Why should environmental and textile specimens be adjusted before testing?
The tester found that the test results were quite different from the same sample which measured between laboratory with 21℃, 65% RH and workshop with 28℃, 40% RH. In addition, the temperature and humidity of the sample itself will also affect the stability of the test results. In order to reduce the errors caused by these external conditions and the moisture content of the textile samples, and to obtain stable and accurate measurement data, it is very important to adjust the temp and humidity of the environment and samples.
Requirements for temperature and humidity in textile testing.
The standard atmospheric: Temp of 20℃ (68℉), RH of 65%.
Standard alternative atmosphere: Temp of 23.0℃, RH of 65.0% or temp of 27.0℃, RH of 65.0% in the tropics. The standard alternative atmosphere is used only with the consent of the parties concerned.
The tolerance range of the standard atmosphere and alternative standard atmosphere: Temp, ±2.0℃ and RH, ±4.0%.
The air pressure is 86kPa – 106kPa, depending on the geographical environment of each country.
Preconditioning (if necessary) and conditioning, so that the sample meets the same requirements as the standard environment through absorbing moisture. If the test environment is required under the standard atmospheric, condition the sample to the standard moisture regain; if the test environment is required to be in a special, alternative standard atmosphere, condition the sample in accordance with the actual requirements and indicate in the report.
Specific methods for the environment and sample adjustment.
1 Environment adjustment
1.1 Instrument requirement
Measurement apparatus for Temperature and RH shall meet the following requirements.
Accuracy: temp ≤ 0.1℃, RH ≤ 0.1%.
The uncertainty of measurement is that the temperature doesn’t exceed ±0.5℃ and the relative humidity doesn’t exceed ±2.0%.
1.2 Control method
In order to monitor the changes of temperature and humidity at different points in the laboratory periodically, the monitoring points should not be less than 1 in 50m³. Check the airflow in the laboratory if the environmental changes in different positions do not conform to tolerance.
The changes of temperature and relative humidity may exist in the whole working area, and the position selected should be close to the main working area.
2 Sample processing
In order to ensure that the sample is balanced by moisture absorption during conditioning, it is necessary to preconditioning the samples with high moisture content and moisture regain. The so-called preconditioning is to put the sample material in the atmosphere with a relative humidity of 10.0%-25.0% and temperature not exceeding 50.0℃ for reducing the moisture content, general 4H can meet the requirements. Note: for some textiles with resins, surfactants, and pastes on its surface, the sample should be treated before preconditioning and preconditioning.
Before each performance test, the textile shall be placed at standard atmospheric conditions for a certain period of time to achieve a moisture absorption balance, such a process is called conditioning. During the conditioning period, the air can flow smoothly through the specimen to be tested until it reaches the moisture balance with the air. Conditioning more than 24H for the general textile, and more than 4H for the synthetic fiber product. The conditioning process should not be interrupted, if interrupted, it must be adjusted again according to the regulations.
Common preconditioning and conditioning are shown in the following table: selected from standard ASTM D1776
3.1 The thermo-hygrometer shall be placed in a well-ventilated place, separate from such devices as control heating, humidity control, and air-conditioning piping, and shall not be installed on the surface of direct sunlight and next to the air conditioner, etc. Display the correct value after 30min.
3.2 To ensure the stability of the thermo-hygrometer, that is, keep the sensor position constant of the debugger / controller.
3.3 In the whole air-conditioning environment, it is necessary to avoid the lamination caused by the shortage of airflow, heat or humidity, and the lack of strict sealing, so as to keep the uniform of temperature and humidity.
3.4 The outer structure of the thermo-hygrometer shall be in good condition, with no mechanical damage, no scratches or rust on the surface, and there are no defects that affect the performance of the measurement.
Humidity and temperature are the most basic conditions in textile fabric testing, the parties concerned should negotiate the conditions of the test according to the relevant standards or their own circumstances, so as to ensure the comparability and consistency of the test results and provide the basic guarantee for improving the quality of textiles.