Thermoplastic polymer foams can be produced using expandable beads like Expancel microbeads. In this work, density graded polyethylene foams were produced by imposing a temperature gradient using compression moulding. This was done by controlling independently the top and bottom plates of the mould at different temperatures. Foaming was done by using different grades of Expancel and blends of them to produce a complex cellular morphology. In this work, a complete morphology in terms of cell size and cell density will be presented in relation with density profile across the foam thickness. The foam behaviour under different types of mechanical loadings will also be discussed.

For any type of polymer foam, it is well known that careful control of the processing temperature has an important effect on final morphology. In this work, density graded polyethylene foams were produced by imposing a temperature gradient while foaming the sample. This was done by controlling independently the top and bottom plates of a compression mold at different temperatures. By doing so, different density profiles across the part's thickness are produced. In this work, the resulting morphologies are presented with their respective flexural moduli.

Density graded polyethylene foams were produced using a chemical blowing agent and compression moulding. To control the local density inside the foams, the top and bottom plates of a compression moulding set-up were placed at different temperatures and moulding times in order to produce symmetric and asymmetric structural foams. Due to different temperature gradients produced inside the samples, complex density profiles were created. From the samples obtained, a complete morphological analysis was performed to extract cell size and cell density across foam thickness in relation with density profiles. Also, to determine the effect of density profile on the mechanical properties, tensile and flexural characterizations were performed. The results obtained are discussed in relation with optimum properties vs. bulk foam density.

In this work, density graded foams were produced using linear medium density polyethylene as the matrix and different grades of Expancel microbeads. Local density inside the foams was controlled by setting independently the top and bottom plates of a compression mould at different temperatures and by controlling moulding time. Due to the temperature gradient, complex density profiles were produced and a complete morphological analysis was performed to extract average cell diameter and cell density across foam thickness. Finally, the tensile and flexural moduli are reported and discussed in relation with foam structure.

This work presents the production and characterization of functionally graded polymer foams produced by compression molding. For the conditions tested (temperature gradient, molding time, type and concentration of Expancel microbeads), it was possible to reach density reduction between 2 and 45% for symmetric and asymmetric polyethylene foams. Tensile properties (modulus and stress at 1% deformation) were then measured to relate with their respective density profiles. From the experimental data obtained, a simple finite element analysis was performed to determine the tensile properties of asymmetric foams. The results show that excellent predictions were obtained with a maximum deviation of 7% for all the conditions tested.