Improvement of toughness and electrical properties of epoxy composites with carbon nanotubes prepared by industrially relevant processes

Abstract

The addition of carbon nanotubes (CNTs) to polymeric matrices or master batches has the potential to provide composites with novel properties. However, composites with a uniform dispersion of CNTs have proved to be difficult to manufacture, especially at an industrial scale. This paper reports on processing methods that overcome problems related to the control and reproducibility of dispersions. By using a high pressure homogenizer and a three-roll calendaring mill in combination, CNT reinforced epoxies were fabricated by mould casting with a well dispersed nanofiller content from 0.1 to 2 wt%. The influence of the nano-carbon reinforcements on toughness and electrical properties of the CNT/epoxies was studied. A substantial increase of all mechanical properties already appeared at the lowest CNT content of 0.1 wt%, but further raising the nanofiller concentration only led to moderate further changes. The most significant enhancement was obtained for fracture toughness, reaching up to 82%. The low percolation thresholds were confirmed by electrical conductivity measurements on the same composites yielding a threshold value of only about 0.01 wt%. As corroborated by a thorough microscopic analysis of the composites, mechanical and electrical enhancement points to the formation of an interconnected network of agglomerated CNTs.

The effect of mixing methods on the dispersion of carbon nanotubes during the solvent‐free processing of multiwalled carbon nanotube/epoxy composites

“…31 Proper selection of solvent and the use of an efficient solvent removal method is essential when considering solvent-based methods to disperse MWCNTs in a polymer matrix. 31 Alternatively, solvent free processing methods (e.g., stirring, kneading, extrusion, shear mixing, 32 high pressure homogenizer, 18 calendaring, or three-roll mill 33 ) have been studied to formulate homogenous MWCNT/polymer composites. While there is a substantial amount of literature available for three-roll mill and US processing methods; limited literature is available on the use of high shear mixing methods, such as planetary shear mixing and microfluidics (MF), to deagglomerate CNTs in polymer nanocomposites.…”

“…While there is a substantial amount of literature available for three-roll mill and US processing methods; limited literature is available on the use of high shear mixing methods, such as planetary shear mixing and microfluidics (MF), to deagglomerate CNTs in polymer nanocomposites. 15,17,18,34 In US, a pulsed ultrasound wave causes generation and collapse of submicron-sized bubbles of the resin mixture and thus deagglomeration of MWCNTs in the polymer matrix. However, processing of MWCNTs and polymer mixture using microfluidizer (MF) involves the fluid flowing at high velocities through microchannels of various geometries, and exposing the mixture to high shear stresses.…”

Comparison of structural health assessment capabilities in epoxy – carbon black and epoxy – carbon nanotube nanocomposites

“…Electronic microscopy revealed radial cracking from the tip of the indent (Figure 3). All samples (epoxy, epoxy -0.2 vol% CB and epoxy -0.2 vol% CNT nanocomposites) retained their integrity because of the small Vickers loadings after indenta- (Figure 4) which is also responsible for improving fracture toughness of epoxy nanocomposites [24]. Such phenomenon was not observed for particulate (carbon black) filled epoxy nanocomposites where isolated CB particles were observed on the edges of the fractured surfaces ( Figure 4).…”

Multiwalled carbon nanotubes incorporated into a miscible blend of poly(phenylenether)/polystyrene – Processing and characterization

“…However, it can be interpreted that lower values of 't' would mean an abrupt variation in the electrical properties in the vicinity of the percolation, as the magnitude of 'w -!w c ' is less than 1. According to [16,25], the estimated 't' values of the PPE/PS-MWCNT composite system show that electrical percolation is principally governed by the 2-D network of MWCNTs in the matrix. The compression molded composite samples showed similar electrical conductivity irrespective of the processing speeds at a fixed MWCNT concentration.…”

“…The degree of dispersion of CNTs and the consequent macroscopic behavior is strongly dictated by the choice of the matrix [4,5], the type of CNT [6][7][8][9] and modification of their surface [10][11][12][13], and the processing method and associated parameters [2,3,14]. Low filler percolation thresholds have been achieved with CNT reinforcements in epoxy [15,16], owing to excellent filler dispersion and better compatibility of the CNTs with the resin. Nevertheless, nanocomposites based on thermoplastic resins show more complexities especially when analyzing the effect of processing method on the final properties.…”