Quantitative analysis of grafted CNT dispersion and of their stiffening of polyurethane (PU)

Abstract

Electroactive devices are developed for energy conversion purposes. In particular, polyurethanes (PU) are lightweight and flexible materials, which have demonstrated their ability to convert electrical energy into mechanical energy (actuation by electrostriction) and vice-versa (energy harvesting). It has been shown that energy conversion efficiency can be increased by incorporating carbon nanotubes (CNTs) into a PU matrix. The counterpart of this improvement is the stiffness increase, which in turn limits the electrostriction efficiency. On the other hand, it is well known that CNTs are hardly dispersed in a polymeric matrix, and that the interfacial adhesion strength is generally poor. One solution to improve both dispersion and adhesion consists in grafting polymeric chains onto the CNT surfaces. As most of the works dedicated to improve material electroactivity are mainly empirical, this work aims to (i) better characterize these material microstructures by electron tomography, through the measurement of the CNT tortuosity, the CNT-CNT minimum distance and the number of their contacts, and (ii) and to predict their mechanical stiffness from these microstructural data. From electron microscopy observations of the studied materials, CNTs can be assumed to be composed of successive stiff rods of measured length and orientation, linked together by flexible kinks. Their mechanical stiffening effect in PU is, simply and in an original way, evaluated using the classical analytical equations derived by Halpin and Kardos, accounting for the microstructural parameters determined by electron tomography. It appears clearly that, due to their tortuosity and despite their ultra-high longitudinal stiffness, CNTs only poorly stiffen soft matrices. Fully stretching 10 m long nanotubes increases the composite modulus by almost 10 for a fraction of only 2 vol.%.

Quantitative evaluation of nanoparticle dispersion based on modeling methods and image analysis: A case study on nano‐Sb2O3 filled Poly (butylene terephthalate) composites

“…Based on the scanning electron microscopy (SEM) images of PBT‐matrix composites, the evaluation of dispersion coefficient is performed via binarization process. [ 48–50 ] Figure 3 shows that the binarization process of SEM images for PBT‐matrix composites and the frequency density distribution of free‐path spacing between the Sb 2 O 3 particle surfaces in the composites filled with 3 wt% Sb 2 O 3 nanoparticles. The transformation of images undergoes image‐processing procedures, including binarization and filter treatment by image analysis software.…”

Research on Micro-Mechanics Modelling of TPU-Modified Asphalt Mastic

“…In Table 4, d v10 represents the particle size of a filler with a volume below 10%, d v50 represents the particle size of a filler with a volume below 50%, and d v90 represents the particle size of a filler with a volume below 90%. Looking at the size of a hypothetical cluster of homogeneous particles, d [3,2] shows the average particle size of the surface area, which means that the particle shape of the particle group is the same, the total volume (weight) is the same, and the total surface area is the same. d [4,3] is the average volume particle size, which refers to the particle size of an imaginary particle group with the same particle shape, the same total volume and the uniform particle size of the same particles.…”

“…At a volume fraction of 80% of mineral powder, the thickness of the structural asphalt layer decreases to 0.1 µm. In this study, the surface area average particle size d [3,2] is used as the average particle size of mineral powders, in which d L of limestone is 5.770 µm, d G of granite is 25.525 µm, d F of fly ash is 4.294 µm, and d C of coal gangue is 11.859 µm. Thus, the model parameter R can be obtained.…”

“…Thermoplastic Polyurethane Elastomer (TPU) is a new polymer material, which has been widely used in many fields due to its flexible formulation and wide range of adjustable properties [1][2][3][4][5]. However, the research into and application of TPU as an asphalt modifier in the field of road engineering are rarely reported [6].…”

Piezoresistive Behaviour of Additively Manufactured Multi-Walled Carbon Nanotube/Thermoplastic Polyurethane Nanocomposites

“…Jin et al [18] conducted coarse-grained molecular statics simulations for studying the electrical properties of CNT thin films and found that the ratio of the mean projected CNT length over the film length is related to the hysteresis of resistance. Jomaa et al [19] evaluated the effect of CNTs on the mechanical properties of CNT/PU composites by analysing the CNT network morphology and found that the CNTs do not stiffen the composite much because of the waviness, but increases the modulus significantly when stretched.…”