09.8.20101Polyvinyl Chloride ResinProcess Chemistry VariationsEPA/Vinyl Institute WebinarSeptember 8, 201009.8.20102GoalTo explain why various PVC resins, withvarying recipe ingredients and productspecifications, emit an assortment ofhazardous air pollutants that differ acrossthe PVC resin manufacturing industry09.8.20103Agenda• Introduction– Typical Polyvinyl Chloride (PVC) product examples– Why does PVC need to be so versatile– How does PVC resin get its versatility• PVC Resin Chemistry– Resin Particle Formation• PVC Resin Classifications & Grades– Process Descriptions for Suspension (S-PVC) &Dispersion (D-PVC)• Hazardous Air Pollutants & PVC Resin– Typical HAPs and likely Emission Sources09.8.20104An Intro• PVC results from the polymerization of vinylchloride monomer (VCM)• PVC cannot be processed on its own; thereforemust be combined with additives– PVC compounds are based on the combination ofpolymers and additives to produce the necessaryformulation for end use• Broad PVC Classifications under40 CFR Part 61:– Suspension (S-PVC) Dispersion (D-PVC)– Bulk Solution09.8.20105Suspension PVC Products09.8.20106Dispersion PVC Products09.8.20107PVC in Art, Hospitals, Homes...• Cars, Packaging, Wall Covering, Floors....09.8.20108Why does PVC Resin needVersatility?• End Users make it into products using avariety of processing techniques:– Extrusion(e.g., S-PVC pipe)– Calendaring– Injection Molding– Stretch blow Molding– Spreading/Coating– Dip, Slush and Roto Molding(e.g., D-PVC pliershandle)09.8.20109Why does PVC Resin needVersatility?The End-User needs PVC resin to be:• Conveyed through process equipment– Can’t clump, melt, stick, solidify, etc.• Rigid.... or Flexible• White... Clear ...or Hold a color• Thin film...or Thick walled...• Flame Retardant; Antistatic; UV resistant..09.8.201010Different End Use = Different PVCResin• Different Molecular Weight (MW) PVCresins are used for different applications– Blow & Injection Molding: Low MW– Flexible Calendaring: High MW• Resins need to work well with additives toget the end product• Through chemistry: The resin is “grown”for its end use09.8.201011Process Chemistry Variations• Variations in resin chemistry stem from a host of differentcomponents or ingredients used to make the variousgrades or types of PVC resin including, but not limitedto:– Primary dispersing agents for proper monomer droplet size;– Secondary dispersing agents for controlling agglomeration ofpolymerized particles;– Buffer agents for pH control of the solution;– Free radical chaininitiatorsto start the polymerization;– Shortstop to terminate polymerization at optimal conversion;– Antioxidants to prevent formation of undesirable peroxides;– Internal reactor coatings to facilitate closed cycle cleanings; and– Anti-static agents to prevent agglomeration of dryresin.09.8.201012H HC CH ClVinyl ChlorideMonomer (VCM)H HC CHClH HC CHClH HC CHClIPoly (Vinyl Chloride) (PVC)H HC CHClPVC Resin Chemistry:The Start09.8.201013PVC ClassificationsFour polymerization processes(i.e., Resin types)are currently being used to manufactureUS PVC resins:– Suspension– Dispersion (emulsion)– Bulk (mass); and– SolutionVI Members do not use the Bulk or Solution Process09.8.201014PVC GradesSubcategories commonly known as “grades ofresin”:• Suspension Resins Examples:– General Purpose: Flexible and Rigid– Specialty– Copolymer• Dispersion Resins Examples:– Micro Suspension Process– Emulsion• "Latex" resin or "Emulsion" resin are common termsthat areused to refer to Dispersion resin.09.8.201015PVC Resin MorphologyThere are four key Product Characteristics to determining theproperties of a particular resin grade and its ultimate end uses.These properties impact a resin’s ability to be stripped andconsequently the resin’s achievable Residual VCM limit (RVCM):•Particle Size(ranges from 1 to 425 microns)•Porosity(amount of pores, or capability of VCM to be removed fromthe particle)•Mechanical Stability(will it sheer or agglomerate?)•Heat Stability(How much heat can be applied during processingwithout product degradation?)Generally, the less Porosity, less Mechanical Stability and the less HeatStability a resin has, the harder the resin is to strip.09.8.201016Stripability and Grades of ResinsPorosity Characteristic example-•General Purpose Suspension Resins:Higher porositythan dispersion, blending or copolymer; necessary forabsorbing the plasticizer so that a free flowing mixtureisformed (extrusion...familiar blue PVC sewer pipe..lessporous than other suspension resins..does not absorbplasticizer as well)•Dispersion Resins: Low porosity; plasticizer notabsorbed; necessary in the formation of a fluid liquiddispersion that can be used in various coating andmolding applications09.8.201017Suspension Process•VCMis polymerized in large scale batchreactors in the presence of:– Water,–Initiators: Soluble in VCM(e.g., organic peroxide)– Suspension Agents(e.g., polyvinyl alcohol, cellulous ethers)• Suspended droplets of liquid VCM are convertedto solid or porous PVC particles• Unreacted VCM is stripped• Polymer is then dried09.8.201018Large Reactor Suspension PVC ProcessReactorsSlurryTankStrippingColumnCentrifugeFluidized BedDryerScreeningSiloRailcar09.8.201019S-PVC Resin Particle300X09.8.201020Internal Morphology09.8.201021Interior S-PVC Particle90% Conversion 3000XNote: Differencebetween M107 &M8260M107: Drives VCM outof particleM8260: MeasuresSurface HAPs09.8.201022Typical S-PVC Properties>.95~0.91~0.68InherentViscosity0.50-0.55>0.550.55-0.60Bulk Densityg/ccHigherMediumLowerPorosityFlexibleExtrusion Pipe,SidingBlow Molding09.8.201023S-PVC Particle Formation• Variables– Dispersant (i.e., Suspension Agent)– Secondary Dispersant• Different Dispersant = Different particle sizes– Temperature: Major effect on Mol Wt.•Higher temps means higher press means particles closer together– Conversion: VCM to PVC• Porosity Decreases & Bulk Density Increases– Agitation:• Increased agitation = smaller particles– Other major issues that impact PVC particle formation:• Local water chemistry• Reactor Design• VCM Supply09.8.201024S-PVC Variables Impact:Color & Heat Stability• Choice of Initiator and Type• Level of Initiator• Temperature of Polymerization• Other Additives• Time and Temperature of Down StreamProcessing– Stripping, Hold Time, Drying09.8.201025S-PVC v. D-PVC• Suspension resin (S-PVC) particle size isdetermine by agglomeration in the reactor and is75 - 450μm in size.• Dispersion resin (D-PVC) has no agglomerationand the particle size is determined bysurfactants and level for emulsion or externalshear for microsuspension. Particle size is 0.2 -2μm.09.8.201026D-PVC: EmulsionDispersion(aka Emulsion)PVC is produced when•VCMis polymerized in batch reactors in the presence of:– Water,–Initiators:Soluble in Watere.g., persulfate, hydr. Peroxide)– Surfactant: “Dispersant” “Emulsifier” - Soap• Soap forms; swollen with VCM;• Water soluble initiator is absorbed• VCM reacts to PVC• Unreacted VCM is stripped• Polymer is then dried• Starts with a “seed” batch to get polymer chains togrow• When resin mixed with liquid plasticizer: “Pasty” liquid resin formed09.8.201027D-PVCEmulsion Particle FormationRVCMDropletSurfactantVCMFreeSurfactantRRRR09.8.201028Dispersion PVC Process09.8.201029D-PVC: MicrosuspensionMicrosuspension PVC is produced when•VCMis mixed with:– Water,–Initiators: Soluble in VCM– Surfactant: “Dispersant” “Emulsifier” - Soap• All raw materials are added to vessel & subjectedto very high shearrates to get small particles– Piston Pump forces material through small office• Small droplets form that are coated with surfactant• Initiation & polymerization occur within the droplets - VCM react toPVC• Unreacted VCM is stripped• Polymer is then dried09.8.201030D-PVCMicrodispersion ParticleFormationPre-dispersed Droplets Surrounded bySurfactant with Initiator InsideR RR RR RR RVCMSurfactantInitiator09.8.201031D- PVC Summary• For Dispersion/Emulsion resin the four criticalproperties are:– Particle size distribution– Surfactant type and level– Degree of agglomeration– Molecular weight• These four criticalproperties affect theliquidPVC used to makeend products:– Rheology– Gelation– Gloss– Clarity– Foam quality– Fusion09.8.201032D-PVC Influencing FactorsParticle Size Surfactant LevelIntensity of MixingMolecular Weight Temperature/AdditivesRheology PSD/Surfactant Level & TypeAdditives/DryingHeat Stability Poly Temperature/Oxygen/Residual Initiator/Impurities/AdditivesGrit Drying & Grinding ProcessFoam Quality Surfactant Level & TypeClarity & Gloss Surfactant Level & TypePSD/Drying & GrindingPSD = Particle Size Distribution09.8.201033Blending Resins• A suspension resin that is– Unique in that its particle size is very fine andvery dense.– Very little porosity compared to conventional PVCsuspension resins.• Low residual suspension agent level• Non-absorptive particles• Advantages– Lower costs– Lower viscosity at low and high shear– Lower gloss• Disadvantages– Lower physical properties– Higher gelation temperature– Possible settling– Lower gloss09.8.201034Copolymer Resins• VCM coupled with a Comonomer– Generally suspension polymerization– Grafted copolymers obtained by VCM polymerization• High bulk density; can be processed at lower temperatures– Low product porosity and lower fusion temperaturedue to the presence of comonomer.– The resulting resin particles are very dense and thediffusion rate of VCM through the resin particles isvery slow.Example:• VCM- Vinyl acetate monomer (VAM) copolymer• Contains 5-15% VAM09.8.201035Recap GoalExplained why there are various PVC resinsProducts from rigid thick-walled pipe to thin flexible gloves to plierhandlesExplained the need for varying recipeingredients and product specificationsSoap; initiators, suspending agents, porosity, heatstability...Because of these varying factors....HAPs emitted duringPVC manufacturing differ across PVCIndustry09.8.201036HAPs & PVC ResinPotential HAP Sources:• Raw Materials– e.g., VCM• Impurities within the Raw Material–e.g.,Methyl chloride, EDC– May carry through the system unreacted• Anti-Foulant -e.g., Formaldehyde• Suspending Agent– e.g. Methanol• Initiator Decomposition Product– e.g.,Cumene09.8.201037HAPs & PVC ResinSee Past Submittal to EPA“VI EPA Submittal 2008-06-26”16 pagesFig 1. Suspension & Dispersion Process Flow Diagrams(page 2 of 16)Table 1: Point Source Emissions (12 of 16)Possible HAP Compound Emission Ranges & Sources (13of 16)Developed before Sec 114 PVC MACT Testing09.8.201038PVC Resin Summary• Four PVC manufacturing processes (e.g., Suspension& Dispersion)• Numerous Grades needed for End UsersTherefore Different HAP emissions across the Industry• HAP Differences can depend on:– End-user’s (customers) Requirements• Processing equipment (e.g., Extrusion)• Applications (e.g., rigid or flexible)• Performance Spec (e.g., anti static; holds color)– Manufacturers Process• Dispersing Agents• Reactor Coatings for Clean outQUESTIONS?