Core–shell expandable graphite @ layered double hydroxide as a flame retardant for polyvinyl alcohol

Expandable graphite (EG) is a kind of halogen-free flame retardant with high efficiency, but EG produces a lot of smoke when used. In order to reduce the smoke produced by EG flame retardant, layered double hydroxide (LDH)-coated EG was designed and prepared by the hydrothermal method to form composite EG@LDH with core–shell structure and used as flame retardant for polyvinyl alcohol (PVA). When EG@LDH particle content reaches 25%, UL-94 test reaches V-0 rating, limiting oxygen index reaches 33.8%, and the density of smoke is reduced by 75.4% compared with ordinary EG. These results are due to LDH's ability to produce stable oxides during combustion, as well as water vapor that absorbs heat and smoke, protecting the expanded graphite carbon layer from destruction. EG@LDH could suppress the “popcorn effect” of EG, improve the flame-retardant performance, expand the application scope of EG and have a broad application prospect in PVA and resin flame retardant with the characteristics of low cost and environmental protection.