General Properties of the Nylons

Typical mechanical properties of some commercial grades of nylon are given in Table 18.1. 

Laboratory tests and experience during use have demonstrated that the nylons have extremely good abrasion resistance. This may be further improved by addition of external lubricants and by processing under conditions which develop a highly crystalline hard surface e.g. by use of hot injection moulds and by annealing in a non-oxidising fluid at an elevated temperature (150-200°C for nylon 66). 

The coefficients of friction of the nylons are somewhat higher than the acetal resins (Chapter 19). Results obtainable will depend on the method of measurement but typical properties are given in Table 18.2.  

The effect of lubricants on the kinetic coefficient of friction of nylon 66 (like surfaces) is shown in Table 18.3  

The glass transition temperatures of the nylons appear to be below room temperature so that the materials have a measure of flexibility in spite of their high crystallinity under general conditions of service. The polymers have fairly sharply defined melting points and above this temperature the homopolymers have low melt viscosities. Some thermal properties of the nylons are given in Table 18.4. 

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The forementioned rules also hold for other physical properties of aliphatic nylons since the odd-even effect comes from crystallinity. The physicochemical properties of the nylons, such as tensile strength, density, hardness and rigidity, creep resistance, resistance to hydrocarbons, and water absorption, are generally increased as the length of flexible methylene spacer is decreased. In contrast, the nylons become more soft, flexible, and less hydrophilic with increase in the spacer length. The correct choice of methylene units in the spacer will produce a wide range of properties to meet diverse requirements in various industrial fields. 

To accommodate the various uses in 100% form and in blends, the tenacities and elongations of the nylon staple offerings range from 0.3 to 0.6 N /tex (3—7 g/den) and from 50 to 100% elongation. Most other fiber properties of nylon staple differ tittle from those of the continuous filament property characteristics of nylon-6 and nylon-6,6 are similar (see Polyamides, general). 

A variety of polymers, both thermosets as well as thermoplastics, can be blended and coreacted with epoxy resins to provide for a specific set of desired properties. The most common of these are nitrile, phenolic, nylon, poly sulfide, and polyurethane resins. At high levels of additions these additives result in hybrid or alloyed systems with epoxy resins rather than just modifiers. They differ from reactive diluents in that they are higher-molecular weight-materials, are used at higher concentrations, and generally have less deleterious effect on the cured properties of the epoxy resin. 

The chapters devoted to structure-permeability properties of the more commercially advanced amorphous nylons (Chapter 5 (50)) and experimental polycarbonates (Chapter 7 (51)) illustrate many of the general principles needed for optimizing the barrier properties of essentially any polymer family. These chapters consider the importance of intersegmental packing and intrasegmental mobility on... 

Table 1 provides average properties on Nylon-6. In reviewing the general properties of this polymer, note the use of the following legend A = amorphous -Cr = crystalline - C = clear - E = excellent - G = good - P = poor - O = opaque - T = translucent- R = Rockwell - S = Shore. 

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