Improvement of properties of medium density fiberboard manufactured from recycled fibers using modified resin with isocyanate

In this study, in order to improve the medium density fiberboard properties made of mixture of virgin and recycled fibers, urea formaldehyde resin was modified by adding 3 and 5% isocyanate. Experimental boards were made by adding recycled fibers to virgin fibers (0, 20%, 40%, 60%,80% and 100%) and using 10% urea formaldehyde as binder. Mechanical (modulus of rupture and internal bond) and physical properties (water absorption and thickness swelling after 2 and 24 hours submerging) were measured based on DIN68761 standard. The results showed that by increasing recycled fibers, the modulud of rupture and internal bond were reduced but inclination was slow up to 40% recycled fibers while by addition the recycled fibers more than 40%, the inclination became faster. On the other hand, the modulus of rupture and internal bond of fiberboards made of mixture of 40% recycled fibers and 60% virgin fibers reduced 7% and 21% respectively. This fault was fixed by modifying urea formaldehyde resin by adding 5% isocyanate adhesive. The results demonstrated that the modulus of rupture and internal bond of fiberboards made in this condition increased 20% and 102% respectively. Furthermore, adding recycled fibers to virgin fibers reduced water absorption and thickness swelling. This improvement can be attributed to the modifying of urea formaldehyde resin with isocyanate. In addition, the fiberboards made of 100% recycled fibers and modified urea formaldehyde resin by adding 5% isocyanate showed the lowest water absorption (29.86%) and also thickness swelling (3.38%).