Sodium silicate/magnesium chloride compound-modified Chinese fir wood

The difference between wood supply and demand was sought to be alleviated by considering fast-growing Chinese fir wood, based on its characteristics of large yield but poor performance. Modification of fast-growing Chinese fir wood is an effective method for improving the wood's characteristics. Sodium silicate/magnesium chloride-modified fir (SS-MCMF) was prepared by adding magnesium chloride (MC) in the process of silicate (SiO₃²⁻) impregnation, with sodium silicate (SS)-modified fir (SSMF) and natural wood (NW) as references. The products were then tested for physical and mechanical properties and bonding mechanisms. The results showed that the bending strengths of SSMF and SS-MCMF specimens were increased by 36.16 and 62.97%, respectively, compared with NW specimens, and the compressive strength of SSMF and SS-MCMF specimens increased by 39.90 and 90.67%, respectively. The hardness of SSMF and SS-MCMF specimens increased from 3685 (of NW) to 5534 and 5843 N, respectively. The water absorption rate of samples after 96 h water exposure decreased from 159.25 to 97.39 and 83.06%, respectively, and the leaching rate at 14 days decreased from 16.01 to 8.92%. In addition to improvements in physical, mechanical, and fixing properties, FTIR and XRD analyses confirmed that SS damaged lignin and hemicellulose in this wood and that Si–O–Si and Si–O–C structures were indeed formed in these modified samples. The addition of MC effectively protected the wood from possible SS damage while also greatly improving its performance. Therefore, the combination of SS and MC for modifying Chinese fir was an efficient, green, and environment-friendly impregnation modification method.