Din 53380 3 1998 standard

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DEU丁SCHENORM

July 1998

Determining the gas transmission rate of plastic film, sheeting and mouldings by the carrier gas method

DIN 53380-3

ICS 8 3.14 0.10; 8 3.14 0.99 Descriptors: Plastics, film, sheeting, plastic mouldings, testing, gas transmission rate.

PrOfung von Kunststoffen －巴estimmung der Gasdurchlassigkeit －丁eil 3 : Sauerstoffspezifisches Tragergas­ Verfahren zur Messung an Kunststoff“ Folien und Kunststoff-Formteilen In keeping with current practice in standards published by the International Organization for Standardiza­ tion (ISO), a comma has been used throughout as the decimal marker.

c 。 ntents Foreword ....... ......................

Page

Page

2

8.7 Load resistor ........................

8.8 Voltage recorder .....................

2 Normative references . ....... .......

2

9 Checking the sensor ..................

6

3 Concepts ...

3.1 Area-related oxygen transmission rate 3.2 Volume-related oxygen transmission rate . ....... ......................

3.3 Length-related oxygen transmission rate ................................

2

10 Calibration constant ..... ...... ...

6

2 2

11 Specimen preparation ...............

11.1 Film and sheeting ...................

11.2 Holl w bodies . ....... . .... . ..

11.3 Number of specimens ...............

7 7 7 7

4 Designati n .

2

5 Principle .

5.1 Film or sheeting 5.2 Hollow-bodies

3 3 3

7 7 8 8

6 Reagents ..

6.1 Carrier gas ...

6.2 Oxygen and oxygen-gas mixture ..

6.3 Vacuum grease .

6.4 Adhesives

3

12 Testing of film and sheeting .... . ...

12.1 Diffusion cell .......................

12.2 Procedure .........................

12.3 Determining the zero level . .... . ..

12.4 Determining the oxygen transmission rate ...............................

12.5 Film or sheeting having a high oxygen transmission脚

3 3

7 Apparatus

4

8 Components of diffusion cells ..........

8.1 Joints .... . ..... . ..... . .......

8.2 Humidification components . . ......

8.3 Components for removal of oxygen from carrier gas ..........................

8.4 Fl wmeter ..... ....... ....... . .

8.5 Valves .............................

8.6 Sensor .............................

5 5 5

1 Scope .....

。

。

2

3 龟

5 5 5 5

。

6 6

8 8

13 Testing hollow bodies ................ 8 13.1 Closed bodies ...................... 8 13.2 Open bodies ....................... 10 13.3 Testing of tubes .................... 10 14 Evaluation ..........................

14.1 Area-related oxygen transmission rate ..

14.2 Volume-related oxygen transmission rate ...............................

14.3 Length-related oxygen transmission rate ....... ................ ......

11 11 11 11

15 Test report ......................... 11

Continued on pages 2 to 11.

Translation by DIN-Sprachendienst.

In case of doubt, the German-language original should be consulted部the authoritative text.

。

© No part of this 甘冒nslation may be re 阳odu四 d without the M r permi部ion of DIN Deutsches lnstitut fur Normung 且以 ， Berlin.

Beuth Verlag GmbH, D 10772 Berlin, has the exclusive right of sale for German Standa时sρ／N-Normen).

Ref. No. DIN 5 3 3 8 0 -3: 1998 -0 7 English price group 08

Sales No. 0108 11.99

Page 2 DIN 53380-3 : 1998-07

Foreword This standard has been prepared by Technical Committee Kunststoff-Folien und kunststoffbeschichtete Flachengebilde (Kunstleder); allgemeine Eigenschaften of the Normenausschuß Kunststoffe (Plastics Standards Committee). It is based on ASTM D 3985-95, but, unlike the ASTM Standard, its application is not limited to film and sheeting, and it also covers plastic hollow bodies (such as packing containers and tubes). Details of humidifying the carrier gas have also been included.

1 Scope The method specified in this standard serves to determine the oxygen transmission rate (permeability to pure oxygen or oxygen gas mixtures, e.g. air) of plastic film and sheeting as defined in DIN 16922 and plastic hollow bodies (e.g. packaging containers, plastic tubes), thereby enabling their suitability for packaging and engineering applications to be assessed. The method can be used to determine transmission rates ranging from about 0,05 cm3/(m2. d . bar) to 1 O00 cm3/(m2 . d . bar) for film and sheeting and from about 0,0005 cmV(d . bar) to 1O cmV(d . bar) for hollow bodies, where d denotes a day as a unit of 24 hours.

2

Normative references

This standard incorporates, by dated or undated reference, provisions from other publications. These normative references are cited at the appropriate places in the text, and the titles of the publications are listed below.

For dated references, subsequent amendments to or revisions of any of these publications apply to this standard only when incorporated in it by amendment or revision. For undated references, the latest edition of the publication referred to applies.

DIN 1343 DIN 16922 DIN 50008-1 DIN 53370 ASTM D 3985-95

Reference conditions, standard conditions and standard volume - Concepts and values Classification of flexible sheeting produced using plastics Artificial climates in technical applications - Controlled atmosphere over saturated salt solutions and glycerol solutions Determination of plastic film and sheeting thickness by mechanical scanning Standard test method for oxygen gas transmission rate through plastic film and sheeting using a coulometric sensor

3 Concepts 3.1 Area-related oxygen transmission rate For flat specimens of a constant thickness (such as film or sheeting), the area-related oxygen transmission rate is the volume of oxygen at standard temperature and pressure’) which passes through the specimen per unit area, time and oxygen partial pressure.

3.2 Volume-related oxygen transmission rate For hollow bodies with an unknown surface area or a varying wall thickness, the volume-related oxygen transmission rate is the volume of oxygen at standard temperature and pressure’) which passes through the specimen per unit time and oxygen partial pressure.

3.3

Length-related oxygen transmission rate

For tubes, the length-related oxygen transmission rate is the volume of oxygen at standard temperature and pressure’) which, for given cross-sectional dimensions of the tube, passes through the specimen per unit length of tube, time and oxygen partial pressure.

4

Designation

Designation of the method of determining the gas transmission rate by the carrier gas method (S):

Test DIN 53380 - S

I)

See DIN 1343 for definition.

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Page 3 DIN 53380-3: 1998-07

5

Principle

The oxygen transmission rate is determined under the conditions given below by measuring the quantity of oxygen which passes through the specimen.

5.1

Film or sheeting

A specimen is mounted as a sealed barrier between the two chambers of a cell. One chamber is purged with a stream of nitrogen, the other chamber contains oxygen. As oxygen passes through the specimen, it is transported to a coulometric sensor where it produces an electrical current, the magnitude of which is proportional to its concentration in the gas flow (cf. clause 1 O).

5.2 Hollow bodies Nitrogen is passed directly through a hollow body whose exterior is exposed to oxygen.

6

Reagents 6.1 Carrier gas

The carrier gas shall be dry nitrogen containing 0,5 YOto 3 YO(V/V) hydrogen and not more than 0,OlYO(V/V) oxygen. High-purity (99,999'0) nitrogen may be used as the carrier gas in equipment as described in subclause 8.3.

6.2 Oxygen and oxygen-gas mixture The oxygen gas used shall be dry and shall contain not less than 99,5YO(V/V)of oxygen or oxygen-gas mixtures (preferably, oxygen containing nitrogen) free of carbon dioxide (cf. subclause 8.6)and having an oxygen content known to within 0.5 YO.

6.3 Vacuum grease Vacuum grease shall be used to seal the diffusion cell.

6.4 Adhesives A gas-impermeable, pore-free, two-part adhesive shall be used when testing hollow bodies; fast-curing adhesives based on methyl methacrylate or adhesives based on epoxy resin are recommended.

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Page 4 DIN 53380-3 : 1998-07

7 Testing o f film sheeting (as i n clause 12)

Testing o f hollow bodies (as i n clause 13)

Testing o f tubes (as i n subclause 13.3)

AH

It

D

T

AH v1 v2 K B G S D L T O

w =.el

Connection to diffusion cell Valve Valve Metal tube, filled with platinum catalyst or oxygen absorbent Gas washing bottle, for humidifying the carrier gas where a low relative humidity of carrier gas is required Gas washing bottle, for establishing specific humidities in the test gas Coulometric sensor Flowmeter and valve, for setting carrier gas flow Load resistor Compressed gas steel cylinder containing carrier gas (with pressure reducing valve and pressure gauge) Compressed gas steel cylinder containing oxygen (with pressure reducing valve and pressure gauge) Figure 1 : Test apparatus (schematic)

2,

Information on sources of supply is available from NormenausschuĂ&#x; Kunststoffe, BurggrafenstraĂ&#x;e 6 , D-10787 Berlin.

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L

Page 5 DIN 53380-3 : 1998-07

8 Components of diffusion cells 8.1 Joints All joints in metallic pipes carrying the gas shall be sealed so as to be gastight. Compression couplings have proved very suitable for this purpose.

8.2

Humidification components

One of the methods described below shall be used to establish specific humidities in the test gas.

8.2.1 The gas to be humidified shall be passed through saturated salt solutions such as those described in DIN 50008-1, by which a standard atmosphere with relative humidities of 12, 33, 53, 75, 85 and 93 YO, for example, at 23 "C is produced. Gas washing bottles of about 250 cm3 capacity and about one-third full of salt solution (including the undissolved salt) shall be used, the surface area of the salt solution being not less than 15 cm2. The gas inlet shall be positioned below the surface of the solution but above the undissolved salt, allowing the gas flow to be checked by observing the gas bubbles.

8.2.2 The gas to be humidified shall be passed through distilled water at a suitable temperature. At a test temperature of 23 "C, this produces a relative humidity ranging from 22 YOto 1O0 YO. A thermostat shall be used to keep the washing bottle at the saturation temperature for the required relative humidity, which can be taken from a water vapour pressure table.

8.2.3 If tests are carried out for a prolonged period at a low relative humidity (less than 50 YOat 23 OC), the sensor (cf. subclause 8.6) may dry out. To prevent this occurring, a small gas washing bottle containing distilled water may be inserted in the carrier gas stream at the inlet to the sensor (see figure 2 (B)). Since the volume of this bottle and the take-up of oxygen in water cause a delay in the steady-state reading both the bottle volume and the quantity of water used shall be minimized. To prevent the specimen from being pressurized, the end of the carrier gas line shall lie above the surface of the water.

8.3 Components for removal of oxygen from carrier gas Before the carrier gas enters the diffusion cell, it shall be passed through a metal tube (K) containing about 5 g of a 0,5% platinum or palladium catalyst on alumina which causes any residual oxygen to react with the hydrogen in the carrier gas to form water.

If the carrier gas is pure nitrogen (99,99 %) (see subclause 6.1), the metal cartridge shall be filled with an oxygen absorbent.

8.4

Flowmeter

A controllable flowmeter (D) having a range from 5 mi/min to 1O0 mumin shall be used, enabling the carrier gas flow to be set and monitored.

8.5 Valves Two four-way ball valves ( V l , V2) shall be used for switching the carrier gas and oxygen flow to either the diffusion cell or the sensor.

8.6 Sensor The oxygen which permeates the specimen shall be detected using an oxygen-sensitive coulometric sensor (S) with nickel, cadmium, and graphite electrodes saturated with potassium hydroxide solution. To prevent the potassium hydroxide solution from drying up, humid carrier gas shall be employed, since the response time of the sensor will be otherwise reversibly prolonged. However, measurements can be carried out for a few days with dry carrier gas without damaging the detector. The oxygen molecules entering the detector react at the surface of the graphite cathode, where each oxygen molecule captures four electrons in the following reaction: O, + 2 H,O + 4 e - - 4

OH-

The OH ions then release four electrons as a result of reacting with the porous cadmium anode, as follows: 2Cd+4OH--2Cd(OH),+4eIf the detector is exhausted, it can be regenerated by applying a countervoltage. The detector will be irreversibly damaged by carbon dioxide, which converts the potassium hydroxide solution into potassium carbonate.

NOTE: Other sensors can be used if they fulfil the following requirements: 1. the reading gives approximately 1O0 YOof the oxygen injected; 2. there is a linear relationship between the output signal and the amount of oxygen injected;

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Page 6 DIN 53380-3 : 1998-07 3. the range of indication is from 2 . 10-8 g O,/h to 6 . 1O-4 g O,/h for a flow of 20 cm3/min; 4. the sensor has no resistance up to a flow of about 60 cm3/min; 5. the sensor is insensitive to moisture; 6. no reaction occurs with hydrogen.

8.7 Load resistor The voltage drop shall be measured across a load resistor through which the current generated by the coulometric sensor flows. Typical values for this resistor are 5,03 Q and 50,3 Q, giving a convenient ratio of output voltage to oxygen transmission rate in units of cm3/(m2 . d) or cmVd in the case of hollow bodies.

8.8 Voltage recorder A multiple range strip chart recorder shall be used to measure the voltage drop across the load resistor. The recorder shall be capable of measuring voltages ranging from 0 , l mV to 50 mV, at a resolution of 1 pV, and shall have an input impedance of not less than 5 kQ. An equivalent electronic display or evaluation system may also be used.

9

In principle, four electrons are produced by the coulometric cell for every oxygen molecule. In practice, the detectors generally achieve an approximately 1O0 YOconversion of the oxygen molecules injected but become less effective if a critical flow of carrier gas is exceeded. The detector may give false readings because of ageing (exposure to carbon dioxide), the electrolyte drying up or because of oxygen breakthrough and shall therefore be checked at regular intervals.

A known quantity of oxygen can be fed to the sensor via an inlet valve or using a gastight syringe. The sensor signal (peak) shall be integrated, and the quantity of oxygen recorded shall be compared with that injected. The cause of any errors exceeding 5 YOshall be identified and, if necessary, the sensor shall be replaced.

Another very accurate method of checking the sensor is that of water electrolysis. This involves allowing the carrier gas to flow through an electrolysis vessel in which water is being decomposed electrolytically. The oxygen produced during electrolysis is fed into the sensor and generates a current equal to the current consumed in electrolysis.

1O

Calibration constant

For a specimen having an oxygen transmission rate of 1O0 cm3/(m2. d . bar) and a test area of 1O0 cm2, a standard oxygen volume of 1 cm3 shall be fed to the sensor over a period of 24 hours with an oxygen pressure difference of 1 bar between the sheet surfaces.

Since each oxygen molecule generates four electrons, 1 moi of oxygen yields a charge of 4 . 96485 A . s = 3,86 . 1O5 A . s, according to Faraday's law. It follows that 1 cm3 of oxygen (= 1/22393 moi) flowing uniformly through the sensor over 24 h (= 86400s) will generate a constant direct current of

I =

3,86 . 1O5 A . s/moi . (1/22 393 moi) 86400 s

= i,99 . i0-4 A If this current is passed through a resistor and the resulting voltage drop is 1 mV, the value of the resistor (resistance), R , will be 1O-3 V/(1,99 . 1O4 A) = 5,03 Q. The connection between resistor, sensor voltage and the oxygen transmission rate of the specimen is shown in table 1.

Table 1 : Oxygen transmission rate as a function of resistance and sensor voltage

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Checking the sensor

Page 7 DIN 53380-3 : 1998-07 Accordingly, the calibration constant for the oxygen transmission rate is as follows: QA = 5,03 . 1O4 cm3 . cm2 . Q/(m2 . d . mV) (area-related); QH = 5,03cm3 . Q/(d . mV) (volume-related); QL = 5,03 cm3. m . Q/(m . d . mV) (length-related).

11 Specimen preparation 11. I

Film and sheeting

The specimens shall be of the sample material and shall be taken at points distributed uniformly overthe surface of the film. They shall be free of any flaws (e.g. holes) and show no signs of damage (e.g. creases).The specimen thickness shall be determined using a DIN 53370 thickness measuring instrument.

If the specimen is composed of several layers firmly bonded together (ยก.e. it is a composite), its surface shall be marked, and the oxygen side and the relative humidity shall be reported.

11.2

Hollow bodies

The hollow bodies used for testing, in particular filled packaging containers, shall be representative of the particular product. It is frequently necessary to empty the container before testing. This shall be done as carefully as possible, ensuring that the opening made is no largerthan necessary and can easily be sealed using a two-part adhesive.

11.3 Number of specimens Not less than three specimens per orientation shall be tested.

12 Testing of film and sheeting Diffusion cell

i

B T OK R VB L UK A

Oxygen or carrier gas inlet Thermometer wells Upper half of diffusion cell O-ring Specim en (fiIm/s heet ing) Metal tubes fixed by soldering or screwing (sealed) Lower half of diffusion cell Inlet/outlet of carrier gas Figure 2: Diffusion cell for film or sheeting (schematic)

The diffusion cell in which the specimen is clamped consists of two metal halves of circular cross section. The exposed specimen area shall be 1O0 cm2 or 50 cm2 and the total internal volume of the two halves of the cell shall be about 50 cm3 or 25 cm3. The temperature in each chamber shall be measured with separate thermometers.

The O-ring seal between the two chambers and the clamped film shall be such that it forces the specimen against the flat rim of the lower chamber as close to its inner edge as possible. The lower chamber (carrier gas side) shall have a flat, raised rim about 5 mm wide which, since it is a critical sealing surface against the specimen, shall be smooth and flat, without scratches. The inside diameter of the lower chamber will determine the specimen area tested. In order to heat the diffusion cell to a temperature of 50 "C, the lower chamber can be connected to a controllable electrical heater to ensure proper thermal conduction.

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12.1

Page 8 DIN 53380-3 : 1998-07 When testing below ambient temperature or above 50 “C, the diffusion cell shall be placed in a controlledtemperature cabinet. An alternative method is to design the two chambers so that the test temperature can be set using a liquid thermostat.

12.2

Procedure

After the specimen has been mounted, any leaks in the test arrangement shall be detected by flushing both sides of the specimen with nitrogen, and the steady-state reading attained shall be recorded as the zero level.

Oxygen shall then be supplied to one side of the specimen and the resultant steady-state value, less the zero level value, is taken to be the transmission rate.

Keep the detector initially switched off using valve V1. Open the cell and apply a thin layer of vacuum grease around the raised rim of the lower half of the cell. Then place the specimen on the greased surface, taking care to avoid wrinkles. Place the upper half on the lower half and, depending on the cell design, either screw or clamp both halves tightly together. Using valve V2, purge the air by passing carrier gas at a rate of 30 cm3/min to 60 cm3/min through the cell. After a few minutes, reduce the rate to 15 cm3/min to 30 cm3/min for the subsequent test.

12.3

Determining the zero level

After flushing the cell for 30 minutes, for example, depending on the sample material, divert the carrier gas from the lower half of the cell to the sensor by switching valve V1 (see figure 3). Generally, the sensor output as displayed by the recorder will then increase slightly, indicating that oxygen is being flushed into the sensor along with the carrier gas, most likely as a result of outgassing of the sample, leaks in the system, or a combination of the two. Wait until the sensor output current has stabilized. Thick samples may require a purge lasting a few hours, or even overnight, before they are oxygen-free, during which time the sensor shall be bypassed using valveV1, except when checking the zero level. The zero level, which should not exceed a value of 0,4 cm3/(m2. d . bar), will have been reached as soon as the reading has stabilized, ¡.e,asteady low value has been reached. If the value is higher, locate the cause of the problem and eliminate it. Inadequate removal of oxygen from the carrier gas may lead to the zero level being dependent on the carrier gas flow (cf. subclause 8.3).

Determining the oxygen transmission rate

Once the zero level, U , has been established, set valve V2 to the ‘test’ position, thereby cutting off the nitrogen flow to the upper half of the cell and replacing it with oxygen. The sensor output voltage as indicated by the recorder will rise gradually after breakthrough and eventually stabilize (cf. figure 3). Depending on the type of plastic and its thickness, steady-state conditions will be reached at any time between seconds and many hours.

During the measurement, a simple leak test can be carried out to check that the specimen is free from pores and cracking by immersing the test gas outlet (hose) in a vessel containing water. The test gas pressure will be increased by a few millibars, but if the specimen is pore-free, there will be no change in the signal except for a short peak (cf. figure 3), whereas there will be a permanent rise if pores are present.

Equilibrium may be established in a short time for thin film orsheeting, but thick samples may take several hours or days to reach a steady-state oxygen transmission rate. During this process, pay particular attention to changes in the oxygen transmission rate of the specimen if extreme relative humidities, such as O YOor 90 YO, are employed. When testing plastics such as nylon 6 or polyvinyl alcohol, several days may elapse before the pores have adjusted to the ambient humidity. In this case, it is advisable to leave valve V1 in the ‘Sensor OFF’ position, setting it to the ‘Sensor ON’ position only for short periods to check for further changes in the oxygen transmission rate.

Once steady-state conditions have been attained and the respective voltage, U,, determined, calculate the area-related oxygen transmission rate, qA, using the equation given in subclause 14.1.

12.5

Film or sheeting having a high oxygen transmission rate

Material with an oxygen transmission rate greater than 200 crn3/(m2. d . bar) will produce a high oxygen concentration in the carrier gas, possibly overloading the sensor and shortening its life. One way of avoiding this problem is to use nitrogen/oxygen mixtures such as air, or commercially available test gases with an even lower oxygen concentration, allowing for this in the evaluation. Another way of reducing the oxygen concentration in the test gas is to use a diffusion cell having a smaller test area and to cover most of the specimen surface by bonding metal foil to it (cf. subclause 6.4).

13 Testing hollow bodies 13.1 Closed bodies Packages in which the contents are sealed on all sides against the ambient atmosphere are generally considered to be closed hollow bodies. It will usually be necessary to remove the contents before testing. Exercise extreme care in doing this so that no damage is caused to the sample, which could produce incorrect results.

As a rule, the opening for removing the contents shall be made at a smooth, easily accessible location since the effect of seams on the oxygen transmission rate is of special interest in packaging testing, and it is therefore essential that they remain unaltered.

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12.4

Page 9 DIN 53380-3 : 1998-07 After emptying the package, seal the opening using a pore-free, gas-impermeable adhesive (see subclause 6.4), then bond the empty package to the device, as shown in figure 4. Mount the glass or metal cylinder used as an enclosure on the flat lower section of the apparatus. The cylinder may be replaced by a plastic bag (cf. figure 5) made of a material having a low gas transmission rate. The total area of its outlet opening shall not be more than a few square millimetres.

For testing at temperatures other than ambient temperature, place the devices shown in figures 4 and 5 in a controlled-temperature cabinet.

Flushing the outside of the specimen with nitrogen in the systems described produces the zero level, U, which takes into account all the leaks in the test arrangement, while flushing with oxygen gives a steady-state voltage, U, (cf. figure 3). Calculate the oxygen transmission rate of the hollow body, qH, using the equation in subclause 14.2.

2

1

t > E

.-c

ai

5

s'" S

m m

f

s

6 t',

St

4 Time, i n minutes 1 Switching from oxygen to carrier gas: (UE; - U), 2 Leak test 3 Switching from carrier gas to oxygen: zero level (U,)

-

4 Oxygen desorption from specimen 5 Sensor switched on 6 Sensor switched off 7 Breakthrough time

Figure 3: Test arrangement for determining the oxygen transmission rate test of plastic film or sheeting (schematic)

VB

VB

S VB Z C B K

Specimen (container) Opening for removing contents, sealed after removal Glass or metal cylinder Oxygen/carrier gas inlet Adhesive seal between carrier gas inlet and outlet tubes and container

Figure 4: Test arrangement for measuring the oxygen transmission rate of closed packaging containers (schematic)

A,

F Vacuum grease L Gastight solder joint between carrier gas tubes and baseplate S Baseplate and legs A Carrier gas inlet and outlet P Plastic bag Figure 5: Test arrangement for measuring the oxygen transmission rate of closed packaging containers using a plastic film bag (schematic)

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Page 1O DIN 53380-3 : 1998-07

VB

Figure 6: Test arrangement for measuring the oxygen transmission rate of open hollow bodies (schematic) (See figure 4 for key to symbols)

X A

Y M L

Length of tube section tested Carrier gas inlet and outlet Metal ring Metal or glass tube Gastight solder joint between plug and carrier gas tube

E N

J B

Coupling piece Rubberseal Specimen (tube section) Oxygen or carrier gas inlet

Figure 7: Test arrangement for measuring the oxygen transmission rate of tubes (schematic)

13.2 Open bodies Open hollow bodies are products having at least one opening, examples being plastic bottles and thermoformed plastic dishes for packaging purposes and not yet sealed with a lid. Before testing, the openings in these containers shall be sealed by bonding to them suitable sheets of 1O0 pm thick aluminium foil using a two-part adhesive. After the adhesive has cured, the containers may be regarded as closed packages (cf. subclause 13.1). Alternatively, an open dish or beaker may be bonded to the baseplate (S) in the test arrangement shown in figure 4 (cf. figure 6).

See subclause 13.1 for testing at temperatures other than ambient temperature and for determining the oxygen transmission rate.

13.3 Testing of tubes Solder metal plugs to the ends of the carrier gas tubes to be tested (cf. figure 7) through which the carrier gas can be fed. The plugs shall be tapered by about 2" and their external diameter shall be such that they can be pressed tightly into the tube. Before inserting the plugs into the tube, apply a film of vacuum grease to them and place metal rings (each about 5 mm wider than the tube) over the ends of the tube to ensure a firm contact.

Place a metal or glass tube having an inside diameter about 1O mm larger than that of the specimen over the tube being tested, as shown in figure 7. Position rubber pieces between the ends of the metal/glass tube and the specimen to provide a seal. The space between may be flushed with nitrogen or oxygen using the inlet and outlet. Flushing with nitrogen produces the zero level, U,, which takes into account all the leaks in the test arrangement, while flushing with oxygen gives the steady-state voltage, U,, for the length of tube section tested.

Use the equation in subclause 14.3 to calculate the oxygen transmission rate per unit length, q4. For testing at temperatures other than ambient temperature (cf. subclause 13.1), place the test arrangement in a controlledtemperature cabinet.

Page 1 1 DIN 53380-3: 1998-07

14

Evaluation

Calculate the oxygen transmission rates using the following equations.

14.1 Area-related oxygen transmission rate ( U , - U , ) . Q A . 1 O0 , in cm3/(rn2. d . bar) q A = A . R . @o2' P a m b where is the steady-state voltage, in mV; is the zero-level voltage, in mV; is the test area of the specimen, in cm2; QA is the calibration constant, in cm3. c m 2 . Q/(m2 . d . mv); R is the resistance of the resistor, in Q; Pamb is the atmospheric pressure, in bar; is the percentage by volume of oxygen in the test gas.

U, U, A

@o2

14.2 Volume-related oxygen transmission rate ( U , - U , ) . Q H . 1 O0 qH = '

, in cm3/(d . bar)

@O2 ' 'amb

where QH is the calibration constant, in cm3 . Q/(d . mV).

14.3 Length-related oxygen transmission rate

where is the length of the tube section tested, in m; QL is the calibration constant, in cm3. m . Q/(m . d . mV).

X

15 Test report The test report shall refer to this standard and include the following details: a) type and description of the product tested; b) composition and relative humidity of the oxygen gas; c) relative humidity of carrier gas; d) orientation of specimen and relative humidity, in the case of composite materials; e) thickness of specimen (mean); f) temperature of diffusion cell; g) oxygen transmission rate (individual values and mean) calculated using equation (l), (2) or (3); h) any deviation from this standard; i) date of testing.

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