Abstract
With the help of Broadband Dielectric Spectroscopy, it has been possible to study the molecular dynamics of disentangled Ultra High Molecular Weight Polyethylene in a wide temperature and frequency range. Catalytic ashes of aluminum oxide act as dielectric probes, allowing the identification of five different processes: an αc-process due to movements in the crystalline phase, two γ-processes attributed to amorphous chain portions close to the crystalline lamellae, and two β-processes that we have attributed to the disentangled and entangled amorphous phases. The entanglement formation has been followed by isothermal runs and a model that predicts the energy spent to form entanglements as a function of time and temperature is thereby proposed. This model allowed us to calculate the associated activation energy of the entanglement process.Our work advances further the understanding of entanglement dynamics of ultra-high molecular weight polymers, and the proposed model could prove useful to describe other similar processes such as cross-linking.
Highlights
Ultra-high molecular weight polyethylene (UHMWPE) is an engineering polymer that finds application in a wide range of fields such as biomedical products, soft ballistic protection and automotive parts [1e3]
UHMWPE differs from high density polyethylene (HDPE) in the average chain length, where it exhibits 10 to 100 times higher degree of polymerization, resulting in average molecular weights above 106 g/mol [4,5]
We have studied dis-UHMWPE samples by means of dielectric spectroscopy in a broad frequency and temperature range to further elucidate the process of entanglement formation
Summary
Ultra-high molecular weight polyethylene (UHMWPE) is an engineering polymer that finds application in a wide range of fields such as biomedical products, soft ballistic protection and automotive parts [1e3]. Interfacial phenomena play a significant role on the properties of heterogeneous materials like polymer composites, semi-crystalline or polymer blends materials and they can be analyzed using BDS [20], [23e25] Some of these models have been proven useful in the analysis of mechanical and rheological data as well [26e28]. To identify and analyze the different processes which are superimposed in the experimental data, semi-empirical formulations that deviate from the ideal Debye behavior have been proposed over the years in both the form of dielectric permittivity and electric modulus These models differentiate from each other in terms of the symmetry of the distribution of relaxation times. We have studied dis-UHMWPE samples by means of dielectric spectroscopy in a broad frequency and temperature range to further elucidate the process of entanglement formation. The model that we propose might find application to describe the entanglement formation or crosslinking of other polymers
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