Henryk Herman

The radiation-grafting of vinylbenzyl chloride onto poly(hexafluoropropylene-co-tetrafluoroethylene) films with subsequent conversion to alkaline anion-exchange membranes: optimisation of the experimental conditions and characterisation

Poly(hexafluoropropylene-co-tetrafluoroethylene) (FEP) was successfully radiation-grafted with vinylbenzyl chloride (VBC). Subsequent amination with trimethylamine followed by ion exchange with aqueous hydroxide yielded alkaline anion-exchange membranes (AAEMs). Experimental parameters were established for maximising the degree of grafting (d.o.g.); the optimum treatment duration for maximum amination was also established. The graft penetration at different degrees of grafting was investigated and related to the grafting conditions. The stabilities of the grafted membranes and the final AAEMs were thoroughly investigated using thermogravimetry and differential thermal analysis (TG/DTA). The ion-exchange capacities (IECs), water uptake levels, and thicknesses of the AAEMs were measured. These AAEMs have potential for application in low-temperature fuel cell systems.

Anion-exchange membranes for alkaline polymer electrolyte fuel cells: comparison of pendent benzyltrimethylammonium- and benzylmethylimidazolium-head-groups

Radiation-grafted alkaline anion-exchange membranes (AAEM) containing pendent groups with either benzyltrimethylammonium (BTM) or benzylmethylimidazolium (BMI) functionality were successfully synthesised from the same base membrane and with identical ion-exchange capacities. The conductivity of the new BMI-AAEM is comparable to the BTM-benchmark AAEM. The fuel cell performance obtained with the BMI-AAEM was, however, significantly poorer due to in situ AAEM degradation. FT-Raman spectroscopic studies on the stability of the two head-groups at 60 °C in aqueous potassium hydroxide (1 mol dm−3) indicates that the BMI-group is intrinsically less chemically stable in strongly alkaline conditions compared to the BTM-benchmark head-group. However, the stabilities of both head-groups are improved when treated at 60 °C in lower pH aqueous carbonate and bicarbonate solutions (1 mol dm−3). Contrary to a portion of the prior literature, there appears to be no real advantage in using anion-exchange polymer electrolytes containing pendent imidazolium groups in highly alkaline systems.

Raman Spectrum of β-Carotene Using Laser Lines from Green (514.5 nm) to Near-Infrared (1064 nm): Implications for the Characterization of Conjugated Polyenes

We have studied the Raman spectrum of β-carotene using excitation wavelengths from visible (514.5 nm) to near-infrared (1064 nm). Qualitatively, the spectrum appears independent of the choice of excitation wavelength, although this is not true in detail; in particular, the ratio of the intensities of the νC-C and νC=C fundamentals to their overtones and combinations varies with the excitation wavelength. The inelastic neutron scattering spectrum shows no evidence for unusual dynamics in this system, and the UV/vis/NIR spectrum shows that there are no allowed electronic transitions from the ground state beyond ∼700 nm. These observations provide strong evidence for the existence of a different mechanism for the enhancement of the bands. Indirect evidence suggests that, with these longer excitation wavelengths, the intensities of the νC-C and νC=C peaks are at least two orders of magnitude smaller than those from resonance enhancement with the use of excitation into the visible absorption bands. The implications for the characterization of polyenes in polymers are discussed.

Non-destructive measurement of the degradation of transformer insulating paper

Knowledge of the condition of power transformer winding insulation paper is fundamental to making optimum asset replacement decisions in the power industry. The ability to assess the aged condition of Kraft paper quickly and non-destructively using portable instrumentation would significantly increase the opportunities for gaining this knowledge. Insulation paper degrades over time in-service and its degree of polymerization (DP) reduces, eventually affecting its mechanical strength. At low DP levels the insulation may start to disintegrate and the risk of electrical breakdown increases. Currently-used methods of estimating DP are either approximate or destructive. The use of spectroscopy together with multivariate statistical analysis (MVSA) provides a powerful non-destructive evaluation of the condition of paper. From initial feasibility studies, we have developed a simple, portable system (TRANSPEC) using fiber-optics and broad-band spectroscopy that can measure the degree of polymerization of various aged transformer papers to a precision of approximately 30 DP units with a spatial resolution of 14 mm. The system can also measure the chemical composition and condition of the insulating mineral oil. MVSA regression models were constructed from library spectral data, and these models are used to predict the DP of other papers with parameters that fall within the range spanned by the set of calibration samples. Separating oil and moisture information from wetted paper is possible and will be reported in a separate publication. With a single TRANSPEC system, non-destructive in-situ analysis of the DP of insulating paper is possible, providing a rapid cost-effective method for transformer insulation condition assessment and monitoring, which correlates well with current destructive methods.

Multivariate analysis of spectra of cyanate ester/bismaleimide blends and correlations with properties

A multivariate approach to the analysis of cured resin blends comprising cyanate ester and bismaleimides is reported. An analysis of samples subjected to accelerated ageing tests by immersion in water at temperatures up to 70 °C shows that simple near infrared spectroscopic measurements on virgin materials can predict dynamic mechanical thermal analysis results, and provide correlations with thermogravimetric analysis. This suggests a rapid screening method for a range of materials, perhaps in conjunction with a combinatorial approach to advanced composites manufacture.

Spectroscopic measurement and analysis of water and oil in transformer insulating paper

A portable fiber-optic spectroscopic system (TRANSPEC) has been developed for nondestructive measurement of aged transformer insulating paper. Following successful measurement of degree of polymerization (DP) of a range of transformer-aged paper samples, the system has now been shown to separate the oil and paper information for measurement of DP in oil-wetted paper samples. In addition, the system has been shown to be capable of the prediction of both oil and water content of paper to a high accuracy, and is also capable of identifying and quantifying different water species. Spectroscopic measurements have been used together with gravimetric water adsorption measurements to investigate the kinetics of uptake of water vapour into paper from air in the case of nominally dry and oil-impregnated samples. Relationships between water adsorption parameters and properties of the paper insulation have also been investigated using measurements under controlled conditions.

Thermal Properties of Composites Filled with Different Fillers

Electrical insulating polymers usually incorporate inorganic fillers to achieve specific electrical, mechanical, thermal properties and reduce cost. In this exploratory work, we have studied the thermal properties, at 40degC, of epoxy resin composites with different filler such as: boron nitride, alumina, diamond, silicon carbide, and silicon nitride, with particle size ranges from micro to nano. The results show that BN is the best material in enhancing the thermal conductivity of the epoxy composites despite the various fillers having comparable or higher thermal conductivities than BN. Our current model shows that large disparities in mechanical modulus - a metric for interfacial compatibility - can cause thermal contact resistance due to increased phonon scattering resulting from the large mismatch between filler particle and resin matrix.

Alkaline ionomer with tuneable water uptakes for electrochemical energy technologies

A simple aqueous-processable alkaline ionomer (amenable to scale-up) has been developed for enhancing electrode/electrolyte interfaces in clean energy devices (e.g. alkaline polymer electrolyte membrane fuel cells). The water uptake of the alkaline ionomer is tuneable allowing its use as a tool for fundamental studies into these interfaces.

On-site analysis of transformer paper insulation using portable spectroscopy for chemometric prediction of aged condition

Non-destructive diagnosis of power transformer condition is an increasingly important area of research. Power transformer coils are typically insulated with Kraft paper and immersed in mineral oil. There is a clear need to be able to estimate the aged condition of the coil insulation non-destructively. A portable fibre-optic spectroscopic probe system has been developed which can achieve this quickly by determining the degree of polymerization (DP), an indicator of degradation, to an accuracy of 30 DP units. The system can also determine water content to an accuracy of 0.1% w/w, and oil content and condition, very rapidly from the same measurements. The system uses a broadband spectroscopic diffuse reflectance probe operating in the visible and near infrared (NIR) range and interfaced to dedicated multivariate analysis software. Following calibration and measurement trials in the laboratory, the instrument has recently been adapted for use in the field, in which DP predictions have been made from in-situ measurements on the exposed windings of de-tanked transformers. These values have been validated when checked against DP measurements of the same paper taken in parallel using conventional viscometric methods. The system is now being further optimized and is being developed for other applications in the power industry and other industrial areas such as the paper industry and the plastics recycling industry. The system is modular and different probe types can be attached allowing the measurement of a wide variety of solid material surfaces and liquid media.

A new approach to condition assessment and lifetime prediction of paper and oil used as transformer insulation

Kraft paper (cellulose) immersed in mineral oil is used as the insulation system for copper windings in large power transformers. As the system ages under load, the paper and oil can degrade potentially leading to catastrophic failure. Reliable condition monitoring, condition assessment and failure prediction of the insulation system is central to effective transformer asset management and non-destructive/non-invasive approaches are preferred. In this paper we will show that near infrared (NIR) spectroscopy combined with chernometrics is capable of providing rapid non-destructive condition assessment of the paper and the oil components individually.