113
4
This equation has additional features and is quite successful in fitting experimental data by choice into its four parameters.
4.7.3 Elastic Behaviour
The study of the elasticity of filled polymer melts has not received as
much attention as steady shear viscosity, possibly due to experimental difficulties in measurements. For unfilled polymers, the first
normal stress difference, N 1 , extrudate swell, and a capillary flow
entrance pressure drop are the common means of measuring elasticity. In steady shear experiments, N 1 is normally used as a measure
of elasticity and is plotted as a function of shear stress. The elasticity
of filled systems depends on various factors (such as filler size,
shape, and concentrations). It has been found that near isotropic
fillers like TiO 2 , CaCO 3 , carbon black, and glass beads show a
decrease in elasticity when compared with the unfilled polymer and
particulate size. However, isotropic fillers also showed that N 1
increases above that of the unfilled system when fibres are used as
fillers. This is possibly due to hydrodynamic particle effect resulting
from strong orientations in the direction of flow. For isometric fillers, the normal component of stress is zero, while the shear component has a finite value, hence lower elasticity. However, in the case
of anisometric fillers (e.g. fibres), the normal stresses are higher,
leading to higher elasticity.
To Be Remembered
1. The study of flow and/or deformation of any material (fluid/
solid) is called rheology.
2. Reynolds numbers <2100 signify laminar flow. The Reynolds
number for liquid resins and molten polymers is <100.
3. In the Weissenberg effect, a non-Newtonian fluid climbs up
the stirrer rod when it is stirred.
4. Dynamic viscosity or the coefficient of absolute viscosity is
a measure of the internal resistance offered to the fluid.
5. Planar Couette flow is the laminar flow in the space
between two parallel plates where one is moving relative to
the other.
6. Demoulding at high temperatures may cause warpages in
composite products.
7. Creep is the permanent deformation at a constant stress.
8. Loss angle of loss tangent is the ratio of the loss modulus
(G″) and the storage modulus (G′).
9. Dispersion is a process where matter is divided into the
smallest possible size and mixed in another substance.
Whereas in distribution, matter is divided into a regular size
and mixed in another substance.
10. Thermosetting matrices in solid form are called novolacs.
Novolacs initially melt like thermoplastics with the
application of heat and then solidify into a polymeric
cross-linked network structure of thermosets.
4.7 · Rheological Measurement
4
This equation has additional features and is quite successful in fitting experimental data by choice into its four parameters.
4.7.3 Elastic Behaviour
The study of the elasticity of filled polymer melts has not received as
much attention as steady shear viscosity, possibly due to experimental difficulties in measurements. For unfilled polymers, the first
normal stress difference, N 1 , extrudate swell, and a capillary flow
entrance pressure drop are the common means of measuring elasticity. In steady shear experiments, N 1 is normally used as a measure
of elasticity and is plotted as a function of shear stress. The elasticity
of filled systems depends on various factors (such as filler size,
shape, and concentrations). It has been found that near isotropic
fillers like TiO 2 , CaCO 3 , carbon black, and glass beads show a
decrease in elasticity when compared with the unfilled polymer and
particulate size. However, isotropic fillers also showed that N 1
increases above that of the unfilled system when fibres are used as
fillers. This is possibly due to hydrodynamic particle effect resulting
from strong orientations in the direction of flow. For isometric fillers, the normal component of stress is zero, while the shear component has a finite value, hence lower elasticity. However, in the case
of anisometric fillers (e.g. fibres), the normal stresses are higher,
leading to higher elasticity.
To Be Remembered
1. The study of flow and/or deformation of any material (fluid/
solid) is called rheology.
2. Reynolds numbers <2100 signify laminar flow. The Reynolds
number for liquid resins and molten polymers is <100.
3. In the Weissenberg effect, a non-Newtonian fluid climbs up
the stirrer rod when it is stirred.
4. Dynamic viscosity or the coefficient of absolute viscosity is
a measure of the internal resistance offered to the fluid.
5. Planar Couette flow is the laminar flow in the space
between two parallel plates where one is moving relative to
the other.
6. Demoulding at high temperatures may cause warpages in
composite products.
7. Creep is the permanent deformation at a constant stress.
8. Loss angle of loss tangent is the ratio of the loss modulus
(G″) and the storage modulus (G′).
9. Dispersion is a process where matter is divided into the
smallest possible size and mixed in another substance.
Whereas in distribution, matter is divided into a regular size
and mixed in another substance.
10. Thermosetting matrices in solid form are called novolacs.
Novolacs initially melt like thermoplastics with the
application of heat and then solidify into a polymeric
cross-linked network structure of thermosets.
4.7 · Rheological Measurement