Crosslinking on ageing of elastomers - III. A new method for evaluation ofcrosslinking based on density measurements

The crosslinking of EPDM has been studied by measuring the density of the s olution in cyclohexane of the soluble part of samples at various extents of crosslinking. All samples had the same weight and were extracted by equal volumes of solvent. Two series of samples have been studied: chemically cro sslinked (by dicumyl peroxide) and photooxidized. In the case of the chemic ally crosslinked samples, the variations of the density of the solution wit h the curing time show that the density tends towards that of the solvent, with kinetics which are a function of the peroxide content. In the case of the photooxidized samples, the results show that after a first period cross linking is predominant leading to a decrease of the density of the solution . In a second period, chain-scissions lake place and a notable increase of the density of the solution is observed. (C) 1999 Elsevier Science Ltd. All rights reserved.