Effect of Water Repellents on Hygroscopicity and Dimensional Stability of Densified Fir and Aspen Woods

This study investigated the effect of pre-impregnation with water-repellent agents on the hygroscopicity and dimensional stability of fir (Abies bornmulleriana Mattf) and aspen (Populus tremula L.) woods. After pre-vacuum treatment, the samples were impregnated at atmospheric pressure with paraffin, linseed oil and styrene, and then densified at compression rates of 20 % and 40 % at 120, 150 and 180 degrees C. The results showed that water repellents significantly affected the hygroscopicity and dimensional stability of the densified wood samples. Compression recovery rate (CRR), thickness swelling (TS), equilibrium moisture content (EMC), and water absorption (WA) values of the densified samples decreased with impregnation pretreatments. The linseed oil treatment gave more positive CRR and TS results than paraffin. Lower EA/IC and WA values were found in the paraffin-treated samples. However, the most successful results for all tested properties were determined in the styrene pretreated samples in which hygroscopicity decreased and dimensional stability increased (especially for aspen) due to increases in the compression rate and temperature related to densification conditions. In the styrene pretreated samples, the high temperature (180 degrees C) and compression rate (40 %) significantly reduced CRR, TS, EA/IC and WA, total dimensional stability was nearly achieved and the water repellent effectiveness was close to 100 %.Research Fund of Duzce UniversityDuzce University [BAP-2017.07.01.522]The authors are grateful for the support of the Research Fund of Duzce University, Grant. No. BAP-2017.07.01.522.WOS:0005208503000042-s2.0-8508247871