Preparation and properties of polyethylene/montmorillonite nanocomposites formed via ethylene copolymerization

BACKGROUND: In situ formation of polyethylene/claynanocomposites is one of the prevalent preparation methods that include also solution blending and melt blending with regard to process simplification, economy in cost, environment protection and marked improvement in the mechanical properties of the polymeric matrix. In the work reported here, the preparation of linear low-density polyethylene (LLDPE) and fabrication of polymer/clay nanocomposites were combined into a facile route by immobilizing pre-catalysts for ethylene oligomerization on montmorillonite (MMT). RESULTS: [(2-ArN=C(Me))(2)C(5)H(3)N]FeCl(2) (Ar = 2,4-Me(2)(C(6)H(3))) was supported on MMT treated using three different methods. The MMT-supported iron complex together with metallocene compound rac-Et(Ind)(2)ZrCl(2) catalyzed ethylene to LLDPE/MMT nanocomposites upon activation with methylaluminoxane. The oligomer that was formed between layers of MMT promoted further exfoliation of MMT layers. The LLDPE/MMT nanocomposites were highly stable upon heating. Detailed scanning electron microscopy analysis revealed that the marked improvement in impact strength of the LLDPE/MMT nanocomposites originated from the dispersed MMT layers which underwent cavitation upon impact and caused plastic deformation to absorb most of the impact energy. In general, the mechanical properties of the LLDPE/MMT nanocomposites were improved as a result of the uniform dispersion of MMT layers in the LLDPE matrix. CONCLUSION: The use of the MMT-supported iron-based diimine complex together with metallocene led to ethylene copolymerization between layers of MMT to form LLDPE/MMT nanocomposites. The introduction of exfoliated MMT layers greatly improved the thermal stability and mechanical properties of LLDPE. (C) 2009 Society of Chemical industry