Asymmetric microcellular composites: Morphological properties

Asymmetric microcellular composites were prepared by injection molding to study the effects of temperature gradient inside the mold (0 to 60℃) as well as blowing agent (0 to 1%) and natural fibers (0 to 30%) contents. High-density polyethylene, flax fiber, and azodicarbonamide were used as the matrix, reinforcement, and chemical blowing agent, respectively. From the samples produced, a complete morphological characterization was performed. As expected, cell size, cell density, and skin and core thicknesses were affected by blowing agent and natural fiber contents and mold temperatures. It was found that a better microcellular asymmetric structure was obtained with higher fiber and blowing agent contents and higher average mold temperature. From the data obtained, a simple mathematical model was used to fit the relative density of asymmetric foams to include skin, core, and transition zone thicknesses.