ABSTRACT
Historically,PVCgainedwidecommercialacceptancebecauseitcouldbe mixedwithorganicliquids(plasticisers)togiveatoughflexiblematerialnot unlikerubberinitspropertiesandthewayinwhichitcouldbeprocessed. Thelargemarketthusdevelopedsoonproducedreductionsinthecostof theVCMmonomerandthemanufacturingprocesssothatitwasnatural forPVCmanufacturersanduserstoconsideritsuseforunplasticised applications.PVCinitsunplasticisedstatewhencorrectlyfabricatedis capableofproducingtoughrigidarticlesofexcellentsurfaceappearance andtransparencyifdesired.However,itisthermallylabileandwill decomposequiterapidlyatornearthetemperaturesneededtomeltthe PVCsufficientlytoproducethefinishedarticles.Hence,beforethefull commercialpotentialofPVCcouldberealised,muchprogresshadtobe madeimprovingthebasicheatstabilityofthePVC,developingimproved heatstabilisersandprocessformulations,anddevelopingequipment capableoffabricatingtherequiredfinishedproducts.Asaresultofthis successfuldevelopmentwork,itisnowpossibletoproducerigid,i.e. unplasticised,articlesofveryconsiderablecommercialimportance(pipes, profiles,etc.)whichareinwidespreaduse.Evenso,theirperformanceis limitednecessarilybythebasicpropertiesofPVC.Someofthesebasic propertiesarelistedinTable4.1forthenarrowrangeofmolecularweight (expressedasK-value)usedforrigidapplications.Attemptstowidenthis propertyrangebymolecularweightchangeleadeithertoanunprocessable material(atK-valuesabove70)orabrittlematerialwithoutthemost desiredpropertyofPVC,itstoughness(atK-valuesbelow50).
