Abstract
The scope of the present work was to study the effects of heat treatment (at different mild temperatures) on the physicomechanical properties of pine wood, and to find out if impregnation with nanosilver may have any potential influence on the impact of heat treatment. Impregnation of wood with a 400-ppm silver nanosuspension was carried out under an initial vacuum pressure of 0.07 MPa, followed by a pressure of 0.25 MPa for thirty minutes, before heat treatment. Heat treatment was carried out under hot air at three relatively mild temperatures, 145, 165, and 185 °C. Results showed improvement of some properties in heat-treated wood at 145 °C. This was indicative of the improving impact caused by hornification and irreversible hydrogen bonding in the course of water movements due to heat treatment; significant fluctuations in the intensities of FTIR spectra bands at 1750–1500 cm−1 were corroborating evidence of chemical alterations in hemicellulose polymer. The high mass loss at temperature 185 °C, and the extreme thermal degradation thereof, overcame the improving effects of hornification and formation of irreversible hydrogen bonds, consequently mechanical properties decreased significantly. Interaction of different elements involved made it hard to predict properties in specimens modified at 165 °C. Impregnation of specimens with nanosilver suspension resulted in significant increase of mass loss in specimens heat-treated at 185 °C, and significant fluctuations in properties of specimens heat-treated at 145 °C.
Highlights
Preliminary studies on heat treatment of wood were carried out more than a century ago with an aim to improve some of the troublemaking drawbacks of wood [1]
When heat treatment takes place at mild thermal conditions, it is reported that semi-crystalline cellulose regions change to crystalline [9]
The physical and mechanical properties of thermally modified beech wood were investigated, a popular and abundant industrial hardwood species, impregnated with silver nanosuspension, and we examined their relationship with the crystallinity of cellulose [46]
Summary
Preliminary studies on heat treatment of wood were carried out more than a century ago with an aim to improve some of the troublemaking drawbacks of wood [1]. A key factor in this process is the proper dispersion of nanoparticles in order to obtain maximum improvements in wood properties Nanosized materials, such as metal nanoparticles (gold, copper, and silver) and metal oxides (zinc and aluminium), are nowadays widely applied to provide wood protection and to facilitate wood modification. To investigate if any potential increase in thermal conductivity, due to silver nano-particles, can be beneficial in both achieving positive effects of mild thermal conditions, and at the same time, avoiding high degradation in cell-wall polymers at higher temperatures. Temperatures below 145 ◦ C would hardly affect wood, and temperatures higher than 185 ◦ C would be too high to clearly demonstrate the effects of impregnation of small specimens with silver nanosuspension; To compare the results obtained in our previous study, which utilized a hardwood species, with the results of the present study, which utilized a softwood species with inferior properties, namely pine, and to identify potential different behaviour between hardwood and softwood species
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