Dependence of electrical properties of polypropylene isomers on morphology and chain conformation

Abstract

The electrical properties of polypropylene isomers were correlated with the morphology and chain conformation of differently obtained isotactic (iPP) and syndiotactic (sPP) samples. In the case of iPP, a crystallized and a smectic sample were prepared, whereas for sPP two crystalline helical samples and a mesophase with the chains in trans-planar conformation were considered. The phase composition was obtained for all the samples comparing x-ray diffractograms and transport properties of vapours, which give the crystallinity and the amorphous fraction, respectively. The fraction of mesophase was obtained by the difference of the previous values. The study of the morphology evidenced similarities and differences among the samples, which were discussed and correlated with the phase composition. The electrical conductivity was measured for all the samples, and the syndiotactic isomer showed the lowest value as well as a dependence on the structure. In contrast, the isotactic isomer showed the same behaviour for either polymorph. Based on the structural and electrical results, a phenomenological explanation of the conduction mechanisms taking place in the different forms has been proposed. In particular, the current in the iPP seems to be controlled by Schottky emission, i.e. by field-assisted thermo-ionic injection of carriers from the electrode into the polymer, whereas for the sPP more than one mechanism is likely to be effective, although the ionic transport appears as the predominant one. The experimental data confirm a different behaviour of the ionic conduction properties for the different polymorphs, highlighting the greater insulating characteristics of the mesomorphic structure of the syndiotactic isomer.

UV Irradiated Graphene-Based Nanocomposites: Change in the Mechanical Properties by Local HarmoniX Atomic Force Microscopy Detection

“…This is an expected result and it is most likely due to the consumption of the resin surrounding the GNPs. In fact, as already evidenced by SEM investigation, the UV treatment can determine, from a morphological point of view, effects very similar to those caused by chemical etching procedures [45]. Furthermore, the distribution of the crystals (BaSO 4 and CaCO 3 ) seems to highlight that the UV radiation determines a disaggregation of the salt crystals as a direct consequence of a little consumption of the hosting matrix between the crystallites.…”

Low Dielectric Constant and Anisotropic Mechanical Properties of Dispenser‐Printed Polyetherimide Films Using Two‐Step Thermal Treatment

“…As polymers show a complex frame of interwoven relationships among the structure, process, and physical properties, understanding the distinct characteristics of polymers before and after solution processing is important in terms of their structure and morphology. [ 25–29 ]…”

“…As polymers show a complex frame of interwoven relationships among the structure, process, and physical properties, understanding the distinct characteristics of polymers before and after solution processing is important in terms of their structure and morphology. [25][26][27][28][29] In this study, we investigated the characteristics of PEI films fabricated by dispenser printing, that is, dielectric constant, CTE, tensile strength, and modulus. N-Methyl pyrrolidone (NMP) was chosen as the solvent to dissolve PEI, and printing condition optimization was conducted based on the pressure and rheological properties of the PEI ink.…”

Influence of multiwall carbon nanotubes on morphological and structural changes during UV irradiation of syndiotactic polypropylene films

“…Actually, CNTs are considered one of the most promising nanofiller to manufacture new materials. CNTs in polymeric matrices offer the possibility to combine complementary interesting properties among which good mechanical and electrical properties and the possibility of this nanofiller to act as flame retardant additive 9–18. A recent review provides a compendium of the existing literature related to the effect of CNTs on polymeric matrices of isotactic and syndiotactic polypropylene (sPP) 19.…”