Abstract
This study reports the functionalization of natural fibers aiming to improve their flame retardancy. Flax fabrics were modified by pre-irradiation grafting method using electron beam radiation treatment. A phosphorus-based flame retardant (FR) dimethyl(methacryloxy)methyl phosphonate (MAPC1), was used as flame retardant grafting agent. The grafting process follows three main steps. Flax fibers were first irradiated at a dose ranging between 5 and 100 kGy and stored cold to preserve the radicals created over the long period before being immersed into an aqueous solution containing MAPC1 monomer. Finally, a washing step of the treated fibers allowed to remove the unreacted monomer units but also the free oligomers and polymers chains which were not covalently bonded to the flax structure. The presence of free radicals on the flax fibers after irradiation was confirmed by Electron Paramagnetic Resonance (EPR). Grafting efficiency was evidenced by infrared spectroscopy (FTIR) and quantified using Inductively Coupled Plasma Atomic Emision Spectroscopy (ICP-AES). The location of the grafted phosphorus polymer chains in the fibers structure was assessed by Scanning Electron Microscope coupled with Energy Dispersive X-ray spectrometer (SEM-EDX). The effect of phosphorus grafting on the thermal properties and fire behavior of flax fibers was studied using thermogravimetric analysis (TGA), pyrolysis combustion flow calorimetry (PCFC) and a preliminary fire test. Different parameters were monitored such as radiation dose, monomer concentration, temperature and reaction duration on the grafting efficiency. In particular, it has been observed that MAPC1 was grafted in a homogeneous way into the bulk of the elementary flax fibers leading to high phosphorus content of around 2 wt% for a dose of 10 kGy and up to 7 wt% for a dose of 100 kGy.