Pulsed n.m.r. studies of molecular motion in wet nylon-6,6 fibres

The influence of water molecules on molecular motion in commercial nylon-6,6 fibres has been investigated by pulsed n.m.r. techniques. Transient n.m.r. signals, T₂ and T₁ relaxation times for the fibre protons were measured as a function of temperature and moisture (D₂O) content. Above the glass transition temperature, T_g, of the fibre, separation of the signal into two components, a ‘rigid’ and ‘non-rigid’ fraction, was possible. For wet fibres, the temperature at which the ‘non-rigid’ or ‘mobile’ component appeared was reduced as the water content was increased and the ‘mobile fraction’ increased with temperature. This behaviour is explained in terms of the mobilization of amorphous chain segments above the T_g and their ability to be ‘plasticized’ by water molecules. The effect of D₂O molecules and paramagnetic Mn²⁺ ions on T₁ relaxation of rigid and mobile segments provided further information on the properties of accessible chain segments between and on the crystallite surfaces. A chain folded model of semi-crystalline morphology has been adopted throughout the discussion.