Ultrasonic delignification and microstructural characterization of switchgrass

Abstract

This present study was undertaken to investigate the ultrasonic delignification of switchgrass (Panicum virgatum L.) and the effects of ultrasonic irradiation on the molecular and microstructure of switchgrass. We investigated this question using response surface methodology (RSM) featuring a four-factor, three-level Box–Behnken experimental design with acoustic power (120, 180, and 240 W), solid–solvent ratio (1/25, 1/20, and 1/15 g/mL), hammer mill screen size (1.6, 3.2, and 6.4 mm), and sonication time (10, 30, and 50 min) as factors, while delignification (%) was the response variable. The native and treated switchgrass samples were further characterized through crystallinity measurements and electron microscopy. The results of lignin analysis show that the percent delignification ranged between 1.86% and 20.11%. The multivariate quadratic regression model developed was statistically significant at p < 0.05. SEM and TEM micrographs of the treated switchgrass grinds resulted in cell wall disruption at the micro-and nano-scales. XRD analysis revealed a reduction in the mean crystallite size and crystallinity index from 15.39 to 13.13 Å and 48.86% to 47.49%, respectively, while no significant change occurred in the d-spacings. The results of this investigation show that ultrasonic irradiation induces chemical and structural changes in switchgrass, which could enhance its use for biofuel and bioproducts applications.