Preparation of Nanocomposites of Poly(ε-caprolactone) and Multi-Walled Carbon Nanotubes by Ultrasound Micro-Molding. Influence of Nanotubes on Melting and Crystallization

Abstract

Ultrasound micro-molding technology was successfully applied to prepare nanocomposites based on a poly(ε-caprolactone) (PCL) matrix and multi-walled carbon nanotubes (MWCNTs). Optimization of processing parameters (i.e., amplitude, force and time) was crucial to obtain nanocomposites without any evidence of degradation, high material saving and short processing time (7-8 s). Good dispersion of nanotubes was achieved after processing previously formed solvent casting films. This dispersion was even partially detected in pieces directly obtained from powder mixtures of both components. Incorporation of MWCNTs had a remarkable influence on melting and crystallization processes, which were systematically studied by time resolved synchrotron experiments. Results indicated higher melting and crystallization temperatures for the nanocomposite, with temperature differences higher than 5 • C. Carbon nanotubes were effective nucleating agents and had an influence on crystallinity, crystallization rate and even on lamellar morphology, which was evaluated by analysis of the correlation function of small angle diffraction profiles. Crystallinity within lamellar stacks was lower for the solvent casting nanocomposite, but in this case lamellae underwent a thickening process during heating that accounted for the increase in the melting temperature. Crystallization from the melt rendered similar lamellar morphologies at the end of the process due to a lamellar insertion mechanism.

Biodegradable Polylactide Scaffolds with Pharmacological Activity by Means of Ultrasound Micromolding Technology

“…An antibacterial scaffold was produced by introducing 6 wt-% of triclosan (TCS) to the previous formulation found out, namely combining the use of PEG and NaCl to obtain a proper pore interconnection and high porosity density. As concluded in the previous work [38]. TCS can be incorporated in the ultrasound micromolding of PLA without causing an appreciable degradation.…”

“…By contrast, sodium chloride (NaCl) with a particle size of 250-100 µm allowed obtaining well molded specimens ( Figure 2d) without modifying the processing parameters previously determined for the selected commercial PLA [38]. Thus, amplitude, force, and time of 24 µm, 300 N, and 1.2 s, respectively, were considered optimal and used in most of the performed tests.…”

“…In spite of PEG being employed as a sacrifice polymer and thus preservation of molecular weight and mechanical properties not being essential, an analysis of the micromolding suitability of PEG and PLA/PEG blends was undertaken, following the protocol previously done for PLA [38].…”

“…Ultrasound heating also increases the flow index of the polymers leading to an effective filling of designed micromold cavities if an appropriate pressure/force is applied [35]. Different studies have been carried out with some commodities, such as polyethylene, polymethylene oxide, and polypropylene, [32], commercial biodegradable polymers such as polylactide (PLA) and polybutylene succinate [36], and polymers loaded with exfoliated clays (e.g., PLA) [37] and multiwall carbon nanotubes (e.g., polycaprolactone) [38]. All of them concluded that an accurate selection of amplitude, force and time parameters could lead to minimum polymer degradation, absences of defects in the micromolded pieces, and an accurate filling of the mold.…”

Thermal Welding by the Third Phase Between Polymers: A Review for Ultrasonic Weld Technology Developments

“…Also, double color molding and sandwich welding methods have been proposed with for the plastic products with high-performance and functionalities due to its simply technology and low cost. Naruse [105] carried out ultrasonic plastic welding using a surface acoustic wave device. There are some advantages to using higher frequencies, namely it makes the joining time shorter, damages of joined parts can be avoided, and positioning accuracy become higher.…”