Thermoplastic and thermoset polymers Flashcards
What type of polymer can be repeatedly melted, shaped and cooled with little degredation of the polymer? what aspect of the polymer allows this?
Thermoplastic, the weak secondary bonds between polymer chains
For semicrystalline thermoplastic polymers, which properties increase with increasing density (7)
stiffness, tensile strength, hardness, heat deflection, chemical resistance, shrinkage
For semicrystalline thermoplastic polymers, which properties degrade with increasing density?
impact strength, ductility
For semicrystalline thermoplastic polymers, what property remains constant regardless of how density changes?
weatherability
What aspect of a high performance TP manufacture is important to of been specified?
it’s thermal history (thermal processing/cycles exposed during manufacture
How can polymer crystal nucleation be enhanced, and why does this enhance it?
adding foreign bodies, as they act as convenient nucleation sites
Without foreign bodies where will crystal nucleation occur?
on the surfaces of moulds or at impurities within a polymer melt
How are Thermoset polymers typically recieved from the manufacturer?
with the crosslinking polymerisation reaction yet to be completed( can be handled in either liquid or solid form depending on the polymer)
How is a crosslinked structure generated for a TS?
a solution of monomers or linear polymers must be mixed with a catalysing agent and a chemical reaction initiated
describe the cure reaction for a TS
exothermic
how is the cure reaction for a TS initiated?
after a period of time, with addition of heat, pressure or UV light
With regards to Intermolecular structure, describe the states that could make up a Thermoset polymer?
only amorphous
What type of bonds connect crosslinks for a TS?
strong covalent bonds
What is the importance in ensuring the cure reaction is completed for a TS?
the better the cure the greater the density of crosslinks, the stiffer and stronger the polymer
What measure is used to identify how far the cure reaction of a TS polymer has progressed?
degree of cure (symbol aplha)
How is the “degree of cure” for a thermoset polymer defined?
Enthalpy released/total enthalpy to be released by reaction
alpha=0 at the start and alpha=1 at the end
How does the degree of cure evolve over time for a thermoset undergoing a cure reaction? and what does it depend on?
depends on how heat is applied or removed from the curing component.
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What is an elastomeric polymer?
elastomers (or rubbers) are polymers that exhibit high amounts of recoverable deformation. (elastic elongation typically > %
Are elastomers thermoset or thermoplastic polymers?
both but majority are TS
Name 5 common TS elastomers (NIBBS)
Natural rubber, Isoprene rubber, Butadiene rubber, Butyl rubber, Silicone
what is the curing process that typical TS elastomers go through?
Volcanisation
