Water in polyurethane networks: physical and chemical ageing effects and mechanical parameters

Abstract The chemical structure, polymer mobility and mechanical properties are studied for a cross-linked amorphous poly(ether urethane) (PU) from glass transition to rubber elasticity juvenile dry samples water-saturated states after exposure humid air (r.h. = 29, 67, 95, 100%) at $$60~^\circ \hbox {C}$$ 60 ? C during 1 y of ageing. For saturated samples, network chain cleavage is the ageing mechanism, but it too weak slow affect on physical significantly within y. Water acts primarily in manner. Within d, $$\hbox {H}_{{2}}\hbox {O}$$ H 2 O molecules replace part urethane H-bonds by –urethane reduce all other interactions between chains solvating hydrophilic segments. Thus, cooperative strongly amplifies: gain specific conformational entropy doubles across caloric transition, which shifts ?17 K. A concentration only {c}_{{\mathrm{H}_2\mathrm{O}}}~\approx ~(0.4~\ldots ~0.5)~\hbox {c}_{\mathrm{\mathrm{H}_2\mathrm{O},max}}$$ c H O ? ( 0.4 … 0.5 ) , max suffices major these fast rearrangements. Some water slowly forms (during 3–4 months) finely dispersed water-rich mixed phase with PU chains. Except new phase, molecular processes damage-free deformation. shear modulus, $$\mu _{\mathrm{relaxed}}$$ ? relaxed (T), viscoelastic stress relaxation depends deformation-induced change—like elastic state. one month, drastically decreases response, as expected plasticisation. However, (T) slightly grows wet PU. cause opposite trends boosting (i.e. extension accessible space reduction energy barriers) occupation free volume compartments. quickly reduces fracture parameters about 50%. We explain that embrittlement -induced facilitation motions, let proceed less energy. In summary, our findings provide detailed conception effects {H}_{2}\hbox have network, they consequences properties.