An intumescent flame-retardant layer with β-cyclodextrin as charring agent and its flame retardancy in jute/polypropylene composites

A flame-retardant jute/PP composite with excellent flame retarding and mechanical properties was prepared by the surface powder spraying process. The flame-retardant layer used the green and pollution-free β-cyclodextrin as a char agent. To improve the char forming ability of β-cyclodextrin, ammonium polyphosphate (APP) and melamine (MEL) were also used as acid source and a blowing agent, respectively. The results indicated that the char forming ability of β-CD could be improved by the reaction between β-CD and APP. The composite with 20% flame retardants containing β-CD, APP and MEL (1:2:1) showed the better flame-retardant properties. The LOI value of the composite increased to 27.8%, which reached the second fire resistance according to Japan's JISD 1201-77 standard, and the self-extinguishing time reached to 37 s. Compared with pure jute/PP, the PHRR value and Av-EHC value of the composites were reduced by 50% and 21%, respectively. The carbon residual at 700 °C was increased by 10.9%. The tensile strength and bending strength were increased by 5% and 19%. These results revealed that the flame retardancy, thermal stabilities and mechanical properties of composites containing β-CD/APP/MEL system were significantly improved by the surface powder spraying method.