Epoxy is a building material that is widely used in applications beyond its original purpose. The term epoxy has been widely adapted for many uses beyond its original use for fiber-reinforced polymer composites. Today, epoxy adhesives are sold in local building materials stores, and epoxy resin is used as a binder in countertops or floor coverings. Although there are numerous uses for epoxy, these areas continue to expand. And epoxy grades are constantly being developed to suit the industries and products in which they are used. This article contains information about the structure and usage areas of epoxy.
Some Areas Where Epoxy Is Used
Some of the things that epoxy resin is used for are:
• General purpose adhesives
• Binders in cement and mortars
• In rigid foams
• Anti-slip coatings
• Solidification of sandy surfaces in oil drilling
• Industrial coatings
• In the storage and encapsulation environment
• In fiber reinforced plastics
In the field of fiber reinforced polymers or plastics, epoxy is used as a resin matrix to effectively hold the fiber in place. Compatible with all common reinforcing fibers including glass fiber, carbon fiber, aramid and basalt.
Common Products For Fiber Reinforced Epoxy
According to the manufacturing process, the products commonly produced with epoxy are:
- Filament Winding
- Pressure vessels
- Rocket slots
- Amusement equipment
- Insulator bars
- Arrow shafts
- Compression Molding
- Aircraft parts
- Skis and snowboards
- Circuit boards
- Prepreg and Autoclave
- Aviation components
- Bicycle frames
- Hockey sticks
- Vacuum Infusion
- Wind turbine blades
The same epoxy resin probably cannot be used for each of these processes. Epoxies are fine-tuned for the desired application and manufacturing process. For example, extrusion and compression molding epoxy resins are heat activated, while an infusion resin can be a medium cure and have a lower viscosity. Compared to other conventional thermoset or thermoplastic resins, epoxy resins have different advantages such as:
- Low shrinkage during curing
- Excellent moisture resistance
- Excellent chemical resistance
- Good electrical properties
- Increased mechanical and fatigue strength
- Impact resistant
- No VOCs (volatile organic compounds)
- Long shelf life
Chemistry of Epoxy Resin
Epoxies are thermosetting polymer resins in which the resin molecule contains one or more epoxide groups. Its chemistry can be perfectly adjusted to the required molecular weight or viscosity for end use. There are two main types of epoxy, glycidyl epoxy and non-glycidyl. Glycidyl epoxy resins can also be defined as glycidyl-amine, glycidyl ester or glycidyl ether. Non-glycidyl epoxy resins are either aliphatic or cyclo-aliphatic resins. One of the most common glycidyl epoxy resins is created using Bisphenol A (BPA) and synthesized by a reaction with epichlorohydrin. Another commonly used type of epoxy is known as a novalac based epoxy resin.
Epoxy resins are cured by the addition of a curing agent, commonly called a hardener. Perhaps the most common type of curing agent is amine-based. Unlike polyester or vinyl ester resins, where the resin is catalyzed by the addition of a small (1-3%) catalyst, epoxy resins can usually be cured by the addition of epoxy resin, thermoplastic polymers at a much higher resin (hardener) ratio of the curing agent.
Epoxy resins can be exchanged and impregnated into the fiber and in the so-called B-stage. In epoxy prepregs, the resin is sticky, but not cured. This allows pre-made layers of material to be cut, stacked and placed in a mold. The prepreg can then be consolidated and cured by adding heat and pressure. Epoxy prepregs and epoxy B-stage film must be kept at a low temperature to prevent premature curing, so companies using prepreg should invest in refrigeration or freezer units to keep the material cold.
Thermoset Epoxy Resins, Basic Properties and Applications
A thermosetting resin or thermoset is a polymer that hardens or turns into a hard shape using a curing method such as heat or radiation. The curing process is irreversible, as it forms a polymer network that is crosslinked by covalent chemical bonds. Upon heating, unlike thermoplastics, thermosets remain solid until the temperature reaches the point where the thermoset begins to deteriorate. Phenolic resins, amino resins, polyester resins, silicone resins, epoxy resins, and polyurethanes (polyesters, vinyl esters, epoxies, bismaleimides, cyanate esters, polyimides, and phenolics) are a few examples of thermosetting resins. Of these, epoxies are one of the most widely used. Today, thermosets are used in structural and special composite applications. Due to their high strength and hardness (due to a high degree of crosslinking) epoxy thermoset resins can be adapted to almost any application.
Why Epoxy Resin Is Versatile
This substance, referred to as epoxy, epoxy resin or epoxide, a-epoxy, refers to a broad group of reactive compounds characterized by the presence of an oxirane or epoxy ring. This is represented by a three-membered ring containing an oxygen atom bonded by two carbon atoms already joined in another way. Thus, the presence of this functional group defines a molecule as an epoxide, where the molecular base can vary greatly resulting in various classes of epoxy resins. And they are successful because they offer a variety of molecular structures that can be produced using the same chemical method. Other epoxy resins can be combined with various curing agents, modifiers to achieve the properties required for a particular application. Epoxy resins are typically formed by the reaction of compounds (polyphenolic compounds, diamines, amino phenols, heterocyclic imides and amides, aliphatic diols, etc.) and epichlorohydrin containing at least two active hydrogen atoms.
Basic Properties of Epoxy Resins
The main properties of epoxies resin include:
- Low Shrinkage
- High power
- Excellent adhesion to various surfaces
- Effective electrical insulation
- Chemical and solvent resistance and
- Low cost and low toxicity
Epoxies harden easily and are compatible with most substrates. They tend to wet surfaces easily, making them particularly suitable for composite applications. Epoxy resin is also used to modify various polymers such as polyurethane or unsaturated polyesters to improve their physical and chemical properties. In addition, the properties of thermosetting epoxies include:
- Tensile strength in the range of 90 to 120 MPa
- A tensile modulus ranging from 3100 to 3800 MPa
- Glass transition temperatures (Tg) varying between 150 and 220 ° C
Besides the above mentioned properties, epoxy resins have two main disadvantages such as their fragility and moisture sensitivity.
Recycling and Bio-Based Epoxy Systems
Thermosetting composites such as epoxy are high performance materials with important industrial applications. However, recycling and filling materials for thermosets are difficult. However, significant research and development has been done to ensure that thermosets are recycled, thus allowing plastics to break down and reformat. There are some new developments in epoxy thermosets that can be recycled to some extent, but their commercial significance is not yet fully understood. In addition, advances in bio-based thermoset resin systems have received considerable attention given their environmental benefits. Some of the bio-sourced thermosets are:
- Natural oil-based (such as soybean, flaxseed)
- Isosorbide based
- Furan based epoxy systems
- Phenolic and polyphenolic epoxies
- Epoxylated natural rubber
- Epoxy lignin derivatives
- Resin based resins
In summary, Epoxy (EP) resins are thermoset polymers, that is, they are cured from their liquid state in a modified form and cannot be remelted into thermoplastics. Thermoplastics are therefore generally recyclable, while thermosets are generally not recycled. Other thermosets include polyester, urethane, melamine and phenolic. And its usage area is very wide and it is a covering material that continues to expand day by day.