Mckeen The Effect of Creep and Other Time Related Factors on Plastics and Elastomers

2. Auflage 2009
ISBN: 978-0-8155-1981-2
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: 6 - ePub Watermark

E-Book, Englisch, 427 Seiten

Reihe: Plastics Design Library

The second edition of the classic data book, The Effect of Creep and Other Time Related Factors on Plastics and Elastomers (originally published in 1991), has been extensively revised with the addition of an abundance of new data, the removal of all out-dated information, and the complete rebuilding of the product and company listings. This new edition also has been reorganized from a polymer chemistry point of view. Plastics of similar polymer types are grouped into chapters, each with an introduction that briefly explains the chemistry of the polymers used in the plastics. An extensive introductory chapter has also been added, which summarizes the chemistry of making polymers, the formulation of plastics, creep-testing, test methods, measurements, and charts, as well as theory and plastic selection. Each chapter is generally organized by product and concludes with comparisons of brand or generic products. The appendices include a list of trade names, plastics sold under those names, and manufacturer. A list of conversion factors for stress measures is also included. ABOUT THE AUTHOR Laurence W. McKeen earned a B.S. in Chemistry from Rensselaer Polytechnic Institute in 1973 and a Ph.D. in 1978 from the University of Wisconsin. He began his career with DuPont in 1978 as a mass spectroscopist, but moved into product development in the Teflon® Finishes group in 1980. Dr. McKeen has accumulated over 28 years of experience in product development and applications, working with customers in a wide range of industries, which has led to the creation of dozens of commercial products.
More than 8 core chapters, which serve as a databank for evaluating the creep of plasticsOver 600 uniform graphs for more than 45 generic families of plastics are explainedTypes of graphs include: (1) Isochronous Stress-Strain Curves at Various Times and Temperatures (2) Creep Strain or Creep Deformation versus Time at Various Stress Levels and Temperatures (3) Various Modulus Measures (Tensile, Compressive, Flexural) versus Time at Various Temperatures (4) Hoop Stress versus Time at Various Temperatures (5) Stress Cracking and Other Plastics Failure versus Time (6) Creep Rupture versus Time

Autoren/Hrsg.

Mckeen, Laurence W.

Leseproben

Chapter 2
Styrenic Plastics
2.1 Background
This chapter on styrenic plastics covers a broad class of polymeric materials of which styrene is an important part. Styrene, also known as vinyl benzene, is an organic compound with the chemical formula C6H5CH=CH2. Its structure is shown in Fig. 2.1. Figure 2.1. Chemical structure of styrene. Styrene is used as a monomer to make plastics such as polystyrene, ABS, styrene-acrylonitrile (SAN), and the other polymers discussed in this chapter. 2.1.1 Polystyrene
Polystyrene is the simplest plastic based on styrene. Its structure is shown in Fig. 2.2. Figure 2.2. Chemical structure of polystyrene. Pure solid polystyrene is a colorless, hard plastic with limited flexibility. Polystyrene can be transparent or can be made in various colors. It is economical and is used for producing plastic model assembly kits, plastic cutlery, CD “jewel” cases, and many other objects where a fairly rigid, economical plastic is desired. Polystyrene’s most common use, however, is as expanded polystyrene (EPS). EPS is produced from a mixture of about 5–10% gaseous blowing agent (most commonly pentane or carbon dioxide) and 90–95% polystyrene by weight. The solid plastic beads are expanded into foam by the use of heat (usually steam). The heating is carried out in a large vessel holding 200–2,000 liters. An agitator is used to keep the beads from fusing together. The expanded beads are lighter than the unexpanded beads, so they are forced to the top of the vessel and removed. This expansion process lowers the density of the beads to 3% of their original value and yields a smooth-skinned, closed cell structure. Then the pre-expanded beads are usually “aged” for at least 24 hours in mesh storage silos. This allows air to diffuse into the beads, cooling them and making them harder. These expanded beads are excellent for detailed molding. Extruded polystyrene (XPS), which is different from EPS, is commonly known by the trade name Styrofoam™. All these foams are not of interest in this book. One of the most important plastics is high impact polystyrene (HIPS). This is a polystyrene matrix that is imbedded with an impact modifier, which is basically a rubber-like polymer such as polybutadiene. This is shown in Fig. 2.3. Figure 2.3. The structure of high impact polystyrene. 2.1.2 Acrylonitrile-Styrene-Acrylate (ASA)
ASA is the acronym for acrylate rubber modified styrene acrylonitrile copolymer. ASA is a terpolymer that can be produced either by a reaction process of all three monomers or by a graft process. ASA is usually made by introducing a grafted acrylic ester elastomer during the copolymerization of styrene and acrylonitrile, known as SAN. SAN is described in the next section of this chapter. The finely divided elastomer powder is uniformly distributed and grafted onto the SAN molecular chains. The outstanding weatherability of ASA is due to the acrylic ester elastomer. ASA polymers are amorphous plastics, which have mechanical properties similar to those of the ABS resins described in Section 2.1.4. However, the properties of ASA are far less affected by outdoor weathering. ASA resins are available in natural, off-white, and a broad range of standard and custom-matched colors. ASA resins can be compounded with other polymers to make alloys and compounds that benefit from ASA’s weather resistance. ASA is used in many products including lawn and garden equipment, sporting goods, automotive exterior parts, safety helmets, and building materials. 2.1.3 Styrene-Acrylonitrile (SAN)
Styrene and acrylonitrile monomers can be copolymerized to form a random, amorphous copolymer that has good weatherability, stress crack resistance, and barrier properties. The copolymer is called styrene-acrylonitrile or SAN. The SAN copolymer generally contains 70–80% styrene and 20–30% acrylonitrile. It is a simple random copolymer. This monomer combination provides higher strength, rigidity, and chemical resistance than polystyrene, but it is not quite as clear as crystal polystyrene and its appearance tends to discolor more quickly. The general structure is shown in Fig. 2.4. Figure 2.4. Chemical structure of styrene-acrylonitrile. SAN is used for household goods and tableware, in cosmetics packaging, sanitary and toiletry articles as well as for writing materials and office supplies. 2.1.4 Acrylonitrile-Butadiene-Styrene (ABS)
Acrylonitrile-butadiene-styrene (ABS) is a common thermoplastic used to make light, rigid, molded products such as pipes, automotive body parts, wheel covers, enclosures, and protective head gear. SAN copolymers have been available since the 1940s and while their increased toughness over styrene made them suitable for many applications, their limitations led to the introduction of a rubber, butadiene, as a third monomer producing the range of materials popularly referred to as ABS plastics. These became available in the 1950s and the availability of these plastics and the ease of processing led to ABS becoming one of the most popular of the engineering polymers. The chemical structures of the monomers are shown in the Fig. 2.5. The proportions of the monomers typically range from 15% to 35% acrylonitrile, 5% to 30% butadiene, and 40% to 60% styrene. It can be found as a graft copolymer, in which the SAN polymer is formed in a polymerization system in the presence of the polybutadiene rubber latex; the final product is a complex mixture consisting of SAN copolymer, a graft polymer of SAN and polybutadiene, and some free polybutadiene rubber. Figure 2.5. Chemical structures of ABS raw materials. 2.1.5 Methyl Methacrylate-Acrylonitrile-Butadiene-Styrene (MABS)
Methyl methacrylate-acrylonitrile-butadiene-styrene (MABS) is a new modification of ABS. It is sometimes called transparent ABS, a copolymer of methyl methacrylate, acrylonitrile, butadiene, and styrene. The key properties of MABS are excellent transparency, high impact strength, and good chemical resistance. This is an exceptional combination of properties for an impact-modified thermoplastic. MABS can be used to create particularly brilliant visual effects such as very deep colors and pearly or sparkle effects. It is easy to process and can also be printed upon. 2.1.6 Styrene-Maleic Anhydride (SMA)
The copolymerization of styrene with maleic anhydride creates a copolymer called styrene-maleic anhydride (SMA). This reaction is shown in Fig. 2.6. SMA has a higher glass transition temperature than polystyrene and is chemically reactive because of active functional groups. Thus, SMA polymers are often used in blends or composites where interaction or reaction of the maleic anhydride group provides for desirable interfacial effects. The reaction of the anhydride with primary amines is particularly potent. Figure 2.6. The production of styrene-maleic anhydride. 2.1.7 Styrenic Block Copolymers (SBCs)
Styrenic block copolymer (SBC) is a commercially important thermoplastic elastomer. The polymer is made of three separate polymeric blocks (see Section 1.4.2 for an explanation of block copolymers). At one end is a hard polystyrene block, in the middle a long polybutadiene (or other elastomeric) block, followed by a second hard block of polystyrene. These blocks are immiscible, so they form discrete domains of polystyrene within a polybutadiene matrix. The separate domains are chemically connected. This is shown in Fig. 2.7, where one might notice that the structure looks a lot like HIPS, except that the continuous phase and the hard discrete phase are switched in SBC and the domains are connected. One additional property of interest is that some SBCs blend well with general-purpose polystyrene, allowing customization of properties. Figure 2.7. The “microscopic” structure of styrenic block copolymers. 2.1.8 Blends
While the number of styrenic blends might seem limitless, compatibility and morphology limit blend types. Styrenic blends are numerous but most are limited to only a couple of types. The most important blend is ABS and polycarbonate (PC). Next in importance is ABS and polyamide (PA) (or nylon). Polystyrene and polyethylene are often used in expandable foams. Polystyrene and polyphenylene ether (PPE or PPO) are commercially important blends, which are covered in a later chapter. The other classes of the styrenic blends are not major product lines but can be very important in some applications. 2.2 Polystyrene (PS)
2.2.1 BASF Polystyrol 143 E—Medium Strength, Easy Flowing General-Purpose Grade PS Resin
Figure 2.8. Isochronous stress–strain at 23°C of Polystyrol 143 E. Figure 2.9. Creep modulus versus time at 23°C of Polystyrol 143 E. 2.2.2 BASF Polystyrene 454 C—Impact Resistant PS Resin
Figure 2.10. Isochronous stress–strain at 23°C of Polystyrene 454 C. Figure 2.11. Isochronous stress–strain at 40°C of Polystyrene 454 C. Figure 2.12. Isochronous...