Editing Shellac (section)

== Properties ==
[[File:Haydn shellac.jpg|thumb|right|A decorative medal made in France in the early 20th century moulded from shellac compound, the same used for [[phonograph record]]s of the period]]
Shellac is a natural [[bioadhesive]] [[polymer]] and is chemically similar to synthetic polymers.<ref>https://pubchem.ncbi.nlm.nih.gov/compound/shellac gives the chief component as 9,10,15-trihydroxypentadecanoic acid and also (2R,6S,7R,10S)-10-hydroxy-6-(hydroxymethyl)-6-methyltricycloundec-8-ene-2,8-dicarboxylic acid, molecular formula C<sub>30</sub>H<sub>50</sub>O<sub>11</sub> with a molecular weight of 586.7 g/mol </ref> It can thus be considered a natural form of [[plastic]].
 
With a melting point of {{convert|75|C}}, it can be classed as a [[thermoplastic]] used to bind [[wood flour]], the mixture can be [[moulding (process)|moulded]] with heat and pressure.

Shellac scratches more easily than most lacquers and varnishes, and application is more labour-intensive, which is why it has been replaced by plastic in most areas.  Shellac is much softer than [[Urushi]] lacquer, for instance, which is far superior with regard to both chemical and mechanical resistance.{{Cn|date=January 2021}} But damaged shellac can easily be touched up with another coat of shellac (unlike polyurethane, which chemically cures to a solid) because the new coat merges with and bonds to the existing coat(s).

Shellac is [[solubility|soluble]] in [[alkaline]] solutions of [[ammonia]], [[sodium borate]], [[sodium carbonate]], and [[sodium hydroxide]], and also in various [[organic solvent]]s. When dissolved in alcohol (typically [[Denatured alcohol|denatured ethanol]]) for application, shellac yields a coating of good durability and hardness.<ref>{{Cite journal |last=Chen |first=Ying |last2=Zhu |first2=Zhu |last3=Shi |first3=Kunbo |last4=Jiang |first4=Zhiyao |last5=Guan |first5=Chengran |last6=Zhang |first6=Liang |last7=Yang |first7=Tao |last8=Xie |first8=Fengwei |date=2024-11-01 |title=Shellac-based materials: Structures, properties, and applications |url=https://linkinghub.elsevier.com/retrieve/pii/S0141813024059087 |journal=International Journal of Biological Macromolecules |volume=279 |pages=135102 |doi=10.1016/j.ijbiomac.2024.135102 |issn=0141-8130|doi-access=free }}</ref>

Upon mild [[hydrolysis]] shellac gives a complex mix of [[aliphatic]] and [[alicyclic]] [[hydroxy acids]] and their polymers that varies in exact composition depending upon the source of the shellac and the season of collection. The major component of the aliphatic component is [[aleuritic acid]], whereas the main alicyclic component is [[shellolic acid]].<ref name="Merck Index, 9th Ed. page 8224">Merck Index, 9th Ed. page 8224.</ref>

Shellac is UV-resistant, and does not darken as it ages (though the wood under it may do so, as in the case of pine).<ref name="naturalhandyman.com" />