Preparation and Properties of PMUF Resin Adhesive SURFACE MODIFICATION OF POPLAR VENEER AND ITS BONDABILITY CROSS—LINKING EFFECT BETWEEN WOOD AND MELAMINE-FORMALDEHYDE Variation of Temperature inside the Mats for Wood-Based Panels by High-Frequency Hot Pressing Process Research on Moisture-Resistance of Finish Foil Impregnated with UMF Resin