<p>Surface-modified PVC (polyvinyl chloride) offers an attractive intumescent flame retardant material due to its ability to enhance fire resistance while maintaining the desirable properties of the polymer. In this paper, the experimental and computational approach was performed to investigate the HCl capture in PVC composites including melamine cyanurate (MCA) as a flame retardant additive. This new candidate triazine char-forming agent (MCA) was compounded with PVC in different ratio to prepare intumescent flame retardant (IFR). Flame retardancy and thermal degradation behaviors of the composites were characterized by Fourier Transform Infrared (FTIR), Field-emission scanning electron microscopy (FE-SEM), oxygen index (OI), vertical burning tests (UL-94), thermogravimetric analyzer (TGA) and static thermal stability (Congo red) test. As a comparative study, the thermal decomposition of PVC and P-MCA compounds has been investigated using the DFT method for the density to explore their effects of PVC combustion and burning properties. It was found that 5.0 phr of IFR could improve the maximum decomposition temperatures, and char residue of PVC, the thermal stability time of P-MCA2 composite. The LOI value of 5.0 phr PVC/MCA composites were also improved. At the same time, a UL-94 V-0 rating were achieved. These results indicate the synergistic effect of the MCA, high efficiency of the proposed strategy, and the broad application prospects of the prepared P-MCA composite materials.&#xa0;</p>