Gravimetric Method-the arbitration method of Water Vapor Permeation Testing

 which have been calibration by gravimetric
Abstract: this article reviews the parametermeans……A standard, calibration film whose
definition as well as the development of testWVTR has been gravimetrically determined in
methods concerning water vapor permeationaccordance with the desiccant method of Test
testing.Methods E96…ISO 15106-1 also has clear
Keywords: arbitration method, gravimetricspecification relating the data source of referential
method, sensor method, water vapor permeation,film. It is required that the data system obtained
calibrationmust be in accordance with gravimetric method.
Water vapor permeation test method is mainlyIn Infrared testing method, infrared detection
divided into two categories: gravimetric methodtechnology is applied to water vapor permeation
and sensor method, with the latter method beingtesting. Electrolytic method adopts electrolytic
the earliest used one. Gravimetric method is thetechnology for high precision testing of micro
arbitration method of water vapor permeationquantity water vapor. These two methods vary
testing. Data system of sensor method should begreatly in terms of the sensor principle but are
calibrated with that of gravimetric method.similar in testing structure, both of which directly
1.Water Vapor Permeation of Materialstest the quantity of water vapor transmitting
Water vapor permeation of materials is the mainthrough specimen. Moreover, these two methods
index in evaluating water proof property ofcan test overall water vapor permeation of
packing materials such as film and sheets. Thispackage. Although gravimetric method cannot
can be determined through water vaporgive consideration to both the weighing range and
permeation testing.test precision when test overall package, it still
The indexes frequently used to evaluate wateradopts referential film to calibrate its data system.
barrier property of materials are water vaporIn ISO 15106-2, it is clearly specified that
Transmission rate?WVT?and water vaporreferential film as well as test data should be
permeation(Pv). WVT represents the quantity ofobtained according to gravimetric means.
water vapor transmitting through per square"Reference test specimen: a test specimen
meter of specimen with certain thickness withinwhose water vapor transmission rate is known,
24 hours. It is measured at a requiredor one for which the water vapor transmission
temperature, relative humidity and vaporrate has been determined in accordance with ISO
pressure. The unit is g/m2·24h. Water vapor2528."
permeation represents the quantity of water3. The Arbitration Method
vapor transmitted through per unit area and perBecause there are several water vapor
unit thickness of specimen at requiredpermeation test methods existing simultaneously,
temperature and relative humidity under per unitan arbitration method becomes necessary when a
water vapor pressure within per unit time. Thelawsuit is brought on data dispute of water vapor
relationship between WVT and Pv is shown below:permeation. The arbitration method should be the
" If the charts, pictures and formulas can notbasic method and needs no extra data system to
display clearly, please visit Labthink website.calibrate its own data system. It should have
Where: d represents specimen thickness, ?p is thescientific test technology and simple procedures.
pressure difference of water vapor on two sidesMoreover, the arbitration method should possess
of specimen, which has nothing to do with relativebetter data repeatability and ideal test error. Here
humidity of the two sides. The value 1.157×10-9is an objective analysis based on the
is used for unit transference. It is clearly stated incharacteristics of each method.
ASTM E 96 that the index of water vaporFirst, as stated previously, the calibration of those
permeation of material is defined in accordancesensor methods needs referential film for data
with gravimetric method.calibration, whether they test the quantity of
2. Development of Water Vapor Permeation Testwater vapor transmission directly or not.  Water
Methodsvapor permeation data of the referential film are
2.1 Gravimetric Methodobtained through gravimetric method?ISO 2528 or
In the middle of nineteenth century, barrierASTM E 96?. In addition, despite the fact that
property of materials became a new index inadjustable infrared testing method is accepted in
evaluating performance of materials. The earliestASTM F 1249 conditionally (permission of relative
permeation testing standard, ASTM E 96, wasconcerns should be obtained first) as arbitration
issued in 1953. This standard defines water vapormethod, its data system must be calibrated
permeation parameters of materials according tothrough gravimetric means. Obviously, the
the principle and parameter definition ofcalibrated data system of infrared method is
gravimetric method. At that time, water vaporconsistent with that of gravimetric method.
permeation testers manufactured according toTherefore, if infrared method can be used as
gravimetric method not only required diversifiedarbitration method, there is no reason that its
accessories, complex operation, longer testingreferential calibration method, gravimetric method,
period and was lower in testing efficiency, thecannot be the arbitration method. What is more,
operators also needed strict training.Micro quantity water vapor sensor adopted in
Gravimetric method at present has made obvioussensor method belongs to the consumptive type.
improvement. The newest gravimetric methodIt should be calibrated by referential film
water vapor permeation testers has combinedperiodically. Data systems of these sensor
testing environment and weighing condition intomethods calibrated through referential film are
one, which not only improves testing accuracy ofunified data system permitting mutual substitution.
instrument and simplifies the operators' operation,But they are not qualified as arbitration test
but also greatly decrease the failure rate of test.method.
At the same time, the development of weighingSecond, as far as data repeatability is concerned,
components and relating technology significantlythe data given in several standards are very
improves test accuracy and efficiency ofsimilar?ASTM E 96/E 96M-05?ASTM E 398-03 and
gravimetric method.ASTM F 1249-06?. As to the test error, ASTM E
2.2 Sensor Method96/E 96M-05 gives such description: "This test
Sensor method includes relative humidity method,method has no bias because water vapor
infrared testing method and electrolytic sensortransmission of materials is defined in terms of
testing method, which are introduced successivelythis test method." To test error of sensor
since 1770.method, ASTM 1249-06 gives an explanation as
Dynamic relative humidity method can be usedfollows: Measured values are derived from
for quick comparison of water vapor permeationcomparisons with known-value reference films.
of specimens. Moreover, its test environment isThe accuracy of this method is therefore
adjustable so that the actual application conditiondependent upon the validity of the values
of package can be better simulated. What thisassigned to these reference films.
method directly measures is not the MicroIn conclusion, for water vapor permeation testing,
quantity of water vapor, but the time or speedgravimetric method is not only the most widely
of water vapor transmitting specimen. Therefore,used approach, but also the arbitration method. It
data system of the tester is calibrated relying onis the standard of those data systems obtained
referential film completely, which is also mentionedthrough other water vapor permeation test
in ASTM E 398-03 as follows: Standard Films,methods.