The effect of thermo-mechanical densification on some surface properties and morphological structure of wood materials impregnated with hydrophobic substances

In this study; the effect of thermo-mechanical densification on some surface properties and morphological structure of wood materials impregnated with hydrophobic (water-repellent) substances was investigated. Samples prepared from Uludağ fir (Abies bornmülleriana Mattf.) and aspen (Populus tremula L.) woods were impregnated with paraffin, linseed oil and styrene after pre-vacuum treatment. Then, the impregnated samples were densified by thermo-mechanical method at three different temperatures (120 °C, 150 °C and 180 °C) and two different compression ratios (20% and 40%). Roughness (TS 6212 EN ISO 4288), gloss (TS EN ISO 2813), color changes (ASTM D 2244) and wettability (contact angle) tests were performed on wood samples to determine surface properties. In addition, scanning electron microscopy (SEM) analyzes were performed to determine the changes in the morphological structure of the wood samples. According to the study results, impregnation processes significantly affected the morphological structure and tested surface properties of the densified wood samples. Especially, more successful results were obtained in wood samples impregnated with styrene and paraffin. Depending on the increase in the densification temperature and compression ratio, the roughness values of the impregnated fir and poplar samples decreased up to 63% and 72%, respectively, while the contact angle values increased up to 68% and 71%, respectively. Thus, more smooth and hydrophobic surfaces with low wettability were obtained. In addition, gloss values increased in all test samples (especially paraffin treated) depending on the increase in compression ratio. In terms of total color change (ΔE*), higher values were determined, especially in linseed oil treated samples, which were densified at high temperature (180 °C) and high compression ratio (40%). In the SEM analyzes, it was observed that the significant cell deformations (cracking, breaking, rupture, etc.) that occurred in the un-impregnated samples during the densification phase did not occur in the test samples impregnated with hydrophobic substances, and the cells were mostly deformed in the form of elastic buckling or bending.