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Prof. Corneliu Balan
| Speaker: |
Prof. Corneliu Balan (Politehnica University, Bucharest)
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| Date: |
Thursday February 23, 2006 |
| Title: |
Rheological
Investigations of Polymeric Precursors for Ceramic Materials
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Abstract
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Present lecture is dedicated to the rheological
investigation of polymers melts and polymer solutions which have
potential applications as precursors for ceramics materials, in
particular ceramic fibers produced by a spinning process.
The cross-linking reaction in the presence of
catalyst and fillers is the main process in conversion of polymers to
ceramics materials. During the extend of reaction, a fast change of
polymer rheology is observed, the route of time-temperature variation
for elasticity and viscosity of the samples being of great importance
for the final properties of 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 of the samples. 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 function of the reaction time. The
constitutive relation describing the change of viscoelastic behavior
during the liquid–solid transition is derived on the basis of Maxwell
and Jeffreys models with time–temperature dependent viscosity and
elasticity.
A procedure to determine experimentally the
extensional viscosity in a fiber spinning process is introduced.
Experimental results in shear tests and spinning process, and their
correlations, are also presented.
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