Effects of an innovative densification process on mechanical and physical properties of beech and Norway spruce veneers

Michela Zanetti,Alex Cencin,Tiziana Urso,Alan Crivellaro

doi:10.1186/s10086-021-01948-w

Abstract

Increased wood density is obtained by compressing the wood porous structure under suitable moisture and temperature conditions to improve its physical, mechanical and color properties. A recently proposed wood densification method based on partial removal of lignin and hemicellulose in hot water solution of sodium hydroxide and sodium sulphite has shown promising results on solid wood. However, its applicability and effect on thin wood veneers have not been tested yet. In this study, the timing of the method has been adapted to estimate the densification treatment intensity dependence of wood properties (wood density and modulus of elasticity) and color change of softwood (Norway spruce) and hardwood (beech) veneers. Compared to control, density and rigidity increased, with improved wood properties peaking after only 90 s of treatment intensity. Furthermore, the color became darker after treatment compared to control, with no significant color difference between treatment intensities. In conclusion, densification of veneers, according to the presented adapted method, provides a significant improvement of veneers physical and mechanical properties, and produces color changes perceptible by the human eye. Our results can be further implemented and adapted to application in industrial plants, calling for new application of densified veneers.

Highlights

The improvement of physical and mechanical properties of low-density wood has been pursued since the beginning of last century when hydrothermal and thermal treatments, and impregnation or densification processes were designed [1, 2]
This is reflected in beech veneers being cut along the tangential plane at 0.6 mm thickness, while Norway spruce veneers were cut along the radial plane and were 0.8 mm thick
Veneer density Densified beech [F(3, 116) = 50.89, p ≤ 0.05] and Norway spruce [F(4, 145) = 63.62, p ≤ 0.05] veneers showed a higher density than the untreated samples (Fig. 2, Table 1)

Summary

Introduction

The improvement of physical and mechanical properties of low-density wood has been pursued since the beginning of last century when hydrothermal and thermal treatments, and impregnation or densification processes were designed [1, 2]. Song et al.’s [17] simple and effective strategy would transform veneers directly into a high-performance material with a more than tenfold increase in strength, toughness and ballistic resistance and with greater dimensional stability This strategy was shown to be universally effective for various species of wood, with processed wood having a specific strength higher than that of most structural metals and alloys, making it a low-cost, high-performance, lightweight alternative [17]. Implementation of the veneer densification process within the wood supply chain could be beneficial as densified veneers could be used as a raw material in the production of panels with improved technological properties

Methods

Results

Conclusion