Study of the morphology, structure, and properties of ammonium polyphosphate materials encapsulated by urea-melamine-formaldehyde resin, and the potential for manufacturing fire-resistant polypropylene composites

Abstract

In this study, ammonium polyphosphate (APP) has been functionalised through encapsulation with urea-melamineformaldehyde (UMF) resin, imparting fire-resistant properties to enhance the flame retardancy of polypropylene (PP) plastic. The results revealed that the successful encapsulation of APP with UMF resulted in a significant morphological transformation from large polyhedral APP particles (5-10 micrometers) to small spherical APP-UMF particles (0.5-1 micrometer). A PP composite material comprising 30% APP-UMF achieved a V-0 rating (according to the UL-94 method) and a limiting oxygen index (LOI) value exceeding 27%, indicating self-extinguishing capabilities. Furthermore, by incorporating APP-UMF (22.5%) and dipentaerythritol (DPER, 7.5%), the LOI of the PP composite material reached a remarkably high value of 34.57%. The thermogravimetric analysis revealed that the PP composite incorporating the APP-UMF fire-retardant system in combination with DPER exhibited superior thermal stability and a significantly higher residue content compared to the composite with unmodified APP. The mechanical properties, as demonstrated through tensile strength and elongation at break, of composite materials using flame retardants show a decrease compared to the original PP plastic, particularly in terms of elasticity, as indicated by the elongation at break measurement.