Properties and mechanism of poplar wood modified by melamine-urea-glucose (MUG) biomass resin and sodium silicate compound

  Objective  In order to provide basis for the application of melamine-urea-glucose (MUG) composite modifier and promote wood green modification, the changes of micro morphology, chemical structure and element composition of modified wood were studied, and the modification mechanism of biomass resin compound modifier on wood was discussed.

  Method  By introducing hydrophobic groups such as organosilane into the compound solution of MUG biomass resin and sodium silicate, the silane hybrid modifier (GS_T) was prepared. Then the poplar wood was modified with it by vacuum pressure impregnating treatment. The physical and mechanical properties of modified wood were tested. Its micro-morphology, chemical structure, element composition and crystallinity were characterized by scanning electron microscopy-energy dispersive X-ray spectrometer (SEM-EDX), Fourier transform infrared spectrometer (FTIR), X-ray photoelectron spectroscopy (XPS) and X-ray diffractometer (XRD). The combustion performance and pyrolysis characteristics were tested by micro calorimeter (MCC).

  Result  SEM-EDX analysis showed that GS_T modifier had good permeability and can effectively penetrate into wood cell cavity and cell wall; the C, O and Si element of modified wood were irregularly distributed in wood cell cavity, cell wall and cell gap, and the modifier was most deposited in wood vessels. Due to the effective filling of wood pores and the swelling of cellulose amorphous zone, wood dimensional stability and mechanical properties were improved. FTIR analysis showed that hemicellulose and other polysaccharides in GS_T modified wood had a cross-linking reaction with the modifier, reducing C=O, —OH and other hydroscopic groups. XPS analysis found that the C1 of GS_T modified wood was the most and its C3 was the least. During the modification process, the active groups such as polysaccharides, lignin alcohol hydroxyl, phenol hydroxyl and carbonyl reacted with the modifier, reducing the active groups and increasing the contents of C—H and C—C structure. XRD analysis showed that the diffraction peaks of the GS_T modified wood had no obvious change, its relative crystallinity increased, indicating that the modifier entered the amorphous region of cellulose to make its molecular arrangement more orderly. MCC analysis showed that the heat release capacity, peak heat release rate and total heat release of GS_T modified wood decreased by 65.7%, 66.2% and 6.2%, respectively, the residual carbon rate at 800 ℃ increased by 122.6%, its heat release intensity was greatly reduced and its fire risk was reduced.

  Conclusion  GS_T compound modifier can effectively penetrate into poplar wood, cross-linked with its hemicellulose and other polysaccharides, reduce active groups such as sugar groups, and make the arrangement of amorphous regions more orderly, so as to improve its physical and mechanical properties.