Dupont Canada Inc.

Evelyn M Lundhild

David A Harbourne

Mark G Dokurno

Filled thermoplastic compositions are disclosed. The compositions comprise (a) 30 to 90 parts of homopolymers of ethylene and/or copolymers of ethylene and C3-C10 alpha-olefins, (b) 10 to 70 parts of homopolymers of ethylene and/or copolymers of ethylene and C4-C10 alpha-olefins modified by grafting with ethylenically unsaturated carboxylic acids or anhydrides thereof, the blend of (a) and (b) having a melt index of less than 15 dg/min. and (c) 20 to 70 percent, based on the amount of (a) and (b) of a filler. The filler is selected from magnesium hydroxide, calcium hydroxide, aluminum trihydrate and hydroxyl-containing carbonates of at least one of magnesium and calcium, and mixtures thereof. The compositions exhibit a useful combination of stiffness and toughness, especially as measured by impact strength and tensile strength.

Filled thermoplastic polymer compositions

A fire-retardant sheet material, the manufacture thereof and a fire-retardant polymer composition are disclosed. The sheet is manufactured from a composition of polyethylene, 55 to 75% by weight of the composition of alumina trihydrate and/or magnesium hydroxide, and optionally zinc borate and/or calcium carbonate, at least 2% by weight of the composition being in the form of a graft copolymer with an ethylenically unsaturated carboxylic acid or anhydride. The composition has a melt index of 0.05 to 4.0 dg/min. In an embodiment, the graft copolymer has a shear viscosity at 200.degree. C. and a shear rate of 400 sec.sup.-1 that is not more than 50% of that of the polyethylene. The sheet material may be used for, in particular, ceiling tile. In embodiments of the composition, 60 to 90% by weight may be alumina trihydrate and/or magnesium hydroxide, and optionally zinc borate and/or calcium carbonate.

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Kingston, Canada

Evelyn M Lundhild