additives for plastic_ii+(3)
TRANSCRIPT
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ADDITIVES FOR PLASTICS
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Characteristics of polymers Low density Low energy to process Corrosion resistant Cheap
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Polymer DegradationVarious processes degrade polymer
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Types of polymer degradation1- Thermal degradation (Temp.)2- Thermo-oxidative degradation (Temp., O2)3- Photodegradation (Light)4- Photo-oxidative degradation (Light, O2)5- Mechanical degradation (stresses)6- Chemical degradation (strong acid & base)7-Biodegradation (bacteria, fungi)8- Degradation by high energy radiation
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Polymers additivesFillers ColorantsPlasticizers Impact modifiersLubricants Coupling agentsFlame retardants Antistatic agentsPhotostabilizers AntiozonantsHeat stabilizers Curing agentsBlowing agents Comptabilizers
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Polymer additivesRetard degradationModify properties
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Polymer AdditivesSolidLiquidRubber Gas
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Features of additives1- Efficient2- Cheap3- Non toxic4- Stable under processing conditions5- Stable under service conditions
6- Should not bleed
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Fillers1- To extend the bulk (lower the cost)2- To modify mechanical properties3- To improve flame retardant properties4- Electrical properties or insulation5- visual properties and colour
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Mineral fillersCaCO3ClaySilica
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CaCO3Cost reductionDimensional stabilityImprove impact strenghSurface uniformity
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ClayCost reductionDimensional stabilityImprove tensile strengthInsulation & thermal stability
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Glass (fibers &solid spheres)Cost reductionDimensional stabilityTranslucency
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Carbon (fibers &powder)Chemical resistanceCorrosion resistance
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Plasticizers
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Plasticizer (liquid esters)
Lower Tm
Lower TgIncrease flexibility
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Slection of plasticizerHigh compatibility with polymerLow volatility & migrationImprove flexibility at low temp.
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LubricantsExternalInternalWax, fatty acids, fatty amides & metallic stearates
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External lubricantsPossess polar gpsLow compatibility with polymerForm thin film between polymer & machine (prevent sticking)
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Internal lubricantsSprayed on the surface of the mold
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Flame retardantsFire triangle
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Fuel
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Oxidizer
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EnergyEnergy required to raise the temp of fuel to its ignition temp.
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Shortcoming of fire triangleCovalent bonded organic cpd extinguished using dry chemicals
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Tetrahedron of fire
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Combustion mechanism
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Fuel (covalent)Free radicalsO2Free radicalsFlammable gases (CO)
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Flame retardantsOrganic (phosphate esters, halogenated cpd)Inorganic (antimony oxide, Mg (OH)2 )
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Flame retardants mechanismsGas phaseCondense phase
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Flame retardant(Free radicals)
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Gas phase
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Condense phaseFlame retadantDecomposing polymer+Compatible cpdChar
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Inorganic Flame retardantsLiberate waterNon flam. gases
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Antioxidants1-Chain breaking2-Preventivea-Metal deactivatorb-Peroxide decomposers
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Chain breaking antioxidantsOxidative degradation
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Chain breaking antioxidants Degenerate chain branching
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Chain breaking antioxidants
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+ ROO.+ ROOH+ ROO.
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Preventive antioxidantsMetal ion deactivator
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Preventive antioxidantsHydroperoxide decomposers
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PhotostabilizersOxidative degradationhv
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Photostabilizers Degenerate chain branching
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Photostabilizers
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Photostabilizers
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PhotostabilizersUV absorber (Hydroxybenzophenon)
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Photostabilizers Quenchers [Ni(II) organic cpd]
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Quencher mechanism
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Heat stabilizers(Diethyl tin maleats)PVC Degradation mechanism
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+ HClMY2 + HClMYCl + HYM = Ca, Zn, Ba, Cd, Pb Y = organic anion
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Blowing agents To obtain cellular polymer 1-Chemical cpd decompose in processing stage to volatile cpd 2- Low boiling liquids volatilize during processing 3-Diffusion of gas in polymer under pressure 4- Powdered solid CO2 with PVC pasts
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Comments on Chemical Blowing agents 1-Gases evolved within a narrow temp range2- Decomposition temp range should be suitable for polymer 3-Gas evolved should not corrode processing machine
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ColorantsMaterials which provide color in polymer
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ColorantsBrightBurnAdd in small quantityVery complex cpdMore expensive Small particle sizeOpaqueFlame retaddantResist light & heatLow conc. produce translucent colorFeO, CoO, CdS
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Curing AgentsAdditives that cause crosslinking of the polymers
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Curing Agents Captax (2-Mercaptobenzothiazole) Santocure (2-Mercaptobenzothiazole sulfonamide)
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Curing Agents Initiators (Benzoyl Peroxide)
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Curing Agents Gama Ray or UV
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Curing Agents
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Curing Agents O2 + Heavy metals (Co, Pb, Mg)
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Curing Agents
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Antistatic Agents (Antistats)Insulating materialsDust attractionSparkingAntistatic agent reduce static charge build on the polymer surface
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Antistatic Agents Dissipation of static chargeReduce static charge on the surfaceEx: Quaternary amm cpd, esters of fatty acids & polyhydric alcohol
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Impact modifiers
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Impact modifiersImprove resistance of materials to stress (impact)Elastomers : ABS, BS, MBS, Chlorinated PE (absorb energy at room temp.)
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Compatibilizers
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CompatibilizersCompounds provide miscibility or compatibility to materials that are immiscible or only partially miscible
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Compatibilizer Mechanisms
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Reactive Compatibilization
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Coupling agents
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Coupling agentsUsed as surface treatment in composites to improve the interfacial bond between the matrix(weak) and fiber(strong)Silans and Titanate
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AntiozonantsDegradation(Ozone cracking on surface)Cracking of rubber tires and hoses
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Antiozonants
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AntiozonantsScavenge O3 at surface before reaction with polymerReacted with degraded product preventing more degradationN,N-disubstituted p-phenelene diamine, phenol, sulfar cpd
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AntiozonantsWaxes Inhibit ozone deteriorationMigration to polymer surfaceLess susceptible coating
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AntiozonantsWaxes + N,N-disubstituted p-phenelene diamine (very effective ozone protection)Wax assists in diffusion of antiozonant to polymer surface