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Epoxy resins are a family of synthetic resins that carry one or more reactive epoxide groups in their molecular structure, forming a three-dimensional thermosetting polymer network when reacted with appropriate hardeners. Due to its properties such as high adhesion strength, chemical resistance, mechanical strength, electrical insulation and low curing shrinkage, it has a wide range of uses in coatings, adhesives, composites, electrical-electronics, construction chemicals, automotive, marine and industrial production.
Epoxy resin is not a single chemical substance. Bisphenol A-based liquid epoxy resins, bisphenol F-based resins, novolac epoxies, cycloaliphatic epoxies, glycidyl amine-based epoxies, solid epoxy resins, brominated epoxies, and different functional modified epoxy systems can be included in the same general chemical family.
The most common class of epoxy resins commercially are Bisphenol A Diglycidyl Ether based resins. This structure is most often identified by the abbreviations DGEBA or BADGE. According to Epoxy Europe, the most common commercial epoxy resin system is based on the structure of Bisphenol A Diglycidyl Ether, which is obtained from the reaction of Bisphenol A with epichlorohydrin.
Low molecular weight liquid Bisphenol A-epichlorohydrin epoxy resins can generally be identified under CAS No 25068-38-6. However, since epoxy resins are mixtures of oligomers and polymers, it is not correct to give a single CAS number, a single molecular formula, or a single molecular weight for all epoxy resins.
One of the most important technical parameters of epoxy resins is the epoxy equivalent weight. Epoxy equivalent weight refers to the mass of resin corresponding to one mole of epoxide function and is one of the key parameters in calculating the amount of hardener stoichiometrically.
Epoxy equivalent weight in standard liquid Bisphenol A based epoxy resins can often be in the range of approximately 180–200 g/eq. For example, for standard liquid Bisphenol A epoxy resin type KER 828, an epoxy equivalent weight of approximately 184–190 g/eq and a viscosity of approximately 12,000–14,000 mPa·s at 25 °C are reported. These values should not be generalized to all epoxy resins.
Epoxy resins alone do not form the final thermosetting product. The epoxide groups of the resin react with suitable amines, polyamides, anhydrides, phenolics, or other functional hardeners to form a cross-linked three-dimensional network.
This reaction can be exothermic. The curing rate depends on the resin's structure, hardener type, mixing ratio, temperature, catalyst, filler amount, and total mix volume.
One of the significant advantages of epoxy systems is that they do not have to create volatile by-products during curing. This property can provide lower volumetric shrinkage and higher dimensional stability compared to polyester or some condensation-based thermoset systems.
Epoxy resins can exhibit strong adhesion to metal, concrete, fiberglass, carbon fiber, wood, and many mineral surfaces. However, final adhesion depends on surface cleanliness, surface energy, moisture, surface roughness, primer usage, and curing conditions.
When purchasing epoxy resin, the term "epoxy resin" should not be considered alone. Epoxy equivalent weight, viscosity, color, hydrolyzable chlorine, total chlorine, amount of water, free epichlorohydrin or other residual substances, solids, functionality and recommended hardener system should be evaluated together.
WHAT ARE EPOXY RESINS?
Epoxy resins are prepolymer or oligomeric resins that carry reactive epoxy rings in their molecule.
The epoxide group is a three-membered ring ether structure. This three-membered ring has high ring tension.
Therefore, the amine can react easily with suitable functional groups such as hydroxyl, carboxyl, or anhydride.
The basic components of an epoxy resin system usually consist of two main groups. The first component is epoxy resin. The second component is the hardener.
The hardener opens the epoxide rings and connects the resin chains together. As a result of this reaction, a three-dimensional cross-linked thermoset structure is formed.
Once curing is complete, the material cannot be remelted and shaped. This property distinguishes epoxy resins from thermoplastics.
The most common family of epoxy resins is obtained from the reaction of Bisphenol A and epichlorohydrin. In this system, the basic low molecular weight structure is Bisphenol A Diglycidyl Ether. The abbreviation DGEBA is used.
The abbreviation BADGE can also be used to describe the same basic structure. For pure Bisphenol A Diglycidyl Ether, CAS No 1675-54-3 can be used.
For commercial low molecular weight oligomeric Bisphenol A-epichlorohydrin resins, CAS No 25068-38-6 is commonly used.
ECHA defines CAS No 25068-38-6 as "4,4'-isopropylidenediphenol, oligomeric reaction products with 1-chloro-2,3-epoxypropane". This expression describes the oligomeric epoxy resin system formed by the reaction of Bisphenol A and epichlorohydrin.
In epoxy resins, the n value, that is, the average degree of oligomerization, may vary, and the resin may be liquid at a low n value.
As the molecular weight rises, the resin can become semi-solid or solid. Therefore, liquid epoxy resins and solid epoxy resins can come from the same basic chemical family.
Low molecular weight liquid DGEBA resins are in particular:
Floor coverings
Adhesives
Composite production
Electrical casting resins
Repair mortars
Lamination
and are common in general-purpose thermosetting applications.
Higher molecular weight solid epoxy resins:
Powder coatings
Oven-cured coatings
Tin can coatings
Industrial protective coatings
It can be used in applications such as.
Bisphenol F-based epoxy resins can provide lower viscosity. This feature can be an advantage in systems with high filler or low solvent needs.
Epoxy novolac resins can have higher epoxy functionality. Therefore, it can be used in systems that require high cross-link density and high chemical/heat resistance.
Cycloaliphatic epoxies are different from aromatic DGEBA systems. They can be preferred for electrical properties, low viscosity, ultraviolet resistance or special curing mechanisms.
Glycidyl amine-based epoxy resins can be evaluated in advanced composites where high temperature performance and high cross-link density are required.
Thus, "Epoxy Resin" is not a single product, but a very large family of thermosetting resins.
COMMON PRODUCT AND CHEMICAL NAMES
Epoxy Resin
Epoxy Resin
Epoxy Resin
Epoxy Prepolymer
Bisphenol A Epoxy Resin
Bisphenol A Diglycidyl Ether
DGEBA
BADGE
Bisphenol A Epichlorohydrin Resin
Bisphenol A-Epichlorohydrin Resin
Liquid Epoxy Resin
Liquid Epoxy Resin
Solid Epoxy Resin
Solid Epoxy Resin
Bisphenol F Epoxy Resin
Epoxy Novolak Resin
Phenolic Novolac Epoxy Resin
Cycloaliphatic Epoxy Resin
Glycidyl Amine Epoxy Resin
Functional Epoxy Resin
Modified Epoxy Resin
CAS 25068-38-6 for common low molecular weight Bisphenol A-epichlorohydrin oligomeric resins
CAS 1675-54-3, Bisphenol A Diglycidyl Ether for monomeric structure
CAS NO, EC / EINECS NO AND CHEMICAL IDENTIFICATION
Product Group: Epoxy Resins
Chemical class: Thermosetting resin prepolymers with epoxide function
The most common basic structure: Bisphenol A Diglycidyl Ether
DGEBA / BADGE CAS No: 1675-54-3
Low molecular weight Bisphenol A-epichlorohydrin oligomeric resin CAS No: 25068-38-6
CAS 25068-38-6 EC / list number: 500-033-5
Single molecular formula: Not defined for the entire epoxy resin family
Single molecular weight: Not defined
Epoxy functionality: Grade dependent
Epoxy equivalent weight: Depends on grade
Viscosity: Grade dependent
Physical form: Liquid, semi-solid, or solid
Curing type: Thermoset
Main reaction: Epoxide ring opening and cross-linking
Major hardeners: Amines, polyamides, anhydrides, phenolic systems, and specialty hardeners
It would be wrong to give a single molecular formula for the epoxy resin family.
Even low molecular weight DGEBA type resins usually do not consist exclusively of pure BADGE.
Epoxy Europe states that commercial liquid epoxy resins can contain dimer, trimer, and higher oligomeric types in different proportions.
Therefore, epoxy equivalent weight and viscosity are more practical quality criteria instead of molecular weight.
CHEMICAL STRUCTURE AND MOLECULAR PROPERTIES OF EPOXY RESINS
The common structural feature of epoxy resins is the epoxide group.
The epoxide group is the three-membered cyclic ether. It consists of two carbon and one oxygen atom.
The bond angles of the ring are much smaller than the ideal tetrahedral bond angles. Therefore, the ring tension is high.
The high ring tension makes the epoxide group susceptible to chemical reactions. Nucleophilic substances can attack the epoxide ring. The ring opens.
New carbon-nitrogen, carbon-oxygen, or other bonds can form. The basic mechanism in amine hardeners is based on this ring opening.
It attacks the nitrogen epoxide carbon in the primary amine group. The epoxide ring opens. A hydroxyl group is formed.
The remaining active hydrogen of the amine can react again with another epoxide group. Thus, the chains are linked together.
Three-dimensional cross-linked network develops because primary amines can mostly react with more than one epoxy group. Secondary amines can also continue to react.
As curing progresses, molecule mobility decreases. Viscosity rises. The system reaches the gel point.
Then the mesh structure continues to develop. The glass transition temperature rises.
Hardness and mechanical strength increase. Cured epoxy no longer behaves as a soluble or fusible linear polymer.
It can only swell or undergo thermal degradation. In bisphenol A-based epoxy resins, aromatic rings contribute to hardness and heat resistance.
Ether bonds provide certain mobility to the chain. Hydroxyl groups can contribute to adhesion by forming hydrogen bonds with surfaces.
Epoxide end groups enable cross-linking with the hardener.
Bisphenol F epoxies may show lower viscosity at some grades due to their more compact aromatic structure.
The number of epoxy groups per molecule may be higher in novolax epoxy resins.
This can increase the cross-link density of the cured structure.
When cruciate ligament density increases:
Glass transition temperature may rise
Chemical resistance may increase
Hardness may increase
Heat resistance can improve
But:
Fragility may increase
Impact resistance may decrease
Elongation may decrease
Therefore, the highest functionality does not mean the best results in every application.
Here are the key properties of epoxy resins at the molecular level:
Carrying reactive epoxy group
Reacting to going public
Cross-linking with stiffeners
Creating a thermoset structure
Forming hydroxyl groups during curing
Demonstrate strong interaction with metal and mineral surfaces
To be able to provide low curing shrinkage
To be able to create high chemical resistance
Ability to adjust properties with cross-link density
Ability to change performance with different resin backbones
PHYSICAL AND CHEMICAL PROPERTIES OF EPOXY RESINS
The physical properties of epoxy resins vary significantly based on the resin family and molecular weight.
General technical specifications:
Physical form: Liquid, semi-solid, or solid
Color: Colorless to light yellow or amber tones
Chemical class: Thermosetting prepolymer with epoxide function
The most common basic structure: Bisphenol A Diglycidyl Ether
CAS No: Grade dependent
Epoxy equivalent weight: Depends on grade
Epoxy group content: Grade dependent
Viscosity: Grade dependent
Density: Grade dependent
Water solubility: Generally low in low molecular weight DGEBA type resins
Volatility: Generally low in solvent-free resins
Color value: Depends on grade
Hydrolyzable chlorine: Grade dependent
Total chlorine: Grade dependent
Amount of water: Depends on grade
Free epichlorohydrine: Depends on manufacturer and grade
Glass transition temperature: Dependent on cured system
Curing temperature: Depends on resin/hardener system
Operating time: Depends on formulation
Full curing time: Formulation and temperature dependent
Approximate technical range common in standard liquid DGEBA resins:
Epoxy equivalent weight: Approx. 180–195 g/eq
25 °C viscosity: Approx. 8,000–15,000 mPa·s
Density: Approx. 1.15–1.20 g/cm³
These values are the general reference range.
The TDS values of a specific commercial product should be taken as a basis.
For example, for standard liquid epoxy resin type KER 828, the epoxy equivalent weight is reported to be approximately 184–190 g/eq and the viscosity of 25 °C is reported to be approximately 12,000–14,000 mPa·s.
In modified epoxy resins containing reactive diluent, the viscosity can be much lower.
In solid epoxy resins, viscosity is not a meaningful liquid parameter at room temperature.
These resins can be characterized by their softening point or melt viscosity.
HOW DO EPOXY RESINS WORK AT THE MOLECULAR LEVEL?
The basic working mechanism of an epoxy resin system is based on the reaction of epoxide groups with the hardener to form a cross-linked thermoset network.
When the resin and hardener are mixed, a mixture with low or medium viscosity is initially formed.
The chemical reaction begins.
Epoxy rings open.
New bonds are formed.
Molecular weight rises rapidly.
The chains are connected to each other.
Initially, the mixture may flow.
After a certain time, the viscosity rises.
The working period is nearing its end.
The system reaches the gel point.
After the gel point, the material can no longer flow freely.
However, the chemical reaction continues.
Cruciate ligament density increases.
Mechanical strength improves.
Full curing can take hours or days.
In some systems, the first hardening occurs at room temperature.
Post-heating can be applied to achieve higher property.
This process is called post-curing.
Final curing:
Glass can raise the transition temperature
It can advance the reaction of the remaining epoxy groups
May improve chemical resistance
Can improve mechanical properties
The amount of hardener is very important.
If insufficient hardener is used:
Unreacted epoxy groups may remain
Curing may not be complete
The surface may remain sticky
Mechanical strength may decrease
Chemical resistance may decrease
If too much hardener is used:
Amen can stay now
Surface properties may deteriorate
Water intake may increase
Chemical resistance may decrease
Color may vary
Therefore, the ratio of resin and hardener should be determined based on the epoxy equivalent weight and active hydrogen equivalent weight given by the manufacturer.
Epoxy equivalent weight refers to the grams of resin corresponding to one epoxide equivalent.
The active hydrogen equivalent weight of the hardener is also used in the reaction calculation.
After the theoretical calculation, the rate recommended by the commercial system manufacturer should be taken as basis.
Curing is exothermic.
As the amount of mixture increases, the heat generated can be more difficult to remove from the environment.
Large mixture mass can heat up much faster than small container.
This can reduce uptime.
Extreme exotherm:
Color change
Bubble
Cracking
thermal degradation and may pose a safety risk.
Therefore, large castings may require specialized low-exotherm resin/hardener systems.
The primary functions of epoxy resins at the formulation level include:
Providing strong adhesion to the surface
Creating rigid and durable film
Providing chemical resistance
Carrying mechanical loads
Bonding composite fibers
Providing electrical insulation
Connecting fillers and pigments
Protecting the concrete surface
Helping to reduce metal corrosion
Creating a low-shrinkage thermoset structure
IN WHICH SECTORS ARE EPOXY RESINS USED?
Epoxy resins are one of the thermosetting resin families with the widest usage area in the industry.
Main areas of use:
Industrial floor coverings
Concrete coatings
Metal coatings
Anti-corrosion primers
Marine paints
Tank coatings
Pipe coatings
Chemical resistant coatings
Adhesives
Structural adhesives
Metal adhesives
Concrete repair systems
Anchoring systems
Repair mortars
Joint systems
Electrical casting resins
Electronic encapsulation
Transformer insulation
Electrical-electronic laminates
Printed circuit boards
Carbon fiber composites
Glass fiber composites
Wind turbine blades
Marine composites
Automotive composites
Aerospace composites
Filament winding systems
Resin infusion
Vacuum infusion
Formwork systems
Tool production
Stone and marble adhesives
Wood adhesives
Furniture applications
Decorative casting systems
Powder coatings
Coil and metal coating systems
Industrial laminates
Process equipment requiring high chemical resistance
This wide range of uses is due to the wide range of performance of epoxy resins with different chemical structures and hardeners.
COATING, FLOOR AND CORROSION PROTECTION APPLICATIONS OF EPOXY RESINS
The coatings industry is one of the primary uses of epoxy resins.
Epoxy coatings can provide strong adhesion on concrete and metal.
On industrial floors:
Abrasion resistance
Chemical Resistance
Compressive strength
Cleanability
Dusting control is requested.
Epoxy resin can provide these properties with the appropriate hardener and filler system.
Surface preparation is critical for concrete floors.
On concrete:
Oil
Powder
Cement laurout
Humidity
Weak surface layer
can reduce adhesion.
Mechanical etching or a suitable surface preparation method may be required.
For damp concrete, standard epoxy resin is not always suitable.
Special epoxy systems with moisture tolerance can be selected.
In metal coatings, the polar groups of epoxy resin can provide strong interaction with the surface.
In anti-corrosion primers, epoxy resin forms a barrier.
It can limit water and ions from reaching the metal surface.
It can be used in combination with zinc phosphate or other anti-corrosion pigments.
However, the aromatic nature of epoxy resins may show yellowing and chalking under ultraviolet light.
For this reason, aliphatic polyurethane or other UV resistant topcoats can be applied on epoxy in outdoor topcoat applications.
Advantages of epoxy coatings:
High adhesion
Chemical resistance
Abrasion resistance
Low shrinkage
Good bonding to concrete
Thick film application
maybe.
Limitations:
Limited UV resistance
Yellowing
Fragility
Slow curing at low temperature
Amine-induced surface defects
It can be seen as follows.
USE OF EPOXY RESINS IN ADHESIVE AND COMPOSITE APPLICATIONS
Epoxy adhesives are common in applications where high structural strength is required.
It can bond metals together.
It can provide metal-composite connection.
It can be used on glass, ceramic, wood and some plastic surfaces.
Actual adhesion depends on surface chemistry.
For plastics such as low surface energy polyethylene and polypropylene, standard epoxy adhesive may not exhibit strong adhesion directly.
Surface treatment may be required.
In epoxy adhesive formulation:
Resin
Hardener
Filling
Thixotropy contributing
Impact resistance enhancer
Adhesion promoter
Pigment
reactive diluent may be used.
In structural adhesives, high cross-link density alone is not enough.
A very fragile system can crack easily under impact.
Therefore, rubber modification, thermoplastic modification, or special core-shell particles can be used.
In the composite industry, epoxy resin acts as the matrix that binds the fibers.
Carbon fiber
Fiberglass
Aramid fiber
The epoxy matrix transfers the load between the fibers, while the reinforcing materials such as epoxy matrix carry loads.
The matrix also protects the fibers from environmental influences.
Good fiber wetting is critical for composite performance.
Too high resin viscosity can make penetration between fibers difficult.
For this reason, low-viscosity epoxy resins are preferred in infusion systems.
Higher viscosity can be tolerated in hand tilt systems.
In prepreg systems, on the other hand, the partially advanced curing state of the resin and the controlled flow behavior are important.
Final properties in epoxy composites:
Resin type
Hardener
Fiber type
Fiber volume ratio
Curing temperature
Void rate
Fiber orientation
determined by.
ARE EPOXY RESINS USED IN FOOD, COSMETICS AND PHARMACEUTICAL APPLICATIONS?
Epoxy resins are not direct food additives.
It is not used in the standard sense as a cosmetic formulation raw material.
It is not a pharmaceutical active ingredient.
Epoxy systems can be used as special coatings on food or drinking water contact surfaces.
However, this use should only be considered if the exact resin, hardener and the entire additive system is verified to comply with the relevant legislation.
Food contact in bisphenol A-based epoxy systems requires special regulatory consideration.
Residual substances and migration limits in the cured epoxy are important.
Therefore, the general statement that "epoxy is inert, it can be used on any food surface" is not true.
For drinking water tank coatings, the exact product must have the necessary certificates and conformity certificates.
Standard industrial epoxy resin is not used in the cosmetic product.
In pharmaceutical applications, too, technical epoxy resin is not automatically suitable.
However, epoxy chemistry can be used in medical devices, dental materials, or specialized equipment.
Such applications should be considered separately from standard general-purpose epoxy resin.
INDUSTRIAL APPLICATIONS OF EPOXY RESINS
Epoxy resins serve as binders, adhesives, and thermosetting matrices in industry.
The following functions may come to the fore in industrial epoxy applications:
Adhesion to metal surface
Adhesion to concrete
Fiberglass bonding
Carbon fiber bonding
Creating a chemical barrier
Corrosion protection
Providing abrasion resistance
Electrical insulation
Electronic component encapsulation
Binding fillers
Creating repair materials
High-strength adhesive production
Low shrinkage casting
Mold and tool production
Lamination
The main control parameters in epoxy formulation are:
Epoxy equivalent weight
Viscosity
Epoxy functionality
Resin molecular weight
Type of hardener
Hardener equivalent weight
Mixing ratio
Operating time
Gel time
Curing time
Curing temperature
Exotherm temperature
Glass transition temperature
Hardness
Tensile strength
Flexural strength
Impact resistance
Adhesion
Water intake
Chemical Resistance
Electrical Specifications
Color
Amount of filler
Amount of reactive diluent
TDS
SDS
COA
In epoxy resin systems, the mixing ratio can be given by weight or volume.
These two ratios should not be used interchangeably.
If the densities are different, the weight ratio and the volume ratio will be different.
If the manufacturer has given a weight ratio of 100:50, it should not be assumed that it is 2:1 in volume.
Exact TDS value should be applied.
Mixing uniformity is also important in epoxy systems.
Insufficient mixing can create a different resin/hardener ratio locally.
These areas may remain soft or sticky.
However, excessively fast mixing can drag air into the system.
Therefore, the process should be controlled.
WHAT PROBLEMS CAN EPOXY RESINS HELP SOLVE?
Epoxy resins can help solve many industrial problems that require high adhesion, chemical resistance, and mechanical strength.
Dusting of the concrete surface
Proper epoxy coating can bind the concrete surface, reducing dusting.
Risk of chemical spillage on the floor
Chemical-resistant epoxy formulation can provide protective barrier.
Corrosion on the metal surface
Epoxy primer can contribute to corrosion protection by limiting water and ion ingress.
Mechanical joining of metal parts
Structural epoxy adhesive can form a connection.
Fixing fibers in composite
The epoxy matrix provides charge transfer between the fibers.
Protection of electronic circuitry from moisture
Casting or encapsulation epoxy can provide electrical and environmental protection.
Repairing cracks or gaps in concrete
Low viscosity epoxy injection systems can be used in suitable cracks.
Need for repair mortar with high filler
Epoxy resin can be strong binder for mineral filler and aggregate.
The epoxy mixture is very viscous
Low viscosity resin or suitable reagent diluent can be used.
However, it should be noted that the reactive diluent may alter the mechanical and thermal properties.
Epoxy cures very fast
Slower hardener
Lower temperature
Smaller mix volume
or different catalysis system
can be evaluated.
Epoxy cures very slowly
Temperature
Type of hardener
Mixing ratio
and catalyst system
should be checked.
The surface remains sticky
Incorrect mixing ratio
Insufficient mixing
Low temperature
Moisture effect
or unsuitable hardener
should be investigated.
Film fragile
More flexible resin/hardener
Flexibility Booster
Rubber modification
or lower cruciate ligament density
can be evaluated.
Yellowing in the external environment
This problem is one of the inherent limitations of standard aromatic epoxies.
It may be necessary to use a UV resistant topcoat system.
Not every problem can be solved by simply changing the epoxy resin grade.
The hardener and the entire formulation should be considered together.
THINGS TO CONSIDER IN THE USE OF EPOXY RESINS
In the use of epoxy resin, resin type, hardener ratio, safety and curing conditions are the basic parameters.
The following issues should be considered when using epoxy resin:
Exact resin grade should be verified.
The epoxy equivalent weight should be checked.
Viscosity should be checked.
The type of hardener must be determined.
The mixing ratio must be verified.
Weight and volume ratios should not be confused.
The operating time should be checked.
Gel duration should be taken into account.
The curing temperature must be determined.
The risk of exotherm should be assessed.
Large mixture volumes should be avoided.
Surface preparation should be done.
Humidity should be checked.
Filling dryness should be checked.
Air drag should be reduced.
The amount of reactive diluent should be checked.
If solvent is to be used, proper ventilation should be provided.
If final curing is required, it should be applied.
TDS should be examined.
SDS should be examined.
The COA should be checked.
REACH/CLP information should be evaluated.
Uncured low molecular weight Bisphenol A-epichlorohydrin resins can be skin sensitizers.
For common low molecular weight epoxy resins classified under CAS No 25068-38-6, there are classifications for skin irritation, eye irritation, allergic skin reaction, and long-term toxicity to the aquatic environment.
Therefore, bare-handed work is not suitable.
Appropriate chemical resistant gloves should be used.
The glove material should be selected according to the exact SDS.
Eye protection should be used.
Epoxy that gets on the skin should not be cleaned with solvent.
It should be removed with the appropriate cleaning method.
INITIAL FORMULATION APPROACHES FOR EPOXY RESINS
The following examples are laboratory initial approaches prepared to show how epoxy resins can be evaluated in coating, adhesive and composite development studies.
These are not verified commercial prescriptions.
Actual quantities should be calculated based on the epoxy equivalent weight of the resin, the active hydrogen equivalent of the hardener, and the manufacturer's TDS information.
All ratios below are a percentage by weight (w/w%) of the finished two-component mixture; resin and hardener together are included in 100%. For the calculation example, DGEBA resin EEW = 188 g/eq, monofunctional glycidyl ether type reactive diluent EEW = 250 g/eq, and amine hardener AHEW = 95 g/eq are assumed. These values are only a calculation assumption; they are not the verified specification of any commercial product. The amount of amine hardener is calculated by the relation of 95 × (DGEBA mass / 188 + reactive diluent mass / 250). Recalculation is mandatory in different commercial raw materials.
EXAMPLE 1: SOLVENT-FREE EPOXY FLOOR COATING SCANNING
Purpose: To evaluate the viscosity, filler acceptance, and mechanical performance of standard liquid Bisphenol A epoxy resin.
Starting components:
Liquid Bisphenol A epoxy resin (EEW 188 g/eq): 100 weight units reference in all trials
Amine hardener (AHEW 95 g/eq): Based on epoxy equivalent calculation
Reactive diluent (EEW 250 g/eq): 0%; the amount of filler is screened by excluding the diluent effect in this sample
Mineral filler, dry micronized calcium carbonate: Screened in three levels
Pigment, titanium dioxide: Fixed 2 units of weight
Deaerator: Fixed 0.30 units of weight
Initial formulation A – low filling (% by weight):
Liquid Bisphenol A epoxy resin: 54.70%
Amine hardener: 27.64%
Mineral filler (CaCO₃): 16.41%
Titanium dioxide: 1.09%
Deaerator: 0.16%
Total: 100.00%
Initial formulation B – medium filler (% by weight):
Liquid Bisphenol A epoxy resin: 46.99%
Amine hardener: 23.74%
Mineral filler (CaCO₃): 28.19%
Titanium dioxide: 0.94%
Deaerator: 0.14%
Total: 100.00%
Initial formulation C – high filling (% by weight):
Liquid Bisphenol A epoxy resin: 41.18%
Amine hardener: 20.81%
Mineral filler (CaCO₃): 37.06%
Titanium dioxide: 0.82%
Deaerator: 0.13%
Total: 100.00%
The hardener ratio in the three recipes is based on the same stoichiometric calculation; as the filler ratio increases, the percentage resin ratio decreases. The percentages are rounded to two decimal places; the following PHR-based starting masses should be used for precise weighing: 100 units of resin + 50.53 parts of hardener + 30/60/90 parts of CaCO₃ + 2 parts of TiO₂ + 0.30 parts of deaerator, respectively. The compatibility of this approach with the actual system should be verified with manufacturer TDS information.
Application approach:
The epoxy equivalent weight of the resin is verified.
Hardener equivalent calculation is made.
The filling is pre-dried.
Resin and additives are homogenized.
The hardener is added at the final stage.
The mixing time is kept constant.
Operating time is recorded.
Standard thickness coating is applied.
Hardness is measured for 24 hours and 7 days.
Adhesion test is performed.
Chemical resistance is compared.
Wear performance is evaluated.
EXAMPLE 2: SCREENING FOR LOW VISCOSITY EPOXY ADHESIVE
Purpose: To compare the effect of resin viscosity and reactive diluent amount on adhesion and mechanical properties.
Starting components:
DGEBA-based epoxy resin (EEW 188 g/eq): 100 weight units reference
Reactive diluent, monofunctional glycidyl ether (EEW 250 g/eq): 0, 5, or 10 weight units
Amine hardener (AHEW 95 g/eq): According to equivalent calculation including diluent
Thixotropy conduit, pyrogenic silica: Fixed 2 units of weight
Mineral filler, dry fine calcium carbonate: Fixed 10 weight units
Adhesion promoter: Not used in this comparative initial scan (0%)
Initial formulation A – diluent-free control (% wt):
DGEBA epoxy resin: 61.53%
Reactive diluent: 0.00%
Amine hardener: 31.09%
Pyrogenic silica: 1.23%
Mineral filler (CaCO₃): 6.15%
Total: 100.00%
Initial formulation B – low diluent (% wt):
DGEBA epoxy resin: 59.02%
Reactive diluent: 2.95%
Amine hardener: 30.95%
Pyrogenic silica: 1.18%
Mineral filler (CaCO₃): 5.90%
Total: 100.00%
Initial formulation C – medium diluent (% wv):
DGEBA epoxy resin: 56.71%
Reactive diluent: 5.67%
Amine hardener: 30.81%
Pyrogenic silica: 1.13%
Mineral filler (CaCO₃): 5.68%
Total: 100.00%
Since the reactive diluent was considered to have an epoxide function, the amount of hardener was recalculated at each scan. For 100 units of DGEBA, 0/5/10 units of reactive diluent, 50.53/52.43/54.33 units of amine hardener, 2 parts of pyrogenic silica and 10 units of calcium carbonate are used. If a diluent with more than one epoxy group or a hardener with different AHEW values is selected, these amounts are not valid.
Application approach:
The control formulation is prepared without diluent.
The reactive diluent is added at different levels.
Viscosity is measured.
The resin and hardener are mixed in the right ratio.
Metal-metal and metal-composite samples are prepared.
A certain thickness of adhesive is applied.
Curing is done at the same temperature.
Shear strength is measured.
The type of fracture is examined.
Impact resistance is evaluated.
Temperature and water aging are applied.
It is evaluated whether low viscosity leads to loss of mechanical properties.
ALTERNATIVES AND COMPARISON OF EPOXY RESINS
When choosing an epoxy resin alternative, one should not evaluate only on cost or hardness.
Adhesion, chemical resistance, UV resistance, curing mechanism, flexibility and process speed should be evaluated together.
EPOXY RESINS AND POLYURETHANE RESINS
Polyurethane systems are based on the reaction of isocyanate and components with hydroxyl or amine functions.
It has different chemistry than epoxy systems.
Polyurethanes can provide higher flexibility and outdoor strength.
Aliphatic polyurethanes have an advantage over epoxy in terms of UV resistance.
Epoxy, on the other hand, can provide strong adhesion to many surfaces and high chemical resistance.
For industrial floors, the combination of epoxy primer + polyurethane topcoat may be the common approach.
The two systems are not directly equivalent.
EPOXY RESINS AND UNSATURATED POLYESTER RESINS
Unsaturated polyester resins are mostly thermosetting systems containing reactive diluents such as styrene.
Epoxy resins can provide higher adhesion and lower curing shrinkage than polyester in many composite applications.
Polyester systems can often be lower cost.
Both systems can be used in boat and glass fiber applications.
When high mechanical performance and low backlash are required, epoxy may be preferred.
In cost-priority general-purpose application, polyester may be advantageous.
EPOXY RESINS AND VINYL ESTER RESINS
Vinyl ester resins are thermosetting resins in which the epoxy backbone has been modified with acrylate or methacrylate end groups.
It can provide higher performance than polyester in terms of chemical resistance.
Epoxy resins, on the other hand, have a different curing mechanism with hardeners such as amine/anhydride.
Vinyl esters are especially common in chemical tank, pipe, and fiberglass composites.
Epoxy can provide lower shrinkage and high adhesion.
The two systems require different processes and hardening technologies.
EPOXY RESINS AND ACRYLIC RESINS
Acrylic resins can provide high UV and color stability.
Epoxy resins may show yellowing in the external environment.
Therefore, acrylic can provide an advantage in decorative exterior or UV-resistant systems.
Epoxy, on the other hand, may be stronger in terms of chemical resistance, concrete/metal adhesion and mechanical protection.
In some coating systems, epoxy primer and acrylic/PU topcoat are used together.
EPOXY RESINS AND SILICONE RESINS
Silicone resins can be advantageous in high temperature and weather resistance.
The standard temperature resistance of epoxy systems is more limited.
Epoxy, on the other hand, can generally be stronger in terms of mechanical strength and adhesion.
In electrical-electronic applications, the two systems can play different roles depending on the application temperature.
QUALITY CONTROL AND PURCHASING CRITERIA FOR EPOXY RESINS
When purchasing epoxy resin, the exact resin family and grade should be determined.
Recommended information to review before purchasing:
Full commercial product name
Manufacturer
Resin type
Bisphenol A based
Bisphenol F based
Novolak
Cycloaliphatic
Glycidyl amine
Modified epoxy
CAS No
Epoxy equivalent weight
Epoxy group content
Viscosity
Viscosity measurement temperature
Density
Color
Solid Matter
Amount of water
Hydrolyzable chlorine
Total chlorine
Inorganic chlorine
If Free Bisphenol A is required
If free epichlorohydrin is required
Functionality
Softening point, in solid resins
Conformal stiffeners
Mixing ratio
Operating time
Gel time
Curing profile
Glass transition temperature
Chemical resistance
Mechanical Properties
Shelf life
Storage temperature
Packaging
Batch number
Origin
TDS
SDS
COA
REACH information
Epoxy equivalent weight is one of the most critical purchasing parameters.
A range of about 185–192 g/eq may be common in standard liquid DGEBA resins.
However, this value may vary in modified or high molecular weight resins.
Epoxy equivalent weight and viscosity should be evaluated together in resins containing reactive diluents.
Low viscosity does not always mean better quality.
Low viscosity:
Easy mixing
High fill loading
Good fiber wetting
advantage.
However, the reactive diluent used is:
Adjust the glass transition temperature
Chemical Resistance
Mechanical strength
and cross-link density
can change.
Color is also important according to the application.
Low color value can be critical in transparent decorative casting systems.
It may not be equally important in floor primer.
In electronic applications, chlorine ions and ionic impurities can become critical.
Therefore, electronic grade epoxy resin should not be purchased with the same criteria as general flooring resin.
STORAGE AND HANDLING OF EPOXY RESINS
Storage: Epoxy resins should be stored in clean, dry, and tightly sealed packaging.
Temperature: Exact manufacturer recommendation should be taken as basis.
Low temperature: Some liquid Bisphenol A epoxy resins can crystallize at low temperature.
Crystallization may not mean chemical degradation.
However, the re-dissolution process should be carried out according to the manufacturer's instructions.
High temperature: Unnecessarily high temperature storage for extended periods can affect viscosity, color, and shelf life.
Moisture: Some hardeners, in particular, can be strongly affected by moisture.
The epoxy resin itself must also be protected from water for formulation purity.
Packing: Steel drum, IBC or other suitable packing can be used.
Contamination: Accidental contact with amines, acids, strong bases or other reactive substances should be avoided.
The resin and hardener should be stored separately.
FIFO: Batch and shelf-life management should be implemented.
Handling: Exact ADR, IMDG and IATA classification must be verified from the product SDS.
The environmental and transport classifications of different epoxy resin grades may not be the same.
EPOXY RESINS SAFETY INFORMATION
Safety assessment in epoxy resins should be separated between uncured resin, hardener, and fully cured material.
NIOSH states that some epoxy resin components can be dangerous before curing and that cured epoxy materials are generally safer.
Low molecular weight Bisphenol A-epichlorohydrin epoxy resins can be skin sensitizers.
Common classifications for CAS No 25068-38-6 include:
Skin irritation
Eye irritation
Allergic skin reaction
Long-term toxicity to the aquatic environment
takes place.
Epoxy systems can be one of the important causes of occupational allergic contact dermatitis.
The DGUV states that epoxy resin systems are one of the frequent causes of work-related allergic skin diseases.
This risk is mainly significant during contact with uncured resin and hardener.
Appropriate gloves should be used.
Not all glove materials provide the same protection against epoxy.
The glove material and permeation time in the Exact SDS should be considered.
Protective glasses should be used.
Skin contact should be minimized.
Contaminated work clothes should be changed.
Adequate ventilation should be provided.
Hardening amines or anhydrides can have separate dangers.
Therefore, it is not enough to just look at the SDS of the resin.
In the two-component system, both component A and component B SDS documents should be examined.
Fully cured epoxy usually consumes a significant portion of the initial reactive epoxy groups.
Therefore, the risk of sensitization may be markedly reduced.
However, dust generated during grinding or cutting requires separate occupational hygiene measures.
WHAT SHOULD BE CONSIDERED WHEN BUYING EPOXY RESINS?
In the supply of epoxy resin, the end usage area should be determined first.
"Epoxy resin" alone is not the definition of adequate purchase.
The following information should be clarified before purchasing:
Use sector
Floor covering
Metal plating
Corrosion protection
Adhesive
Composite
Electronics
Casting
Repair mortar
Mold
Powder coating
Resin type
Bisphenol A
Bisphenol F
Novolak
Cycloaliphatic
Modified system
Liquid or solid form
Epoxy equivalent weight
Viscosity
Target uptime
Curing temperature
Curing time
Hardener type
Mixing ratio
Low viscosity requirement
Transparency
Color
Chemical resistance
UV requirement
Flexibility
Impact resistance
Glass transition temperature
Electrical Specifications
Chlorine limit
Water limit
BPA or residual monomer requirements
Manufacturer
Origin
Packaging
Estimated order quantity
TDS
SDS
COA
REACH documents
If the existing epoxy resin is to be replaced, the TDS and hardener system of the existing product
The price of epoxy resin should not be compared solely based on its cost per kilogram.
Low viscosity resin can allow higher filler use.
Higher functionality can provide higher chemical resistance.
Lower color can provide value in decorative systems.
Low chlorine can be critical in electronic applications.
Therefore, the total formulation and process cost should be taken as a basis.
EPOXY RESIN SUPPLY FROM ATAMAN KIMYA
Epoxy resins; It is a family of reactive thermosetting resins used in industrial coating, flooring, adhesive, composite, electrical-electronics, construction chemicals, automotive, marine and different technical applications.
Companies that want to get information about Epoxy Resin supply from Ataman Kimya can request information about the appropriate resin type, current supply conditions, packaging options and price offer by sharing their usage areas and target technical specifications.
The current stock status, manufacturer, origin, Bisphenol A/Bisphenol F/novolac structure, epoxy equivalent weight, viscosity, packaging and other quality characteristics of the product should be confirmed from Ataman Kimya before ordering.
Sharing the following information in the request for quotation facilitates the evaluation of the appropriate epoxy resin:
Use sector
Final Product
Resin type
Epoxy equivalent weight
Target viscosity
Stiffener used
Mixing ratio
Operating time
Curing temperature
Chemical resistance requirement
Mechanical property expectation
Color requirement
Low chlorine requirement
Electronic quality requirement
Transparency
Low viscosity
If there is a composite application, fiber type
Estimated order quantity
Requested packing
Requested technical documents
TDS or COA information of the epoxy resin present, if applicable
FREQUENTLY ASKED QUESTIONS ABOUT EPOXY RESINS
What is epoxy resin?
It is a family of resins that carry epoxide groups and are cross-linked with suitable hardeners to form a thermosetting polymer.
Is epoxy resin a single chemical?
There are many different epoxy resin families and commercial grades.
What is the most common type of epoxy resin?
Bisphenol A and epichlorohydrin-based DGEBA type resins are among the most common commercial epoxy systems.
What is DGEBA?
Bisphenol A is the abbreviation of Diglycidyl Ether.
What is BADGE?
Bisphenol A Diglycidyl Ether is another abbreviation used for its structure.
What is the CAS number of epoxy resin?
There is no single CAS number. In low molecular weight Bisphenol A-epichlorohydrin resins, CAS No 25068-38-6 is commonly used.
What is the CAS number of DGEBA?
For pure Bisphenol A Diglycidyl Ether, CAS No 1675-54-3 can be used.
What is the molecular weight of epoxy resin?
It varies according to the resin family and oligomer distribution. It is not correct to give a single value.
What is epoxy equivalent weight?
It is the amount of grams of resin corresponding to an epoxide equivalent.
Why is epoxy equivalent weight important?
It is used for accurate calculation of hardener quantity and resin quality control.
What is the epoxy equivalent weight of standard liquid epoxy resin?
In many standard DGEBA resins, it can be in the range of about 180–195 g/eq.
What is epoxy resin viscosity?
It depends on the grade. Values of approximately 10,000 mPa·s and above at 25 °C are common in standard liquid DGEBA resins.
How does epoxy resin harden?
The epoxide groups react with the hardener to form a three-dimensional cross-linked polymer network.
What hardeners are used for epoxy resin?
Amine, polyamide, anhydride, phenolic and different special hardener systems can be used.
How does an amine hardener work?
The amine group opens the epoxide ring and cross-links the resin chains by forming new bonds.
Does epoxy curing release heat?
The curing reaction is exothermic.
Why does a large amount of epoxy mixture heat up faster?
As the reaction heat generated in a large volume moves away from the surroundings more slowly, the temperature rises and the reaction accelerates.
What is epoxy working time?
It refers to the amount of time the material remains applicable after the resin and hardener are mixed.
What is the gel duration?
It refers to the time during which the mixture transitions from a fluid state to a gel-like structure.
Why does epoxy resin stay sticky?
Incorrect mixing ratio, inadequate mixing, low temperature, or improper curing conditions can be the cause.
Why does epoxy resin turn yellow?
Aromatic epoxy structures may show color change under UV light.
Is epoxy suitable for the outdoor environment?
It may be chemically and mechanically suitable, but standard aromatic epoxies have limited UV resistance. UV-resistant topcoat may be required.
Does epoxy stick on concrete?
With proper surface preparation, it can provide very strong adhesion.
Does epoxy stick on metal?
It can provide strong adhesion on clean and properly prepared metal surfaces.
Is epoxy used on wood?
It can be used in adhesive, coating, and composite applications.
Can epoxy be used with carbon fiber?
It is one of the most common matrix resins in carbon fiber composites.
Is epoxy resin used for flooring?
It is one of the basic resin systems of industrial floor coverings.
Can epoxy resin be used as an adhesive?
It is widely used in structural adhesives.
Does epoxy provide electrical insulation?
It can provide high electrical insulation in suitable formulations.
Is epoxy water resistant?
Cured systems can show good water resistance, but performance depends on the resin/hardener system.
Is epoxy chemical resistant?
It can show high resistance to many chemicals. Exact strength depends on chemical type, concentration, temperature and resin system.
Why is Bisphenol F epoxy used?
Some Bisphenol F epoxy resins can provide lower viscosity and high filler acceptance.
Why is novolax epoxy used?
Thanks to its high epoxy functionality, it can provide high cross-link density, heat and chemical resistance.
Can epoxy be too brittle?
High cross-link density can increase fragility.
Can epoxy be made pliable?
Flexible hardeners, special modified resins or impact strength enhancing additives can be used.
What is epoxy reactive diluent?
It is a low-viscosity component with epoxy or other reactive function, which can also participate in the curing reaction while reducing viscosity.
Does reactive diluent affect mechanical properties?
According to the type and quantity, glass transition temperature can change chemical resistance and mechanical properties.
Is epoxy the same as polyester?
Their chemical structures and curing mechanisms are different.
Is epoxy the same as vinyl ester?
Vinyl ester can be derived from the epoxy backbone but has different reactive end groups and different curing chemistry.
Can epoxy be used on food contact surface?
It can only be used if the exact system's compliance with the relevant food contact legislation is verified.
Can epoxy be dangerous before curing?
Low molecular weight epoxy resins can be skin sensitizing and irritating.
Can epoxy cause allergies?
Uncured epoxy resin and some hardeners can lead to allergic contact dermatitis.
EPOXY RESINS – TECHNICAL SUMMARY
Epoxy resins are a large family of synthetic resins that have reactive epoxide groups in their molecular structure and react with suitable hardeners to form a three-dimensional thermoset network.
The most common commercial epoxy resin class is Bisphenol A Diglycidyl Ether based DGEBA/BADGE resins obtained from the reaction of Bisphenol A and epichlorohydrin.
For pure BADGE, CAS No 1675-54-3 can be used. In low molecular weight oligomeric Bisphenol A-epichlorohydrin epoxy resins, CAS No 25068-38-6 is common.
Epoxy resins are not single-molecule pure chemicals. Commercial liquid resins can contain different proportions of monomeric, dimeric, trimeric, and higher oligomeric species.
For this reason, it is not correct to give a single molecular formula or a single molecular weight for epoxy resins.
One of the most important quality parameters is the epoxy equivalent weight.
An epoxy equivalent weight of about 180–195 g/eq is common in standard liquid DGEBA epoxy resins.
A sample of standard liquid epoxy resin type KER 828 shows an epoxy equivalent weight of approximately 184–190 g/eq and a viscosity of approximately 12,000–14,000 mPa·s at 25 °C.
Epoxy resin reacts with suitable amine, polyamide, anhydride, or other hardeners.
Epoxy rings open.
Resin chains are linked together.
A cross-linked thermoset structure occurs.
Curing is the exothermic reaction.
Mixing ratio, temperature and mixing volume have a great impact on working time.
Epoxy resins are widely used in floor coatings, protective paints, adhesives, composites, construction chemicals, and electronic systems due to their strong adhesion, high chemical resistance, mechanical strength, electrical insulation, and low shrinkage properties.
Bisphenol A epoxy resins are general purpose.
Bisphenol F epoxies can provide the advantage of low viscosity.
Novolak epoxies can be used for high functionality and chemical/heat resistance.
Cycloaliphatic and glycidyl amine epoxies can be evaluated in special advanced performance applications.
Standard aromatic epoxy systems have limited UV resistance and may yellow in the external environment.
For this reason, it may be necessary to use a UV-resistant topcoat for outdoor coatings.
Uncured low molecular weight epoxy resins can be skin sensitizers.
There are skin and eye irritation, allergic skin reaction, and long-term hazard classifications for the aquatic environment for common Bisphenol A-epichlorohydrin resins under CAS No 25068-38-6.
When purchasing epoxy resin, epoxy equivalent weight, viscosity, resin type, color, water, chlorine impurities, hardener compatibility, operating time, and target application-specific performance should be evaluated together.
Companies planning to supply Epoxy Resin from Ataman Kimya are recommended to confirm the current product and offer conditions by sharing their usage area, resin family, target epoxy equivalent weight, viscosity, hardener system, chemical and mechanical performance requirements, packaging and technical document needs.
