n,n-dimethylcyclohexylamine applications in epoxy resin curing
n,n-dimethylcyclohexylamine: a comprehensive review of its application as an epoxy resin curing agent
contents
- introduction
- 1.1. overview of epoxy resins
- 1.2. the role of curing agents in epoxy resin systems
- 1.3. introduction to n,n-dimethylcyclohexylamine (dmcha)
- product parameters and chemical properties
- 2.1. physical properties
- 2.2. chemical structure and reactivity
- 2.3. specification table
- mechanism of action in epoxy resin curing
- 3.1. amine curing mechanism
- 3.2. catalytic effect of dmcha
- 3.3. influence of dmcha concentration
- advantages and disadvantages of using dmcha
- 4.1. advantages
- 4.1.1. accelerated curing speed
- 4.1.2. low viscosity
- 4.1.3. improved physical properties
- 4.2. disadvantages
- 4.2.1. toxicity and handling precautions
- 4.2.2. potential for blooming
- 4.2.3. sensitivity to humidity
- 4.1. advantages
- applications in epoxy resin systems
- 5.1. coatings
- 5.2. adhesives
- 5.3. composites
- 5.4. casting and potting compounds
- formulation considerations and optimization
- 6.1. stoichiometry
- 6.2. blending with other curing agents
- 6.3. impact of temperature on curing
- 6.4. use of accelerators and modifiers
- safety, handling, and storage
- 7.1. safety precautions
- 7.2. handling procedures
- 7.3. storage conditions
- comparison with other amine curing agents
- 8.1. aliphatic amines
- 8.2. aromatic amines
- 8.3. cycloaliphatic amines
- 8.4. polyamidoamines
- recent advances and future trends
- 9.1. modified dmcha derivatives
- 9.2. encapsulation techniques
- 9.3. bio-based dmcha alternatives
- conclusion
- references
1. introduction
1.1. overview of epoxy resins
epoxy resins are a class of thermosetting polymers characterized by the presence of epoxide groups (oxirane rings). these resins are widely used in various industrial applications due to their excellent adhesive properties, chemical resistance, mechanical strength, and electrical insulation. epoxy resins typically consist of a resin component and a curing agent (also known as a hardener). the resin component is usually a diglycidyl ether of bisphenol a (dgeba) or a similar glycidyl ether oligomer. the curing agent initiates a chemical reaction that crosslinks the epoxy resin molecules, transforming the liquid resin into a solid, three-dimensional network.
1.2. the role of curing agents in epoxy resin systems
the curing agent plays a critical role in determining the final properties of the cured epoxy resin. the choice of curing agent significantly influences the curing speed, glass transition temperature (tg), mechanical properties (e.g., tensile strength, flexural modulus), chemical resistance, and thermal stability of the cured epoxy. different types of curing agents are available, each offering a unique set of properties and suitability for specific applications. common types include amines, anhydrides, phenols, and thiols. the selection of the appropriate curing agent is crucial to achieving the desired performance characteristics for the intended application.
1.3. introduction to n,n-dimethylcyclohexylamine (dmcha)
n,n-dimethylcyclohexylamine (dmcha) is a tertiary amine commonly employed as a curing agent or accelerator in epoxy resin systems. it is a colorless to slightly yellow liquid with a characteristic amine odor. dmcha acts primarily as a catalyst, accelerating the reaction between the epoxy resin and other curing agents, particularly anhydrides. it can also function as a co-curing agent in certain formulations. its use can lead to faster cure times, improved physical properties, and lower viscosity of the epoxy mixture, making it a valuable component in various applications.
2. product parameters and chemical properties
2.1. physical properties
dmcha exhibits the following typical physical properties:
- appearance: colorless to slightly yellow liquid
- molecular weight: 127.23 g/mol
- boiling point: 160-162 °c
- melting point: -70 °c
- density: 0.845 g/cm³ at 20 °c
- refractive index: 1.449 at 20 °c
- flash point: 43 °c (closed cup)
- vapor pressure: 1.3 hpa at 20 °c
- viscosity: low viscosity (dependent on temperature)
- solubility: soluble in organic solvents, slightly soluble in water
2.2. chemical structure and reactivity
dmcha is a tertiary amine with the following chemical structure:
ch3
|
c6h11-n-ch3the tertiary amine group in dmcha is responsible for its catalytic activity in epoxy resin curing. the lone pair of electrons on the nitrogen atom can initiate the ring-opening polymerization of the epoxide groups or accelerate the reaction between the epoxy resin and other curing agents. dmcha is relatively stable under normal storage conditions but can react with strong acids and oxidizing agents.
2.3. specification table
the following table summarizes the typical specifications for commercially available dmcha:
| property | specification | test method |
|---|---|---|
| purity (gc) | ≥ 99.0 % | gc |
| water content (kf) | ≤ 0.2 % | karl fischer titration |
| color (apha) | ≤ 20 | astm d1209 |
| specific gravity (20/20°c) | 0.840 – 0.850 | astm d1298 |
| refractive index (20°c) | 1.447 – 1.451 | astm d1218 |
| appearance | clear, colorless liquid | visual |
3. mechanism of action in epoxy resin curing
3.1. amine curing mechanism
amine curing of epoxy resins involves the reaction of the amine group with the epoxide ring. this reaction results in ring-opening of the epoxide and the formation of a new carbon-nitrogen bond. the hydrogen atoms attached to the nitrogen atom of the amine are responsible for the curing reaction. primary and secondary amines can react directly with the epoxy resin. tertiary amines, like dmcha, typically act as catalysts, accelerating the reaction of other curing agents, especially anhydrides, with the epoxy resin.
3.2. catalytic effect of dmcha
dmcha’s catalytic activity stems from its ability to initiate the polymerization of epoxy resins via an anionic mechanism. it can also accelerate the reaction of anhydrides with epoxy resins through a nucleophilic addition mechanism. specifically, dmcha can react with an anhydride to form a reactive intermediate, which then reacts with the epoxy resin, leading to ring-opening and crosslinking.
the proposed mechanism involves the following steps:
- complex formation: dmcha forms a complex with the anhydride curing agent.
- epoxide ring opening: the complex attacks the epoxide ring, leading to its opening and the formation of an alkoxide anion.
- proton transfer: the alkoxide anion abstracts a proton from another molecule, regenerating the catalyst (dmcha) and propagating the polymerization.
- crosslinking: the process continues, leading to the formation of a three-dimensional crosslinked network.
3.3. influence of dmcha concentration
the concentration of dmcha significantly affects the curing rate and the properties of the cured epoxy resin. increasing the concentration of dmcha generally leads to a faster curing rate. however, excessive amounts of dmcha can negatively impact the final properties of the cured resin, potentially leading to lower glass transition temperature, reduced mechanical strength, and increased brittleness. therefore, optimizing the dmcha concentration is crucial for achieving the desired balance between curing speed and performance characteristics. typically, dmcha is used in concentrations ranging from 0.1 to 5 phr (parts per hundred resin).
4. advantages and disadvantages of using dmcha
4.1. advantages
4.1.1. accelerated curing speed
one of the primary advantages of using dmcha is its ability to accelerate the curing speed of epoxy resins, particularly when used in conjunction with anhydride curing agents. this faster curing speed can lead to increased productivity and reduced manufacturing cycle times.
4.1.2. low viscosity
dmcha has a relatively low viscosity, which can help to reduce the overall viscosity of the epoxy resin mixture. this lower viscosity can improve the processability of the resin, making it easier to apply and allowing for better penetration into substrates.
4.1.3. improved physical properties
in some formulations, the use of dmcha can improve the physical properties of the cured epoxy resin, such as its impact resistance, flexural strength, and adhesion. this is often achieved by optimizing the crosslinking density and network structure of the polymer.
4.2. disadvantages
4.2.1. toxicity and handling precautions
dmcha is a corrosive and potentially toxic chemical. it can cause skin and eye irritation, and inhalation of its vapors can be harmful. proper handling procedures and personal protective equipment (ppe) are essential when working with dmcha. refer to the material safety data sheet (msds) for detailed safety information.
4.2.2. potential for blooming
blooming, also known as amine blush, is a phenomenon where amine curing agents migrate to the surface of the cured epoxy resin, forming a white, hazy film. this can be particularly problematic in humid environments. dmcha, being a relatively volatile amine, has the potential to cause blooming. careful formulation and curing conditions are necessary to minimize this effect.
4.2.3. sensitivity to humidity
the curing process of epoxy resins with amine curing agents can be sensitive to humidity. moisture can react with the amine, consuming the curing agent and leading to incomplete curing or altered properties. dmcha is no exception, and controlling humidity during mixing and curing is important for achieving consistent results.
5. applications in epoxy resin systems
dmcha is used in a variety of applications involving epoxy resins, including:
5.1. coatings
dmcha is used in epoxy coatings to accelerate the curing process and improve the overall performance of the coating. it can enhance properties such as chemical resistance, abrasion resistance, and adhesion to various substrates. applications include protective coatings for metal, concrete, and wood.
5.2. adhesives
in epoxy adhesives, dmcha can improve the bonding strength and reduce the curing time. it is used in structural adhesives, automotive adhesives, and electronics adhesives.
5.3. composites
dmcha is employed in epoxy composites to facilitate the curing of the resin matrix. this can lead to improved mechanical properties and reduced processing time. applications include aerospace components, automotive parts, and sporting goods.
5.4. casting and potting compounds
dmcha is used in epoxy casting and potting compounds to accelerate the curing process and provide good electrical insulation properties. applications include encapsulating electronic components, manufacturing electrical insulators, and producing molds and tooling.
table: applications of dmcha in epoxy resin systems
| application | benefits of dmcha use | examples |
|---|---|---|
| coatings | accelerated cure, improved chemical resistance, enhanced adhesion | protective coatings for pipelines, automotive primers, marine coatings |
| adhesives | faster bonding, increased bond strength, improved temperature resistance | structural adhesives for aircraft, automotive assembly, electronics bonding |
| composites | reduced processing time, improved mechanical properties | wind turbine blades, aircraft wings, automotive body panels |
| casting & potting | accelerated cure, good electrical insulation | encapsulation of electronic components, potting of transformers |
6. formulation considerations and optimization
6.1. stoichiometry
the stoichiometry of the epoxy resin and curing agent is crucial for achieving optimal curing and desired properties. while dmcha is primarily a catalyst, its concentration still needs to be carefully considered in relation to the other curing agents present in the formulation. too little dmcha may result in slow curing, while too much may lead to undesirable side reactions or reduced performance.
6.2. blending with other curing agents
dmcha is often used in combination with other curing agents, such as anhydrides, to achieve a specific balance of properties. the type and concentration of the other curing agent will influence the overall curing process and the final properties of the cured epoxy resin. careful consideration should be given to the compatibility and reactivity of the different curing agents.
6.3. impact of temperature on curing
the curing temperature significantly affects the curing rate and the properties of the cured epoxy resin. higher temperatures generally lead to faster curing rates, but can also result in increased shrinkage and thermal stress. dmcha’s activity is temperature-dependent, and its effectiveness as a catalyst increases with temperature.
6.4. use of accelerators and modifiers
other accelerators and modifiers can be added to the epoxy resin formulation to further enhance the curing process or improve the final properties of the cured resin. examples include:
- accelerators: other tertiary amines, metal catalysts
- modifiers: toughening agents, fillers, plasticizers
table: effect of formulation parameters on curing and properties
| parameter | effect on curing rate | effect on tg | effect on mechanical strength | effect on viscosity |
|---|---|---|---|---|
| dmcha concentration | increases | may decrease | may decrease | slight decrease |
| curing temperature | increases | may increase | generally increases | decreases |
| anhydride concentration | increases (with dmcha) | increases | generally increases | increases |
7. safety, handling, and storage
7.1. safety precautions
- wear appropriate personal protective equipment (ppe), including gloves, safety glasses, and a respirator if necessary.
- avoid contact with skin and eyes.
- work in a well-ventilated area.
- read and understand the material safety data sheet (msds) before handling dmcha.
7.2. handling procedures
- dispense dmcha carefully to avoid spills.
- clean up any spills immediately with appropriate absorbent materials.
- avoid mixing dmcha with incompatible materials.
- use appropriate containers and equipment for handling dmcha.
7.3. storage conditions
- store dmcha in a tightly closed container in a cool, dry, and well-ventilated area.
- keep away from heat, sparks, and open flames.
- protect from direct sunlight.
- store away from incompatible materials, such as strong acids and oxidizing agents.
8. comparison with other amine curing agents
dmcha is just one of many amine curing agents available for epoxy resins. each type of amine curing agent offers different advantages and disadvantages, making them suitable for different applications.
8.1. aliphatic amines
aliphatic amines (e.g., diethylenetriamine (deta), triethylenetetramine (teta)) are typically fast-curing and provide good mechanical properties. however, they can be more toxic and have a higher vapor pressure than other amine types.
8.2. aromatic amines
aromatic amines (e.g., diaminodiphenylmethane (ddm), diaminodiphenylsulfone (dds)) offer excellent thermal stability and chemical resistance but typically require high curing temperatures.
8.3. cycloaliphatic amines
cycloaliphatic amines (e.g., isophoronediamine (ipda)) provide a good balance of properties, including good chemical resistance, mechanical strength, and color stability. they offer better handling characteristics than aliphatic amines.
8.4. polyamidoamines
polyamidoamines are derived from fatty acids and polyamines. they offer good flexibility, adhesion, and resistance to humidity, making them suitable for coatings and adhesives.
table: comparison of amine curing agents
| curing agent type | curing speed | toxicity | thermal stability | chemical resistance | applications |
|---|---|---|---|---|---|
| aliphatic amines | fast | high | low | fair | general-purpose adhesives, fast-curing coatings |
| aromatic amines | slow | moderate | high | excellent | high-performance composites, structural adhesives |
| cycloaliphatic amines | moderate | moderate | moderate | good | coatings, adhesives, composites |
| polyamidoamines | slow | low | fair | good | coatings, adhesives |
| dmcha | accelerates | moderate | moderate | moderate | coatings, adhesives, composites |
9. recent advances and future trends
9.1. modified dmcha derivatives
researchers are exploring modified dmcha derivatives to improve its performance and address some of its drawbacks. for example, attaching bulky groups to the nitrogen atom can reduce its volatility and potential for blooming.
9.2. encapsulation techniques
encapsulation of dmcha in microcapsules or nanoparticles can provide controlled release and improve the shelf life of epoxy resin formulations. this can also reduce the potential for toxicity and improve handling safety.
9.3. bio-based dmcha alternatives
with increasing emphasis on sustainability, there is growing interest in developing bio-based alternatives to dmcha. researchers are investigating the use of amines derived from renewable resources as potential curing agents or catalysts for epoxy resins.
10. conclusion
n,n-dimethylcyclohexylamine (dmcha) is a valuable tertiary amine curing agent and accelerator widely used in epoxy resin systems. its ability to accelerate curing, reduce viscosity, and potentially improve physical properties makes it suitable for a variety of applications, including coatings, adhesives, composites, and casting compounds. however, its toxicity, potential for blooming, and sensitivity to humidity must be carefully considered. proper handling procedures, formulation optimization, and storage conditions are essential for achieving the desired performance and ensuring safety. ongoing research efforts are focused on developing modified dmcha derivatives, encapsulation techniques, and bio-based alternatives to further improve its performance and address its limitations.
11. references
- smith, j. g. "advanced polymer chemistry." academic press, 2002.
- goodman, s. h. "handbook of thermoset resins." william andrew publishing, 2015.
- ellis, b. "chemistry and technology of epoxy resins." blackie academic & professional, 1993.
- may, c. a. "epoxy resins: chemistry and technology." marcel dekker, 1988.
- pascault, j. p., sautereau, h., verdu, j., & williams, r. j. j. (2002). "thermosetting polymers." marcel dekker.
- riew, c. k., & kinloch, a. j. (eds.). (1989). "toughened plastics i: science and engineering." american chemical society.
- oswald, t., and weber, t., "epoxy resins", wiley-vch, weinheim, 2017.
- european chemicals agency (echa). registration dossier for n,n-dimethylcyclohexylamine. available on echa website.
- various material safety data sheets (msds) for n,n-dimethylcyclohexylamine from different manufacturers.
