Abstract:
The effect of adding poly(vinyl chloride) (PVC) and coke filler on the rheological behavior
and thermal properties of a coal tar pitch was investigated with a view to developing an
appropriate viscoelastic binder for the injection molding of graphite components. Dynamic
mechanical analysis revealed that the pitch formed compatible blends with PVC featuring a
single glass transition temperature (Tg) intermediate to the two parent Tg’s. Adding PVC to
the pitch increased melt viscosity substantially and resulted in strong shear thinning
behavior at high PVC addition levels. Adding coke powder as filler increased the melt viscosity
even further and enhanced shear thinning trends. Pyrolysis conducted in a nitrogen
atmosphere revealed interactions between the PVC and pitch degradation pathways: the
blends underwent significant thermal decomposition at lower temperatures but showed
enhanced carbon yields at high temperatures. Pyrolytic carbon yield at 1000 C was further
improved by a heat treatment (temperature scanned to 400 C) in air or oxygen. However,
carbon yield decreased with addition of PVC. In addition, the degree of ordering attained
following a 1 h heat treatment at 2400 C also decreased with increasing PVC content.
