Natural and modified wood cyclic interaction with water | Dabīgās un modificētās koksnes cikliska mijiedarbība ar ūdeni

English. Wood application as a construction material has restrictions in the environment with changing humidity. Wood acetylation is well accepted method to diminish water influence. Woods hydroxyl group hydrogen atoms are replaced by acetyl group that decreases possibility of hydrogen bond formation with absorbed water. Substitution of the one hydrogen atom in each wood’s hydroxyl group with spatially greater acetyl group having six atoms creates wood cell wall permanent swelling that decreases wood possibility to swell with water. Wood impregnation with oil is often used to increase its hydrophobic properties. It might be used as simpler and un-expensive alternative of acetylation to protect wood against humid environment. The more spacious triglycerides molecules fail to penetrate into cell wall and they might to form only hydrophobic barrier against water molecules. Acetylated wood cell walls having more pronounced hydrophobic properties than natural one might be more tightly associated with vegetable oil molecules, and it might be highlighted as synergetic effect. The first objective of presented work was to decrease acetic anhydride consumption in the wood hydrophobization with the replacement of acetyl groups with hydrophobic substance – vegetable oil. Fatty acid radicals of the vegetable oil might interact with introduced by acetylation into wood acetyl group non-polar methyl group with hydrophobic interaction. The tighter bonding might be achieved with this interaction. The rapeseed oil was used due to, its semi-hardening feature, that protect formation of fragile polymer network during oil curing. Such gel like polymerised oil will resist mechanical stresses originated by wood swelling and shrinking in the changing humidity. The introduced by acetylation acetyl groups will act as anchors of polymerized rapeseed oil.

Latvian. Koksnes briešanas un bioloģiskās noārdīšanās mitrā vidē cēlonis ir koksnes īpašība saistīt ūdeni. Ūdens saistīšanos ar koksni var samazināt ar koksnes impregnēšanu ar ūdeni atgrūdošām vielām vai modifikāciju, kas būtu mazāk kaitīgas videi. Pētījuma mērķis bija samazināt apses (Populus tremula) koksnes ūdens absorbciju un uzbriešanu, apvienojot koksnes acetilēšanu ar etiķskābes anhidrīdu un impregnēšanu ar rapša (Brassica napus) sēklu eļļu, pielietojot divas metodes: 1) koksnes acetilēšana ar etiķskābes anhidrīdu (Ac) un secīgu impregnēšanu ar rapša eļļu (Ac+RE); 2) koksnes secīga impregnēšana ar etiķskābes anhidrīdu un rapša eļļu ar acetilēšanu paaugstinātā temperatūrā (EA+RE). Modificētās koksnes mijiedarbību ar ūdeni novērtēja ar ciklisku hidrotermisku testu (CHT), secīgi koksnes paraugus izturot karstā ūdenī, sasaldējot un žāvējot. Kontrolei paralēli veica CHT nemodificētai (Dab), acetilētai (Ac) un ar rapša eļļu impregnētiem (RE) paraugiem. Modifikācijas ietekmi novērtēja, salīdzinot ūdens absorbciju, masas zudumu, uzbriešanu, rukumu, ūdens absorbcijas samazinājuma un uzbriešanai efektivitāti, indukcijas periodu līdz paraugu sabrukšanai un sabrukšanas intensitāti salīdzinājumā ar nemodificēto, acetilēto un ar rapša eļļu impregnēto apses koksni.