Rheological investigations of a polymeric precursor for ceramic materials: experiments and theoretical modeling

The paper is concerned with the rheological investigation of a commercial polysiloxane of the form [CH3-SiO3/2](x) which has potential application as precursor for the synthesis of silicon oxycarbide ceramics. The cross-linking reaction of pre-ceramic polymers in the presence of catalyst and/or fillers is one of the key steps in the successful polymer-to-ceramic transformation process. During the proceeding cross-linking reaction, a fast change of the polymer rheology is observed. The route of time-temperature variation for elasticity and viscosity of the samples is of great importance for the final properties of the resulting ceramic material. Dynamic test at constant oscillatory frequency and different constant temperatures or temperature gradients have been performed in order to establish the time evolution of the elastic and viscous moduli, as a function of the catalyst and filler concentration. The experimental data are modelled with a novel constitutive relation which is able to reproduce the rheology of isothermal and non-isothermal cross-linking processes as a function of the reaction time. The qualitative agreement between experiments and numerical simulations of the process is obtained for all the tests. The results of the present study indicate the value of rheological measurements to determine the thermomechanical properties of pre-ceramic polymers