The effect of ionic surfactants and manufacturing methods on the separation and distribution of multi-wall carbon nanotubes (CNTs) in a silicone matrix are investigated. The CNTs are dispersed in an aqueous solution of the anionic surfactant dodecylbenzene sulfonic acid (DBSA), the cationic surfactant cetyltrimethylammonium bromide (CTAB), and in a DBSA/CTAB surfactant mixture. Four types of CNT-based composites of various concentrations from 0 to 6 vol.% are prepared by simple mechanical mixing and sonication. The morphology, electrical and thermal conductivity of the CNT-based composites are analyzed. The incorporation of both neat and modified CNTs leads to an increase in electrical and thermal conductivity. The dependence of DC conductivity versus CNT concentration shows percolation behaviour with a percolation threshold of about 2 vol.% in composites with neat CNT. The modification of CNTs by DBSA increases the percolation threshold to 4 vol.% due to the isolation/separation of individual CNTs. This, in turn, results in a significant decrease in the complex permittivity of CNT–DBSA-based composites. In contrast to the percolation behaviour of DC conductivity, the concentration dependence of thermal conductivity exhibits a linear dependence, the thermal conductivity of composites with modified CNTs being lower than that of composites with neat CNTs. All these results provide evidence that the modification of CNTs by DBSA followed by sonication allows one to produce composites with high homogeneity.
Microscopical, differential scanning colorimetry (DSC), and X-ray structural investigations of solution crystallized carbon nanotube (CNT) composites with linear polyethylene (LPE), isotactic polypropylene (iPP), polybutene-1 (PB-1), and nylon 6 (PA6) disclosed varying degrees of surface interaction and nucleation effect of CNT in these polymers and formation of oriented shish-kebab overgrowths on the CNT ropes in LPE and PA6. The character of the attraction and orientation forces at the CNT-polymer interface is discussed.
23 February 2019 in Journal of Macromolecular Science, Part B
The possibilities to influence the 4 major phase transitions of isotactic polybutene – 1 (iPB-1) and their transformation rate are described. The phase transformations result in new polymer structures with new physical and, in some cases, practically important properties. The transformation of phase II to I is spontaneous contrary to the phase transformation of III to I or II, which depends on the temperature (96 °C or higher). For the practically most important phase transition, II → I, there are 3 major transformation types (plus (P), neutral (N) and minus (M)) depending on the phase transition rate.
The application of biopolymer-based materials is increasing due to better sustainability and environmental protection properties. Gelatin fibers have a specific surface and high porosity, which is why their use in medicine and the food industry is being researched. This article explores the potential of centrifugal spinning to produce gelatin fibers. Gelatin for fiber preparation was obtained from a non-traditional source of collagen (chicken by-products) using a unique enzymatic process. The fiber quality was compared with those prepared from gelatins produced from traditional collagen tissues (porcine, bovine). The results showed that fibers cross-linked with glutaraldehyde vapor preserved their structure even in contact with water. Using a cross-linker controlled swelling ability and solubility while maintaining the fiber structure. On the contrary, uncross-linked gelatin fibers were water soluble due to a high surface-to-volume ratio, facilitating water penetration and dissolution. Scanning electron microscopy (SEM) provided a clearer picture of the morphology of gelatin fibers obtained by centrifugal spinning. Differences in the amount of bonding depending on the raw material used and the presence of a cross-linker were analyzed using Fourier transform infrared spectroscopy (FTIR). The overall results showed that chicken gelatin is a suitable alternative to gelatins from traditional sources and can be used for preparing food and pharmaceutical packaging and coatings, fibers, or bioprinting of 3D matrices.