Microencapsulation of bisneopentyl glycol dithiopyrophosphate and its flame retardant effect on polyvinyl alcohol

Bisneopentyl glycol dithiopyrophosphate (DDPS) has been successfully microencapsulated with melamine formaldehyde (MF) resin as a shell material by in-situ polymerization process in this study. Chemical structures of DDPS and microencapsulated DDPS (MDDPS) were characterized by Fourier-transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Morphologies were investigated by scanning electron microscopy (SEM), while particle size and distribution were investigated by granulometry. The results show that microencapsulation can make DDPS particles be coated by MF resin entirely. After microencapsulation, the mean diameter of DDPS increased slightly from 1.405 μm to 2.757 μm, DDPS and MDDPS both were applied in polyvinyl alcohol (PVA) films to compare their flame retardancy. The flame retardation property was evaluated by limiting oxygen index (LOI). Decomposition mechanism was investigated by TG-FTIR, FTIR and SEM. The results indicated that MDDPS has better flame retardancy to PVA, and the LOI of MDDPS/PVA composite is 31.8%. As a fire retardant for PVA, DDPS mainly functions in the gaseous phase rather than in the condensed phase, while MDDPS works in both the gaseous and condensed phase.