Wettability of the surface of heat-treated juvenile teak wood assessed by drop shape analyzer

Juliana De Oliveira Lopes,Alexandre Miguel Do Nascimento,Rosilei Aparecida Garcia

doi:10.4067/s0718-221x2018005002801

Juliana De Oliveira Lopes, Alexandre Miguel Do Nascimento + Show 1 more

Open Access

https://doi.org/10.4067/s0718-221x2018005002801

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Abstract

This study investigated the effect of the heat treatment on the wettability of the surface of juvenile teak (Tectona grandis) wood assessed by drop shape analyzer. Heartwood and sapwood samples were heat-treated at 180 and 200ÂºC. Contact angle measurements were done every 5 s for 120 s using a KRÃSS DSA100. Heartwood had lower wettability than sapwood. Heat-treatment decreased the surface wettability of both heartwood and sapwood, especially in the wood treated at 200ÂºC. Heartwood had lower wettability than sapwood, even after heat treatment.

Highlights

The heat treatment or thermal modification has been widely studied because it promotes several advantages to the wood such as lower hygroscopicity, lower equilibrium moisture content, higher dimensional stability (Giebeler 1983), higher decay fungi resistance (Lekounougou and Kocaefe 2013) and color change (Garcia et al 2014, Lopes et al 2014)
Contact angle values of heartwood are higher than sapwood for a same treatment condition
The teak heartwood has a large amount of hydrophobic extractives (Yamamoto et al 1998) and this may explain its lower surface wettability

Summary

Introduction

The heat treatment or thermal modification has been widely studied because it promotes several advantages to the wood such as lower hygroscopicity, lower equilibrium moisture content, higher dimensional stability (Giebeler 1983), higher decay fungi resistance (Lekounougou and Kocaefe 2013) and color change (Garcia et al 2014, Lopes et al 2014). The heat-treated wood undergoes physical (Awoyemi and Jones 2011, Bernabei and Salvatici 2016) and chemical modifications (Esteves et al 2011) but the last one is the most important in terms of impact on the properties of the material. Among the chemical changes of the wood following heat treatment, we can highlight the degradation of the hemicelluloses, changes in the lignin structure due to its crosslinking with the products from the thermal degradation, modifications of the cellulose (degradation of the amorphous region and increase in crystallinity) (Bhuiyan and Hirai 2000), volatilization of the original extractives and formation of the new compounds such as anhydrosugars and phenolic compounds (Esteves et al 2011). The wettability of the wood surface is a complex phenomenon and depends on its physical and chemical properties. The physical factors include cell morphology, roughness, specific surface area

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