Biomimetic flow field flame retardant modification of sisal fiber and its polypropylene composites

The lumen of sisal fiber provides a good space for loading flame retardants and constructing a three-dimensional flame-retardant network, effectively improving the flame retardancy of their polymer composites. In this study, we combined water/nutrient transport mechanism of plant fiber with layer-by-layer self-assembly technology, innovated a biomimetic flow field flame retardant modification method and successfully deposited ammonium polyphosphate (APP) and polyethyleneimine (PEI) into sisal fiber lumen. After 20 cycles modification, the flame retardants in fiber increased to 18.36 wt%. Its TG residue achieved to 43.23 % from 17.35 % (unmodified) and its limited oxygen index (LOI) value achieved to 39.1 % from 20.7 % (unmodified). Compared to directly immersing fiber in APP/PEI solution, this method mitigated the blockage of flame retardants at lumen entrance and realized a uniformly deposition in lumen interior. When blending this modified fiber with polypropylene (PP) at 30 wt% (the flame retardant content is only about 4.65 wt%), the composite TG residue increased from 3.10 % (unmodified) to 15.77 %, and its LOI value increased from 19.4 % (unmodified) to 23.2 %. This composites also has better flame retardancy than APP/PEI directly dispersed in PP matrix (TG residues 11.10 %, LOI value 21.1 %). For sisal fiber polymer composites, employing fiber lumen as flame retardant carrier could improve its flame retardancy efficiently. The carried flame retardants inhibit the combustion of flammable sisal fiber, and the constructed flame-retardant network restrict PP matrix combustion.