Responses Of Polycarbosilane Melt Under Oscillatory Shear

Polycarbosilane(PCS)is an important primary material for producing high strength continuous silicon carbide fibers and ceramic matrix composites,it is of great important for PCS process to understand and know well the rheological properties of PCS melt.However,the structure and properties of PCS were obvious influenced by temperature variation,and conventional rheological test methods were no suitable for PCS melt measurement,what more,the research on dynamic rheological properties of PCS melt is very immature.Therefore,it is necessary to study the dynamic responses of PCS melt with exploring and developing suitable methods for PCS rheological tests and analyses.In this paper,the dynamic rheological test procedures for PCS melt samples were explored and determined,on the base of these,the dynamic rheological properties of PCS were obtained with the angular frequency in 0.005 rad/s?500 rad/s and strain in 0.0001?1,then the measurement parameters ranges of repeatable tests results were determined.Both strain signals under oscillatory shear and stress responses signals of PCS were analyzed,and the rheological models of PCS melt were preliminary discussion.The results indicated that the process conditions with the best repeatability in rheological test results for PCS melt which has the softening point temperature 215?,is raising the temperature to 315 ? and keep for 10 min,followed with setting the temperature to 295 ? and keep for 5 min,then the test started.The best measurement parameters ranges with the angular frequency in 0.005 rad/s-500 rad/s and strain in 0.0001?1,which have the experimental data errors are less than 10%.Stress responses is less than the effect range of rheometer with too small strain or angular frequency,and rheological test results can not be repeat with too large strain or angular frequency.The test results show that although main frequency of stress responses is identical to the frequency of sine strain,the phase difference and not negligible nonsinusoidal strain are existence.Analysis results show that PCS is yielding fluid.PCS has the linear viscoelastic behavior at small strain(0.005),nonlinear viscoelastic behavior at middle strain(0.005)and yielding fluid behavior at large strain(?0.5).Therefore,the linear viscoelastic model of rheometer is unsuited to represent the responses of PCS.