Effect of cold‐crystallization on the AC and DC conductive properties of polylactide biocomposites with carboxylic or neat large aspect ratio MWCNT

Abstract

After DC and AC conductivity measurements, percolation parameters, universality, and time‐temperature‐concentration superposition are evaluated in biocomposites based on poly(lactide) loaded with multiwalled carbon nanotubes either carboxylic, PLA/c‐CNT, or pure but with a larger aspect ratio, PLA/LAR‐CNT, in weight concentrations up to 7%. The polymer matrix is either 100% amorphous or cold‐crystallized. Wide angle X‐ray scattering is used to extract the crystallinity at each temperature. The nucleating effect for the cold crystallization of the PLA is greater for the LAR‐CNT than for the carboxylic ones. DC and AC conductivities are measured in broad frequency and temperature ranges, from 1 mHz to 1 MHz and from 133 to 378 K, respectively. The critical percolation value increases for c‐CNTs (from 1.8 to 2.4 vol%) upon cold crystallization of the PLA matrix as the formation of a conductive path is hindered by the existence of a crystalline phase, which is dominant over the reduction of the amorphous regions. No significant changes upon crystallization were found in the critical concentration value (0.6 vol%) for the LAR composites, where the conductive path is 2D. The universal scaling found here for different concentrations is lost when temperature varies. However, time‐temperature superposition is present for each concentration of LAR or carboxylic CNTs. POLYM. COMPOS., 2013. © 2012 Society of Plastics Engineers

Free volume-related microstructural properties of lithium perchlorate/sodium alginate polymer composites

“…In this case, only a deformational moment will be observed. The AC conductivity for all samples is continuously increases with salt concentration and frequency and it is reported in our previous communications . The decrease in dielectric constant with increase in frequency for all dopant concentrations may be appropriately explained on the basis of charge carriers being blocked at the electrodes.…”

Crystallization of Poly(l-lactide) Confined in Ultrathin Films: Competition between Finite Size Effects and Irreversible Chain Adsorption

“…In this work, we present the crystallization study of poly( l -lactide) (PLLA) ultrathin films, capped between two aluminum layers via dielectric relaxation spectroscopy. PLLA is, nowadays, a widely used biodegradable and biocompatible polymer in a broad range of applications such as bone implants, , tissue engineering and biocomposites. , Previously, the crystallization of PLLA has been studied in bulk, − via DRS. As the crystallization takes place, there is a reduction of the amount of polymer segments involved in the α relaxations and there is an overall slow-down of the relaxation.…”

Effect of Microwave Cure on the Thermo-Mechanical Properties of Tung Oil-Based/Carbon Nanotube Composites

“…The study of CNT composites with bio-based resins has, so far, focused heavily on the use of polylactic acid as the matrix [28], finding application mainly in the biomedical field [29]. Nevertheless, vegetable oil-based thermosetting resins have been reinforced with continuous glass fibers and cationically cured at 110 °C [30], which suggests that cationic tung oil resins may be cured in a similar fashion in the presence of CNTs.…”