PolyurethanePolyurethane (ˌpɒliˈjʊərəˌθeɪn,_-jʊəˈrɛθeɪn; often abbreviated PUR and PU) refers to a class of polymers composed of organic units joined by carbamate (urethane) links. In contrast to other common polymers such as polyethylene and polystyrene, polyurethane is produced from a wide range of starting materials. This chemical variety produces polyurethanes with different chemical structures leading to many different applications. These include rigid and flexible foams, and coatings, adhesives, electrical potting compounds, and fibers such as spandex and polyurethane laminate (PUL).
FoamFoams are materials formed by trapping pockets of gas in a liquid or solid. A bath sponge and the head on a glass of beer are examples of foams. In most foams, the volume of gas is large, with thin films of liquid or solid separating the regions of gas. Soap foams are also known as suds. Solid foams can be closed-cell or open-cell. In closed-cell foam, the gas forms discrete pockets, each completely surrounded by the solid material. In open-cell foam, gas pockets connect to each other.
Dimensionless physical constantIn physics, a dimensionless physical constant is a physical constant that is dimensionless, i.e. a pure number having no units attached and having a numerical value that is independent of whatever system of units may be used. In aerodynamics for example, if one considers one particular airfoil, the Reynolds number value of the laminar–turbulent transition is one relevant dimensionless physical constant of the problem. However, it is strictly related to the particular problem: for example, it is related to the airfoil being considered and also to the type of fluid in which it moves.
SawdustSawdust (or wood dust) is a by-product or waste product of woodworking operations such as sawing, sanding, milling, planing, and routing. It is composed of small chippings of wood. These operations can be performed by woodworking machinery, portable power tools or by use of hand tools. Wood dust is also the byproduct of certain animals, birds and insects which live in wood, such as the woodpecker and carpenter ant. In some manufacturing industries it can be a significant fire hazard and source of occupational dust exposure.
Combustibility and flammabilityA flammable material is something that can burn (i.e., sustain a flame) in air under certain conditions. A material is flammable if it ignites easily at ambient temperatures. In other words, a combustible material ignites with some effort and a flammable material catches fire immediately on exposure to flame. The degree of flammability in air depends largely upon the volatility of the material - this is related to its composition-specific vapour pressure, which is temperature dependent.
DecaffeinationDecaffeination is the removal ("de-") of caffeine from coffee beans, cocoa, tea leaves, and other caffeine-containing materials. Decaffeinated products are commonly termed by the abbreviation decaf. Decaffeinated drinks contain typically 1–2% of the original caffeine content, and sometimes as much as 20%. Friedlieb Ferdinand Runge performed the first isolation of caffeine from coffee beans in 1820, after the German poet Goethe heard about his work on belladonna extract, and requested he perform an analysis on coffee beans.
