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Ground calcium carbonates (GCCs) are commonly used to extend more expensive polymer resins such as polyolefins polyethylenes and polypropylenes. The finer grades also make a positive contribution to the impact strength and flexural modulus or stiffness of the composite.

While the greatest increase in flexural modulus derives from the use of ultrafine high aspect ratio minerals such as talc, fine ground calcium carbonates also add some stiffness, as well as improving impact strength. This improvement in impact strength can be further enhanced by surface treating the GCC particles with a comptabilizing agent such as stearic acid. The higher the GCC filler concentration, the greater the improvement in impact strength.

The tables below show how the mineral filler concentration and coating improve impact and stiffness of a 4 melt index polypropylene homopolymer. The formulations for the study, listed in the table, consist of the ground calcium carbonates and the polymer, along with a stabilizer.



Vicron® 15-15 and Hi-Pflex® 100 GCCS are 3.5 microns each. Both improve the flexural modulus (stiffness) of the polypropylene by the same amount at each concentration. 



The surface treatment on the Hi-Pflex® 100 GCC improves the dispersion of mineral filler in the polypropylene and greatly increases the impact strength of the composite compared to the untreated Vicron® 15-15 GCC.



Click here for more information on the fundamentals of flexural modulus, stiffness, and click here for more information on the fundamentals of impact strength in plastics.

 

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