10/14/2011

DuPont

Tests show DuPont™ Tyvek® protective clothing provides excellent permeation resistance to chemicals.

Recent tests conducted by an independent accredited laboratory show that Tyvek® material has an excellent barrier performance that provides protection against liquid permeation. To assess the barrier performance, permeation tests (according to EN ISO 6529 - Method A) were conducted to determine the breakthrough times of commonly used chemicals with DuPont™ Tyvek®, MPF (Microporous Film) and SMS (Spunbound-Meltblown-Spunbound) – materials which are frequently used for Type 4, 5, 6 single-use chemical protective clothing. With a breakthrough time of over 480 minutes with 2 water-based inorganic chemicals, Tyvek® offered a significantly higher barrier than the Microporous Film, while SMS showed immediate chemical breakthrough.

The tests were conducted at atmospheric pressure and at 23°C room temperature. To conduct the permeation test and determine the actual and normalised breakthrough times, 40% sodium hydroxide and 18% sulphuric acid, two commonly used chemicals in the industry, were selected. The results revealed the minimum value for each sample set. Tyvek® achieved a normalised breakthrough time of 480 minutes with both substances. The Microporous Film showed faster chemical breakthrough, even at a more dilute concentration of 10% for the sodium hydroxide. Because of its more open structure, SMS offered no protection against such chemical permeation.

Penetration test results (according to EN ISO 5630) showed virtually no difference between the three materials, indicating the liquid barrier of the three materials seems to be of equal protection. However, the penetration test according to EN ISO 6530 stipulates just one minute of exposure to the hazardous substance (which is rarely the case in working conditions), whereas the permeation test according to EN ISO 6529 (“Protective Clothing – Protection against Chemicals – Determination of Resistance of Protective Clothing Materials to Permeation by Liquids and Gases”) provides indications of the long-term response up to a 8 hour-working day of a material and therefore has greater practical relevance.




Background
Liquid penetration is a physical process whereby a liquid penetrates a fabric by passing through pores or holes in the fabric. Permeation is the process by which a hazardous liquid chemical moves through a protective clothing fabric on a molecular level. The resistance of a protective clothing fabric to permeation by a potentially hazardous chemical is determined by measuring the breakthrough time and the permeation rate of the chemical through the fabric. Permeation rate is the rate at which the hazardous chemical permeates through the test fabric. Permeation rate is expressed as a mass (in µg) of hazardous chemical flowing through a fabric area (in cm2) per unit of time (in min). The actual breakthrough time is the time elapsed between initial contact of the chemical with the outside surface of the fabric and the detection of the chemical at the inside surface by the analytical device. The normalized breakthrough time – according to EN ISO 6529 and EN 374-3 – is the elapsed time between initial contact of the chemical with the outside surface of the fabric and the time at which the chemical is detected at the inside surface of the fabric at a permeation rate of 1,0 µg/(cm2 x min).