# Recent Advances in Bio-Based Wood Protective Systems: A Comprehensive Review
## 2 Bio-Based Coating's Matrix
### Vegetable Oils and Their Derivatives
Another natural oil with a putative potential for wood protection is extracted from the seeds of the soybean. Among the many studies available in the literature, [PERSON] et al. reported that soybean oil could improve the functional performance of a waterborne polyurethane acrylate resin. After modification with acrylic acid, the researchers introduced the modified epoxy soybean oil into the resin, and this resulted in a fast-curing resin that provided good mechanical and thermal properties to the wood substrate [61]. Furthermore, the plasticizer effect of epoxidized soybean oil might be exploited to counter the issues related to the high britteness and low toughness of furfuryl alcohol treatment. The work published by [PERSON] et al. proved that epoxidized soybean oil improved the toughness and the mechanical properties of the wood substrate, with increased values of tensile stress and impact bending strength compared with the values reported for the simple furfuryllated wood [62]. Epoxidized soybean oil has also been found to synergistically enhance the activity of succinic anhydride to protect wood samples against the photooxidation damage induced by ultraviolet (UV) radiation [63]. In another study, by mixing epoxidized soybean oil with epoxidized grapesed and corn oils, diglycidyl ether of bisphenol A (DGEBA), and maleopimaric acid (MPA), a wood coating was obtained, which was able to reduce the passage of water and fungi into the sample and thus to provide anti-fungi resistance [13]. Ultimately, the addition of a modified betulin sample, an organic compound isolated from the bark of birch trees, could improve the coating properties of acrylate epoxidized soybean oil owing to the formation of a cross-linked rigid structure between the two components [64]. [PERSON] et al. used acetylated epoxidized soybean oil together with the flame retardant FRC-6 and itaconic anhydride to prepare waterborne coatings with good hardness, adhesion, and solvent resistance [65]. Additionally, good flammability properties were provided by the presence of the flame retardant. Nonetheless, the coating performance of the acrylate epoxidized soybean oil was shown to be exceeded by an acrylate obtained from cardanol-modified fatty acid from camelina oil. Compared with the former, the latter displayed higher tensile strength and hardness, resistance to solvents, and higher thermal decomposition temperature [66]. Epoxidized camelina oil (ECO) and acrylate epoxidized camelina oil (AECO) were proven to be effective wood coatings with better mechanical properties and thermal behaviour compared with soybean oil polymers. Both typologies of camelin oil-based coatings had high pencil hardness values and good adhesion to the substrate. Nevertheless, ECO displayed reduced mechanical strength and gloss values compared with AECO [67]. Despite being less exploited compared with other most famous essential oils, peanut oil also represents a source of bio-precursors for the design of wood coatings. In the study published by [PERSON] and co-workers, N,N-bis(2-hydroxyethyl) fatty amide was produced from peanut oil and used as precursors for the synthesis of polyurethane [68]. The obtained wood coating displayed excellent behaviour, both in terms of mechanical and thermal properties, but also antimicrobial and chemical resistance, representing a valid alternative in substitution of petroleum-based coatings. In addition to the most explored vegetable oils, for which many studies can be traced in the literature, other less-known oils of natural origin have been investigated for their potential to provide a barrier effect to wood. The Mahua tree is a medium/large-sized tree, which mostly grows in India. The oil extracted from this plant was identified as a possible precursor for the synthesis of polyurethane. Mahua oil was indeed used as raw material for the synthesis of polyetherimide polyol, and the consequently obtained polyurethane displayed high resistance to water, solvents and chemicals, and good mechanical, thermal, and antimicrobial properties [69].