BackgroundMan-made vitreous fibres (MMVF) are produced on a large scale for thermal insulation purposes. After extensive studies of fibre effects in the 1980ies and 1990ies, the composition of MMVF was modified to reduce the fibrotic and cancerogenic potential via reduced biopersistence. However, occupational risks by handling, applying, disposing modern MMVF may be underestimated as the conventional regulatory classification -combining composition, in-vivo clearance and effects- seems to be based entirely on MMVF after removal of the binder.ResultsHere we report the oxide composition of 23 modern MMVF from Germany, Finland, UK, Denmark, Russia, China (five different producers) and one pre-1995 MMVF. We find that most of the investigated modern MMVF can be classified as “High-alumina, low-silica wool”, but several were on or beyond the borderline to “pre-1995 Rock (Stone) wool”. We then used well-established flow-through dissolution testing at pH 4.5 and pH 7.4, with and without binder, at various flow rates, to screen the biosolubility of 14 MMVF over 32 days. At the flow rate and acidic pH of reports that found 47 ng/cm2/h dissolution rate for reference biopersistent MMVF21 (without binder), we find rates from 17 to 90 ng/cm2/h for modern MMVF as customary in trade (with binder). Removing the binder accelerates the dissolution significantly, but not to the level of reference biosoluble MMVF34. We finally simulated handling or disposing of MMVF and measured size fractions in the aerosol. The respirable fraction of modern MMVF is low, but not less than pre-1995 MMVF.ConclusionsThe average composition of modern stone wool MMVF is different from historic biopersistent MMVF, but to a lesser extent than expected. The dissolution rates measured by abiotic methods indicate that the binder has a significant influence on dissolution via gel formation. Considering the content of respirable fibres, these findings imply that the risk assessment of modern stone wool may need to be revisited based on in-vivo studies of MMFV as marketed (with binder).Electronic supplementary materialThe online version of this article (doi:10.1186/s12989-017-0210-8) contains supplementary material, which is available to authorized users.

When assessing a mixing process, mixing quality is a characteristic parameter. To determine the optimum mixing time, it is necessary to measure the mixing efficiency as a function of mixing time. Mixing efficiency is determined by a sufficient number of sample analyses after certain mixing times. The novel method of image analysis allows to rapidly determine the optimum mixing time without sampling and complex sample analysis being required. In this study the model products have different particle sizes and colors to see a difference between them in the image analysis program. Analyzing a real mixture to find chemical substitutes for all particle components is impossible. The study can help the plant engineer to mark a component of interest for finding the optimum point of stationary equilibrium. In this paper the theory for sampling and comparing multi-component mixtures by image analysis to determine the mixing efficiency will be also described and discussed.

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This study reports on research results in the field of powder mixing in a discontinuously operated charge mixer. The mixing time for a confidence interval can be determined from the mixing efficiency that characterizes the mixing of the participating solid components as a function of the mixing time. The mixing efficiency is determined here with the help of an image analysis method developed for these purposes. The particle fraction, that is interesting in terms of its distribution, is partially replaced for this purpose by a similarly behaving but optically well identifiable tracer material. A dispersion coefficient can be obtained from the analysis of the mixing trial. The practical application of statistics on image analysis is described and discussed along with a description of the possibilities and limitations of the measurement method. The description of the procedure to determine the dispersion coefficient is built on that.

Powder mixing is a typical operation in particle technology. This work presents a method for the determination of the homogeneity of dry nanoparticle powder mixtures to measure the limit of mixing quality. The research results given here reflect the experimental effort required to study nanoscale solid mixtures consisting of a two-component system of Aerosil 200 and the titanium dioxide additive P25. The experimental effort can be evaluated by means of statistical methods. The parameter measured is the so-called homogeneity or mixing efficiency. It is determined by means of an energy-dispersive X-ray spectroscopy detector attached to a transmission electron microscope. The results will show that the optimal homogeneity depends on the additive concentration, the magnification of the transmission electron microscope, and the number of agglomerates, which have to be analyzed.