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
