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Vinyl, phenolic, and cyanate ester resin systems

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chichi's version from 2018-04-03 09:50

Section 1

Question Answer
Discuss in detail the modifications that you can do to improve the toughness and reduce emissions during the processing of vinyl ester resin systems.Vinyl ester resin can be modified to improve toughness and reduce emissions by the reduction of styrene. Styrene acts as an elastic agent. It gives the polymer chain additional range of movement which is beneficial for elastic modulus however does not increase strength-to-failure/toughness properties. Styrene additive is also higly volatile an handling and, manipulation can prove hazardous.You can also change the way in which you process vinyl ester resin systems by using processes like bag molding or vacuum assisted resin transfer molding you cut down on energy intensive processes. This will reduce overall emissions the toughness is ultimately improved only if the fibers are reinforced uniformly and there is additional reinforcement in the transverse direction
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Section 2

Question Answer
Explain carbamates formation in cyanate ester resin systems. What are the effects of these on the laminated composites? Carbamate formation can occur when moisture is able to diffuse into the laminate or adhesive and react with the polymer system during the cure process. The formation of the carbamate group proceeds by hydrolysis of the OCN functional group to form a carbamate. With additional heating above 150C, the carbamate group decomposes and forms an amine and carbon dioxide. The carbon dioxide gas can cause blistering and delamination in laminates. The amount of carbamate formed is also dependent on the catalyst use in the formulation zinc is often used. During thermal decomposition of the carbamate into CO2 and amine, it is possible for unreacted OCN groups to react with the amine and form a more stable linear polymer structure, or isourea.
What can be done to avoid any deleterious effects?Predrying and dry storage of composite tools trying and outgassing of foam cores, drying fabrics, and modifying the cure cycle to remove moisture from the materials before the cure reaction begins. Even changes in the vacuum bag lay-up, for instance, allowing a good path for trapped moisture to be removed from the vacuum bag and keeping the part under an active vacuum thoughout the cure, have been bound to be useful in minimizing the problem.
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Section 3

Question Answer
What are the unique properties of phenolic resin systems?Superior fire resistance, excellent high-temperature performance, long-term durability, and resistance in hydrocarbon and chlorinated solvents
State the two types of phenolic resins and explain the reactions involved in their formationNovolacs and resoles. Novolacs--the intial reaction is the formation of a carbonium ion by the action of the acid catalyst on the methlyene glycol; this ion then reacts with phenol to produce methylophenol.. In an acidic medium, the methylol group is extremely unstable and will react immediately with an additional phenol or methylolated pehnol to produce novolac. Resoles contain various orthomethylol and para methylol groups, free phenol, free formaldehyde, water, and/or solvent. Does not require on external catalyst and undergo self-polymerization under heat with evolution of water
Compare the smoke optical density and flame spread index of phenolic resin systems with other types of polymersphenolic resin systems an LOI of 78, this means it is not easily flammable in open air. It also has a flame spread index and smoke density of 10, which is the lowest compared to vinyl ester and polyester resin. Polyester has a flame spread index of 15, smoke density of 600-800. Vinyl ester: flame spread index of 45, smoke density of 600-800
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Section 4

Question Answer
Ways to incorporate thermoplastic polymers with fiber: (Hot-melt coating)Hot melt impregnation is successfully done with low molecular weight polymers that are not highly viscous, the fibers are pulled from a mandrel and blown on to straighten the fibers, then placed into a polymer solution, which reaches above Tg in a die which melts through a uniform die until exiting which is down lastly
Ways to incorporate thermoplastic polymers with fiber: (Solution processing)this process is not very every thermoplastic and solution used is ultimately dependent on the product end use. Solution is added into the fibers to help improve viscosity and handling however, if the solution is not entirely removed there is a high chance of void propagation and delamination
Ways to incorporate thermoplastic polymers with fiber: (Film stacking)similar to hand lay-up except for the fact the films are not as tacky but have good drape. Films or layers of thermoplastics fiber prepreg are placed one layer after another and are spot welded to hold _______ This is mold which will be then reduced? in an autoclave to be held in increasing heat however constant pressure for easy delamination. This is beneficial due to cheaper tooling costs (only one due cost) heavier one side will be uniform while the other at risk.
Ways to incorporate thermoplastic polymers with fiber: (Powder coating)powder coating and fiber hybridization are the best methods of fiber and thermoplastic incorporation. This is due to the uniformity of the powder coating method. True, it is costly due to thermoplastic powder is labor and energy intensive. Unlike fiber hybridization, powder coating has wonderful fracture toughness and good mechanical properties, Particulates and other uniform mixtures can sneak into the processing so caution must be maintained. The process of powder coating is that continuous fibers are combed and sometimes intertwined and pulled through light treatment (pre-treatment) this is an extraneous step but does help with even distribution of powder and provides sufficient coverage. Then the fibers are pulled through a blower which pulls the powder through an electrostatic material which changes the charges so the powder will easily grapple onto the fibers. Once distributed evenly throughout the powder the fibers are put through a heat unit which makes the board sufficiently tacky and good drape
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