To improve the flame-retardant efficiency and water resistance of ammonium polyphosphate (APP)

the UV-curable pentaerythritol triacrylate (PETA) was used to microencapsulate APP via the UV curing polymerization method. The prepared PETA-microencapsulated APP (PETA-APP) was characterized by Fourier transform infrared spectroscopy (FTIR)

scanning electron microscopy (SEM)

and thermogravimetric (TG) analysis. PETA-APP was used as intumescent flame retardant (IFR) alone to flame retard polypropylene (PP). The water resistance of PP/PETA-APP composites was investigated

and the effect of PETA on the combustion behaviors of PP/APP composites was studied through limiting oxygen index (LOI)

vertical burning test (UL-94) and cone calorimeter (CC) test

respectively. With 40 wt% of PETA-APP

the PP/PETA-APP system could achieve a LOI value of 30.0% and UL-94 V-0 rating after treatment in hot water for 168 h

while the LOI value of the system containing 40 wt% uncoated APP was only 19.2%

and it failed to pass the UL-94 rating. CC test results showed that the heat release rate (HRR)

mass loss rate (MLR) and smoke production rate (SPR) of PP/PETA-APP system decreased significantly compared with PP/APP system

especially the peak of HRR was decreased by 51.4%. The mechanism for the improvement of flame reatardancy for PP/PETA-APP composites was discussed based on FTIR and X-ray photoelectron spectroscopy (XPS) tests. All these results illustrated that simultaneous improvement of flame retardancy and water resistance for PP/APP was achieved through coating UV-curable PETA onto APP.