Metallocene PP Copolymers With ‘Breakthrough’ Clarity

WEB EXCLUSIVE

A novel family of metallocene-based PP copolymers reportedly offers the ultra-high clarity of amorphous engineering resins such as PC and PETG, along with good physical properties and processing advantages. Developed by Basell North America Inc., a LyondellBasell company, Wilmington, Del., using its proprietary single-site catalyst, the new Pristene family is initially comprised of two grades: RM 2091, said to be the “first of its kind” low-MFR (3.5 g/10 min) PP copolymer for extrusion blow molding, and RM 2073 for injection molding. Both grades allow molders to achieve an unprecedented 2% haze in a 1-mm-thick plaques, compared with 6% to 10% haze values for existing PP-based resins. Says global marketing manager Amit Gupta, “Transparency at that level can now be compared to PC and other engineering polymers that deliver glass-like clarity.

This performance opens the door for a wide variety of new opportunities.” The 2% haze value translates to haze levels of 5% to 6% in blow molded and injection molded parts, depending on thickness. RM 2091 extrusion blow molding grade. with 0.91 g/cc density, also features excellent stiffness, with a flex modulus of 240,000 psi, notched Izod impact strength of 0.8 ft-lb/in., elongation of 7% @ yield, and HDT of 117 C, as well as excellent melt strength. Its good processing characteristics have been exhibited in lab and field studies in both Europe and North America. According to Gupta, this high-transparency resin is being aimed at baby bottles, food/beverage applications, and personal-care items as both a BPA-free alternative to PC, and also an alternative to PETG in applications such as cosmetic packaging where PETG’s chemical resistance falls short.

RM 2091 also offers a lower cost alternative that requires no predrying. “Extrusion blow molders have desired a cost-competitive alternative with reasonable toughness for transparent, hot-fill bottles. It is now possible to achieve benchmark optical properties of competitive resins such as PC, PVC, and PETG. It can also be considered for use in applications requiring refrigerated impact performance.”

RM 2073 injection molding grade has a 0.910 density and a high MFR of 40. It is said to offer excellent shear-thinning behavior that can translate into improved output for molders and the potential for reduced wall thickness. It has a tensile strength at yield of 4300 psi, flexural modulus of 160,000 psi, elongation @ yield of 10%, and notched Izod impact strength of 0.5 ft-lb/in. Significant improvements in chemical resistance are also cited. Its wide range of potential applications include, food and beverage packaging, foodservice trays/covers, drinking cups/pitchers, storage containers, CD/DVD cases, as well as medical devices. Compared to PC, RM 2073 reportedly exhibits better environmental stress-crack resistance and also requires lower processing temperatures, which should translate into lower energy costs. Its added rigidity is said to be ideal for those applications requiring strength as well as thin walls.