model with an elastic element. When a spring is fixed at one end and a load is applied at the
other, it becomes instantaneously extended. Then, after the load is removed, it immediately
recovers its original length [2] (Fig 1). On the other hand, the dashpot complies with
Newton’s law of viscosity as a mechanical model with a viscous elememt. When a load is
applied to a dashpot, it opens gradually, strain being a function of time. Then, after the load
is removed, the dashpot remains open and recovery does not occurs [2] (Fig 2). The
mechanical model which consists of a Hookean spring and a Newtonian dashpot in parallel
is a Voigt element (Fig 3), and that in series is a Maxwell element (Fig 4) [3]. These are
simple models and the behavior of polymers can be explained by combining these models