Foamed plastic, mechanical

Density. Density is the most important variable in determining mechanical properties of a foamed plastic of given composition. Its effect has been recognized since foamed plastics were first made and has been extensively studied. 

Mechanically foamed plastic Cellular plastic whose structure is fabricated by physically incorporated gases. 

Until 1920, the only flexible foam available was the natural sponge, but chemically foamed rubber and mechanically foamed rubber latex were introduced before World War II. These foams may consist of discrete unit cells (unicellular, closed cell), or they may be composed of interconnecting cells (multicellular, open cells) depending on the viscosity of the system at the time the blowing agent is introduced. Over 1.5 million tons of foamed plastic is produced annually in the United States. 

Mechanical Properties of Commercial Foamed Plastics. The properties of commercial rigid fuamed plastics are presented in Table 2. The properties of commercial flexible foamed plastics are presented in Table 3. 

On the other hand, syntactic materials may also be thought of as reinforced or filled plastics, with the gas-containing particles being the reinforcing component. This classification is also justifiable in view of the manufacturing technology. The matrix is not foamed chemically, but is filled mechanically with the hollow spheres. Syntactic foamed plastics are thus called physical foams 6,7). 

In the physical methods the cell walls are destroyed by physical forces, usually by mechanical load. According to one of the most widespread and cheapest methods , the walls are broken through blast-wave impact. To this effect, the blowing gas is removed from the foamed plastic and the material is saturated with a gaseous explosive (e.g. a stoichiometric O /Hj mixture, an air/Hj mixture, acetylene, or atomic oxygen) in a special chamber where blast occurs under a controlled pressure (up to 2 atm). Other physical methods suitable for preparing reticulated foams use a thermal shock or repeated compression cycles. 

Romanenkov, I. G. Physico-Mechanical Prop rties of Foamed Plastics. Moscow Standartgiz Press 1970, pp. 32 (Russ.)... 

The formation of usually coarsely disperse systems during gaseous phase evolution is of importance in the industrial production of various solid foams with valuable mechanical, thermal insulating and sound insulating properties. Examples of such materials include various types of foam concretes (production of these usually involves the evolution of C02 gas in the reaction between CaC03 and HC1), foam plastics, and microporous rubber. In nature the degassing of magma leads to the formation of pumice stones and tuffs. 

Obtained forms of foamed plastics are blocks, sheets, slabs, boards, molded products, and extruded shapes. These plastics can also be sprayed onto substrates to form coatings, foamed in place between walls (i.e., poured into the empty space in liquid form and allowed to foam), or used as a core in mechanical structures. It has also become possible to process foamed plastics by conventional processing machines like extruders and injection-molding machines. 

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