**Author details**

**13. Sol-gel method**

116 New Technologies in Protective Coatings

**14. Fire resistance of timber**

In recent years, sol-gel processes have also become recognized for the purposes of incorporating fire retardants into products. The process comprises hydrolysis and condensation reactions that lead to the formation of inorganic or organic-inorganic hybrid coatings. This technique is well documented for different polymers. Giudice et al. synthesized the polysiloxanes in wood pores by sol-gel process using aminopropylmethyldiethoxysilane, aminopropyltriethoxysilane and a mixture of both (50/50 ratio), and then, impregnated panels were subjected to 2-foot tunnel test (flame spread index, panel consumption, and smoke density). Impregnation process was carried out at 40–50°C in an autoclave and controlling the operating conditions for achieving different weight gains. It was shown by the authors that aminopropyltriethoxysilane-treated wood sample showed best fire retardant efficiency. This is because of more reactivity of alkoxide, which forms hybrid structure [81]. Another study showed that the transparent fire retardant coating for wood (pine and larch) was prepared by a sol-gel method using vinyl functionalized zirconium oxy-clusters copolymerized with vinyl trimethoxysilane. Results showed that coating has improved the fire retardant properties and

The use of timber components in the loading structure in a building relies on fire engineering design to ensure that the building can retain its structural integrity for sufficient time either for building occupants to be evacuated, or for the fire to be extinguished. In construction using large cross-section timber members, like cross-laminated timber, this may be done by assuming a rate at which the timber chars and therefore the cross-section of timber remaining after a given time [83]. The strength and stiffness of timber both reduce at lower temperatures than steel and concrete. For example, timber's strength is reduced by more than 50% at 100°C, compared with that at 20°C [84]. Timber structural members may still perform well at high temperatures in comparison with steel, however, since the char layer can act to insulate the material within, whereas the high thermal conductivity of steel means that the complete section quickly heats up. Where steel is used to connect timber elements, heat can be quickly conducted through the connectors, degrading the strength and stiffness of the wood around them. The behavior of timber in fire is fundamentally different to steel and reinforced concrete; however, since it is combustible, research groups have identified that the key research needs to be addressed for the next generation of large timber buildings [85, 86]. They address the performance of systems with various levels of encapsulation, the effect of flame spread due to a combustible structural material, and the fire performance of connections. Another potential use for coatings is to increase the fire resistance of structural timbers. It was showed that significant increases in fire resistance can be achieved by using fire resistant coatings. This concept should be pursued by the timber industry, as it would be possible to improve the fire resistance of structural timbers in old buildings that are being remodeled. The application of a fire resistive coating would be simpler and cheaper than cladding the members in fire resistive board materials, or replacing the timber member with a concrete or steel member.

also without affecting the macroscopic appearance of wood surface [82].

Thirumal Mariappan

Address all correspondence to: thirumal.mariappan@asianpaints.com

Research and Technology Center, Asian Paints Limited, Navi Mumbai, Maharashtra, India
