Thermoset polymer matrices

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Thermoset Polymer Matrices are synthetic polymer reinforcements that have been developed and used in many applications, including glass–reinforced polyester radar domes on aircraft and graphite-epoxy payload bay doors on the space shuttle. They have been used from World War II up to the present,

Thermoset polymers are the most widely used matrix material in composite materials. In this paper it contains the thermoset polymer matrices used in composites, relative to their individual composition, properties and applications. The different types of thermoset polymer matrices used in composites are: Bis-Maleimids (BMI), Epoxy (Epoxide), Phenolic (PF), Polyester (UP), Polyimide, Polyurethane (PUR), Silicone.

Bis-Maleimides (BMI)

Main article: Maleimide

This is the most recent polymer this polymer is produced by the condensation reaction of a diamine with maleic anhydride. It can be processed basically like the epoxy (350 °F (177 °C) cure). After an elevated post-cure (450 °F (232 °C)), it will exhibits superior properties. These properties are influenced by a 400-450°F continuous use temperature and a glass transition of 500 °F (260 °C).

This polymer is merged into composites as a prepreg matrix used in electrical printed circuit boards, structural aircraft – aerospace composites, etc. It is also used as a coating material and as the matrix of glass reinforced pipes, particularly in high temperature and chemical environments.

Epoxy (Epoxide)

Main article: Epoxy

Epoxy is used widely in numerous formulations and forms in the aircraft-aerospace industry. It is called "the work horse of modern day composites". Standard epoxies (90%) are based on bisphenol A diglycidyl ether formula.

In recent years, the epoxy formulations used in composite prepregs have been fine-tuned to improve their toughness, impact strength and moisture absorption resistance. Maximum properties have been realized for this polymer.

This is not only used in aircraft-aerospace demand. It is used in military and commercial applications and is also used in construction. Epoxy-reinforced concrete and glass-reinforced and carbon-reinforced epoxy structures are used in building and bridge structures.

Properties of Epoxy

  • High-Strength Glass Fiber Reinforced
  • Relative Density 1.6-2.0
  • Melting temperature(°C)
  • Thermoset Processing Range(°F) C:300-330,I=280-380
  • Molding pressure 1-5
  • Shrinkage 0.001-0.008
  • Tensile strength 5,000-20,000
  • Compressive strength 18,000-40,000
  • Flexural Strength 8000-30,000
  • I Zod impact 0.3-10.0
  • Linear expansion (10-6 in./in./°C) 11-50
  • Hardness Rockwell M100-112
  • Flammability V-0
  • Water absorption 24h (%) 0.04-0.20

Phenolic (PF)

Main article: Phenol formaldehyde resin

This polymer was developed by man back in the late 19th century. Phenolic was the first truly synthetic polymer and it is often referred to as the “workhorse of thermosetting (T.S.) resins”. A heat-cured T.S. resin has overall excellent properties, particularly dimensional stability, elevated temperature, creep resistance and applications requiring heat resistance.

General purpose molding compounds, engineering molding compounds and sheet molding compounds are the primary forms of phenolic. Phenolic is also used in some Honeycomb core (H/C) as the matrix binder. This Phenolic is used in many electrical applications such as breaker boxes, brake lining material and even, recently, combined with various reinforcements in the molding of an engine block-head assembly, called the polimotor. Phenolics may be processed by the various common techniques, including compression, transfer and injection molding.

Properties of Phenol-Formaldehyde

  • High-Strength Glass Fiber Reinforced
  • Relative Density 1.69-2.0
  • Water Absorption 24h(%) 0.03-1.2
  • Melting Temperature (◦c)
  • Thermo set Processing Range (◦F) C:300-380 I:330-390
  • Molding pressure I-20
  • Shrinkage 0.001-0.004
  • Tensile Strength 7000-18000
  • Compressive Strength 16,000-70,000
  • Flexural Strength 12,000-60,000
  • Izod Impact(ft-lb/in) 0.5-18.0
  • Linear expansion 8-21
  • Hardness Rockwell E54-101
  • Flammability V-0

Polyester

Main article: Polyester

This is an extremely versatile, fairly inexpensive, polymer. Unsaturated polyester combines an unsaturated dibasic acid and a glycol dissolved in a monomer, generally styrene, including an inhibitor to stabilize the resin. Organic peroxides, such as methyl ethyl ketone peroxide (MEKP) and a promoter are combined with the resin to initiate a room temperature (R.T.) cure. In this liquid state, polyester may be processed by numerous methods, including Hand Layup (HLU), vacuum bag molding, spray-up and compression molded Sheet Molding Compound (SMC), etc.

The resin can also be B-staged after application to chopped reinforcements and continuous reinforcement, pre-preg. Solid molding compounds in the form of pellets or granules are also used in processes such as compression and transfer molding.

Polyimide

Main article: Polyimide

This polymer is presently the most advanced of all T.S. matrices. It has characteristics of high temperature (H/T) physical and mechanical properties. It is available as uncured resin, prepreg, stock shapes, thin sheets, laminates, and machined parts.

Along with the H/T properties, this polymer must be processed at very high temperatures and relative pressure to produce these characteristics. With prepreg materials, 600 °F (316 °C) to 650 °F (343 °C) temperatures and 200 psi (1,379 kPa) pressures are required. The entire cure profiles are inherently long as there are a number of intermediate temperatures dwells, duration of these are dependent on part size and thickness.

The cut of P.I. is 450 °F (232 °C), highest of all T.S., with short term exposure capabilities of 900 °F (482 °C). Normal operating temperatures range from cryogenic to 500 °F (260 °C).

Properties of Polyimide

  • Good mechanical properties at H/T
  • Good electrical properties
  • High wear resistance
  • Low creep at high temperatures
  • Good compression with glass or graphite fiber reinforcement
  • Good chemical resistance
  • Inherently flame resistant
  • Unaffected by most solvents and oils

Polyimide film

Polyimide film [1] possesses a unique combination of properties that make it ideal for a variety of applications in many different industries.

High-performance resin

The high-performance resin is used in electrical, wear resistant and as structural materials when combined with reinforcement for aircraft-aerospace applications, which are replacing heavier more expensive metals.

High temperature processing causes some technical problems as well as higher costs compared to other polymers. Hysols [2] PMR series is an example of this polymer.

Polyurethane (PUR)

Main article: Polyurethane

These T.S. polymers are produced by combinations of polyisocyanate and polyol as well as other ingredients and reactive materials. Forms of the material are broad, ranging from flexible to rigid foams and foam moldings, as well as solid elastomeric moldings and extrudates. These combined with various reinforcement–fillers can be applied to numerous applications.

Polyurethane foam

Polyurethane foam [3] structural core can be combined with glass-reinforced or graphite-reinforced composite laminates to produce a lightweight, strong, sandwich structure.

Silicone

Main article: Silicone

Silicone is a unique, partly organic, polymer structure made of alternating silicon and oxygen atoms rather than the familiar carbon-to-carbon backbone characteristics of organic polymer. Silicone can be in the form of a liquid, gel, elastomer or solid. It has a broad temperature use range, elasticity, chemical resistance, good release properties, etc.

In the area of composites, silicone is used as a sealant and coating material. It is often used as a reusable bag material for vacuum-bag curing of composite parts.

Miscellaneous

Urea-formaldehyde and melamine-formaldehyde, although not widely used in modern day composite applications, are characteristically used in molding compounds where some use of fillers and reinforcements occurs.

Also, the urea resin is often used as the matrix binder in construction utility products such as particle board, wafer board, and plywood, which are true particulate and laminar composite structures.

Advantages and Disadvantages of thermoset polymers

Advantages

  • Well established processing and application history
  • Overall, better economics than thermoplastic (T.P.) polymers
  • Better high temperature (H/T) properties
  • Good wetting and adhesion to reinforcement

Disadvantages

  • Resins and composite materials must be refrigerated
  • Long process cycles
  • Reduced impact –toughness
  • Poor recycling capabilities
  • More difficult repair ability

References

  1. ↑ http://www.profma.com/polyimide.htm
  2. ↑ http://www.henkel-cee.com/cps/rde/xchg/SID-0AC83309-79FA31DA/henkel_cee/hs.xsl/5497_COE_HTML.htm?countryCode=com&BU=industrial&brand=0000000386
  3. ↑ http://www.ciba.com/index/ind-index/ind-pla/ind-pla-polymersandpolymerprocessing/ind-pla-pol-polyurethane.htm

External links

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