Stem Porosity Determination of Straws Using Conventional Laboratory Tests and Image Processing Methods

Abstract

For sustainable thermal insulations, vegetable fibers/stems are widely used, which have very dispersed material properties even within a variety. The examination of the fibers’ porosity in the conventional way provided reference values in this study, but it can be problematic for cellulose-based fibers. This study examines the porosity of two straw types (barley and wheat) and searches for faster and easier tests; it reveals the inaccuracies that can occur in different methods. The image processing method is applied on records of intact cross-sections made by scanning electron microscope; the essential circumstances to reach the intact cross-section are also discussed in the paper. Stitched cross-sections, made from overlapping records using the same magnification, are supplemented by detailed images with higher magnification. On the fused/detailed images, the entire region of the cross-sections was segmented. Each pore was automatically analyzed (area, diameter, perimeter) to determine porosity; the result was compared to the conventional method. Comparing the entire and the detailed cross-sectional image gives information about the importance of magnification in the analysis. The presented method is suitable for porosity measurement but needs some modification in sample preparation and image capturing. Both the conventional and image processing methods provide the same results in ratios between the two straw types but different absolute values.