared Nanocellulose Hybrids as Gas Barrier, Flame Retardant, and Energy Storage Materials

Cellulose nanofibril (CNF) hybrid materials show great promise as sustainable alternatives to oil-based plastics owing to their abundance and renewability. Nonetheless, despite the enormous success achieved in preparing CNF hybrids at the laboratory scale, feasible implementation of these materials remains a major challenge due to the time-consuming and energy-intensive extraction and processing of CNFs. Here, we describe a scalable materials processing platform for rapid preparation (<10 min) of homogeneously distributed functional CNF−gibbsite and CNF−graphite hybrids through a pH-responsive self-assembly mechanism, followed by their application in gas barrier, flame retardancy, and energy storage materials. Incorporation of 5 wt % gibbsite results in strong, transparent, and oxygen barrier CNF−gibbsite hybrid films in 9 min. Increasing the gibbsite content to 20 wt % affords them self-extinguishing properties, while further lowering their dewatering time to 5 min. The strategy described herein also allows for the preparation of freestanding CNF−graphite hybrids (90 wt % graphite) that match the energy storage performance (330 mA h/g at low cycling rates) and processing speed (3 min dewatering) of commercial graphite anodes. Furthermore, these ecofriendly electrodes can be fully recycled, reformed, and reused while maintaining their initial performance. Overall, this versatile concept combines a green outlook with high processing speed and material performance, paving the way toward scalable processing of advanced ecofriendly hybrid material

Shaping 90 wt% NanoMOFs into Robust Multifunctional Aerogels Using Tailored Bio-Based Nanofibrils

Metal-organic frameworks (MOFs) are hybrid porous crystalline networks with tunable chemical and structural properties. However, their excellent potential is limited in practical applications by their hard-to-shape powder form, making it challenging to assemble MOFs into macroscopic composites with mechanical integrity. While a binder matrix enables hybrid materials, such materials have a limited MOF content and thus limited functionality. To overcome this challenge, nanoMOFs are combined with tailored same-charge high-aspect-ratio cellulose nanofibrils (CNFs) to manufacture robust, wet-stable, and multi-functional MOF-based aerogels with 90 wt% nanoMOF loading. The porous aerogel architectures show excellent potential for practical applications such as efficient water purification, CO2 and CH4 gas adsorption and separation, and fire-safe insulation. Moreover, a one-step carbonization process enables these aerogels as effective structural energy-storage electrodes. This work exhibits the unique ability of high-aspect-ratio CNFs to bind large amounts of nanoMOFs in structured materials with outstanding mechanical integrity-a quality that is preserved even after carbonization. The demonstrated process is simple and fully discloses the intrinsic potential of the nanoMOFs, resulting in synergetic properties not found in the components alone, thus paving the way for MOFs in macroscopic multifunctional composites

Nanocellulose and PEDOT:PSS composites and their applications

The need for achieving sustainable technologies has encouraged research on renewable and biodegradable materials for novel products that are clean, green, and environmentally friendly. Nanocellulose (NC) has many attractive properties such as high mechanical strength and flexibility, large specific surface area, in addition to possessing good wet stability and resistance to tough chemical environments. NC has also been shown to easily integrate with other materials to form composites. By combining it with conductive and electroactive materials, many of the advantageous properties of NC can be transferred to the resulting composites. Conductive polymers, in particular poly(3,4-ethylenedioxythiophene:poly(styrene sulfonate) (PEDOT:PSS), have been successfully combined with cellulose derivatives where suspensions of NC particles and colloids of PEDOT:PSS are made to interact at a molecular level. Alternatively, different polymerization techniques have been used to coat the cellulose fibrils. When processed in liquid form, the resulting mixture can be used as a conductive ink. This review outlines the preparation of NC/PEDOT:PSS composites and their fabrication in the form of electronic nanopapers, filaments, and conductive aerogels. We also discuss the molecular interaction between NC and PEDOT:PSS and the factors that affect the bonding properties. Finally, we address their potential applications in energy storage and harvesting, sensors, actuators, and bioelectronics