Influence of molecular parameters on the sink effect in test chambers

The determination of the specific emission rates of individual products and materials under indoor-related conditions requires the use of climate-controlled emission test chambers. However, most chambers demonstrate an inherent sink effect, i.e. the released components undergo adsorption/desorption processes with construction materials. Furthermore, this sink effect is enhanced by introducing an adsorbing sample surface into the test chamber. The degree of adsorption, as well as the extent of the recovery, can vary significantly for different chambers and samples and also depends on the physical properties of the relevant substance. Whereas the sink effect caused by the chamber itself can be reduced by using appropriate construction materials, it is not possible to avoid the sink effect attributable to the actual sample. For this reason it is of importance to evaluate chambers and samples for possible sink effects, taking into consideration the physical properties of substances. This can be achieved by kinetic modeling of emission data and determination of rate constants. The kinetic parameters obtained from curve fitting were combined with molecular parameters and applied to multivariate statistics. The properties of three different chambers with and without sink could be compared by cluster analysis. Principal component analysis revealed that the sink effect essentially depends on the boiling point of the substances examined.

Emission test chambers are operated by research institutions and testing laboratories for different purposes. The determined emission rate value of a building product is a function of the chamber construction, the material to be tested and the molecular properties of the target compound. In this work it is demonstrated, which parameters have the main influence on the test result. Furthermore it is shown how multivariate statistical analysis can be applied to experimental data to characterize the sink effect under dynamic conditions. This new technique provides a suitable tool for the evaluation and comparison of test chambers.