Viscoelastic properties of latex paint films in tension: Influence of the inorganic phase and surfactants

The tensile properties of latex coatings were investigated with a set of custom formulated artist-type paints at an age of 1 year. All films in the study contained a poly(methyl methacrylate-cobutyl acrylate) binder exhibiting a glass-transition at approximately 10 °C. The viscoelastic behaviour of the latex matrix is first highlighted through a series of experiments involving different strain histories and temperatures. Influence of the inorganic particle concentration and geometry is then illustrated using TiO₂ and calcined kaolin for the secondary phase. Experimental data from a wide range of conditions are summarised through master curves of secant modulus and failure strains using time–temperature superposition. The results indicate that the latex films behave in a rheologically simple manner and it is possible to predict the response outside of the experimental time-scale. An analysis by similar methods is also given for TiO₂ pigmented films with/without surfactant removed by immersion in water. Differential scanning calorimetry and atomic force microscopy were also used in conjunction with mechanical tests. The combined findings suggest that a fraction of surfactant migrates to the TiO₂ interface during film formation, where it interferes with adhesion of the acrylic matrix.     

Tensile properties of latex paint films with TiO2 pigment

The tensile properties of latex paint films containing TiO₂ pigment were studied with respect to temperature, strain-rate and moisture content. The purpose of performing these experiments was to assist museums in defining safe conditions for modern paintings held in collections. The glass transition temperature of latex paint binders is in close proximity to ambient temperature, resulting in high strain-rate dependence in typical exposure environments. Time dependence of modulus and failure strain is discussed in the context of time–temperature superposition, which was used to extend the experimental time scale. Nonlinear viscoelastic material models are also presented, which incorporate a Prony series with the Ogden or Neo-Hookean hyperelastic function for different TiO₂ concentrations.     

Estimation of film accumulation in percolating filters: Comparison of methods

Estimation of film accumulation is necessary for the successful operational management of percolating filters. Prevention of ponding and loss of performance due to excessive film accumulation, and the optimization of the recirculation and alternating double filtration processes can only be achieved by regular monitoring of film growth. Five methods of determining film accumulation are compared; total film weight, total dry solids, volatile solids, percentage settlement of solids and the neutron scattering technique. The methods were used to monitor the film growth in pilot filters containing a mineral and a random plastics medium, over two twelve-month loading periods at 1.68 m³ m⁻³ day⁻¹ (0.28 kg BOD m⁻³ day⁻¹) and 3.37 m³ m⁻³ day⁻¹ (0.63 kg BOD m⁻³ day⁻¹).

Good correlations (P < 0.001) are found between all methods at the lower loading although the neutron scattering results are not significantly correlated (P > 0.10) with any of the gravimetric methods at the higher loading. Although the neutron scattering technique does provide a rapid and sensitive measure of hydrogen atoms in the filter, the results, expressed as percentage saturation of the voids, are not directly transferable to film weights and should be treated separately and not as a true measure of film accumulation.     

Comparative pilot-scale investigation into uprating the performance of percolating filters by partial medium replacement

A pilot-scale investigation was carried out to ascertain whether the loading to conventional single-pass percolating filters could be increased by partially replacing mineral medium with a random plastic medium. The treatment efficiency of a mixed-media filter (1.2m³ blast furnace slag topped by 0.8 m³ Flocor RC plastic medium) was compared over 26 months with the treatment efficiencies of two single-medium filters containing 2 m³ blast furnace slag and 2 m³ Flocor RC respectively. Two hydraulic loadings, 1.68 and 3.37 m³ m⁻³ d⁻¹, average organic loadings 0.28 and 0.63 kg BOD m⁻³ d⁻¹, were used for consecutive periods of 13 months. Medium replacement has been shown to be a viable system for uprating conventional filters. The mixed filter was more versatile and was also markedly more efficient than the slag filter at the higher hydraulic loading. It is estimated that at this loading the mixed filter could treat a 30% greater organic load than the slag filter.     

High Transmission LiF Prism Monochromator for Separation of VUV Wavelengths in Frequency Mixing Experiments

Abstract

We describe a simple, high throughput, LiF prism monochromator for the vacuum ultraviolet (VUV). The instrument throughput is 30% at 145 nm and the output can be tuned within the range 120–185 nm. The very high dispersion of LiF in the VUV means that neither narrow slits nor high precision are required. The suitability of this instrument for separation of coherent VUV radiation, generated by four-wave mixing, from the intense fundamental laser radiation (at 212 nm and the visible) is demonstrated. General advantages in throughput, polarization and resistance to radiation damage of such a prism instrument compared to a diffraction grating monochromator are discussed.     

The distribution and ecology of the naididae (oligochaeta) which inhabit the filter-beds of sewage-works in Britain

A survey of sewage filter-beds situated throughout Great Britain showed that naidid worms were frequently an important component of the faunal community. The three commonest species were Nais variabilis, N. elinguis, and Pristina idrensis. Their occurrence and abundance were determined principally by the organic loading received by the beds, the amount of film present, and the presence of industrial waste. All the species found are considered beneficial to the functioning of the filter-bed.     

A pilot-scale percolating filter for use in sewage treatment studies

A pilot-scale filter is described which can be quickly and easily constructed, even by those with limited engineering skills, using materials most of which are likely to be available in the stores department or on the site of a normal sewage works. It is robust, durable, easily modified and produces a well purified effluent using either mineral or random plastic media at conventional loadings. The simple design offers a low cost, reliable and versatile pilot-filter system suitable for a wide range of research, evaluation and development work.