Dielectric spectroscopy of recycled polylactide

The effects of multiple mechanical recycling on amorphous polylactide (PLA) were simulated by means of five successive injection-grinding cycles. The influence of the induced thermo-mechanical degradation on the dielectric properties of PLA was analysed. The relaxation spectra were studied in terms of the complex dielectric permittivity (ε0 and ε00) and the dielectric loss tangent, tg(d) in the frequency range from 102 to 107 Hz over the temperature interval from 0 C to 140 C. It was possible to distinguish two relaxations zones, one at low temperatures and high frequencies (b relaxation) and another at higher temperatures and lower frequencies (a relaxation). The individual relaxations were characterised using the HavriliakeNegami model and the effect of conductivity at high temperatures was subtracted. The thermal activation of the b relaxations was explained on an Arrhenius model basis while the a relaxation was modelled using VogeleFulchereTammanneHesse (VFTH) equations. The study of the segmental dynamics showed a decrease in the fragility parameters, connected with the decrease of molar mass, along with an increase in the free volume, the higher the number of reprocessing cycles were applied, particularly up to the second reprocessing step. 2014 Elsevier Ltd. All rights reserved.The authors would like to acknowledge the Spanish Ministry of Economy and Competitiveness, through the Research Project ENE2011-28735-C02-01. The Vice-Rectorate for Research, Innovation and Technology Transfer of Universitat Politecnica de Valencia is also thanked for additional support through PAID-06-SP20120581 project.Badía Valiente, JD.; Monreal Mengual, L.; Sáenz De Juano Arbona, V.; Ribes Greus, MD. (2014). Dielectric spectroscopy of recycled polylactide. Polymer Degradation and Stability. 107:21-27. https://doi.org/10.1016/j.polymdegradstab.2014.04.023S212710

Dielectric Behavior Induced by Vitamin E and Electron Beam Irradiation in Ultra High Molecular Weight Polyethylene

[EN] Radiation cross-linked ultra high molecular weight polyethylenes (UHMWPEs) have been successfully used as wear resistant bearing surfaces in total joint arthroplasty. A recent development in this field is the incorporation of the antioxidant vitamin E into radiation cross-linked UHMWPE. This study investigates the effects of radiation cross-linking and vitamin E incorporation on the dielectric behavior of UHMWPE. The dielectric relaxations of virgin and 0.1 wt % vitamin E-blended UHMWPE and their irradiated counterparts (up to 300 kGy dose) were investigated. To determine the effect of vitamin E content alone, vitamin E-loaded UHMWPEs were used. The results showed that radiation cross-linking and vitamin E content both increased dielectric polarization in UHMWPE and under some conditions induced electrical conductivity. This result is significant because it shows that the conductive response of UHMWPE-bearing surfaces may depend on manufacturing processes and additivesResearch funded by the Comision Interministerial de Ciencia y Tecnologia (CICYT), Spain. Project MAT 2010-16175 from the Ministerio de Ciencia e Innovacion. The authors also acknowledge support from Project ENE2011-28735-C02-01 and Mr. Teruel Grant GRISOLIAP/2012/056.Puertolas, JA.; Martínez-Morlanez, MJ.; Teruel Juanes, R.; Martinez-Felipe, A.; Oral, E.; Pascual, FJ.; Ribes Greus, MD. (2014). Dielectric Behavior Induced by Vitamin E and Electron Beam Irradiation in Ultra High Molecular Weight Polyethylene. Journal of Applied Polymer Science. 131(19):40844-40844. https://doi.org/10.1002/app.40844S40844408441311