Vol.:(0123456789) 1 3 Eur. J. Wood Prod. DOI 10.1007/s00107-017-1207-6 ORIGINAL Efect of surface modifcation of fbers on the medium density fberboard properties Mehdi Jonoobi 1,2  · Maryam Ghorbani 3  · Ali Azarhazin 3  · Hamid Zarea Hosseinabadi 1   Received: 15 March 2016 © Springer-Verlag GmbH Germany 2017 1 Introduction One of the most commonly used wood-based panels that are composed of wood fbers bonded together with inte- rior adhesive under pressure and heat is medium density fberboard (MDF) (Ustaomer et al. 2008). The MDF is made by adding a thermoset resin to the fbers followed by hot pressing process. The most widely used thermo- set resins are urea or phenol formaldehyde which are polar (Mwaikambo and Ansell 2002). Because of the presence of hydroxyl groups on the fber surface, wood fbers are also highly polar and are readily available for hydrogen bonds formation with interacting resin (Cord- eiro et al. 2012). In general, the mechanical properties of wood-based composites strongly depend on the nature of the fbers as well as the quality of the adhesion matrix/ fbers (Mills et al. 2009; Cordeiro et al. 2012; Gamelas 2013). Fiber-adhesive interaction plays a very important and efective role in the fberboard quality. However, the fbers are covered by non-cellulosic impurities such as pectin and wax, thus hindering the hydroxyl groups from reacting with polar resins (Kabir et al. 2013). These com- ponents have been supposed to be responsible for inad- equate adhesion between accessible OH groups on the fber surfaces and diferent resins. Removal of the surface impurities can improve the fber–matrix interface bonding properties and consequently improve the properties of the composites (Kostic et al. 2008; Rahman et al. 2009; Rosa et al. 2009). Therefore, to remove the impurities from the fbers surface and also introduce the reactive hydroxyl groups for adhesion with polar resins, physical and/or chemical treatment need to be used (Kostic et al. 2008). Chemical modifcation has been widely used to modify the surface of cellulosic fbers (Wong et al. 2004; Ndazi et al. 2007). Among the diferent modifcation methods, Abstract Surface modifcation of mixed hardwoods fb- ers by sodium hydroxide (NaOH) was conducted to inves- tigate the efect of chemical treatment on the fber proper- ties along with physico-mechanical characteristics of the medium density fberboard (MDF). The results indicated that the NaOH treatments can dissolve a portion of hemi- celluloses and almost all amount of extractives from the fb- ers, but it was not strong enough to remove the lignin thor- oughly. The FTIR results illustrated that chemical changes can occur during the various NaOH treatments of the fb- ers. X-ray difraction analysis revealed that the crystallinity of the studied fbers increased after the alkaline treatment. Investigation of mechanical properties of the MDF showed that modulus of rupture and internal bond strength of the treated samples were decreased compared to the control ones. In addition, water absorption and thickness swell- ing of treated boards were higher than that of untreated samples. This study indicated that the physico-mechanical properties of the boards were negatively afected by the NaOH treatment. * Hamid Zarea Hosseinabadi hzareah@ut.ac.ir 1 Department of Wood and Paper Sciences and Technology, Faculty of Natural Resources, University of Tehran, P.O. Box 31585-4313, Karaj, Iran 2 Division of Materials Science, Luleå University of Technology, 97187 Luleå, Sweden 3 Faculty of Natural Resources, Sari University of Agricultural Sciences and Natural Resources , Sari, Iran