Adam W. McMahon

Photoyellowing and discolouration of UV cured acrylated clear coatings systems: influence of photoinitiator type

The discolouration and yellowing of acrylated coating films after photocuring with a broad range of photoinitiators have been measured by colorimetry with the CMC (CIELab) system. The yellowing of the photoinitiators was evaluated and related to the chemical structure of the photoinitiator fragments and to the unreacted photoinitiator itself. The total colour difference was related to the type of chromophoric substitutent in the basic structure of the photoinitiator. The implications of these results are discussed in relation to clear coats.

Surface activity studies on carbon-silica dual phase fillers using flow microcalorimetry and multiple probe temperature programmed inverse gas chromatography

Carbon–silica hybrid particles (or carbon silica dual phase fillers (CSDPF)) are used as high performance fillers for elastomers and were originally developed to combine the best aspects of carbon black and silica in one package. In this work a range of such fillers with differing silicon content have been analysed, together with a range of carbon black and silica samples, using flow micro-calorimetry (FMC) and multiple probe temperature programmed inverse gas chromatography (MPTPIGC). The probe set for FMC comprised: ethyl acetate, pyridine, tributylamine; and propan1-ol. The linear increase in both heat and level of adsorption (from dry heptane) of all the probes within the CSDPF silicon content range investigated indicated that the interactions in the FMC were with the silica phase of the CSDPFs. FMC data for a variety of silica reference samples clearly indicates that the linear increase in adsorption activity does not continue beyond ca. 15% w/w silicon. MPTPIGC data obtained using a range of saturated and unsaturated linear and cyclic hydrocarbons together with benzene and pinacolone showed no clear relationship to silicon content. In fact the retention characteristics of CSDPF resembled those of carbon black more than silica. Differences in the carbon phase of the CSDFS and carbon blacks could be resolved using MPTPIGC. This study therefore highlights the complimentary nature of FMC and MPTPIGC in surface analytical studies of fillers.

Investigation of a radioactive particle and a soil sample obtained from the Windscale area in 1956

Specimens of an irradiated uranium oxide particle and soil contaminated with fission products and actinides, which originated from the deposition of irradiated uranium oxide particles in the Windscale area during the 1950s, have been investigated with the primary aim of assessing whether the analytical procedures used in the 1950s for the determination of 90Sr in soil would correctly have reflected the 90Sr content of soils contaminated with such particles. The key issue is whether the use of 6 mol l–1 HCl as an extractant would be effective in taking 90Sr contained in irradiated uranium oxide particles into solution. In this investigation, extraction efficiencies for 90Sr of 95 and 96% were measured for the soil and particle specimen, respectively, thus indicating that the early analytical procedures would be effective for soil samples containing irradiated uranium oxide particles. The relative amounts of the Pu isotopes assayed (238Pu, 239/240Pu and 241Pu) were consistent with those expected for material emitted from the Windscale Piles in the 1950s, based on operating conditions and conventional radionuclide inventory codes for irradiated fuel. However, the amounts of 90Sr and 137Cs relative to the Pu isotopes suggest that some removal of the former radionuclides may have occurred by leaching in the environment between the time of deposition and collection. The results of this investigation differ from other recently published work, which shows lower extraction efficiencies for 90Sr by HCl leaching; one explanation is the likely importance of sample preparation procedures.

Tertiary phosphine complexes of nickel (II) thiocyanate: an evaluation of the photostabilisation of polystyrene.

Polystyrene films have been prepared incorporating zinc stearate and nickel(II) thiocyanate complexes of methyldiphenyl- and alkenyldiphenyl-phosphines (alkenyl=vinyl, allyl, but-3-enyl, pent-4-enyl). Investigation of the thermal and fluorescence properties of the nickel complexes indicates high thermal stability and minimal photochemical activity. Polymer films containing the zinc and nickel complexes were photodegraded under artificial conditions and referenced to a similarly exposed nickel-free standard. The degradation of films containing nickel additives and the nickel-free standard was assessed using diffuse reflectance IR spectroscopy, CIELab colour space and 31P{1H} NMR. Within the polymer films nickel complexes do not degrade at a significantly greater rate than the polymer matrix, and whilst those containing vinyl, but-3-enyl and pent-4-enyl functions appear passive (displaying neither photosensitisation nor photostabilisation), methyl and allyl substituted complexes do offer significant stabilisation. Phosphine oxide species are identified by 31P{1H} NMR as the principal decomposition products, suggesting that peroxide oxidation of co-ordinated phosphines may represent the principal mode of photostabilisation. Assessments of colour space fastness on exposure to aqueous, acidic and alkaline media were made. These indicate comparable decomposition of nickel(II) thiocyanate and zinc stearate complexes in all three environments, suggesting that hydrolytic processes predominate in complex decomposition.