The effects of coupling agents, silicone oil, and three types of polymeric modifiers on the mechanical properties of linear low density polyethylene (LLDPE) composites highly filled with aluminium hydroxide [Al(OH)(3)] were studied. Polymeric modifiers that contain polar groups, such as silane-grafted polyethylene (Si-g-PE) and acrylic-acid-grafted ethylene-vinyl acetate copolymer (AA-g-EVA), improve the mechanical properties dramatically, while nonpolar modifiers improve them to some extent. When Al(OH)(3) was treated using a titanate coupling agent, the silicone oil increased the impact strength and elongation at break of the LLDPE/Al(OH)(3) composites. Introduction of a polymeric modifier containing polar groups destroys the beneficial effects of silicone oil on film mechanical properties, while the introduction of a nonpolar elastomeric polymeric modifier retains the high impact strength and elongation at break. SEM analyses provide the indirect evidence of the encapsulation of silicone oil around the filler. (C) 2002 John Wiley & Sons, Inc.