CHARACTERIZATION, ANALYSIS, AND PHYSICAL TESTING OF POLYMERS LABORATORY PRACTICAL WORKNOTE STUDENT NAME:__________________________________________________ MATRICULATION NUMBER:_______________________________________ ACADEMIC SESSION: _____________________________________________ CLASS:___________________________________________________________ DATE: ____________________________________________________________ Compiled by: Ekebafe, L.O. Oladebeye, A.O. 1 Points to remember while performing the experiment in a real laboratory: 1. Always wear laboratory coat and gloves when you are in the laboratory. When you enter the laboratory, switch on the exhaust fan and make sure that all the chemicals and reagents required for the experiment are available. If it is not available, prepare the reagents using the components for reagent preparation. 2. Make sure you do not use an unknown reagent. Do not assume that all plastic containers contain water. 3. Cover-shoe or, preferably, safety boots should be put on to ensure safety of the feet. 4. Make sure to clean all your working apparatus with chromic acid and distilled water and ensure that all the apparatus are free from water droplets while performing the experiment. 5. Make sure to calibrate the electronic weighing balance before taking the measurements. 6. Ensure that the stop watch and hot air gun are working properly. 7. Clean all glass wares with soap and distilled water. Once the experiment is completed, recap the reagent bottles. Switch off the light, and exhaust fan before leaving the laboratory. 8. Discard the used gloves in a waste bin. 2 EXPERIMENT 1 Determination of Molecular Weight by Dilute Solution Viscometry Intrinsic Viscosity Measurements Practical Date:_________________________________________________ Aim/Objectives 1. Determine the absolute viscosity of Polymer solutions of different concentrations 2. Determine the viscosity average molecular weight of a polymer. Theory One of the most important parameters in molecular characterization is the determination of the average molecular weight of the polymer chain. One of the simplest and most widely used methods for molecular weight determination is dilute solution capillary viscometry. In this experiment, the molecular weight of a commercial polystyrene sample of industrial grade polymers will be determined. The background information for this laboratory session can be found in the references given below. Viscosity is an internal property of a fluid that offers resistance to flow. It is due to the internal friction of molecules mainly depends on the nature & temperature of the liquid. Many methods are available for measuring viscosity of polymer solution. The Ostwald method is a simple method for the measurement of viscosity, in which viscosity of liquid is measured by comparing the viscosity of an unknown liquid with that of liquid whose viscosity is known. In this method viscosity of liquid is measured by comparing the flow times of two liquids of equal volumes using same viscometer. Consider two liquids are passing through a capillary of same viscometer. Then the coefficient of viscosity of liquid (η2) is given by equation: Here, t1 and t2 are the time of flow of the liquids and ρ1 and ρ2 are the respective densities. And η1 is the coefficient of viscosity of water. For a given liquid η has a specific value at the same temperature. Various mixtures of two non-interacting liquids viscosities will lie among the viscosities of those pure components. The time of flow of liquid depends on the viscosity and composition. In this method the flow times are measured for different known compositions and a graph is plot for time of flow and compositions. The unknown composition can be determined by plotting a graph for the time of flow and compositions. The molecular weight of the polymer is measured by using viscometer and the molecular weight obtained by this technique is called viscosity average molecular weight. The molecular weight of the polymer solution is very high so the viscosity of polymer solution is very high compared to that of pure solvent. 3 From the Mark-Houwink equation the relationship among the molecular weight and viscosity are given below: where, [η] is the intrinsic viscosity, M is Molecular weight, K and α are constants for a particular polymer solvent system. If we know the K and α values for a given polymer solution the intrinsic viscosity and molecular weight can be calculate using the above equation. Materials Required 1. Safety glasses for all group members at all times. 2. Ubbelohde viscometer 3. 5ml or 10 ml pipette and a plastic pipetter 4. Stopwatch 5. Ring stand and appropriate clamps 6. 25 ml volumetric flask 7. solvent (common PS solvents are Toluene and THF) 8. Polystyrene Sample Procedure 1. In the Polymer Handbook find the section on Viscosity-Molecular Weight Relationships and look up the Mark-Houwink-Sakurada (MHS) parameters for polystyrene in a variety of solvents. Pick a "good" solvent for PS in which to conduct the experiment. How does one determine the "goodness" of solvent from the MHS parameters? 2. Once the solvent is chosen, calculate the starting concentration for the dilute solution viscometry experiments. Experiments should be conducted at four (4) decreasing concentrations:. These should be made by the successive dilution method directly in the viscometer if possible. This typically leads to less experimental error than making four separate solutions, especially when small sample weights are involved. What is the "drawback" to this method? NOTE: Make certain to mix the diluted samples well in the viscometer and always run the new solution up through the capillary once before taking data. 3. Select Ubbelohde viscometer to do the experiment. Which viscometer are you using? What do you expect to be the difference?). The viscometer should first be rinsed thoroughly (including the capillary bore) with the solvent to be used before starting the experiment. 4. Flow Time Measurement 5. Follow the instructions below for performing a flow time measurement (a demonstration will be given). With reference to the diagram in the polymer handbook, a. Load 8 ml of solvent into tube 1 (reservoir B) using the pipette. b. Attach the pipette to the top tube 2 and cover the hole of tube 3 (sidearm) with your thumb. 4 c. With the sidearm firmly blocked, suck the solvent up into reservoirs A, C, and D (just past the upper mark). Remove the pipette from tube 2, then remove your finger from the sidearm. NOTE: You must remove the pipette BEFORE taking your finger off the sidearm! d. Measure the flow time for the solution (solvent or polymer). The flow time of interest is the time for the meniscus to pass from the upper to lower marks on the capillary. Note: The choice of Viscometer # (capillary diameter) is made by the criteria of a solvent flow time greater than 60 sec. (minimum) and preferably 100 sec. Why must the solvent flow time be kept to this low value? NOTE: Repeat the measurements until you get flow times within 0.2 - 0.5 sec. If agreement is not obtained in 3-5 measurements, you may have to clean the viscometer and start over. Many times dust or other foreign material in the capillary is the cause for erratic results. Once at least three (3) consistent flow times have been obtained, go on to the next dilution. e. Once the next dilution is done or the next solution is loaded in the viscometer allow it to equilibrate for 3-5 minutes, then run the new solution through the capillary at least two (2) times before taking your next set of readings. f. When the experiment is complete, thoroughly clean the viscometer with solvent paying particular attention to the capillary. Run the solvent flow time one more time to check for consistency with the previous measurement. (Is the solvent flow time the same as at the start of the experiment? Why not and what do you do about it?) The viscometer should be stored with tubes 1, 2, and 3 covered to prevent contamination by foreign material. Using the references provided for information, do the following for each material tested: 1) In the space provided, present a clean and neat table of your raw data, including solvent and polymer flow times, viscometer # and type, etc. 2) Calculate ηrel, ηsp, and ηinh for each concentration of each solution. 3) On the same graph, plot ηsp/c versus c and ηinh versus c. Determine [η] as the common intercept at C=0 of the best straight lines through the data (Note: Use Engineering judgment in doing the curve fit – exclude "spurious" points that are obviously not following the observed trend.) Comment on your method of determining the "best" fit of the data. Explain any differences in the intercept obtained by the two techniques. Which is more reliable or more accurate? 4) Using the value of [η] measured; calculate the molecular weight of the sample. 5) If you had to choose another solvent for polystyrene, what would it be and why? What are the MHS parameters for your alternative polymer/solvent system? HINT: You need the Polymer Handbook or equivalent on-line resource to answer this question. Discussion Questions Briefly explain, give the relationship for, or define the following: 1) Define the following viscosity terms: relative viscosity; specific viscosity; reduced viscosity; inherent viscosity; intrinsic viscosity. 2) Mark-Houwink-Sakurada (MHS) Equation. a) Explain the significance of the various terms in the equation. 5 b) Is this a "universal" equation (i.e., for any polymer/solvent system)? c) From a physical chemistry