Wood thermal properties

Wood has very useful thermal properties. Dry wood has a low thermal conductivity and a high heat capacity, and is resistant to thermal decomposition at temperatures up to 250°C for short periods of time. 

Table 8-26 Examples of thermal properties of foams compared to wood ...

The thermal properties of C3 materials at high temperatures are most remarkable if protected from oxidation. This issue is discussed below in more detail. If they are not oxidized, the C3 materials exhibit similar stability data as ceramics [22], in particular at temperatures above 1500 K where protective coatings applied behave like a plastic and close developing surface cracks against air attack. C3 materials expose the advantages of their hierarchical structure being present in both filler and binder phase and develop wood-like properties under ambient conditions. A descriptive pa-... 

The replacement of timber products by nonrenewable materials is an unfortunate development, since it has been repeatedly shown that the use of timber does have associated environmental benefits compared with the use of nonrenewables (e.g. Marcea and Lau, 1992 Hillier and Murphy, 2000 Bowyer etal., 2003 Lippke etal., 2004). Timber has a lower embodied energy content (and hence a more favourable carbon emission profile) compared to most other building materials and can provide other benefits, such as improved thermal properties. It and the products made from it (in common with other renewable materials) can be used as a repository for atmospheric carbon dioxide. Wood is derived from a renewable resource, albeit potentially an exhaustible one unless it is managed correctly. Disposal of wood can be readily achieved with little environmental impact (subject to how the wood has been treated prior to disposal). 

It has been reported that thermoplastic properties can be imparted to wood by modification of wood particles with fatty acid chlorides in a dinitrogen tetroxide -dimethylformamide - pyridine mixture (Funakoshi etal., 1979 Shiraishi etal, 1979, 1983). A method has also been developed for the modification of wood sawdust without the addition of organic solvents (Thiebaud and Borredon, 1995), and the thermal properties of such modified wood determined (Thiebaud etal, 1997). 

The thermal properties of composite boards were the subject of a recent report by Place and Maloney (58). Thermal conductivity tests were made on three-layer boards with surfaces of white pine wood flakes and cores of either Douglas-fir or grand fir bark. Density was varied at 34, 42, and 52 pounds per cubic foot. The composite boards containing bark proved to be better insulators than wood particleboard of comparable density. Douglas-fir bark cores had lower thermal conductivity than did grand fir. 

The FDS5 pyrolysis model is used here to qualitatively illustrate the complexity associated with material property estimation. Each condensed-phase species (i.e., virgin wood, char, ash, etc.) must be characterized in terms of its bulk density, thermal properties (thermal conductivity and specific heat capacity, both of which are usually temperature-dependent), emissivity, and in-depth radiation absorption coefficient. Similarly, each condensed-phase reaction must be quantified through specification of its kinetic triplet (preexponential factor, activation energy, reaction order), heat of reaction, and the reactant/product species. For a simple charring material with temperature-invariant thermal properties that degrades by a single-step first order reaction, this amounts to -11 parameters that must be specified (two kinetic parameters, one heat of reaction, two thermal conductivities, two specific heat capacities, two emissivities, and two in-depth radiation absorption coefficients). 

Related problems must be considered in individual products. Bromine, chlorine, and antimony add to the smoke of a fire, while phosphorus and water do not, and some metal oxides can actually reduce it. Toxicity of combustion gases is a major concern but the main problem is that oxidation of carbon compounds in an enclosed space—indoors— produces carbon monoxide, no matter whether the carbon compounds are wood or plastics. Other problems include the cost of flame-retardants, difficulties in processing, and loss of mechanical or thermal properties. 

Shiraishi and Goda [16] reported that allylated wood meals were given thermoplastic properties by blending with appropriate synthetic polymers or low molecular weight plasticizers such as dimethylphthalate or resorcinol. Mere allylation did not render wood thermally meltable. Films from the allylated wood-polyethylene and allylated wood-polypropylene (1 2) blends exhibit tensile strengths of 92.2 and 159.0 MPa and elongations of 14.6 and 3.8% respectively, [16]. 

Recently, Hon and San Luis [23] studied the thermal properties of cyanoethylated wood by DSC and dynamic mechanical thermal analyzer (DMTA). Depending upon the N content, the cyanoethylated wood exhibited a softening temperature ranging from 162°C to 177°C and melting temperature ranging from 240°C to 270 C. The DMTA measurements suggest that wood materials are susceptible to degradation upon cyanoethylation. 

It is noteworthy that acetylated wood meals prepared by the TFAA method melted clearly at 320°C under a pressure of 0.29 MPa [4,5]. Other methods of acetylation resulted in products that did not undergo complete flow. However, thermal properties of the acetylated wood were enhanced by mixed esterification with other acyl groups. That is, esterified woods containing either propio-nyl or butyryl groups in addition to acetyl revealed meltable properties [4,5]. A film prepared from the acetylated-butyrylated wood meal has a tensile strength of 41.0 MPa and an elongation of 12.5% [41. 

SOLUTION The R value and the t/-factor of a wood frame wall as well as the rate of heat loss through such a wall in Las Vegas are to be determined. Asiumptl ns 1 Steady operating conditions exist. 2 Heat transfer through the wall is one-dimensional. 3 Thermal properties of the wall and the heat transfer coefficients are constant. 

Other Physical Properties. In addition to its important effect on the strength of wood, moisture also affects wood s other physical properties. Moisture s effect on electrical properties was described in the section on Electrical Resistance Moisture Meters (p. 130). Other properties such as specific gravity and thermal properties are discussed here. 

Thermal Properties. Some of the important thermal properties of wood are aflFected by its moisture content. These include specific heat, thermal conductivity, and thermal diffusivity. 

For flaming combustion, the - AH and the rate of producton of the volatiles are important. The latter value could be determined by thermogravimetry and its derivative under simulated pyrolysis conditions, which indicate the progress and the rate of weight loss. Figure 26 shows the dynamic TG of cottonwood and its components and indicates that lignin contributes mainly to char, whereas cellulose and hemicelluloses form mainly the volatile pyrolysis products that are responsible for the flaming combustion. These data also indicate that wood shows the collective thermal properties of its components. 

V. Hristov and S. Vasileva. Dynamic mechanical and thermal properties of modified poly(propylene) wood fiber composites. Macromol. Mater. Eng., 2003, 288(10), 798-806. 

Polymers are broadly classified as synthetic and natural polymers. Synthetic polymers have become significant since the 1940s and continue to replace glass, wood, constructional materials and metals in many industrial, domestic and environmental applications [2-5]. Synthetic polymers are made from hydrocarbons derived from petroleum. Some of these polymers, such as nylon, polyethylene, polyurethane and so on, are an indispensable part of our daily lives. Due to their stability and durability they offer good mechanical and thermal properties [6], making them suitable for a variety of applications, e.g., in automobiles, cosmetics, medicines, biosensors,... 

The thermal properties of the regenerated wood ester product reveal a single glass transition temperature (Tg) (Fig. 4) which varies with both degree of substitution (DS) (i.e., reaction-time) (Fig. 5) and (to a lesser extent) lignin... 

Bouguerra, A. et al (1998) Effect of microstmcture on the mechanical and thermal properties of hghlweight concrete prepared from clay, cement and wood aggregates. Cement and Concrete Research 28,1179—1190. 

Picciani, P, Medeiros, E., Pan, Z, Wood, D., Orts, W., Mattoso, L., and Soares, B. (2010) Structural, electrical, mechanical, and thermal properties of electrospun poly(lactic acid)/polyaniline blend fibers. Macromol. Mater. Eng., 295, 618—627. 

B.L. Shah, S.E. Selke, M. B. Walters, and P.A. Heiden, Effects of wood flour and chitosan on mechanical, chemical, and thermal properties of polylactide. Polym. Compos 9(6), 655-663 (2008). 

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