Selected Physical and Mechanical Properties of Microwave Heat Treated Rubberwood (Hevea brasiliensis)

Abstract

The objectives of this study were to evaluate some of physical and mechanical properties of rubberwood (Hevea brasiliensis) as function of microwave heat treatment process. The specimens were heat treated at three temperature levels of 150 °C, 180 °C, and 220 °C for 20 min in a small microwave oven connected to a computer. Bending characteristics, namely modulus of elasticity (MOE), modulus of rupture (MOR) as well as hardness of the samples were tested. Dimensional stability in the form of swelling and water absorption of the specimens were also determined. Based on the findings in this work it appears that microwave can be used successfully for heat treatment of rubberwood. Overall mechanical properties of the samples were adversely influenced by the treatment. MOE, MOR and hardness values of the samples treated at a temperature of 220 °C had 2.37, 3.69, and 2.12 times reduced than those of control samples, respectively. Dimensional stability of the heat treated samples as a result of 2-h and 24-h water soaking improved. Micrographs take from scanning electron microscope (SEM) and transmission electron microscope (TEM) revealed that certain amount of damage took place in the cellwall of the treated specimens. Overall discoloration on the samples due to microwave heat treatment was found insignificant.

State of the Art of Microwave Treatment of Wood: Literature Review

“…Thus, the physical and mechanical properties of woods may diminish [33], which, in some situations, can be an advantage, as highlighted by Peres et al [46]. Terziev et al [33] explained that, in certain situations, MW treatment led to temperatures around 160 • C, in agreement with other studies [3,4]. Accordingly, the authors [33] intended to show the changes in micro-and ultrastructure levels of Norway spruce and radiata pine wood using two MW frequencies, 0.922 and 2.45 GHz.…”

“…Regarding the microstructural changes, it was observed that the cell walls were damaged, creating cracks on the samples. Lastly, the authors [4] stated that, compared to traditional approaches, 20 min MW treatment provided noticeable energy saving.…”

“…Chotikhun et al [4] argued that MW treatment is a novel technique that has become more popular because it has a more homogeneous heat distribution throughout wood specimens and saves time. Thus, the authors analyzed the physical and mechanical properties of MW treated rubberwood (Hevea brasiliensis) specimens.…”

“…Thus, wood industries are constantly seeking new methodologies, techniques, and technologies that lead to the best wood use, avoiding losses, whether in terms of time, mechanical resistance, durability, or economics [1]. The microwave (MW) treatment or modification of wood is an innovative and modern technology [2][3][4] for wood treatment. Microwaves are electromagnetic energies at frequencies between 0.300 GHz and 300 GHz [5][6][7] and, although the industry uses six frequency values, only two of them are commonly used for MW wood drying and treatment: 0.922 GHz (or 0.915 GHz) and 2.45 GHz [8].…”

“…MW treatment has become more popular in the field of heat-treated wood products [4], and it has been used for a variety of purposes, including wood drying, [12][13][14][15], improvement of fluid permeability [7,8,[16][17][18][19], and impregnation by preservative agents [18,20]. Torgovinikov and Vinden [21] explained that hardwood species tend to take longer in the drying process.…”