This document discusses rheology methods for analyzing the mechanical properties of materials. It begins with an introduction to rheology, defining it as the study of flow and deformation of materials. Important variables in rheological analysis are then outlined, including shear stress, shear rate, strain, and viscosity. Three main methods of rheological measurement are described: melt index instruments, rotational rheometers, and capillary rheometers. Rotational rheometers measure viscosity using different plate and cylinder geometries under varying shear rates and temperatures. Capillary rheometers examine processing behavior by forcing material through a die. The document concludes that rheology is a useful characterization tool for understanding structure-property relationships in materials development.

1. RHEOLOGY METHODS
By
Asabuwa N. F.

2. Presentation Outline:
Introduction
What is rheology?
Importance of rheology Studies
Functioning principle of rheology
Important variables in rheology methods
 Rheometry
Measurement of rheological properties
Melt Index instrument
Rotational rheometers
Capillary rheometers
 Conclusions

3. Introduction
The term 'Rheology' was invented by Professor Bingham
Lafayette College in 1920s,and was inspired by a Greek
quotation “panta rei” meaning “everything flows”.
This method of material analysis was first used by Professor
Bingham and Reiner on the 29th of April 1929 when the
American Society of Rheology was founded in Columbus,
Ohio State, USA.
Rheology mostly analyses mechanical properties which
include physical properties of liquids and solids by describing
the strain and flow behavior.

4. What is Rheology?
Rheology is the study of flow and deformation of
materials and how the flow is affected by stresses,
strains and time.
It applies to substances which have a complex
structure such as polymers, cheese, emulsion and other
biological materials.

5. Rheology (particularly in the study of
the viscous flow of polymers) is very
important because it gives a
relationship between the properties,
structure and processing of the
materials.
Rheology helps describe the
mechanical behavior of materials as
a function of stresses (shear rate),
strain , temperature and pressure in
order to develop materials with the
correct processing behavior based on
their viscosity, elasticity and time.
These parameters can be calculated
using a dynamic mechanical testing
method at melt temperatures.
Importance of Rheology Studies

6. Functioning Principle of Rheological analyses
This method is mostly
based on the analyses of
the viscous(Newtonian
Fluids) and viscoelastic
(Non Newtonian Fluids)
behavior of material at
their melt temperature.
This method is based on
the flow and deformation
of matter in all the three
states (solid, liquid and
gas).

7. Important variables in Rheology methods
In order to measure a material’s rheology, five criteria must be met:
geometric boundary conditions, stress, strain, strain rate and mode of
deformation (shear rate) .
In regards to this we have some important variables during analysis;
• shear stress =
Force (F)
Area (A)
=
Newton(N)
m²
= Pa
• shear rate =
Velocity(V)
Distance(h)
=
m/s
m
= s−1
• Strain =
Change in distance(ΔX)
Distance(h)
=
m
m
= Dimensionless
• Viscosity =
Shear stress
Shear rate
=
Pa
s−1 = Pas

8. Rheology (Viscosity models)
- ideal fluid
the viscosity is zero, this is used for the
analysis of potential flow
problems such as found in aerodynamics
- Newtonian fluid
a good viscosity model for gases and
simple liquids such as water
- Non Newtonian fluid
the viscosity of the fluid changes with
shear rate. For some fluids, it
increases with shear rate (dilatant fluids)
while for others it decreases
with shear rate (pseudoplastic behavior).
This pseudoplastic (or shear thinning)
behavior is what we observe for polymers.
Factors affecting viscosity
- pressure
- molecular weight
- temperature
- shear rate
- Time

9. Rheometry
This is the use of rheometers or
viscometers to determine the
rheological properties of materials
with the measured values based on
force, length and time.
Rheometers are devices use to
determine both the viscous and
viscoelastic properties of materials
depending on the force exerted in
both the rotational and oscillatory
test.
While on the other hand
viscometers are devices use to
determine the viscosity depending
on the rotation, temperature and
time.

10. Measurement of Rheological properties
Rheological properties
can be measured using
either
1. Melt Flow Indexer:
Actually this instrument is
mostly use for quality
control. It does not
compute a material
property. Its mainly to
compare the relative flow
behavior of
different materials based
on the viscosity.

11. 2. Rotational Rheometers
In a rotational rheometer the sample is sheared between
two plates or a cone and plate geometry. The viscosity is calculated as the ratio of the applied
stress and the applied deformation rate (rotation speed). This instrument in the case of polymers
is use to extract information about the average molecular weight and molecular weight
distribution via measurement of the viscoelastic properties and thus determine how this affects
the processing characteristics of the material.
Modern rotational rheometers are capable of many tests for a full characterization of the material
which involves;
• Flow Rates
• Creep Tests
• Stress Relaxation
• Small amplitude sinusoidal Oscillatory Testing

12. Types of Rotational rheometers
(a) concentric cylinder rheometer consist of an inner rotating
cylinder with a stationary outer cylinder
(b) cone and plate rheometer consist of a flat plate and a low
angle cone rotating against the flat plate.
(c) parallel plate rheometers consist of two disk with an
adjustable gap for holding the sample.
(d) Dual slit plate rheometer consist of two plate with one
sliding over the other

13. (e) Van Rheometers
Provides a useful method for
analyzing rheologically complex
materials. It is mainly use to measure
the yield stress and examine the
structural characteristics of a
dispersion or suspension.
Advantages:
1. The wall slip is avoided
2. There is less disturbance of the
sample structure compared to the
other rheometers
3. Can be also use for larger particle
size samples.

14. 3. Capillary Rheometers
Capillary rheometers are mostly used to
examine processing behavior, rather than
just determining the rheological parameters.
In a capillary rheometer the material is
forced through a slit or round die. From the
pressure drop and the volume flow rate, a
steady state viscosity as a function of the
applied rate (piston speed) or stress (applied
pressure) is measured.
Advantages:
(1) Can operate at high shear rates
(2) May be closer to real processing
situation than a rotational rheometer
Disadvantages:
(1) Shear rate is not uniform
(2) Wall slip
(3) Melt fracture
(4) Difficult to clean
In addition we also have gravity driven
capillary rheometers also called viscometers
but mostly function for viscous Newtonian
fluids.

15. Conclusion
Rheology is very sensitive to small changes of the material’s
structure therefore its an ideal for characterization with the
rheology structure relationship being the key to the development
of new materials. Thus rheology is one of the most suitable tool
for process and quality control.
Notwithstanding rheology is a standard in most material
industries (e.g polymer Industry) to characterize materials with
the goal to develop
new and better materials with the desired processing and end-use
properties.

16. Teşekkürler