Dynamic Mechanical Analysis INTRODUCTION PRINCIPLE The Modulus Curve Polymers vary from liquids and soft rubbers to very hard and rigid solids. Many structural factors determine the nature of the mechanical behavior of such materials. In considering structure-property relationships, polymers may be classified into one of several regimes, shown in the volumetemperature plot (Fig. 23.1). Dynamic mechanical analysis (DMA) or dynamic mechanical thermal analysis (DMTA) provides a method for determining elastic and loss moduli of polymers as a function of temperature, frequency or time, or both [1-13]. Viscoelasticity describes the time-dependent mechanical properties of polymers, which in limiting cases can behave as either elastic soUds or viscous liquids (Fig. 23.2). Knowledge of the viscoelastic behavior of polymers and its relation to molecular structure is essential in the understanding of both processing and end-use properties. DMA can be appUed to a wide range of materials using the different sample fixture configurations and deformation modes (Table 23.1) [10,11]. This procedure can be used to evaluate by comparison to known materials: (a) degree of phase separation in multicomponent systems; (b) amount type, and dispersion of filler; (c) degree of polymer crystallinity, (d) effects of certain pretreatment; and (e) stiffness of polymer composites [8,11]. Dynamic mechanical experiments yield both the elastic modulus of the material and its mechanical damping, or energy dissipation, characteristics. These properties can be determined as a function of frequency (time) and temperature. AppHcation of the time-temperature equivalence principle [1-3] yields master curves like those in Fig. 23.2. The five regions described in the curve are typical of polymer viscoelastic behavior. In the glassy region, the polymer is below its glass transition temperature, Tg, and typically has a modulus of 10^^ dynes/cm^. The transition region includes the Tg, which is taken as the point of inflection of the modulus or the maximum in the damping curve. The modulus drops by a factor of 1000 in this region. The
Dynamic Mechanical Analysis INTRODUCTION PRINCIPLE The Modulus
Curve
Polymers vary from liquids and soft rubbers to very hard and
rigid solids. Many structural factors determine the nature of the
mechanical behavior of such materials. In considering
structure-property relationships, polymers may be classified into
one of several regimes, shown in the volumetemperature plot (Fig.
23.1). Dynamic mechanical analysis (DMA) or dynamic mechanical
thermal analysis (DMTA) provides a method for determining elastic
and loss moduli of polymers as a function of temperature, frequency
or time, or both [1-13]. Viscoelasticity describes the
time-dependent mechanical properties of polymers, which in limiting
cases can behave as either elastic soUds or viscous liquids (Fig.
23.2). Knowledge of the viscoelastic behavior of polymers and its
relation to molecular structure is essential in the understanding
of both processing and end-use properties. DMA can be appUed to a
wide range of materials using the different sample fixture
configurations and deformation modes (Table 23.1) [10,11]. This
procedure can be used to evaluate by comparison to known materials:
(a) degree of phase separation in multicomponent systems; (b)
amount type, and dispersion of filler; (c) degree of polymer
crystallinity, (d) effects of certain pretreatment; and (e)
stiffness of polymer composites [8,11]. Dynamic mechanical
experiments yield both the elastic modulus of the material and its
mechanical damping, or energy dissipation, characteristics. These
properties can be determined as a function of frequency (time) and
temperature. AppHcation of the time-temperature equivalence
principle [1-3] yields master curves like those in Fig. 23.2. The
five regions described in the curve are typical of polymer
viscoelastic behavior. In the glassy region, the polymer is below
its glass transition temperature, Tg, and typically has a modulus
of 10^^ dynes/cm^. The transition region includes the Tg, which is
taken as the point of inflection of the modulus or the maximum in
the damping curve. The modulus drops by a factor of 1000 in this
region. The
