Microcrack propagation in transverse surface from heartwood to sapwood during drying

Hiroki Sakagami

doi:10.1186/s10086-019-1812-6

Abstract

Microcracks, which are difficult to be observed with naked eyes, occur on the transverse surface during the first stage of wood drying. The precise investigation of their appearance is critical for understanding the mechanism of crack occurrence and propagation, which influence the properties of wood. In this study, the location and time difference of microcrack occurrence on the transverse surfaces of outer heartwood to sapwood via the intermediate wood of Cryptomeria japonica were investigated. Using the developed confocal laser scanning microscope system and a digital microscope, the microcrack propagation was captured dynamically with the wide range of high-quality images; microcracks appeared initially in the heartwood region, immediately after drying. On the other hand, in sapwood, microcrack generation occurred only after microcracks appeared in intermediate wood, and the ones in heartwood started to close or were closed. Finally, most of the microcracks almost closed and some completely disappeared towards the end of the drying process. From this result, it can be established that appropriate drying conditions should be prepared during the early stage of drying to produce high-quality wooden products because microcracks can appear in heartwood, even though the moisture content of the specimen is high.

Highlights

Wood is of two types: sapwood, which is the outer part of the tree stem, including the outside bundle of growth rings adjacent to the bark of the wood disc, and heartwood, which is the inner part of the growth rings and does not exist in younger trees
Significant information on the properties of wood for final use can be determined in the early stage of drying because microcracks appeared in heartwood, even though the moisture content (MC) was high
In this study, the area on the specimen and the time difference in microcrack occurrence were focused upon, using radially long fresh specimens of Cryptomeria japonica containing both heartwood with low MC and sapwood with high MC, with a digital camera and the developed Confocal laser scanning microscope (CLSM) system

Summary

Introduction

Wood is of two types: sapwood, which is the outer part of the tree stem, including the outside bundle of growth rings adjacent to the bark of the wood disc, and heartwood, which is the inner part of the growth rings and does not exist in younger trees. In many trees, these two types can be commonly distinguished based on their different colours caused by heartwood substances, which are identified with expensive methods [1]. One of the prominent effects is the low liquid/gas permeability caused by aspirated or encrusted pits [5, 6]; bordered pits, which control the movement of free water, are aspirated or

Methods

Results

Conclusion