Melting Kinetics, Ultra-Drawability and Microstructure of Nascent Ultra-High Molecular Weight Polyethylene Powder

For the production of high-performance polyethylene fibers and tapes by ultra-drawing, using solid-state processing of disentangled nascent ultra-high molecular weight polyethylene (UHMWPE), the maximum draw ratio is an important design parameter, as it determines the maximum degree of chain alignment and, therewith, the properties of the final product. It would, therefore, be advantageous to have a fast scanning method to estimate the maximum drawability of reactor powders.

In the present work, the melting behavior of nascent ultra-high molecular weight polyethylene (UHMWPE) reactor powder is studied by differential scanning calorimetry, followed by isoconversional analysis to evaluate the apparent activation energy barrier of melting for the different UHMWPE grades of different level of disentanglement.Powder samples are solid-sate processed into tapes at elevated temperature. Ultra-drawing of these tapes at the optimum drawing temperature allowed for the evaluation of the maximum draw ratio (λ_max) that is determined by the entanglement density. The morphology of the lamellar structure of the nascent powder was studied by small-angle X-ray scattering and by scanning transmission electron microscopy analyses.A correlation between the melting kinetics, the microstructure and the maximum draw ratio was observed for all grades, suggesting that the apparent activation energy of melting can be used as a screening method to estimate the maximum draw ratio.The effect of molecular weight on the melting kinetics and microstructure is also discussed.