Polymers Flashcards
Name the three main secondary bonds.
Van Der Waals Force
Dipole-dipole forces
Hydrogen bonds
What are the three classes of polymers?
Thermoplastics
Thermosets
Elastomers/Rubbers
What bonding structure do Thermoplastics have?
Amorphous or semi-crystalline
What boding structure do Thermosets have?
Amorphous
What bonding structure do elastomers and rubbers have?
Amorphous
What is the main type of bond in a thermoplastic?
Secondary bonds such as hydrogen bonds, dipole-dipole forces or Van der Waals forces.
What is the main type of bond in thermosets and elastomers?
Chemical bonds such as a covalent bond. Secondary bonds are still present but their effect on the material is negligible.
What are the effects of increased crystallinity in polymers?
Increased stiffness
Increased hardness
Increased density
Lower ductility
Higher resistance to heat and solvents
What is the maximum level of crystallinity in a polymer?
95% Crystallinity
What thermal behaviour do amorphous polymers display?
Glass transition temperature (Tg)
How would an amorphous polymer behave below Tg?
The polymer remains hard and brittle
Chain motion is limited to short scale vibrations
How would an amorphous polymer behave below above Tg?
Chain movement gradually increases
The polymer softens however this can be limited dependant on the extent to which the polymer is cross linked.
The polymer gets tougher.
What thermal behaviour do crystalline polymers display?
Melting temperature (Tm)
Below Tm how would a crystalline polymer behave?
Chain packing is regular
The polymer is rigid and dense
Above Tm how would a crystalline polymer behave?
Crystal structure breaks down into amorphous “open” liquid structure. (It fucking melts)
The density reduces largely.
The polymer no longer has an ability to carry loads.
