Any plastic material possessing cellular structure and density lower than the original solid material is known as foamed plastic. Their density ranges from 0.5 to 40 or 60 pounds per cubic feet (Pcf). They are also known as sponged, expanded or cellular plastics.
Special type of plastic foam using hollow spheres made of phenolic resin, clay, glass or other hollow particles. These spheres (micro spheres) are dispersed throughout a matrix of either epoxy or polyester resin which when cured resembles a conventional foam plastic.
Weight of foam in pounds per cubic feet (Pcf) i.e. 6 pound foam have a density of 6 Pcf. Density range for foam is 2-20 Pcf. Density range for syntactic foam is 10-60 Pcf, depending on the type and the percentage of the micro spheres used in the resin.
Closed cell foam (Unicellular):
Foam in which the greatest proportions of the cells are not connected together by open passage ways are known as closed cell foam. Such a material (in a flexible grade) when squeezed under water, absorbs water in the surface cells and a few cells under the surface. They are used for floatation devices and similar items. They are not used satisfactorily for sound absorption.
Open cell foam (interconnecting cells):
Foam in which the greatest proportions of the cells are connected together by open passage ways are known as open cell foam. Such a material (in a flexible grade) when squeezed under water, absorbs water throughout its mass. They are good sound absorbing material.
For flexible foams it is the force required to compress up to 25% of one square inch of the flexible foam.
For rigid foam it is the force in per square inch required to cause permanent crushing. (Compression resistance is also called the compressive strength).
It is exclusively applied to flexible foams and/or solid rubber like material. It is the percentage of permanent compression in a sample after a definite sized specimen has been compressed for a given period of time at a given temperature. Common test procedures employs one inche2 sample compressed to 25% for 22 hours at 700 C, and then measured 20 minutes after removal from the oven and the compression test fixtures.
It refers to the heat insulating properties of the material. It indicates the thermal conductivity of the foam in BTUs per hour, per square feet, per inch of thickness under a thermal difference of 10 C. K Factor range for foam is 0.15 to 0.35 at room temperature. K Factor is directly proportional to the temperature. K Factor is inversely proportional to the insulating quality. R-Factor indicates the resistance of the material to the transmission of heat. K Factor is inverse of R-Factor.
Material that causes any given plastic to foam is known as blowing agent.
Types of blowing agents are:
a) Gas: It is introduced into the molten or liquid plastic material.
b) Chemicals: they are incorporated in the polymer. It decomposes to liberate gas, at a given temperature.
In both the cases if the gas is evenly dispersed, it expands to form the cells in plastic. Different ways to bring about cell formation depend on the gas being used; the CBA; the type of resin; and the particular process being used.