High Density Foamed Polymers in Extrusion

Polymer expansion technology has given rise to a whole range of products known as polymer foams.

Depending on their relative density (ratio between the density of the foam and that of the polymer used), a distinction is made between :

• BD "low density" foams with a relative density of less than 0.20 ;

• HD "high density" foams, with a relative density greater than 0.70 ;

• and, between these two limits, "medium density" (MD) foams.

BD and MD foams have been on the market for several decades. But BD foams are the most widely used: they're inexpensive and easy to handle, with the added bonus of being ultralight and shockproof, while retaining good rigidity.

HD foams are more recent. BD and MD foams are referred to as lightened polymers, as opposed to expanded polymers.

The mid-2000s saw the rapid development of lightweight polymers. Injection-molded parts for the automotive industry, thermoformed packaging: all these industrial applications are on the increase, as lightweighting is a source of weight savings while enabling these parts to retain sufficient mechanical qualities.

This article is dedicated to expanded sheet for thermoforming in the packaging industry, an application for which polystyrene is the reference polymer. For this reason, general principles and mechanisms are discussed for this polymer, but these principles are not restricted to polystyrene and also apply to most other plastics used in the industry to manufacture foams.

Low-fat products are presented by describing the similarities and differences with foams. This comparative analysis is presented in each paragraph of this article.