Acoustics and Forming of Novel Polyolefin Blend Foams

Novel acoustical materials have been developed for sound absorption and insulation. The materials are macrocellular thermoplastic foams made from blends of polyethylene and polypropylene. The closed cell foams exhibit good acoustic performance over a broad frequency range and are especially effective at low frequencies. The foams are able to withstand high service temperature environments in industrial applications. Other advantages, relative to conventional acoustic media, include resilience, structural integrity, ease of fabrication, moisture resistance and recyclability. Techniques to improve the acoustical performance by profiling the foam with Helmholtz resonators and quarter wave attenuators are discussed. Forming is the shaping of thermoplastic foams by the application of heat and pressure. This process is used to make acoustic parts with the desired shape and size for space constrained applications such as appliance and automotive. This process can also be used to modify the skin quality and surface aesthetics of the foam. Studies were conducted in laboratory scale equipment to determine the process conditions for forming polyolefin foam and to evaluate the effect on cell structure, foam properties and acoustics. Techniques to preserve the acoustical performance of the foam during the forming process are reviewed.