Sometimes referred to as Colophony or Greek pitch, gum rosin is a solid resin at room temperature derived from pines and other conifer trees. The sap of the tree is tapped, heated to evaporate the volatile liquid terpene compounds, and then purified. Gum rosin can come in different forms and manufacturers dope their rosins with various substances, such as beeswax, tin or gold. These substances alter the properties of the rosins to exhibit varying levels of friction, colour or acidity. The final product is composed of approximately 90% resin acids (primarily abietic acid). They are monocarboxylic acids and have a typical formula C20H30O2.
Gum rosin is used extensively in the printing and paint industries as it is easily dissolved in alcohol, petroleum, turpentine and other organic dissolvents. It is commonly used in road markings, which requires a specific set reflection. This paint is composed of thermoplastic resin, pigment, and reflective glass beads. In most of the cases, the thermoplastic resin is rosin maleate ester, which is made from the reaction between rosin maleate and polybasic alcohol. Rosin can also be used as a sizing agent; preventing printing oil soaking and dispersing on paper and improves the strength and smoothness of paper. Additionally, it acts as a colour carrier and enhances colour adhesion in printing ink.
Rosin is also used in electrical solder. It’s weak acidic nature makes it a good compound to remove oxidation film from metal surfaces. The solder used in electronics contains 1-3% rosin by weight, which helps the metal flow and forms a film over the solder joints to prevent reoxidation.
Some rosin biopolymers are reported to have excellent biocompatibility. It is commonly used to produce vegan soaps as their properties are close to aliphatic acid with the added benefit of being cheaper to produce. Pine gum’s popularity has increased in recent years due to its density, strength and biodegradability which sets it apart from other resins. The production of Gum Rosin encourages the conservation of pine forests which, due to their fast growth, make excellent carbon sinks while providing a stable income for local farmers.
The resin acids can be used in the synthesis of novel compounds. The characteristic ring structure of gum rosin acids is similar to that of some aromatic compounds. This makes its derivatives potential substitutes in polymers, and could be used for the synthesis of a multi-functional hard monomer or bio-epoxy. Recently, gum rosin was used, along with silver nano-particles, to produce antibacterial composites, which could one day be used in biodegradable medical devices.
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