Thermoset polymer matrix
They were first developed for structural applications,[1] such as glass-reinforced plastic radar domes on aircraft and graphite-epoxy payload bay doors on the Space Shuttle.
They were first used after World War II, and continuing research has led to an increased range of thermoset resins, polymers or plastics,[2] as well as engineering grade thermoplastics.
[5] Cure is characterised by expansion rather than shrinkage and uses include structural prepregs, liquid molding and film adhesives for composite construction, bonding and repair.
[7] When postcured, all residual cyanate ester functionality polymerises by cyclotrimerisation leading to tightly crosslinked polycyanurate networks with high thermal stability and glass transition temperatures up to 752 °F (400 °C) and wet heat stability up to around 400 °F (200 °C).Cyanate ester resin prepregs combine the high temperature stability of polyimides with the flame and fire resistance of phenolics and are used in the manufacture of aerospace structural composite components which meet fire protection regulations concerning flammability, smoke density and toxicity.
[8] The diglycidyl ethers of bisphenol-A (DGEBA) and bisphenol-F (DGEBF) are the most widely used due to their characteristic high adhesion, mechanical strength, heat and corrosion resistance.
In recent years, the epoxy formulations used in composite prepregs have been fine-tuned to improve their toughness, impact strength and moisture absorption resistance.
They are used in printed wire/circuit board laminating and also for electrical encapsulation, adhesive and coatings for metal where there is a need to provide protection from corrosion, erosion or chemical attack at high continuous operating temperatures.
They are characterised by high bonding strength, dimensional stability and creep resistance at elevated temperatures, and frequently combined with co-curing resins such as epoxies.
Phenolics find use in many electrical applications such as breaker boxes, brake lining materials and most recently in combination with various reinforcements in the molding of an engine block-head assembly, called the polimotor.
Properties of phenolic composites have the following properties: Unsaturated polyester resins are an extremely versatile,[12][13] and fairly inexpensive class of thermosetting polymer formed by the polycondensation of glycol mixtures often containing propylene glycol, with a dibasic acid and anhydrides usually maleic anhydride to provide backbone unsaturation needed for crosslinking, and phthalic anhydride, isophthalic acid or terephthalic acid where superior structural and corrosion resistance properties are required.
The entire cure profiles are inherently long as there are a number of intermediate temperatures dwells, duration of which are dependent on part size and thickness.
[16][17][18][19][20] High-performance polyimide 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.
[26] They differ from polyureas which are thermoset elastomeric polymers with carbamide (-NH-CO-NH-) links made by combining diisocyanate monomers or prepolymers (OCN-R-NCO) with blends of long-chain amine-terminated polyether or polyester resins (H2N-RL-NH2) and short-chain diamine extenders (H2N-RS-NH2).
They have the general formula (R2SiO)n and the physical form (liquid, gel, elastomer or solid) and use varies with molecular weight, structure (linear, branched, caged) and nature of substituent groups (R = alkyl, aryl, H, OH, alkoxy).
[29] Vinyl ester resins are used for wet lay-up laminating, SMC and BMC in the manufacture and repair of corrosion and heat resistant components ranging from pipelines, vessels and buildings to transportation, marine, military and aerospace applications.
Urea-formaldehyde and melamine-formaldehyde resins, although not widely used in high performance structural composite applications, are characteristically used as the polymer matrix in molding and extrusion compounds where some use of fillers and reinforcements occurs.
