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What Is Resin?
Resins are viscous polymeric liquids that can be of either organic or synthetic origin. One of their most remarkable properties is the ability to transform from a liquid state into customizable solids, forming a homogeneous structure.
In polymer chemistry and materials science, resin refers to either a solid substance or a highly viscous material derived from plant sources or synthetic origins.
Plants naturally produce resin as a protective response to cellular or tissue damage. This secretion defends the plant from insects and pathogens (microorganisms like bacteria and viruses). A classic example of the durability of resins is the encapsulation of insects in amber.
Today, many of these natural resins are widely used in preservation and protective applications. Their synthetic equivalents, which exhibit similar properties, are produced in the petrochemical industry and used in products such as paints and coatings, repair mortars, and structural adhesives.
In addition to forming homogeneous structures—such as protective coatings and linings—resins are also commonly used in mold-making applications.
Polymers are composed of numerous similar units (monomers) linked together. Resins and plastics are typical examples of synthetic polymers.
Main Categories of Resins:
Types of Resin
Thermoset Resins:
Thermoset resins are formulated to undergo a chemical reaction that creates a three-dimensional crosslinked network once cured. These resins require a curing agent to initiate the process before the resin reaches full saturation. The result of the curing process is a rigid structure that cannot be re-melted or reshaped. (Curing refers to the chemical process where the resin reaches its maximum strength and final hardened form.)
In reinforced composites, the system usually consists of the resin matrix (including curing agents, hardeners, inhibitors) and fillers or reinforcements.
Thermoset-based composites exhibit high dimensional stability, excellent heat resistance, and strong solvent resistance due to their crosslinked molecular structure. Common types of thermoset resins include:
Thermoplastic Resins:
Thermoplastics make up a smaller segment of the resin industry. These resins are sold as non-reactive solids and do not undergo chemical reactions during processing. Unlike thermosets, thermoplastics are shaped and molded under the application of heat and pressure and can be re-melted multiple times.
When heated, thermoplastics soften and become highly viscous liquids. Upon cooling, they revert to a solid state. Since the curing process is not chemically driven, a key advantage of thermoplastics is their fast mold cycling capability. One common product made from thermoplastic resins is waterstop strips.
Although the focus of this article is primarily on thermoset resins, it is worth noting that thermoplastics are also widely used in construction, aerospace, marine structures, and machinery.
Examples of Thermoset Resins
Polyester Resins:
Two common types:
Unsaturated polyester resin is a macromolecular compound with a molecular weight ranging from 1,000 to 3,000 kDa. It is synthesized through polycondensation reactions involving dicarboxylic acids and diols. Some of the acids contain carbon–carbon double bonds, making the resin unsaturated.
At room temperature and prior to curing, polyester resin typically has a high viscosity and appears as a transparent pink liquid.
Polyester resin is widely used for fiberglass lamination. Glass fibers act as reinforcement material in composites used in flat roofing, ship repairs, and various structural applications.
Epoxy Resins:
Epoxy resin is used in composites to enhance strength, durability, and chemical resistance. It performs well in both dry and humid environments and can withstand high temperatures (up to 121°C).
Epoxies are available in liquid, solid, or semi-solid forms and are typically cured by reacting with amines or anhydrides.
Unlike polyesters, epoxies do not require a catalyst for curing. However, a curing agent or hardener (component B) must be mixed with the resin base (component A) in a precise ratio for proper curing. This reaction, known as an addition reaction, ensures the resin fully hardens and performs effectively.
Accurate mixing following manufacturer specifications is essential to ensure complete curing and optimal performance.
For more information and professional consultation, please contact Abadgaran's technical support team.