Interfacial effects on the melt state behavior of polyethylene-EPDM-calcium carbonate composites

Dynamic mechanical spectra of various composites of high density polyethylene (PE), ethylene propylene diene rubber (EPDM), and calcium carbonate were obtained at 190°C with a parallel plate instrument. Interfacial effects were found to have a significant influence on the dynamic mechanical behavior of these composites.Composites of calcium carbonate in PE displayed prominent particle—particle interaction effects. This resulted in a greatly enhanced dynamic shear modulusG _d due to the filler addition. Treatment of the calcium carbonate with gamma-aminopropyltriethoxysilane (-APS) or gamma-methacryloxypropyltrimethoxysilane (-MPS) significantly reduced the particle—particle interactions. Solution deposition of EPDM or EPDM grafted with maleic anhydride (EPDM-MA) on the calcium carbonate, before incorporation into a PE composite, also had a significant effect on the composite properties. Comparison of data from composites treated with EPDM vs. EPDM-MA suggested the presence of an interaction between the calcium carbonate surface and the maleic anhydride modification. This conclusion was further supported by solid state proton NMR relaxation model experiments which showed significant immobilization of the EPDM-MA chains on the filler surface. The treatment of calcium carbonate with-APS or-MPS before incorporation into multicomponent polyethylene-rubber-filler composites also had a significant influence on the dynamic mechanical properties of the resultant composites. There is evidence for a reaction between-APS and EPDM-MA during processing on the roll mill.