Abstract
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 UHMWPE reactor powder was 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 were 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 (λmax) 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.
Highlights
Polymeric materials often represent an attractive compromise be tween the properties of the final product and ease of processing
An alternative method, which avoids the use of excessive amounts of solvent, is solidstate processing of disentangled nascent ultra-high molecular weight polyethylene (UHMWPE) reactor powder, followed by ultra drawing into high-performance polyethylene fibers or tapes
It was found that the more disentangled mate rials exhibit a lower apparent activation energy, confirming earlier studies that the level of disentanglement of nascent UHMWPE is depicted in its melting kinetics
Summary
Polymeric materials often represent an attractive compromise be tween the properties of the final product and ease of processing. The isoconversional analysis allows for a reliable way of evaluating a calorimetric dataset, without assuming any particular reaction model beforehand and has been utilized for the investigation of melting kinetics of polymers in numerous studies [24,25,26,27,28,29,30,31,32] It is, the objective of this study to apply the isoconver sional method to determine the melting kinetics of various nascent UHMWPE samples of approximately equal molecular weight, but with different entanglement densities, resulting in different maximum draw ratios. We will attempt to correlate the maximum draw ratio to the apparent activation energy for melting and the lamellar thickness
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