Effects of organically-modified montmorillonite and alkalinization on physical, mechanical, chemical, morphological, and thermal properties of wheat straw/recycled polypropylene nanocomposites

Valorization of wheat straw fiber/recycled polypropylene nanocomposites was investigated through studying the individual and combined effects of organically modified montmorillonite (OMMT) and alkali treatments on the given composites. FTIR spectra indicated the reduction of wheat straw fibers' hydroxyl groups due to hemicellulose removal resulting from alkali treatment. There were also trace diminutions in C-O peak intensities due to the degradation of little amounts of lignin. X-ray analysis revealed the intercalation of nanoclay in the polymer matrix. The improved interaction of fiber-polymer interfaces brought about by alkali treatment was also confirmed by scanning electron microscopy. The water absorption and thickness swelling properties of the nanocomposites were improved due to the barrier properties of nanoclay against water ingress. The flexural strength and modulus of elasticity increased by the individual, and likewise combined treatments. Thermogravimetric analysis demonstrated that the temperatures of first and second stages of composites' thermal degradation increased via the formation of a carbonized char layer thermally insulating the deeper composite layers. Differential scanning calorimetry showed some slight increases in the melting temperature, melting enthalpy, crystallisation temperature, crystallisation enthalpy, and crystallinity index of the treated composites due to the nucleating effect of nanofillers. The overall results showed that the combined treatment of OMMT and NaOH (vs. the individual ones) could significantly improve the overall properties of the studied composites. This was due to some interesting synergistic effects of the given treatments converting the wheat straw fiber/recycled polypropylene nanocomposites to high performance materials of choice for industry.