Improving the flame retardancy and water resistance of polypropylene by introducing microcapsule flame retardant system and modified zinc oxide

Intumescent flame retardant (IFR) and zinc oxide (ZnO) were successfully microencapsulated by polysiloxane, resulting in the preparation of Si-IFR and Si-ZnO, respectively. These microencapsulated additives were then incorporated into polypropylene (PP), leading to a synergistic enhancement of the flame retardancy, mechanical properties, and water resistance. By means of limiting oxygen index (LOI), UL-94 vertical burning test, and cone calorimetry test, an assessment was conducted to analyze the combustion characteristics of PP composite materials containing 2% Si-ZnO and 24% Si-IFR additives. The LOI value and UL-94 of PP/24%Si-IFR/2%Si-ZnO achieved to 39.8% and V-0 rating respectively, with significant decreases in both the total heat release (THR) and total smoke production (TSP). Furthermore, the introduction of polysiloxane significantly improved the water resistance of the PP composites. After a 168-hour water immersion test, notable reductions were observed in water absorption, the precipitation of flame retardants, as well as alterations in the mechanical properties of PP/24%Si-IFR/2%Si-ZnO.