09.8.2010 1

Polyvinyl Chloride Resin

Process Chemistry Variations

EPA/Vinyl Institute Webinar

September 8, 2010
09.8.2010 2

Goal

To explain why various PVC resins, with 

varying recipe ingredients and product 

specifications, emit an assortment of 

hazardous air pollutants that differ across 

the PVC resin manufacturing industry
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Agenda

• 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 Sources
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An Intro

• PVC results from the polymerization of vinyl 

chloride monomer (VCM)

• PVC cannot be processed on its own; therefore 

must be combined with additives

– PVC compounds are based on the combination of 

polymers and additives to produce the necessary formulation for end use

• Broad PVC Classifications under 40 CFR Part 61:

– Suspension (S-PVC) Dispersion (D-PVC)– Bulk Solution
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Suspension PVC Products
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Dispersion PVC Products
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PVC in Art, Hospitals, Homes...

• Cars, Packaging, Wall Covering, Floors....
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Why does PVC Resin need 

Versatility?

• End Users make it into products using a 

variety 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 pliers 

handle)
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Why does PVC Resin need 

Versatility?

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..
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Different End Use = Different PVC 

Resin

• Different Molecular Weight (MW) PVC 

resins are used for different applications

– Blow & Injection Molding: Low MW– Flexible Calendaring: High MW

• Resins need to work well with additives to 

get the end product

• Through chemistry: The resin is “grown”

for its end use
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Process Chemistry Variations

• Variations in resin chemistry stem from a host of different 

components or ingredients used to make the various grades or types of PVC resin including, but not limited to: 

– Primary dispersing agents for proper monomer droplet size;– Secondary dispersing agents for controlling agglomeration of 

polymerized particles;

– Buffer agents for pH control of the solution;– Free radical chain initiators to 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 dry resin.
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H H

C C 

H Cl

Vinyl Chloride Monomer (VCM)

H HC C H Cl

H HC C H Cl

H HC C H Cl

I

Poly (Vinyl Chloride) (PVC)

H H

C C 

H Cl

PVC Resin Chemistry: The Start
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PVC Classifications

Four polymerization processes (i.e., Resin types)

are currently being used to manufacture US PVC resins:

– Suspension– Dispersion (emulsion)– Bulk (mass); and– Solution

VI Members do not use the Bulk or Solution Process
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PVC Grades

Subcategories commonly known as “grades of 

resin”:

• Suspension Resins Examples:

– General Purpose: Flexible and Rigid– Specialty– Copolymer

• Dispersion Resins Examples:

– Micro Suspension Process– Emulsion

• "Latex" resin or "Emulsion" resin are common terms that are 

used to refer to Dispersion resin.
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PVC Resin Morphology

There are four key Product Characteristics to determining the 

properties of a particular resin grade and its ultimate end uses. 

These properties impact a resin’s ability to be stripped and 

consequently 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 from 

the particle)

• Mechanical Stability (will it sheer or agglomerate?)• Heat Stability (How much heat can be applied during processing 

without product degradation?)

Generally, the less Porosity, less Mechanical Stability and the less Heat 

Stability a resin has, the harder the resin is to strip.
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Stripability and Grades of Resins

Porosity Characteristic example-• General Purpose Suspension Resins: Higher porosity 

than dispersion, blending or copolymer; necessary for absorbing the plasticizer so that a free flowing mixture is formed (extrusion...familiar blue PVC sewer pipe..less porous than other suspension resins..does not absorb plasticizer as well)

• Dispersion Resins: Low porosity; plasticizer not 

absorbed; necessary in the formation of a fluid liquid dispersion that can be used in various coating and molding applications
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Suspension Process

• VCM is polymerized in large scale batch 

reactors 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 converted 

to solid or porous PVC particles

• Unreacted VCM is stripped• Polymer is then dried
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Large Reactor Suspension PVC Process

Reactors

Slurry

Tank

Stripping

Column

Centrifuge

Fluidized Bed

Dryer

Screening

Silo

Railcar
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S-PVC Resin Particle

300X
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Internal Morphology
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Interior S-PVC Particle

90% Conversion 3000X

Note: Difference between M107 & M8260M107: Drives VCM out of particleM8260: Measures Surface HAPs
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Typical S-PVC Properties

>.95 ~0.91 ~0.68 Inherent 

Viscosity

0.50-0.55 >0.55 0.55-0.60 Bulk Density

g/cc

Higher Medium Lower PorosityFlexible Extrusion Pipe, 

Siding

Blow Molding
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S-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 Supply
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S-PVC Variables Impact:

Color & Heat Stability

• Choice of Initiator and Type• Level of Initiator• Temperature of Polymerization• Other Additives• Time and Temperature of Down Stream 

Processing

– Stripping, Hold Time, Drying
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S-PVC v. D-PVC

• Suspension resin (S-PVC) particle size is 

determine by agglomeration in the reactor and is 75 - 450 μm in size.

• Dispersion resin (D-PVC) has no agglomeration 

and the particle size is determined by surfactants and level for emulsion or external shear for microsuspension. Particle size is 0.2 -2 μm.
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D-PVC: Emulsion

Dispersion (aka Emulsion) PVC is produced when • VCM is polymerized in batch reactors in the presence of:

– Water, – Initiators: Soluble in Water e.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 to grow• When resin mixed with liquid plasticizer: “Pasty” liquid resin formed
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D-PVC

Emulsion Particle Formation

VCM

R

Droplet

Surfactant

VCM

Free Surfactant

R

R

R 

R
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Dispersion PVC Process
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D-PVC: Microsuspension 

Microsuspension PVC is produced when • VCM is mixed with:

– Water, – Initiators: Soluble in VCM 

– Surfactant: “Dispersant” “Emulsifier” - Soap

• All raw materials are added to vessel & subjected to very high shear 

rates 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 to 

PVC

• Unreacted VCM is stripped• Polymer is then dried
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D-PVC

Microdispersion Particle 

Formation

Pre-dispersed Droplets Surrounded by 

Surfactant with Initiator Inside

R R

R R 

R R

R R 

VCM

Surfactant

Initiator
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D- PVC Summary

• For Dispersion/Emulsion resin the four critical properties are:

– Particle size distribution– Surfactant type and level– Degree of agglomeration– Molecular weight

• These four critical properties affect the liquid PVC used to make 

end products:

– Rheology– Gelation– Gloss– Clarity– Foam quality– Fusion
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D-PVC Influencing Factors

Particle Size Surfactant Level

Intensity of Mixing

Molecular Weight Temperature/AdditivesRheology PSD/Surfactant Level & Type

Additives/Drying

Heat Stability Poly Temperature/Oxygen/

Residual Initiator/Impurities/Additives

Grit Drying & Grinding ProcessFoam Quality Surfactant Level & TypeClarity & Gloss Surfactant Level & Type

PSD/Drying & Grinding

PSD = Particle Size Distribution
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Blending Resins

• A suspension resin that is 

– Unique in that its particle size is very fine and very dense. – Very little porosity compared to conventional PVC 

suspension 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 gloss
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Copolymer 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 temperature 

due to the presence of comonomer. 

– The resulting resin particles are very dense and the 

diffusion rate of VCM through the resin particles is very slow.

Example:• VCM- Vinyl acetate monomer (VAM) copolymer• Contains 5-15% VAM
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Recap Goal

Explained why there are various PVC resins

Products from rigid thick-walled pipe to thin flexible gloves to plier 

handles

Explained the need for varying recipe 

ingredients and product specifications

Soap; initiators, suspending agents, porosity, heat stability...

Because of these varying factors....HAPs emitted during 

PVC manufacturing differ across PVC Industry
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HAPs & PVC Resin

Potential 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., 

Cumene
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HAPs & PVC Resin

See Past Submittal to EPA

“VI EPA Submittal 2008-06-26”

16 pages

Fig 1. Suspension & Dispersion Process Flow Diagrams 

(page 2 of 16)

Table 1: Point Source Emissions (12 of 16)Possible HAP Compound Emission Ranges & Sources (13 

of 16)

Developed before Sec 114 PVC MACT Testing
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PVC Resin Summary

• Four PVC manufacturing processes (e.g., Suspension & Dispersion)• Numerous Grades needed for End Users

Therefore 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 out

QUESTIONS?