Nylon humidity effects

The nylons are reasonably good electrical insulators at low temperatures and under conditions of low humidity but the insulation properties deteriorate as humidity and temperature increase. The effects of the amount of absorbed water on the volume resistivity of nylon 66 is shown in Figure 18.15. This effect is even greater with nylon 6 but markedly less with nylon 11. Some typical electrical properties of the nylons are given in Table 18.5. 

Figure 18.16. Effect of relative humidity on the water ab.sorption of the nylons...

Not only is low tensile shear strength noticed on moisture aging, but also the mode of failure changes from one of cohesion to adhesion. Table 7.6 shows the effect of humidity and water immersion on an epoxy-nylon adhesive compared to a nitrile-phenolic adhesive. Substrate primers have been used with epoxy-nylon adhesives to provide improved moisture... 

TABLE 7.6 Effect of Humidity and Water Immersion on the Tensile Shear Strength of Epoxy-Nylon and Nitrile-Phenolic Adhesives 10... 

Researchers have examined the creep and creep recovery of textile fibers extensively (13-21). For example, Hunt and Darlington (16, 17) studied the effects of temperature, humidity, and previous thermal history on the creep properties of Nylon 6,6. They were able to explain the shift in creep curves with changes in temperature and humidity. Lead-erman (19) studied the time dependence of creep at different temperatures and humidities. Shifts in creep curves due to changes in temperature and humidity were explained with simple equations and convenient shift factors. Morton and Hearle (21) also examined the dependence of fiber creep on temperature and humidity. Meredith (20) studied many mechanical properties, including creep of several generic fiber types. Phenomenological theory of linear viscoelasticity of semicrystalline polymers has been tested with creep measurements performed on textile fibers (18). From these works one can readily appreciate that creep behavior is affected by many factors on both practical and theoretical levels. 

Nylon fibers are used extensively in outdoor textiles and as a result are subject to sunlight, varying temperatures and acid precipitation. The degradation of nylon by light, heat, humidity and air polluted with sulfur dioxide has been widely studied (8-13). However, little data is available on the effect of aqueous acid on nylon in the presence of heat, light and moisture (i.e. acid rain conditions). Therefore, the purpose of this work was to determine the effect of acid rain conditions on nylon. The synergistic effects of aqueous acid, light and heat on nylon were also examined. 

All of these accelerating effects were found to occur only in the presence of light. Since acid alone is also known to degrade nylon (12, 13) it is reasonable to suspect a synergistic action by light, humidity, heat, and aqueous acid (i.e. acid rain conditions) on the chemical and physical properties of the nylon fabric. 

The combined effect of acid, heat, and humidity without light on the breaking strength of nylon fabric is presented in... 

The sorption of water by nylon has a major effect on properties of engineering and scientific importance. In molded 66 nylon at room temperature, the modulus decreases by about a factor of five, the yield stress decreases by more than half, and there are major Increases in the elongation and energy to break as the water content is Increased from dryness to saturation ( ). Thus, reported properties of nylon are frequently those of a mixture of nylon and water. It is important to specify the water content or the relative humidity with which the polymer is in equilibrium. 

Because of the presence of amide groups, the nylons absorb water. Figure 4.14 shows how the equilibrium water absorption of different nylons varies with humidity at room temperature, and Figure 4.15 shows how the rate of moisture absorption of nylon-6,6 is affected by the environmental conditions. Since dimensional changes may occur as a result of water absorption this effect should be considered when dimensional accuracy is required in a specific application. Manufacturers commonly supply data on the dimensional changes of their products with ambient humidity. 

I The effect of humidity also can be significant with certain plastics when the Innahanical strength, and in particular the impact strength, depends on the Ipioant of water absorbed (i.e., a typical example is nylon). 

When A = 1, this expression reduces to Langmuir s equation for monomolecular adsorption. If 0 < A < 1, there is a finite maximum hygroscopic moisture content. While many textile fibers approach such a moisture content asymptotically at high relative humidities, some man-made fibers such as nylon and viscose appear to have well-defined maximum hygroscopic moisture contents [9]. In many cases, the coefficient k is greater than 1. Jaafar and Michalowski [8] interpret this behavior as the thermal effect of adsorption being equal to the heat of condensation only after a multimolecular layer has been formed. 

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