Polymers Flashcards
Lecture 16
What are the moduli of polymers and elastomers?
Generally low moduli materials ~ E < 10 GPa
also low density
What are the common characteristics of polymers?
- lightweight
- corrosion resistant
- low strength
- low stiffness
- unsuitable for high temperatures
- CHEAP!
What are the characteristics of engineering polymers?
Improved strength - high specific strength
Greater temperature performance
What are some desirable properties of polymers in structures?
- low density -> lightweight
- easy shaping
- good adhesions -> not always
- goof thermal and electrical insulation
What are some low-duty structural components of polymers in structures?
- surfaces
- membranes (moisture control)
- insulation foams
- adhesives (bonding)
- pipes
- grouts (gap filling)
- geotextile (used for soil support)
What is the definition of polymer?
a class of MACROMOLECULES consisting of a set of regularly REPEATED CHEMICAL UNITS
- mers -> of the same type
- or possibly of a very limited number of different types to form a chain molecule
What are polymers made of?
Long chains
- typically molar mass x10^4 - x10^6 gmol^-1
- c.f. the molar mass of NaCL 58.4 gmol^-1; Fe 55.845 gmol^-1
What are polymer types and their uses?
- natural - e.g. wood, cotton, wood, etc
- semi-synthetic - e.g. leather, rubber, cellophane etc
-> Natural materials with additional - synthetic - starting materials:
-> coal - carbo-chemistry
-> oil and gas - petrochemistry - thermoplastics
- thermosetting polymers
- elastomers
What kind of raw materials are used in polymers?
- crude oil - a mixture of hydrocarbons
- natural gas
- primarily methane (~75 - 95%) - other hydrocarbons and gases also present
- separation and purification processes
- eventually produce monomer units
- these are combined in polymerisation reactions
-> addition polymerisation
-> condensation polymerisation
What are the two ways you can use to measure how big polymers are?
- (relative) molecular weight (MW)
- degree of polymerisation (number of monomers)
Calculate the degree of polymerisation of polyethylene with a MW of 182,000 gmol^-1 ?
- one (mono)mer = C2H4
- monomer MW = (2 x 12) + ( 4 x 1) = 28 gmol^-1
Degree of polymerisation = polymer MW/ monomer MW
= 182000/28 = 6500
What is the structure of a polymer?
polymers can contain
- crystalline regions - chains are aligned
- amorphous regions - chains are not aligned
MORE CRYSTALLINE
- better mechanical properties
What are some additives you can add to polymers?
used to modify properties to improve serviceability
- stabilisers
-> UV and oxidation can lead to polymer degradation
-> Stabilizers help counteract such processes to help expand their lifetime
-> complex range of materials
- fillers
- plasticisers -> make it softer
- colourants
- flame retardants
What can fillers improve?
Tensile and compressive strengths
Abrasion resistance
Toughness
Dimensional stability
What do fillers include?
wood flour
silica flour
sand
glass
clay
talc
limestone
What can fillers do?
fillers can also reduce costs because using waste materials
What can plasticisers improve?
strength and ductility
What can plasticisers reduce?
hardness and stiffness
What is a plasticiser?
Small molecules that sit between the larger polymer chains
- increasing interchain distance
- reducing secondary intermolecular bonding
- large additions result in a liquid
What are colourants?
Dyes - dissolve into the polymer
Pigments - remain as a separate phase
useful for using colour for information
What are flame retardants?
Most polymers are flammable in their pure form
- essentially are fuels because made from oil and gas
- Major exceptions contain significant amounts of CI or F (e.g. PVC/PTFE)
FLAME RETARDANTS
- interfere with combustion in the gas phase
- initiate reactions that cool the combustion region
What is the stress-strain behaviour of polymers?
What are the types of macromolecular chains?
What are the different addition polymerisation?
