2.7.3 Physical Properties of Resins
The various physical properties of resins can be generalized as detailed below:
1. Resins, as a class, are hard, transparent or translucent brittle materials.
2. They are invariably heavier than water having the specific gravity ranging from 0.9-1.25.
3. Resins are more or less amorphous materials but rarely crystallisable in nature.
4. On being heated at a relatively low temperature resins first get softened and ultimately melt down thereby forming either an adhesive or a sticky massive fluid, without undergoing any sort of decomposition or volatilization.
5. On being heated in the air i.e., in the presence of oxygen, resins usually burn readily with a smoky flame by virtue of the presence of a large number of C-atoms in their structure.
6. On being heated in a closed container i.e., in the absence of oxygen, they undergo decomposition and very often give rise to empyreumatic products i.e., products chiefly comprising of hydrocarbons.
7. Resins are bad conductors of electricity, but when rubbed usually become negatively charged.
8. They are practically insoluble in water, but frequently soluble in ethanol, volatile oils, fixed oils, chloral hydrate and non-polar organic solvents e.g., benzene, n-hexane and petroleum ether.
