A new ultrasonic micro-molding system was used to process polylactide (PLA) and fabricate reduced dimension specimens. Plasticization and molding of PLA were achieved by applying ultrasonic waves after feeding the polymer into a plasticizing chamber. Chemical and physical characteristics of processed PLA varied depending on the processing window (i.e. changes in ultrasonic wave amplitude between 14.2 and 48.1 μm and molding pressure between 0.5 in 6 bars). In terms of chemical effects, the application of ultrasound can lead to lower molecular weights (e.g. decreases of more than 45% in the weight average molecular weight), revealing partial degradation of the material. Also, the processed materials exhibited slightly higher thermal degradability than pure PLA because ultrasonic vibrations break molecular linkages and worsen the polymer structure. Finally, the processing conditions for the preparation of PLA specimens could be optimized without causing degradation and preserving structural characteristics and mechanical properties. Specifically, the use of an amplitude of 48.1 μm and a pressure of 3 bars gave samples with the same molecular weight as the raw material (i.e. 117,500 g/mol as opposed to 117,300 g/mol for Mw).

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Ultrasonic processing is known to be an efficient means of aluminium melt degassing with additional benefits of being economical and environment friendly. This paper describes the performance of ultrasonic degassing in preparing melt for low pressure die casting. Efficiency of ultrasonic degassing is compared with conventional Ar rotary degassing, by direct measurements of hydrogen concentration in the melt with a Foseco Alspek-H probe and by reduced-pressure test in different stages of the casting process. Significant reduction in dross formation along with the similar efficiency of hydrogen degassing was shown for ultrasonic degassing as compared with conventional Ar rotary degassing. The mechanical properties, microstructure and porosity level of components produced by low pressure die casting after both degassing techniques are determined. The results show that the components produced after ultrasonic degassing treatment have similar hardness, tensile properties, porosity level and microstructure as the components degassed with conventional Ar rotary degassing.