ABSTRACT
Theimportanceofunderstandingthemechanismofgelationcanbegauged bythefactthatinvirtuallyeveryfabricationprocessunplasticisedPVC (UPVC)undergoesgelationpriortoenduse.DuringprocessingUPVC formulationsareconvertedfromthe130J.Lmpolymerisedgrains(Chapter 7)throughanumberofstagestothefinishedproductonawidevarietyof machines.Thevariousprocessingroutesinvolvethreeinterconnected stagesofpre-mixingwithadditives,compoundingandshaping.Eachstepis notmutuallyexclusiveoftheothersbutthereisconsiderablemergingof stagesparticularlyinmodernmachineswherethelattertwostagesareoften completedinasinglestep.
