Effects of Carbon Nanotube Type and Surface Functionalization on the Carbon Nanotube-Unsaturated Polyester Resin Composite Properties

Abstract

The goal of this research was to understand the dispersion of carbon nanotubes (CNT) in unsaturated polyester resin (UPR), the relative strength of nanotube-resin interactions, and curing into nanocomposites. These are three of the most critical parameters for controlling nanocomposite properties. UPR was chosen for the matrix because even though it is one of the most widely used thermoset resins there has been relatively little research on CNT/UPR composites. The first aim of this research was to establish a framework for evaluating the effects of carbon nanotube purity and chirality on dispersion in resin matrices. A protocol for comparing percolation thresholds, fractal structure, and differences in the relative strength of nanotube-nanotube and nanotube-resin interactions using rheological characterization was established. The second aim of the research was to understand the effects of CNT type and surface chemistry on curing kinetics using a combination of rheology and differential scanning calorimetry (DSC). In the first part of the research, the effects of SWNT chirality distribution and purity on dispersion microstructure and nanotube-resin interactions were investigated using four of Southwest Nanotechnologies’ SWNT products: a low and high purity semiconducting grade (SG65 and SG65i) and a low and high purity metallic grade (CG200 and CG300). Analysis of the dispersions’ viscoelastic properties revealed differences in dispersion microstructure and the relative strength of SWNT-resin interactions. While all four products had a similar percolation threshold, the concentration of non-SWNT carbon impurities had a greater effect than chirality on viscoelastic properties and the relative strength of resin−SWNT interactions. In the second part of the research, viscoelastic properties and curing kinetics near the onset of percolation were investigated for MWNT two pristine SWNT types, and two types of functionalized SWNT. The viscoelastic behavior showed differences in nanotube cluster morphology, nanotube-nanotube and nanotube-polymer interfacial interactions. The viscoelastic properties also showed that rheological percolation by nanotube clusters with a better polymer interface will have a higher elastic behavior. In contrast, nanotube clusters that are more aggregated and have less polymer interface will have a transition to solid-like behavior at shorter time scales. Among the CNT/UPR dispersions, the lower cost, lower purity Tuball SWNT displayed a better dispersion state, greatest enhancement of elastic and viscous moduli, higher gelation modulus and higher curing kinetic rate constant. The results of this research provide new insights into dispersion of CNT into UPR. In addition, they established a robust methodology for evaluating new nanomaterial-resin composite systems.