Plastic classification thermoplastics

Chapters 10 to 29 consisted of reviews of plastics materials available according to a chemical classification, whilst Chapter 30 rather more loosely looked at plastics derived from natural sources. It will have been obvious to the reader that for a given application plastics materials from quite different chemical classes may be in competition and attempts have been made to show this in the text. There have, however, been developments in three, quite unrelated, areas where the author has considered it more useful to review the different polymers together, namely thermoplastic elastomers, biodegradable plastics and electrically conductive polymers. 

ISO 4433-4 1997 Thermoplastics pipes - Resistance to liquid chemicals - Classification -Part 4 Poly(vinylidene fluoride) (PVDF) pipes ISO 9393-2 1997 Thermoplastics valves - Pressure test methods and requirements - Part 2 Test conditions and basic requirements for PE, PP, PVC-U and PVDF valves ISO 10931-1 1997 Plastics piping systems for industrial applications - Poly(vinylidene fluoride) (PVDF) - Part 1 General... 

The broadest classification for plastics is the old thermoplastic and thermosetting . Examples of the former group are polyethylene, polystyrene, and poly-(methyl methacrylate) examples of the latter are urea-formaldehyde condensation polymers, powder coatings based on polyesters, epoxy resins, and vulcanized synthetic elastomers. 

Figure 12 represents all steps of craze formation in crystalline polymers in a single model. It is based on Hornbogen s model for a crack tip in a polymer crystal, under the utilization of individual block drawings by Schultz for the fine scale nature of plastic deformation in semicrystalline thermoplastics. The classification into four regions A to D (after ) helps to describe and imderstand the influence of molecular parameters on craze strength and craze breakdown. 

Polymers can be classified in many ways, such as by source, method of synthesis, structural shape, thermal processing behavior, and end use of polymers. Some of these classifications have already been considered in earlier sections. Thus, polymers have been classified as natural and synthetic according to source, as condensation and addition (or step and chain) according to the method of synthesis or polymerization mechanism, and as linear, branched, and network according to the structural shape of polymer molecules. According to the thermal processing behavior, polymers are classified as thermoplastics and thermosets, while according to the end use it is convenient to classify polymers as plastics, fibers, and elastomers (Rudin, 1982). 

The Shore A scale, or as it is sometimes called, durometer hardness, enjoys considerable success in North America and in particular is widely accepted by the automotive industry the scale is an integral part of the classification system for elastomeric materials used in automotive applications (ASTM D2000). Shore hardness has also become the industry standard for the rapidly growing thermoplastic rubber sector, where advantage can be taken of the complementary Shore D scale for harder grades and for rubber-modified plastics. Seven Shore scales are described in ASTM D2240, while Shore A and D hardness are also detailed in the international standard for pocket hardness meters. ISO 7619 (BS903. Part A57). The latter also specifies a pocket meter based on the IRHD scale. 

In the broad classification of plastics there are two generally accepted categories thermoplastic resins and thermosetting resins. 

Further classification of polymers in the groups of additional polymers and condensation polymers has been on monomer composition, because this provides an orderly approach, whereas classification based on polymer uses, such as plastics, elastomers, fibers, coatings, etc. would result in too much overlap. For example, polyamides are used not only as synthetic fibers but also as thermoplastics molding compounds and polypropylene, which is used as a thermoplastic molding compound has also found uses as a fiber-forming material. 

It is not possible to discuss here the special properties of all the different types of plastic materials that can occur within these three groups. The plastics industry today, by employing copolymerization or chemical modification, is capable of producing an extraordinary number of combinations of properties, making the identification of corresponding plastics more complicated. Its physical appearance and its classification as a thermoplastic, thermoset, or elastomer therefore permit us to draw conclusions about the chemical nature of the plastic only in simple cases. But they often provide a useful additional way of characterizing the material. 

The family of plastics is classified several ways. The two major classifications are thermoplastics (TPs) and thermosets (TSs). Over 90wt% of all plastics used are TPs. The TPs and TSs in turn are classified as commodity or engineering plastics (CP and EP). Commodities such as polyethylenes (PEs), polyvinyl chlorides (PVCs), polypropylenes (PPs),... 

As technology advances, materials have been developed which evade the above classification. Mixtures of thermoplastics and thermosetting resins have been developed in which the thermoplastics material acts as a toughening agent for the thermosetting resin. Alloys or blends of two or more thermoplastics, or of plastics and rubbers, are becoming commonplace. 

As shown in Fig. 1, plastics are classified as thermoplastics, elastomers, and duroplastics. In practice, classification is made in accordance with a number of different aspects. In Fig. 1, thermoplastics are categorized in physical terms (according to stmcture), elastomers in chemical terms (double bond), and duroplas-tics according to process pressure. 

Figure 5 shows the structural model for elastomers. Table 3 presents the classification and applications of elastomers. TPE are two-phase or multiphase plastics (block copolymers) with elastic properties similar to those of elastomers, but with a melting temperature that allows for processing as with thermoplastics. Figure 6 illustrates the classification of TPE. 

Fig. 17.15. Classification of i-PP samples prepared with different catalysts, as stiff-plastic materials, fiexible-plastic materials, and thermoplastic elastomers depending on concentration of rr defects of stereoregulaiity and Young s modulus (E)...

Figure 8.2 Classification of thermoplastics. Source Laura Pugliese, Defining Engineering Plastics, Plastics Machining and Fabrication, January-February, 1999, Courtesy DSMEngineering Plastic Products.)...

SAE J2273, Classification System for Automotive Thermoplastic Polyester Plastics. ... 

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