A nucleating/clarifying agent for polypropylene based on new chemistry has been introduced by Crompton Corporation, Greenwich, CT. Moldpro™ 931 is melt-blendable, but sells for much less than melt-blendable sorbitol-type (DBS) clarifiers or non-melt-blendable organophospate salts. Moldpro™ 931 costs $5/lb. vs. $12 to $20/lb. for the others.
Moldpro™ 931 is based on FDA-grade carboxylic acids. It is said to be distinguished by inherently excellent organoleptics (no odor and taste).
Moldpro™ 931 induces PP crystallization at 129°C, said to be comparable or better than DBS products, allowing potential for faster cycles and higher stiffness. The PP resin must contain at least 25 ppm of aluminum catalyst residue for the clarifier to work efectively. Moldpro™ 931 is not effective in the presence of glycerol monostearate (GMS).
Moldpro™ 931 comes as a non-dusting flake and is used at levels of 9.10% to 0.25%. Haze values obtained in a gas-phase PP homopolymer are better than those with sodium benzoate (39-55% vs. 63%), but not as good as those achieved with the latest generation DBS (12-27%). However, Crompton reports that stiffness with Moldpro™ 931 is 25% higher in a random copolymer than with a top-end DBS product, while still maintaining impact strengh.