New SATRA test method for odour control

The recently published SATRA TM360:2018 test method evaluates the effectiveness of odour-absorbing materials, so will be useful when developing and comparing such items.

by Martin Heels

There are several SATRA test methods that can be helpful in order to substantiate claims of footwear materials having odour-absorbing or odour-reducing properties. The suite of appropriate test methods has been extended recently with the publication of SATRA TM360:2018 – ‘Method for the determination of the odour-absorbing properties of insole materials’ to quantitatively evaluate both the odour-absorbing and odour-retaining properties of test specimens. Although the test method was developed primarily for insoles, it can be relevant for lining materials and other components in contact with the foot if the material is designed to absorb and retain odour.

Test principle

The principle of the test method involves pre-weighed specimens being prepared from the test material and stored in a saturated atmosphere containing butyric acid – a very odourous chemical (figure 1). The amount of butyric acid absorbed by the test specimen is measured by the increase in its mass. A standard carbon reference material is placed in the saturated atmosphere alongside the test specimen, and the mass gain is expressed as a percentage of the original mass compared to the measured absorption of the standard carbon. Hence, the amount absorbed is reported as a percentage of the standard carbon’s mass gain. It should be noted that butyric acid has a strong, unpleasant odour and causes skin burns and eye damage. Therefore the testing procedure should only take place with suitable local exhaust ventilation.

Figure 1: Apparatus configuration for the absorption of materials

Odour retention

If the material readily released the absorbed odour, it would not be satisfactory to the end user or wearer. As a result, any absorbed odour must stay absorbed and not be released. SATRA TM360 includes a procedure to determine how effectively the odour is retained by the test specimens. After the five days of the absorbing stage, a flow of clean air that has passed through a desiccant is blown across the specimens to remove butyric acid from the atmosphere surrounding the test specimen and standard carbon (figure 2). If the test specimen does not retain odour effectively, it will also be removed during this process. However, because some losses are to be expected, the reduction in mass is compared to that of the standard carbon.

Figure 2: Apparatus configuration for the desorption of materials

Alternative SATRA test methods

SATRA TM435:2010 – ‘Qualitative odour absorption test’ is a qualitative test to determine odour absorption. In this procedure, an odour panel compares the effectiveness of the odour-reducing property of the test specimen alongside commercially-available odour-absorbing reference materials. Each member of the odour panel grades the test specimens using a scale of zero (‘no odour’) to five (‘very strong odour’). As this grading is subjective and only considers the absorbing properties, SATRA TM360 has been developed to provide an objective alternative.

A odour panel assessing the odour-reducing property of test specimens in accordance with SATRA TM435

Materials can have odour-reducing behaviour as a result of antimicrobial properties, and this is subjectively assessed using SATRA TM351:1996 – ‘Bottle incubation test’. Test specimens are inoculated with an artificial perspiration solution and a soil suspension which provides a source of microorganisms. The test specimens are sealed in glass jars which are incubated at 30°C, and the odour from the jars is assessed regularly by an odour panel. If the test specimen contains antimicrobial properties, the odour in the vial will be negligible. However, if there is no treatment to control the growth of microorganisms, there will be a build up of ammonia gas from the breakdown of the urea from the artificial perspiration solution, and so a strong odour will be created.

Assessing odour control properties

It is important to have test data available for use when substantiating claims that footwear materials have odour-reducing properties. The mechanism by which the odour-reducing material is effective needs to be understood so that the most appropriate testing can be selected. SATRA TM360:2018 provides a quantitative method to determine odour absorption and retention, whereas SATRA TM435 provides a qualitative method for odour absorption. If the odour-reducing material relies on an antibacterial treatment, SATRA TM351 would be a more appropriate analysis.

How can we help?

SATRA’s chemistry laboratory can undertake analysis to all of the methods mentioned in this article. Please contact chemistry@satra.com for further details.

Publishing Data

This article was originally published on page 46 of the March 2019 issue of SATRA Bulletin.