Coating, Weathering And Anti-Mold Performances Of Wood Modified With Mixing Solution Of Sucrose And N-methylol Resin

Wood from fast-growing species is soft, less dense, and low resistant to weathering and fungal decay. Chemical modification is one of strategies improving the quality of fast-growing wood species. Modification can usually change the surface energy of wood surface, thereby influencing the coating performance of finishes, especially the waterborne finishes. Previously, we have already modified poplar and Radiata pine wood with a mixing aqueous solution of sucrose and a N-mehtylol resin, 1,3-dimethylol-4,5-dihydroxyethyleneurea (DMDHEU). The modified wood exhibits good fixation of chemicals, dimensional stability, and durability to fungal decay. In this study, we measured the performance of coating, weathering and mildew resistance of the modified wood coated with five types of waterborne finishes and wood wax.The results show that the contact angel of water on the modified poplar and pine decreases by 6.17% and 5.56% respectively, and the drying time of finishes on the modified wood surface increases compared to that on the unmodified controls; the surface drying time is 4-63% longer and the full drying time is 4-80% longer. Adhesion test of finishes according European standard prENV 927-8 indicates that modification causes decrease in transversal tensile strength between wood cells and increase in the wet adhesion.After 12-month outdoor weathering (from July 2014 to July 2015) according to European standard EN 927-3, the contact angel of water on the surface of modified wood is bigger than that on the unmodified wood. And with the aging time going on, all uncoated wood surfaces present darker color; poplar wood surfaces exhibits greater change in color than Radiata pine wood. Modification causes smaller AE* compared to the unmodified wood. Uncoated wood surfaces present visual tiny checks and cracks after 9-month weathering, but the numbers on the modified wood are less than on the unmodified controls. FT-IR spectral analysis indicates that bands located at 1595 cm-1 and 1505 cm-1 assigned to lignin disappear after 12-month weathering. The surface color and FTIR spectra of coated wood, either modified or unmodified, does not change obviously after such a short-term weathering. The adhesion of five waterborne finishes on the modified and unmodified wood decreases after 17-month weathering. The wet adhesion of the modified pine is greater than the untreated controls. The modifying effect on the wet adhesion is limited for poplar wood after weathering.The mildew resistance test according to America standard ASTM D3273-00 indicated that only on the uncoated and unmodified wood surface molds were observed after 72-day incubation. The molds cannot grow on the surface of the treated and coated samples.Consequently, modification with sucrose/DMDHEU can improve the wettability and the wet adhesion of the finishes on wood, but reduce the drying rate. The modified wood is resistant to mold growth and weathering. This facilitates to alongate the service life of wood.