This work investigates the structural and chemorheological modification of polyethylene terephthalate in the melt phase with low molecular weight multifunctional glycidyl compounds as reactive additives. Polyethylene terephthalate undergoes chain extension and/or branching reactions with the additives that result in modified rheological properties suitable for certain polymer processing operations such as extrusion blow molding or extrusion foaming to low densities.

Among five different low MW difunctional and trifunctional epoxy compounds, triglycidyl isocyanurate is shown to be an efficient reactive melt modifier for commercially available polyethylene terephthalate polymers. Its stability at the polyethylene terephthalate melt temperatures is confirmed offline through thermogravimetric and FT-IR techniques. Melt modification of polyethylene terephthalate is followed in an intensive batch mixer by torque changes, analyzing the products for residual carboxyl content, insoluble content, and by dynamic mechanical analysis. The importance of undesirable melt degradation reactions occurring simultaneously with the branching/extension reactions is analyzed. Valuable information is obtained from the designed batch mixer experiments regarding the effects of various process parameters on the kinetics of the reactive modification. The melt-modification reaction products from the batch mixer are evaluated offline for melt viscoelastic properties using a dynamic mechanical analyzer.