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Two new nanotechnologies were recently launched to meet the automotive sector’s need for parts with improved ductility and for reduced solar radiation transmission in glazing applications. This article describes the first of these, a new "high modulus ductile" technology.
(Published on November-December 2008 – JEC Magazine #45)
LIONEL RAUSER, PLATFORM MANAGER FOR AUTOMOTIVE OEMS, SABIC INNOVATIVE PLASTICS
For a number of years, SABIC Innovative Plastics (formerly GE Plastics) has been conducting research into nanotechnologies to enhance the performance of engineering plastics. The first nanotechnology product, a conductive Noryl GTX* PPO/PA alloy used for the manufacture of automotive mirror housings, came onto the market around 1992.
Since the European regulation to lower CO2 emissions was proposed, car producers have been demanding lighter material solutions. SABIC Innovative Plastics has developed several solutions, such as the Xenoy* products, for outside body panels and large components.
Unfilled thermoplastic materials have lower stiffness and are more influenced by temperature variations than steel or thermosets, as can be seen when comparing their CLTE (coefficient of linear thermal expansion). Material producers usually add fillers, either glass or mineral, to overcome this limitation in thermoplastics (and in the final product). But some fillers create aesthetic surface issues in large body parts. To obtain class A surface appearance after painting, mineral fillers have been preferred over the past years. However, while such fillers, in a PC/PBT substrate, improve some mechanical characteristics of the unfilled material, they also degrade one of the most crucial properties for automotive body panels or components, which is impact-resistance behaviour.
Typically, PC/PBT blends display a tensile modulus around 2 GPa and notched Izod impact strength of over 500 joules/m. In the quest for higher modulus materials, mineral fillers are usually added, but this also reduces the impact performance. For example, a PC/PBT blend with 15% mineral filler has a 3.5 GPa modulus, but reduced impact strength of only around 80 joules/m. Adding extra impact modifier can help, but at the expense of a lower tensile modulus.
High modulus ductile (HMD) technology changes this paradigm, enabling higher modulus and impact strength at the same time. High stiffness is achieved by the use of mineral fillers as in traditional PC/PBT blends, and a nano-structure network has been introduced for additional impact performance (Fig. 2).
Stiffness, impact resistance and gap and flush management are three of the most critical parameters requested by OEMs for large components and body parts.
The following data show the contribution of the SABIC Innovative Plastics technology to these performance requirements in automotive applications.
In Xenoy* materials, each different component contributes to material performance, i.e. polycarbonate brings dimensional stability, paint adhesion and ductility, polyester ensures flow and chemical resistance, and the impact modifier provides lowtemperature ductility.
In Xenoy iQ* HMD, the filler contributes to modulus, tensile elongation, creep and fatigue performance without degrading the overall material integrity (Fig. 3 and Table 1).
In 2005, at the Plastics in Automotive VDI conference in Mannheim, GE Plastics (now SABIC Innovative Plastics) announced a new technology that could improve the modulus of thermoplastics materials without severely degrading their ductility. Since then, several automotive manufacturers have approved this material and are now using it for mass-production parts.
SABIC Innovative Plastics recently introduced new polyester resins and blends based on post-consumer PET drink-bottle waste that can lower greenhouse gas emissions while using sustainable feedstocks (Fig. 5 and Table 1). Through a glycolysis process, post-consumer PET waste is depolymerized and then reacted with BDO to produce PBT (polybutylene terephthalate). Green Order (New York, USA) and Recycle One (Tokyo, Japan) evaluated the most commonly used thermoplastics materials for automotive applications, demonstrating that Valox iQ* PBT resin and Xenoy iQ* PC/PBT blends are among the products with the smallest carbon footprint (Fig. 6).
About SABIC Innovative Plastics
SABIC Innovative Plastics is a leading, global supplier of engineering thermoplastics with a 75-year history of breakthrough solutions that solve its customers’ most pressing challenges. Today, SABIC Innovative Plastics is a multi-billion-dollar company with operations in more than 25 countries and over 10,500 employees worldwide. The company continues to lead the plastics industry with customer collaboration and continued investments in new polymer technologies, global application development, process technologies, and environmentally responsible solutions that serve diverse markets such as automotive, electronics, building & construction, transportation, and healthcare. The company’s extensive product portfolio includes thermoplastic resins, coatings, specialty compounds, film, and sheet. SABIC Innovative Plastics is a wholly-owned subsidiary of Saudi Basic Industries Corporation (SABIC), one of the world’s top five petrochemicals manufacturers.
Quality is a major concern in automotive applications. Moreover, the reproducibility of material performance, lot after lot, is key to guarantee the performance of an application over its life span. The linearity of the production capability is a commitment taken by SABIC Innovative Plastics for all its products, including iQ materials. Thanks to the Xenoy* and Valox iQ technology, which uses the same processes as non-iQ materials, this is also possible for the iQ green product.
HMD technology was recently applied to sustainable Xenoy iQ* PC/PBT, and the first serial parts − rear door handles for the Toyota Tundra − are now in production (Fig. 7). Toyota required a paintable material with high stiffness, good fatigue and thermal aging performance. Xenoy iQ* resin met these needs, offering a 3- 7% lower specific gravity, a 20-25% lower CTE, and six times the impact strength of a standard mineral-filled PC/PBT blend.
For trucks and light vehicles, the target applications include body panels (fenders, tailgate skin, etc.) and components such as door handles and spoilers.
Xenoy* HMD is a tough, durable and versatile resin that is potentially an excellent material choice for parts requiring higher stiffness and structural strength at lower weight, ductility in thinner parts, chemical resistance, resistance to repetitive stress and fatigue, better dimensional stability (low CLTE), longer product life (resistance to tough heat and hydro conditions). It also offers the ability to utilize a more environmentally responsible material in the automotive industry.