More processing protection for PP, PE.

New melt-processing stabilizers for PP and PE are based on novel chemistry that outperforms conventional phenolic/phosphite antioxidant systems. New Irganox HP products were unveiled by Ciba Additives Div., Ciba Specialty Chemicals, Tarrytown, N.Y., at last month's SPE Polyolefins Conference in Houston. Although resin producers are expected to be the primary users of the new additives, processors reportedly will benefit as well.

Irganox HP products are synergistic combinations of new HP-136 cyclic ester processing stabilizer, which has lactone functionality, together with Ciba's Irganox B-Blends. The latter contain a phenolic antioxidant such as Irganox 1010, 1076, or 3114 plus Irgafos 168 phosphite. The new lactone stabilizer functions as a carbon-centered radical scavenger. By reacting with the polymer radicals before they combine with oxygen, it serves to inhibit autoxidation and regenerate the phenolic antioxidant.

RUN HOTTER AND FASTER

In PP, use levels of Irganox HP products are said to be 30-40% lower than for B-Blends or other phenolic/phosphite combinations alone, says marketing specialist Dr. Peter Goman. Users can therefore realize cost savings of at least 10% in PP, he claims.

Irganox HP reportedly yields several advantages to processors as well. "Processors can expect to get a resin with a much wider processing window and that can run hotter and faster," says Goman.

Significant improvements in both melt flow and color stability are key advantages, as shown in the two accompanying bar graphs. In field tests, Ciba has shown HP products to provide discoloration-free processing at up to 640 F in PP and 570 F in PE.

Benefits of the new stabilizers are said to be most pronounced in PP homopolymers and copolymers and in high-temperature processing of HDPE and LLDPE. Ciba recommends HP stabilizers wherever there is high temperature and high shear, and for processing higher-viscosity polymers (narrow-MWD and HMW grades). Other uses are processes with long residence times, such as pipe, rotomolding, and large-part injection or blow molding.

Granular HP products are hydrolytically stable and listed on the EPA's ToSCA inventory. The company has petitioned the FDA for their use in food packaging.