Published on March 14, 2014
Muddiest Points Muddiest Points: • “I don’t get the difference between a monomer, a mer, and a polymer?” • “How do I calculate degree of polymerization?” • “How does degree of polymerization affect polymer properties?” • “I don’t get polymer microstructures and how they affect properties?” • “I don’t get the different techniques for processing polymers.” Polymers I: Introduction to Polymers
What is a Polymer? Poly mer Many Units repeat unit repeat unit repeat unit What is a Polymer? Definition: PE Milk Container PVC Pipe PP Rope
•C-C rotations along the chain give the polymer molecule a loosely-coiled, string-like shape Polymer Chain Geometry Carbon Hydrogen
What are Important Polymer Concepts & Terminology?Monomers, Mers, Polymers, and Degree of Polymerization Degree of Polymerization: Concept and Definition • Monomer - small, unreacted single molecule for polymer. Ethylene Monomer: • Mer – single repeat unit of a polymer Polyethylene Mer: 2 C-C chain bonds / mer • Polymer – entire polymer chain Polyethylene Molecule: n mers / chain molecule n = degree of polymerization (DP) = n mers / chain molecule n= DP = n = DP = • n is typically 100 10,000 but may go higher than 100,000 number of mer units polymer molecule molecular weight of polymer molecule molecular weight of mer Hydrogen Carbon Ethylene Monomers
Candle (Paraffin) Container (HDPE) n (DP) 10 10,000 MW Chain (g/mol) (28 g/mol )(10) = 280 g/mol (28 g/mol)(10000) = 280,000 g/mol Tm (°C) MW of Molecule = n * MW Mer 2.Why does the Tm increase with more C atoms in chain? 1. What are the similarities and differences of candles and plastic milk containers? How Degree of Polymerization Affects Properties: Melting Point n= Degree of Polymerization (DP) Molecular Weight= MW Temperature(°C) Number of carbons= 2n = 2* DP
What are the Four Different Types of Polymer Structure and Morphology? • Polymer – a long chain molecule of 1-D covalently bonded repeat units or a network of 3-D covalently bonded repeat units • Length of molecule varies from 1,000s to 100,000s of atoms long. • Four main classes of polymer solids we will consider are: –Thermoplastic AMORPHOUS polymers are 1-D covalently-bonded chains. They are randomly-oriented and form a glassy solid. When heated, they melt; when cooled, they solidify; and they can be remelted (melt recyclable). - Thermoplastic SEMICRYSTALLINE polymers also have 1-D covalently-bonded chains. They form layers of thin, chain-folded crystalline lamellae separated by amorphous regions and are connected with tie molecules. When heated, they melt. When cooled, they solidify and can be remelted (melt recyclable). – Heat Set ELASTOMERS are 3-D LIGHTLY to MODERATELY crosslinked networks of long chain molecules that are covalently crosslinked during a curing chemical reaction. After the cure, the 3-D network maintains its structural integrity when heated (not melt recyclable). –Heat Set THERMOSETS are 3-D HIGHLY crosslinked networks of covalently- bonded molecules. The thermoset reaction forms a rigid amorphous solid with very good thermal resistance (not melt recyclable). PS Glass PE Trash Bag Rubber Shoe Sole Bakelite Billiard Balls
How can Polymers be Classified?
What is the Effect of Structure & Morphology on Mechanical Properties? Polymer E (MPa) TS (MPa) %EL Natural Rubber 2.5 20 600- 1000% HDPE 830 28 300- 600% Polystyrene 3100 40 1.2- 2.5% Bakelite 6900 55 0.1% A B C PS Glass PE Trash Bag Rubber Shoe Sole D Bakelite Billiard Balls
Morphology and Thermal & Mechanical Properties Lightly X-linked Elastomer Heavily X-linked Thermoset Semicrystalline Polymer Amorphous Polymer Thermoplastic Polymers Heat Set Polymers Tg = 100C T25 < Tg Glassy Tg = -103C Tg < T25 Elastic Tg = -90C; Tm = 130C Tg < T25 < Tm Flexible Tg = 163C T25 < Tg Rigid Tg = Glass Transition Temperature, below which a polymer is rigid and brittle PS Glass PE Trash Bag Rubber Shoe Sole Bakelite Billiard Balls
1010 What is the Effect of Structure on Processing of Plastics? • Thermoplastics – Amorphous & Semicrystalline • Processing can be continuous – only cooling required • Heat to melt, shape & cool below Tg or Tm • Can be reversibly melted and solidfied, i.e. recyclable • Ex: PE, PP, PS. • Heat Sets – Thermosets and Elastomers – Processing not continuous – one part at a time – Heating & crosslink reaction require time in fixed shape mold – Permanent 3-D crosslinked network – not recyclable – Shape is permanent – does not change with heat; will only degrade – Elastomer + crosslink agent (S, O) mixed, shaped, reacted – Ex. polybutadiene, polyisoprene – Thermoset prepolymer pressed into a shape & reacted – Ex: Bakelite, urethane, epoxy For additional information on polymer processing terminology go to: GOOGLE “matsciasu” and get Quizlet.com vocabulary e-flash cards for 6.2 Polymers II – Processing PS Glass PE Trash Bag Rubber Shoe Sole Bakelite Billiard Balls
Processing for Thermoplastic and Crosslinked Polymers PS Glass PE Trash Bag Rubber Shoe Sole Bakelite Billiard Balls Thermoplastic Amorphous Thermoplastic Semicrystalline Heat Set Elastomers Heat Set Thermosets Processing: Film Blowing Processing: Injection Molding Processing: Transfer Molding Processing: Compression Molding
Effect of Molecular Weight and Bonding on Properties Metals Ceramics Polymers 0.2 8 0.6 1 Wood( gr AFRE( fib CFRE* GFRE* Glass fibers Carbon fiber Aramid fiber Epoxy only 0.4 0.8 2 4 6 10 20 40 60 80 100 200 600 800 1000 1200 400 CFRE( fib GFRE( fib GFRE(|| fib AFRE(|| fib CFRE(|| fib Why is elastic modulus of polymers two orders of magnitude less than metals or ceramics? How do Polymer Properties Compare to Metals and Ceramics? Property Polymer Metal Ceramic E (GPa) 0.2-4 40-400 10-1200 Tensile Strength (Mpa) 26-60 (Fibers~700) 200-3400 70-140 Ductility (% elongation) 2-500 1-8 1< Tm (°C) 100-250 200-2800 500-4000 Coefficient of Thermal Expansion (m/m-K) 15 x10-6 - 100 x10-6 5x10-6 - 12x10-6 1x10-6 - 5x10-6 E(GPa)
Wrap-Up • “What is a polymer?” • “I don’t get the difference between a mer and a monomer.” • “How do I calculate degree of polymerization?” • “How does degree of polymerization affect polymer properties?” • “I don’t get polymer microstructures and how they affect properties.” • “I don’t get the different techniques for processing polymers.” Polymers I: Introduction to Polymers
This video serves as an introduction to polymers from the perspective of muddiest points taken from materials science and engineering classes.
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