A novel approach for 3D in situ visualization of morphological changes in dilute sulfuric acid-pretreated straw by micro-computed tomography

Lignocellulosic biomass is a crucial agricultural and industrial product. Dilute acid pretreatment is a common step to break down the dense and complex lignocellulose-based structure of straw to enhance its biochemical conversion efficiency. The straw derived from diverse crops, such as corn, cotton, and rape, displays diverse internal morphologies and varying responses to pretreatment methods. It is, therefore, necessary to understand the underlying mechanisms of these microstructural changes, to maximize their industrial value. This is the first study to demonstrate X-ray micro-computed tomography (micro-CT) based 3D visualization to observe the changes in the histology of straw caused by pretreatment using dilute acids, understand the mechanism of dilute sulfuric acid pretreatment, and visualize the reason behind the resulting morphological changes in the microstructure of straw. Three types of straw from corn, cotton, and rape were treated with 1.5% (w/w) dilute sulfuric acid at 121 °C for 30 and 60 min. Subsequently, the straw samples were imaged using Skyscan1275 under optimized micro-CT scan and image reconstruction conditions. In addition, the algorithms for image segmentation were determined. Volume- and slice-rendered images were analyzed via pseudo-color processing for different straw samples. Furthermore, the results of the micro-CT 3D in situ visualization aligned with the chemical analysis of lignocellulose composition. Overall, the presented non-invasive 3D micro-CT technique can provide crucial insights into the morphology and thus microstructural changes of lignocellulose-based materials not only qualitatively, but also semi-quantitatively. The non-invasive imaging methodology described in the present study will prove to be extremely helpful in prompt in situ analysis and comparison of diverse treatment approaches using lignocellulosic biomass.