# Optimizing the Performance of Window Frames: A Comprehensive Review of Materials in China
## 3 Improvement Methods and Sustainability Assessment
### Wood
This technique allows the formation of one or multiple controllable high-density layers along the thickness of the wood, with control over the position and thickness of the compression layers, while achieving improvements in mechanical performance through compression requires a high compression ratio, leading to elevated manufacturing costs. Heat treatment is a simple and effective strategy for improving the dimensional stability and durability of wood; unfortunately, heat treatment may result in the collapse of the wood structure, limiting the final use of heat-treated wood [42; 43; 44]. Typically, pre-treatment with chemical substances before heat treatment can effectively mitigate this issue. [PERSON] et al. [45] demonstrated a method of enhancing the mechanical properties of heat-treated wood without compromising its dimensional stability through pre-treatment with chemical substances; the combination of impregnation and heat treatment results in superior mechanical and durability properties of the wood [46; 47]. Coating technology is widely applied in various fields, and different types of coatings can be used to protect wood based on desired characteristics and applications; these coatings include preservatives (anti-fungal agents), flame retardants, waterproofing agents, fillers, and more [48; 49; 50]. In addition, [PERSON] et al. [51] effectively isolated wood from water contact by constructing a superhydrophobic coating on the wood surface; this coating alleviates issues such as deformation, cracking, and decay caused by the wood's strong moisture/water absorption capacity. Simultaneously, it imparts new functionalities to the modified wood, including waterproofing and self-cleaning properties. * Chemical modifications  
Subtractive chemical modification involves the partial or complete removal of certain components from wood (such as cellulose, hemicellulose, lignin, extractives, and other functional groups), resulting in the creation of new chemical or pore structures, which can give wood new functions. The removal of wood components introduces more nanopores on the cell wall without disrupting the original cell structure of the wood [52; 53; 54; 55; 56]. Delingification is a common subtractive chemical modification strategy, involving the removal of lignin from natural wood through chemical treatment. Delingification retains the pore structure of natural wood and the cellulose nanofibers in the cell wall and can be used to produce \"white wood\" (also called \"nano wood\"). For example, delignified wood reflects most incident light and appears white, as well as possessing a lower thermal conductivity than natural woods [54; 57]. Carbonization is another common subtractive chemical modification strategy that can remove wood components (such as cellulose, hemicellulose, lignin, and extractives) and convert the residual material into amorphous carbon; carbonized wood inherits the cell structure of natural wood while enhancing the wood's light absorption properties and corrosion resistance [58; 59]. The additive chemical modification involves the addition of various components (such as inorganic particles, polymers, metals, and metal-organic frameworks) or functional groups to wood, resulting in different structures and materials with additional properties and/or functionalities [58; 60; 61]. In situ polymerization and mineralization have been extensively explored, achieving structural changes in wood at the cell wall level by coating, impregnating, or filling polymers or inorganic components into the cell wall and/or cavities [62; 63]. In addition to the inherent properties of the added components, the location of the additives and the relationship between additives and wood components play a crucial role in the modification.