The test method of Water vapour permeability of leather

§ A precision balance with specific readout precision

§ An instrument for determination of moisture content /dry mass content/ in vvarious samples

As the Sampler 2000 is installed in the moisture analyzer, it is possible to perform control process in which permeability of water vapour through various kinds of leather is tested. The procedure is clearly described in the latter part of the publication. A design including a moisture analyzer and sampler is a new developed technology for testing water vapour permeability. the method presented below does not require leather seasoning. Thus, it causes significant shortening testing procedure if compared to method no. PN-P-22138.

 As comparison tests, there have a series of tests performed for water vapour permeability through different kinds of leather. The tests were conducted in RADWAG Testing Laboratory and Chair of Technology and tanning Shoes at Technical University in Radom. 

 

Description of a method for water vapour permeability with application of moisture analyzers. 

Water vapour permeability is precise measurement of mass decrement of water which evapourates from sampler interior through tested leather sample. Water vapour permeates through leather as result of its pressure increase, which is caused by increasing temperature inside the sampler. 

A testing device for permeability method is a moisture analyzer. It is designed from a precision balance with readability of 1 mg and a drying chamber with set of halogen lamps temperature sensor and converting circuits with a digital display. Precision balance is to precisely determine mass in testing cycle. Electronic circuit through feedback from temperature sensor and halogen lamps maintains set temperature. Electronic components of a moisture analyzer process collected data and indicate results on moisture analyzer display. Data recording takes place automatically with no operator action, with set time interval. Data can be processed on: 

§ Personal computer with installed and active software PomiarWin.

§ Printer

§ Manually by making notes. 

 

The most convenient and recommended solution is a computer with installed software. 

Collected data are used for designing a graph from drying process. The graph indicates speed of water vapour permeation though testes leather sample, and speed of water evapouration in “zero” method. 

 

As for test conditions, the operator should monitor ambient temperature and humidity. Ambient temperature should be set between 21o C to 26 oC, and humidity between 40% to 60%. Temperature changes during test procedure should not exceed ± 2 oC. Humidity change during test procedure should not exceed ± 5 %. It is assumed, that drying chamber temperature in which the sampler is located is stable during test procedure. 

 

Devices and substances used for method processing

A workstation for water permeability test should be equipped with below specified devices and substances:

- A moisture analyzer with readability 1mg

- Sampler 2000

- Thermohigrobarometer /record of ambient conditions /

- A pipette /transport of distilled water /

- Distilled water

- Control thermometer PT 101 / control of distilled water temperature and control of temperature inside drying chamber of a moisture analyzer – optional equipment /

- A computer with PomiarWin software /optional equipment / 

 

Testing of water permeability should be performed in stable ambient conditions. It is assumed, that ambient conditions are stable if temperature and humidity are within specified

thresholds, and mentioned in point 3.1 above.

A moisture analyzer should be plugged to mains at least 30 minutes before test initiation.

Distilled water that is used for the test should have temperature close to ambient temperature of test room. Water should be stored in test room for at least 24 hours before test procedure initiation for its thermal stabilization. 

 

Cut a disc section of 54 mm ± 2mm from a selected piece of leather. As they are cut, place

them in test room in which the permeability test will be performed. It is recommended, that sample temperature is close to ambient temperature of test room.

 

Test procedure consists of two activities. Sequence of their performance does not influence

the result of test procedure. The first step is determination of distilled water decrement, which permeates through a sample as result of pressure created inside the Sampler 2000. The second part of test procedure is determination of water vapour decrement with no sample put into the Sampler.

 

1. Start a moisture analyzer according to procedures described in user manual of the instrument

2. Take out the standard cross holding the weighing pan and install cross from Sampler 2000 kit. Cross mass is adjusted in such a way that it equals mass of standard cross. 

3. Start computer and software PomiarWin (if this means of data record is required))

4. place a leather sample inside the sampler cover (the top side of a sample should face upwards, towards the holes in sampler cover) 

5. Place below components inside drying chamber of a moisture analyzer:

- Sampler cover with leather sample,

- Pressure ring,

- Sampler body

- As the display indication stabilizes, press

ZERO/TARE button (all elements put on weighing pan of the instrument are tarred) 

6. Program drying parameters for:

- temperature 40o

C

- test time 60 minutes /time defined switch off /

- displayed result [g]

(a moisture analyzer sends current weighing data through RS 232 according to set time interval. Communication time interval is set in menu P5-03 Line_t “print time interva.

7. Start drying process. During drying process, the display of a moisture analyzer will indicate data like:

- current quantity of distilled water

- test time,

- temperature in drying chamber, etc. 

8. At the moment of placing a sample, using a pipette, dose approximately 5 g - [M1] of distilled water to sampler interior.

If a moisture analyzer does not cooperate with any peripheral devices, note down mass of dosed water. 

9. Take the sampler out of drying chamber and close tight the sampler cover to its body. The sample should be seized. Pay attention not to pour distilled water from the sampler.

10. As closed, place the sampler inside drying chamber of a moisture analyzer. 

11. On analysis completion, the display of moisture analyzer will indicate final mass [M2] that is in the sampler. 

 

Zero test is determination of evapouration speed of distilled water from a sampler that is

located in drying chamber of a moisture analyzer with temperature set for 40oC and test time 60 minutes. The test does not require seizure of a leather sample in sampler interior. The test procedure is described below:

1. Start a moisture analyzer according to procedures described in user manual of the instrument

2. Start computer and software PomiarWin (if data record is necessary)

3. Install a sampler according to below presented schema 

4. Locate the mounted sampler inside drying chamber of a moisture analyzer , and as it stabilizes, press ZERO/TARE button 

5. Program drying parameters for:

- temperature 40o

C

- test time 60 minutes / time defined switch off /

- displayed result [g]

(a moisture analyzer sends current weighing data through RS 232 according to set time interval. Communication time interval is set in menu P5-03 Line_t “print time interval”) 

6. Start drying process – at moment of placing a sample, using a pipette, dose approximately 3g - [M01] of distilled water to sampler interior. If a moisture analyzer does not cooperate with any peripheral devices, note down mass of dosed water.

7. Start drying process. During drying process, the display of a moisture analyzer will indicate data like:

- current quantity of distilled water

- test time,

- temperature in drying chamber

8. On analysis completion, the display of moisture analyzer will indicate final water mass that is in the sampler [M02]. 

Assuming that test conditions are compatible with the recommendations from point 3.1., and

that temperature of distilled water is stabilized with ambient temperature of test room, than

result of zero test can be accepted as constant. Decrement of water during test depends on:

- Quantity of heat which is directed to the sample /temperature in drying chamber of a moisture analyzer /

- Initial temperature of distilled water /too low temperature will require consumption of some energy for balancing thermal balance /