Preparation and Properties of Flame Retardant Polypropylene with an Intumescent System Encapsulated by Thermoplastic Polyurethane

A novel intumescent flame retardant (IFR), using thermoplastic polyurethane (TPU) as a carrier resin to encapsulate melamine pyrophosphate/pentaerythritol (MPP/PER), was adopted to flame retard polypropylene (PP). The effects of TPU encapsulation on the mechanical properties, flame retardancy, thermal stability, and water-resistance of flame retardant PP were investigated. It was found that the dispersion of the IFR particles and the compatibility between the IFR and PP matrix were improved, which was responsible for the enhanced mechanical properties and flame retardancy of the flame retardant PP. Moreover, the incorporation of TPU could effectively prevent the esterification reaction between MPP and PER during the processing of flame retardant PP, and prevent the IFR from leaching out of the PP matrix. It thus remarkably improved the thermal stability and water-resistance of the IFR. Furthermore, PP/TPU-encapsulated IFR composite showed better charring performance than that of PP/MPP/PER.