ABSTRACT:A new method using high-intensity ultrasonic waves, instead of peroxide-aided reactive extrusion, was applied to modify a linear polypropylene into a branched structure. The ultrasonic waves induced chain scission and created reactive macromolecules of polypropylene successfully in the melt state without any peroxide. To enhance and control the recombination reaction during sonication, a multifunctional agent and an antioxidant were used. The rheological property measurements clearly confirmed that the modified polypropylene had a nonlinear branched structure. It showed shear-thinning behaviors in its viscosities at low frequencies, high elastic behaviors in Cole-Cole plots, and a high rheological polydispersity index in comparison with a linear polypropylene. The degradation or recombination of polypropylene was adequately controlled by an antioxidant, which stabilized the structure during sonication. Also, the use of an antioxidant was quite effective in improving the extrusion processability by delaying the instability of the extrudate to a higher shear rate.

Compression and stirring tests were performed to investigate the rheological behaviour of wrought aluminium alloys with varying processing parameters, such as liquid fraction, strain rate, shear rate and materials. The present paper shows the results of an experimental investigation using Al2024, Al6061 and Al7075. Specimens of each aluminium alloy were characterised by their rheological behaviour during partial melting and holding in the semisolid state. The compression and stirring tests allow the apparent viscosity of the alloys to be determined as a function of the liquid fraction and shear rate. Moreover, the change of grain size and shape was examined by considering shear rate, stirring time and liquid fraction during stirring. These experimental results could be used in flow and solidification analyses and could be useful for manufacturing good rheological products by observing the microstructures according to changes in solid fraction and compression rates.