PET and PBT thermoplastic polyesters are engineering resins offering a good balance of mechanical, thermal, and electrical properties. PET and PBT polyester compounds are available in a wide range of formulations such as unfilled, glass reinforced, mineral filled, and flame retardant and they are also commonly used in blends with other polymers such as polycarbonate and ASA. While unfilled PET and PBT have good ductility and toughness in un-notched tests, they show sensitivity in notched impact tests. Because of this, PET and PBT are often compounded with impact modifiers to reduce their notch sensitivity and improve their toughness, ductility and impact performance. Impact modifiers that have been successfully used in polyester compounds include acrylate copolymers (Dow Elvaloy™ AC) and polymers modified with glycidyl methacrylate (Dow Elvaloy™ PTW).

Dow Elvaloy™ PTW would be considered as a premium impact modifier in that it cannot only make polyester compounds have ‘super tough’ impact performance, it can also provide good impact performance at temperatures down to about -20°C as well as improve hydrolysis resistance.

Dow Elvaloy™ AC acrylate copolymers also make very good general purpose impact modifiers for polyester compounds. While they do not achieve the same level of impact improvement as Elvaloy™ PTW, they can reduce the viscosity of the final polyester compound which provides for improved processability. In some cases, blends of Elvaloy™ PTW and Elvaloy™ AC are used to achieve a balance of impact performance, processability and cost.

Markets for impact modified PET and PBT polyester compounds includes automotive, electrical and electronic. Specific applications include switches, sockets, bobbins, handles, gears, machinery components, motor covers, motor brushes, windshield wiper arms, door handles headlamp bezels, lamp components and home appliances.

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