Dynamic-mechanical and nuclear magnetic resonance study of relaxation processes in ultra-high molecular weight polyethylene fibres

Abstract

The relaxation processes (α, β, and γ) in UHMW PE fibres drawn to different draw ratios λ have been studied by dynamic-mechanical and nuclear magnetic resonance methods. The temperature dependences of tensile loss moduli E and spin-lattice relaxation times T1 have been analyzed assuming distribution of correlation times τ according to the Davidson-Cole function. The activation energies Ea and parameters ε characterizing widths of distribution, and asymptotic value τ0 for correlation times have been determined from experimental data for low-temperature γ-process and for high-temperature α-process. A weak β-process has been found by dynamic-mechanical method and quantitative analysis was made only for fibres with λ = 9. The temperature dependences of second moment M2 of the broad-line NMR spectra have been analyzed according to the Gutowsky-Pake formula, which includes only a single correlation time τc without distribution. In this case the activation energies Ea and values of τ0 have been determined.

Mechanical relaxation of medical grade UHMWPE of different crosslink density as prepared by electron beam irradiation

“…7 and 8) and consequently, it is difficult to determine the corresponding activation energy (Δ E a ). The weakness of the β relaxation has already been reported by other authors, e.g., Hronský et al14 and Zamfirova et al8 Only in the case of the nonirradiated WIAM 0, the frequency shift in the G ″ modulus provides a trustful value for Δ E a , which is 116 kJ/mol (Table V). With respect to Kawai et al,18 the β relaxation arises from interlamellar grain boundary phenomena associated with orientational and distortional dispersions of noncrystalline materials between oriented lamellae.…”

“…Polyethylene is known for its three kinds of relaxation processes in the entire temperature range as is seen in dynamic mechanical thermal (DMTA),7–14 dielectric,15, 16 and nuclear magnetic (NMR) experiments,10, 14, 17 With respect to, e.g., Zamfirova et al,8 UHMWPE exhibits the γ, β, and α relaxations, characterized by a loss modulus ( E ″) maximum at −113 to −111°C, −4°C, and 57–58°C, respectively, as determined from tensile DMTA measurements at an angular frequency (ω = 2π f ) of 18.8 Hz.…”

Poole–Frenkel conduction in polyvinyl chloride stabilized with dibutylin laurate–maleate

“…Polymeric materials, with interesting electrical properties, have been studied in great details [1][2][3][4][5]. A good amount of work on the conduction mechanisms of PVC in the form of metal-polymer-metal (MPM) structure has been reported in the literature [6][7][8][9][10].…”