Miscellaneous Hardener System
1. In addition to amine, acid and anhydride hardeners many other curing agents such as a number of amides that contain amine groups are used. Eg- polyamides.
Comparison of Hardening Systems
1. As a general rule that the amines are fast curing and give good chemical resistance but most are skin sensitive.
2. Organic anhydrides are less toxic and give cured products with high HDT. They do not cross-link the resin at room temperature.
3. As a general rule, with increasing aliphatic amines and their adducts, the time and temperature of cure will improve the properties.
PHYSICAL PROPERTIES
Mechanical Properties
2. Mechanical properties of cast resins depend on
Chemical structure of curing agent and epoxy resin,
Epoxy-amino stoichiometry or cross-link density of the cured network,
Cure schedule and test temperature.
2. TGDDM / DDS system (tetraglycidyl derivative of 4,4’ Diamino-diphenylmethane/4.4’ diamenodiphenyl sulphur) is used in high performance composite because of its high glass transition temperature (Approx.250ºC) and good strength retention even after prolonged exposure to elevated temperature
Thermal Properties
1. Thermal properties of epoxy resin are dependent on the degree of cross-linking, the flexibility of the resin molecule and the flexibility of the hardener molecule
2. Rigid structure obtained by using cycloaliphatic resins or hardeners such as pyromellitic dianhydride will raise the heat distortion temperature.
3. Tg of epoxy moulded materials is markedly affected by the curing conditions. Example; cold cured system is 70ºC and that of a hot-cured system 140ºC
Electrical Properties
1. Epoxy resin system exhibit good electrical properties over a wide range of frequencies and temperature.
2. Excellent insulating materials having high dielectric strength, arc and tracking resistance.
3. Resins are somewhat polar and this is reflected in the comparatively high dielectric constant and power factor for an insulating material.
CHEMICAL PROPERTIES
1. Resistance to chemicals
Resistant to weak acids, weak alkalis, alcohols, petroleum, benzene, oils, fats, solvents
2. Limited resistant to hot water
3. Not attacked by strong acids, strong alkalis, ammonia, acetone, esters, ketones.
Resistance to weathering
1. Epoxy resin system serves as excellent moisture barriers exhibiting low water absorption and resistance to most of the fungi growth.
2. Absorb only a tiny parts of UV component of sunlight
Resistance to High Energy Radiation
1. Epoxy moulded materials are like PF and UP moulded materials, very resistant to radiation.
Flammability
1. Use of tetrachlorobisphenol A or tetrabromobisphenol A as hardener imparts to the product a high flame retardancy
Toxicological Assessment
1. In appropriate handling of epoxy reactive resins and reactive materials such as acid anhydrides, polyamides and accelerators can cause skin irritation. In contract the cured moulded materials are non-toxic
PROCESSING OF EPOXY RESINS
1. Casting of epoxy resins
2. Glass fiber reinforced moulding
3. Epoxy Laminates
4. Powder coating
5. Epoxy Prepregs
Casting of epoxy resins
1. Though the volatile content is very small in epoxy resin system, degassing is necessary when making high performance electrical mouldings.
2. All additives used in the formulations must be dry. It is preferable to stir additives and resin under vacuum.
3. Casting resin prepared at the given mixing temperature is poured into the mould which has been pre-warmed to the curing temperature. Items to be encapsulated must also be pre-dried.
4. Moulds may be of steel, light alloy or epoxy cast resin.
5. High curing temperatures and highly reactive resin systems shorten the occupation time of moulds but which lead to poorer mechanical and electrical properties in the finished products
6. Advantages of epoxy casting resins such as good mechanical and electrical properties, low shrinkage and the lack of disruptive by-products during processing contribute towards their wide use.
Glass fiber reinforced moulding
1. Fiber reinforced articles are manufactured by hand lay up or filament winding process.
2. Curing time for mouldings manufactured by hand lay up is between 6 and 24 hours at room temperature.
3. Wound containers and tubes cure in an oven in 15 minutes to 3 hours.
4. Techniques are similar to those used for unsaturated polyester reactive resins.
Epoxy Laminates
1. Resin, curing agent and accelerator are dissolved in acetone.
2. Webs to be impregnated (usually glass fiber fabrics) are drawn through the impregnating bath.
3. In the drying tunnel the solvent vaporizes and a pre-reaction of resin starts. The prepregs are dried and wound up.
4. Later cut-to-size pieces are pressed in a multi-platen press at pressures of 40 bar and temperature of 170℃.
Powder coating
1. Epoxy powder is sprayed electrostatically on the pre-heated parts; it melts and cure in 15 to 30 seconds.
2. Welds and damaged parts are protected with an epoxy putty (curing time 3 hours at 20℃).
3. Coatings of 50 - 300 micron protect against corrosion.
Epoxy Resin moulding Compounds
1. EP moulding compounds can be processed by compression, transfer and injection moulding.
2. Excellent flowability allows the manufacture of complicated moulded items at low injection pressures.
3. Moulded items produced from these moulding compounds are having the following properties
Low processing shrinkage,
High dimensional stability,
No tendency to stress crack formation,
Good adhesion on all materials,
Mouldings with many inserts can be manufactured.
Epoxy Prepregs
1. Glass fibre prepregs with epoxide resins have been available for the manufacture of reinforced EP moulded items.
2. Glass content lies between 37 and 60%
Shelf life of these prepregs is six months at -18 °C and 10 days at room temperature.
3. Prepregs pressed at temperatures between 120 and 160 °C and pressures of 0.7 to 7.0 bar
4. EP prepregs reinforced with carbon fiber are also available commercially.
Secondary Processing
Secondary processing of epoxy resin such as cutting joining and surface finishing are similar to that of unsaturated polyester resin.
AVAILABILITY
1. Epoxy reactive resins are available in great variety as casting, impregnating, paint and coating resins.
2. Epoxy reactive resins are available in solid and liquid (unthinned and thinned with solvent) forms as well as glass fiber prepregs.
TYPICAL APPLICATIONS
Coating Applications
1. Coating application consume more than fifty percent of epoxy resin production.
2. Epoxy’s chemical resistance, toughness and durability and good adhesion are the prime features for this arena.
3. Used as coatings in appliance and automotive primers, industrial maintenance paints, and corrosive protection coatings for marine products.
4. Two component, water based epoxy emulsion paints are being used in architectural applications.
5. Traditional coal-tar epoxies and zinc-rich wash coat primers are used for maintenance and marine products protection coatings.
6. UV curable epoxy coatings have been developed for environmental protection of printed circuit boards.
Casting and Encapsulation Applications
1. High resistivity and relatively low dissipation factor, and high mechanical properties, allow for widespread use of epoxies in electrical and electronic applications as a insulators.
2. Encapsulation and coating of transistors, switches, coils, insulators, and integrated circuits, outdoors transformers, switching gears etc., are some of the routine usages of epoxy resins.
3. Tools like Patterns, jigs, metal shaping moulds and vacuum forming moulds are frequently made from epoxy castings
4. Deep diving submersible pump from acrylic and epoxy resins will provide diving capability to depths of 6500 feet.
Adhesives and Bonding Sealants
1. Since from the early stage of introduction of epoxy resins, they have been a dominant force in adhesives and bonding.
2. Volatile-free curing and minimal shrinkage combined with excellent lap-shear strength make epoxies the premier adhesive.
3. Epoxy adhesive systems successfully bonded to and filled enamel dentin and cementum in the dental field.
4. Automotive industry have promoted the replacement of welding riveting and other traditional metal joining processes with epoxy adhesive bonding
Laminates and Composites
1. Glass, graphite and polyaramid reinforced epoxy composites continue to find major use in industries such as space, printed circuitry, tanks and pressure vessels and pipes.
2. Epoxide resin laminates are of particular importance in the aircraft industry. It has been stated that the Boeing 757 and 767 aircraft use 1.8 tons of carbon fibre/epoxide resin composite for structural purposes per aeroplane.
3. Epoxy resin also been used with Aramid fibres for filament wound rocket motors and pressure vessels.
4. Epoxy/carbon fibre composite also being used in large quantities in aircraft helicopter blades.
5. Epoxide resins reinforced with carbon and aramid fibres have been used in small boats with a 40% saving in weight over traditional polyester/glass fibre composite.
6. Aramide/epoxy composites also being used as helmets for military purposes to replace steel.
7. One fourth of the epoxy resin production is being used in the application of printed circuit boards.
8. A violin is constructed with the composite replacing traditional woods. Cost and fabrication time were substantially reduced.
Surface Coating
1. Largest end use of epoxide resins is surface coating.
2. Industrial chemically resistant flooring remains a major use of epoxy resins.
3. Some decorative `pour-a-floor’ systems are still popular because of the ease of application and excellent adhesion to glass, quartz, marble chips and other attractive inclusion materials.
Aerospace application
Boeing’s 787 Dreamliner aircraft is being built using over 50% (by weight) composite materials, mainly using carbon fiber.
Major Carbon Fibre Reinforcement Plastic (CFRP) Applications in A - 380
Launch Vehicles / Missile
1. Nozzles – Divergent / Convergent
Silica – Phenolic
Carbon – Phenolic
Carbon – Carbon
2. Heat Shield / Nose Cone
Carbon Fibre Epoxy
Silica – Epoxy
Carbon – Carbon
3. Radomes
Silica-Silica Composite
Glass Phenolic
4. Re-Entry Vehicle Heat Shield
Ceramic Tiles
5. Gas Bottles
Graphite Fibre - Epoxy
Kevlar Fibre - Epoxy
6. Inter Stage Rings
Graphite Fibre - Epoxy
7. Motor Case
Kevlar – Epoxy
Glass - Epoxy
Epoxy in Spacecrafts:
1. Antennas
Carbon - Epoxy
Graphite Fibre – Epoxy
2. Structures
Carbon - Epoxy
Graphite – Epoxy
3. Gas Bottles
Graphite Fibre - Epoxy
Kevlar – Epoxy
4. Solar Panels
Carbon Fibre – Epoxy
5. Inserts
Silica - Epoxy
Carbon Fibre – Epoxy
Filament winding on a four axes, three spindle winder using carbon/fiberglass fibers for CNG tanks for buses and cars.
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