6 research outputs found
Fire-retardant and transparent wood biocomposite based on commercial thermoset
Transparent wood (TW) biocomposites combine high optical transmittance and good mechanical properties and
can contribute to sustainable development. The safety against fire is important for building applications. Here, a
“green” bleached wood reinforcement is impregnated by water soluble and flame-retardant melamine formaldehyde (MF) in a scalable process, for a wood content of 25 vol%. FE-SEM is used for characterization of optical
defects and EDX to examine MF distribution at nanoscale cell wall pore space. Curing (FTIR-ATR), mechanical
properties, optical transmittance (74% at 1.2 mm thickness) and flame-retardant properties are also characterized (self-extinguishing behavior and cone calorimetry), and scattering mechanisms are discussed. The fire
growth rate of transparent wood was less than half the values for neat wood. Transparent wood/MF biocomposites show interesting wood-MF synergies and are of practical interest in building applications. Critical
aspects of processing are analyzed for minimization of optical defect
Coloration and Fire Retardancy of Transparent Wood Composites by Metal Ions
Transparent wood composites (TWs) offer the possibility of unique coloration effects. A colored transparent wood composite (C-TW) with enhanced fire retardancy was impregnated by metal ion solutions, followed by methyl methacrylate (MMA) impregnation and polymerization. Bleached birch wood with a preserved hierarchical structure acted as a host for metal ions. Cobalt, nickel, copper, and iron metal salts were used. The location and distribution of metal ions in C-TW as well as the mechanical performance, optical properties, and fire retardancy were investigated. The C-TW coloration is tunable by controlling the metal ion species and concentration. The metal ions reduced heat release rates and limited the production of smoke during forced combustion tests. The potential for scaled-up production was verified by fabricating samples with a dimension of 180 x 100 x 1 (l x b x h) mm(3)
Reversible dual-stimuli responsive chromic transparent wood bio-composites for smart window applications
Transparent wood (TW)-based composites are of significant interest for smart window applications. In this research, we demonstrate a facile dual-stimuli-responsive chromic TW where optical properties are reversibly controlled in response to changes in temperature and UV-radiation. For this functionality, bleached wood was impregnated with solvent-free thiol and ene monomers containing chromic components, consisting of a mixture of thermo- and photoresponsive chromophores, and was then UV-polymerized. Independent optical properties of individual chromic components were retained in the compositional mixture. This allowed to enhance the absolute optical transmission to 4 times above the phase change temperature. At the same time, the transmission at 550 nm could be reduced 11−77%, on exposure to UV by changing the concentration of chromic components. Chromic components were localized inside the lumen of the wood structure, and durable reversible optical properties were demonstrated by multiple cycling testing. In addition, the chromic TW composites showed reversible energy absorption capabilities for heat storage applications and demonstrated an enhancement of 64% in the tensile modulus as compared to a native thiol−ene polymer. This study elucidates the polymerization process and effect of chromic components distribution and composition on the material’s performance and perspectives toward the development of smart photoresponsive windows with energy storage capabilities.QC 20210201</p
Supramolecular Route for Enhancing Polymer Electrospinnability
Electrospinning
of polymers typically requires high solution concentrations
necessitated by the requirement of sufficient chain overlaps to achieve
the required viscoelastic properties. Here, we report on a novel supramolecular
approach, involving polymer/surfactant complexes, which allows for
a significant reduction in the solution concentration of polymer for
electrospinning. The approach involved supramolecular complexation
of poly(4-vinylpyridine) (P4VP) with a surfactant, dodecylbenzenesulfonic
acid (DBSA), via ionic interactions. The supramolecular complexation
of P4VP with DBSA led to a significant increase in the solution viscosity
even at a DBSA/4VP molar ratio as low as 0.05. Furthermore, the solution
viscosity of the P4VP/DBSA complex increased significantly with the
DBSA/4VP molar ratio. The increase in the viscosity for the P4VP/DBSA
complexes was plausibly due to the formation of physical cross-links
between P4VP chains driven by hydrophobic interactions between the
surfactant tails. The formation of such physical cross-links led to
a significant decrease in the solution concentration needed for the
onset of semidilute entangled regime. Thus, the P4VP/DBSA complexes
could be electrospun at a much lower concentration. The critical solution
concentration to obtain bead-free uniform nanofibers of P4VP/DBSA
complexes in dimethylformamide was reduced to 12% (w/v), which was
not possible for neat P4VP solution even up to approximately 35% (w/v).
Furthermore, small-angle X-ray scattering and polarized optical microscopy
results revealed that the electrospun nanofibers of P4VP/DBSA complexes
self-assembled in lamellar mesomorphic structures similar to that
observed in bulk. However, the electrospun nanofibers exhibited significantly
improved lamellar order, which was plausibly facilitated by the preferred
orientation of P4VP chains along the fiber axis
Charge Regulated Diffusion of Silica Nanoparticles into Wood for Flame Retardant Transparent Wood
The preparation of wood substrates modified by charged inorganic nanoparticles (NPs) diffusing into the internal cell wall structure is investigated for generating functional properties. The flammability problem of wood biocomposites is addressed. NPs applied from colloidal sols carry charge to stabilize them against aggregation. The influence of charge on particle diffusion and adsorption should play a role for their spatial distribution and localization in the wood substrate biocomposite. It is hypothesized that improved dispersion, infiltration, and stability of NPs into the wood structure can be achieved by charge control diffusion, also restricting NP agglomeration and limiting distribution to the wood cell wall. Cationic and anionic silica NPs of ≈30 nm are therefore allowed to diffuse into bleached wood. The influence of charge on distribution in wood is investigated as a function of initial sol concentration. Transparent wood is fabricated by in situ polymerization of a thiolene in the wood pore space. These biocomposites demonstrate excellent flame retardancy with selfextinguishing characteristics. The approach has potential for commercial fabrication of flame retardant transparent composites for glazing and other building applications.QC 20220523</p