New Polypropylene/PPO Alloys Fill a Cost/Performance Gap

A brand-new family of thermoplastics for automotive and other markets offers an intermediate range of cost and performance between those of TPOs and engineering resins such as nylon, ABS, long-glass PP, and some modified PET and PBT materials. GE Plastics, Pittsfield, Mass., has broadened its Noryl range of PPO alloys by adopting a new matrix material: polypropylene. New patent-pending technology allows the incompatible PP and PPO materials to be blended so as to create new balances of stiffness, toughness, and heat resistance in a moderate price range. Initial Noryl PPX grades are priced between $1.20 and 1.80/lb.

The first members of the Noryl PPX family are two unfilled and two glass-reinforced grades that are aimed at automotive uses, as well as power-tool housings, food-handling trays, and fluid-handling components like pump housings. In the automotive arena, unfilled Noryl PPX7110 and 7125 are suitable for bumper fascias and underhood components. They are paintable with plasma or flame pretreatment. Grades suitable for use with adhesion promoters are in development. Glass-filled Noryl PPX630 and 640 are targeted for front-end modules, seat backs, load decks, and underhood parts. Noryl PPX addresses the auto makers’ interest in materials compatibility for recycling because it can be reground together with other PP-based resins or with standard polystyrene-based Noryl.

Competitive properties

According to Noryl product manager Keith DuPont, Noryl PPX offers three key properties: ductility or toughness, chemical resistance, and heat resistance. Compared with TPOs used in bumper fascias, Noryl PPX offers both higher heat resistance and 30-50% greater stiffness for the same level of toughness (see table). For example, Noryl PPX7125 with 194,000-psi flexural modulus is similar in toughness to TPOs at 120,000 to 155,000 psi modulus. High stiffness and high flow of Noryl PPX can allow for thinner walls and faster molding cycles, GE claims. Those factors together with very low specific gravity could make overall cost of Noryl PPX fascias lower than those molded of TPO, says Noryl product manager Keith DuPont. Noryl PPX also boasts higher creep and scratch resistance. For underhood parts, power tools, and pump housings, Noryl PPX is said to offer a combination of good chemical resistance and nearly zero moisture growth—an advantage over nylon. Toughness of Noryl PPX also beats that of nylon, DuPont notes. For power tools, 30% glass-reinforced PPX630 is said to show very good surface quality. And for industrial food-handling trays—today mostly wood or metal—olefinic Noryl PPX offers good non-stick or “peel” properties.

PROPERTIES OF NEW NORYL PPX ALLOYS
	PPX7110 Unfilled	PPX7125 Unfilled	PPX630 30% Glass	PPX640 40% Glass
Specific Gravity	0.97	0.99	1.19	1.30
MFR, g/10 min	10.6	8.4	2.6	1.3
Tensile Strength, psi Yield Break	5200 4700	5300 5100	11,500 11,500	13,900 13,900
Elongation, % Yield Break	6.5 195	8.0 150	— 7.7	— 6.4
Flex. Strength, psi	7500	7300	18,800	21,900
Flex. Modulus, psi	235,000	194,000	806,000	120,600
Notched Izod, ft-lb/in. 73 F -22 F	8.2 2.8	10.6 6.8	3.1 1.9	2.0 1.8
Unnotched Izod, ft-lb.in.	—	—	15.5	10.8
Instrumented Impact, Total Energy, ft-lb 73 F -22 F	336 246	328 331	169 181	149 125
Vicat Temp., F	282	285	324	326
HDT, F 66 psi 264 psi	236 171	256 198	311 273	318 295