Sodium silicate was used to form Si–O–Si framework by gel process and optimize the effect of the methylolurea impregnation on poplar wood. The modifier cured within the wood micropores by in-situ gel polymerization during the kiln drying. The results showed that treated wood acquired higher mechanical strength, but lower hygroscopicity. New positions of the XRD peaks appeared which caused by silicate sodium indicated that, modifier polymerized as kind of crystal within wood fiber amorphous areas. FT-IR analysis showed that the wood–OH, Si–OH from Si–O–Si framework and N–CH2–OH from methylolurea could reacted with each other to form C–O–Si bond and C–O–C bond. TEM showed that the Si–O–Si framework were embeded averagely in impregnated modifier. SEM-EDX analysis showed that the modifier remained ranging from a thin layer on the cell walls to big props filling the lumen.

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