KNITTED FABRICS: EVALUATION OF ANTIMICROBIAL ACTIVITY
UNI EN ISO 20743:2007 method
Absorption test with inoculum of the microorganism done directly on the fabric sample. The standard predicts 18-24 hours of contact but it can be adjusted to the product use (for example: if the athlete wears a shirt for 6 hours, it is possible to assess the antimicrobial effect for the actual time that the garment is used).
The microorganisms generally used to test are:
- Streptococcus aureus (human)
- Klebsiella (human)
The following potentially interesting microorganisms may be added (in order of importance):
- Escherichia coli (human)
- Pseudomonas aeruginosa (environmental)
- Bacillus subtilis (environmental)
UNI EN ISO 20645:2004 method
This test evaluates the release of the active antimicrobial (Ag) ingredient on the fabric in order to verify if there could be risks for the wearer (penetration in the organism through the skin) and/or for the environment (release during the wash). To verify if a halo forms around the fabric sample that is in contact with the selected microorganisms. This is a qualitative test.
Both above-mentioned antimicrobial tests may be performed on the fabric as is and/or after a number of washes.
KNITTED FABRICS: EVALUATION OF THERMO PHYSIOLOGICAL PROPERTIES (COMFORT)
ISO 11092:2014 method
Determination of physiological properties. Measurement of thermal resistance and to water vapour in stationary conditions (proof of breathable hot plate). This method serves to determine both the thermal resistance (Rct) and resistance to water vapour (Ret) relating to textiles, membranes, coatings, etc. by simulating heat and mass transfers that are produced close to human skin. The equipment used in this type of test is called Sweating guarded hotplate or “Skin Model”. It is an instrument that simulates the process of heat and body humidity transfer occuring at the interface of the human body. The unit is placed within a weather chamber at a maintained constant temperature and humidity with an air flow presence.
Measurement of thermal Resistance
The thermal resistance of the apparel represents the resistance to heat flow compared to the clothing and the layer of air present between the clothes and the skin. To determine Rct, the test tube is placed directly on the perforated plate maintained at a temperature of 35°C. Air temperature is of 20°C with a relative humidity of 65%. The test consists in measuring heat flow through the surface of the test tube as soon as the state of equilibrium is reached.
Measurement of Water Vapour Resistance (Ret)
The evaporative resistance Ret (Resistance to Evaporative Heat Transfer) evaluates the breathability of a fabric, in other words, its capacity of humid air passing through. Breathability is generally linked to the porosity of the material. A more breathable material lowers the possibility of creating condensation on the surface of the material. More breathable materials ensure that body humidity is removed more easily, thus decreasing the condensation of sweat and increasing comfort. To determine RET, both the unit of measure and air are maintained at 35°C (isothermal) with relative humidity of 40%. A cellophane membrane is placed above the porous plate that is permeable to water vapour but waterproof to liquid water. Water is sent to the plate generating vapour simulating perspiration of the human body. The fabric to be tested is placed over the membrane, usually with the side in contact with the human body that is in contact with the plate. The heat flow required to maintain the plate at a constant temperature represents a measure of evaporation water flow that gathers the resistance to the test tube water vapour. The lower the resistance, the greater the breathability of the fabric.
- < 6 Very good or extremely breathable. Comfortable during intense activity.
- 6-13 Good or very breathable. Comfortable during moderate activity.
- 13 – 20 Satisfactory or breathable. Not comfortable during intense activity.
- 20 – 30 Unsatisfactory or slightly breathable. Not comfortable during moderate activity.
- > 30 Unsatisfactory or not breathable. Not comfortable and short tolerance period.