Name 5 Thermosets
Polyurethanes
Epoxy resin
Furanic resin
Vinyl esters
Phenol foraldehyde
Name 4 Elastomers
Silicone resin
Natural rubber
Styrene-butadiene Rubber
Nitrile-Butadiene Rubber
What are the characteristic properties of Thermosets?
high degree of crosslink
high Tg
high rigidity
thermal stability
chemical resistance
What are the characteristic properties of elastomers?
low degree of crosslink
low Tg
high extension at break
What is understood under a cure?
The process of crosslinking a polymer
What is the Gel point?
The point in the cure, when the material is no longer able to flow.
(storage modulus=loss modulus)
What is understood under the functionality of a monomer? What value is needed for crosslinking
The number of sites available for bonding.
eg. 2 for double bonds
For crosslinking a funcitonallity value of 3 is needed.
What is a TTT diagramm? (Explain abbrevation)
Time-Temperature-Transformation Cure Diagramm
What are processes that can occur during curing?
chemical reactions
heat evolution
evolution of volatiles
gelation
vitrification
devitrification
Describe the TTT diagramm of a Thermosetting Polymer, by naming the critical temperatures and the zones
liquid region, gelled rubber region, gelled glass region, ungelled glass region
Tg:glass transition of fully reacted material
Tg,gel: gelification Temperaturre
Tg,0:glass transition of ungelled educts
Describe the structure of an epoxy group.
What are the properties of epoxy resins?
exellent chemical resistance
low shrinkage
good adhesion to many substrates
many possible hardeners
two component system with control over final properties
What are the most common monomers for producing epoxy resins and what is the product?
Monomers:
Product:
What are curing agents?
Determine the type of curing reaction and the final product
“part B” of the two component system epoxy resin
Determines reaction kinetics
What are the most common curing agents for epoxy?
amines (R-NH2)
anhydrides (products of dehydration of acids)
Lewis acids
What are the general properties of Phenolic resins?
comperatively cheap
How are phenolic resins produced?
condensation reaction with evaporating water
educts are
What is the basis of Furan resins?
What are the general process characteristics of furan resins?
production under h2o condensation
crosslink at 260°C
Describe the structure of the most common silicone
How can Silicones be produced? (name the reactions)
Hydrolisis
linear condensation
Ring opening polymerization
crosslinking and network forming
Describe the TTT diagramm of a vulcanized Elastomer
What are the properties of Alkyd resins?
What is special about the delivery state of Polyester resins?
Polyester is delivered unsaturated (double bonds present) <=> the crosslinking is conducted when needed
What initiates the crosslinking in Polyester?
Radicals
What does the polyurethane family have in common ?
The urethane group at some point in their chain
Why are Polyurethanes soft?
They hace and alternating block copolymer of thermoset and elastomer. (hard and soft)
With which methods can the crosslinking of a thermoset be determined?
Differential scanning calometry DSC
Thermogravimetric analysis TGA
FTIR analysis
What is measured in Thermogravimetric analysis?
The mass over time and changing temperature
How is the DTG measurement obtained?
By derivating the TGA analysis after time and plotting it against the temperature.
What polymer properties are determined by the TGA analysis?
oxidative stability
decomposition kinetics
estimation of product lifetime
What is the application of XRD measurements in the Polymer field?
measureing the degree in crystallinity
identification of polymers
identifying fibre orientation
What are the properties of elastomers?
viscoelastic behaviour
no creep relaxation
What is the basis for most polymers?
polybutadien
one double bond for the chain another for crosslinking
How much of a rubber normally consists of additives?
40%
Name the type of rubber addititves
activators
accelerators
vulcanizing agents
fillers
plasticizers
antioxidants
What are the steps of vulcanization? How does the torgue force in rheometric analysis evolve over the time and the steps?
shaping
curing
overcuring
Where does the curing/vulcanization take place in rubber injection molding?
Withing the tool.
How is natural rubber obtained?
By harvesting the tree sap of the rubber tree
What is the most common substitute for natural rubber? How do the properties differ?
Styrene Butadiene Rubber
better abrasion resistance
poorer fatigue resistance
better heat resistance
poorer low temperature tensile strength
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