Effect of Si–Al molar ratio on microstructure and mechanical properties of ultra-low density fiberboard

Si–Al compounds represent the substances having silicium (Si) and aluminum (Al) in the mixed aqueous solution of sodium silicate and aluminum silicate. Their chemical structure depends on Si–Al molar ratio. In this study, several Si–Al molar ratios were used to prepare different Si–Al compounds. These Si–Al compounds were added in the manufacturing process of ultra-low density fiberboards (ULDFs) to examine the effects of Si–Al molar ratio on the microstructure and the mechanical properties of ULDFs. Scanning electron microscope-energy dispersive spectroscopy, X-ray photoelectron spectrometer, infrared spectrometer, X-ray diffractometer and electronic universal testing machine were used to analyze the microstructure and mechanical properties of ULDFs. The results showed that the microstructure and bulk density of ULDFs were affected by Si–Al molar ratios. The mechanical properties of ULDFs were also significantly affected because of Si and Al components being uniformly distributed on the fibers’ surface and formation of Si–O–C bond. When Si–Al molar ratio was 2:1, the modulus of elasticity, modulus of rupture and internal bond strength of the ULDF was up to 20.78, 0.17, and 0.025 MPa, respectively.