An overview of the current state of art of the ultrasonic treatment technology applied to polymer melts is presented. The research and technological advancements of the ultrasonic treatment as applied to development of polymeric materials are discussed. An analysis of the technological progress shows that the mechanism of the effects of ultrasound on polymer melts is not fully understood at present. Such lack in fully understanding the mechanism could limit the use of this versatile technology in future applications. Based on the critical analysis of the research progress to date, some key issues for a deeper understanding of the chemical and physical effects of ultrasound on polymer melts are identified. © 2012 Wiley Periodicals, Inc. Adv Polym Techn 32: E582–E602, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/adv.21303

A novel, green route for pre-exfoliation of graphite based on a biodegradable polymer and high-power ultrasound is presented. Candelilla wax (CW), derived from the leaves of the candelilla plant, has been used for the first time as a natural non aqueous medium to induce the pre-exfoliation of expanded graphite (EG) under ultrasonic irradiation in an economical way. The proposed method uses also D-limonene as a natural organic solvent for reducing viscosity and increasing the affinity between the polar groups of EG and candelilla wax, thus improving the intercalation/exfoliation of EG. The quality of dispersion of the nanofiller in the natural wax matrix has been evaluated using multiple techniques. The addition of EG to wax and use of ultrasonic treatment leads to a reduced crystallinity, probably due to restrictions of the molecular movements, improved thermal stability of wax, and to an increased shear thinning exponent, which are all indicative of a high degree of EG dispersion. The ultrasonic dynamic mechanical results suggest a reduction in the cluster size and a better filler dispersion in the wax matrix promoted by polar or chemical reactions between the CW fractions and the graphite stacks, which was observed by XPS analysis. The results were compared to those obtained with paraffin, a synthetic wax, and confirmed the dispersion improvement obtained by using natural wax as a pre-exfoliating medium.

The need for new measurement techniques able to assess the nanofiller dispersion is still receiving great consideration when nanocomposites are developed. This occurs since different routes to disperse nanostructures generate molecular changes in polymer matrices that promote complex polymer-polymer and polymer-nanofiller interactions, which make difficult a suitable estimation of the dispersion. In this paper, ultrasonic waves at different frequencies and power were used for preparing nanocomposite samples and for evaluating the nanofiller dispersion. First, a patented method was used to disperse multiwall carbon nanotubes (MWCNTs) in polyamide 12 through extrusion assisted by low-frequency and high power ultrasound (with frequency ranging between 20 and 50 kHz). This “green” processing method was able to induce different states of dispersion of the nanofillers, as well as chemical modifications to polymer chains promoting branching reactions. Then, ultrasonic dynamic mechanical analysis (UDMA with ultrasound frequency in the megahertz range) was used to estimate the dispersion of the different nanocomposite samples. Compared to rheological measurement methods, UDMA provided a better estimation of the quality of dispersion, being sensitive both to the complex molecular architectures in polymer matrices and to the scattering due to MWCNT agglomerates.