Solid-state modification for improved flame retardancy

The European Union's regulations on halogenated flame retardants have led to investigations of alternatives. Poly(butylene terephthalate) (PBT), commonly used for its attractive properties in terms of use in electrical and electronics applications, is one of the polymers at risk under these guidelines. Indeed, its poor fire resistance often restricts its use or requires the addition of potentially toxic elements. The improvement of its flammability properties is thus crucial, and solid-state modification (SSM) is an ideal method to achieve this while preserving its crystalline structure and thermomechanical characteristics. Therefore, an intumescent copolyester made by SSM using a biobased co-monomer has been prepared. First, PBT was modified with a carbonizing agent, 2,3:4,5-di-O-isopropylidene-galactarate (GalX). The optimization of this process involved study of the effects of temperature, time, and pressure. The thermal properties of P(BT-co-GalXT) demonstrates that the positive qualities of PBT are retained reflecting the preservation of the crystalline phases during the solid-state reactions. Finally, pure PBT may be combined with the copolyester and ammonium polyphosphate to obtain an intumescence system which exhibits V-0 rating in the UL 94 test. This composition displays the desirable properties of the homopolymer as well as improved fire behavior.