ADDITIVES FOR PLASTICS

Characteristics of polymers Low density Low energy to process Corrosion resistant Cheap

Polymer DegradationVarious processes degrade polymer

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

Polymers additivesFillers ColorantsPlasticizers Impact modifiersLubricants Coupling agentsFlame retardants Antistatic agentsPhotostabilizers AntiozonantsHeat stabilizers Curing agentsBlowing agents Comptabilizers

Polymer additivesRetard degradationModify properties

Polymer AdditivesSolidLiquidRubber Gas

Features of additives1- Efficient2- Cheap3- Non toxic4- Stable under processing conditions5- Stable under service conditions

6- Should not bleed

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

Mineral fillersCaCO3ClaySilica

CaCO3Cost reductionDimensional stabilityImprove impact strenghSurface uniformity

ClayCost reductionDimensional stabilityImprove tensile strengthInsulation & thermal stability

Glass (fibers &solid spheres)Cost reductionDimensional stabilityTranslucency

Carbon (fibers &powder)Chemical resistanceCorrosion resistance

Plasticizers

Plasticizer (liquid esters)

Lower Tm

Lower TgIncrease flexibility

Slection of plasticizerHigh compatibility with polymerLow volatility & migrationImprove flexibility at low temp.

LubricantsExternalInternalWax, fatty acids, fatty amides & metallic stearates

External lubricantsPossess polar gpsLow compatibility with polymerForm thin film between polymer & machine (prevent sticking)

Internal lubricantsSprayed on the surface of the mold

Flame retardantsFire triangle

Fuel

Oxidizer

EnergyEnergy required to raise the temp of fuel to its ignition temp.

Shortcoming of fire triangleCovalent bonded organic cpd extinguished using dry chemicals

Tetrahedron of fire

Combustion mechanism

Fuel (covalent)Free radicalsO2Free radicalsFlammable gases (CO)

Flame retardantsOrganic (phosphate esters, halogenated cpd)Inorganic (antimony oxide, Mg (OH)2 )

Flame retardants mechanismsGas phaseCondense phase

Flame retardant(Free radicals)

Gas phase

Condense phaseFlame retadantDecomposing polymer+Compatible cpdChar

Inorganic Flame retardantsLiberate waterNon flam. gases

Antioxidants1-Chain breaking2-Preventivea-Metal deactivatorb-Peroxide decomposers

Chain breaking antioxidantsOxidative degradation

Chain breaking antioxidants Degenerate chain branching

Chain breaking antioxidants

+ ROO.+ ROOH+ ROO.

Preventive antioxidantsMetal ion deactivator

Preventive antioxidantsHydroperoxide decomposers

PhotostabilizersOxidative degradationhv

Photostabilizers Degenerate chain branching

Photostabilizers

Photostabilizers

PhotostabilizersUV absorber (Hydroxybenzophenon)

Photostabilizers Quenchers [Ni(II) organic cpd]

Quencher mechanism

Heat stabilizers(Diethyl tin maleats)PVC Degradation mechanism

+ HClMY2 + HClMYCl + HYM = Ca, Zn, Ba, Cd, Pb Y = organic anion

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

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

ColorantsMaterials which provide color in polymer

ColorantsBrightBurnAdd in small quantityVery complex cpdMore expensive Small particle sizeOpaqueFlame retaddantResist light & heatLow conc. produce translucent colorFeO, CoO, CdS

Curing AgentsAdditives that cause crosslinking of the polymers

Curing Agents Captax (2-Mercaptobenzothiazole) Santocure (2-Mercaptobenzothiazole sulfonamide)

Curing Agents Initiators (Benzoyl Peroxide)

Curing Agents Gama Ray or UV

Curing Agents

Curing Agents O2 + Heavy metals (Co, Pb, Mg)

Curing Agents

Antistatic Agents (Antistats)Insulating materialsDust attractionSparkingAntistatic agent reduce static charge build on the polymer surface

Antistatic Agents Dissipation of static chargeReduce static charge on the surfaceEx: Quaternary amm cpd, esters of fatty acids & polyhydric alcohol

Impact modifiers

Impact modifiersImprove resistance of materials to stress (impact)Elastomers : ABS, BS, MBS, Chlorinated PE (absorb energy at room temp.)

Compatibilizers

CompatibilizersCompounds provide miscibility or compatibility to materials that are immiscible or only partially miscible

Compatibilizer Mechanisms

Reactive Compatibilization

Coupling agents

Coupling agentsUsed as surface treatment in composites to improve the interfacial bond between the matrix(weak) and fiber(strong)Silans and Titanate

AntiozonantsDegradation(Ozone cracking on surface)Cracking of rubber tires and hoses

Antiozonants

AntiozonantsScavenge O3 at surface before reaction with polymerReacted with degraded product preventing more degradationN,N-disubstituted p-phenelene diamine, phenol, sulfar cpd

AntiozonantsWaxes Inhibit ozone deteriorationMigration to polymer surfaceLess susceptible coating

AntiozonantsWaxes + N,N-disubstituted p-phenelene diamine (very effective ozone protection)Wax assists in diffusion of antiozonant to polymer surface