Chain extension of poly(butylene terephthalate) by reactive extrusion

Abstract

The chain extension reaction in poly(butylene terephthalate) (PBT) melt was studied in detail. A high-reactivity diepoxy, diglycidyl tetrahydrophthalate, was used as a chain extender that can react with the hydroxyl and carboxyl end groups of PBT at a very fast reaction rate and a relatively high temperature. A Haake mixer 600 was used to record the torque during the chain extension reaction. The data show that this chain extension reaction could be completed within 2 to 3 min at temperatures above 250°C, and the reaction time decreased very fast with an increase in the temperature. Shear rate also had some effects on the reaction rate. The effect of the diepoxy chain extender on the flowability, thermal stability, and mechanical properties of PBT were investigated. The melt flow index (MFI) of the chain-extended PBT dramatically decreased as the diepoxy was added to PBT. In addition, the notched Izod impact strength and elongation-at-break of the chain-extended PBT also increased. The chain-extended PBT is more stable thermally. Compared with the conventional solid post-polycondensation method, this approach is simpler and cheaper to obtain high-molecular-weight PBT resins.