Polymers: Types, Properties & Characterization

• The lecture material is for academic purposes and acknowledges the contributions of various sources.

Grading Breakdown for Sessional Marks

• 2 Tests: 10 points total
• Mid-term: 20 points, Week 08
• Graded Homework/Assignment: 10 points, Week 12

Overview of Course Content

• Part 1 reviews different polymers, their applications, and properties.
• Focuses on commodity and engineering thermoplastics, thermosets, and high-performance engineering polymers.
• Covers elastomers, thermoplastic elastomers, specialty polymers, polymer additives, and blending.
• Part 2 focuses on characterization and testing of polymers and polymer blends.
  • Topics include molecular weight determination, molecular spectroscopy, thermal characterization, microscopy, X-ray diffraction, and mechanical characterization.

Polymers and Polymerization

• A polymer is a large molecule constructed from many covalently bonded small molecules (monomers).
• Polymerization is the process of converting a monomer or a mixture of monomers into a polymer.
• Polymerization reactors are vessels designed for synthesis (chemical) reactions to take place.

Destructive vs. Non-Destructive Testing

• Destructive testing alters the dimensions or physical/structural integrity of the specimen; examples include tensile, compression, shear, and Rockwell hardness tests.
• Non-destructive testing does not affect the structural integrity of the sample; examples include weighing, measurements (optical, acoustical).

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 Testing

• Tensile testing is a standard test for materials such as metals, wood, and plastics.
• Tensile loads pull a specimen apart, putting it in tension.
• Tests can be performed on specimens with known cross-sectional area and gage length.
• Tensile tests determine the mechanical behavior of materials under static, axial tensile, or stretch loading.
• Data from tensile tests determines elastic limit, elongation, proportional limit, reduction in area, yield point, and other tensile properties.
• A Universal Testing Machine (UTM) is used to check the tensile strength of a material.
• Gauge Length refers to the original length between two marks on a test piece where the change in length is determined.

Flexural Testing

• Flexural strength refers to the resistance offered by a sample against bending force.
• The flexural test measures the force needed to bend a beam under certain loading conditions.
• During flexural testing of a rectangular beam, continuous change occurs from maximum tensile stress on one surface to maximum compressive stress on the other.
• Three-point bending is a common setup in standard flexural tests
• Flexural stress in a rectangular beam supported at the midpoint, can be given by σf = 3FL/2bh²

Impact Testing

• Notch impact tests assess a material's resistance to sudden fracture with stress concentrators.
• Determines energy absorption during high-velocity fracturing.
• Main test types: Izod and Charpy.
• Izod Impact Test:
  • A pendulum hammer fractures a standard-size, notched piece of material with one blow.
  • Measures impact strength or notch sensitivity.
• Charpy Test:
  • A pendulum hits a notched specimen supported at both ends like a single beam.
  • Measures impact strength and notch toughness by the energy absorbed.
• Izod Test uses a V-shaped notch
• Charpy Test uses Key-hole, U-notch, and V-notch specimen types.
• The Izod specimen is held in a cantilevered manner
• The Charpy test the specimen rests against two supports on either side of the test notch.
• 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.

Falling Dart Test

• The falling dart impact test evaluates impact strength and toughness of plastic film.
• The specimen is clamped in a pneumatic ring at the base of a drop tower.
• The dart is released from a set drop height onto the center of the specimen.
• The drop weight and test results are recorded.

Hardness Tests

• Hardness is the property of a material to resist plastic deformation, usually by penetration.
• Three principle types:
• Resistance to fracture or plastic deformation caused by friction from a sharp object (Scratch Hardness).
• Resistance to plastic deformation from constant load from a sharp object (Indentation Hardness).
• Height of bounce of an object dropped on material (Rebound Hardness).
• Common measurement methods include Shore and Rockwell tests.
  • Shore A scale is for softer rubber
  • Shore D scale is for harder materials.
• A Durometer measures shore hardness.

Lecture notes on polymers, covering types like thermoplastics and thermosets, their properties, and applications. Includes characterization techniques such as molecular weight determination and thermal analysis. Also contains grading breakdown for sessional marks.