Nylon also additives, effect

Chapters 10-12 are three chapters that address special areas of interpretation. Chapter 10 is focused on the interpretation of polymer spectra. Exercise Sections 1 and II have three exercises that involve the identification of relatively simple polymer spectra. These spectra were introduced to demonstrate to the reader that the extension of the group frequencies approach to the interpretation of polymer spectra is, in general, straightforward. However because of the importance of polymer spectra, we now consider this area in some detail in Chapter 10. Section I of the chapter builds on the interpretation of the spectra of hydrocarbon polymers started in exercise sections I and II. In section II the problem of the presence of plasticizers is examined and in addition the polymerization of hetero-atom monomers is explored. The sampling of polymers to acquire infrared and Raman spectra often requires specialized techniques. A short introduction to a few of these techniques is given in Section III. The chemistry involved in the formation of polymers is reviewed in part IV with examples of condensation (nylon) and addition (polyethylene) polymerization presented. Copolymers are examined next (V) with methylmethacrylate-stryene used as an example. The effects on the spectra of block and random copolymerization are also noted. Next crosslinked polymerization is studied (VI) with phenol-formaldehyde. Tacticity (VII) is then explored with evidence for its presence in the spectra of polypropylene. This discussion leads to a concise examination of conformational isomerism (VIII) and the impact of this... 

Other factors which can affect impact behaviour are fabrication defects such as internal voids, inclusions and additives such as pigments, all of which can cause stress concentrations within the material. In addition, internal welds caused by the fusion of partially cooled melt fronts usually turn out to be areas of weakness. The environment may also affect impact behaviour. Plastics exposed to sunlight and weathering for prolonged periods tend to become embrittled due to degradation. Alternatively if the plastic is in the vicinity of a fluid which attacks it, then the crack initiation energy may be reduced. Some plastics are affected by very simple fluids e.g. domestic heating oils act as plasticisers for polyethylene. The effect which water can have on the impact behaviour of nylon is also spectacular as illustrated in Fig. 2.80. 

Electrolytes are used to promote the exhaustion of direct or reactive dyes on cellulosic fibres they may also be similarly used with vat or sulphur dyes in their leuco forms. In the case of anionic dyes on wool or nylon, however, their role is different as they are used to facilitate levelling rather than exhaustion. In these cases, addition of electrolyte decreases dye uptake due to the competitive absorption of inorganic anions by the fibre and a decrease in ionic attraction between dye and fibre. In most discussions of the effect of electrolyte on dye sorption, attention is given only to the ionic aspects of interaction. In most cases, this does not create a problem and so most adsorption isotherms of water-soluble dyes are interpreted on the basis of Langmuir or Donnan ionic interactions only. There are, however, some observed cases of apparently anomalous behaviour of dyes with respect to electrolytes that cannot be explained by ionic interactions alone. 

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. 

Sulfides. In addition In serving as the primary natural source of molybdenum, purified molybdenum disullide MoS is an excellent lubricant when in Ihc form of a dry him. or as an additive to oil or grease. The compound also is used as a filter in nylons, and as an effective catalyst for hydrogenation-dehydrogenation reactions. Molybdenum also combines with sulfur as Ihe sesquisullide Mo Si and the trisulftde MoS.r, uses for which arc under study. 

The toughness of an epoxy-nitrile adhesive is nearly equivalent to that of an epoxynylon adhesive. However, the epoxy-nitrile system has much better hydrolytic stability. Also, the low-temperature properties of an epoxy-nitrile adhesive are superior to those of epoxy-nylon adhesive. Table 7.3 illustrates the effect of nitrile addition on tensile shear and peel strength. 

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