Modelling the non Fickian water absorption in polyamide 6

Abstract

This paper investigates the water absorption of polyamide 6. The high amount of absorbed water in the polymer and the large resulting decrease in the glass transition temperature (Tg) leads to a non Fickian water diffusion when samples are immersed, which is a significant difficulty when trying to model the water profile in thick specimens. The aim of this study is to be able to model this particular behaviour based on physical considerations. First, it is shown that the non Fickian water diffusion is caused by an increase in the diffusivity during water absorption. Two cases are then identified; one below Tg where the diffusivity is described using an Arrhenius law and one above Tg based on the free volume theory. Then, these two laws are implemented in a specific model that is able to describe the non Fickian water diffusion over a wide range of temperatures.

Influence of water on the short and long term mechanical behaviour of polyamide 6 (nylon) fibres and yarns

“…Water uptake in the Nylon 6 appears to follow Henry's law for low water activity (below a=0.5), for higher activity water quantities deviate from this law. Similar results were observed in previous studies of bulk polyamide [6], [17]. These studies showed that the deviation is due to cluster creation inside the material, and it appears to be controlled by the Eq.…”

“…Then, we subtract the linear term from the initial maximal moisture content and identify b and m over the second part of the curve. These parameters appear to be independent of the temperature as previously shown in [6], [17]. In the case of Nylon 6 fibres we obtain the following parameters: H 0 = 1.39; E a = -7kJ.mol -1 ; b = 3; m = 7.…”

“…The theoretical enthalpy of fusion of 100% crystalline polyamide 6 was taken as 188 J/g (value from [6]). Using this value and the ΔH f obtained by DSC, a degree of crystallinity of 40.1% was determined.…”

“…5, with C ∞ (a) and a the water activity. It has been shown that H can be represented by an Arrhenius law characterised by a preexponential factor H 0 and activation energy E a [6], [17] ∞ ( ) = . + .…”

“…Various authors have examined the influence of water on bulk nylon properties. For example, Arhant et al presented a water diffusion model which accounted for the change in water uptake due to the passage from the glassy to the rubbery state during wet aging [6]. Experimental examination of the rates of transport of liquid water along a wide variety of yarns supports the view that water travel occurs essentially by capillary action [7].…”