Polypropylene in automotive applications

The introduction of HALS led to a large increase of the UV stability of polymeric materials. Without the discovery of HALS, the outdoor applicability of many polymers would be limited. So would the use of polypropylene in automotive application without the use of HALS be impossible. 

J. Gosden, Proceedings of Polypropylene in Automotive Applications, Rapra Technology Limited, Shawbury, UK, 1992, Paper 15. 

The use of ABS has in recent years met considerable competition on two fronts, particularly in automotive applications. For lower cost applications, where demands of finish and heat resistance are not too severe, blends of polypropylene and ethylene-propylene rubbers have found application (see Chapters 11 and 31). On the other hand, where enhanced heat resistance and surface hardness are required in conjunction with excellent impact properties, polycarbonate-ABS alloys (see Section 20.8) have found many applications. These materials have also replaced ABS in a number of electrical fittings and housings for business and domestic applications. Where improved heat distortion temperature and good electrical insulation properties (including tracking resistance) are important, then ABS may be replaced by poly(butylene terephthalate). 

The advantages offered by the use of expanded polypropylene in automotive bumper cores and other applications are considered, and its properties are compared with other materials traditionally used in such applications in terms of impact strength, energy absorption, resilience, and compressive strength. 

Automotive seat back substrates are among large bow-molded parts made from very-low-melt-flow, high-melt-strength PP. Automotive is a major polypropylene market. The ease of recycling of PP is an important consideration in automotive applications. 

Polypropylene accounted for about half of the nonwoven products in industrial uses in 2001. Its share in ropes and nets was 55-60%, and 70-80% in civil construction, where polyester claimed 20-24%. In automotive applications, polypropylene shared 26-30%, nylon almost 50%, and polyester about 20%. Polypropylene contributed to over 86% of agricultural nonwoven, 100% of packaging cloth, 85% of sanitary items, and 64-70% of medical applications. The world consumption of industrial nonwoven products was 1.329 MT in 2000. Polypropylene topped all synthetic fibers with a share of over 40% in this market segment. 

Due to its low thermal stability, wood flour is usually used as filler only in plastics that are processed at temperatures lower than about 200 °C. The majority of wood-plastic composites use polyethylene as the matrix (Figure 15.2). This is, in part, due to that fact that much of the early wood-plastic composites were developed as an outlet for recycled film. Polypropylene is more commonly used in automotive applications, and polyethylene is more commonly used in exterior building applications. 

These trends are illustrated by DuPont Dow Elastomers range of Engage polyolefin elastomers, intended as impact modifiers for polypropylene in automotive bumpers and fascias. They combine stiffness with ductility, and are claimed to give very good low temperature impact strength. Engage 8842 is said to have a particularly wide range of applications. 

LCA for the end-of-Ufe was used for seven plastic components that are commonly used in automotive applications. The parts included the bumper cover made from polypropylene (PP), windshield washer fluid container made from polyethylene (PE), air-intake manifold made from 30% glass-filled nylon, air duct made from 20% talk-filled PP, seat cushion made from polyurethane foam, head lamp lenses made from polycarbonate, and mirror housing made from acrylonitrile butadiene styrene (Jenseit et al. 2003). 

Outdoor use of polypropylenes has only become possible since the development of HALS light stabilizers. UV-stabilized polypropylene formulae can now be found in numerous injection molded parts, in particular in automotive applications and, e.g., in stadium seats. The market for UV-protected polypropylene fibers has developed significantly above average. Reference [546] provides a good overview of photo stabilization in polypropylene. 

Natural fiber reinforced polymer composites have attracted the attention of the research community [88] and extended to almost all the fields. Much work is done in the application of natural fiber as reinforcement in polymer composite [114]. Natural fibers are an attractive research area because they are eco-friendly, inexpensive, abundant and renewable, lightweight, have low density, high toughness, high specific properties, biodegradability and non-abrasive to processing characteristics, and lack of residues upon incineration [120, 119]. Natural fiber composites such as hemp fiber-epoxy, flax fiber-polypropylene (PP), and china reed fiber-PP are particularly attractive in automotive applications because of lower eost and lower density. 

TPO applications are in automotive bumpers and dashboards because of their higher toughness than conventional polypropylene copolymers. 

Borealis has developed a high-performance short glass fibre reinforced polypropylene (HPGF) family that has the technological and economical potential to replace long glass fibre (LFRT) in highly stressed parts for technical automotive applications. 

Compounds based on S—EB—S usually contain polypropylene, which improves solvent resistance and processibility and raises upper service temperatures. Compounds intended for use in the automotive industry are able to survive 1000 hours air exposure at temperatures of 125°C with only minor changes in properties (54). Very soft compounds have been developed to replace foam mbber for interior trim parts. In this and similar applications, these soft compounds are usually insert molded over polypropylene or metal and then coated with flexible polyurethane paint (55). Other automotive applications include products intended for sound deadening, flexible air ducts, and gear shifter boots, as well as improving the properties of sheet molding compounds. 

As a result of its saturated polymer backbone, EPDM is more resistant to oxygen, ozone, UV and heat than the low-cost commodity polydiene rubbers, such as natural rubber (NR), polybutadiene rubber (BR) and styrene-butadiene rubber (SBR). Therefore, the main use of EPD(M) is in outdoor applications, such as automotive sealing systems, window seals and roof sheeting, and in under-the-hood applications, such as coolant hoses. The main drawback of EPDM is its poor resistance to swelling in apolar fluids such as oil, making it inferior to high-performance elastomers, such as fluoro, acrylate and silicone elastomers in that respect. Over the last decade thermoplastic vulcanisates, produced via dynamic vulcanisation of blends of polypropylene (PP) and EPDM, have been commercialised, combining thermoplastic processability with rubber elasticity [8, 9]. 

These are physical blends of NR and polypropylene, mixed in different proportions to give mbbers with different stiffness properties. The method of dynamic vulcanization is possible in TPNR [15]. They are suitable for injection molding into products for automotive applications such as flexible sight shields and bumper components. Grafting is another method used for the modification of NR. The properties of PMMA-g-NR, PS-gg-NR, and PAN-g-NR have been analyzed by Thomas and co-workers [16, 17]. 

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