Nanocomposites are a new class of materials that have attracted increasing interest from both scientific and industrial perspectives. This is because adding just a small amount of clay particles to the polymer could produce a significant improvement in the physical, mechanical and thermal properties of the material. Polyethylene nanocomposite consists of a host polymer as a matrix, filled with modified clay particles in which at least one dimension of the dispersed particles is in the nanometre scale.
Polyethylene compounded with montmorillonite clay particles has been widely studied in the past few years. However, the size of the particles used is almost similar to the molecular size of the host polymer. The goal of this work is to study the effect of adding very fine lucentite clay particles (smaller than molecular size of polyethylene) on the mechanical properties of the polymer such as Young’s modulus, yield strength and toughness. It was hope that the addition of very fine filler particles will result in a better dispersion of clay within polymer matrix and consequently will produce better improvement in the properties of pure polyethylene.
The polyethylene used in this study is a commercial linear low density rotational moulding grade, ‘LL711UV’ supplied by Qenos Pty. Ltd. Different amount of lucentite clay particles with surface modification was added to the polyethylene at a rate of 1.0wt%, 3.5wt%, 5.0wt%, 7,5wt% and 10.0wt%. The stiffness, yield strength and toughness of filled and unfilled polyethylene were investigated in order to determine the optimum particle load which maximises the mechanical properties of the host polymer.
Thus, tensile test was performed on the base polyethylene as well as on each of polyethylene/clay nanocomposites to obtain the stress – strain curve, whereas the toughness of the materials was investigated via Charpy impact test. Earlier research indicates that exfoliated systems have better mechanical properties than intercalated composites. Therefore, the classification of filled polyethylene was done by wide angle x-ray diffraction (WAXD) in order to determine the degree of exfoliation of clay particles in the polymer matrix.
In this work, it was found that polymer chain tends to intercalate within clay layers rather than having a nanocomposite with well dispersed particles in the polymer matrix. Moreover, the crystalline structure of polymer/clay nanocomposite was characterised via differential scanning calorimetry (DSC) to establish a relationship between the degree of crystallinity and mechanical properties of the composites.
The results obtained from mechanical testing on polyethylene with and without clay particles were used for comparison. The modulus of polyethylene was found to increase with clay content, but the opposite result was obtained for the yield strength, the elongation to break and toughness of the polymer. Results from the DSC test revealed that there is no significant increase in the crystallinity of the polymer, therefore lucentite clay is not a nucleating agent for polyethylene. Hence, it is concluded that the change in modulus, yield strength and toughness is attributable to the restriction of molecular movement and.