Water-resistant toughening modification of wood fiber-reinforced gypsum-based composites

The poor water resistance and toughness of wood fiber-reinforced gypsum-based composites limit their further development, and the water resistance and toughening modification of wood fiber-reinforced gypsum-based composites were carried out for the above two defects of this material to improve the application fields and economic benefits of gypsum-based composites.

The effect of silicate cement as inorganic modifier and polyvinyl alcohol solution (PVA) as toughening agent was investigated on the mechanical properties and water resistance of wood fiber-reinforced gypsum-based composites in synergy, and the microstructure of the composites was characterized by X-ray diffraction (XRD), Fourier infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM).

Silicate cement and PVA produced synergistic effect in the composites, and the synergistic effect could make up for the defects of low strength of single admixture of cement and poor water resistance of single admixture of PVA. The flexural and compressive strengths of the composites were 5.56 MPa and 10.01 MPa, respectively, which were 40% and 63% higher than those before modification. 2 h water absorption and 24 h water absorption were 19.83% and 20.14%, respectively, which were 10.17% and 11.97% lower than those before modification, and the softening coefficient was increased by 0.4. XRD, FT-IR, and SEM results showed that the hydration reaction of cement with gypsum produced hydrates such as calcium vanadate and calcium silicate gel, and the hydrates filled the cement gypsum matrix. The results of pore structure analysis showed that the addition of cement and PVA reduced the porosity of the composites and reduced the appearance of oversized pores, and the water resistance and mechanics of the composites were improved.

The addition of silicate cement affects the internal hydration reaction of the composites, resulting in the mechanical strength of the composites. The addition of PVA results in a tightly connected material inside the composites, which improves the mechanical properties of the composites, but the water resistance is poor. The synergy of silicate cement and PVA can improve the mechanical properties and water resistance of the composites, and make up for the defects of the composites with reduced mechanical properties of silicate cement alone and poor water resistance of the composites with PVA alone.