Nanocomposites are a recent development in polymer technology, and are in process of commercialisation. This has been of great interest to researchers and the plastic industry, as the modified polymer has generated significant improvements in its mechanical properties. This project will study the effects of clay nanoparticles on polyethylene (PE) properties. An important issue is their toughness, which can be measured by the essential work of fracture. Investigations on how fracture toughness can be improved are the main objectives of this work.To manufacture polymer nanocomposites, Somasif ME-100 (layered silicates) was added to, a linear low-density polyethylene (LLDPE), alkatuff 711, and a semi crystalline copolymer, Exxelor VA 1801. Specimens were made with and without the clay, so that the work of fracture of the materials can be compared. As Somasif ME 100 has a large platelet size, these results will also show if varying platelet sizes has an effect on the fracture toughness.A dry mix was made by accurately measuring the pellets of the PE material and adding 5wt% of Somasif ME-100. The mix was then heated, mixed and pressed to produce square sheets with a thickness of less than one millimetre. Specimens were cut for tensile and work of fracture tests, to experimentally obtain the mechanical properties of the PE. From these results, the essential work of fracture of both the nanocomposites and their respective polyethylene material can be compared, showing the effects of the Somasif nanoparticles. Tensile tests determined improvements of strength, fracture toughness, stiffness and strain at break.With the addition of organoclay particles, the yield stress was found to have an increase of less than 2% for 711, and almost 20% in Exxelor. As for the modulus of the PE,an increase of approximately 10% and 40 % was found, for 711 and Exxelor respectively. For the fracture toughness of the nanocomposites, a decrease of more than 60% in the work of fracture was found for both materials. This was also evident in the tensile test, where the strain at break was lower for the clay-modified polyethylene, than their host polymer.