| Urea formaldehyde (UF) resin is the main adhesive used in the manufacture of medium density fibreboard (MDF). Methods were developed to characterize the effects of four factors related to UF resin efficiency on MDF application. The four factors include resin distribution, resin penetration, resin pre-cure and resin loss. The resin coverage distribution on, and penetration into MDF fibres were determined with a confocal laser scanning microscope (CLSM) and an image analysis system. The resin pre-cure degree and resin loss were quantified with differential scanning calorimeter (DSC) and Kjeldahl analyzer, respectively. The fibre size strongly affected resin coverage ratio distribution and the chance to collect resin droplets but it was not significant in resin droplets size distribution. The main penetration direction of UF adhesive was toward the cell/fibre lumen. The penetration of UF into wood fibre was very easy and rapid under high moisture and temperature conditions. Along the different processing stages of the MDF manufacture, maximum penetration depth was reached in the second dryer stage. After the second dryer stage, the penetration/diffusion was practically almost terminated. The resin pre-cure and resin loss had significant negative effects on resin efficiency. The storage of blended fibres in warm conditions for a long period of time was also a main reason for lower resin efficiency. |
