Film embrittlement criteria were determined for photo-oxidative degradation of linear low density polyethylene (LLDPE) films by using a range of characterisation techniques: tensile, high-temperature GPC, MAS-NMR, FTIR-ATR, WAXS and SAXS. The key embrittlement criteria was the loss of 95% elongation at break and the reduction in interlamellar distance, reduced down to approximately 30–50 Å, as a result of recrystallisation of mobile short chain fragments produced from chain scission reaction. Interlamellar thinning correlated well with the changes in double yield points seen in the tensile data, where the absence of the second yield point signified that the tie molecules at the lamellar interface underwent chain scission and could no longer transfer the tensile stress to reach c-axis slip of the lamellar crystals. This was also supported by a reduction in amorphous–lamellar interfacial width with ageing time, extracted from SAXS data using the linear correlation function. Crown Copyright (C) 2012 Published by Elsevier Ltd. All rights reserved.