Preparation of flame-retardant natural rubber by grafting with phosphorus-containing monomers

Abstract

Graft copolymers of natural rubber with poly(2-methacryloyloxyethyl diphenyl phosphate) (NR-g-PMEDP) and poly(2-methacryloyloxyethyl phenyl benzenephosphonate) (NR-g-PMPBP), were prepared by seeded emulsion polymerization using cumene hydroperoxide and tetraethylenepentamine as a redox initiator system to improve flame-retardant properties of NR. The investigation of factors on grafting properties revealed that high reaction temperature afforded high grafting efficiency but the latex stability decreased. When the monomer concentration increased, the grafting efficiency was not significantly different, while the conversion decreased to 50%. In addition, the initiator concentration of 0.25 phr showed the highest grafting efficiency and percent conversion. Both graft copolymers on NR particles showed the core-shell morphologies. Thermal degradation of graft NRs indicated two stage decompositions under N2 atmosphere. The first stage corresponded to the decomposition of graft copolymers and the second stage exhibited the decomposition of rubber backbone. The limiting oxygen index (LOI) values of graft NRs increased with increasing monomer contents leading to enhancing the flame retardant properties of NRs. Mechanical properties of graft NR films were not significantly different compared with unmodified NR due to the low amount of graft copolymers.