Radiation-induced graft copolymerization of a phosphonate monomer onto short flax fibers and Miscanthus x giganteus stem fragments: Influence of substrate composition

Abstract

The functionalization of Miscanthus x giganteus stems fragments (R-MSF) by dimethyl(methacryloyloxy)methyl phosphonate (MAPC1) using pre-irradiation was studied. The influence of the composition and the structure of the substrate on the grafting efficiency was investigated by comparing the results with short flax fibers (SFF) and bleached Miscanthus x giganteus stems fragments (B-MSF). The lignocellulosic substrates were irradiated at several target doses ranging from 11 to 108.1 kGy using e-Beam. Electron Paramagnetic Resonance spectroscopy (EPR) highlighted major differences in terms of radical nature between R-MSF, SFF, and B-MSF samples. Following the polymerization reactions, washing, and drying steps, the phosphorus contents were measured by X-ray fluorescence spectrometry (XRF). Unlike Flax, pre-irradiation grafting was not efficient on R-MSF. The role of lignin content on grafting reactions was then evaluated by comparing R-MSF with SFFand B-MSF), showing only a minor impact. Using a reducing agent, it was possible to reach a phosphorus content of about 1.4 wt% for R-MSF and up to 4.0 wt% for B-MSF for a 100 kGy dose. Furthermore, phosphorus mapping using scanning electron microscopy coupled with energy-dispersive X-ray spectrometry (SEM-EDX) highlighted a homogeneous dispersion of the grafted macromolecules. This demonstrates the possibility of conducting pre-irradiation grafting on lignin-rich substrates without bleaching. Efforts were then made to optimize the operating conditions in terms of storage temperature, reaction temperature and Fe2+ concentration. Finally, the fire behavior of treated Miscanthus x giganteus stem fragments was evaluated by pyrolysis-combustion flow calorimetry (PCFC).