Materials for engineering, 3rd Edition - (Malestrom)

Organic polymeric materials 165
5.5 Rotations about bonds in a polymer chain.
The mechanical properties of polymers are therefore time and temperature
dependent and Fig. 5.6 illustrates schematically how, for a constant loading
time, the elastic modulus of a polymer will change with the temperature of
deformation normalized with respect to T g . At temperatures well below T g ,
it will be brittle-elastic, then, passing through the T g range, it becomes viscoelastic,
then rubbery and eventually viscous. As indicated in Fig. 5.6, the
modulus can change by a factor of 10 3 or more over this range.
10 4
10 3
Glassy plateau
Constant
loading
time (t)
Modulus (MPa)
10 2
10
1
10 –1
Secondary
transitions
Glass transition
Rubbery plateau
Viscous flow
10 –2
0 0.5 1.0 1.5 2.0 2.5
Normalized temperature (T/T g )
5.6 Showing for a constant loading time how the elastic modulus of a
polymer changes with temperature.