J. Verdu

KINETIC MODELLING OF MACROSCOPIC PROPERTIES CHANGES DURING CROSSLINKED POLYBUTADIENE OXIDATION

The thermal oxidation of additive free hydroxyl‐terminated polybutadiene (HTPB) isocyanate crosslinked rubber bulk samples has been studied at 80, 100 and 120u2009°C in air. The oxidation kinetics has been monitored by gravimetry and thickness distribution of oxidation products was determined by FTIR mapping. Changes of elastic shear modulus G’ during oxidation were followed during oxidation at the same temperatures. The kinetic model established previously for HTPB has been adapted for bulk sample oxidation using previously determined set of kinetic parameters. Oxygen diffusion control of oxidation has been introduced into the model. The mass changes kinetic curves and oxidation products profiles were simulated and adequate fit was obtained. Using the rubber elasticity theory the elastic modulus changes were simulated taking into account the elastically active chains concentration changes due to chain scission and crosslinking reactions. The reasonable fit of G’ as a function of oxidation time experimental c...

LIFETIME PREDICTION OF POLYETHYLENE PIPES TRANSPORTING DRINKING WATER IN THE PRESENCE OF CHLORINE DIOXIDE

A kinetic model for lifetime prediction of polyethylene pipes transporting pressurized water disinfected by chlorine dioxide (DOC) has been elaborated. This model is composed of three sub‐models:—A system of differential equations, derived from a realistic mechanistic scheme for radical chain oxidation in the presence of DOC of stabilized polyethylene (PE), giving access to the spatial distribution of structural changes in the pipe wall and its evolution against time of exposure;—The classical Saito’s equation to predict the profiles of average molar masses from the spatial distribution of chain scissions and crosslinking events;—An empirical creep equation and an empirical fracture criterion derived from regression curves obtained in pure water. It is assumed that chemical degradation modifies only the time to transition tc between ductile and brittle regimes of failure, and that tc is linked to the weight average molar mass by a power law.By combining these three sub‐models, it is possible to predict th...