Micro-molding with ultrasonic vibration energy: New method to disperse nanoclays in polymer matrices

Abstract

Ultrasound technology was proved as an efficient processing technique to obtain micro-molded specimens of polylactide (PLA) and polybutylene succinate (PBS), which were selected as examples of biodegradable polyesters widely employed in commodity and specialty applications. Operational parameters such as amplitude, molding force and processing time were successfully optimized to prepare samples with a decrease in the number average molecular weight lower than 6%. Ultrasonic waves also seemed an ideal energy source to provide effective disaggregation of clay silicate layers, and therefore exfoliated nanocomposites. X-ray diffraction patterns of nanocomposites prepared by direct micro-molding of PLA or PBS powder mixtures with natural montmorillonite or different organo-modified clays showed the disappearance of the 001 silicate reflection for specimens having up to 6 wt.% clay content. All electron micrographs revealed relatively homogeneous dispersion and sheet nanostructures oriented in the direction of the melt flow. Incorporation of clay particles during processing had practically no influence on PLA characteristics but enhanced PBS degradation when an organo-modifier was employed. This was in agreement with thermal stability data deduced from thermogravimetric analysis. Cold crystallization experiments directly performed on micro-molded PLA specimens pointed to a complex influence of clay particles reflected by the increase or decrease of the overall non-isothermal crystallization rate when compared to the neat polymer. In all cases, the addition of clay led to a clear decrease in the Avrami exponent.

Effect of sonication on high temperature properties of bituminous binders reinforced with nano-additives

“…Since mixing operations can influence the rheological behaviour of nano-reinforced materials [16,18], two mixing techniques were compared in the whole study. The first one is based on a simple shear mixing protocol previously developed by the authors [12,13].…”

“…A successful bitumen-clay interaction may generate intercalated or exfoliated morphologies. Intercalation occurs when the galleries between the layers are expanded but silicate platelets still retain a well-defined spacing, whereas exfoliation results from complete separation and random dispersion of clay sheets [18,19].…”

Heat generation and distribution in the ultrasonic hot embossing process

“…Several papers have been published on ultrasonic hot embossing and its variants Liu and Dung 2005;Mekaru et al 2007a, b;Khuntontong et al 2008;Yu et al 2009;Lee et al 2010;Altmann et al 2012;Šakalys et al 2015;Planellas et al 2014), but up to now only few investigations have been performed on the physical processes during fabrication. Liu and Dung measured the temperature inside of a polymethylmethacrylate (PMMA) plate, 2 mm in thickness, with thermocouples inserted into drilled holes and discovered that in less than 0.5 s temperatures were rising up to 200 °C (Liu and Dung 2005).…”

“…Although ultrasonic molding had its beginning with the molding of plastic powders (Fairbanks 1974;Paul and Crawford 1981), the influence of additive-powders on the process is rarely considered. Planellas et al found a new method to disperse nanyclays in polymer matrices: They used ultrasonic waves to produce nanocomposites of mixtures of semicrystalline polylactide and polybutylenesuccinate plastic powders and nanoclays (Planellas et al 2014). Since the polymer flow is a strong function of its temperature, the temperature distribution during ultrasonic hot embossing is of large interest.…”

Dispersion of Functionalized Silica Micro- and Nanoparticles into Poly(nonamethylene Azelate) by Ultrasonic Micro-Molding

“…Therefore, optimization of processing parameters to obtain minimally degraded samples is an essential step in applying the new micro-molding technology. In this sense, we have recently found that it is possible to establish appropriate conditions for biodegradable polymers that could be interesting for the production of biomedical devices such as polylactide (PLA) [13], poly(butylene succinate) (PBS) [14], and poly(nonamethylene azelate) (PE99) [15]. Degradation logically increases with irradiation time and amplitude, but a minimum period is necessary to ensure complete injection into the mold, as well as a minimum amount of vibration energy.…”