Novel millet husk crop-residue based thermoplastic composites: Waste to value creation

Abstract

The objective of the current research endeavor is to explore the potential of novel natural lignocellulosic crop-residue fibers (husk) extracted from the finger millet (Eleusine coracana) and barnyard millet (Echinochloa frumentaceae). The extracted finger millet husk (FMH) and barnyard millet husk (BMH) were characterized for their physical (extractive and density), chemical (X-ray photo spectroscopy and Fourier transform infrared spectroscopy), thermal (Thermo-gravimetric analysis), and morphological (X-ray diffraction and Scanning electron microscopy) behavior. The major objective was to explore their potential in the development of thermoplastic composites. Thermal kinetics of the fibers were studied with Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS) models. After fiber characterization, the composites were developed using injection molding process and characterized for mechanical, thermal, and morphological behavior. In the end, the flammability properties of the developed composites were investigated with Thermo-gravimetric analysis, UL-94 Horizontal burning, and Limiting Oxygen Index testing. Chemical constituent analysis reveals higher cellulosic and lower lignin content of FMH (cellulose; 38.01% and lignin; 16.25%) than BMH (cellulose; 34.5% and lignin; 21.31%). Thermal kinetics shows higher activation energy (Ea) for BMH (207.17 kJ/mol) than FMH (129.82 kJ/mol) as per the FWO model. BMH reinforced composites offer higher thermal stability and flame resistance than FMH reinforced composites, while FMH reinforced composites show higher mechanical properties than BMH reinforced composites. Overall, both husks show the potential to be used in developing thermoplastic composites.