1、Chapter 4 ThermosetsThermosets Resin Phenolics Epoxies Melamines Silicones Polyesters Composites Thermoset vs. thermoplasticGeneral Properties of Thermosets Strength Flexibility Thermal Creep Ability to reinforce Ability to cure at room temperatureFormaldehyde Resins Phenolics Urea formaldehyde Mela
2、mine formaldehydeCrosslinking of Phenolics Reactive GroupsPhenolics CCCCCCOHHHHHHPhenolCOHHFormaldehydePlusCompression MoldingCompression molding was specifically developed for replacement of metal components with composite parts. The molding process can be carried out with either thermosets or ther
3、moplastics. However, most applications today use thermoset polymers. In fact,compression molding is the most common method of processing thermosets.Resin Transfer Molding In the RTM process, dry (i.e.,unimpregnated ) reinforcement is pre-shaped and oriented into skeleton of the actual part known as
4、the preform which is inserted into a matched die mold. The heated mold is closed and the liquid resin is injected The part is cured in mold. The mold is opened and part is removed from mold.Injection MoldingGlass Reinforced Composites Plastic pellets with glass fibers are melted in screw, injected i
5、nto a cold mold, and then ejected.Glass filled resin pelletsApplication of Phenolics Wiring devices Switch gear Circuit breakers Insulators Gears Wear guides Pulleys RollersAmino Resins (UF and MF) Formaldehyde + -NH2(amine group) (1) Urea-formaldehyde (2) Melamine-formaldehydeCrosslinking Reactive
6、GroupsAmino plasticsNHHRNHHAminePlusCOHHFormaldehydeUrea formaldehydeMelamineCNCNCNNNNHHHHHHCrosslinking as Polymers are FormedThree active sitesFormaldehydeCOHHPlusCrosslinking as Polymers are FormedMelamine FormaldehydeWaterCrosslinking as Polymers are FormedCNCNCNCNNCNCNCNCNCNNCNCNCNCNNNCCNCNCNCN
7、CNNCNCHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHMelamine FormaldehydeOHHWaterAmine plastics clear adhesiveChipboard Applications: wood particleboard, plywood, boat hulls flooring furniture assemblies Cellulose-filled urea compound: Electrical wall plates, receptacles, knobs, handle Cellulose-filled melami
8、ne compound: dinnerware, buttons, control buttons, knobApplication of melamine plastics Melamine PlasticsPolyester Thermosets (TS) or Unsaturated Polyesters (UP) Largest group of thermosets Most like to be reinforced with fiberglassOOR1RInitiator(usually peroxide)CCR1RHHCarbon-carbonDouble bondCross
9、linking Reactive GroupsUnsaturated polyestersPlusViscosity and Thermal Control during CrosslinkingThermoset Types Unsaturated PolyestersCrosslinking Mechanism for Thermoset PolyestersCCCCOOOOHHHHCCCCOOOOHHHHOOR1RPolyesterPeroxideStyrene(large quantities)CCCCHCHCHCHCHHHHCrosslinking HeatROHROHCCCCHCH
10、CHCHCHHHHCCCCOOOOHHHHCCCCOOOOHHHHPeroxidebreaks apartCrosslinking Approach of styreneROHROHCCCCHCHCHCHCHHHHCCCCOOOOHHHHCCCCOOOOHHHHCrosslinking bond to styreneROHCCCCHC HC HC HC HHHHHHROHCCCCOOOOHHHHCCCCOOOOHHHHHalf of peroxide bonds with other end of broken styrene moleculeWhen styrenes double bond
11、 breaks, one end forms a free radicalCrosslinking approach to polymerCCCCHC HC HC HC HHHHHHROHCCCCOOOOHHHHCCCCOOOOHHHHHHStyrene free radical causes the polymers double bond to break and allows it to accept a new pi bondCrosslinking bonding to polymerCCCCOOOOHHHHHHCCCCHC HC HC HC HHHHHHROHCCCCOOOOHHH
12、HProblems: Polymers not lined up, steric interferenceSolution: StyreneCCCCHCHCHCHCHHHHNew bondNew free radicalCrosslinking approach of styreneCCCCOOOOHHHHHHCCCCHC HC HC HC HHHHHHROHCCCCOOOOHHHHCCCCHCHCHCHCHHHHCrosslinking activation of styreneCCCCOOOOHHHHHHCCCCHC HC HC HC HHHHHHROHCCCCHC HC HC HC HH
13、HHHHCCCCOOOOHHHHStyrenes double bond opens, allowing two new free radical sitesCrosslinking bonding of styreneCCCCOOOOHHHHHHCCCCOOOOHHHHHHCCCCHC HC HC HC HHHHHHROHCCCCHC HC HC HC HHHHHHProblems: Polymers still not lined up, steric interferenceCCCCHCHCHCHCHHHHSolution: Still more styreneNew bondDoubl
14、e bond opens but cant create a bond with any other open bond because of steric effectsCrosslinking bonding of 2nd styreneCCCCOOOOHHHHHHCCCCOOOOHHHHHHCCCCHC HC HC HC HHHHHHROHCCCCHC HC HC HC HHHHHHCCCCHC HC HC HC HHHHHHNew bondFree radicalCrosslinking bonding with 2nd polymerCCCCOOOOHHHHHHCCCCOOOOHHH
15、HHHCCCCHC HC HC HC HHHHHHROHCCCCHC HC HC HC HHHHHHCCCCHC HC HC HC HHHHHHUp to 8 styrenes might be needed in the bridgeNew bondCrosslinking bonding with 2nd polymerCCCCOOOOHHHHHHCCCCOOOOHHHHHHCCCCHC HC HC HC HHHHHHROHCCCCHC HC HC HC HHHHHHCCCCHC HC HC HC HHHHHHEtc.CCCCOOOOHHHHHHCrosslinking more styr
16、eneCCCCOOOOHHHHHHCCCCOOOOHHHHHHCCCCOOOOHHHHHHCCCCHC HC HC HC HHHHHHROHCCCCHC HC HC HC HHHHHHCCCCHC HC HC HC HHHHHHCCCCHC HC HC HC HHHHHHCrosslinking more styreneCCCCOOOOHHHHHHCCCCOOOOHHHHHHCCCCHC HC HC HC HHHHHHROHCCCCHC HC HC HC HHHHHHCCCCHC HC HC HC HHHHHHCCCCHC HC HC HC HHHHHHCCCCHC HC HC HC HHHH
17、HHCCCCOOOOHHHHHHCrosslinkingbonding to 3rd polymerCCCCOOOOHHHHHHCCCCOOOOHHHHHHCCCCOOOOHHHHHHCCCCHC HC HC HC HHHHHHROHCCCCHC HC HC HC HHHHHHCCCCHC HC HC HC HHHHHHCCCCHC HC HC HC HHHHHHCCCCHC HC HC HC HHHHHHLaminating ResinsAdditives to Thermoset PolyestersFillers like Calcium CarbonateTougheners like
18、 rubbersAntioxidants and UV stabilizersReinforcementsGlass fiber reinforced plastics (GFRP)Sheet Molding Compound (SMC)Sheet Molding Compound (SMC)RNNHHHHHardener(amine shown)CCORCCOHHHHHHEpoxy RingsEpoxies Reactive GroupsEpoxies PlusReaction schemes for the synthesis of DGEBA-type epoxy resinbisphe
19、nol A (DGEBA)Thermoset Types EpoxiesCrosslinking of Polyurethanes Reactive GroupsPolyurethanes PlusOORHHPolyolsCNRNCOOHHHHDiisocyanatesChemical structures of common isocyanates used for PU synthesis异佛尔酮二异氰酸酯Synthesis of PU resin from polyol and diisocyanateCrosslinking Between two Existing Polymer C
20、hainsCCOOHHHHHHCCCCOOOOHHHHPolymerizationActive SitesCrosslinkingActive SitePolyurethane Processing Polyurethane can be processed by Casting, painting, foaming Reaction Injection Molding (RIM)Structural RIM Fiber preform is placed into mold. Polyol and Isocyanate liquids are injected into a closed mold and reacted to form a urethane.Thermoset Types PolyurethanesThank You
