Epoxy Resins Part 2

chichi's version from 2018-02-28 18:47

Section 1

Question Answer
One of the newer trends in the composites indursty is to look at cutting production costs and decreasing cyrcle times by usingradiation-curable resin systems like UV, IR, or EB
Advantages or radiation-curable resin sytemsenergy efficiency rapid cure ties measured in seconds, dimension stability, pollution abatement as solvent is eliminated from the process, low exotherm potential that permits the use of temperature-sensitive substrates, and no cure until source exposure
Disadvantages of radiation-curable resin systemslarge capital expense, difficulty in penetrating thich parts, and the sensitivity of the reaction mechanism to impurities

Section 2

Question Answer
Modifiersused to provide specific physical and mecanical performance in both the uncrued and cured resin
General categories of modifiers include...rubbers, thermoplastics, diluents, flame retardants, fillers, and pigments and dyes
Rubber additivesused to increase flexibility, fatigue resistance, crack resistance, and energy absorption (toughness) in epoxy resins and can be separated in two categories
Two categories of epoxy resinsreactive or nonreactive
Liquid rubbersCTBNs
Long-chain polymers have terminal carboxyl groups that may be reacted with epoxy to decrease cross-link density and increase tensile elongationCTBNs
Solid acrylonitrile-butadiene rubbers have higher molecular weights than the liquid rubbers
Preformed rubber particles are occasionally used in composites when...both the particle sie distribution and the volume fraction of particles in the cured resin need to be closely controlled

Section 3

Question Answer
Thermoplastic additivesused much like rubbers to increase the fracture toughness of epoxy resins
Thermoplastics commonly used in epoxy composites are...phenoxy, polyether block amides, poly vinyl butyral, poly vinyl formal, polysulfone, polyethersulfone, polyimide, polyetherimide, and nylon
What makes thermoplastic differ from rubbers?Thermoplastics differ from rubbers in that they are more effective tougheners in highly cross-linked matrices because phase separation will occur at lower concentrations as mztrix rigidity increases

Section 4

Question Answer
Monofunctional resins such as...butyl glycidyl ether, phenyl glycidyl ether, and cresyl glycidyl ether
What makes monofuncional resins effective?they are effective in reducing viscosity, their use will result in a reduction of thermal and mechanical properties
Flame retardantsadded to epoxy resins as a filler, or matrix can be built to incorporate FR characteristics
The presence of ___________ and _______________ in epoxy-curative based resin decrease flammabilityhalogens; char-forming aromatics
Fillers such as _____ and _____ are effective in inhibiiting combustion by undergoing endothermic decomposition and liberating water into the gaseous state during combustionalumina trihydrate; magnesium hydroxide
Chlorinated or brominated epoxy resins and curing agents may be combined with antimony, phosphorous, or boron compounds lower flammability of epoxy composites
How does the compounds in epoxy resin work for FR properties?These compounds work in the gas phase to liberate free radicals trapping *H and *OH, thereby blocking the chain reactions that contribute to decomposition

Section 5

Question Answer
Unreactive fillersfillers are used in epoxt resins as extenders, reinforcements, and to impart specific physical characteristics such as low density, low flow, shrinkage reduction, and thermal or electrical conductivity
Categories of unreactive fillersminerals, metals, glass, fibers, carbon, and miscellaneous ogranics
Forms unreactive fillers come inpowders, pulps, flaskes, flocks, spheres, microballoons, short fibers, and whiskers
Increasing filler aspect ratio increases...the resistance to crack propagation, but it also rapily increases resin viscosity, decreasing the amount of illfer that can be used
When compounding filled systems, variables to take into consideration are...the volume fraction of the filler, particle characteristics, filler aspect ration, the strength and modulus of the filler, adhesion of the filler to the resin, the viscosity of the base resin, and the toughness of the base resin

Section 6

Question Answer
Epoxy resins may be colored using a wide variety of ______ and _____, both organic and inorganicpigments; dyes
Pigmentsinsoluble particles dispersed in a resin
Dyessoluble organic molecules
Generally not suitable for epoxy composite applications due to temperature limitations. If they are to be used, care should be taken to identify materials that are compatible with target systems and remain inert in themDyes
Additional additives occasionally found in epoxy resins are...flexibilizers, plasticizers, liquid and resinous extenders, antioxidants, light stabilizers, internal mold releases, and antifoams

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