Characterization of chemical wood modification with melamine-urea-formaldehyde prepolymer on fast-growing wood.

To improve their overall performance, fast-growing poplar logs were modified by impregnation with a melamine-urea-formaldehyde (MUF) prepolymer. The results showed that density, dimensional stability, and mechanical properties of fast-growing poplar were markedly improved. The vertical density profile curves confirmed the even distribution of wood modifier in wood cells after impregnation. The water uptake for 72 h improved from 118.5 to 77.2%. Meanwhile, swelling of the modified wood in cross-section, radial section, and volume was decreased to 2.6, 3.1, and 4.8%, respectively. Significant improvements occurred in wood mechanical properties such as bending strength, compressive strength parallel to grain, modulus of elasticity in static bending, and hardness. The mechanism of modification was characterized by X-ray diffraction (XRD), Fourier transform IR spectroscopy (FTIR), and scanning electron microscopy with energy-dispersive X-ray analysis (SEM-EDXA). Dynamic mechanical analysis showed that the storage modulus value of wood samples increased from 6.4 to 7.48 GPa. XRD showed that crystallinity of wood increased and formed a quasi-crystalline. FTIR analysis demonstrated that a chemical crosslinking reaction existed between the function groups of -NHCH 2 OH from the MUF prepolymer and the wood carboxyl C=O. Finally, SEM-EDXA indicated good dispersion of the modifier in wood fiber and other vertical cells.