POLYMERS Polymer Technology Thermoplastic Polymers Thermosetting Polymers Elastomers John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing

Polymer Long‑chain molecules repeating units connected together Millions of units in a single polymer molecule Polymer derived from the Greek poly, meaning many meros (reduced to mer), meaning part Most polymers are based on carbon John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing

Types of Polymers Polymers Plastics Rubbers Engineering materials Thermoplastic polymers Thermosetting polymers Elastomers John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing

Thermoplastic Polymers - Thermoplastics Solid material at room temperature Viscous liquids when heated Injection moulding processes TP Linear Structure Branched Structure John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing

Thermosetting Polymers - Thermosets Cannot tolerate repeated heating cycles Elevated temperatures produce a chemical reaction that hardens the material If reheated, thermosets degrade and char rather than soften TS Cross-linked or Networked Structure John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing

Elastomers (Rubbers) Polymers exhibit extreme elastic extensibility subjected to low mechanical stress Elastomers can be stretched by a factor of 10 completely recover to their original shape Elastomer Structure John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing

Loosely Cross-linked Structure Stress-Strain Curves Unstretched Tensile Stress John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing

Examples of Polymers Thermoplastics: Polyethylene, polyvinylchloride, polypropylene, polystyrene, and nylon Thermosets: Phenolics, epoxies, and certain polyesters Elastomers: Natural rubber (vulcanized) Synthetic rubbers, which exceed the tonnage of natural rubber John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing

General Properties of Polymers Low density relative to metals and ceramics Good strength‑to‑weight ratios High corrosion resistance Low electrical and thermal conductivity John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing

Polyermerization of Polyethylene Synthesis of polyethylene from ethylene: (1) n ethylene monomers yields (2a) polyethylene of chain length (2b) concise notation John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing

Addition Polymerization Initiation Rapid addition of monomers Long chain molecule John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing

Addition (chain) Polymerization John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing

Step Polymerization n‑mer attaching a single monomer to form a (n+1)‑mer n1‑mer combining with n2‑mer to form a (n1+n2)‑mer John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing

Step Polyermization John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing

Possible Arrangements of Atom Groups Polypropylene Isotactic Syndiotactic Atactic John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing

Crystalline Polymer Structure folded chain lamella, the typical form of a crystallized region long molecules forming crystals randomly mixed in with the amorphous material John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing

Strength vs. Temperature Relationship of mechanical properties: amorphous thermoplastic 100% crystalline (theoretical) thermoplastic partially crystallized thermoplastic Tg = Glass transition temperature John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing

SME Video John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing

In-class example A test specimen in a tensile test has a gage length of 2.0 in and an area = 0.5 in2. During the test the specimen yields under a load of 32,000 lb. The corresponding gage length = 2.0083 in. This is the 0.2 percent yield point. The maximum load = 60,000 lb is reached at a gage length = 2.60 in. Determine the following: (a) yield strength (b) modulus of elasticity (c) tensile strength. fracture occurs at a gage length of 2.92 in (d) the percent elongation specimen necked to an area = 0.25 in2 (e) percent reduction in area John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing

ASSIGNMENT – STUDENT MUST SHOW SOLUTION TO PROFESSOR DURING LAB PERIOD A tensile test uses a test specimen that has a gage length of 50 mm and an area = 200 mm2. During the test the specimen yields under a load of 98,000 N. The corresponding gage length = 50.23 mm. This is the 0.2 percent yield point. The maximum load = 168,000 N is reached at a gage length = 64.2 mm. Determine the following: (a) yield strength (b) modulus of elasticity (c) tensile strength fracture occurs at a gage length of 67.3 mm (d) percent elongation specimen necked to an area = 92 mm2 (e) percent reduction in area John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing