On the characterization of an electrically conductive polyaniline complex

This paper reports on the characterization techniques performed to evaluate the suitability of three different samples of a polyaniline (PANI) complex (PANIPOL) for the production of composites exhibiting a phase separated morphology with continuous elongated structures of PANI embedded in the bulk of an insulating polymer matrix by following an in-situ deformation process. The characterization techniques included rheometry, differential scanning calorimetry and thermogravimetry. In addition, X-ray diffraction, gravimetry, infrared spectroscopy, conductivity measurements, and optical and scanning electron microscopy were used to fully characterize the samples. The thermal limitations and stability of the samples were determined. At the same time, their flow properties in the molten state under different levels of shear were also analysed. The experimental results assisted in the identification of the samples' components and revealed that the PANI particles were 7 m in diameter or smaller.     

Water absorption and termite attack on a Kraft paper-based composite treated with recycled polystyrene and three commercial resins

Lignocellulosic–plastic composites are materials widely used in the construction industry; however, their mechanical performance and durability constitutes a serious issue due to the nature of the lignocellulosic component which makes it prone to biological degradation. This article gives account of the protective performance of a novel eco-friendly solvent based coating obtained from recycled expanded polystyrene dissolved with Limonene, and three different coating systems used generally for outside wood protection, applied on a Kraft paper for potential structural use. Three aspects were evaluated, namely coating interaction with the lignocellulosic substrate, water absorption and resistance to Nasutitermes corniger termite attack. Scanning electron microscopy revealed two types of interaction namely—adsorption and absorption—of the coatings systems in the fibrous structure. Coating absorption revealed better protection for water absorptiveness of the paper structure. After biotic exposure, sample weight loss and damaged structure were observed, highlighting the aggressiveness of this type of termites which attack any kind of material studied here, in order to reach their food source.     

In-situ production of electrically conductive fibres in polyaniline-SBS blends

Blending of electro-conductive monofilaments with more traditional insulating materials is a promising approach for the production of composites for applications in static dissipative packaging and in industrial textiles. Accordingly, we report on a favourable method for manufacturing these kinds of material which involves generating the fibres in-situ, that is, during the actual forming process. Electrically conductive polyaniline (PANI) was thermally blended with polystyrene-polybutadiene-polystyrene (SBS) at different weight compositions. The resultant blends were capillary extruded in order to induce a drawing process in the dispersed phase (PANI) of the blend and hence, the in-situ formation of PANI fibres within the above mentioned polymeric matrix. Microscopic analysis on the extrudates revealed that PANI was deformed during the process to produce elongated structures, i.e. ellipsoids or even short fibres, in the blends. Electrical measurements were performed and it was found that blending SBS with no more than 20 weight percent of PANI could produce an electrically conductive composite with a good level of conductivity. The relationship between the volume conductivity and content of PANI in the PANI-SBS blends, was found to be characteristic of a percolation system, with a threshold as low as 5 weight percent of PANI.     

Investigation of directional effects on the electrical conductivity and piezoresistivity of carbon nanotube/polypropylene composites obtained by extrusion

The electrical conductivity and piezoresistivity of multiwall carbon nanotube (MWCNT)/polypropylene (PP) composites obtained by extrusion are investigated, with particular attention to the possible directional effects generated during the extrusion process. This is accomplished by investigating the electrical and electromechanical responses of the nanocomposites at three MWCNT weight concentrations (3, 4 and 5 wt%) in three directions, viz. the extrusion direction, transverse to extrusion (in-plane) and through thickness. Higher electrical conductivity in the extrusion direction was more evident for the lowest MWCNT content. However, the piezoresistive sensitivity was similar in all directions. Films with 4 wt% showed the highest piezoresistive sensitivity, reaching gage factors of?~?4.5 for strains between 0 and 0.8%, and?~?10.2 for strains between 1 and 3%. After an initial drop in the electrical resistance, concomitant with stress relaxation, the changes in electrical resistance showed large reproducibility. Digital image correlation conducted during cyclic piezoresistive testing at 0.8% strain indicates small accumulation of local plasticity as the number of cycles increases, especially in zones near the electrodes. These irreversible changes in the material are expected to trigger the permanent changes in the electrical resistance measured.

Graphical abstract

     

Structure formation in polyaniline-based polymer blends

This paper provides evidences on the feasibility of using an in-situ deformation process to produce elongated structures of a polyaniline complex (PANI CX), embedded in the bulk of filament-like polymer composites, and longitudinally oriented along the composites' main axial direction. The polyaniline complex was thermally blended with polystyrene- polybutadiene-polystyrene (SBS) at different weight compositions, and the resultant blends were capillary extruded into filaments. The extrudates' microstructure was analysed by scanning electron microscopy (SEM). The results of the analysis revealed a phase- separated morphology in the extrudates, which consisted of elongated domains of PANI CX embedded in the bulk of the SBS. The elongated structures displayed a considerable degree of uniformity and continuity, and were preferentially oriented in the extrusion direction. The formation of these structures was ascribed to a combination of factors, the main ones including elongational and shearing flows occurring in the molten/softened blends during the processing, and the stresses transferred from the highly viscous matrix to the particles of the PANI complex filler.