The Role of Coated Ground Calcium Carbonate Fillers (cGCCs) 82 in the Thermal Stability of Polyolefin Resins During Processing, 2002 PLACE Conference Proceedings

The market for polyolefin film is enormous - over 5 million tons in North America alone. A proportion of this film is filled with mineral extenders. The role of the filler is diverse and filler levels may range from just a few percent to over 50 % by weight. The impact of the filler on various processing and property changes can be substantial. This paper deals with one aspect of these effects, namely the thermal melt stability of filled polyolefins.

The thermal stability of polymer melts is dependent on a number of parameters including temperature, stabilizer levels and types, resin type and so forth. The presence of mineral fillers, which are incorporated in order to confer specific processing and property improvements, can also influence melt stability. This paper examines the role of coated GCCs (cGCCs) in the degradation of molten polyolefins (POs). The use of a modified oxidative induction time test (OIT) is first reported and this is followed by a description of the efforts aimed at identifying the underlying mechanisms of polymer degradation in filled POs.

The melt stability of filled POs is of increasing concern as processors seek to operate at higher temperatures. The demands placed upon the stabilizer package are especially acute but the role of other parts of the formulation, in particular the filler, cannot be overlooked. The filler level in certain applications can be very high. For example, in breathable film applications a filler level in excess of 50 wt% is usual. Coated GCCs are widely used in a number of high mineral load film applications. The impact of the filler on melt stability becomes commensurately greater at these high filler levels. This paper attempts to understand the role of cGCCs at elevated temperatures in the melt and their impact on compound stability.