# Recent Advances in Bio-Based Wood Protective Systems: A Comprehensive Review
## 2 Bio-Based Coating's Matrix
### Natural Biopolymers for Wood Protection
Its potential for wood protection has been investigated through the synthesis of a vanillin-based polyurethane [86]. The results showed that, when divanillin was incorporated with a proportion of 30% into a polyurethane dispersion, the coating displayed the highest measured hardness. Moreover, the innovative bio-based coating conferred the wood samples high resistance towards acid substances, but also towards alkali substances. Additionally, a vanillin-derived epoxy was cross-linked with polysiloxane to obtain a wood coating with high thermal stability. When applied to bamboo wood, the new coating formulation was shown to improve the flammability resistance of the substrate [87]. In a separate study, polyurethane coatings were synthetized, starting from oleic and dimer fatty acids, which were investigated as renewable sources to obtain environmentally sustainable wood coatings [88]. According to the illustrated results, the bio-based polymer afforded good coating properties to wood, with high mechanical properties and resistance to natural weathering, validating the potential for the protection of wood surfaces. As a natural compound, citric acid has also been exploited for the synthesis of a coating matrix for the treatment of wood surfaces. [PERSON] et al. started from citric acid to generate a hyperbranched polyester-urethane-acrylate [89], which exhibited improved thermal properties compared with a commercially available urethane acrylate. Nevertheless, the chemical resistance of the new coatings was found to be lower if compared with that of a standard used as a reference, suggesting that further studies are needed to optimize the properties of citric acid-based wood coatings. A different and Innovative approach involves the exploitation of a biofilm coating based on living cells. [PERSON] et al. investigated the potential of the living fungus _Aureohsidium pullulans_ to protect Scots pine wood during natural weathering [90]. The innovative wood coating was able to improve the colour stability and aesthetic properties of the wood surface, suggesting a new route of research for the identification of wood protective solutions. It has been shown that the research toward new bio-based components for the matrix of wood coatings is a current and hot field of study, which is attracting the interest of both industries and academic scientists. Table 1 presents a condensed overview of the key findings provided by bio-derived matrices used in wood coatings. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Matrix/Additive** & **Properties** & **Results** & **Ref** \\ \hline Bio-based and fossil-based & Lower hardness and higher & Hardness (Shore D) lower than 70 and wear & [43] \\ acrylate monomers & abrasion resistance & index W (g/cycle) higher than 2.5 \(\times\) 10\({}^{-5}\) & [43] \\ and oligomers & Antimicrobial and & & \\ Essential oils & antifungal features & Termite mortality between 10 and 100\% & [44] \\ Vegetable oils & Lower coefficient of friction & Static friction coefficient \(\mu_{\text{s}}\) below 0.6 & [45] \\ Tung and linseed oils & Higher hydrophobicity & Water contact angle above 80\({}^{\circ}\) over 28 days & [47] \\ Tung and linseed oils & Fungicidal activity & Mass loss below 10\% after exposure to & [48] \\ Tung oil & Lower moisture absorption & wood-decay fungi for 12 weeks & [49] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Summary of the main insights regarding the use of bio-based matrices in the formulation of wood coatings.