Currently, the predominant adhesives utilized in the wood industry are derived from Abstract: Currently, the predominant adhesives utilized in the wood industry are derived from petroleum-based sources, primarily formaldehyde resins. These resins are widely employed in the wood-based panel sector due to their exceptional bonding properties. However, the finite nature of fossil resources, coupled with the environmental pollution resulting from their extraction processes, poses significant risks to ecosystems. Moreover, common formaldehyde adhesives release formaldehyde during application, jeopardizing human health. In contrast, biomass presents an ideal green raw material, characterized by its abundance and renewability. Consequently, there has been increasing interest among researchers in developing green adhesives for wood-based panels. It is of great significance to harness plentiful biomass resources to formulate biomass-based adhesives or to explore inorganic adhesives as viable complements to conventional formaldehyde resin systems. Recent investigations have spotlighted the potential of natural polymers (such as tannin, lignin, proteins, and starch) in the development of biomass-based adhesives. This approach not only mitigates the emission of harmful substances like formaldehyde but also diminishes environmental pollution, thereby enhancing the safety of human habitats. Additionally, biomass adhesives offer significant performance adaptability, fulfilling the diverse needs of the wood industry regarding bond strength, water resistance, and thermal stability. Furthermore, inorganic adhesives have gained traction as a robust complement to traditional organic adhesives. Their implementation in the production of various wood-based panel products is driven by their favorable environmental characteristics and high-temperature stability. Unlike organic adhesives, inorganic formulations do not emit harmful gases during the curing process, resulting in reduced risks to both environmental integrity and human health, thereby enhancing their green credentials. This paper aims to review recent advances in replacing or modifying conventional petroleum-based adhesives with biomass alternatives. It will summarize the historical development and bonding mechanisms of wood adhesives, emphasizing the applications of biomass adhesives, such as tannin, lignin, protein, and starch, as well as inorganic adhesives, including silicate, magnesium oxychloride, magnesium oxysulfide, and phosphate, within the wood-based panel industry. By analyzing the strengths and weaknesses of various adhesive types, this study will evaluate the substitution potential and modifying effects of biomass, discuss its prospects in the wood-based panel sector, predict the future direction of green wood adhesives, and provide fresh insights for the development of new eco-friendly adhesive solutions.
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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.
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