Development of a high-strength and uniformly-dispersed nanoclay/epoxy composite

Abstract

Recently, organomodified montmorillonite (MMT) (commonly called "Nanoclay") has become popular for most composite component development. It is found that only a small amount of nanoclay being added into polymers can enhance their strength without inducing any weight penalty. However, to achieve this goal, the uniformity of nanoclay inside the polymer matrix plays a key role to control the mechanical, thermal, and even electrical properties of resultant composite. Unfortunately, most literatures can only produce localized evidences extracted from samples through either Scanning Electron Microscope (SEM) or Transmission Electron Microscope (TEM) imaging techniques. In this project, a new method to developed homogenous nanoclay cluster/epoxy composite has been conducted. Through experiments, it was found that small nanoclay clusters were formed and evenly-distributed inside the nanoclay cluster/epoxy composite. The size of clusters looks similar and is within the range between 100 and 200 nm. A tensile property test was conducted and followed by the investigation on the samples' fracture behaviour. SEM was used to investigate the homogeneity of the samples with different weight content of nanoclay by the fractographic observation. In addition, TEM was used to provide direct visualization of the fracture structure morphology. TEM image was retrieved that nanoclay clusters with the diameter of 10 nm could induce the mechanical interlocking inside the composites and thus, stopping up crack propagation. The formation of boundaries between the nanoclay clusters and epoxy could refine the matrix grains and could further improve the flexural strength of the composite. In short, a relatively small amount of nanoclay, typically in the range between 3-5 wt.%, can significantly improve the mechanical properties of polymer-based composite. However, most of recent researches have seldom focused on studying the interfacial bonding properties between nanoclay and the matrix for this composite despite that many mechanical and thermal property tests were conducted. In view of this, this study used Fourier Transform Infrared Spectroscopy (FTIR) and X-Ray Photoelectron Spectroscopy (XPS) to monitor the structural properties at molecular level of the composite. Both results proved that the chemical bonding at the interface between the epoxy and nanoclay did exist. Based on a forementioned findings, it can be assumed that the bonding in the composite is in a perfect adhesion and thus, this assumption can be used to estimate its mechanical properties, such as the Young's Modulus, ultimate strength and other properties. Many literatures have laid down different equations that can be used to predict different properties of nanoclay cluster/epoxy composite. However, most of them ignored the occupancy of epoxy inside the nanoclay clusters. In this regard, this study found that around 7.5 wt.% of epoxy existed in a cluster, and this result is well agreed with experimental finding. With the consideration of different key material factors, it is found that Eqs. (4) and (11) as shown in Chapter 6 can be effectively used to predict the properties of the composites with the nanoclay content less than 5 wt.%