The effect of annealing on slow crack growth in an ethylene-hexene copolymer

A quenched ethylene‐hexene copolymer was annealed in the temperature range of 86 to 127°C. The morphological changes were monitored by differential scanning calorimetry (DSC) and density. The slow crack growth resistance tested at 80°C was a maximum at an annealing temperature of 113°C and a minimum of 123°C. The lifetimes can be varied by more than a factor of 20 depending on the thermal treatment. The increase in slow crack growth resistance between 86 and 113°C is attributed to an increase in the strength of the crystals by becoming more perfect and to the conversion of loose tie molecules into taut tie molecules. The decrease in strength between 113 and 123°C is attributed to the decrease in tie molecules when a large fraction of the as‐quenched crystals begin to melt.