Chemical Permeation Testing

lab_shot_2.jpgPermeation is a process by which a chemical passes through a polymer by means of molecular diffusion. This occurs without there being any physical holes in the fabric.

How is permeation measured?

Permeation is measured by exposing the outer surface of a sample of fabric to the chemical against which it is being tested. The exposure is total and constant, and emulates total immersion conditions. The inner surface of the fabric is monitored analytically to determine the amount of chemical (if any) passing through the fabric.

What is the “breakthrough time”

The breakthrough time is the elapsed time between first exposure of the fabric to chemical and the rate of permeation reaching a target value. The target permeation rate for tests carried out according to BS EN ISO 6529 or BS EN 374-3 is one microgram of chemical passing through each square centimetre of fabric every minute. When measured according to a standard method, the breakthrough time is a value by which the performance of different fabrics can be compared.

How do we conduct the test?

All samples are conditioned for 24 hours prior to testing.

In the case of gloves, homogeneity will be assigned if not already done so by a customer. Where gloves are of homogeneous design, three samples shall be taken from the palm area. In the case of non-homogeneous design, samples shall be taken from the palm, back and wrist of glove. Gloves made of multiple constructions and/or with seams will require additional testing and sampling will be agreed with the customer.

In the case of garments, samples may be taken from:

  • The fabric of whole garments
  • Sheets of garment fabric which has not been manufactured into a garment
  • Seams cut from whole garments
  • Sample seams in garment fabric which has not been manufactured into a (whole) garment.

Challenge Chemicals

Neat challenge chemicals used i.e. at full concentration, in an undiluted state, will be of a minimum AR (analytical reagent) grade. The percentage purity of neat chemicals will be indicated on the test report.

Chemical solutions will either be purchased at the requested concentration or prepared in-house from neat chemicals and diluted using distilled water. The concentration of the solution will be indicated on the test report.

In the case of mixtures, please contact us directly for further information.

Our experimental conditions for in-house procedures include the following:

CP20 – Open loop system with dry nitrogen as the collecting medium. Fourier Transform Infrared (FT-IR) Spectroscopy is used as means of detection. 

CP30 – Closed loop system with potassium chloride solution as the collecting medium. Conductivity by hydrogen ion selective electrode is used as means of detection.

CP40 – Closed loop system with TISAB:distilled water (1:1) as the collecting medium (Total Ionic Strength Adjustment Buffer). Conductivity by fluoride ion selective electrode is used as means of detection.

CP50 – Open loop system with dry air as the collecting medium. Photo ionisation Detection (PID) is used as means of detection.

Open loop – refers to a testing mode in which fresh collection medium flows continuously through the collection chamber of the test cell and is not reused or recycled.

Closed loop – refers to a testing mode in which the collection medium is fixed.

Based on the analytical techniques employed at our Laboratory:

  • An aqueous collection medium is routinely used for detection of water soluble challenge chemicals
  • A gaseous collection medium is routinely used for detection of volatile challenge chemicals.

Of the four detection methods currently available:

  • pH (hydrogen ion selective electrode) is used as a means of detecting acids and alkalis in aqueous solution
  • ISE (ion selective electrode) is used as a means of detecting fluoride ions (F¯) in aqueous solution
  • FT-IR is used as a means of detecting gaseous phase chemicals that absorb infra-red energy
  • PID is used as a means of detecting gaseous phase chemicals that are susceptible to photo ionisation.

In some cases, only one combination of collection medium and detection technique would be appropriate, in some cases two or three options may be appropriate.

Where a chemical can be collected by more than one collection medium, it is widely acknowledged that results may differ depending on whether the medium is aqueous or gaseous.

We can advise on:

  • Where more than one option is available
  • Which is the optimum collection medium and detection technique for a given challenge chemical
  • Which system has the lowest lead time from receipt of samples

Contact Us

By telephone:

+44 (0)1737 77 86 00

Our office hours are between 9am and 5pm GMT/BST.

By email:

Fill in our enquiry form and we will get back to you ASAP.