An investigation into the relationship between ‘gel-effective’ and total numbers of crosslinks in irradiated LLDPE

Abstract

Rheological data for crosslinked LLDPE samples have been related to previous studies of similar materials. It has been found possible to attribute a range of time constants (λ0in) and characteristic moduli (G0i) to the ‘gel-network’ strength factor (S) of all these materials. Comparability established, the number of crosslinks estimated rheologically are compared with those computed by molecular modelling for equivalent gel fractions. Below about 0·4 gel fraction, all crosslinks are found to be effective in forming the gel. Beyond about 0·85 gel fraction, further increase in crosslinks produces only small changes in moduli; this is observed at around five crosslinks per pre-irradiated molecule. A simple power relationship is found between the rheological and ‘gel-effective’ numbers of crosslinks. A previously postulated relationship between the gel fraction and numbers of ‘gel-effective’ crosslinks appears to be universal for LLDPEs. ‘Gel-networks’ arise at low gel fractions. Rheological data suggest that there is a dose-related progression of ‘gel-network’, from initial viscoelastic polymer, through a medium containing a mobile distribution of ‘gel-networks’ of increasing size, to a temporary ‘gel-network’, still able to relax, and finally a saturated permanent network. ©1997 SCI