Mechanical improvement of P(VDF-TrFE) /nickel nanowires conductive nanocomposites: Influence of particles aspect ratio

Nickel nanowires with high aspect ratio (250) were elaborated and incorporated into poly(vinylidene difluoride-trifluoroethylene) up to 30 vol% via solvent mixing way. These nanocomposites are characterized by a conductive behavior with a high electrical conductivity value (10² S m^?1) above a very low percolation threshold (0.75 vol% of metallic nanowires). The introduction of nanowires strongly depressed the matrix crystallinity. Static and dynamic mechanical analysis have been realized at low nanowire volume fraction (< 10 vol%). Below 5 vol% of nanowires, nanocomposites remain ductile. The dynamic mechanical properties are related to the volume fraction of nanowires. A strong increase of the viscoelastic contribution related to the increase of the percentage of amorphous phase is observed. The major effect is the increase of the rubbery modulus. The highest increase of 300% is obtained for only 5 vol% of nanowires; it represents an original mechanical result for low filled composites. The dependence versus nanowire content has been described by adapting the Halpin–Tsai model to high aspect ratio filler. Metallic nanowires create additional entanglements that are randomly distributed in the rubbery polymeric matrix. With their low percolation threshold, metallic nanowires based nanocomposites constitute a new class of multifunctional materials with a high conductivity associated with a ductile polymer matrix characterized by a high rubbery modulus.     

Original Preparation of PEKK Dispersion for Coating by Transfer from a Chloroform Stable Dispersion to an Aqueous Stable Dispersion,by Emulsion/Solvent Evaporation

In this work, aqueous dispersions of PolyEtherKetoneKetone (PEKK) oligomers were obtained by an emulsion/dispersion solvent evaporation technique. The PEKK oligomers were synthesized by a Friedel–Crafts acylation with a number average degree of polymerization of 4. The synthesized PEKK oligomers had very good thermal stability and spontaneously formed a stable dispersion of swollen micrometric fibers in chloroform. After sonication of the chloroform dispersion in water in the presence of sodium dodecyl sulfate (SDS) and evaporation, we obtained aggregated particles with a mean diameter between 120 and 160 nm, decreasing linearly with the PEKK concentration. The most stable dispersions were obtained with 0.5% wt of surfactant and, at a fixed concentration of SDS, the stability decreased when the PEKK concentration was increased. The different dispersions of PEKK in water were very stable and, after water evaporation, formed homogeneous films for high-performance coating.     

Thermal,mechanical and dielectric behaviour of poly(aryl ether ketone) with low melting temperature

New poly(aryl ether ketone)s (PAEKs) with a low melting temperature (relative to PEEK) are of interest in order to simplify the manufacturing of high-performance polymers or composites. In this study, we propose to investigate the physical properties of a new PAEK from Victrex, namely PAEK LM. Combinations of thermal analyses were used as follows: standard and modulated temperature differential scanning calorimetry, dynamic mechanical analysis, dynamic dielectric analysis and guarded hot plate technique. We found that the global mechanical, dielectric and thermal properties are very similar to the PEEK reference. The glass transition temperature was observed in the same range than PEEK (∼ 150 °C) while the melting temperature T_m was measured at 307 °C for PAEK LM which is about 35 °C below the melting temperature of PEEK. The degree of crystallinity of PAEK LM was found to be 27% while for PEEK it is 38%, depending on the processing conditions. This work explored crystalline structure–property relationships to explain the behaviour of PAEK LM.