**2.6 Classification of adhesives for EWPs**

Wood adhesives can be broadly categorized as petroleum-based or natural adhesives. Petroleum-based adhesives can be further categorized as thermosets,

**Figure 9.** *Physical diagram of CLT.*

**Figure 10.**

*Dimension diagram of CLT for different purposes.*

#### **Figure 11.**

*The classification of wood adhesives.*

thermoplastics, and elastomers. Natural or bio-based adhesives can be derived from four main sources, namely lignin, proteins, starch, and tannin. **Figure 11** shows the classification of wood adhesives and their subclassifications.

Commonly used petroleum-based adhesives include UF, phenol-formaldehyde (PF), melamine formaldehyde (MF), resorcinol formaldehyde (RF), and isocyanate-based adhesives [15]. However, growing environmental concerns and the increasing depletion of petroleum-based resources have put pressure on the wood composites industry to develop environmentally friendly adhesives using renewable resources [16].

*Current Applications of Engineered Wood*
