Effect of hybrid filling with short glass fibers and expanded graphite on structure, rheological and mechanical properties of poly(ethylene terephthalate)

Abstract

Effect of short glass fibers (GF), added as roving, and thermally expanded graphite (EG) on structure, rheological, static and dynamic mechanical properties of poly(ethylene terephthalate) (PET) is studied. The materials were compounded by reactive extrusion using a co-rotating twin screw extruder with a sectional design of the material barrel in presence of 0.9 wt% of a diisocyanate chain extender. It is established that fragmentation of GF in the grinding section is accompanied with an intensified dispersion of EG, enhanced with the increasing concentration of GF, while addition of EG promotes an increase in the mean length of GF. Increasing content of the fillers intensifies degradation of PET macromolecules, accompanied by a decreasing molecular mass, increasing melt flow rate, crystallization rate and degree of crystallinity. The modulus of elasticity of the hybrid composites is found to increase synergistically which is attributed to inter-dependent changes in the fillers’ dispersity – enhanced dispersion of EG and retarded decrease of the mean GF length compared to the single filler composites.