Influência do carbonato de cálcio nas propriedades físicas da espuma de EVA.

Abstract

EVA foams have been widely used in footwear components owing to combination of good mechanical properties and low density. The calcium carbonate is the filler more used in EVA foams mainly due to its low price and good processability. However, this filler also has influence in the physical and mechanical properties of the foam. The most frequently used calcium carbonates are the natural ones, followed for the synthetic carbonates, known as precipitated CaC03. These last ones are more expensive and they are used when better mechanical properties are desired. In this work, the foams were prepared in a laboratory hot press after mixing in an industrial intensive mixer (Banbury) and roll mill. The composites were prepared with two types of natural and two types of precipitated calcium carbonate, both having crystalline structure, with sizes between 1,7 and 8,3 \.im. The amount of calcium carbonate in the foam varied between 5 and 45 phr. The density, the hardness and tensile properties of the various types of foams were evaluated and also the topography, through scanning electron microscopy. The results showed a very good correlation between the increase in properties and concentration and particle size of the filler. The precipitated calcium carbonate had more influence than of the natural calcium carbonate. The scanning electron micrographs showed a good filler dispersion and distribution in polymer matrix and illustrate clearly the different sizes of filler used in this work. The study also showed that the properties of the foam are highly heterogeneous, as a function of the position in the foam sheet and through the thickness direction.