An Investigation of Sample Bag Hydrocarbon Emissions and Carbon Dioxide Permeation Properties

The equipment for collecting dilute exhaust samples involves the use of bag materials (i.e., Tedlar®) that emit hydrocarbons that contaminate samples. This study identifies a list of materials and treatments to produce bags that reduce contamination. Based on the average emission rates, baked Tedlar®, Capran® treated with alumina deposition, supercritical CO₂ extracted Kynar® and supercritical CO₂ extracted Teflon NXT are capable of achieving the target hydrocarbon emission rate of less than 15 ppbC per 30 minutes. CO₂ permeation tests were also performed. Tedlar, Capran, Kynar and Teflon NXT showed comparable average permeation rates. Based on the criteria of HC emission performance, changes in measured CO₂ concentration, ease of sealing, and ease of surface treatment, none of the four materials could be distinguished from one another. Additional information from further testing would need to be added to the results of this study in order to choose a single optimum sample bag material for vehicle emission testing.