Chemical changes of wood fibers after hydrothermal recycling of MDF wastes

Annually, a large volume of medium density fiber board (MDF) wastes are generated which consists of used furniture and other constructed items, the parts obtained from trimming and edge cutting of boards in MDF producer factories and cutting of boards during conversion processes. In this study, changes in the chemical properties of wood fibers after hydrothermal recycling of MDF wastes as an important aspect of recycling process which may be effective on quality of recycled MDF boards was investigated. Hydrothermal recycling was done at 3 different temperature (105, 125 and 150 degrees C) in which subsequently defibrillation step was performed. Recycled fibers were analyzed by determination of chemical composition of fibers, pH value and possible existence of UF resin residues on the surface of recycled fibers. Gel time of UF resin in the mixture of fibers was measured. Additionally, laboratory MDF boards with dimension of 35 x 35 x 12 mm and density of 0.7 g/cm(3) were manufactured. Practical properties of MDF boards were studied according to EN standard. Significant quality fall off was observed in recycled MDF boards as compared to original ones. Also, the results showed that some chemical changes were occurred in fibers after recycling process which may be effective on properties of new (recycled) MDF boards. FTIR results confirmed the presence of UF resin residues on the surface of recycled fibers which considered as reason for deterioration in properties of recycled MDF boards. Also, the results obtained from gel time measurements confirmed the negative effect of recycled fibers on the curing of UF resin.