Relationships on the effect of water on glass transition temperature and young's modulus of nylon 6

The glass transition temperature Tg of nylon 6 decreases monotonically toward a finite value Tgl upon increase of the moisture content. The mechanism of this decrease entails the reversible replacement of intercaternary hydrogen bonds in the accessible regions of the polyamide. The limiting glass transition temperature Tgl is approached when the moisture content approaches Wl, which corresponds to the amount of water required for complete interaction with all accessible amide groups. Denoting with Tg0 the glass transition temperature of the dry polymer, the effect of water on Tg is represented by the equation, Tg = (ΔTg)0 exp{−[ln(ΔTg)0]W/τWl} + Tgl, where (ΔTg)0 = Tg0 −Tgl, and τ = W(Tgl+1)/Wl. This equation appears to be generally applicable to hydrophilic polymers, since correspondingly calculated data are also in very good agreement with experimental data for polymers such as nylon 66, poly(vinyl alcohol), and polyN-vinylpyrrolidone. The effect of water of Young's modulus E of nylon 6 is represented by an analogous relationship, and the quantity In[(E−El)/(Tg−Tgl)] is a linear function of the moisture content.