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202 FINAL > polymers and Fiber reinforced polymers > Flashcards

polymers and Fiber reinforced polymers Flashcards

1
Q

what is a polymer

A

manmade material generally consisting of a small molecular unit (monomer), combined in a chain or a network

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2
Q

what is a small molecular unit called

A

monomer

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3
Q

what is polymerization

A

stitching together monomers into chain

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4
Q

what has an influence on the properties of polymers

A

specific type of chain and technique of polymerization

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5
Q

what are the two types of polymerization

A
  • addition
  • condensation
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6
Q

what is an addition polymerization

A

monomers combined together in a line or network, with no by-products
- can be of one or more monomer in a wide variety of configurations
- polymers with two monomer species are called ‘copolymers’

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7
Q

what do you call a polymer with two monomer species

A

copolymers

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8
Q

what is condensation polymerization

A

a chemical reaction that stitches together the polymer chain and produces by-products

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9
Q

in addition polymerization what are the two types

A
  • homogeneous type A+A….
  • copolymer trype A+B+A+B
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10
Q

where does most macroscopic strength come from

A
  • strong covalent bonds
  • van der waals forces will attract adjacent chains together but less strength than covalent
  • stronger polymers have higher degree of cross-linking between polymer chains
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11
Q

The more possible sites for chains to attach on a monomer, the more….

A
  • more chances for cross linking
  • moving to a 2D or 3D structure instead of 1D
  • the stronger it will be
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12
Q

consequence of having larger and longer molecule chains

A

more possibilites for cross linking
- higher utlimate strength (more resisting links)
- higher melting point ( more links to expend energy and break down)
- less flexibility (less chance of plastic deformation)

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13
Q

what other than chain molecules can be added to change polymer properties

A
  • plasticizers: improve plastic behavior
  • fillers: inert material used to pad bulk volume and lower casts
  • reinforcers: improve mechanical properties
  • stabilizers: improve durability resistance of material
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14
Q

what are the three categories of polymers based on differences in material properties and production

A
  • thermoplastic
  • thermoset
  • elastomer
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15
Q

what consists of a thermoplastic polymer

A
  • polymer which displays plastic behavior at a high temperature (above glass transition temperature Tg and below melting point)
  • solidifies into solid material upon cooling below Tg
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16
Q

what are the characteristics of thermoplastic polymer

A
  • recyclable: reversible process
  • can be reshaped and reformed if brought above Tg range
  • polymer chains plastically deform past each other
  • anisotropic properties depending on orientation of long molecules
17
Q

what type of polymer falls into thermosets

A
  • polymers usually formed by condensation polymerization which produces an irreversible final product
18
Q

characteristics of thermosets

A
  • more 2D and 3D covalent bonds as compared to the thermoplastic type
  • net result is a more isotropic and strong material
  • doesn’t become plastic upon reheating
  • stiffness lowers upon heating
  • may be susceptible to UV radiation
19
Q

what type of polymer falls into elastomers

A
  • they possess linear polymer structures with some cross-linking between molecules, thus helping to provide the unique elastic properties
20
Q

what type of elastic moduli do elastomers possess, and how does that benefit them

A

a very low elastic moduli
- giving them the ability to elastically deform under relatively low loads without permanently changing in shape

21
Q

what causes a risk to the durability of a polymer

A
  • susceptible to UV radiation damage
  • heating
22
Q

why does UV radiation damage affect polymers

A
  • reaction between photons and polymer may break links or form new by-products
  • results in weaker and more brittle material
  • sunlight can be detrimental
23
Q

why does heating damage polymers?

A
  • causing brittleness in thermosets and plastic behaviour in elastomers
  • may off-gas toxic fumes
24
Q

the microstructure composition of an FRP

A
  • matrix
  • interface
  • fibres
  • additives
25
Q

what is the matrix

A

holds fibres in place and protects them from the environment

26
Q

what is the interface

A

area in matrix that transfers stress between matrix and fibres

27
Q

what do the fibres do

A

provide primary strength and stiffness resistances
- only capable of resisting along fibre direction due to high aspect ratio

28
Q

what do additives do

A

admixtures to provide durability, improve material characteristics

29
Q

comment on the variety of macaroscopic configurations of FRP composites

A
  • enormous
  • unidirectional sheets, 2 ( or more) ply sheets
30
Q

what type of fibres are used in FRP

A
  • can use fibres made from glass, aramid, carbon fibre
  • need small diameter, long strings for optimal behavior
31
Q

name some types of fabrication methods fro RCP

A
  • pulltrusion
  • injection molding
  • hand lay up
  • spray up
  • filament winding
  • etc
32
Q

what are the three characteristics that high performance fibres must possess

A
  1. Small Diameter (increases tensile strength)
  2. high aspect ratio (increases surface area/volume ratio)
  3. high flexibility (allows for easy fabrication of FRPs)
33
Q

why are thermoplastics usually recyclable while thermosets are not recyclable?

A
  • in thermoplastics, usually manufactured via addition polymerization, the polymer can be torn apart into individual monomers
  • in thermosets, usually manufactured via condensation poly., recycling is not posisble bc there is no economic or efficient way of getting the by-product(ex: water molecule) back into the individual components
34
Q

why do fibres gain strength when the fibre diameter decreases?

A
  • due to size effect (larger volume, lower strength, since higher probability of critical flaw)
  • fibres work in other direction: making fibres as small as possible and reducing volume = increases strength
  • manufacturing process eliminates critical flaws in the longitudinal direction or else there wouldnt be continuous fibres
  • perpendicular direction to the length of the fibres, the fibres get down to a size relative to the size of flaws, so no flaw in fibres
  • makes overall strength much higher
35
Q

why do FRPs have good impact resistance?

A
  • in an impact, there is damage
  • damage uses energy
  • bc many fibres in FRP, if one breaks, energy is used up
  • with many fibres breaking, lots of energy is used up
  • reduces kinetic enregy of the impacting object, until it is zero
  • but, once impact damage is done, impact resistance of an FRP is decreased
  • in extreme cases, the FRP has to be replaced bc fibres can only break once
36
Q

how is it possible to increase the surface bond of pultruded FRP rebar with concrete? why is it difficult to take the same approach as done in steel rebar?

A
  • in steel rebar, there are raised ridges. In FRP, using pultrusion, the specimen must be cast with a constant cross-section, which makes it not possible to create ridges on the bar
  • but, during the pultrusion process, the epoxy is still not cured, once can add sand to the surface of the bar to increase surface area and thus bond with concrete, and this also increases mechanical interlock
37
Q

why durability issues might be an issue if FRP is used on the exterior of a structure? what other issues might be a concern if FRP is used on the interior?

A

exterior: might have strength issues due to denaturing of polymer covalent bonds due to UV radiation

interior: in case of a fire, toxic fumes would be hazardous to occupants health

38
Q
A

202 FINAL (7 decks)

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