Effect of Lignin Modification of Recycled and Fresh Wood Fibers on Physical, Mechanical, and Thermal Properties of Fiberboard

In this study, some physical properties; the thickness swelling, water absorption, surface absorption, formaldehyde emission, and some mechanical properties; internal bond strength, bending strength, bending modulus, and surface soundness of the MDF panels produced using recycled fibers obtained from the waste MDF and fresh wood fibers were investigated. Moreover, the effect of the kraft lignin modification to the recycled fibers and fresh fibers on the bond strength and mechanical properties of the MDF panels was determined. The results were compared with the MDF panels produced using fresh wood fibers. Although replacing fresh fiber with recycled fibers adversely affected the thickness swelling/water absorption (water resistance) and strength properties of fiberboard, the modification of the fibers using the lignin improved the properties of the fiberboard. The internal bond strength of the MDF produced with the 10 wt% recycled fibers modified at the 5 wt% and 7.5 wt% lignin contents was found to be higher than that of the specimens produced with 100 wt% fresh pine fibers. The formaldehyde emission of the MDF increased with increasing recycled fibers content. The lignin modification slightly decreased the formaldehyde emission of the MDF with the recycled fibers. Consequently, it can be said that the utilization of untreated recycled fibers decreased the mechanical properties of the MDF while the modification of these fibers using kraft lignin (5 wt% and 7.5 wt%) improved the mechanical properties, water resistance, and decreased formaldehyde emission of the MDF.