Foamed Plastics

Foamed plastics, also known as cellular plastics or plastic foams, have been important since primitive man began to use wood, a cellular form of the polymer cellulose. Cellulose is the most abundant of all naturally occurring organic compounds, comprising approximately one-third of all vegetable matter in the world (Ott et al., 1954). Its name is derived from the Latin word cellula, meaning very small cell or room, and most of the polymer does indeed exist in cellular form as in wood, straws, seed husks, etc.

A cellular plastic is defined as a plastic the apparent density of which is decreased substantially by the presence of numerous cells disposed throughout its mass. The gas phase in a cellular polymer is usually distributed in voids or pockets called cells. If these cells are interconnected, the material is termed open-celled. If the cells are discrete and the gas phase of each is independent of that of the other cells , the material is termed closed-cell.

Foaming processes (Ronald and David, 1986) are characterized by techniques that cause tiny bubbles to form within the plastic material such that when the plastic solidifies the bubbles, or at least the holes created by the bubbles, remain, the solidified bubble-containing material thought of as a cellular structure The products made by these processes are referred to as forams or cellular plastics.

Plastic foams can also be classified on the basis of wall stiffness, if the walls are stiff, the foam is called a rigid foam. If the walls collapse when presssed, the foam is called a flexible foam. Bothe open and closed cell foams can either flexible walls or rigid walls,

Plastic foams have some physical characteristics that are valuable for several important applications. The cellular structure means that much of the space in the plastic foam is filled with air or some other gas. The low thermal conductivity of gases means that these foams are very good thermal insulators. Some aplication that utilize this insulating property are hot and cold cups, building insulation slabs, and pipe insulation.