Volume 73, Issue 6

Two impact modifiers, based respectively on polybutadiene (PB) and poly(butyl acrylate-co-styrene) (PBA), are compared in blends with four glassy polymers: polycarbonate (PC), poly(methyl methacrylate) (PMMA), poly(styrene-co-acrylonitrile) (PSAN), and poly(vinyl chloride) (PVC). Dynamic mechanical tests show glass transitions at about -80 °C in PB and -15 °C in PBA. Both modifiers have grafted PMMA shells, which are seen in the transmission electron microscope (TEM) to be about 10 nm thick. The two-stage PB particles have 200-nm-diameter polybutadiene cores, whereas the three-stage PBA particles have 260-nm-diameter PMMA cores, with 20-nm thick PBA rubber inner shells. Under tension, the PB particles cavitate to form single voids on reaching a critical volume strain, and subsequently offer little resistance to dilatation. By contrast, tensile tests performed in situ in the TEM show that the PBA shells form fibrils that are anchored to the rigid core, and act as constraints on further dilatation: the stresses developed in the PBA fibrils can be sufficient to draw fibrils from both the PMMA core and the PSAN matrix. There is evidence that the PMMA shells can debond from the matrix both in cryogenic fracture and in fatigue at 23 °C. Tensile dilatometry shows that the PB particles cavitate at higher strains than the PBA particles, but that the PB particles then cause a rapid volume increase, leading to a low strain at break. By contrast, the PBA particles produce a more controlled dilatation, and higher strains to break. Later papers in this series treat the mechanical and rheological behavior of these blends in more detail.

The influence of impact modifiers composed of an elastomer-based core and a poly(methyl methacrylate) (PMMA) shell on the melt flow properties of different thermoplastics has been studied, using both steady-state and dynamic viscosity measurements. The melt viscosities of the rubber-toughened blends were similar to those of the matrix polymers, over the range of shear rates commonly applied during melt processing. In the case of the matrix polymers, viscosity curves obtained under dynamic conditions coincided with those obtained under steady-state conditions. However, for blends the two curves show a slight divergence at low strain rates, where yielding is observed.

Expressing the amount of a catalyst is often most conveniently done by assessing its catalytic effect. Under zero-order kinetics the catalyzed rate of conversion for a specified reaction is constant and proportionate to the amount-of-substance concentration of catalyst present. Defining the kind-of-quantity "catalytic activity" as a property of the catalyst measured by the catalyzed rate of conversion, the coherent SI unit is mole per second. Following thorough discussions in the IUPAC, the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC), the International Union of Biochemistry and Molecular Biology (IUBMB), and the World Health Organization (WHO), a petition was presented by the IFCC to the International Committee for Weights and Measures (CIPM) on a special name "katal", symbol kat, for "mole per second" when used in measuring catalytic activity. This request was granted by the General Conference for Weights and Measures (CGPM) by Resolution 12 (1999). Hereafter, the coherent SI unit katal = 1 mol s­1 should replace the off-system IUB unit "(enzyme) unit" = 1 mmol min­1 16.67 nkat. Thus, by suitable definition of reaction conditions, results for catalytic activity and derivative kinds-of-quantity are metrologically traceable to the SI.

_ Human exposure to outdoor air pollution is believed to cause severe health effects, especially in urban areas where pollution levels often are high, because of the poor dispersion conditions and high density of pollution sources. Many factors influence human health, and a good assessment of human air pollution exposure is, therefore, crucial for a proper determination of possible links between air pollution and health effects. Assessment of human exposure is, however, not straightforward, and this is the background for the present paper, which recommends how to carry out such assessments. Assessment of human exposure to air pollution may be carried out by use of: categorical classification, application of biomarkers, analysis of air pollution data from routine monitoring networks, personal portable exposure monitors, or application of mathematical air pollution exposure models. The categorical classification is a crude indirect method based on indicators of exposure such as type of residence, type of job, presence of indoor sources, etc. Categorical classification is generally inadequate for application in air pollution epidemiology. Biomarkers can be a strong instrument in assessment of health effects and provide information about air pollution exposure and dose. Use of biomarkers is, therefore, particularly useful when applied in combination with exposure assessment through one of the methods 3 to 5. The main focus of this paper is on these three methods for determination of human air pollution exposure. The optimal solution is clearly a combination of methods 2 to 5, but the available resources often set a limit to how far the assessment is carried out, and the choice of strategy will, therefore, often be very important for the outcome of the final study. This paper describes how these approaches may be applied and outlines advantages and disadvantages of the approaches used individually and in combination. Furthermore, some examples of specific applications in Denmark and the Netherlands are given for illustration.

The IUPAC/IUPAP joint working party on the priority of claims to the discovery of elements 110, 111, and 112 has reviewed the relevant literature pertaining to the several claims. In accordance with the criteria for the discovery of elements, previously established by the 1992 IUPAC/IUPAP Transfermium Working Group, it was determined that the claim by the Hofmann et al. research collaboration for the discovery of element 110 at GSI has fulfilled those criteria. For elements 111 and 112, the collaboration of Hofmann et al. produced high-quality data with plausible interpretations, but confirmation by further results is needed to assign priority of discovery for these elements. The working party was not convinced that claims of other collaborations have satisfied the discovery criteria.

The paper presents a revision of terms in the IUPAC "Nomenclature for Chromatography", Pure and Applied Chemistry, 65, 819-872, 1993. The terms revised pertain to hold-up volumes in gas, liquid, and supercritical-fluid chromatography, as well as to basic retention parameters, especially in gas chromatography. A number of related and derived definitions are described, including definitions of the terms "chromatographic process" and "chromatographic phase system". A number of the original terms were found to be misleading or superfluous, including such terms as corrected retention time, net retention time, total retention volume (time), and specific retention volume at 0 °C, and their use is strongly discouraged In Part A, the concept of the hold-up volume in chromatography is discussed. The paper also compares methods described in the literature to determine the hold-up volume. In Part B, retention parameters in gas chromatography are discussed with the aim of (i) emphasizing the physical meaning of the terms and (ii) specifying the temperatures and pressures for the terms for gas volumes and flow rates. The appendix presents revised recommendations for the terminology of some items, as well as those that are not recommended.

This paper reviews the methodology available for risk assessment of exposure to substances in the workplace. Assessment starts with the identification and classification of hazard, which must be related to the dose­effect and dose­response information available for the hazards identified. Once the potential for exposure has been characterized, it should be quantified and compared with an established safe exposure level. The degree to which it exceeds that level is a measure of the risk. Even if the assessed risk is regarded as acceptable, there is the possibility that the situation will change with time, so it is important to monitor potentially harmful exposures. Factors relevant to effective monitoring are reviewed. Addresses of Internet sites where further information may be obtained are listed along with further reading.