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1、Chapter 4 Thermosets,Thermosets,Resin Phenolics Epoxies Melamines Silicones Polyesters CompositesThermoset vs.thermoplastic,General Properties of Thermosets,StrengthFlexibilityThermalCreepAbility to reinforceAbility to cure at room temperature,Formaldehyde Resins,PhenolicsUrea formaldehydeMelamine f
2、ormaldehyde,Crosslinking of Phenolics,Reactive GroupsPhenolics,Phenol,Formaldehyde,Plus,Compression Molding,Compression molding was specifically developed for replacement of metal components with composite parts.The molding process can be carried out with either thermosets or thermoplastics.However,
3、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 the preform which is inse
4、rted into a matched die mold.The heated mold is closed and the liquid resin is injectedThe 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 into a cold mold,and then eje
5、cted.,Glass filled resin pellets,Application of Phenolics,Wiring devicesSwitch gearCircuit breakersInsulatorsGearsWear guidesPulleysRollers,Amino Resins(UF and MF),Formaldehyde+-NH2(amine group)(1)Urea-formaldehyde(2)Melamine-formaldehyde,Crosslinking,Reactive GroupsAmino plastics,Amine,Plus,Formald
6、ehyde,Urea formaldehyde,Melamine,Crosslinking as Polymers are Formed,Formaldehyde,Plus,Crosslinking as Polymers are Formed,Melamine Formaldehyde,Water,Crosslinking as Polymers are Formed,Melamine Formaldehyde,Water,Amine plastics clear adhesive,Chipboard,Applications:wood particleboard,plywood,boat
7、hulls flooring furniture assemblies Cellulose-filled urea compound:Electrical wall plates,receptacles,knobs,handle Cellulose-filled melamine compound:dinnerware,buttons,control buttons,knob,Application of melamine plastics,Melamine Plastics,Polyester Thermosets(TS)or Unsaturated Polyesters(UP),Large
8、st group of thermosetsMost like to be reinforced with fiberglass,Initiator(usually peroxide),Carbon-carbonDouble bond,Crosslinking,Reactive GroupsUnsaturated polyesters,Plus,Viscosity and Thermal Control during Crosslinking,Thermoset Types,Unsaturated Polyesters,Crosslinking Mechanism for Thermoset
9、Polyesters,Polyester,Peroxide,Styrene(large quantities),Crosslinking Heat,Crosslinking Approach of styrene,Crosslinking bond to styrene,Half of peroxide bonds with other end of broken styrene molecule,When styrenes double bond breaks,one end forms a free radical,Crosslinking approach to polymer,Styr
10、ene free radical causes the polymers double bond to break and allows it to accept a new pi bond,Crosslinking bonding to polymer,Problems:Polymers not lined up,steric interference,Solution:Styrene,New bond,New free radical,Crosslinking approach of styrene,Crosslinking activation of styrene,Styrenes d
11、ouble bond opens,allowing two new free radical sites,Crosslinking bonding of styrene,Problems:Polymers still not lined up,steric interference,Solution:Still more styrene,New bond,Double bond opens but cant create a bond with any other open bond because of steric effects,Crosslinking bonding of 2nd s
12、tyrene,New bond,Free radical,Crosslinking bonding with 2nd polymer,Up to 8 styrenes might be needed in the bridge,New bond,Crosslinking bonding with 2nd polymer,Etc.,Crosslinking more styrene,Crosslinking more styrene,Crosslinkingbonding to 3rd polymer,Laminating Resins,Additives to Thermoset Polyes
13、ters,Fillers like Calcium Carbonate,Tougheners like rubbers,Antioxidants and UV stabilizers,Reinforcements,Glass fiber reinforced plastics(GFRP),Sheet Molding Compound(SMC),Sheet Molding Compound(SMC),Hardener(amine shown),Epoxy Rings,Epoxies,Reactive GroupsEpoxies,Plus,Reaction schemes for the synt
14、hesis of DGEBA-type epoxy resin,bisphenol A(DGEBA),Thermoset Types,Epoxies,Crosslinking of Polyurethanes,Reactive GroupsPolyurethanes,Plus,Polyols,Diisocyanates,Chemical structures of common isocyanates used for PU synthesis,异佛尔酮二异氰酸酯,Synthesis of PU resin from polyol and diisocyanate,Crosslinking B
15、etween two Existing Polymer Chains,Polyurethane Processing,Polyurethane can be processed byCasting,painting,foamingReaction 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,Polyurethanes,Thank You,
