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Classes of Polymeric Materials Chapter 3 Thermosets Professor Joe Greene CSU CHICO 1 Thermosetting Resins thermosets Introduction Thermoplastics are supplied as pellets powders or granules and do not undergo a chemical reaction Thermoplastics have large molecular weights long molecules The high viscosities are reduced by high temperatures Thermoset resins are supplied as liquid chemicals low MW and low viscosity and undergo a chemical reaction that features polymerization and crosslinking Liquid chemicals have short chains that polymerized into long chains and high molecular weights and high viscosity The chains are crosslinked attached to each other to make a stiff molecule Rubbers involve cross linking of already polymerized molecules to stiffen the molecules together in Vulcanization Heat is needed to cause polymerization to build MW and to cause stiffening of molecule through cross linking Heat reduces the viscosity of the chemicals until the reaction occurs and then causes the viscosity to get very large during crosslinking 2 Thermosetting Resins thermosets Types of thermosets Temperature activated Catalyst activated Mixing activated Temperature activated Fig 3 84 All thermosets require heat to undergo chemical reaction Lower temperature thermosets room temperature cure react to a more rubbery polymer that gets stiffer upon additional heat Pot life time that it takes for the thermosets to react to a solid after mixed Gel time time it takes for two liquid thermoset polymers that are mixed to form a gel or skin and stop flowing Several thermosets are supplied as powder or granular form Heat reduces the viscosity and melts the polymer to allow it to flow mold Additional heat triggers a chemical reaction which forms a cross linked 3D Common heat activated polymers Formaldehyde FOR phenoplasts PF amnioplasts UF polyester vinyl ester alkyd allyl furan some epoxies and polyimides 3 Thermosetting Resins thermosets Catalyst activated Fig 3 85 Some thermosets supplied as



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