Polymeric Materials & Their Characterization - Lecture Slides

Polymeric Materials & their Characterization PP-212 Engr. Ali Raza [email protected]  Acknowledgement – copy right issues The lecture material (text and figures) presented in class is prepared for academic purposes (non commercial use) only and it may be...

Polymeric Materials & their Characterization PP-212 Engr. Ali Raza [email protected]  Acknowledgement – copy right issues The lecture material (text and figures) presented in class is prepared for academic purposes (non commercial use) only and it may be used in similar way. A number of text books and academic presentations downloaded from various sources were consulted and copied in preparing these slides. Their contribution is hereby acknowledged.  Grading - for sessional marks 2 Tests (5 + 5 ) = 10 Points Mid-term = 20 Points Week (08) Graded Homework/ = 10 Points Week (12) Assignment  Recommended Books 1. Polymer Science and Technology, Robert O. Ebewele 2. Lutx J Grossman R. (2000) Polymer Modifiers and Additives, Marcel Dekker, NY 3. Introduction to Physical Polymer Science, L.H. Sperling 4. Applied Polymer Science_ Clara D. Craver and Charles E. Carraher  Understanding Why ‘Outcome Based Education’ System? An Engineering Program must have! Program Mission (PM) Program Educational Objectives (PEOs) 12 Program Learning Outcomes / Program Outcomes (PLOs/POs) Course Learning Outcomes (CLOs/COs) Course outline! 1st Part Review of Different Polymers & Its Application And Properties Commodity and engineering thermoplastics & thermosets, High performance engineering polymers. Elastomers and Thermoplastic Elastomers, Specialty Polymers Polymer additives & blending 2nd Part Characterization & Testing of Polymers and Polymer Blends Molecular Weight Determination. Molecular Spectroscopy Thermal Characterization Microscopy. X-ray Diffraction. Mechanical characterization. Introduction to Polymer Testing o Polymer: Large molecule(Polymer) constructed from many small molecules (monomers) covalently bonded in any conceivable pattern. o Polymerization: Process of converting a monomer or a mixture of monomers into a polymer. o Polymerization Reactor: Vessels designed to synthesis (chemical) reactions in take place. Destructive testing is changes the dimensions or physical and structural integrity of the specimen. (It is essentially destroyed during the test) e.g., Tensile, Compression, Shear and Rockwell Hardness Non-Destructive testing does not affect the structural integrity of the sample.( A measurement that does not effect the specimen in any way) e.g., weighing, measurements Optical, Accost. Material Behavior Stiffness is how well a material resists deformation. Toughness is the ability of a material to absorb energy before failure/fracture.. Ductile materials undergo observable plastic deformation and absorb significant energy before fracture Brittle fracture is characterized by very low plastic deformation and low energy absorption prior to breaking.  Tensile Test - Introduction The tensile test is a common test performed on metals, wood, plastics, and most other materials. Tensile loads are those that tend to pull the specimen apart, putting the specimen in tension. They can be performed on any specimen of known cross-sectional area and gage length to which a uniform tensile load can be applied. Tensile tests are used to determine the mechanical behavior of materials under static, axial tensile, or stretch loading. ASTM standards for common tensile tests may be found in sections D638 (plastics), D2343 (fibers), D897 (adhesives), D987 (paper), and D412 (rubber) Continue… Force in tension required to pull or break the sample. It is used for determining behavior of material under axial stretch loading. The data obtained from these test is used to determine elastic limit, elongation, proportional limit, reduction in area, yield point and other tensile properties. The machine required to check the tensile strength of material is UTM (Universal Testing Machine). Test Method: Gauge Length: The original length between two marks on test piece over which the change in length is determined or the distance between two gaps. 13 14  Flexural Test The resistance offered by a sample during the application of bending force is called flexural strength. Flexural test measures the force required to bend a beam under certain loading condition. When a rectangular beam is bent, a continuous change occurs from maximum tensile stress on one surface through the thickness to maximum compressive stress on other. Three Point Bending Three point bending is the type most commonly used in standard test. For a rectangular beam supported at the midpoint, the flexural stress is given by σf = 3FL/2bh2 Where, “F” is the force at mid point. “L” is the span length. “b” is the width of the sample 15 “h” is the height  Flexural Test At fracture, Flexural Strength = 3FmL/ 2bh2 Where Fm is the maximum force recorded. 16  Impact Test Notch impact test provide information on the resistance of material to sudden fracture, where a sharp stress concentrator or fracture is present. Impact test determines the energy absorb in fracturing a test piece at high velocity. Main types are Izod and Charpy. 1. Izod Impact: Mechanical test in which a pendulum hammer (swinging through a fixed distance) fractures a standard size notched piece of material with one blow. This test is meant to measure the impact strength of the object or notch sensitivity. 2. Charpy Test: It is pendulum type single blow impact test in which the specimen usually notched, is supported at both ends as a single beam and broken by falling pendulum. The energy absorbed is a measured of impact strength and notch toughness. 17 Impact Tester 18  Impact Test IZOD TEST CHARPY TEST 19  Difference between Izod and Charpy: 1) The test notches for the impact specimens for the tests have different dimensions. The Izod test is a V-notch; the Charpy test has three different specimen types: Key-hole, U-notch, and V-notch. However, other specimen types may be specified as required for both tests. 2) The specimens are held differently. The Izod specimen is held in a cantilevered manner; the Charpy test is held such that the specimen rests against two supports on either side of the test notch. 3) The impact location is different. The Izod test impact is against the end of the exposed cantilever; the Charpy test is struck directly behind the test notch such that the specimen undergoes three point bending. 20  Impact Test FALLING DART TEST Falling dart impact is a traditional method for evaluating the impact strength and toughness of plastic film. The test specimen is clamped securely in a pneumatic ring at the base of the drop tower. The mounting bracket is adjusted to the appropriate drop height and the dart is inserted into the bracket. The dart is released to drop onto the center of the test specimen. The drop weight and the test result are recorded. 21  Hardness Hardness is the property of the material that enables it to resist plastic deformation, usually by the penetration. There are three principle types of hardness. There are three principle types of hardness 1. Resistance to fracture or plastic deformation due to friction from a sharp object (Scratch Hardness) 2. Indentation Hardness: Resistance to plastic deformation due to constant load from a sharp object. 3. Rebound Hardness: Height of bounce of an object dropped on material. The hardness of the plastic is commonly measured by Shore test or Rockwell Hardness. Shore hardness, using either the Shore A or Shore D scale, is preferred method for the rubbers elastomers and also commonly used for softer plastic such as polyolefins. The shore A scale is used for softer rubber while Shore D is used for harder one. The shore hardness is measured with an apparatus known as Durometer. Hardness