Relation of chemical and mechanical properties ofEucalyptus nitenswood thermally modified in open and closed systems

Abstract

Eucalyptus nitens is a fast growing plantation species that has a good acclimation in Chile. It is commonly used for pulp and paper, but there is a growing market for solid wood products made from this species and an interest on producing high quality material. Thermal modification technology have been used to obtain high quality product out of fast growing plantation species. In this study we modified Eucalyptus nitens to analyse the influences of the process conditions and evaluated its mechanical properties under several process conditions. The material was modified in a closed system under elevated pressure and controlled relative humidity (30 and 100% relative humidity) at temperatures between 150 and 170°C, and in an open system with a standard thermal modification procedure between 160 and 230°C. Modulus of elasticity, modulus of rupture, deflection and work in bending (in elastic and inelastic proportions) and the resistance to impact milling in high energy multiple impact tests were determined. Mass loss after each modification was also measured and correlated with the mechanical properties. Anatomical properties of selected modifications were analysed. There were no significant differences between open and closed system modifications in both mechanical and anatomical properties.

Dynamic and static mechanical properties of Eucalyptus nitens thermally modified in an open and closed reactor system

“…The loss of MOR at the higher temperatures, in both open and closed systems, can be related to the degradation of hemicelluloses (Zaman et al 2000). This was confirmed by Wentzel et al (2018b), where the degradation of xylans was closely related to the decrease of MOR. The degradation was higher in the closed system modifications due to the high concentrations of acids that build up because of the pressure, meaning that even at lower temperatures, closed system modifications can cause an increasing degradation of the hemicelluloses than high temperature modifications in the open system.…”

“…CML is related to the amount of extractive content, which also considers part of the degradation products caused by the thermal modification, deducted from the oven dry mass for its measurement, a higher degradation would mean a lower CML. When the E. nitens wood was modified over 210°C, its relative content decreased (Wentzel et al 2018b). As the RIM in the open system did not decrease linearly as the CML increased, it could mean that other chemical changes also could have influenced the RIM and should be taken into consideration when evaluating the results.…”

Physico-mechanical properties of thermally modified Eucalyptus nitens wood for decking applications

“…In Eucalypt species, durability increases after thermal modifi cation, as it has been shown in the resistance against the brown rot fungus Gloeophyllum trabeum for modifi ed E. globulus from durability class 3 (DC 3, moderately durable) to DC 1 (very durable) (González-Prieto and Touza Vázquez, 2009). Changes in mechanical properties of thermally modifi ed Eucalypt species, such as a slight increase of MOE and a decrease in MOR (Table 1), were not a detriment of the potential for using this species for outdoor materials (Esteves et al, 2007a;Calonego et al, 2012;de Cademartori et al, 2015;Knapic et al, 2018;Wentzel et al, 2019), as the MOE and MOR were still higher than those of commonly used WPC boards (Dias and Alvarez, 2017), a material commonly used for decking production (Zeller, 2018).…”

“…Most thermal modifi cation processes apply temperatures between 160 °C and 240 °C and limit the oxygen content during the process (Hill, 2006;Esteves and Pereira, 2009;Militz and Altgen, 2014). E. nitens (durability class 4, Australian Standard 5604 2005) and other eucalypt species, such as E. globulus, E. grandis, E. regnans and E. pellita (durability in ground contact class 3 -4, Australian Standard 5604 2005), have been used as material for thermal modification (Esteves et al, 2007a;Esteves et al, 2007b;González-Prieto and Touza Vázquez, 2009;Calonego et al, 2012;Wang et al, 2014;de Cademartori et al, 2015;Wentzel et al 2019). In most cases research has been focused on the variation of color, the changes of the mechanical and physical properties and variations of the chemical composition.…”

“…This also occurred in both our Spanish and Chilean specimens, shown to be statistically signifi cant in Table 3. Wentzel et al (2019) showed that there was a decrease in the degree of polymerization of the cellulose in thermally modifi ed E. nitens wood, which means that there was a change in the cellulose crystallinity. Estevez and Pereira (2009) suggest that changes in the cellulose crystallinity infl uence the mechanical The abrasion expressed as Δt increased with increasing modifi cation temperature in the Spanish spe- cimens, while the Chilean specimens showed only small differences between modifi cations ( Figure 6).…”