Flexural Modulus of Symmetric and Asymmetric Structural Foams

In this work, the preparation and characterization of symmetric and asymmetric structural foams is presented. Using low-density polyethylene and modified azodicarbonamide, a compression molding technique is presented to produce structural foams while controlling the skin thickness on both sides. The resulting foams were characterized in terms of foam density, skin thickness, and flexural modulus. It was found that foams having equal skin thickness on each side have the same apparent flexural modulus irrespective of the side the load is applied and the results are well predicted by the modified I-beam model of Hobbs. On the other hand, foams having unequal skin thickness have a higher apparent flexural modulus when the load is applied on the thicker side. This asymmetry in flexural modulus can be well described by a simple correlation using the skin thickness asymmetry ratio and the core void fraction.