m141_ch03-tset

m141_ch03-tset - Classes of Polymeric Materials Chapter 3:...

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1 Classes of Polymeric Materials Chapter 3: Thermosets Professor Joe Greene CSU, CHICO
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2 Thermosetting Resins (thermosets) Introduction Thermoplastics are supplied as pellets, powders, or granules and do not undergo a chemical reaction. 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.
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3 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. Additional heat triggers a chemical reaction which forms a cross-linked 3D Common heat activated polymers Formaldehyde (FOR), phenoplasts (PF), amnioplasts (UF), polyester, vinyl
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4 Thermosetting Resins (thermosets) Catalyst activated: Fig 3.85 Some thermosets supplied as stable liquid form Small amount of liquid (catalyst) is added which starts a chemical reaction and leads to formation of 3D structure. Chemical type and amount of catalyst controls the extent of reaction and the speed of polymerization. Many systems can set at room temperature. Useful for casting resins and for glass fiber reinforced composites. Common polymer is unsaturated polyester resin (UPR)
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5 Thermosetting Resins (thermosets) Mixing activated systems: Fig 3.86 Some thermosets supplied as two stable liquids. When the two are added together, a chemical reaction starts and forms a 3D structure.
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This note was uploaded on 01/22/2012 for the course ME 2733 taught by Professor Meng during the Fall '10 term at LSU.

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m141_ch03-tset - Classes of Polymeric Materials Chapter 3:...

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