Disentangled ultra-high molecular weight polyethylene and its nanocomposites: relaxation dynamics, entanglement formation and anisotropic properties due to orientation

In the present doctoral research, the chain relaxations and dynamics present in linear disentangled ultra-high molecular weight polyethylene (both pure and as a composite) were investigated and presented. Considering its disentangled character, the relaxation dynamics and the formation of entanglements were primarily analysed. Additionally, the presence of fillers and the effect of uniaxial orientation were also studied. With respect to the chain relaxation analysis, torsional rheology and broadband dielectric spectroscopy were employed to identify the disentangled amorphous phase in comparison with fully entangled samples. The rheological results gave significantly different relaxation behaviour for the disentangled sample, affecting all the mechanical processes namely αc-, β- and 𝛾-relaxations, with the latter exhibiting a non-Arrhenius temperature dependence, indicative of the dynamic glass-to-rubber transition. This indication would support previous studies that would locate the glass transition temperature of linear polyethylene around -100oC. The dielectric analysis was only possible in the presence of Al2O3 catalytic ashes and expanded further the relaxation investigation by showing two types of interfacial polarization attributed to the disentangled and entangled amorphous phases. [Continues.]