<p>High density polyethylene composites have been prepared by melt mixing method along with microencapsulated intumescent fire retardant additives. The additive was synthesized using ammonium polyphosphate and charring agent (propane terephthalamide), microencapsulated in melamine formaldehyde resin. The prepared composites were evaluated for mechanical, thermal and fire retardancy properties. The results revealed that as the microencapsulated additive in the composites increased from 0 to 18%, the tensile and compressive strength increased by about 8% and 21%, respectively, and gradually reduced to 10% and 15% with increase in microencapsulated additive content up to 40%. The tensile and compressive modulus gradually increases by about 5% and 29%, respectively, as the microencapsulated additive content increases from 0 to 40%. The tensile fractured morphology and dispersion of additive in the composites were studied using scanning electron microscopy and transmission electron microscopy, respectively. Fire retardancy of the HDPE composites loaded with 40% microencapsulated additive, resulted in significant reduction in heat release rates, enhancing their thermal stability and formation of thick compact char residue. Thus the effect of variations in microencapsulated additive content on the mechanical properties, thermal behavior and fire retardancy of the composites is systematically investigated which would be beneficial in naval applications, such as in workboats hulls, cables and buoys and are suitable for other offshore environments.</p> Graphical abstract <p></p>