Characterization of thermally modified short and long rotation teaks and the effects on coatings performance

Abstract

Many wood processing industries use short rotation teak, which has lower quality especially in durability and dimensional stability. Heat treatment is an eco-friendly method to improve dimensional stability and durability of wood. The objectives of the study were to investigate the effects of thermal modification on chemical composition, colour, dimensional stability and durability as well as coating's performance after accelerated weathering of short and long rotation teak for exterior utilization. In this study, the samples were heated in oven at 220 °C for 20 h under nitrogen atmosphere. Results showed that independently of growth conditions teak woods underwent hemicelluloses degradation and an increase of lignin content after heat treatment. Extractives contents were lower in short rotation than in long rotation teak, and decreased in all cases after heat treatments. Dimensional stability was considerably improved as indicated by anti-swelling efficiency values of 64,9% and 58,9% for short and long rotation teak, respectively. Heated teak woods were more resistant against Trametes versicolor and the durability of short-rotation teak increased from moderate to very durable. Coatings on heat treated teaks had better bonding quality and better photo-stability when compared to unheated. Heated short rotation teak could be considered for exterior application.

Properties of thermally modified teakwood

“…When analyzing the chemical constituents of the teakwood Chagas et al (2014) and Pratiwi et al (2019) found lower extractives content (4,76% and 7,41 %), higher insoluble lignin content (30,43% and 32,57 %) and holocellulose content (64,01% and 67,42 %) to the values of the untreated teakwood in the present study.…”

“…After the heat treatment at 220 °C for 20 h Pratiwi et al (2019) found a mean holocellulose reduction of 15,18% and total extractives of 21,32%, while an increase in lignin content of 31,3% occurred. While in this work an increase in total extractive content (48,59%) and lignin (26,44%) and a reduction in holocellulose content of 19,84% were found.…”

“…These color changes in wood are attributed to the formation of colored compounds after the chemical reactions caused by the heat treatment (Chen et al 2014, Cetera et al 2019, as well as phenols (Cetera et al 2019) and quinones (Tjeerdsma et al 1998). Pratiwi et al (2019) emphasizes a lower photodegradation in the color stability after the heat treatment of teakwood, this improvement being justified due to the increase of the lignin content formed by condensation during the heat treatment (Ayadi et al 2013). The thermal degradation of the wood can be divided into three temperature ranges.…”

“…Tectona grandis, commonly known as teak, grows naturally in Southeast Asia and is one of the most valuable tropical species in the international market (Niamké et al 2011, Nocetti et al 2011, Niamké et al 2014, Pratiwi et al 2019. Besides its natural occurrence, teak is planted in many tropical regions of the Americas and Africa (Kokutse et al 2004).…”

Effect of Thermal Modification on Decay Resistance of Corymbia Citriodora and Pinus Taeda Wood

“…Alternative technologies are able to change the chemical structure of wood and improve its biological resistance (Klüppel et al 2015, Treu & Larnøy 2016. Thermal modification has provided improved decay resistance, dimensional stability, weathering resistance, reduced water absorption, material darkening and colour stability (Silva et al 2015, Sivrikaya et al 2015, Pratiwi et al 2019) in many species of wood.…”