Implications of a tailored non-equilibrium polymer melt state on the viscoelastic response and crystallisation behaviour of UHMWPE
thesisposted on 23.06.2016 by Ele de Boer
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In this thesis a non-equilibrium polymer melt with a heterogeneous distribution of entanglement density is investigated. This melt is achieved on melting of Ultra-High Molecular Weight Polyethylene (UHMWPE) which has been synthesised in specific conditions to yield a nascent material with a low amount of entanglements compared to its equilibrium state. In time the melt equilibrates by formation of entanglements, continuously increasing its elastic modulus, until the equilibrium state is reached, having a homogeneous distribution of entanglements. Step strain and step stress rheology on the non-equilibrium melts show that relaxation times and viscosity increase during equilibration following a power law dependence on the instantaneous elastic modulus. In this way, information of the elastic modulus increase can be used to transfer relaxation modulus or creep compliance, of experiments started out of equilibrium, to an effective time domain where time translational invariance is regained and equilibrium viscoelastic behaviour is observed. To increase the range of available characterisation techniques, deuterated UHMWPEs with an initially low amount of entanglements are synthesised, as well as block copolymers consisting of blocks of protonated and deuterated UHMWPE. [Continues.]
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