The aim of the present work was to study the effect of the composition and operating conditions on the properties of nanostructured polyamide blends obtained by reactive extrusion. The ultimate objective consisted in optimizing the high impact energy of these materials using an experimental design based on the D-optimality and rotatability criteria. A thermodynamic approach of relaxation phenomena called distribution of nonlinear relaxations (DNLR) was proposed to account for the nonlinear mechanical behaviour of the obtained polyamide blends for different compositions and extrusion conditions. Five parameters of the DNLR law have thus been modelled as functions of these operating conditions using quadratic polynomial relations. The accuracy of this modelling was evaluated by establishing some comparison between the experimental data and the predictive results and by performing statistical tests. (c) 2008 Elsevier Ltd. All rights reserved.