Toward the cottonization of hemp fibers by steam explosion. Flame-retardant fibers

The goal is to produce cottonized hemp fibers with improved thermal stability. It was first found that the fine hemp fibers produced from technical non-retted hemp fibers by steam explosion exhibited an enhanced thermal stability. An efficient and low-cost process was developed using a mixture of urea/etidronic acid in aqueous solution in order to achieve a high phosphorus content and produce flame retardant fibers by chemical grafting. ICP, P-31 and C-13 NMR, SEM, thermogravimetric, Pyrolysis-Combustion Flow Calorimetry analyses and a flame test were used to characterize the grafted fibers. Fibers modified with relatively high P and N contents have been produced (approximate to 6 wt % and approximate to 4 wt % respectively) but lower grafting rates (P approximate to 0.5 % and N approximate to 0.35 %) are sufficient to produce non-flammable fibers. A synergistic effect between N and P has been proposed to induce the formation of a stable char.