Effect of crystallization and of water uptake on the free-volume hole size in polyamides 6 and 66

Positron lifetime spectroscopy has been applied to estimate the free-volume hole sizes in the polyamides (nylons) 6 and 66 exposed to quenching, crystallization and water uptake. Three well separated peaks were observed in the lifetime distribution analysed via the MELT routine, the third of which (o-Ps) was found to split into two sub-peaks. From the analysis of computer generated spectra we were unable to conclude whether the sub-lifetimes represent two real annihilation channels or whether they appear as an artefact of analysing very broad o-Ps lifetime distributions. Assuming that the two lifetimes reflect the real situation tau(3(i)) similar to 1.3 ns may be attributed to o-Ps annihilation from crystallites and tau(3(ii)) = 1.8-2.2 ns from free-volume holes of the amorphous phase. Indications were found that during crystallization of quenched polyamides the hole size increases. Water uptake of the polyamides also leads to an increase in the hole size which is attributed to plasticization of the polyamides.