Analytical Investigations on a Releasing Agent Application in Aluminium Diecasting (6 pp)

Abstract

Releasing agents, applied in the aluminium diecasting process, usually consist of water, oils, waxes, polysiloxanes, as well as of a set of additives like emulsifiers, corrosion inhibitors, and biocides. During spray application and part release, gases and aerosols are emitted into workplace air. The chemical compositions of these emissions are determined by the components of the releasing agents and their reaction products formed during thermal stress of more than 700 degrees C. In the frame of the joint project, the analytical tasks were to develop an appropriate sampling strategy for this production environment, to draw conclusions about the occurrence of hazardous chemicals from production plant studies and from laboratory-scale thermolysis experiments, and to determine the biodegradability of customary releasing agents. During realistic test production, active air sampling was performed in a production hall using different adsorption materials. Cotton fabric sheets were positioned in the production area as passive samplers. Thermolysis experiments were performed at 600 degrees C with sealed quartz ampoules. The biodegradability of different releasing agents was determined according to German industry standard DIN 51828 (2000). For analyses, GC/MS (headspace), FTIR, HPLC, IC, and ICP-OES techniques were applied. The substance spectrum, which was found in workplace air, was dominated by saturated and nonsaturated aliphatic hydrocarbons. Besides these, alcohols, alkyl phenols, xylenes and other benzene derivatives, aldehydes, glycols, carboxylic acid esters, and amides were present. The German limiting value of 40 mg/m3 of complex hydrocarbon mixtures in a diecasting workplace atmosphere was clearly under-run. Total hydrocarbon contents ranged between 2.7 and 6.3 mg/m3. Five different PAH were found in the air close to the diecasting machine, with maximum concentrations between 0.05 and 3.06 microg/m3. Concentrations of nonylphenols ranged from 10 to 200 microg/m3, and those of triethanolamine from 20 to 30 microg/m3. From 17 elements analyzed, only B, Fe, P, S, Si, and Ti were emitted in small amounts. It was striking that the PAH patterns resulting from thermolysis experiments were quite the same compared to those determined during the diecasting process. An influence of water and of Fe/Al on the composition of the thermolysis products could mostly be shown. The degrees of biodegradation of three releasing agent extracts after 21 days were 21%, 29%, and 55%, respectively. A sampling strategy was developed, which allows an emission assessment for the industrial process of aluminium diecasting. It enabled one to control limiting values, to characterize a wide variety of compounds emitted, and to identify and quantify relevant pollutants. Only a few hazardous substances could be detected during the exemplary use of one releasing agent within the compounds emitted into workplace air. Indications were found, that the prediction of the formation of harmful substances from releasing agent components should be possible via thermolysis experiments. The biodegradability test can serve to assess the expenditure of disposal of the usual leakage run-off of excess agent during production. Investigations on further differently composed releasing agents, e.g. powders, would be desirable. A substitution of nonylphenol ethoxylates by less harmful components would surely be an improvement of a releasing agent with regard to work safety and health care, because of avoiding the emission of toxic and endocrine active nonylphenols. The surprisingly wide range of biodegradability of the investigated releasing agents points to an optimization potential, that has obviously not yet been considered.