Thermal stability of NaOH modified rice husk fiber-reinforced polylactic acid composites: Effect of rice husks and clay loading

Abstract

This work studied the synthesis, thermal behaviour and combustion properties of clay/modified rice husk fiber-reinforced PLA composites. Raw rice husks, NaOH modified rice husks, clay and Polylactic acid (PLA) were used as raw materials. SEM analysis revealed that at 1 wt% clay and 10 wt% rice husks loadings, bonding was enhanced between filler/fiber and PLA matrix. Composites' respective tensile strengths and Young's moduli varied from 21.17 to 29.19 MPa and 1.70–2.13 GPa (raw rice husks) as well as from 21.15 to 32.44 MPa and 1.64–1.97 GPa (modified rice husks). Composites' ignition and burnout temperatures ranged from 317.56 to 364.48 °C and 380.28–415.07 °C respectively. Flammability indices, combustion characteristic indices As well as mean reactivities varied from 1.45 × 10−5 to 2.00 × 10−5%/min°C2, 0.55 × 10−8 to 0.86 × 10−8%2/min2°C3 and 4.06 × 10−3 to 6.97 × 10−3%/min/°C respectively. Adding rice husks to the PLA matrix led to an increase in the melting temperatures of the accruing composites. TGA showed that incorporation of clay and rice husks resulted into delayed weight loss by 10–20% and increased char residues to 6.38−16.96%, hence higher thermal stability than neat PLA. Addition of rice husks inhibited neat PLA's pyrolysis process. PLA composites' activation energy ranged from 112.95 to 125.87 kJ/mol, which is significantly higher than that of the neat PLA (104.80 kJ/mol). These findings revealed that thermal stability, kinetic parameters and combustion characteristics of PLA composites are better, compared to some conventional polymer products.