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To cite this version:Heiko Thoemen, Thomas Walther, Andreas Wiegmann. 3D simulation of macroscopic heat and mass transfer properties from the microstructure of wood fibre networks.

Composites of wood in a thermoplastic matrix (wood-plastic composites) are considered a low maintenance solution to using wood in outdoor applications. Knowledge of moisture uptake and transport properties would be useful in estimating moisture-related effects such as fungal attack and loss of mechanical strength. Our objectives were to determine how material parameters and their interactions affect the moisture uptake and transport properties of injection-molded composites of wood-flour and polypropylene and to compare two different methods of measuring moisture uptake and transport. A two-level, full-factorial design was used to investigate the effects and interactions of wood-flour content, wood-flour particle size, coupling agent, and surface removal on moisture uptake and transport of the composites. Sorption and diffusion experiments were performed at 208C and 65 or 85% relative humidity as well as in water, and diffusion coefficients were determined. The wood-flour content had the largest influence of all parameters on moisture uptake and transport properties. Many significant interactions between the variables were also found. The interaction between wood-flour content and surface treatment was often the largest. The diffusion coefficients derived from the diffusion experiments were different from those derived from the sorption experiments, suggesting that different mechanisms occur.

Specific modification of properties such as porosity and pore size of engineered wood‐based source material enables the custom design of porous wood‐derived SiC that is produced by carbothermal reduction between the carbonized wood‐based material and an infiltrated silica sol. In contrast to bulk wood, the anisotropic shrinkage of the source material is less distinctive and can be controlled. Furthermore, the obtained structural properties of the material are isotropic. Material processing and properties of the wood‐derived ceramic material are described in this paper.

Diffusion of CO 2 in polylactide was modelled by assuming the diffusion coefficient to depend on CO 2 concentration, c, according to D[c] ¼ D[0]exp [Ac], where D[0] and A are empirical constants, with the aim of optimizing impregnation of nominally amorphous and semicrystalline polylactide/CO 2 -based precursors for physical foaming. Numerical simulations provided a consistent description of desorption at different temperatures, T, from polylactide impregnated with liquid CO 2 at 10 C and 5 MPa, and D[0, T] could be represented analytically using Arrhenius or Williams-Landel-Ferry-type expressions, allowing interpolation and extrapolation. Sorption was argued on this basis to involve a step-like diffusion front, such that the CO 2 content of a plate of thickness l increased as (D[0]t) 1/2 l À1 F[Ac o ], where c o is the value of c at saturation and F is a function of Ac o only. A major practical concern with polylactide/ CO 2 precursors is that the glass transition temperature, T g , decreases strongly with c, so that amorphous polylactide saturated with CO 2 at 10 C and 5 MPa degasses spontaneously at room temperature and pressure. However, it was inferred from the models and confirmed experimentally that partial impregnation in liquid CO 2 for relatively short times could provide a relatively rapid means of preparing precursors with a roughly uniform CO 2 content of around 0.1 g/g that were stable with respect to rapid CO 2 loss on heating to room temperature. The resulting precursors gave satisfactory foam morphologies and densities on foaming at 100 C. Moreover, it was also possible to adapt the impregnation conditions so as to obtain partially foamed structures from semicrystalline polylactide under these conditions, in spite of its

A flame retardant composition (FRC) composed of a surface-treated calcium carbonate-based mineral, having high porosity and loaded with deliquescent calcium chloride, was assessed for its potential as a flame retardant. Two FRCs with 16% and 26% calcium chloride (dry solid) stored in the pore structure, respectively, were studied with respect to their ability to absorb and release free water and their efficacy in melamine-urea-formaldehyde (MUF)bonded wood composites was investigated. Water absorption capacity was determined by performing absorption tests at a temperature of 20°C and relative humidity (RH) of 65% and 95% and the water release behaviour was studied by performing thermogravimetric analysis. The FRCs have the capacity to hold substantial amounts of water (up to 60 wt. %), however still behave as a free-flowing powder. The influence of addition of 10 and 20 wt.% FRC in wood composites on reaction to fire and strength properties was determined by measuring the selfextinguishing time after flame exposure and internal bond strength, respectively. These effects were evaluated by comparing to ground calcium carbonate (GCC) and commercially available nitrogen containing phosphorus based fire retardant. Although the FRCs had a negative impact on internal bond strength, the results confirmed their flame retardant potential and showed that 10-15 % by weight of the flame retardant would be a good compromise, in terms of the trade-off between flame retardancy and mechanical properties. The synergistic effects of multiple flame retardancy reaction mechanisms due to the presence of inorganic minerals and a hygroscopic agent, CaCl2, are also discussed. The unique properties of the FRC, which allow to exploit the fire retardant potential of CaCl2 while at the same time eliminating the risk associated with the emission of hydrogen chloride gas during combustion, is confirmed by the results of FTIR spectroscopic analyses of the flue gas.