# Optimizing the Performance of Window Frames: A Comprehensive Review of Materials in China
## 3 Improvement Methods and Sustainability Assessment  
### Wood  
* Adhesive technologies  
The moisture content of wood significantly influences its properties, and within the moisture range from bone-dry to the fiber saturation point, the uptake or release of moisture induces dimensional changes in the wood cell wall [31; 32; 33]. In current applications where wood is used as a material for window frames, it is often processed into gluam, which improves the dimensional stability and durability of the wood. Glulam is typically based on solid wood, and the production involves cutting, grading, drying, and sterilization as pre-treatments; high-performance adhesives are then used to bond the wood pieces in a specific arrangement, as depicted in the typical process flow in Figure 5. For gluam, it is very common to have window frames consisting of three or four lamellas in thickness. The production process of gluam determines that its material properties are closely related to the properties of bonded layer wood and adhesives. Table 1 provides a brief list of wood types, properties, and adhesives commonly used for gluam window frames. Furthermore, different methods of assembly during this process significantly impact the performance of the resulting integrated wood product [34; 35]. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Plywood Type** & **Properties** & **Natural Durability** & **Maintenance** & **Adhesives** \\ \hline \multirow{4}{*}{_Pison spp._} & Low density, light & \multirow{2}{*}{Poc, need anticorrosive treatment} & Check every year and record every & \multirow{4}{*}{\begin{tabular}{} \\ 2-3 years \\ \end{tabular} } \\  & weight, moderate & & & 2-3 years \\ \hline \multirow{4}{*}{_Pims sylestris_} & Low density, light & \multirow{2}{*}{Medium, requires} & \multirow{2}{*}{\begin{tabular}{} \\ \end{tabular} } \\  & weight, easy to process & & & \\ \cline{1-1}  & & & & \\ \cline{1-1}  & \multirow{2}{*}{_Larix_} & Medium density, high & \multirow{2}{*}{\begin{tabular}{} \\ \end{tabular} } \\  & length, good weather & & & \\ \cline{1-1}  & & & & \\ \cline{1-1}  & & & & \\ \cline{1-1}  & \multirow{2}{*}{_Quercus rubra_} & High density, high & \multirow{2}{*}{better, needs to be treated with} & \multirow{2}{*}{\
\begin{tabular}{} \\ \end{tabular} } \\  & hardness, good wear & & & \\ \cline{1-1}  & & & & \\ \cline{1-1}  & & & & \\ \cline{1-1}  & \multirow{2}{*}{_Tectana grandis_} & High density, High & \multirow{2}{*}{
\begin{tabular}{} \\ \end{tabular} } \\  & stability & & & \\ \cline{1-1}  & & & & \\ \cline{1-1}  & & & & \\ \cline{1-1}  & & & & \\ \cline{1-1}  & & & & \\ \cline{1-1}  & & & & \\ \cline{1-1}  & & & & \\ \cline{1-1}  & & & & \\ \cline{1-1}  & & & & \\ \cline{1-1}  & & & & \\ \cline{1-1}  & & & & \\ \cline{1-1}  & & & & \\ \cline{1-1}  & & & & \\ \cline{1-1}  & & & & \\ \cline{1-1}  & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: A brief list of wood types, properties, and adhesives commonly used for gluam window frames; refer to [36]. Figure 4: Typical processes of aluminum corrosion (adapted from [22]). The layered and porous structure of wood allows for the design and modification of the material at its own structural and/or compositional levels. Improvement strategies generally fall into three major categories: physical, chemical, and composite modifications. Chemical modifications can be further divided into two techniques: subtractive modification and additive modification, as illustrated in Figure 5.  
* Physical modifications  
Compression densification is an effective approach for enhancing the mechanical properties, including the hardness and strength of wood [37; 38; 39]. [PERSON] et al. [40; 41] introduced a novel method of inter-layer compression, providing a unique avenue for selective and partial densification of wood.