Dimensional stability at elevated temperature

 

 

Principle
The test measures the lateral dimensional changes of specimens from the laminate under test over an extreme range of relative humidifies at elevated temperatures.

Apparatus
1. Oven, capable of being maintained at (70 ± 2) °C.
2. Conditioning chamber, with an atmosphere of relative humidity within the range 90 to 95 % and at a temperature of (40 ± 2) °C.
3. Conditioning chamber, in accordance with EN ISO 291, with a standard atmosphere of (23 ± 2) °C and relative humidity (50 ± 5) %.
4. Means for measuring lengths, of 200 mm to the nearest 0,02 mm.
5. Desiccator, of suitable size.

Test specimens
Each specimen shall be (250 ± 2) mm long, (50 ± 1) mm wide and of the thickness of the laminate under test. The edges shall be smooth and free from cracks. Measuring marks shall be made on the decorative face of the specimens approximately 200 mm apart and 25 mm from each end.
Eight specimens shall be tested, four of them with their major axes parallel to the machine direction of the fibrous sheet material (for example paper) from which the sheet has been made, and four with their major axes at right angles to the machine direction. Two specimens from each direction shall be used for the dry-heat test and two for the high-humidity test.
If the machine direction is not known, carry out flexural strength tests at various angles. The highest value will usually be given by the specimen cut parallel to the machine direction.
Before making the first measurements, all specimens shall be kept for at least 72 h in a standard atmosphere of (23 ± 2) °C and (50 ± 5) % relative humidity.

Procedure
All measurements of length shall be made to the nearest 0,02 mm. Measurements shall be made within 5 min after removal of the specimens from the conditioning atmosphere or the desiccator.

1. Dry-heat test
Taking two specimens in each direction, measure the distance between the marks on each specimen with the specimens laid flat, and then place them in the oven  maintained at (70 ± 2) °C.
At the end of 24 h, remove them and allow them to cool to ambient temperature in the desiccator for 1 h, and then re-measure the distance between the marks.
2. High-humidity test
Taking the remaining two specimens in each direction, measure the distance between the marks and then place them in the conditioning chamber (see 17.2.2) at (40 ± 2) °C and relative humidity within the range 90 to 95 %. After (96 ± 4) h, remove each specimen, wipe it free of surface water with a cloth, and immediately re-measure the distance between the marks.

Expression of results
Calculate the change in measured length of each specimen as a percentage of the initial measured length.
Calculate the mean percentage change in measured length for each of the four pairs of specimens, to the nearest 0,05 %.
Calculate the cumulative dimensional change for each direction of the sheet. This change is the sum of the mean absolute percentage changes in each of the dry-heat and high-humidity tests. The absolute figure shall be reported.