Lab 4. Tensile Test Plastic Flashcards
polymer is
an organic substance composed of molecules with large molecular mass composed of repeating structural units……
what is a polymer connected by
covalent bonds… may contain hundreds or thousands of repeat units
what is small definition of polymer.
many chains.
name two forces that hold polymer chains together
covalent molecules and van-der-waals
Difference between monomer and repeat units
A monomer is a single molecule, a polymer is a long chain of monomers, repeating units are a simplified method of drawing a polymer, whose chain may extend for a long time.
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name some natural polymers
proteins, enzymes, starches, and cellulose
where are natural polymers important
biological and physiological processes in plants and animals
plastics
are materials that have some structural rigidity under load, and are used for general-purpose applications
elastomers-
polymer which contributes to rubber, fibers, adhesives, films and foams
name some plastics
polyethylene, polypropylene, polystyrene, fluorocarbons, epoxies,
what are the two types of polymers/plastics
thermoplastics and thermosetting
qualities of thermoplastics
high molecular weight, soften or liquid when heated, harden when cool, process is reversible regardless of repeated cycles
qualities of thermosettings
(polymers that cure, through the addition of energy/heat to a stronger forms by a cross-linkage process)
harden or solidify when heated
irreversible process (thermoset materials cannot be easily melted and re-shaped after i is cured
crosslinkage of thermoplastic
little to none
crosslinkage of thermoset
alot network
what are factors the influence properties of polymers/plastics
Molecular weight
degree of polymerization
molecular structure
linear polymers
van der waals bonding between chains.
branched polymers
chain packing efficiency is reduced compared to linear polymers lower density
cross-linked polymers
chains are connected by covalent bonds. often achieved by adding atoms or molecules that form covalen links between chains. many rubbers have this strucuture
network polymers
3D networks made from trifunctional mers.
give in the direction of increasing strength, the type of crosslinkage
linear, branched, crosslinked, network
how are amorphous plastics bonds
they have no strong bonds between molecular chains
how are bondings with crystalline plastics
they have strong bonds between molecular chains
an amorphous/semi crystalline plastic will exhibit….
a glass transition temperature TvG
below glass transition temperature molecules have….
little relative mobility
above glass transition temperature molecules have….
great mobility
what is the glass transition temperature usually around
.5-.8 of the melting temperature….
glass transition temperature-
often define the maximum service temperature of plastics and control very important processing parameters
like metals,….
plastics yeild at the end of the elastic region
plastics also start necking
what happens during necking?
the molecule chains stretch from agglomerated polymers to aligned polymers
plastics can endure….
significant strain after the onset of necking
brittle deformation
does not cause to much molecular stretches and plastic region during the failure. it is usually seen in thermosetting and glassy polymers
plastic deformation
is defined by the interaction between crystalline and amorphous regions, and it is partially reversible
crazes
are regions of very localized plastic deformation, which lead to the the formation of small and interconnected microvoids
as the tensile stress enlarges a craze, the stress introduced…
will be distributed over an increasing volume which means that force peaks are avoided.
.what are some advantages of plastics
good electrical insulation
good thermal insulation
high specific strength..strength/weight per unit volume
can be recycled
low density
application in composite materials
disadvantages of plastics
low toughness
less resistance to abrasion
can produce hazaradous fumes when burned
in general, cannot be used in high temperature applications
although special utlra high temperature resistant plastic is available.
