Rheometer

1. Introduction to polymer science & engineering(IPSE ) Lab Presented to: Sir Sajid Naseem

2. Rheology& R heometers

3. Scientists are still confused that how to define rheology R heology Rheology=study of deformation and flow

4. What is rheology to scientists? Rheology is Yield stresses Viscoelastic effects Memory effects Shear thickening and shear thinning

5. Deformation is the relative displacement of points of a body. It can be divided into two types: flow and elasticity. Flow is irreversible deformation; when the stress is removed, the material does not revert to its original form. This means that work is converted to heat. Elasticity is reversible deformation; the deformed body recovers its original shape, and the applied work is largely recoverable. Viscoelastic materials show both flow and elasticity. Rheological measurements

6. Flows are of following main types Steady simple shear flow Unsteady simple shear flow Extensional flow Flow classification

7. Shear flow is a flow which occurs when the fluid is placed between the two plates and the two plates move at different velocities The viscosity function η ,the primary and secondary normal stress coefficients ψ 1 and ψ 2 respectively are the three viscometric functions which completely determine the state of stress in any rheologically steady shear flow. Steady simple shear flow

8. Unsteady simple shear flow occurs when the stresses are time dependent Small amplitude oscillatory flow, stress growth, stress relaxation, creep and constrained flow are some examples of such flows Unsteady simple shear flow

9. There is no shear flow in this type. The volume of the fluid remains constant in this type of flow It occurs when the material is longitudinally stretched as for example in fiber spinning Extensional Flow

10. The viscoelastic nature of the polymers whether filled or unfilled bring them under the category called the non newtonian fluids Newtonian fluids as we know are the fluids which obey the newton’s law of viscosity The simplest example of newtonian fluid is water F low behaviour

11. At low shear rate range the unfilled polymer behave as Newtonian fluids As shear rate increases the viscosity begins to decrease showing the pseudo plastic behavior.Under normal conditions the high shear rate regions are neglected and the curve of unfilled polymers become similar to the filled polymers Models for the Shear viscosity

12. Polymer Processing Polymers are used in the construction and a large number of other applications so these are now indispensable In most of the cases the melt processing is been carried out but there are many examples in which processing of solution is also taking place such as in the formation of films and fiber of heat sensitive polymers Polymer applications

13. Rheology of paints

14. Capillary rheometer

15. Calculation of shear stress Calculation of shear rate Calculation of power law parameters Calculation of viscosity Correction of results or baggley correction. Calculations

16. Dilute polymer solution Concentrated polymer solution Polymer solution

17. Viscosity of dilute polymer solution G lass capillary tube viscometer

18. Viscotek relative viscometer

19. Not a viscosity Unit:dl/g Inverse of molecular density Intrinsic viscosity

20. Applications: Fiber spinning Film casting Polymer manufacturing process Methods: Capillary viscometer Extrusion rheometer Rotational viscometer Viscosity of concentrated polymer solution

21. Rheological Measurements Viscometers are used to measure rheological properties Viscometer is defined as instruments used to measure viscosity They differ on the basis of geometry and shear rates There are three main types Capillary Viscometer Rotational Viscometer Moving Body Viscometer

22. Choice of a Viscometer There are number of criteria to be kept in mind; Nature of material to be tested Material’s viscosity Materials elasticity The dependence of viscosity on temperature The degree of accuracy required

23. Capillary Viscometer It is the most oldest and popular way follows Hagen_poiseulle equation i.e. η= π r^4pt/8VL If we are assuming laminar flow and pressure is constant then equation becomes ν = η/ρ They are useful for measuring precise viscosities of dilute polymer solutions They can’t measure absolute viscosities Always measure viscosity relative to a reference liquid

24. Design of Capillary viscometer Three main design of capillary viscometer Ostwald glass capillary viscometer , Cannon– Fenske viscometer , Ubbelohde viscometer Ostwald glass capillary viscometer, It is a u shaped tube with to bulb reservoirs The time of flow of liquid between to etched marks is taken as function of viscosity

25. Cannon– Fenske viscometer It is excellent for general use It consist of long capillary tube Both reservoirs are present on the same vertical axis Ubbelohde viscometer. It is particularly useful for measurement at different concentration It is the modified form of Ostwald viscometer

26. Orifice viscometers It is also known as cup viscometer It is typically a cup with a hole in t he bottom The time required for the liquid to flow out is measured to determine viscosity Uses It is used to measure control flow properties in the manufacturing, processing and applications of inks, dyes, paints and lubricating oils

27. Limitations It should not be used for setting product specifications It is only designed for Newtonian fluids It should not be used for thixotropic materials

28. R otational viscometer

29. What is rotational viscometer Construction Working principle Determination of viscosity Types and their brief introduction and working Moving body viscometer Types and their brief introduction CONTENTS

30. Rotational viscometer What is rotational viscometer? “ rotational viscometer is an instrument that is used to find out the viscosity of a fluid by using action of rotation ”

31. construction Rotational viscometers consist of two basic parts separated by the fluid being tested These parts may be concentric cylinders (cup and bob ) two parallel plates a low angle cone and a plate

32. WORKING PRINCIPLE

33. DETERMINATION OF VISCOSITY Viscosity can be calculated by this formula η= K(stress term/shear rate term ) K =is constant Stress term=may torque load and deflection Shear rate term=rpm ( revolution per min) ASTM followed =D2196

34. Types Concentric cylinder viscometer Plate and cone viscometer Parallel plate viscometer

35. Concentric cylinder viscometer It consists of two cylinders, one within the other (cup and bob), keeping the specimen between them Outer cylinder (cup) Inner cylinder(bob)

36. Concentric cylinder The relationship between viscosity, angular velocity, and torque for a Newtonian fluid in a concentric cylinder viscometer is given by the Margules equation M= torque Ω= relative angular velocity H= length of inner cylinder Ri= radius of inner cylinder Ro= radius of outer cylinder Error in calculations can be reduced by reducing the ratio of inner to outer radius that ratio should be equal to 1

37. Error correction In case of Newtonian fluids: Reduce Ro/Ri In case of non N ewtonian fulids: The correction appears as an addition, ho The data are plotted as M/ Ω vs h and extrapolation is made to a value of ho at M/ Ω = 0. The quantity (h + ho) is substituted for h in the various equations.

38. Likewise we can find out shear rate and torque:

39. Cone-plate viscometer In a cone–plate viscometer (Fig. 25), a low angle (≤3◦) cone rotates against a flat plate with the fluid sample between them. With careful calibration and good temperature control it can be a very effective research and Viscosity can be measured through this formula

40. Parallel plate viscometer In parallel plate viscometers the gap width is usually larger and can be varied freely The wide gap means that there is less sensitivity to temperature changes with the plate–plate instrument, the velocity, and therefore the shear rate, varies with the distance from the center of the plate. This makes viscosity data more difficult to evaluate . Rp = radius of plate H= distance between two plates

41. CHARACTERISTICS more efficient than capillary viscometer They can be used with a wide range of materials because opacity, settling, and non-Newtonian behavior do not cause difficulties. shear rates as a function of time can be measured. Therefore, they are useful Viscosities over a range of for characterizing shear thinning and time-dependent behavior .

42. Moving body viscometer In moving body viscometers, the motion of a ball, bubble, plate, needle, or rod through a material is monitored. The Stokes’ equation relating viscosity to the fall of a solid body through a liquid may be written as equation 34, where r is the radius of the sphere; ds and dl are the density of the sphere and the liquid, respectively; g is the gravitational force; and v is the. velocity of the sphere

43. Ball viscometer Ball is fall in the fluid Travel through the fluid Speed of ball in fluid determines the viscosity of fluid Used for suspension and polymer melts ASTM D3121

44. Rod viscometer The falling rod viscometer, sis based on the movement of a rod rather than a plate through the fluid. In the 1990s , the Laray falling rod viscometer became a standard test instrument in the ink industry (ASTM D4040 ), and more recent versions of the falling rod viscometers are capable of precise measurements of polymer melts and solutions

45. Needle viscometer In the falling needle viscometer (ASTM D5478 ), the moving body is a glass or stainless steel needle that falls vertically through the fluid. The viscous properties and density of the fluid are derived from the velocity of the needle. technique is useful for the characterization of polymer melts and concentrated solutions.

46. RHEOMETER A rheometer is an instrument for measuring the rheological properties: 1 . It can apply a deformation mode to the material and measure the subsequent force generated. 2 . It can apply a force mode to a material and measure the subsequent deformation. Rheometers used for determining the material functions of thermoplastic melts can be divided into two broad categories: 1. rotational type and 2. capillary type

47. ROTATIONAL VISCOMETERS For thermoplastic melt studies, rotational viscometers with either the cone-n plate or parallel-disk configuration are used . B : cone-and-plate viscometer.  C : parallel disk viscometer . The basic limitation in rotational viscometers is that they are restricted in their use only to low shear rates for unidirectional shear and low-frequency oscillations during oscillatory shear .

48. 1. CONE-N-PLATE VISCOMETER The sample, is trapped between the circular conical disk at the bottom and the circular horizontal plate at the top. The cone is connected to the drive motor which rotates the disk at various constant speeds, whereas the plate is connected to the torque-measuring device in order to evaluate the resistance of the sample to the motion. It can be used to measure shear rate, shear stress, normal stress difference, oscillatory shear .

49. 2. PARALLEL-DISK VISCOMETER The parallel-disk viscometer used for measuring the shear stress and normal stress difference of molten thermoplastics is similar in principle to the cone-n plate viscometer except that the lower cone is replaced by a smooth circular disk. This type of viscometer was initially developed for measuring the rheological properties of rubber. It can be used for polymer melts of extremely high viscosity and elasticity.

50. CAPILLARY RHEOMETERS They are used for determining the rheological properties of polymer melts. Constant Plunger Speed Circular Orifice Capillary Rheometer: It extrudes the polymer melt through a capillary with a circular orifice using a plunger at constant speeds. The major advantage of this type of capillary rheometer is that higher-shear rate levels than those attainable in rotational viscometers can be achieved.

51. Constant Plunger Speed Slit Orifice Capillary Rheometer: This rheometer has a slit orifice cross section rather than a circular one . It extrudes the polymer melt through a capillary with a slit orifice using a plunger at constant speeds

52. 3. Constant Speed Screw-Extrusion-type Capillary Rheometers : These type of capillary rheometers are capable of generating rheological data from medium-to-high shear rates. These rheometers have been used for rheological studies of polymer melts but have not become as popular as the plunger type capillary rheometers because they need a much larger quantity of polymer feed .

53. 4. Constant Pressure Circular Orifice Capillary Rheometer (Melt Flow Indexer ): This rheometer is also similar to Constant Plunger Speed Circular Orifice Capillary Rheometer except for two differences. First , the capillary used is of very short length, and second, the polymer melt is extruded by the use of dead weights (i.e., constant pressure) rather than constant plunger speed.

54. CONCLUSION: Rheological measurements are often used as an effective tool for 1 . Quality control of raw materials, manufacturing process/final product 2. Predicting material performance •Melt rheology is concerned with the description of the deformation of the material under the influence of stresses. Deformation and flow naturally exist when the thermoplastics are melted and then reformed into solid products of various shapes.

55. All polymer melts are viscoelastic materials; that is, their response to external load lies in varying extent between that of a viscous liquid and an elastic solid . A polymer melt represents a cluster of entangled, flexible strings of varying lengths. It is these entanglements that provide the resistance to deformation and, therefore, with increasing molecular weight, the melt viscosity goes up, processibility worsens although, of course, mechanical properties improve.