Flame retardant sisal rope: combustion properties and characterization

A new mechano-chemical formulation is developed for making flame resistant sisal fibre rope with low chemical loading. Sisal yarn is treated with a different formulation of ammonium sulfamate (AS) (50 g/L and 100 g/L) by following dip-dry approach at room temperature. Limiting oxygen index (LOI) measures the minimum amount of oxygen required in the mixture of nitrogen and oxygen for burning of the sample. Treated sisal showed LOI values of 28–32 and self-extinguishment in vertical flammability test whereas control sisal yarn showed LOI value of 21 and burnt easily within a minute. Forced combustion results revealed that AS treated sisal yarn exhibited 50% lower peak heat release rate (PHRR) than the control sisal yarn. Sisal yarn based rope was prepared by following braiding technique with three single yarns, using different combinations of untreated and treated sisal yarn. Fire retardant sheath yarn is used to cover the untreated sisal yarn present in the core by twisting or braiding. Rope made from sisal yarn has shown LOI value 30–40. Besides, a new method of simultaneous dyeing and flame retardant finishing of sisal rope is also proposed. The physical properties of the ropes were measured and it was found that the extent of strength loss is statistically insignificant at 95% confidence level. The thermal stability of the AS-treated sisal yarn is measured by thermo-gravimetric analysis. Charring behaviour of the control and AS treated sisal fibre was examined using microscopic images and scanning electron microscopy. Besides, in detail mechanism behind flame retardancy is revealed in the context with the help of XRD and FTIR analysis techniques. Graphical Abstract