Effect of thermal treatments on technological properties of wood from two Eucalyptus species

Abstract

The effect of thermal treatments on physical and mechanical properties of rose gum and Sydney blue gum wood was evaluated. Wood samples were thermally modified in a combination: pre-treatment in an autoclave (127°C -1h) and treatment in an oven (180-240°C -4h); and only treatment in an oven at 180-240°C for 4h. Chemical changes in the structure of woods were evaluated through infrared spectroscopy. Evaluation of physical properties was performed through mass loss, specific gravity, equilibrium moisture content and dimensional stability tests. Surface changes were analyzed through apparent contact angle technique and static bending tests were carried out to evaluate the mechanical behavior. Use of pre-treatment in autoclave affected the properties analyzed, however oven, resulted in the highest changes on wood from both species. Chemical changes were related to the degradation of hemicelluloses. Moreover, a significant decrease of hygroscopicity and mechanical strength of thermally modified woods was observed, while specific gravity did not significantly change for either of the species studied. The best results of decrease of wettability were found in low temperatures, while dimensional stability increased as a function of temperature of exposure in oven. The highest loss of mechanical strength was observed at 240°C for both species.

Prediction of the physical, mechanical and colorimetric properties of Eucalyptus grandis heat-treated wood using artificial neural networks

“…This may be due to degradation of hemicellulose, reducing the wood capacity to resist to elastic deformations when subjected to mechanical stress and thus, reducing its deformation before rupture (SANTOS, 2000). A similar trend was reported for Eucalyptus globulus (SANTOS, 2000); however, in other works, the modulus of elasticity has not altered (CADEMARTORI et al, 2015) or its value was reduced after heat treatment (ZHANG et al, 2015). This shows that the modulus of elasticity behavior can vary with heat treatment.…”

“…This reduction was more severe at higher temperatures, being 46.65% at 230°C, a temperature at which degradation of carbohydrates is higher in hardwoods (CADEMARTORI et al, 2013b) and softwoods (SEVE-RO et al, 2012) and thus, resulting in higher EMC reduction. The total volumetric swelling, which is related to the holocellulose content and water adsorption capacity (CADEMARTORI et al, 2015;DUBEY et al, 2012), followed a similar trend of that of EMC, dropping significantly from 170°C onward and with an intense decrease at higher temperatures.…”

“…At 230°C, the lightness (L*) reduction was less intense, because most of the compounds that darken the wood had been degraded at lower temperatures (BRITO et al, 2008;PEREIRA, 2009). The wood darkening with increasing temperature was also reported for E. grandis , Eucalyptus saligna (CADEMARTORI et al, 2015) and Pinus pinaster heat treated (ESTEVES et al, 2014), besides pre-hydrolysated Eucalyptus grandis and Pinus elliottii (CARVALHO et al, 2014). (PINCELLI et al, 2012), which are degraded by heat.…”

Physical and Mechanical Properties of Fast-Growing Wood Subjected to Freeze-Heat Treatments

“…However, the results from these works do not corroborate each other. In general, the mechanical properties of the treated wood do not follow any pattern, as they can increase (Boonstra et al 2007;Pfriem et al 2010;Todorovic et al 2012), decrease (Cademartori et al 2012Bal and Bektaş 2013;Missio et al 2016) or remain unchanged (Calonego et al 2012;Cademartori et al 2015). The effect of thermal treatments in these properties depends on the parameters of the treatment and the wood species (Hill 2006).…”

Tratamento térmico da madeira em atmosfera de glicerina

“…Para tanto, seguiu-se a metodologia proposta por Cademartori et al (2015); Conte et al (2014) e Delucis et al (2014).…”