Development of polymeric foam materials with improved mechanical and acoustic properties

This thesis addresses the processing, morphology, mechanical properties, and acoustic properties of new polymeric foam materials. A batch foaming process, a rotational mold foaming process and a constrained mold foaming process were designed and applied in the producing of polymeric foams. Microcellular closed cell polymethyl-methacrylate (PMMA) foams were produced using the batch foaming process. The foam morphologies and mechanical properties such as elastic modulus, tensile strength and elongation at break were investigated by varying the foaming parameters. The PMMA microcellular foam showed superior mechanical properties in tensile strength and elongation at break over conventional foams. Nanoclay was used as reinforcement filler and a nucleation agent for PMMA in the batch foaming process. The nanoclay affected the foaming behavior and enhanced the mechanical properties of the microcellular PMMA foams. The PMMA nanocomposite foam with 0.5 wt % nanoclay exhibited optimized mechanical properties. Fine celled Polypropylene (PP) and low density Polyethylene (LDPE) foams were also produced using the rotational mold foaming. The processing parameters such as the particle sizes and processing time were important parameters in this process. The obtained PP foam exhibited a greatly improved energy absorption capacity. Opened cell PMMA foams were produced using a particulate leaching/gas foaming method for acoustic absorption applications. The foam morphology i.e. porosity and cell sizes were independently controlled by altering the processing settings. Consequently, the acoustic performance of the foams was manipulated. Finite element analysis was then employed to predict the macroscopic properties of polymeric foams correlated to their microstructure. The predicted elastic responses of both opened cell and closed cell foams showed great agreement with experimental results.