Effect of ionic liquids pretreatment on thermal degradation kinetics of agro-industrial waste reinforced thermoplastic starch composites

Abstract

Converting agricultural lignocellulosic waste into marketable composite product is a promising approach to protect the environment and earn financial gain. Ionic liquids (ILs) have emerged as the innovative and effective solvents for pretreatment of lignocellulosic materials to produce potential reinforcements for biocomposite manufacturing. Kinetic predictions are particularly essential for practical utilization of kinetic analysis for process design and to assess the performance of composite product during service life. This work aims to explore the impact of ILs assisted pretreatment of oil palm biomass on the thermal degradation kinetics of their fabricated biocomposites with thermoplastic starch as polymer matrix. The approach combines the pretreatment of oil palm frond (OPF) fiber with ILs 1-butyl-3-methylimidazolium chloride ([Bmim][Cl]) and 1-ethyl-3-methylimidazolium diethylphosphate ([Emim][dep]) prior to fabricate thermo-molded composite panels. Flynn–Wall–Ozawa method based on the model-free isoconversional approach was chosen to predict the activation energy of the biocomposites. Further, the influence of ILs pretreatment on physico-chemical properties of the OPF fiber was assessed by lignocellulosic characterization and crystallinity measurement. The results indicated that composites prepared with ILs pretreated OPF fiber exhibited 10–125% higher activation energy as compared to untreated composite over a conversion range of α=0.1–0.6. Characterization of the untreated and pretreated fibers by examining the lignocellulosic fraction and analyzing the degree of crystallinity evidenced that ILs pretreatment increased the cellulose contents by 1.5–1.8 folds and caused significant reduction in the crystallinity of the OPF fiber. The present findings plainly indicate the promising potential of ILs based pretreatment as a new and clean processing approach for manufacturing of engineered composite panels from agricultural waste.