Density graded polymer composite foams

This article reviews the main developments associated with density graded polymer composite foams. After a short introduction, a discussion is made on both density graded polymer-based composites and foams separately to better understand the challenges when both structures are combined together to produce composite foams. In all cases, the basic concepts, fabrication methods, main properties and general applications are presented. Opening for future works are also presented to conclude.

Effect of the skin layer on the overall behavior of closed-cell polyethylene foam sheets

This article presents an experimental investigation of the effect of the skin layer on the mechanical behavior of a closed-cell polymeric foam material. The skin layer is a thin layer with increased density due to the manufacturing processes, which results in inhomogeneity. The skin-layer effect is investigated by comparing the stretch-stress characteristics of specimens with and without this skin layer on a particular closed-cell polyethylene foam sheet. The characteristics were recorded via uniaxial tension and compression tests, respectively, in all principal manufacturing directions. Thus, the skin-layer effect can be obtained by analyzing the recorded data points, which are also presented. The skin-layer-free specimens are prepared with a particularly designed assembly in accordance with the ASTM standards.

Asymmetric microcellular composites: Mechanical properties and modulus prediction

In the first part of this study, asymmetric microcellular composites were prepared by injection molding to study their morphological properties as a function of temperature gradient inside the mold (0–60℃), as well as foaming agent (0–1%) and natural fiber (0–30%) contents. High-density polyethylene, flax fiber, and azodicarbonamide were used for the matrix, reinforcement, and chemical blowing agent, respectively. From the samples produced, mechanical properties (tensile, flexion, torsion, impact) are analyzed in this second part. Mechanical properties were found to be strongly influenced by density reduction and natural fiber content. It was also found that fiber addition provides higher reinforcement in flexion than torsion and tension. Also, flexural modulus and impact strength were relatively unaffected by foaming agent content for the range of parameters studied. From the experimental data obtained, a simple mechanical model based on density profile is presented to predict the elastic moduli of asymmetric structural composite foams.