Surface and Physical Features of Thermo-Mechanically Modified Iroko and Tauari Wood for Flooring Application

Monika Marchwicka,Agata Trzaska,Agnieszka Laskowska,Piotr Boruszewski

doi:10.3390/coatings11121528

Abstract

The aim of the study was to determine the selected surface and physical properties of iroko (Milicia excelsa (Welw.) C.C. Berg) and tauari (Couratari spp.) wood after thermo-mechanical treatment (TMT) in relation to extractive content. During TMT, no chemicals are introduced into the wood, which distinguishes this method from a number of wood modification methods. The iroko and tauari wood were subjected to volumetric densification in a hydraulic press. The wood was densified in a radial direction at a temperature of 100 and 150 °C. The wood color parameters were measured using the mathematical CIE L*a*b* and L*C*h color space models. The roughness parameters of Ra and Rz parallel and perpendicular to the grain were investigated. The contact angle (CA) of the wood with distilled water was determined based on the sessile drop method. The equilibrium moisture content (EMC) and dimensional changes of the wood were determined for a climate with a temperature of 20 °C and a relative humidity (RH) of 9%, 34%, 55%, 75% and 98%. The tauari wood was less prone to color changes under the influence of TMT than the iroko wood. After densification, the iroko and tauari wood displayed a different character of roughness changes. The iroko wood featured the lowest level of roughness after TMT at 100 °C, and the tauari wood after TMT at 150 °C. The densified iroko and tauari wood were characterized by weaker dynamics in the changes in their respective contact angles than the non-densified wood. The higher the temperature of the TMT, the lower the EMC of the wood. Higher EMC values were observed for the tauari wood than for the iroko wood. This was due to the lower content of chloroform-ethanol extractives. Similar dependencies were obtained in the case of hot water extractives. The thermo-mechanically treated wood displayed a greater tendency towards dimensional changes in a climate with high relative air humidity, i.e., above 70%, compared to the non-modified wood.

Highlights

Every species of wood is characterized by specific physical and mechanical properties [1–3]
After the samples were conditioned in a normal climate, the moisture content (MC) of the wood was determined according to ISO 13061-1:2014 [41]
Wood densification affects a number of wood properties, including density

Summary

Introduction

Every species of wood is characterized by specific physical and mechanical properties [1–3]. Knowing these properties results in optimal material selection for conditions of use, such as temperature, relative air humidity and class of use. Various modification methods are used to improve the properties of wood. One of the widely most investigated methods is thermo-mechanical treatment—TMT, often described as densification [4–7]. TMT affects a number of wood properties and is mainly focused on the production of high-density assortments translating into high wood hardness [8–10]. As an effect of TMT, the chemical properties change, resulting in, for instance, changes in the physical properties of wood [7,11,12], which are an important factor in the context of the use of wood, e.g., for flooring

Objectives

Methods

Results