Sven Pegel

Melt Mixing as Method to Disperse Carbon Nanotubes into Thermoplastic Polymers

Abstract This paper presents melt mixed composites where two ways of introducing nanotubes in polymer matrices were used. In the first case, commercially available masterbatches of nanotube/polymer composites are used as the starting materials that are diluted by the pure polymer in a subsequent melt mixing process (masterbatch dilution method) while in the other case nanotubes are directly incorporated into the polymer matrix. As an example of the masterbatch dilution method, composites of polycarbonate with MWNT are presented which are produced using a Brabender PL‐19 single screw extruder. In this system, electrical percolation was found at about 0.5 wt% MWNT. The nanotube dispersion as observed by TEM investigations is quite homogeneous. The direct incorporation method is discussed in composites of polycarbonate with MWNT and SWNT. For commercial MWNT percolation was found between 1.0 and 3.0 wt% depending on the aspect ratio and purity of the materials. For HiPCO‐SWNT from CNI percolation occurred between 0.25 wt% and 0.5 wt% SWNT. The incorporation of nanotubes significantly changes the stress‐strain behavior of the composites: modulus and stress are enhanced; however, the elongation at break is reduced especially above the percolation concentration.

Liquid sensing: smart polymer/CNT composites

Today polymer/carbon nanotube (CNT) composites can be found in sports equipment, cars, and electronic devices. The growth of old and new markets in this area has been stimulated by our increased understanding of relevant production and processing methods, as well as the considerable price reduction of industrial CNT grades. In particular, CNT based electrically conductive polymer composites (CPCs) offer a range of opportunities because of their unique property profile; they demonstrate low specific gravity in combination with relatively good mechanical properties and processability. The electrical conductivity of polymer/CNT composites results from a continuous filler network that can be affected by various external stimuli, such as temperature shifts, mechanical deformations, and the presence of gases and vapors or solvents. Accordingly, CNT based CPCs represent promising candidates for the design of smart components capable of integrated monitoring. In this article we focus on their use as leakage detectors for organic solvents.

Comparisons Among Electrical and Rheological Properties of Melt-Mixed Composites Containing Various Carbon Nanostructures

The present investigation compares different carbon-based nanoscaled materials with regard to their effectiveness in producing thermoplastic polymers with antistatic and electrically conductive behavior. The dispersed phases are carbon black (CB) as spherical particles, multiwalled carbon nanotubes (MWNT) as fiber-like filler, and expanded graphite (EG) as platelet-like filler. Each was incorporated into polycarbonate by small-scale melt mixing. The electrical percolation concentrations were found to be 2 wt% for MWNT, 4 wt% for EG, and 8.75 wt% for CB which parallels the aspect ratios of the fillers. For EG a strong dependence of morphology and electrical resistivity on mixing time was observed, indicating a structural change/destruction during intensive shear mixing. Rheological percolation thresholds were found to be lower than electrical percolation threshold for the MWNT and CB, but similar in the case of EG. The general impact on complex melt viscosity decreases in the order MWNT, CB, EG. For EG, at higher loadings (above 4wt%) the viscosity increase with filler content is delayed as is the decrease in resistivity.

Influence of material and processing parameters on carbon nanotube dispersion in polymer melts

Abstract: Melt processing of polymer–carbon nanotube (CNT) composites is of great industrial importance for the large-scale production of composite materials and desired products. The properties of these composites greatly depend on the quality of CNT dispersion. In this chapter, a broad overview of the influence of material and processing parameters on the dispersion of multi-walled CNTs in thermoplastic polymer matrices during melt processing is provided. The results discussed here are based on small-scale batch mixers as well as on laboratory-scale continuous extruders. To analyse and quantify the state of dispersion, microscopic methods were applied.

Quantification of dispersion and distribution of carbon nanotubes in polymer composites using microscopy techniques

Abstract: Different stereological approaches have been applied to micrographs of light microscopy and transmission electron microscopy to estimate the degree of carbon nanotube dispersion in polymer composites at different length scales. Quantitative information about the spatial relationships between individual carbon nanotubes has been obtained by means of the spherical contact distribution function and a Boolean fibre model. The correlation function has been used to gain an orientation factor as a measure of carbon nanotube alignment. The corresponding theoretical foundations and suitable digital image processing techniques are introduced and illustrated with some specific examples.