Effect of Surface Functionalization of SiO2 Nanoparticles on the Dynamic Mechanical, Thermal and Fire Properties of Wheat Straw/LDPE Composites

The scope of the present article is to study the effect of surface functionalization of SiO2 nanoparticles on the dynamic mechanical, thermal and fire properties of wheat straw flour (WSF) reinforced low-density polyethylene (LDPE) composites. Firstly, the SiO2 nanoparticles were modified by 3-aminopropyl-trimethoxysilane (APTMS), and then the WSF/LDPE composites containing different percentages of modified nano-SiO2 were prepared via a melt compounding using an internal mixer followed by injection molding. Changes in the chemical structure of treated SiO2 were tracked by Fourier transform infrared (FTIR). The appearance of N–H bond at 695 cm−1 and aliphatic C–H bonds at 2841 cm−1 and 2947 cm−1 were indications of successful grafting of APTMS on the SiO2 nanoparticles. Finally, the viscoelastic behavior, thermal stability and fire retardancy of the nanocomposites were evaluated by means of DMTA, TGA, DSC and CCT techniques. Results indicated that the dynamic modulus of the composites was greatly improved through the addition of functionalized SiO2 nanoparticles. In general, the specimens filled with 3 phr modified nano-SiO2 showed the highest values of storage and loss modulus compared with the other ones. Moreover, the tan δ peak signifying the glass transition temperature of nanocomposites shifted to higher temperature. The TGA results demonstrated that the introduction of APTMS grafted SiO2 nanoparticles can distinctly enhance thermal stability of the composites by increasing the thermo-oxidation decomposition temperature and char residues. The maximum activation energy value represents a higher thermal stability of the nanocomposites was obtained with modified nano-SiO2 at 5 phr content. In addition, the DSC data revealed that both the melting temperature and the degree of crystallinity of the specimens tended to substantially increase in presence of modified nano-SiO2. The surface functionalization of SiO2 particles produced remarkable evolution in the fire performance as indicated by reductions in the heat release rate, burning rate and mass loss rate. Furthermore, promoting the time to ignition and limiting oxygen index of the specimens equally to accommodate the addition of treated SiO2 nanoparticles.