Thermally insulating structural products

Wood chips, saw dust [4] -50 Thermally insulating structural products... 

Fireclay bricks are used principally in furnace construction to confine hot atmospheres and to thermally insulate structural members from excessive temperatures. For fireclay brick, strength is not ordinarily an important consideration because support of structural loads is usually not required. Some control is normally maintained over the dimensional accuracy and stability of the finished product. 

There has been a tremendous interest in polymers since World War 11. In the US, consumption was 18 million metric tons in 1974, 25.7 million metric tons in 1984, and 41.3 million metric tons in 1994 [1]. Polymer production has increased from essentially zero at the end the World War II to about 101 million metric tons worldwide in 1993 [2] and 241 million metric tons in 2006 [3]. The reason for this increase is quite simple. Synthetic polymers are numerous in structure and are very diverse in their structure-property relationships. Polymers are used extensively in electrical applications, including insulators, capacitors, and conductors. They are also used in many optical applications, the biochemical industry, structural applications, packaging, and they are used extensively as thermal insulation [4]. 

Thermal degradation of foams is not different from that of the solid polymer, except in that the foam structure imparts superior thermal insulation properties, so that the decomposition of the foam will be slower than that of the solid polymer. Almost every plastic can be produced with a foam structure, but only a few are commercially significant. Of these flexible and rigid polyurethane (PU) foams, those which have urethane links in the polymer chain are the most important. The thermal decomposition products of PU will depend on its composition that can be chemically complex due to the wide range of starting materials and combinations, which can be used to produce them and their required properties. Basically, these involve the reaction between isocyanates, such as toluene 2,4- and 2,6-diisocyanate (TDI) or diphenylmethane 4,3-diisocyanate (MDI), and polyols. If the requirement is for greater heat stability and reduced brittleness, then MDI is favored over TDI. 

In Sections 24.3 and 24.5 the flammability and fire resistance of individual fiber/fabric type are discussed. However, as also discussed before, the fire resistance of a fabric not only depends upon the nature of components and the FR treatments applied, but also on fabric area density, construction, air permeability, and moisture content. Nonwovens, for example, will have superior properties to woven or knitted structure, even if all other variables are kept the same.93 The air entrapped within the interstices of any fabric structure and between layers of fabrics within a garment assembly provides the real thermal insulation. For effective thermal and fire resistance in a fabric structure, these insulating air domains need to be maintained.22 In general, for protective clothing and fire-block materials, for best performance multilayered fabric structures are employed. The assembly structures can be engineered to maximize their performance. It is beyond the scope of this chapter to go into details of these composite structures hence the reader is referred to the literature on specified applications and products available. 

The most Important distinction is between closed- and open-cell foams. In closed-cell (unicellular) foams, each gas bubble is separated from the others by thin walls of polymer these foams are optimal for flotation applications, structural rigidity, and thermal insulation. In open-cell foams, the cells are all interconnecting, and fluids and especially air can flow freely through the foam structure these are optimal for sponge products and for soft flexible materials. In the extreme case, when the last few remaining cell walls (windows) have been chemically dissolved out of an open-cell foam, it is sometimes called "reticulated."... 

Thermosets also benefit from the foam structure, as evidenced by improved thermal insulation, sound dampening and mechanical stress absorption responses to temperature changes or impact. Hollow spheres with an already set volume are normally used, that is, pre-expanded microspheres. The reason is that the curing reactions often interfere with any expansion before a sufficient volume increase has been obtained. Hollow organic spheres are found in products such as sealants, adhesives, putties, pipes, cultured marble, body fillers, model-making materials, and pastes [2, 3, 19]. Common suitable matrix materials are epoxies, PUR, and polyesters. 

Silica aerogels are being extensively promoted for use in polycarbonate and glass/polyester structural panels, typically as an aid to thermal insulation, although aerogels are also recommended for acoustic insulation. Cabot s product is called Nanogel because of the small size of the pores in the silica, the particles of which are less than 10% solid. 

This series of products possess low density, high specific surface area, high porosity ratio, light blue translucent particles or monoliths. They have low thermal conduction constant, good insulation property, strong adsorptive ability, are environment friendly, nontoxic, fireproof and noncorrosive, with no toxicity to human, and can be widely applied as functional structural interlayer, filling layer and composite layer for thermal insulation and preservation, air purification and water treatment (Figures 40.11 and 40.12). 

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