Mechanical-Properties by hedongchenchen

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									                                 EMA 4161C
                     PHYSICAL PROPERTIES OF POLYMERS
          COMPRESSION MOLDING/ MECHANICAL PROPERTIES LABORATORY


PURPOSE:

        To learn how mechanical properties are affected by orientation induced during processing

MATERIALS:

        A sheet of amorphous PET
        2L PET soda bottle (2)
        Polished steel plates
        Brass shim stock

EQUIPMENT:

        Carver hydraulic press (20 kg) w/ heated platens
        Thermocouple
        Heavy duty pliers
        Punch die for ASTM D-638 dogbone samples
        Instron 1122 Tensile tester or equivalent
        Caliper
        Personal computer
        Razor blade or scissors
        Thermal protective gloves (high temperature)
        Safety glasses

PROCEDURE:

        1. Place the brass mold on the lower polished plate which should be position in the center
           of the lower platen. Place the second plate on the top of the brass mold. Close the
           platens to within a few millimeters. This will help heat the plates uniformly.
        2. Preheat the platens to 180C. This will require at least 30 minutes.

                       BE CAREFUL THE HEAT FROM THE PLATENS AT 150C
                        CAUSES SEVERE BURNS IF CONTACTED WITH SKIN.

        3. With the thermal protective gloves on, place the PET sheet onto the center of the lower
           plate when a stable 180C is achieved.
        4. Apply approximately 1 kpsi load to the sample. Hold for 3 minutes, then increase the
            load to 10 kpsi.
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        5. Hold for 5 minutes, then release pressure. Apply the 10 kpsi load again for 10
            minutes, then release pressure. Remove the assembly from the platens and place on a
            solid steel block to assist in cooling.
        6. While waiting for the samples, carefully cut the 2L bottle length wise. Using a Carver
           press, obtain 3 dogbone samples oriented parallel to the long axis of the bottle.
        7. Next obtain 3 dogbone tensile specimens oriented perpendicular to the long axis of the
           bottle.
        8. Next obtain 3 dogbone tensile specimens from the amorphous PET sheet.
        9. Record the average thickness using the caliper. Load into the grips of the Instron and
            test at a rate of 1.0 in/min or equivalent. Be careful to label each sample as to
            orientation.
        10. Obtain three dogbone samples from the PET film. Orientation is not a factor, however
            select sample orientations that are consistent for a given sample. Test on the Instron.

ANALYSIS:

        1. Determine the Young’s modulus, tensile stress at yield, tensile stress at break, percent
           elongation at yield and percent elongation at break for each sample.
        2. Calculate the mean, standard deviation of the results.

QUESTIONS:

        1. Sketch and label the structure of LDPE, HDPE, and PET. What features are critical in
           the morphology of these materials, i.e. branching, chain rigidity or flexibility? Discuss
           how you would expect each material to respond to the processing conditions outlined
           in this experiment. Support your statements with experimental results.
        2. Compare and contrast the effect of orientation in PET. Evaluate the influence of the
           blow molding process on the properties of the bottle.
        3. List the possible sources of error with the determination of mechanical properties via
           tensile tests using dogbone samples.
        4. Discuss the different failure mechanisms of the PET samples tested and sketch the
           expected morphology of each sample.
        5. Explain why PET is used for coke bottles as opposed to LDPE, HDPE.


REFERENCES:

       1. Rosen, S. L., Fundamental Principles of Polymeric Materials, 2nd Edition (1993),
          Chapters 19 and 20.
2. Sperling, L. H., Introduction to Physical Polymer Science, 2nd Edition (1992), Chapter 6
3. Morton-Jones, D. H., Polymer Processing,(1989), Chapter 6
4. Griskey, R. G., Polymer Process Engineering, (1995)




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