Rapid Determination of Package Water Vapor Permeability

Abstract: although barrier property is one of thecontainer packaging that cannot be sealed
key parameters affecting shelf life of products,repeatedly. When desiccant and its holding
traditional water vapor permeability test methodsaccessories are placed into specimen container, a
still fall short not only in test efficiency but also inopening needs to be made on the wall of package
terms of operation conveniences. For that reason,and is then sealed with seal wax after the placing
a method that can rapidly determine water vaporof desiccant and the accessories has finished.
permeability of package is introduced in thisHowever, such operation is repeated each time
article.keywords: water vapor permeability,the specimen is weighed, which not only increases
container, test, and electrolytic methodthe difficulty of operation, but also increases the
Containers are directly used in liquid package. Sinceratio of test failure.
raw material of containers is often processed with 3. Poor repeatability. Operators' habit of
high temperature and cooling, some indexes ofspecimen preparation and weighing will affect test
the raw material cannot indicate the finalresults.
properties of container. The special shape of In addition, because precision of gravimetric
container adds difficulty to its barrier propertysensor is restricted by its measuring range, the
testing. In the past, gas permeance and waterprecision of container package testing is much
vapor permeability are estimated by testingpoorer than that of film testing. At the same
package sheet material. However, containertime, unit of the test results in this method is g
packages are not uniform in thickness and them2·30d, indicating the need to accurately
property of materials will be changed in themeasure surface area of container package,
process of production, which will cause certainwhich presents another problem for container
disparity between estimated and tested results.package of irregular shape.
Traditional water vapor permeability test methods 4. Test Water Vapor Permeability Using Sensor
still fall short not only in test efficiency but also inMethod
their operation conveniences. For that reason, aTest principle of sensor method water vapor
method that can rapidly determine water vaporpermeability testing for container package is the
permeability of package is introduced in this article.same with that of gas permeability testing, which
1. Traditional Methods to Determine Water Vaporforms a good basis in the actual application of
Permeability of Containerssensor method.
The commonly used methods of package waterSTRONG>The first thing is specimen
vapor permeability testing at present arepreparation. The method of preparation is almost
developed on the basis of gravimetric method filmthe same with that of package oxygen
water vapor permeability testing, using testpermeability test. However, specimen placement
principle of gravimetric method. Relevant testvaries to specific testing position. Water vapor
standards are GB/T 6981-1986?GB/T 6982-1986permeability testing of container package includes
and ASTM D 3079-94. According to the nature ofwater vapor permeability test of bottle body and
materials, there are water vapor permeabilitythe integral test of bottle cap and bottle body. To
testing of flexible package and rigid package.test barrier property of bottle body, the package
Although these two methods vary to someshould be laid upside down and fixed onto special
extent in their detailed operation procedures, thebottle pedestal. Then seal bottle neck by filling
basic test methods are similar.special glue into bottle pedestal in order to avoid
Test procedures are as below: put desiccantthe transmission of water vapor from connecting
(holding accessories can be used) into sampleplace of bottle pedestal and bottleneck into bottle
container and then seal the container. Quicklybody. Generally, the finished specimen is shown as
place the preheated specimen into constantfigure 1. To test barrier property of bottle cap
humidity and temperature cell for moist heatand bottle body, make a hole on the bottom of
testing. After that, the specimen should becontainer first. It is recommended that the size of
weighed periodically according to water vaporthis hole just fits the inlet pipe and outlet pipe of
permeability of materials. When the transmissionnitrogen gas.  Place the bottle upward on the
reaches equilibrium, calculate water vaporcenter of tailor-made bottle pedestal then fill the
permeance of the specimen using the incrementsealing glue evenly into between bottle body and
of specimen’s weight.bottle pedestal. Make sure that the space
Although this method is developed on the basis ofbetween bottom recess and input and output
gravimetric method film testing, automaticpipes is also filled with sealing glue.
detection is hard to realize. Therefore this method1. Replace the upper test chamber of sensor
has the disadvantages of inconveniences inmethod film water vapor permeability tester with
empirical application, lower test efficiency andspecial enclosure (attached with instrument), and
lower credibility of test results, with the onesthen use the package to divide the permeation
listed below being the obvious weak points:chambers into two independent airflow systems
Longer test duration. According to specifications(see figure 3) with one side being flowing test gas
of standards, to determine transmission(dry) and the other side maintain certain humidity.
equilibrium, at least three weight data should beThe concentration of water vapor on two sides
obtained. Although weighing interval of specimen isof specimen is different and there is a constant
decided by operators in accordance with waterconcentration difference of water vapor existing
vapor permeability of packaging materials, the(relative humidity).   Under the function of
interval below is recommended in standards: forconcentration difference of water vapor (relative
materials possessing high water vapor barrierhumidity), water vapor transmits through the wall
property, the shortest weighing intervalof container and is then diverted into the sensor
recommended is 2?3 days. While for lower waterby carrier gas. Water vapor transmission rate of
vapor barrier materials, a interval of 15?30 days isthe package can be calculated according to the
recommended. In this way, even packages madequantity of water vapor contained in carrier gas,
of very lower barrier materials needs seven orwhich is accurately measured by the sensor.
eights days to complete one test. To testLabthink TSY-W3 electrolytic method water
container package that is made of high barriervapor permeability tester can test integral water
materials, several months are needed.vapor permeability of container package with the
 The test cannot be completed under a stableprecision no less than 0.001g/pkg·d. Generally,
condition. During weighing process, the specimenthe duration of test is only three or four days,
(or desiccant and its holding accessories) is movedthus realizes rapid and accurate determination of
between test environment and weighingwater vapor permeability testing. Comparing with
environment. In principle, transmission of waterrelevant parameters of tradition test method
vapor should be tested under an equilibrium state.previously introduced, TSY-W3 is outstanding both
But the movement during weighing will destroyin aspects of test precision and test efficiency.
transmission equilibrium established under test 6. Conclusion
state, which in turn affect accuracy of testTraditional test method for integral water vapor
results. Moreover, the shorter the weighingpermeability testing of package is low in efficiency
interval, the more obvious the affection will be.and precision, which impedes the development of
There is also such explanation in standards. Forintegral water vapor permeability testing of
example, it is clearly pointed out in standards thatcontainer package. That is why the traditional
frequent weighing affects accuracy of test.method does not obtain better application in the
 A stable differential pressure of water vapor ispast years. Sensor method makes a significant
hard to maintain on two sides of specimen.progress in testing integral water vapor
Because the weight of desiccant contained inpermeability of package and can test water
specimen container usually limits to 80-100g,vapor permeability of almost all current flexible
moisture absorption ability of desiccant decreasespackages (including package bag, paper box and
after a period of test. Correspondingly, differentialbottle), which can provide more accurate and
pressure on two sides of specimen will alsooverall test data in comprehensively investigating
change. In such a case, the desiccant should bethe influence of water vapor permeability on shelf
replaced to continue test. However, the desiccantlife of inner packed matters.
can hardly be replaced completely consistent inFurther information please feel free to contact
quantity. Therefore, test will be influenced toShirley Wu via trade2@labthink.cn,
some extent.skype:shirley-labthink, or (tel)0086-531-85068709.
 2. The sealing lacks reliability, especially for