Chapter 15. Automotive Components Composed of Polyolefins
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Automotive components composed of polyolefins 15 Rotimi Sadiku1, David Ibrahim1, Oluranti Agboola1,2, Shesan J. Owonubi1,3, Victoria O. Fasiku3, Williams K. Kupolati1, Tamba Jamiru1, Azunna A. Eze1, Oludaisi S. Adekomaya1, Kokkarachedu Varaprasad1,4, Stephen C. Agwuncha1, Abbavaram B. Reddy1, Bandla Manjula1, Bilainu Oboirien5, Clara Nkuna1, Mbuso Dludlu1, Adetona Adeyeye1, Tobi S. Osholana1, Goitse Phiri1, Olayinka Durowoju1, Peter A. Olubambi6, Frank Biotidara7, Mercy Ramakokovhu1, Brendon Shongwe1 and Vincent Ojijo8 1Tshwane University of Technology, Pretoria, South Africa, 2University of South Africa, Johannesburg, South Africa, 3North-West University, Mmabatho, South Africa, 4Centro de Investigacio´ n de Polı´meros Avanzados, Concepcio´ n, Chile, 5CSIR Materials Science & Manufacturing, Pretoria, South Africa, 6University of Johannesburg, Johannesburg, South Africa, 7Yaba College of Technology, Lagos, Nigeria, 8Council for Scientific and Industrial Research, Pretoria, South Africa 15.1 Introduction: brief survey of polyolefin resins and their general properties The last three and half decades have witnessed tremendous growth in the quantity of polyolefin materials employed by the automotive industry. This is as a result of the several technological breakthroughs (such as the catalloy process technology of Basell), which have, unwittingly, extended the useful properties and potential range of polyolefins: polymers derived from hydrocarbon molecules that possess one or more alkenyl (or olefinic) groups. Typically, the term polyolefin refers to polymers derived from ethylene, propylene, and other α-olefins, isobutylene, cyclic olefins and butadiene, and other diolefins. Polyolefins are the largest group of thermoplastics, often referred to as commodity thermoplastics; they are polymers of simple olefins, such as ethylene, propylene, butenes, isoprenes, and pentenes, and copolymers and their modifications. The term polyolefins means “oil-like” and refers to the oily or waxy feel that these materials have. Polyolefins consist only of carbon and hydrogen atoms and they are nonaro- matic. Usually, extrusion, injection molding, blow molding, or rotational molding methods are used to process polyolefins. However, thermoforming, extrusion, calendaring, and compression molding techniques are used to a lesser degree. Inherent characteristics common to all polyolefins are that they are nonpolar, Polyolefin Fibres. DOI: http://dx.doi.org/10.1016/B978-0-08-101132-4.00015-1 Copyright © 2017 Elsevier Ltd. All rights reserved. 450 Polyolefin Fibres nonporous, and their low-energy surface that is not receptive to inks and lacquers without special oxidative pretreatment. The two most important and common poly- olefins are polyethylene (PE) and polypropylene (PP) and they are very popular because of their low cost and wide range of applications. The family of polyolefins is made up of semicrystalline and amorphous polymers and also copolymers—all are used as commodity plastics, engineering plastics, and elastomers. Their chemical structures, molecular weights, stereoregularities, and crystallinities differ substantially in some cases. Resins from these polymers are manufactured using a number of technological processes. These processes include radical initiator polymerization of ethylene at temperatures between 160C and 360C, catalytic polymerization processes in hydrocarbon slurry, in a neat monomer, in solution and gas phase, using ZieglerÀNatta catalysts, chromium oxide-based catalysts, and metallocene catalysts [1À6]. There are a large number of polyolefin applications, but emphasis will be laid on their uses in the automotive sector. The world’s largest commercially manufactured polymer products, which total about half of the world consumed plastics, are made from polyolefin resins; this is as a result of their versatility [7]. Table 15.1 provides the total amount of polymers used in auto- mobile production and Fig. 15.1 represents the share of thermoplastics for the interior of an automobile. Homopolymers made from the family of polyolefin come from the monomers: ethylene, propylene, butylene, and methyl pentene. Other olefin monomers such as pentene, hexane, and octene are used to make copolymers. Linear α-olefins are a range of industrially important α-olefins that include 1-butene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, and higher blends of C20ÀC24,C24ÀC30, and C20ÀC30 ranges. Table 15.1 Polymer fractions in use for automobile parts [8] Parts Main type Weight in average of plastic car (kg) Bumpers PP, ABS, PC 10 Seats PUR, PP, PVC, ABS, PA 13 Dashboard PP, ABS, PA, PC, PE 15 Fuel systems PE, POM, PA, PP 7 Body (including body panels) PP, PPE, PBT 6 Interior trim PP, ABS, PET, POM, PVC 20 Electrical components PP, PE, PBT, PA, PVC 7 Lighting PP, PC, ABS, PMMA, UP 5.0 Upholstery PVC, PUR, PP, PE 8.0 Exterior trim ABS, PA, PBT, ASA, PP 4 Under-the-hood components ABS, PA, PBT, ASA, PP 9 Other reservoirs PP, PE, PA 1.0 Total 105 Automotive components composed of polyolefins 451 Figure 15.1 The shares of the various thermoplastics in the automotive interior, with PP having about 50% usages [7]. 15.1.1 1-Butene (butylene) There are four isomers of alkenes, which have the chemical formula C4H8, but dif- ferent structures. The IUPAC (and common) names, respectively, are but-1-ene (α-butylene), cis-but-2-ene (cis-β-butylene), trans-but-2-ene (trans-β-butylene), and 2-methylpropene (isobutylene). As a result of the double bonds, these four-carbon alkenes can act as monomers in the formation of polymers and have other uses as petrochemical intermediates. They are used in the production of synthetic rubber. But-1-ene is a linear or normal α-olefins and isobutylene is a branched α-olefin. In a rather low percentage, but-1-ene is used as one of the comonomers, along with other α-olefins, in the production of high-density polyethylene (HDPE) and linear low-density polyethylene (LLDPE). Butyl rubber is made by cationic polymeriza- tion of isobutylene with between 2% and 7% isoprene. Isobutylene is also used for the production of methyl tert-butyl ether (MTBE) and isooctane, both of which improve the octane rating/combustion of gasoline used to power automotive. 15.1.2 1-Hexene and 1-octene These are higher olefins or alkenes, with formulae C6H12 and C8H16, respectively. They are α-olefins, meaning that the double bond is located at the α (primary) posi- tion, endowing these compounds with higher reactivity and thus useful chemical properties. They are industrially important linear α-olefins. The overwhelming use of these two olefins is as comonomers in production of PE. HDPE and LLDPE use approximately 2%À4% and 8%À10% of comonomers, respectively. The chemical and electrical properties of all olefins are similar; hence they often compete for the same applications. Their crystalline structures differ from each other, sometimes significantly. However, since the strength properties vary with the 452 Polyolefin Fibres type and degree of crystallinity, the tensile, flexural, and impact strength of each polyolefin may be quite different. Stress-crack resistance and useful temperature range also vary with crystalline structure. Apart from the solid polyolefin resins, these materials are also available as beads from which very low-density foam shapes and blocks are produced. Their resilience and energy absorption (EA) characteristics are excellent when compared with those of conventional polystyrene (PS) foams. Polymers available as moldable beads include PE, PP, and a PE/PS copolymer alloy. The same methods used for the pro- cessing of expandable polystyrene (EPS) can also be employed for the processing of the bead forms of polyolefins. Following the expansion of the beads (usually B40 times that of the solid resins), they are poured into a mold and heated by direct injection of stream. This softens, expands further, and fuses the particles together, forming a uniform, free of void, closed-cell shape. After holding, the shapes are usually annealed and stored at a temperature of 50À70C to stabilize the shape and dimensions of the foams. With a volume of about 90% air, the foamed shapes are not quite as strong as solid moldings. They find applications primarily to cushion impact, insulate the rally, and provide high stiffness-to-weight materials in composite components. For instance, a 10 cm thick section of foam can absorb the energy of an 8 km/h impact. Other applications of PE and PP foams include package cushioning for fragile and valuable products such as electronic or auto component. The toughness of PE/PS alloy foams allows them for material-handling applications where repeated use is required. The two main resins of the polyolefin family are PE and PP. Other polyolefin polymers and their copolymers include ethylene vinyl acetate (EVA), ionomer, polybutylene, polymethyl pentene, and polydicyclopentadiene. Polyolefins are suitable candidates to substitute polyvinylchloride (PVC) in a num- ber of applications, including automotive interiors, where thermoplastic olefins (TPOs) show up prominently as a leading contender and also, functional polyolefins (EVA, PE (LD, LLD, and HD), and ethylene butyl acrylate, and ethylene methyl acrylate, EMA, and their copolymers), as wire and cable compounds, both in low (,1 kV) and medium-high ( .1À600 kV) voltage cabling. This group of polyolefin can be coupled by an agent or filler such as alumina trihydrate (ATH) and magne- sium hydroxide (Mg[OH]2) to produce a halogen-free,