Toughness and stiffness

Polyamides (nylon). There are several different types of nylon (e.g. nylon 6, nylon 66, nylon 11) but as a family their characteristics of strength, stiffness and toughness have earned them a reputation as engineering plastics. Table 1.3 compares the relative merits of light metal alloys and nylon. 

Acrylonitrile-butadiene-styrene (ABS). ABS materials have superior strength, stiffness and toughness properties to many plastics and so they are often considered in the category of engineering plastics. They compare favourably with nylon and acetal in many applications and are generally less expensive. However, they are susceptible to chemical attack by chlorinated solvents, esters, ketones, acids and alkalis. 

Polystyrene has a wide range of applications. Because it can be processed simply and efficiently to a great variety of articles, has an attractive combination of stiffness and toughness, is an outstanding electrical insulator, can be colored as desired and - above all - because the price was right, it has since 1950 conquered many more fields of application, ousted traditional materials and created many new uses for itself. A comparison of the applications in the U.S.A. in 1955 with those in Western Europe in 1979 conveys an idea of how the emphasis has shifted. 

While it was possible to produce sPP, employing the Zeigler-Natta solid systems, commercial sPP has only recently become commercial through the use of the soluble metallocene catalysts. These materials have a similar Tg as iPP, but they have a different balance between stiffness and toughness. 

Impact Modifiers. Notched impact strength and ductility can be improved with the incorporation of impact modifiers, which also can lower the britde— ductile transition temperature and give much improved low temperature toughness. Impact modifiers are rubbers (often olefin copolymers) that are either modified or contain functional groups to make them more compatible with the nylon matrix. Dispersion of the mbber into small (micrometer size) particles is important in order to obtain effective toughening (29). Impact modifiers can be combined with other additives, such as glass fiber and minerals, in order to obtain a particular balance of stiffness and toughness. 

Acrylonitrile-butadiene-styrene (ABS) and acrylonitrile-styrene-acry- late (ASA) are rubber-toughened plastics based upon the styrene-acrylonitrile (SAN) copolymer matrix. The combination of the stiffness and toughness exhibited by these materials has made them increasingly attractive in engineering applications, and the activity of the patent literature testifies to a continuing interest in improving properties through modifications of structure. The aim of this paper is to discuss a quantitative approach to structure-property relationships in ABS and ASA polymers. 

Isotactic polypropylene is a rather stiff and tough solid material with a melting point of 164°C. Closely packed, CHs-studded helices (Figure 17), rigidly interwoven in crystalline domains (Figure 18), account for the mechanical and thermal resistance of isotactic polymers. Syndiotactic polypropylene has a related crystalline structure, but atactic polymers are amorphous and form oily or waxy materials depending on chain lengths. 

First let s consider the mechanical properties of polymers treated as solids. By this we mean that we will discuss the usual properties, strength, stiffness and toughness, although not necessarily in that order. We ll... 

The testing of laminates for strength, stiffness and toughness is standardized using the same philosophy that holds for metals and polymers, i.e., the use of long and narrow specimens. This is a very reasonable approach for isotropic materials, as it minimizes the effects of stress concentrations. 

Everyone has been exposed to wood and its use in everyday life. The terms strong , stiff and tough are familiar words. However, such familiarity should not be... 

The blends could also contain inorganic fillers, other resins, elastomers, and additives. The materials had good impact and notched impact strength, combined with stiffness and toughness. They have been used for the same applications as new materials, instead of having to be downcycled [Timmermann et al., 1994]. 

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