Electrical and Mechanical Properties of new Recyclable Power Cable Insulation Materials based upon Polyethylene Blends

Chemically crosslinked polyethylene (XLPE) has been used as electrical insulation for power cables since the 1970s due to its favourable combination of electrical and mechanical properties. However, as the electrical engineering community has become increasingly aware of the life cycle environmental impacts, XLPE has come under scrutiny for its lack of recyclability and the high process energies used in its manufacture. Although technologies are being developed to facilitate the re-use of XLPE at the end of its initial service life, the use of this material is inferior to fully recyclable and low process energy alternatives. In this investigation, we concentrated on the use of binary blends of linear and branched polyethylene (LPE / BPE) as potential replacement materials for XLPE, since such systems have the potential to combine comparable mechanical properties and enhanced breakdown strength with good recyclability. We compare the thin film AC ramp breakdown behaviour of blends as a function of temperature up to 97 oC. These consist of the same BPE in virgin and crosslinked states and in a blend with 20wt% LPE. These data are augmented with dynamic mechanical analysis. In concert, these data indicate that with appropriate morphological control the blended thermoplastic material exhibits superior properties to XLPE under conventional operating conditions and may even be suitable for higher temperature operation than XLPE. The paper will discuss the importance of polymer blending and blend physical properties in the context of the process requirements and the implications for cable manufacture and on cable electrical and environmental performance in comparison with XLPE

Thermoplastic cable insulation comprising a blend of isotactic polypropylene and a propylene-ethylene copolymer

There is much interest in the development of replacement materials for crosslinked polyethylene (XLPE) that are both recyclable (i.e. thermoplastic) and capable of high temperature operation. Thermally, polypropylene is the ideal choice, although its stiffness and low electrical breakdown strength make for a challenging materials design problem. We report here on the compositional optimization of a propylene homopolymer/propylene-ethylene copolymer blend in terms of its dynamic mechanical properties and thin film electrical breakdown strength. The extrusion of a trial mini-cable using the optimized blend is also discussed, which is shown to exhibit a significantly improved electrical performance, as gauged by its DC breakdown strength, than an XLPE-insulated reference

On the Temperature Dependence of Electrical and Mechanical Properties of Recyclable Cable Insulation Materials based upon Polyethylene Blends

Crosslinked polyethylene (XLPE) has been used as cable insulation since the 1960s, due to its favourable combination of electrical and mechanical properties. However, a fundamental consequence of crosslinking is limited recyclability. Although technologies are being developed to facilitate the re-use of XLPE at the end of its service life, such approaches are inferior to a fully recyclable alternative. In this paper, we report on the use of binary blends of linear (LPE) and branched (BPE)polyethylenes as possible replacement materials for XLPE, since such systems have the potential to combine comparable mechanical properties and enhanced breakdown strength with recyclability. Specifically, we consider the thin film AC ramp breakdown behaviour as a function of temperature up to 90 oC; the behaviour of a non-isothermally crystallized blend is contrasted with that of the constituent BPE in virgin and crosslinked states. These data are augmented with dynamic mechanical thermal analysis. In concert, these data indicate that, with appropriate morphological control, the blended thermoplastic material can exhibits superior properties to XLPE within the temperature range studied

Recyclable power cable comprising a blend of slow-crystallized polyethylenes

Crosslinked polyethylene (XLPE) has a successful history as a cable insulation material. Nevertheless, in recent years, as environmental awareness has grown, concerns about the ease with which it can be recycled have emerged. Although technologies have been developed for XLPE recycling, this report concentrates instead on the development of a thermoplastic alternative. Specifically, a 20 : 80 blend of high density and low density polyethylene (HDPE : LDPE) was selected and subjected to a non-isothermal crystallization procedure. It was found that, provided the cooling rate falls between 0.5 and 10 K min-1, the blend exhibits superior breakdown strengths and high temperature mechanical stiffness compared to XLPE. A trial cable was then extruded from this blend using such a cooling rate. The breakdown behavior of the morphologically-designed cable was finally compared with that of LDPE and XLPE reference systems

RapidArc, SmartArc and TomoHD compared with classical step and shoot and sliding window intensity modulated radiotherapy in an oropharyngeal cancer treatment plan comparison

Backround: Radiotherapy techniques have evolved rapidly over the last decade with the introduction of Intensity Modulated RadioTherapy (IMRT) in different forms. It is not clear which of the IMRT techniques is superior in the treatment of head and neck cancer patients in terms of coverage of the planning target volumes (PTVs), sparing the organs at risk (OARs), dose to the normal tissue, number of monitor units needed and delivery time. The present paper aims to compare Step and Shoot (SS) IMRT, Sliding Window (SW) IMRT, RapidArc (RA) planned with Eclipse, Elekta VMAT planned with SmartArc (SA) and helical TomoHDTM (HT). Methods: Target volumes and organs at risk (OARs) of five patients with oropharyngeal cancer were delineated on contrast enhanced CT-scans, then treatment plans were generated on five different IMRT systems. In 32 fractions, 69.12 Gy and 56 Gy were planned to the therapeutic and prophylactic PTVs, respectively. For the PTVs and 26 OARs ICRU 83 reporting guidelines were followed. Differences in the studied parameters between treatment planning systems were analysed using repeated measures ANOVA. Results: Mean Homogeneity Index of PTVtherapeutic is better with HT(.06) followed by SA(.08), RA(.10), SW(.10) and SS(.11). PTVprophylactic is most homogeneous with RA. Parotid glands prescribed mean doses are only obtained by SA and HT, 20.6 Gy and 21.7 Gy for the contralateral and 25.6 Gy and 24.1 Gy for the ipsilateral, against 25.6 Gy and 32.0 Gy for RA, 26.4 Gy and 34.6 Gy for SW, and 28.2 Gy and 34.0 Gy for SS. RA uses the least monitor units, HT the most. Treatment times are 3.05 min for RA, and 5.9 min for SA and HT. Conclusions: In the treatment of oropharyngeal cancer, we consider rotational IMRT techniques preferable to fixed gantry techniques due to faster fraction delivery and better sparing of OARs without a higher integral dose. TomoHD gives most homogeneous target coverage with more sparing of spinal cord, brainstem, parotids and the lower swallowing apparatus than most of the other systems. Between RA and SA, SA gives a more homogeneous PTVtherapeutic while sparing the parotids more, but the delivery of RA is twice as fast with less overdose to the PTVelective. © 2013 Van Gestel et al; licensee BioMed Central Ltd