1. EBP 200/3 POLYMER RHEOLOGY DR AZURA A.RASHID Room 2.19 School of Materials And Mineral Resources Engineering, Universiti Sains Malaysia, 14300 Nibong Tebal, P. Pinang Malaysia

2. Flow process in manufacturing polymer products can be represented as follows: Introduction Processing Activities: Rheology & equipment design studies Final Products Activities: Product design & End properties investigation Raw Materials Activities: Molecular and compositional modification & enhancement

3. Rheology = Science of deformation and flow of matter A very high performance polymer granules or pellets (raw materials) is useless if it cannot be transformed into a practically useable products Transformation means deformation and flow of polymer raw materials into a specified and required shapes In melt processing of thermoplastics polymers  rheological studies give initial information on how these polymer behave during actual polymer processing.  e.g: effect of temperature, pressure & geometry on polymer flow behaviour in processes such as extrusion & injection moulding Introduction

4. Rheology can be defined as the science of the flow and deformation of materials. For many simple fluids the study of rheology involves the measurement of viscosity  the viscosity depends primarily on temperature and hydrostatic pressure However the rheology of polymers is much more complex because the fluid shown non ideal behaviour Polymer has complex shear viscosity behaviour and also show elastic properties  normal stress phenomena and prominent tensile viscosities

5. All these rheological properties depend upon the rate of shear, the molecular weight, structure of polymers the concentration of additives and temperature. In most cases, flow is involved in the processing and fabrication of the plastics. Flow behaviour is important in injection molding, compression moulding, blow moulding, calendering cold forming and spinning of fibres It is also importance in the formulation of polymeric materials in preparing for fabrication process especially extrusion and mill rolling

6. Rheology involved in many aspects of polymer science for example polymers which are made from emulsions of monomers in stirred reaction vessels etc The rheology of polymer powder or pallet is importance in first section melts or liquids. Rheological behaviour influenced the mechanical behaviour of a finished project as the molecular orientation influenced the mechanical properties of moulded object films and fibres The degree of orientations is determined by rheological behaviour of the polymer and nature of the flow in fabrication process

7. Materials that deformed under the pressure deformation will shown a yield points and will have mechanical response In molecular aspect  Deformation will interfere in the conformation of polymer molecules  When forced or stress being applied either uniaxial stress or shear stress  chain molecule will move relatively and get a new conformation.  Brownian movements will gives the equilibrium (the conditions where there is no force), So the average deformation that has been produced depends on  the competitive effects in between the two effects above

8. Flow is the continuous deformation under an influenced of constant force  any particle of materials will not back to the original positions after the force of deformation been released All the body in the nature will flow if given a period of time and appropriate temperature even with very low applied force Ability to flow for a molten materials depends on the molecular chain mobility that hold molecule together.  Low mobility with high degree of chain entanglement  will influenced the ability to flow and the process ability of polymeric materials Flow

9. Example of flow Plate of area A Fluids Direction of flow Force =F Velocity -v Stationary Plate

10. Mechanical properties that shown by any polymer products is the most importance factors considered by manufactured and user. In actual conditions  the optimum mechanical properties is not importance if the product could not be process as faster, simple or easier and relatively low cost Flow involved is rheological studies that also involved:  types and degree of orientation  Flow properties in actual processing Importance of rheology

11. The importance of rheological studies are: a. Can identify the behaviour of flow during flowing together with factors that influenced the flow of polymers. b. Can predict the real complex processing condition  through easier component and predict the final properties of polymer c. Can relate the qualitative and quantitative parameters such as output and used of materials properties

12. d. Can choose the suitable polymer for specific processing conditions and services – To produce a product with optimum processing properties.  importance in real processing to produce maximum output with minimum input e. In some cases, factors as a.Molecular structure, b.morphology, c.Polymer melt, d.Blends and polymer modification  Can be studies by relationship between the rheological properties and materials structure.

13. A stable, Simple and ideal flow  where the flow in between two parallel plate with cross section area A is separated by a distance h. When a shear force F is applied at upper plate  it will equivalent moves and the force F applied is proportional with the viscosity  of the flow Newtonion flow

14. Starting position of the fluid particles Force = F Velocity = V Direction of flow Velocity Profile Stationary plate

15. Shear Rate Newtonian Fluid Shear stressShear stress

16. The importance of Kinematics aspects for stable shear flow  every elements of materials will have the same and constant deformation According to the Newtonian flow, shear stress is proportional with the shear rate Where  is constant viscosity  a constant value that not dependence with applied shear rate

17. When relate the relationship of shear stress  versus shear rate  and get not a straight line curve  two types of viscosity at any value of shear rate can be obtained: 1. Apparent viscosity  from slope taken from a line that connect the value of shear stress with shear rate at any point of shear rate from the origin 2. Constant viscosity  from slope taken from a line at particular value of shear rate for materials that showed non n ewtonian behaviour

18. Most of the polymer systems not follow Newtonian law. Non Newtonian flow can be classified into 3 parts as: 1. Non time dependence flow, 1. Time dependence flow 1. Viscoelastic flow Non- newtonian flow

19. Materials will demonstrate behaviour: 1. At low strain rate – behave according to the Newtonian relationship 2. Totally dependent with time. 3. Stress being function of strain rate 4. Stress independent of strain  = viscosity de/dt = strain rate Behaviour of viscous material

20. Shear rate for non time dependence flow can represents mathematically the shear stress as : In rheological studies there are 4 types of flow that not dependence with time 1. Bingham body flow, 2. Pseudoplastic flow, 3. Newtonian flow 4. Dilatan flow Non time dependence flow

21. Shear rate Vs flow for non time dependence flow

22. Bingham Body Pseudoplastic fluid Newtonian fluid Dilatan fluid Shear Rate Shear StressShear Stress

23. Body Bingham is elastic solid  ideal materials that their structure will collapse when the stress applied greater than their yield stress  y, Shear stress for body Bingham are proportional with shear rate given as: where  plastic viscosity that reach a infinity when shear rate almost zero (   0) and reach a value  when shear rate approach infinity value (   no limits). Materials that represents model Bingham  including emulsion and suspension with high concentration such as paint, printing ink, clay slurry and plastic emulsion. Body Bingham flow

24. Viscosity of pseudoplastic flow decreased with the increased in shear rate  it showed the shear thinning behaviour During real processing that involved a higher range of shear rate  no problems of flowing for pseudoplastic materials At suppressed condition  molecule has higher entanglement and will have random conformation or orientation Under the applications of shear force  uncoiled of molecule chain occur and the orientation of molecule increased even though the occurrence of Brownian movement will try to gives the original conformation (the condition where no force occurred) At very high shear rate  the almost Newtonian behaviour was observed for materials with pseudoplastic flows Pseudoplastic flow

25. Newtonian & Pseudoplastic Flow Viscosity Newtonian Shear Thinning Shear Rate

26. Viscosity value for Dilatan flow increased with increasing shear rate  its enable the polymer to be process at high shear rate due to the ability to flow polymer is low. Dilatan behaviour normally shown by polymer with high suspension such as PVC and materials with non uniform particles shape   materials that difficult to be compressed under high shear rate. Dilatan behaviour is hardly shown for molten polymer except under a special condition  where the melt crystallization occurred during flow. Dilatan Flow

27. Flow properties that dependence with time are dependence on: 1. Types of shear flow, 2. Flow history 3. Moulding time. This types of flow showed a reversible conditions Time dependence flow

28. This flow are shown by materials that has the dominant viscous behaviour but has the elastic recovery after the deformation. Viscoelastic flow has a properties in between the solid and liquid behaviour. ** Please refer the viscoelastic behaviour (viscoelasticity) Viscoelastic Flow

29. Polymer is called viscoelastic because: Showing both behaviour elastic & viscous behaviour Instantaneously elastic strain followed by viscous time dependent strain Viscoelastic behaviour

30. Understanding the influenced of temperature with the melt viscosity is importance in:  Polymer processing  To estimate the thermal resistance of particular materials Big variation in viscosity with range of temperature  represent the materials need a higher activation energy polymer molten viscosity that dependence on temperature have a higher temperature from glass transition temperature T g or their melting temperature T m. Influenced of temperature on viscosity

31. The Andrade or Arrhenius equations can relate the activation energy during chain mobility as Where  = viscosity of polymer melt AE a = activation energy R = Universal gas constant T = Temperature (°K) A = Arrhenius constant

32. When taking the logarithm plot from log  against  log (1/T)  will given one straight line where the slope is the same  activation energy according to this equations:  If viscosity at various temperature taken at constant shear stress  activation energy is supposed to be constant and not dependence on shear stress where it been taken.  If the viscosity at constant temperature at various shear rate  activation energy dependence on shear rate  example activation energy decreased with increasing shear rate  However the flow according to Arrhenius equations  activation energy almost not dependence on temperature.

33. A very popular types of instruments to measure viscosity is capillary rheometer or viscometer It function in conditions of load and forced is constant or at constant volume rate In conditions of constant shear stress  measurement of flow rate was taken based on the speed of piston Pressure at the outer layer of die  is measured using the pressure transducer Instruments for rheology measurements

34. Instruments for viscosity measurements Atmosphere pressure Pressure Transducer Polymer melt Barrel Piston Extrudate Constant shear rate Rheometer

35. Example of flow

36. Flow phenomena: Rod climbing & extrudate swell

37. What are the importance of rheological studies in polymer processing. Discuss the non-newtonian behaviour of polymeric materials. What are the influenced of pseudoplastic flow towards polymer processing? Most polymers melt exhibit pseudoplastic characteristics under shear conditions. How these differ from those of Newtonian fluids Example of exams question