Effects of Different Energy Intensities of Microwave Treatment on Heartwood and Sapwood Microstructures in Norway Spruce

Abstract

Microwave modification can increase the permeability of wood by delaminating and rupturing its anatomical microstructures at their weak points. A high degree of intensity of microwave modification can cause significant structural damage to the microstructures of wood, resulting in poorer strength properties. The objective of this study was to evaluate the changes in the anatomical structure of Norway spruce (Picea abies (L.) Karst.) heartwood and sapwood after microwave modification in order to develop the most effective treatment in terms of applied energy without causing significant structural damage. Analysis with light and scanning electron microscopy were performed to evaluate the effect of microwave treatment for two different energy intensities, moderate and high intensity. The results indicated structural changes in the tracheid cells. Microscopy showed varying degrees of modification within the wood microstructure, with the heartwood samples showing a greater anatomical distortion compared to their sapwood counterparts. Furthermore, the samples were subjected to pycnometric density measurements, which indicated a reduction in skeletal and absolute density after microwave modification, for both high and moderate intensity treatment on sapwood and heartwood samples. With increasing microwave energy, a gradual increase in specific pore volume and porosity percentage of the samples were also detected.

State of the Art of Microwave Treatment of Wood: Literature Review

“…Tracheids of samples under high intensity collapsed in earlywood for both heartwood and sapwood spruce. Under the same conditions, the tracheids of the sapwood of spruce were partially damaged in latewood, while the heartwood of spruce exhibited middle lamella detachment between latewood tracheids [61].…”

“…To investigate the effects of MW treatment on the microstructure of Picea abies (L.) Karst wood samples, analyze the volume of their pores, and establish an efficient MW treatment (in terms of MW energy) with the least damage possible in the wood microstructure, Ganguly et al [61] carried out experimental tests on the heartwood and sapwood of wood samples. Two MW intensities were used, moderate (700 MJ/m 3 ) and high (1260 MJ/m 3 ).…”

“…Using SEM images and light microscopy, Ganguly et al [61] analyzed the anatomical structure of specimens, visualizing the damage in the anatomical structure of Norway spruce. The samples treated under both intensities exhibited delamination between the walls of the cells and distortions in the tissues of earlywood of heartwood specimens.…”

“…Ganguly et al [61] concluded that the sapwood of Norway spruce under moderate and high MW intensity could be used without generating serious damage to the wood structure. On the other hand, heartwood under high intensity experienced severe anatomical issues; thus, it was not recommended.…”

Scanning Electron Microscopy Protocol for Studying Anatomy of Highly Degraded Waterlogged Archaeological Wood

“…For this purpose, the samples were freeze-dried in a Telstar LyoQuest lyophiliser at 0.040 mbar and −82 • C [44]. The bulk volume and density of each sample were determined using the GeoPyc 1365 density analyser (Micromeritics Inc., Norcross, GA, USA) [45][46][47].…”