Characteristics of Polymers Low density 1 1 5 g cm3 Low TM or Tg Low thermal and electrical conductivity Low elastic modulus stiffness and much more sensitive to temperature than metals or ceramics Low hardness strength Low creep resistance heat distortion Applications Insulators Flexible parts e g seals Pipe packaging toys Thermoplas cs and Thermosets Thermoplastics become plastic soften melt upon heating and harden upon cooling repeatable Linear or branched structures semicrystalline and non crystalline Thermosets become hard set by polymerization or crosslinking curing usually by heating and do not melt upon reheating Network structures non crystalline 2 Polymer Structures Summary 4 3 D Polymeriza on Network structures Highly cross linked or multi dimensional polymerization Phenolics e g phenol formaldehyde Bakelite 1909 Once polymerized set 3 D covalent Network does not melt Thermosets Epoxies resin hardener or curing agent 6 Thermoplas cs Polystyrene Nylon PVC 7 The degree of crystallinity in polymers depends on several factors including molecular weight chain length chain morphology cooling rate etc Techniques like di eren al scanning calorimetry can be used to measure the degree of crystallinity HDPE LDPE 8 Sensi vity of Viscosity to Temperature Change depends on chain length molecular weight 9 Data Sheet Accompanying LDPE Resin 10 Melt Index a simple a reproducible way to es mate the ow characteris cs of a polymer resin ASTM D 1238 190 C 2 16 kg units of g 10 min 11 Viscosity Melt Index E ects 12 Extruder no ce that the screw increases in diameter thereby pressurizing the molten polymer and pushing it into the die An extruder is generally combined with down stream components that shape the extruder polymer to coat wire make plas c shee ng and tubes among other things 13 Injec on Molding 14 Takes quite a bit of me to remove heat from an injec on molded polymer slab because polymers have a low thermal conduc vity 15 Low thermal conduc vity of the polymer resin limits the thickness of injec on molded parts This reminds me of the stress state of tempered glass except that polymers have much much lower Young s moduli than glass 1 GPa vs 70 GPa 16 Polyethylene terepthalate polyester 17 Stretch Blow Molding of PET Boeles 18
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