The influence of chain constraints on the kinetics of oriented crystallization under low stress

Abstract

The kinetics of strain-induced crystallization of swollen, crosslinked polyethylene fibres have been measured under low draw conditions (α = 1.2 or 1.4) using dynamometry in combination with birefringence. Crosslinking was carried out in dicumyl peroxide to produce a range of chemical and trapped entanglement concentrations. Avrami analysis showed that transformation proceeds by heterogeneous nucleation followed by one-dimensional growth of c-axis oriented crystallites. Growth rates and the size of the corresponding critical nuclei show a strong dependence on crosslink density and entanglement concentration at high crosslink concentration. When entanglement concentration is comparable to the crosslink concentration, the effects of the two constraints become indistinguishable. The latter observation is in line with published results for flow-induced crystallization under comparably low stress levels showing that growth rates are relatively insensitive to entanglement concentration. At higher crosslink concentrations, growth rate decreases in a non-linear fashion indicating potential thermodynamic as well as mobility effects. A physical model illustrates the role of chain constraints on the kinetics of oriented crystallization. © 1992.