The optical properties of the stable icosahedral quasicrystal Al63.5Cu24.5Fe12 have been measured from 40 to 25 000 cm -1 at 300 K and at 80 K. Unlike metallic glasses with a Drude spectrum with strong elastic scattering by disorder, or semiconductors with a conductivity gap, the optical conductivity of this quasicrystal is distinctive: Starting from the very low dc value it increases linearly with frequency well into the near infrared. A prominent peak in the conductivity is observed at 245 cm -1 ; its position and strength suggest that it arises from a direct excitation of phonons.

The extrusion foaming process involves several critical steps, in which the physical foaming agent plays a significant role: plasticization, solubility, nucleation and bubble growth. Although these aspects can be studied by different techniques, a novel method based on ultrasonic sensors has proven to provide valuable information with respect to the thermoplastic foaming process. This technique can be either used off-line as a characterization tool to improve our understanding of the foaming agent characteristics, or it can be installed in-line, on the extrusion line, as a control device. Review of the different applications of this technique will be covered in this paper, with numerous examples given to the mixture of PS with CO2. The degree of plasticization of the polymer as a function of the blowing agent concentration will be addressed first, followed by the detection of the conditions prone to induce nucleation, in terms of pressure, temperature, type of nucleating agents and flow conditions. The evaluation of the kinetics of bubble growth will also be explored.

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We present results on foaming of a thermoplastic elastomer (TPE) using water as the physical blowing agent. The TPE is a blend of polypropylene and fully crosslinked EPDM rubber made by a dynamic vulcanization process. The influence of the blowing agent content, and the processing conditions on foam density, cell nucleation, and foam structure are discussed. A brief discussion about the similarities and the differences between foaming in homopolymers and in TPEs is also included.

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