Emission of Volatile Organic Compounds from the Heat Treatment of Afrormosia and Newtonia Wood: Effects of Air and Palm Oil Heat Media

Abstract

The objective of this work was to study the influence of palm oil on the VOCs emitted during the heat treatment of Afromosia (Pericopsis Elata Van Meeuwen) and Newtonia (Newtonia paucijuga Harms) wood by comparing to the VOCs emitted during the heat treatment under air. Two batches of Afrormosia and Newtonia wood samples were heated under air and palm oil at temperatures of 160 °C, 180 °C, and 200 °C for 2 h. Then, the VOCs were collected by Solid Phase Micro Extraction (SPME) and measured using a Gas Chromatograph and Mass Spectrometer (GC-MS). The results showed that the temperature, the wood species, and the treatment medium have a great influence on the categories and percentages of VOCs emitted. In the air heat treatment, ethers were the most emitted VOCs from Afrormosia and Newtonia when these woods were thermally treated at 160 °C. Newtonia treated under air at 180 °C emitted more esters, while Afrormosia continued to emit more ethers under the same conditions. Moreover, Afrormosia and Newtonia treated at 200 °C emitted more ketones and aldehydes, respectively. Regarding the heat treatment of Afrormosia and Newtonia wood under palm oil, a similarity of the VOCs emitted from Newtonia with those emitted from Afrormosia under the same conditions was observed. Furthermore, palm oil was the main factor conditioning the nature of the VOCs emitted during the heat treatment. In general, for the treatment of Afrormoshia wood with palm oil, the VOCs emitted, such as alcohols, alkanes, and ethers, decreased with the treatment temperature. Ethers and ketones increased with the processing temperature. At 160 °C and 180 °C, the percentage of aldehydes was highest, while, at 200 °C, the percentage of esters was highest. Similarly, for Newtonia treated under palm oil, adehydes, ethers, and alcohols were the most abundant VOCs emitted at 160 °C. However, their percentages decreased with the increase in the treatment temperature; on the contrary, esters and ketones were weakly emitted at 160 °C and became abundant with the increase in temperature. Additionally, the ethers formed during the heat treatment of Afrormosia and Newtonia wood treated under air carry acetyl groups, while those formed during the treatment of the said wood under palm oil carry hydroxyl groups.

Effects of different heat treatment media on odorous constituents, chemical decomposition and mechanical properties of two hardwoods

“…On the other hand, acetic acid is not emitted during and after heat treatment of Afrormosia with palm oil (Table 1), in addition, palm oil heated to 160 °C, 180 °C and 200 °C does not emit acetic acid. 21 We therefore conclude that acetic acid comes mainly from the degradation of wood structural polymers and in the case of heat treatment with palm oil, acetic acid interacts chemically with palm oil to produce new compounds 22 with different odors.…”

“…Hexanal is found in untreated wood and this is due to the chemical oxidation of wood while drying prior to heat treatment. 20 Hexanal is emitted before heat treatment, but regardless of the heat treatment medium (air or palm oil), it is practically not emitted during 21 and after heat treatment carried out at 160 °C, 180 °C and 200 °C (Table 1). This leads us to assert that hexanal molecules present in wood fragment under the effect of high temperatures, 3 which explains their absence in VOC emissions after heat treatment.…”

“…This leads us to assert that hexanal molecules present in wood fragment under the effect of high temperatures, 3 which explains their absence in VOC emissions after heat treatment. Similarly, acetic acid is emitted by Afrormosia before, during 21 and after heat treatment under air. On the other hand, acetic acid is not emitted during and after heat treatment of Afrormosia with palm oil (Table 1), in addition, palm oil heated to 160 °C, 180 °C and 200 °C does not emit acetic acid.…”

“…Reduction in the percentage area of acetic acid, [bis[(trimethylsilyl)oxy]phosphinyl]-, trimethylsilyl ester is due to temperature-induced chemical interactions between this compound and palm oil. 21…”

Oil Heat Treatment of Wood—A Comprehensive Analysis of Physical, Chemical, and Mechanical Modifications

“…Palm oil treatment formed an elastic film on the wood surface, enhancing wood hygroscopicity by reducing water penetration into the wood structure. This film formation also contributed to the darker appearance of the palm oil-treated wood compared to the air-treated wood, resulting from the interaction between the unsaturated fatty acids in palm oil and the wood surface [66].…”