| dc.description.abstract | The best way to combat challenges of conventional petroleum-based polymers like environmental unsustainability, is to produce fully bio-based composites. Fiber-reinforced polylactic acid (PLA) composites can be incorporated in manufacturing industrial components that require high thermal stability. The overall goal of this research therefore, was to develop rice husks fiber-reinforced PLA composites with clay fillers. Rice husks were used as fiber to investigate the effect of alkali (Mg(OH)2 and NaOH) pre-treatments on mechanical and thermal properties of the developed fiber-reinforced PLA composites. Rice husks and clay materials were milled, and part were used as is. The other part was treated with alkali solutions using 1wt.%, 2wt.% and 4wt.% concentrations, at 5:1 and 15:1 liquor ratios to modify their fiber surface. Composites were produced using the compression molding technique. Box-Behnken Design optimization technique using Design Expert software was used to set up experiments from 5 factors namely; filler loading, fiber loading, alkali concentration, rice husk variety and alkali type. Tensile tests were done using a universal testing machine. TGA/DSC was used to determine composites’ thermal properties.
PLA composites’ respective tensile strengths and Young’s moduli varied from 21.17 to 30.22MPa and 1.70 to 2.16GPa (raw husks) as well as 19.54 to 33.63MPa and 1.64 to 2.16GPa (modified husks). Water absorption capabilities of the developed composites ranged between 0.58 to 1.56%. From SEM, fewer voids were observed in PLA composites with modified rice husks, due to enhanced compatibility between the fiber-clay-matrix phases. Ignition and burnout temperatures ranged from 311.01−364.48 ℃ and 358.41−415.07℃, respectively. Peak temperatures were in the 340.26−399.48℃ thermal stability range. Flammability indices, combustion characteristic indices and mean reactivities had low values; ranging from 1.40×10-5 to 2.17×10-5%/min.℃2, 0.54×10-8 to 0.91×10-8%2/min2.℃3 and 3.93×10-3 to 6.17×10-3%/min/℃, respectively. TGA showed that incorporation of filler/fiber delayed weight loss and increased char residues; hence higher thermal stability and enhanced flame retardancy at high temperatures. Peak temperatures ranged between 399.48 and 340.26℃. PLA composites’ activation energy had maximums of 148.83, 145.50 and 145.61kJ/mol using OFW, KAS and Coats Redfern methods, respectively, signalling high thermal stability and enhanced flame retardancy. PLA composites with low energy barrier (<6kJ/mol) favoured formation of an activated complex, due to low difference between activation energy and enthalpy. Overall, due to enhanced thermal properties with rice husks and clay incorporation, the current study revealed that rice husks fiber-reinforced PLA composites have good prospects for utilization in applications where thermal safety, health and security are desired. | en_US |
