Integral Foam Based on Polyolefins

Abstract

Integral foams based on PE, PP, and their copolymers can be manufactured by all processes designed for obtaining IF’s, i.e., by low and high-pressure injection molding, extrusion, and rotamolding ^{1 – 5)}. Compositions are foamed using PBA’s (nitrogen) or CBA’s, the latter frequently being employed as concentrates (see Chapter 2). In the ‘Phillips Petroleum’ process, integral foam items are manufactured on standard injection molding machines by feeding the concentrates and other additives, mixed with pelletized PO, into the plasticator. High counterpressure in the plasticator reduces the plasticization time. Injection is carried out at a low pressure and without additional feeding. The use of the concentrated BA differs mainly in that the composition is injected into a cold mold, both the female and male dies being subjected to deep cooling. The distribution channels and inlets have to be 2 or 3 times larger than those used when molding unfoamed polymers. The thickness of the mold walls should not be less than 2.5 to 3.8 mm The most uniform core structure is achieved by using linear PE with a narrow molecular-mass distribution (MMD) ^2,3).