Andre Hamel

Application of Ultrasonic Sensors in the Study of Physical Foaming Agents for Foam Extrusion

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.

Influence of Er:YAG and Nd:YAG wavelengths on laser-induced breakdown spectroscopy measurements under air or helium atmosphere

Laser-induced breakdown spectroscopy (LIBS) is widely dependent on the conditions of its implementation in terms of laser characteristics (wavelength, energy, and pulse duration), focusing conditions, and surrounding gas. In this study two wavelengths, 1.06 and 2.94 microm, obtained with Nd:YAG and Er:YAG lasers, respectively, were used for LIBS analysis of aluminum alloy samples in two conditions of surrounding gas. The influence of the laser wavelength on the laser-produced plasma was studied for the same irradiance by use of air or helium as a buffer gas at atmospheric pressure. We used measurements of light emission to determine the temporally resolved space-averaged electron density and plasma temperature in the laser-induced plasma. We also examined the effect of laser wavelength in two different ambient conditions in terms of spectrochemical analysis by LIBS. The results indicate that the effect of the surrounding gas depends on the laser wavelength and the use of an Er:YAG laser could increase linearity by limiting the leveling in the calibration curve for some elements in aluminum alloys. There is also a significant difference between the plasma induced by the two lasers in terms of electron density and plasma temperature.

Effect of Different Nucleating Agents on the Degassing Conditions as Measured by Ultrasonic Sensors

Ultrasonic sensors have proven to provide valuable information on the thermoplastic foaming process in polymers. Measurement of the attenuation of the ultrasonic signal can be easily related to the nucleation process, i.e., the onset of bubble formation in the foam matrix (degassing). The ultrasonic sensors can be installed in-line, on the extrusion line, and thus allow direct access to the prevailing processing conditions. In this work, the degassing conditions (pressure and temperature) of a mixture of polystyrene and a physical blowing agent (PBA), HCFC 142b, are determined for two different nucleating agents as well as in absence of any nucleating agent. The resulting cellular structure of the extruded foams is correlated to the degassing conditions determined by the ultrasounds. The results are discussed in light of other observations on the nucleation process.

Characterization of Isotropic Composites Containing Inclusions of Specified Shapes by use of Ultrasonics In The Long Wavelength Limit

The presence of an additional heterogeneous phase, dispersed in a matrix can bring about important improvements in the properties of the original material and make it appropriate for more specific purposes. Most engineering needs require the optimization of the strength to weight ratio of materials and from this point of view, polymer composites offer excellent characteristics. This factor and others such as versatility, ease of fabrication and cost effectiveness are some of the reasons why composite plastics are rapidly gaining ground over the more usual engineering materials.

On-line analysis of liquid samples by laser induced plasma spectroscopy (LIPS)

A LIPS monitor for real-time analysis of aqueous and other liquids has been developed. This system enables the laser to sample a fresh surface while preventing problems associated with the laser liquid interaction. We outline its successful laboratory and on-line industrial operation.