12.5 Polyvinyl chloride - Treccani · Polyvinyl chloride (PVC) is one of the most widely used plastic materials in the world. In 2004, in Europe, some 6 million tonnes was transformed

12.5.1 Introduction

Polyvinyl chloride (PVC) is one of the most widelyused plastic materials in the world. In 2004, in Europe,some 6 million tonnes was transformed intomanufactured goods and around 30 million tonnes wasused worldwide.

PVC is a thermoplastic polymer, which is theproduct of the polymerization of the vinyl chloridemonomer (VCM), and is made up of 57% chlorine, theremainder being carbon and hydrogen.

Historical summaryVCM and its ‘metamorphosis-polymerization’ into

white PVC powder originated in Germany, in the years1835 and 1860, as a result of the work of H.V.Regnault and A.W. Hoffman, respectively (Regnault,1835; Hoffman, 1860). In 1912, F. Klatte, on behalf ofChemische Fabrik Griesheim-Elektron (Klatte, 1912),patented the synthesis of VCM from acetylene(available in significant quantities, since it was nolonger used for lighting) and hydrogen chloride. In1914, the Chemische Fabrik (Klatte, 1914), laterincorporated into Hoechst, patented the use ofperoxides to accelerate the reaction from VCM toPVC. The hypothesis behind using PVC was for it tosubstitute celluloid (nitrate of cellulose plus camphor),which was highly inflammable, in photographicapplications. This first attempt at the industrialdevelopment of VCM and its product PVC was notsuccessful and the patents on which their productionwas based were allowed to lapse. In 1930, still inGermany, the industrial development of PVC wasrevived thanks to H. Fikentscher (Mark et al., 1937),of IG Farbenindustrie, who adopted the technology ofpolymerization in emulsion, which was derived fromthe production of butadiene rubber, which was alreadyin use. The first PVC production plant to operate using

this technology was built in 1936 by Carbide-CarbonChemical in the United States and used VCM obtainedas a by-product of the production of1,2-dichloroethane (DCE). For PVC to be developedindustrially there were still the problems to be solvedof its thermal decomposition and its processibility intransforming equipment at high temperatures (around150°C). In 1934, Carbide-Carbon Chemical (Doolittle,1934) patented lead salts as thermal stabilizers of PVCand during the same period W. Semon (1933) of BFGoodrich patented the use of plasticizers to producePVC-based blends capable of replacing rubber.Plasticizers, such as the 2-ethylhexyl phthalate used bySemon, are liquids with a high boiling point capable ofmelting PVC by means of heat. At ambienttemperature, these solutions are resilient, rubberysolids. These first significant and fundamental steps inthe industrial production of PVC, of its thermalstabilizers and of the plasticizers capable of facilitatingthe processing of PVC and enhancing the physical andperformance characteristics of the products obtainedfrom it were followed, in the period from 1935 to1940, by numerous further industrial developmentsboth in the United States and in Europe. Thesedevelopments of PVC and of its additives took placeindustrially, against the background of an urgent needduring Second World War for materials to replacerubber and metals, in Germany, Great Britain and theUnited States with the production and testing underworking conditions of PVC-based electrical insulationand rigid and flexible pipes. Thus began the initiallytentative but then accelerated introduction of PVCproducts into all sectors of civil and industrial life inEurope and the United States.

The spread of PVCAt the beginning of the first decade of this

century, in Europe, about 50% of all plastic pipes

863VOLUME II / REFINING AND PETROCHEMICALS

12.5

Polyvinyl chloride

for waste water from buildings and 20% of pipesfor drinking water were in PVC and, moreover, thesheathing of around 75% of all electrical andtelephone cables in buildings was made up ofPVC-based blends. Bags and tubes fortransfusions, oxygen tents and single-use gloves inhospitals everywhere were predominantly in PVCand similarly food packaging (for meats, cheeses,etc.) was in part PVC-based. Windows and shuttersin PVC were widely used because of their excellentthermal insulation, their long maintenance-freeoperational life, and their resistance to burning.

The growth in consumption of PVC in Europe since1970 is shown in Fig. 1. This growth has taken place inparallel with the construction of new civil and industrialbuildings and the increase in services available inevolved societies.

As shown schematically in Table 1, in the majorityof the end-user application sectors, PVC products havea long operational life, with the retention over thatperiod, of the required chemico-physical andperformance characteristics.

The broad spectrum of applications of PVC withinnumerous industrial sectors is due to itschemico-physical composition, which makes it easy tomix with a vast number of additives, forming strongphysical bonds. This miscibility with the formation ofstrong and stable bonds, which is a particularcharacteristic of PVC compared with the majority ofother polymeric materials, makes it possible to obtainboth rigid and flexible products in PVC, with propertiesdiffering according to the requirements of theapplication, but having in common a high degree ofimperviousness to chemical attack and an inherentresistance to both the ignition and propagation of flames.

The properties of the many and diverse PVCproducts include, for example: a) hardness andresilience, such as is found in pipes for transportingwater which have an operating life in excess of 50years; b) high transparency, balanced permeability andsterility, as in rigid and flexible packaging for foods andmedicines; c) shiny and opaque surfaces, such as inraincoats, in credit and identity cards, and in luggage;d) compatibility with human tissue and liquids, such asin transfusion bags and tubing for extracorporeal fluidcirculation.

All the applications, starting with those in the mostcritical sectors, such as medical devices and foodpackaging, are tightly regulated and controlled throughnational and international standards and by laws, towhich PVC products conform even obtaining widemargins of safety. Apart from the obligatoryobservance of the law, decades of usage of PVC

864 ENCYCLOPAEDIA OF HYDROCARBONS

POLYMERIC MATERIALS

0

1

2

3

4

5

6

7

19751970 1980 1985 1990 1995 2000 2005

mil

lion

t/ye

ar

time (year)

Fig. 1. The growth in consumption of PVC in western Europesince 1970 (Centro di Informazione sul PVC, Milan; PlasticConsult, Milan).

Categories based on lifespan of articles Total ofmade of PVC

Articlesarticles %

PackagingShort (�1 year) Toys 10

Medical applications

Flexible pipesMedium (1-10 years) Shoes 15

Wallpaper

FlooringLong (10-20 years) Tarpaulins 25

Profiles

Rigid pipesVery long (�20 years) Windows 50

Cables

Table 1. Distribution of operational lifespans of PVC articles (Centro di Informazione sul PVC, Milan)

products in a multiplicity of applications, in the mostdisparate and differing environmental conditions allover the world, have demonstrated the suitability andeffectiveness of the performance of these products.

The discussion which follows relates essentially tothe average European industrial and commercialenvironment. The principal factors which emerge fromthis analysis are, however, applicable to other areas ofproduction.

12.5.2 Industrial production of PVC

The polymerization reaction of VCM to PVC occursexclusively through a radical mechanism, by meansof free radicals. It progresses by the formation of aradical on the VCM molecule and the subsequentand rapid addition of numerous units of VCM to theradical, which always remains at the extremity of thegrowing polymer chain. The polymerization thenproceeds by the reaction of the growing radical withanother radical or its transfer to another monomericunit, with the formation, in each case, of a moleculeof PVC polymer. The simultaneous and continuousappearance of numerous initiating molecular actions– propagation, transfer and termination of thegrowing radicals – creates the molecules of PVCpolymer which, because of the radical reactionmechanism, are characterized by a probabilisticdistribution of molecular lengths. Thepolymerization reaction of the VCM is exothermicand the PVC polymer produced is insoluble in themonomer from which it originates.

The industrial technologies for the polymerizationof VCM have, therefore, had to solve the followingproblems:• Steady removal of the heat of polymerization, with

the purpose of achieving controlled rather thanexplosive production processes.

• Control of the morphology of the PVC polymer,which separates itself from the medium of theVCM reaction in which it forms and in which it isvirtually insoluble, so as to avoid the formation ofnon-homogeneous agglomerations of PVC withvarying densities.

• Conferring to the PVC polymer, which is obtainedthrough the production processes, the chemical,physical and morphological characteristics whichwill make it suitable for, and compatible with, theindustrial operations of being mixed with additives,processed and transformed into the many anddiverse products intended for the application sectors. The VCM polymerization technologies, which �

as a result of the work in the development and growthof PVC � have become the most widely used

industrially, are the polymerization of VCM in anaqueous suspension and polymerization of VCM in anaqueous emulsion. Around 95% of PVC currentlybeing marketed is obtained from polymerization insuspension and in bulk and the remaining 5% frompolymerization in emulsion. Bulk polymerization ofVCM (that is, in the absence of compounds other thanVCM) was significantly developed industrially inFrance in the 1970s and 1980s and currently the PVCproduced by large-scale polymerization accounts forseveral percentage points of the total PVC produced;these products have substantially the same targetapplications as PVC obtained in suspension. Thepolymerization of VCM in solution (in media that aresolvents of VCM and PVC) belongs to the history ofpolymerization technology development and has noindustrial relevance. Each VCM polymerizationtechnology, although it takes place by means of aradical mechanism, uses specific and differingprocesses: to achieve the control and removal of thereaction heat; to influence the morphology anddimensional distribution of the particle-granules of thepolymer; and to impart to the PVC granules propertiesthat make them suitable for subsequent specificprocesses and applications. Below are discussed andexamined the production technology and the PVCproducts obtained in an aqueous suspension(suspension PVC), which form the basis for most ofthe PVC used in all application sectors.

Industrial process for the polymerizationof VCM in aqueous suspension

Process and product As VCM is virtually insoluble in water, its

polymerization in an aqueous suspension is carriedout with small drops of VCM dispersed in acontinuous medium made up of water whichenables removal of the reaction heat and generatesregular polymerization in isothermal and controlledconditions. As mentioned above, most PVCproduced and consumed in Europe and the UnitedStates is obtained through the polymerization insuspension of VCM in industrial processes in whichVCM is dispersed in water in reactor vessels. Theseprovide the system, made up of water, VCM and theadditives, with the energy needed to maintain thesystem in turbulent motion. The radicalpolymerization, in each drop of VCM in theaqueous suspension, is regulated and controlled by:• The production of radicals and the removal of the

heat from the reaction, regarding the reaction speed.• A combination of mechanical energy (provided by

the agitation of the VCM suspension in water) andadditives, such as the primary suspending agents


POLYVINYL CHLORIDE


POLYMERIC MATERIALS

(that have stabilizing and surfactant actions whichinfluence the dimensional distribution) and thesecondary suspending agents (which influence the internal morphology), concerning the physical characteristics of the final particles ofpolymer, usually referred to as granules.

• The reaction temperature, with regard to themolecular weight of the PVC produced.The PVC polymer suspension is fairly unusual in

comparison with other polymers inasmuch as itsphysical properties, and in particular the dimensions ofthe granules and their internal morphology whichforms during the polymerization of VCM, conditionthe subsequent phase of processing and transformingthe particle-granules into manufactured products. Thetypical dimensional distribution of a commercialsuspension PVC is shown in Fig. 2, while Figs. 3 and 4illustrate some examples of external and internalmorphologies typical of the particle-granules of asuspension PVC.

In current industrial practice, the processes ofPVC production in an aqueous suspension make itpossible to directly obtain, by rigorously controlling

the process: polymer particle-granules 95% of whichhave diameters of between 100 and 200 mm(dimensional distribution like that in Fig. 2);particle-granules with a uniform internalmorphology and porosity varying between 20 and40%; differing molecular weights and molecularweight distributions depending on the

0 100 15050 200 250 300 350

frac

tion

in v

olum

e (%

)

diameter (µm)

0

0.4

0.8

1.2

1.6

2.0

2.4

2.8

Fig. 2. Dimensional distribution of the particle-granules ofsuspension PVC (Ineos Vinyls, Italy).

Fig. 3. Dimensions and external morphology of suspension PVC particle-granules (Ineos Vinyls, Italy).

time/temperature profile adopted in thepolymerization process.

The temperatures adopted for the industrialpolymerization of VCM in an aqueous suspension arenormally between 50 and 70°C; depending on theinitiator used and the heat exchange capacity of thereactor vessel, the initial polymerization temperaturecan rise in a non-uniform manner within the dropswhere the reaction takes place. The fundamentalphysical properties of VCM and PVC which affect anddetermine how the polymerization process takes placeare: a) the vapour pressure of the liquid VCM, whichwithin the usual temperature range of industrialpolymerization is between about 7 and 10 bar (hencepolymerization is carried out in pressurized reactorvessels); b) the insolubility of the PVC polymer inVCM; c) the solubility of VCM in PVC, which at thenormal temperatures of industrial polymerization isaround 30%; d) the significant contraction in volumewhich accompanies the conversion of VCM into PVC(at 50°C the density of VCM is 0.860 g/cm3 and thatof PVC is 1.393 g/cm3).

Because of the solubility of VCM in PVC and theinsolubility of PVC in VCM, the polymerization ofVCM in each drop of the aqueous suspension can bedescribed in two phases. One phase consists of themonomer with minute quantities of polymer (phasediluted in the polymer). The other consists of themonomer dissolved in the polymer (phaseconcentrated in the polymer; Talamini et al., 1988).This concentrated phase, made up of PVC in which30% of VCM has dissolved, has a glass transitiontemperature of around �70°C and at normalpolymerization temperatures is a highly viscous liquid(Bueche, 1962).

Fig. 5 shows a diagram of the process ofpolymerization in suspension of VCM and Fig. 6 showshow the industrial production process of PVC, togetherwith the linked and integrated industrial production ofVCM, takes place in a closed industrial system. Afterfeeding in the raw materials (ethylene, chlorine, andhydrogen chloride) and the additives, the PVC isproduced, then following appropriate processing andpurification, the waste gases and liquids are expelled.


POLYVINYL CHLORIDE

Fig. 4. Dimensions and internal morphology of suspension PVC particle-granules (Ineos Vinyls, Italy).

Kinetics of polymerization, molecular weight and tacticity

The kinetics of the radical polymerization of VCMinto PVC is common to all radical polymerizationprocesses. In summary, it includes, as shown in Table 2,the reactions, each one with its specific rate constant k,of the decomposition of the initiator I into radical I�,the start of polymerization by the addition of radical I�to the monomer M and the formation of radical IM�.The latter is propagated to become the macroradical�M� through the subsequent addition of monomericunits until the chain is transferred to the monomer M(reaction 4), and terminates through the interaction(in diluted and concentrated phases, reactions 5 and 6respectively) between two macroradicals with theformation of the polymer molecules P.

Reaction 3 is the propagation stage ofpolymerization and the specific rate constant k3 is

equal to k2. Reaction 4 is very important in thepolymerization of VCM because the transfer of themacroradical �M� to the monomer conditions andcontrols the molecular weight of the polymer.Termination reactions 5 and 6 take place in the twophases, diluted and concentrated in polymer, inwhich the polymerizing system separates outduring polymerization. In the diluted phase, theVCM is almost totally pure, whereas in theconcentrated phase (also called the gel phase) theconcentration of VCM is 25-30%, while theremainder is polymer. Once the conversion ofVCM into PVC reaches around 75% completion,the diluted phase ends and the concentration of themonomer in the gel phase diminishes aspolymerization proceeds (Davidson and Gardner,1983). Based on this model, it has been found(Talamini, 1966) that the velocity of the


POLYMERIC MATERIALS

VCMrecovery

VCMstrippingcolumn

PVCstorage

steamheatexchanger

driersblowdownvessel

centrifugePVC slurry

PVC slurry

VCM gasVCM

water, initiator,suspending agents

reactor

Fig. 5. Diagram of the process forthe polymerization in suspension of VCM (Ineos Vinyls, Italy).

incinerator

incineratorstripping ofchlorinatedcomponents

liquid effluents

hydrogen chloride

hydrogenchloride

oxigen

ethylene

chlorine

water

gas effluents

raw materials monitored area product

waterfiltration

biologicaltreatment

sludgesincinerator

DCE

DCE VCM PVC

PVC polymer

DCE

Fig. 6. Diagram of the integrated production process of VCM and suspension PVC in a closed industrial system (Ineos Vinyls, Italy).

polymerization reaction Vpolym can be described,with a good degree of approximation, by the Eq.:

Vpolym�V0polym (1�q) �e(k1t/2)

where t is the time, q is the autocatalysis factor and V0polym is the velocity of polymerization in the diluted phase at time zero in relation to a monomer concentration M0.

The speed of polymerization in the diluted phase at time zero is given by:

1 k2V0polym�kR01/2M0 with k �

12 �123�2 k5

and R01/2�(2 fm k1I0)

1/2

where fm is the efficiency of the initiator introduced(since not all the radicals of the initiator becomepolymeric macroradicals) and I0 is the concentration ofthe initiator at time zero. When the processes aretraditional and carried out with initiators that produceradicals at a constant rate during polymerization, thespeed of polymerization of VCM in an aqueoussuspension and the consequent production of heatreach a maximum and then decrease as shown inFig. 7. The corresponding profiles of the temperatureand pressure trends in the reactor vessel and thetemperature of the water in the reactor vessel coolingjacket are presented in Fig. 8.

Currently, the industrial processes for thepolymerization of VCM in an aqueous suspensionare achieved at a constant reaction rate through theuse of combinations of initiators which modulate thespeed of production of the radicals in inverseproportion to the overall speed of polymerization.The constant velocity is that (or close to that) allowedby the polymerization reactor vessel’s maximumcapacity for disposing of the heat, under theconditions in which it is possible to obtain granules

of PVC in suspension with the morphological andchemico-physical characteristics desired.

The average molecular weight of the PVC polymer,expressed as the numeric average

12

DPn degree ofpolymerization (number of structural units making upthe polymer chain), is controlled by reaction 4 (seeagain Table 2), the transfer of growing macroradicalsto the monomer, and is dependent on thepolymerization temperature; this is obtained, with agood degree of approximation, by the Eq.:

12

DPn�k3�k4�9.2�10�3e(7,400�RT )

where the rate constant k is expressed in l/(mole·s)and the degree of polymerization

12

DPn, virtuallyindependent of the monomer-polymer conversion,depends only on the polymerization temperature T(in K); at 323 K (50°C), the numeric averagemolecular weight

12

MWn (12

MWn� 62.5 12

DPn) typically isequal to 65,000 and at 343 K (70°C) to 35,000. It ispossible to reduce

12

DPn by the addition duringpolymerization of transfer agents (e.g. thioesters andisobutyraldehyde) onto which the growing radicalchains (macroradicals �M�) are transferred, or toincrease it with reticulating agents (for example,diallyl maleate and phthalate). Nevertheless, chainand reticulating transfer agents are not widely usedindustrially because the characteristics of the PVCproduced depend primarily on the morphology,porosity and structure of the particle-granules. Eventhe tacticity and crystallinity of the PVC polymersproduced, as with the molecular weight, depend onthe polymerization temperature. The stericconfiguration of the monomeric unit which enters thegrowing polymer chain in reaction 3 (see again Table2) is not influenced by the steric layout of the activeterminal macro-radical group and as a consequencethe distribution of the lengths of the tactic sequencesof the PVC in suspension, as for PVC obtained withother technologies, it is of a statistical type with a


POLYVINYL CHLORIDE

0

1

2

3

4

5

6

0 100 200 300 400 600500

rate

of

poly

mer

izat

ion

time (min)

Fig. 7. Time-related rate of polymerization in suspension of VCM (Ineos Vinyls, Italy).

[1] I k1 2I��

[2] I��M k2 IM��

[3] IM��M k3 �M��

[4] �M��M k4 P �M��

[5] �2M� k5 P��(into VCM)

[6] �2M� k6 P��(into PVC/VCM)

Table 2. Schematic of the radical polymerizationreactions of VCM into PVC

degree of syndiotacticity, which diminishes as thepolymerization temperature increases from 0.60 at0°C to 0.55 at 55°C (Talamini and Vidotto, 1967).

Dimensional distribution of the particle-granules ofsuspension PVC and their internal morphology

The particle-granules of PVC in suspension arederived from the drops of liquid VCM dispersed inwater, where the polymerization takes place. As aresult of the energy supplied by means of specificagitators in polymerization reactor vessels, the VCMis dispersed in an aqueous system maintained inconditions of turbulent motion. The surface tension atthe interface between the VCM and the water ismodified by small quantities of agents, called primarysuspending agents, which also have the effect ofstabilizing and protecting the drops, keeping themseparate during the collision phase where they mightcoalesce. On the other hand, during polymerization,the interfacial tension between the VCM and the PVCwithin the drops is modified by surfactant agents,called secondary suspending agents, which also havethe effect of stabilizing and protecting themicroparticles of polymer which form within thedispersed drops. The drops of VCM dispersed inwater contain the dissolved initiator which, indecomposing, produces radicals. When the initiator(or initiators) begins to decompose, the conversion ofVCM into PVC is triggered. The heat ofpolymerization, equal to 30 kcal/mole, is removed bymeans of cold water which flows over the sides orthrough the jacket of the reactor vessel and/or bymeans of the VCM which evaporates, condenses, thenturns back into the drops where the reaction takesplace. When the required monomer-polymerconversion level (usually around 90%) has beenreached, the non-polymerized VCM is removed andrecovered, the particle-granules of PVC are separated

from the water in which they were dispersed by meansof a centrifuge and then dried to eliminate the residualwater (equal to about 15%) in rotating or fluid bedovens. The mass of particle-granules of suspensionPVC thus obtained is the PVC product destined to beprocessed into manufactured items.

The dimension of the particle-granules of polymer,their internal morphology and their porosity aredetermined and controlled both by the energy and itsdistribution as supplied in the reactor vessel by meansof the agitating system, and by the nature andconcentration of the primary and secondarysuspending agents in the polymerizing system.Although all the production processes of PVC insuspension are basically similar, the system fordistributing the energy throughout the reactor vessel(which can be up to 250 m3 in size), the primary andsecondary suspending agents and the initiators useddiffer significantly and reflect the specific abilities ofthe various producers. The average diameter d of thedrops of VCM dispersed in the water, in a systemcontaining various surfactant and stabilizing agentsand in a condition of equilibrium between dispersionand coagulation, depends on the mechanical energysupplied by the agitation; this energy is connected tothe number of revolutions N of the agitator with adiameter D, as well as to the specific gravity r and thesurface tension s of the dispersed phase by theequation (Johnson, 1936):

d �gD(rN2D3�s)0.6

where g is the interfacial tension which exists betweenthe VCM-specific phase and the water-specific phase.The equation is derived from the balance of the forcesoperating on the drops dispersed in a field of turbulentmotion. On the one hand there is a tangential actionwhich has the effect of breaking the drops and on theother the surface tension s, whose effect is to maintain


POLYMERIC MATERIALS

0

10

20

30

40

50

60

70

80

100

90

0 50 250200150100 350300 400

tem

pera

ture

(°C

)

pres

sure

(kP

a)

time (min)

temperature of cooling watertemperature of the reactorpressure of the reactor

400

1,200

1,100

1,000

900

800

700

600

500

Fig. 8. Reactor vesseltemperature and pressure profiles for polymerization of VCM in suspension and temperature profile of the cooling water (Ineos Vinyls, Italy).

their integrity and identity. The dimensionaldistribution of the VCM drops and, at the end ofpolymerization, of the particle-granules of PVC insuspension, is correlated with the average diameterthrough the Weber number rN2D3�s, which is anadimensional parameter containing the physicalcharacteristics r and s of VCM and of the dispersedphase and the mechanical parameters (N and D) of theagitator, in a given system in turbulent motion.

Qualitatively, the formation of the particle-granulesof PVC in suspension can be divided into two parts:the first is when the VCM phase breaks up in dropsdispersed in water with the initial formation ofparticle-granules in the polymerization reactor vessel;the second consists of the construction-consolidationof the supporting structure of the particle-granules andthe development of their porosity.

Dispersion of the VCM in water and the initialformation of the particle-granules of PVC

At the start of the process, the mechanical energy,supplied to the water-VCM system by the reactorvessel (agitator, baffles), disperses the VCM intodrops which have diameters of between 5 and 50 mm.The dispersion of the monomer phase is assisted bythe presence in the water-VCM system of suspendingagents (primary) with surfactant and stabilizingactions, which are absorbed in the water-monomerinterface. This absorption reduces the interfacialtension between the water and the VCM andconsequently the energy required to sub-divide indrops the VCM phase. The most commonly usedsuspending surfactant-stabilizing agents are polymersand copolymers, characterised by an appropriatebalance of hydrophilic and lipophilic groups. Once

they have been absorbed into the interface of the VCM drops, the elastic properties of thesurfactant-stabilizing polymer provide goodprotection against coalescence of the VCM particleswhich, in a turbulent motion regime, are prone tofrequent collisions. The dimensions of the VCMdrops depend on the agitation the chemical natureand the concentration of the surfactant-stabilizingagents present and added to the system. In the firstphase of the polymerization process, in the presenceof high concentrations of suspending agents with astrong stabilizing effect and a moderate surfactanteffect, and with the adoption of relatively gentleagitation systems in the reactor vessel (still in aturbulent regime), the relatively large (30-40 mmdiameter) and stable monomer drops have a goodprobability of maintaining their identity, as illustratedin scheme 1 of Fig. 9.

The procedure of polymerization of VCM intoPVC heavily modifies the VCM-H2O interface, sincethe suspending surfactant-stabilizing agents (based, forexample, on polyvinyl alcohol, vinyl acetate-vinylalcohol copolymers and various esterified celluloses)are increasingly absorbed into the interface of thedrops, with a consequent increase in the bonding ofthe PVC and of the viscosity of the drops. In thiscondition, the stabilizing action having diminished, ata monomer-polymer conversion level of around 10%,the monomer-polymer drops aggregate and coagulatein a regular fashion, forming the final particles with adiameter of between 100 and 200 mm, from which thefinal polymer granules are produced.

In low concentrations of suspending agents with astrong surfactant effect and a moderate stabilizingeffect, and with vigorous agitation in the reactorvessel, the initial dimensions of the VCM drops arerelatively small (diameters of between 10 and 20 mm)and in the first phase of the polymerization processthey are in dynamic equilibrium between breakage andcoalescence, as illustrated in scheme 2 of Fig. 9. Inthis instance, the controlled aggregation-coagulationof the drops polymerizing into particles with diametersbetween 100 and 200 mm occurs when the physicalstructure of the PVC, which forms inside the drops,increases the viscosity of the polymerizing system insuch a way as to prevent further breakage andcoalescence (Smallwood, 1989).

Once the agglomeration of the polymer-monomerdrops has taken place, the number of particle-granulesof polymer remains constant until completion of thepolymerization reaction. Those polymerizations whichcorrespond to scheme 1 of Fig. 9 produce sphericalparticle-granules with low porosity and high apparentdensity. In extreme cases, the initial drops of VCM areso stable that no aggregation process takes place. With


POLYVINYL CHLORIDE

� 5% � 10% � 15%0

VCM

VCM-PVCconversion

scheme 1

scheme 2

VCM

Fig. 9. Diagrams of the aggregation of VCM particles duringsuspension polymerization (Ineos Vinyls, Italy).

very vigorous agitation and suspending stabilizingagents that are not very effective (scheme 2 of Fig. 9)particle-granules of PVC which are more porous andwith a more open structure are obtained as a result of asignificant process of aggregation in a system initiallyin a high state of dispersion.

Construction of the supporting structure within thedrops and within the particle-granules during theprocess of VCM polymerization

Since the density of PVC is greater than that of itsVCM monomer (1.393 g/cm3 against 0.860 g/cm3 at50°C), the drops of VCM in suspension contractduring polymerization. If the contraction werecompleted, the particles of PVC produced would haveno internal porosity. If the contraction were preventedcompletely, the particles of polymer would have aporosity of up to 40%; intermediate porosities areobtained through intermediate contractions. At verylow monomer-polymer conversions (less than 1%), thedrops of VCM contain a high number ofelectrostatically stabilized microparticles of PVC(with diameters of some tenths of a mm), which moveby means of Brownian motion. As the conversionincreases these microparticles grow in size thanks to aseries of successive aggregations. The probable causeof this aggregation lies in the fact that themicroparticles of PVC, swollen by VCM, have a lowglass transition temperature (about �70°C), being, infact, viscous gels and when they collide, theyaggregate creating increasingly larger particles. Aspolymerization proceeds, the dimensions of thepolymeric microparticles increase and the free VCMfraction diminishes. The result is the formation of acontinuous network of microparticles of PVCaggregated within the drops, as schematically shownin Fig. 10. The construction of an adequate supportingreticulated structure, in the majority of industrialprocesses, achieves a conversion of VCM into PVC ofaround 10%, which is also that at which the drops of

VCM-PVC in suspension complete theiragglomeration, forming the particles from which thefinal granules of polymer originate. If the structuresaggregated within the drops of polymerizing VCM arestrong enough, they prevent any further contraction ofthe drops and the aggregates of microparticles wherepolymerization continues and is completed. The lowerthe conversion at which the formation of a strongstructure of particles within the drops takes place, thehigher the porosity of the final particle-granulesproduced.

The quantity and the stability of the PVCmicroparticles within a polymerizing drop are alsoinfluenced by:• The additives soluble in the VCM (secondary

suspending agents) which, due to their surfactantand stabilizing effects on the VCM/PVC interface,modify the supporting network-structure within thedrops and hence the porosity of the final granules.

• The agitation and the energy given to theaqueous solution polymerizing system; thegreater the agitation, the more intensive is thestress on the polymeric microparticles whichform a stable low conversion network and resultin more porous particle-granules of polymer. Theincrease in porosity due to the intensity of theagitation is well-known in the industrial practiceof polymerization in suspension of VCM(Visentini, 1999).

• The polymerization temperature as it rises alsocauses the dimensions of the polymericmicroparticles to increase with the consequentformation of weaker supporting network-structureswhich are less able to resist contraction. Hence theparticle-granules of polymer that are produced arerelatively less porous.Once the supporting network-structure made up of

microparticles has formed within a drop, the growth ofthe polymeric microparticle continues as polymerizationprogresses with the porous part of the reticulatedstructure gradually being filled. The interior of eachparticle-granule of PVC contains polymeric particlesswollen by VCM, and less and less non-polymerizedfree VCM and H2O. In these conditions themicroparticles within the particle-granules are subjectedto powerful capillary actions, which tend to fuse them,thus reducing their porosity. The addition in this phaseof polymerization of a specific surfactant which reducesthe capillary forces is among the most commonly usedtechnologies for significantly increasing the porosity ofthe PVC produced.

TechnologyIn the process of polymerization in suspension, the

liquid VCM is initially dispersed uniformly in water,


POLYMERIC MATERIALS

� 20%� 2% � 40% � 90%

VCM VCM VCM water water

VCM-PVC conversion

Fig. 10. Construction of the supporting structure in the dropsof VCM as the suspension polymerization progresses (IneosVinyls, Italy).

in which it is not easily soluble, throughout the reactorvessel, as a result of the mechanical energy distributedthrough the water-VCM system. Small quantities ofsurfactant-stabilizing substances added to the system,which attach themselves to the VCM-water interface,facilitate the initial dispersion of the VCM in the waterand contribute to stabilizing the particles of dispersedVCM, enabling them to maintain their individualityeven in multiple collision conditions, such as occur inturbulent motion regimes. Other small quantities ofsurfactants which attach themselves to the interfacebetween VCM and PVC in the polymerizingmicroparticles within the drops, at a given temperatureand with a given amount of agitation, regulate thenumber and the coagulation of these PVCmicroparticles as the polymerization progresses,influencing the internal physical structure (porosityand accessibility) of the particle-granules ofsuspension PVC produced.

The industrial process of polymerization insuspension of VCM is the result of about 50 years ofresearch and development. It is currently carried out inreactor vessels lined with stainless steel, withcapacities in excess of 200 m3, equipped with specificagitation systems (agitators with paddles at differentheights and appropriately placed baffles) and capableof removing the heat from polymerization usingtraditional methods (cooling jacket, injection of cooling water into the reactor vessel) and with acondenser for the VCM, which evaporates and isreturned into the drops where the reactions take place.These reactor vessels ensure uniform agitation of theentire reaction system in conditions of turbulentmotion, operating in a closed cycle handling hundreds,if not thousands, of batches (thanks to anti-foulingreactants which keep all the internal surfaces clean soas to allow an even heat exchange) and reachproductivity levels of up to 700 t/m3/yr.

The overall result of these years of research anddevelopment is that a batch process with phases in anopen reactor vessel, which was the way VCM waspolymerized in suspension originally, has beentransformed into a continuous closed-cycle process,optimized in terms of control, uniformity of theproduct and productivity.

Environment and safety Currently, in Italy and in the rest of Europe,

industrial production of VCM and suspension PVCtakes place in closed systems in integrated productionfacilities (see again Fig. 6). The raw materials, chlorine,ethylene, oxygen and hydrogen chloride, enter theclosed system and particle-granules of the PVCpolymer product leave it. Within a closed system,chemical reactions take place, along with processes to

transform the intermediate 1,2-dichloroethane andVCM, resulting in the production of PVC polymer. Theprocesses within a closed system are automated andremote controlled. Moreover, the reactor vessels andthe loading and transporting systems operate in closedcycles; the operators do not come into contact with theintermediate 1,2-dichloroethane and VCM, which aresubstances known to be toxic, whereas the PVCcoming out of the closed system is inert and practicallyfree from VCM (the content is around 1 ppm). Theby-products of the industrial production of PVC are recovered and processed to obtain raw materials andenergy; the gaseous wastes are collected, treated andfinally incinerated; liquid wastes are collected, purifiedand filtered to remove the solids and finally undergobiological treatment, the mud products from which areincinerated. The atmosphere within the closed systemis subjected to continuous checking of the VCMcontent. There are fixed points for taking samples ofthe atmosphere for chromatographic and spectrometricanalysis, repeated at frequencies of minutes, and thereis personal equipment which measures the operators’exposure to VCM during their period of work in theplant; assessments are made of the 1,2-dichloroethanein the atmosphere. The operators who work in themonitored area of the closed system are subjected toperiodic medical examinations and the data relating totheir exposure are monitored by the health authorities.The adoption of specific technologies and operatingprocedures in this production environment, has had thefollowing results: the incinerators for the waste andby-products have dioxin emissions of less than 0.1 ng/m3;the average exposure to VCM by operators in VCMand suspension PVC production plants is between 10 to20 times lower than the 3 ppm required by Europeanlaw; the PVC polymer that comes out of the closedsystem and is used to manufacture the differentproducts made from PVC has a residual VCM contentof around 1 ppm and is inert.

12.5.3 Suspension PVC products,transformation into articlesand application sectors

Suspension PVC productsPolymerization in suspension of VCM, carried out

with the above-described technologies, makes itpossible to obtain products with differing averagemolecular weights, internal morphologicalcharacteristics and dimensional distributions of theparticle-granules. The principal physical and chemicalfactors responsible for this diversity are the temperatureof polymerization, the additives introduced into thepolymerization process and the energy supplied to the


POLYVINYL CHLORIDE

VCM/PVC reaction system dispersed in water in thepolymerization reactor vessels. The suspension PVCproducts, commonly used for industrial transformationinto articles intended for the many application sectors,are obtained from the polymerization of VCM carriedout in temperatures ranging from 50 to 70°C, havenumeric average molecular weights (

23

Mn) in the range20,000 to 100,000 and average weight molecularweights (

23

Mw) in the range of 40,000 to 500,000 (seeChapter 12.1). In industrial and commercial practice,the different suspension PVC products are defined anddifferentiated by Fikentscher’s K index (obtained frommeasurements at 25°C of the viscosity of solutions ofPVC in cyclohexanone at concentrations of 0.5 g/100 cm3), which is in relation to the polymer’smolecular weights. The suspension PVC products ingreatest commercial use have K values of between 55and 80 and the most used by far are between 65 and 70.Table 3 shows K values and their corresponding averagemolecular weights for the range of suspension PVCsmost used industrially.

As far as configuration and tacticity are concerned,the molecules of PVC, as obtained from the industrialprocesses of polymerization in suspension attemperatures ranging from 50 to 70°C, are primarilymade up (around 90%) of sequences of structurallyatactic units, that is, not positioned in any specific order(arrangement in space) one to another. With tacticity ofless than 10%, the crystallinity achievable in suspensionPVC products of commercial interest does not exceed10%. This crystallinity, which derives from the smallfraction of syndiotactic sequences present in PVC, ismade up of small and imperfect crystalline zoneswhich, however, have an influence on, and significancefor, the physico-mechanical characteristics of the relatedmanufactured articles (Illers, 1969).

The suspension PVC products most usedcommercially are made up of particle-granules with anaverage diameter of 150 mm with a dimensionaldistribution of 50 to 200 mm (as shown for example inFig. 2), normally having an apparent density ofbetween 0.45 and 0.6 g/cm3 and a particle-granuleinternal porosity ranging from 0.2 to 0.3 cm3/g. Thesegeneral physical characteristics (diameter anddimensional distribution, porosity and apparentdensity) are obtained directly from the polymerizationprocess and ensure on the one hand a good flow of thePVC particle-granules in pneumatic transport (flowlike that of a liquid) and on the other hand goodinteraction with the stabilizing, lubricating and filleradditives, as necessary for a regular and uniformprocess for transforming suspension PVC intomanufactured articles.

Transformation processesThe transformation of suspension PVC into

manufactured articles comes about through differenttechnologies (formulations and processes) dependingon the type of article desired. Before thetransformation process, the suspension PVC alwayshas one or more additives (stabilizers, lubricants,fillers, plasticizers and pigments) with which it ismade to interact, added to it. These protect thepolymer during transformation and the article once itis in use and, moreover, provide thephysico-mechanical characteristics required for thearticles’ end use.

The stabilizers serve to protect the PVC duringtransformation and to give the articles made from it along working life; they can be based on metallic soaps,such as those of lead and calcium-zinc, on organiccompounds such as antioxidants, and onorganometallic compounds such as those of tin. Theyare added to the PVC in quantities of around 1% andare firmly incorporated into the polymer matrix of thePVC articles.

The lubricants, in particular those defined asexternal, have the purpose of reducing the frictionbetween the transforming equipment and thePVC-based mixture which is being processed; themost used are those based on zinc, magnesium andcalcium stearates which are added to the PVC inamounts of about 0.1%. Their action, often insynergy with that of the stabilizer, is essentiallylinked to the hydrocarbon part of the lubricants’molecules (to the length, branching and groupspresent in the hydrocarbon chain) and is based onthe one hand on their solubility and compatibilitywith the PVC polymer and on the other on theirinteraction with the metallic parts of thetransforming equipment.


POLYMERIC MATERIALS

K value23

Mn23

Mw45 20,000 40,000

50 30,000 54,000

55 36,000 70,000

60 45,000 100,000

65 55,000 140,000

70 64,000 200,000

75 73,000 260,000

80 82,000 340,000

83 91,500 480,000

Table 3. Relationship between Fikentscher’s K valuesand the average molecular weights of samples of

suspension PVC (Ineos Vinyls, Italy)

The fillers, made up of inorganic material, usuallygranules of calcium carbonate or kaolin appropriatelycoated and with average dimensions of less than 1 mm,are specially made to be added to suspension PVC.These serve to improve certain characteristics of thePVC-based articles, such as their dimensional stability,their rigidity, their hardness and resistance to chemicalagents, at the same time lowering the cost of the PVC-based mixture.

The plasticizers are low volatility solvents of PVC;particularly liquids with a high boiling point, such asesters of phthalic, adipic, trimellitic, sebacic and citricacids, or solids with low melting points. Because oftheir chemical structure and molecular dimensions,these plasticizing compounds interact slowly withPVC at ambient temperatures, whereas at temperaturesaround 150°C they rapidly dissolve PVC and togetherwith it form homogeneous and continuous masseswhich, when returned to ambient temperature, displayflexibility and elasticity, which are the functions of thequantity and type of plasticizer used. The capacity ofPVC to interact with different quantities and types ofplasticizers, and be transformed into products that, atambient temperature, have varying degrees offlexibility, is almost unique and fundamental for amultiplicity of PVC-based products and applicationswhich include products which are flexible even at lowtemperatures (�30°C) and products which are flexibleand suitable for use at high temperatures up to 110°C.

Other additives are also added to PVC in smalleramounts before transformation, such as colouringpigments, fibres, rubbers, reinforcers and UVprotectors, and all have specific functions inoptimizing the performance of a specific article. Themultiplicity of formulations used and the processingprocedures are usually a result of the expertise of eachmanufacturer of PVC articles.

Before being processed in a transforming machine,the suspension PVC and the additives in theproportions and of the types desired, are mixed (eithercold or heated) to obtain the most uniform distributionpossible of the additives within the PVC. Thesubsequent processing of this blend, in which theadditives are uniformly distributed, takes place intransforming machines (extruders, calender pressesand injection moulding presses). These transformingmachines provide mechanical and thermal energy tothe PVC-based mixture which is able to break up thePVC particle-granules which have interacted with theadditives and to reassemble them after appropriatefusion-gelation, resulting in the formation of the finalarticle. The ideal gelation of a PVC-based mixturedoes not necessarily involve the total and completefusion of the microparticles and microstructures,including the small crystalline zones present in the

particle-granules of suspension PVC. For theproduction of rigid items such as pipes and windows,the ideal gelation-fusion of the PVC particle-granulesfor obtaining the best physico-mechanicalcharacteristics (such as impact resistance in windowprofiles and resistance to internal pressure in pipes forthe transportation of drinking water) is not total, butpartial and even varies according to the molecularweight of the PVC used.

The transformation technologies most used in theprocessing of mixtures of suspension PVC andadditives and the production of articles are extrusion,calendering and injection moulding.

Extrusion technology is the most widely used and isused for the production of continuous items such aspipes, profiles for doors and windows, thin films forpackaging and continuous coatings for electricity andtelephone cables. The main part of the transformationtechnology used, the extruder, is made up of a cylinderwithin which a worm screw turns. To reduce timescalesand improve processing uniformity and thecharacteristics of the manufactured articles twin screwextruders have been developed and are extensively used.In the processing, the PVC mixture containinguniformly dispersed stabilizers, lubricants and fillers, ifit is the case, is fed continuously into the extruder’shopper. While it is being transported between the screwand the cylinder it is heated up and compressed; thefriction between the mixture and the transformingmachine also has a heating effect. The result is that themixture melts in a correct manner before being pushedthrough the exit hole. This hole, called the threader ordie, is shaped according to the form required for thearticle. On issuing from the threader, the fused product issolidified, under constant thermal cooling, to give theitem its final desired form as well as the requiredphysical characteristics. Extrusion technology, combinedwith blow moulding, is also normally used for theproduction of hollow objects such as bottles and jars.

Calendering is widely used for the transformationof PVC into rigid film sheets and flexible film ofvarious widths and thicknesses. PVC polymer, treatedwith stabilizing, lubricating and colouring additives, isfirstly hot processed in an extruder to be thentransformed into a uniform mass. This uniform mass isthen processed in the calender press, made up of aseries of progressively closer pairs of parallel heatedcylinders, where it is transformed into rigid sheets,which are subsequently cut into the sizes desired ortransformed into film which is then wound onto a reel.The calendered film in rigid PVC can be subjected tofurther enhancing treatments, such as metallicizing(obtained through the sublimation of aluminium underhigh vacuum), which is largely used to give anaesthetic effect to the manufactured item.


POLYVINYL CHLORIDE

Injection moulding makes it possible to produceitems with great precision, such as pipe fittings,regulating valves for the flow of liquids, casings fortypewriters and calculators and prostheses for thehuman body. The most commonly used techniques forinjection moulding include piston presses with heatedcylinders, where the PVC-based mixture is melted andforced through a small nozzle by a piston, and screwpresses in which the PVC-based mixture is fused in aheated cylinder and forced through the nozzle by arotating screw. In both instances, the fused mixture isinjected under pressure into a mould until the cavityhas been completely filled; once it has solidifiedthrough constant, controlled cooling, the mould isopened to reveal the desired manufactured article.

In Europe the importance of the principalsuspension PVC transformation technologies in termsof quantity of manufactured articles is showngraphically in Table 4.

Applications sectors of suspension PVC-basedarticles

The sectors in which suspension PVC articles aremost used are building and construction, packagingand paper conversion, coating of electricity andtelephone cables and furnishings, followed bynumerous special and significant applications andpurposes, such as telecommunications and medicaldevices. These applications can be grouped in the sectors of usage and areas of application, asshown in Table 5.

Some of the principal characteristics and propertieswhich have encouraged the spread of PVC articles intothe building and construction, packaging, electricalcabling and medical device sectors are discussed below.

Building and constructionIn building and construction, PVC is widely used

for pipes and fittings for water mains (drinking,sewerage and waste from buildings), door and windowframes, roller blinds and flooring. The thicknesses ofPVC pipes for the transportation of drinking water aredetermined by the operating pressure, which can reach25 bar. If they conform to the UNI-EN standards and

are put into operation correctly, pipes can beguaranteed to have a working life in excess of 50years. In recent years these pipes have undergonedevelopment as far as the composition of the PVCpolymer used is concerned (molecular weight,molecular weight distribution and content of residualVCM) and their stabilization systems, such as forexample, stabilization systems based on calcium-zincsalts and those based on organic stabilizers, whichhave been used alongside, and in part are replacing,those based on lead. Obviously pipelines and mainshave to conform to standards and to the specific lawsregulating the transportation of drinking water.

In the sector dealing with the disposal of sewageand waste water from buildings, of all the pipes madeof plastic materials, PVC pipework enjoys a leadingposition in Europe. Pipework for sewerage is buried, asis that for road and land drainage, and pipes for theremoval of water by gravity are included in public andindustrial buildings. Among the properties required forunderground pipes are resistance to compression bystatic and dynamic loads and, within the safety limits,the withstanding of deformation, to avoid flatteningand leakages at the joints. PVC pipes, which havediameters of up to 1,000 mm, have an elasticresistance to deformation of about 25-30%, with nopermanent damage, even though in their design amaximum deformation of 3% is allowed for.Moreover, all PVC pipes intended for watertransportation possess strong impact resistance(sufficient to enable them to withstand the normaloperations of transport and installation) and goodchemical resistance, since they are attacked only byhalogenated solvents and by the more active oxidantsand are inherently resistant to fire. For PVC pipesintended for the different application sectors, on aEuropean level there are both specific standards and agroup of experts who are involved in continuallyupdating and improving the technical content of thesestandards and in guaranteeing the performance of thepiping. The development of new engineering projectsfor the sewerage sector has led to PVC pipes whichhave been lightened (up to about 30%) compared withcompact pipes. Interestingly, pipes have been


POLYMERIC MATERIALS

Transformation technology Articles produced %

Rigid and flexible pipesExtrusion Rigid and flexible profiles 77

Cable and wire sheathing

Calendering Rigid and flexible sheets and films 19

Injection mouldingPipework connectors and valvesCasings for typewriters, computers, TVs

4

Table 4. Principal transformation technologies used in Europe

developed and are now being marketed with channelsrunning longitudinally through their thickness; threelayer pipes, an inner expanded layer and two compactouter layers, manufactured through co-extrusion;double-walled pipes, made by co-extrusion of asmooth internal and a corrugated external wall; pipeswith external ribbing, made by moulding starting froman extruded pipe; bi-oriented pipe (known as PVC-Opipes), with physico-mechanical characteristicsimproved by as much as 50% when compared with theusual pipes of the same thickness.

Features of all PVC pipes intended for thetransportation of water include lightness, ease ofinstallation and connection, chemical resistance, highsmoothness and ease of flow of fluids; they also areresistant to corrosion, attacks from fungi and bacteriaand to ageing generally. These characteristics andtesting through many decades of use in differentenvironmental conditions, are the reasons for themarket penetration and the continued usage of PVCpipes in transporting water.

The PVC-based formulations used for themanufacture of doors, windows and shutters allow forthe production of rigid items which are resistant toimpact and atmospheric agents, have low thermalconductivity and do not burn. These characteristics,together with their durability, proved by examples thathave been in use for decades, are at the root of therapid penetration of PVC into the door and windowsector; 50% of windows currently installed inGermany and Great Britain are in PVC. Thecharacteristics and performance of doors and windowsin PVC and especially of windows, are defined ingreat detail in relevant European EN standards. Thesecharacteristics include: low thermal conductivity,which prevents the formation of condensation on thedoors and windows even at low temperatures; lowacoustic conductivity, which helps keep out externalnoises; high resistance to atmospheric agents, such as

smog, saline fog and airborne industrial dischargeswith a consequent reduction of maintenance, to thepoint of being virtually maintenance free.

Moreover PVC doors and windows can bemanufactured in the most varied styles, shapes andsizes and with different surfaces and appearances, sothat they can be installed in any urban setting and inthe widest range of building styles.

PVC flooring is used extensively in publicbuildings, such as hospitals, schools and gymnasia; innorthern Europe it is also widely used in privatedwellings. In general terms their features are long life,excellent abrasion resistance and reduced need formaintenance; they do not accumulate pathogenicgerms and can be sterilized easily, allowing the highlevel of hygiene required in public buildings and inhospitals in particular. The components of thePVC-based mixtures which make up vinyl flooring areessentially those commonly used in plasticformulations, with specific additives included toproduce anti-static, heat-conducting, non-slip floors,with resistance to denting and a reduction inflammability and the propagation of flames in theevent of fire. As a result of this the range of vinylfloorings available is very broad and specific todefined requirements (including the aesthetic) andapplications.

PackagingRigid and flexible packaging, produced from a

multiplicity of PVC-based formulations, can beimpermeable in various ways to gas, steam and CO2and are made to contain a wide range of products suchas food, detergents, medicines and cosmetics. Thesepackaging materials can be transparent, moulded intoshapes or with cavities obtained by thermoformingdepending on the shape of the object to be contained,such as for example the blisters used forpharmaceutical products and trays for food. Because


POLYVINYL CHLORIDE

Types of PVC Sectors of usage Applications areas

Building, water supply network Pipes and connectors

Building Profiles for doors and windowsRigid PVC Packaging and paper-transformation industry Extruded and calendered film, sheets

Packaging for food, pharmaceuticals, detergents Jars and bottles and cosmetics

Water-proofing, packaging, paper conversion Extruded film and sheets

Flexible PVCElectricity and telephone insulation Electricity and telephone cables

Building Flooring

Leisure Footwear, sporting goods and toys

Table 5. Sectors of usage and applications areas of PVC articles (Centro di Informazione sul PVC, Milan)

of the sensitive and critical nature of the applications,such as packaging for food and medicines, all thecomponents (polymer, stabilizers and plasticizers) ofthe PVC-based mixture to be used, must conform topre-defined criteria and controls on non-toxicity, laiddown in national and European standards and laws.The mandatory European standards framework for theproduction of food packaging includes a positive listof materials (polymers and additives) permissible foruse, and checks and controls on the packaging’s abilityto prevent damage to the food and to preserve itsqualities, including its organoleptic ones, over a periodof time. To summarize in general terms, PVC-basedpackaging encompasses a variety of products with theproperties demanded by the specific application; anextensive range of products is characterized bychemical inertness, resistance to oil and grease,balanced permeability to oxygen and carbon dioxideand impermeability to aromas; these characteristicshave prompted the widespread penetration ofPVC-based products into food packaging.

Electricity cablesBecause of the combination of their properties,

flexible PVC-based mixtures are widely used inprimary and secondary electrical insulation in cablesfor power transmission with voltages of up to 6 kV.They are especially used in electrical installations inbuildings, for electrical wiring on machinery, radiocircuits and telephone equipment. The characteristicsexplaining this extensive usage are their high electricalresistivity, good dielectric resistance and excellentmechanical robustness in a wide range of operatingtemperatures. Moreover, PVC-based electricalinsulation possesses good resistance to oxygen, ozoneand the majority of chemical agents and goodcombustion resistance, with a reduced tendency topropagate flame in the event of a fire. Thecharacteristics and performance of the wide range ofPVC-based electrical insulators are defined completelyand in detail according to the specific applications ofusage, in national and international standards and laws.

Medical devicesApproved for medical use by the international

pharmacopoeia, PVC-based formulations are used inthe manufacture of tubing for dialysis, circuits forextra-corporeal blood circulation, components forcardiovascular surgery, catheters, endotracheal tubes,containers for drips, bags for collecting blood andphysiological liquids, sterile gloves and oxygen tentsfor surgeries and operating theatres. The characteristicsrequired of materials used in biomedical applicationsare that they be transparent and biocompatible withhuman tissue and fluids, perfectly weldable, capable of

being sterilized and of remaining sterile, able to resistbreakage under the force of a centrifuge and able tostore blood at low temperatures. All thesecharacteristics, defined and described in detailedstandards and monitored by the appropriate healthauthorities, are qualities inherent to the PVC-basedformulations used extensively all over the world.

12.5.4 Compatibility and environmentalsustainability of PVC-basedproducts

Each manufactured item has an impact on theenvironment deriving from the production process of the material, its transformation into a manufactureditem, its operational life and how it is disposed of after use.

To be meaningful and to provide a basis ofcomparison between different articles whichperform the same function and have the sameoperating performance, an evaluation of the overallenvironmental impact of a given item must becarried out according to a defined, standardized anduniform scheme. The ISO 14040 standard of 1998provides such a scheme and the evaluation ofenvironmental impact, usually called the Life CycleAssessment (LCA), is related to a unit representativeof the function and performance of the specificarticle (functional unit). In accordance with thescheme of ISO 14040, the lifecycle assessment of afunctional unit consists of compiling and evaluating,over the course of all the stages and phases of thelife of the manufactured functional unit, the flowsput into the system (such as energy and rawmaterials) and those output (such as waste andemissions) and their associated environmentalimpact. To go into detail, the LCA of an articleconsists of the following phases:• Preliminary definition of the functional unit to be

evaluated and of its limits relating to the phases ofthe beginning of its life (raw materials, production ofintermediates and the final product), its operationallife (length of life, energy consumption and/or othertypes of resources) and the end of the article’s life(disposal, incineration, recycling) after use.

• Development, for all the lifecycle phases of thefunctional unit (production, operating life anddisposal), of a detailed flow-chart, with definitionsand allotments given to each phase of the relatedinput and output flows.

• Evaluation of the extent of the environmentalchange which is generated during production,operating life and disposal of the functional


POLYMERIC MATERIALS

manufactured unit, including the consumption ofenergy and raw materials and the release into theenvironment of emissions and waste. Based onspecified objectives, in the preliminary phase, thecategories of environmental impact relevant to thefunctional unit in question are selected. In generalterms, these include the consumption of resources,climatic change (usually called global warming),

the effect on the ozone layer, toxicity to humans andin water, photochemical oxidation, acid rain andeutrophication of water. In some instances,categories such as exploitation of the land, noisepollution, emission of odours, etc. may also beevaluated. The environmental impact in eachcategory is expressed usingconversion-equivalencies factors which make itpossible to relate the impact in a category to anindividual substance; in this way the impact onglobal warming of each emission is expressed in kgequivalents of CO2 and the impact on thedestruction of the ozone layer is expressed in kgequivalents of chlorofluorocarbon (CFC-11). Thecombination of the impact in all the categoriesconsidered, each expressed by a single valuethrough the use of conversion-equivalencies factors,represents the overall environmental impact of thefunctional unit being examined, throughout its life.

• Normalization of the results of the environmentalimpact in the individual impact categories throughweighting parameters and reference to the globalimpact (for example in a given period in a definedgeographical area). This normalization makes itpossible to make the environmental impact offunctional units with the same performance,succinct and comparable.

• Interpretation of the LCA results, highlighting thesignificance of individual categories ofenvironmental impact for a given functional unit


POLYVINYL CHLORIDE

raw materials

emissions

energyFig. 11. Limits at the boundaries of the flexible PVCfunctional unit for food packaging(by courtesy of M. Levi and V. Acierno,Politecnico di Milano).

filmmanufacture

raw materials

emissions

energy

energy LDPE (3.5 g)

LDPE film (3.5 g)

LDPE production

extrusion

Fig. 12. Limits at the boundaries of the LDPE functional unitfor food packaging (by courtesy of M. Levi and V. Acierno,Politecnico di Milano).

and definition of any prospective decisions forspecific modifications and improvements. LCA evaluations, relating to a given functional unit

and carried out in accordance with the ISO 14040standard, are capable of providing appropriate andquantitative replies to questions on the environmentalcompatibility and sustainability of a given article, inrelation to a defined context of usage, and incomparison with articles made of alternative materials.

PVC articles and the industry which producesthem have been, and still are being, examined andinvestigated closely for their impact on the

environment and on humans, given that someintermediates in the production chain (in particular1,2-dichloroethane and VCM) are known to be toxic tohumans and to the environment and certain stabilizingadditives used in the transformation of PVC intomanufactured goods, like lead-based stabilizers andcadmium-based stabilizers (now no longer used), alsohave a known environmental and toxic impact. Eventhe disposal of PVC articles at the end of theiroperating life has been, and is, extensively investigatedin order to identify and develop technologies capableof recovering and recycling the raw materials that they


POLYMERIC MATERIALS

0

5.10�15

resourceconsumption

globalwarming

ozone layerdepletion

humantoxicity

aquaticecotoxicity

terrestrialecotoxicity

flexible PVC

LDPE

photochemicaloxidation

acidification eutrophication

1.10�14

1.5.10�14

Fig. 13. Lifecycle comparison of functional units in flexible PVC and in LDPE with end-of-lifecycle dumping; CML-2000 standardization (by courtesy of M. Levi and V. Acierno, Politecnico di Milano). The environmental impact values shown in the vertical axis are normalized, i.e. they are the ratios between the specific impact measured in manufactured products and the corresponding total specific impact in Europe in 1995. The methodology is used in thenormalization process.

Impact category Unit PVC PET LDPE

Consumption of resources* kg Sb eq 0.0256 0.0365 0.0394

Climate change kg CO2 eq 2.11 4.35 2.06(GWP100 – time 100 years)**

Destruction of the ozone layer*** kg CFC-11 eq – – –

Toxicity to humans**** kg 1,4-DB eq 0.0432 0.408 0.0157

Ecotoxicity to water**** kg 1,4-DB eq 0.00507 0.00767 0.00172

Ecotoxicity to soil**** kg 1,4-DB eq 0.0111 0.0109 0.00951

Photochemical oxidation kg C2H4 eq 0.000499 0.00267 0.000461

Acidification kg SO2 eq 0.00984 0.05 0.00991

Eutrophication kg PO4 eq 4.05E-5 5.61E-5 1.95E-5

Table 6. Characterization of environmental impact associated with the production of 1 kg of PVC, PET and LDPE(by courtesy of M. Levi and V. Acierno, Politecnico di Milano)

(*) The consumption of resources is expressed and harmonized in kg of antimony/kg of minerals and fossil fuels extracted.

(**) GWP, Global Warming Potential.

(***) The destruction of the ozone layer is evaluated on a global geographical scale and an infinite time scale.

(****) Toxicities are expressed and harmonised in kg of 1,4-dichlorobenzol and is related to an infinite time scale.

contain and transform them into other useful items, aswell as it has the aim of defining the extent of theproblem and the solutions for the disposal of useditems in dumps and through incineration.

The results of extensive LCA studies arereproduced below, in order to respond to questions onenvironmental impact and on the sustainability ofdifferent PVC-based functional manufactured units. Inorder to provide information on the recyclability ofPVC goods at the end of their operating life, examplesare given of industrial recycling technologiesoperating in Europe.

LCA evaluation of PVC articles To reply to questions on the environmental

compatibility and sustainability of PVC-based articles, the results of in-depth and extensive LCA evaluations are summarised below (Levi andAcierno, 2005).

By way of example, Figs. 11 and 12 show the limitsof the functional units in flexible PVC and low density

polyethylene (LDPE) for food packaging. Inevaluating the environmental impact of eachfunctional unit, for PVC, LDPE, polyethyleneterephathalate (PET) and high density polyethylene(HDPE) plastic materials, the data used were from theAssociation of Plastic Manufacturers in Europe(APME) database and the Bundesamt für Umwelt,WAld und Landschaft (BUWAL, Swiss federal agencyfor the environment, forests and countryside) database.For ductile cast iron, the data were from the Idematdatabase – of the Faculty of industrial design of thePolytechnic of Delft, Netherlands –, BUWAL andETH-ESU 96 (Eidgenössische TechnischeHochschule-Energie Stoffe Umwelt) – of the Swissfederal technical institute of Zurich –, the latterparticularly for the process of galvanising cast iron.For aluminium, the data came from the Swiss databaseof ECO-Invent, based on the situation in the sector inEurope as provided by the European association ofaluminium producers (EAA-2000). For the productionof cardboard, the data were from the BUWAL


POLYVINYL CHLORIDE

0

5.10�14

2.5.10�14

resourceconsumption

globalwarming


humantoxicity

aquaticecotoxicity


PVC box

cardboard box



7.5.10�14

1.10�13

Fig. 15. Lifecycle comparison of box functional units in PVC and cardboard with end-of-lifecycle dumping; CML-2000standardization (by courtesy of M. Levi and V. Acierno, Politecnico di Milano).

0

5.10�14

resourceconsumption

globalwarming


humantoxicity

aquaticecotoxicity


PVC box

PET box



1.10�13

1.5.10�13

Fig. 14. Lifecycle comparison of box functional units in PET and PVC with end-of-lifecycle dumping; CML-2000standardization (by courtesy of M. Levi and V. Acierno, Politecnico di Milano).

database; for wood, data from the ECO-Inventdatabase were used. By way of example, Table 6 showsthe environmental impact values, obtained fromAPME, for the production in western Europe of 1 kgof the plastic materials PVC, PET and LDPE, thecategories of environmental impact of significance inaccordance with the CML-2000 method of the Centreof Environmental Science 2000 of the University ofLeiden (Netherlands) and the conversion equivalentsubstance, on which each impact category has beenunified.

In Fig. 13, the normalized results of the LCA forPVC and LDPE-based flexible film for functionalunits of flexible food packaging, with dumping at theend of the lifecycle, can be seen. Figs. 14 and 15 showthe LCA results for a functional unit of rigidpackaging, consisting of a chocolate boxes made ofPVC, PET and cardboard, with dumping at the end ofthe lifecycle.

As far as PVC and LDPE-based flexible packagingwas concerned, (see again Fig. 13), the overallenvironmental impact of the functional units made upof the two alternative materials can be compared eventhough they are not equivalent; in detail, thePVC-based films have lower environmental impact interms of consumption of resources while those basedon LDPE polyethylene have lower impact in terms ofenvironmental toxicity, while the differences betweenthe two materials for the other impact categories arenegligible.

The LCA results for rigid packaging, thefunctional unit being the chocolate box (see againFigs. 14 and 15), indicate that the PVC-basedpackaging has lower environmental impact values thanthat based on PET for all impact categories, while the

packaging made of cardboard, when compared withPVC, has lower energy consumption and lower globalwarming impact, but greater impact on water andhuman toxicity and on eutrophication. With regard tothe last point, it should be borne in mind that theenvironmental impact data for plastic and cardboardpackaging come from different databases and that asmall contributing factor in the differences in the LCAresults may derive from the differing degree of detailin the processes taken into consideration and from thefact that the limits of the two systems considered donot correspond exactly.

With regard to the LCA of pipes made of PVC,HDPE and ductile cast iron for transporting drinkingwater, the non-normalized quantitative data onenvironmental impact are displayed in Table 7. Insummary, these results indicate that, although theitems made of ductile cast iron offer a significant andunquestionable saving of resources due to recycling(pipes in cast iron are totally recoverable and sent to berecycled), overall, in all the other impact categories, inrelation to their current manufacture and industry inEurope, they are less sustainable from theenvironmental point of view compared withcorresponding items made of PVC and HDPE. Themost important causes of this situation relating toductile cast iron are the use of coal as the primarysource of energy for its production and the galvanizingprocess required to protect the ductile cast iron pipes.

The results of the LCA of door and windowfunctioning units made of PVC, aluminium and woodshow that those made of aluminium, without a thermalbreak, have greater environmental impact than thecorresponding items made of wood and PVC. Doorsand windows made of aluminium with a thermal break


POLYMERIC MATERIALS

Impact category Unit HDPE PVC Cast iron

Consumption of resources kg Sb eq 1.216 0.834 �0.205

Climate change kg CO2 eq 78.4 79.2 81.9(GWP100 – time of 100 years)

Destruction of the ozone layer kg CFC-11 eq 3.48E-06 3.32E-06 2.14E-05

Toxicity to humans kg 1,4-DB eq 3.46 4 75.8

Ecotoxicity to water kg 1,4-DB eq 0.272 0.348 4.15

Ecotoxicity to soil kg 1,4-DB eq 0.348 0.366 1.08

Photochemical oxidation kg C2H4 eq 0.0274 0.0195 0.0124

Acidification kg SO2 eq 0.582 0.38 0.726

Eutrophication kg PO4 eq 0.00442 0.00528 0.0278

Table 7. Environmental impact of a functioning unit of pipe in HDPE, PVC and ductile cast ironfor the transportation of drinking water; end of lifecycle in dump for HDPE and PVC pipes and recycling

for that in cast iron (by courtesy of M. Levi and V. Acierno, Politecnico di Milano)

have environmental impact comparable to those inPVC with some advantage in terms of ecotoxicity. Thedoors and windows with the smallest overall burdenon the environment are those made of soft wood (fir),irrespective of the end-of-lifecycle scenario, becausefor windows it is the operational phase of the lifecyclethat has a significant bearing on the overallenvironmental impact.

Overall, the LCA of different functional units(packaging, pipes, windows) in PVC, with regard toand in comparison with those of similar items made ofLDPE, HDPE and PET polymeric materials and frompaper, cast iron, aluminium and wood, indicates thatthe items made of PVC offer advantages as far asenvironmental impact is concerned and somedisadvantages compared with those made of othermaterials. In general terms, they certainly do not havethe greatest environmental impact and the LCAevaluations highlight that flexible PVC packaging forfood compares favourably with that in LDPE, inparticular. Rigid PVC packaging has advantages overthat made of PET and has some disadvantagescompared with that made of cardboard. Rigid PVCpipes compare well with those in HDPE and incomparison with cast iron, which is continuallyrecycled, have greater impact on the consumption ofresources but lower impact in all the other categories.Windows in PVC have lower environmental impactcompared with those in aluminium without a thermalbreak, similar impact to those with a thermal breakand slightly greater impact than those made of wood.

The results of the reported LCA could change ifmodifications were made to both the environmentalimpact in the single phases of the functional unit, andthe productive and commercial industrialcircumstances on which they are based and fromwhence came the functioning units examined.

Recovery and recycling of articles at the end of their lifecycle

The end-of-lifecycle phase of an item, after thecompletion of its operational phase, is the one towhich a great deal of attention has been paid in thepast and still continues to be paid in order, afterappropriate processing, to reuse the article or torecover and re-use, in other words to recycle, thematerial from which it is made. Experience andindustrial developments show that the collection ofarticles made of PVC (for example packaging,windows, flooring, pipes) at the end of their lifecycleand their separation from non-PVC materials throughspecial processes and operations, makes the recoveryand recycling of PVC and the production of new itemspossible. In Germany, window profiles with a core(around 70% of the material) recovered from old

windows are widely marketed. Moreover, afterappropriate processing, PVC-based coatings from usedelectricity and telephone cables are normally recycledin the production of flooring and waterproofmembranes. The general problems to be addressed andovercome for the recycling of used articles in PVC arethose relating to separated collection, the developmentof specific applications for the recycled materials andabove all the financial support and justification for allthe costs involved in the recycling process. A recentand effective technology in the recycling of used PVCarticles is what is known as Vinyloop technology(Solvay EP 0945481), developed by Solvay andcurrently in industrial operation in Ferrara (Italy). Thistechnology makes it possible to obtain a PVCcompound from used items such as, for example, thecoatings from electricity and telephone cables,resilient flooring and both rigid and flexiblepackaging. The Vinyloop technology involves the useof suitable solvents to dissolve the PVC contained inthe used items followed by its precipitation, drying andrecovery. The technology operates in a closed cycleand makes it possible to produce a compound of PVCpowder, in the required particle size, from which it ispossible to produce articles with physico-mechanicaland performance characteristics similar to those of thesame items made from virgin PVC.

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POLYVINYL CHLORIDE

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Graziano VidottoCentro di informazione sul PVC

Milano, Italy


POLYMERIC MATERIALS

Documents

12.5 Polyvinyl chloride - Treccani · Polyvinyl chloride (PVC) is one of the most widely used plastic materials in the world. In 2004, in Europe, some 6 million tonnes was transformed