The Advantages of Water Vapor Permeability Instrument of Sensor Method

Abstract: This article presents the comparison ofcup are carried out in constant temperature and
two test methods of water vapor permeability.humidity atmosphere before and during test, the
Taking Labthink TSY-W3 electrolyzation as anneeded volume of test atmosphere is rather big,
example, it also briefs on the test advantages ofwhich is not beneficial to the controlling of
sensor method.atmospheric temperature and humidity.
Keywords: water vapor permeability, sensorAccording to the type of the employed sensor,
method, cup method, temperature controllingsensor method is divided into infrared sensor
 method, electrolyzing analysis method and
The content of water vapor within package candynamic relative humidity method. The former
cause qualitative changes to some products.two methods are very similar in terms of test
Special attention should be paid to water vaporstructure and test principle. In these two
permeability of packing materials, which will varymethods, the specimen is sealed in the upper and
significantly to different materials. Therefore,lower chambers. One side of the specimen
water vapor permeability test becomes verymaintains high humidity state with saturated saline
important. There are many factors influencing thesolution while the other side keeps dry by purging
test of water vapor permeability, with the stabilitydry gases. In this way, two sides of the specimen
of test temperature and the humidity differenceform a specific humidity difference. Water vapor
on two sides of the specimen as the mosttransmitting through specimen into dry chamber
influential factors on test results.will be carried by dry carrier gas to the sensor,
1 The Importance of Temperature Controlling inwhere the content of water vapor is measured
Water Vapor Permeability Testto determine the water vapor permeance.
Most of the crystalline polymers areInstruments based on these two test principles
semi-crystalline polymer. Theoretically, crystallizedpossess better working independence and the
part of the polymer is thought as an area thatneeded volume of test chambers is very small,
cannot be permeated during the diffusion ofwhich make the controlling of temperature and
infiltration molecules within polymer material. It ishumidity easy. Dynamic relative humidity method
the non-crystalline part that most of the diffusionvaries with the former two methods in terms of
takes place. The longer the polymer moleculetest principle. Temperature controlling of this
chain, the more its conformation will be. Whenmethod is easy to realize. However, due to its
temperature increases, conformation changing oftest principle, humidity difference on two sides of
the molecule chain will be accelerated as a resultthe specimen is constantly changing during the
of thermal motion and this in turn will decreasetest process.
the extent of polymerization.  Then the diffusion4 The Advantages of Sensor Method Water
of infiltration molecule in the polymer isVapor Permeability Tester in Temperature and
accelerated. That is to say, a rising in temperatureHumidity Controlling
will reduce the barrier property of material.Volume is one of the main factors to realize
The permeation of water vapor to polymers isconstant temperature and humid in certain space.
significantly influenced by temperature. Its relationThe smaller the volume is, the better the
with temperature can be demonstrated bycontrolling effect of temperature and humidity will
Arrhenius equation.be. As stated above, instrument structure of
With the rising of temperature, the coefficient ofsensor method makes the controlling of constant
water vapor permeability increases, though thetemperature and humidity easier to realize than
increase varies in terms of different polymercup method and can obtain ideal controlling effect
films. It is stated in some literature that thewith special technological treatment. Here we take
coefficient of water vapor permeability ofLabthink TSY-W3 as an example for explanation.
amorphous materials increases rapidly with theLabthink TSY-W3 of electrolyzed method adopts
rising of temperature while that of materials withthe high precision electrolyzing humidity sensor. Its
certain crystallinty increases somehow slower.salient feature is using constant recycled water to
2 The Influence of Humidity Difference on Testmaintain the temperature of test chamber, which
Datais improved on the basis of temperature
Because molecules of water vapor are polarized.controlling of water bath. one thing to be noted
During the permeable process of water vaporhere is that the cycle controller possesses the
molecules, some polymers can adsorb waterfunction of both heating and cooling with a
vapor and appear the phenomenon of swelling, bytemperature range of 0?100?. The controlling
which inner free volume will be enlarged. Waterprecision is ±0.1?, which not only meets the
vapor permeability coefficient of materials isrequirements of national and international
obviously related with the concentration of waterstandards, but also becomes the instrument with
vapor. Correspondingly, water vapor permeance isthe most ideal temperature controlling. Using
also obviously affected by humiditysaturated saline solution to control humidity can
variation?which presents as an nonlinearmakes the humidity on the high humidity side
relationship between water vapor permeance andstable. Moreover, the low humidity side is
the relative humidity difference to some polymercontrolled by desiccators, which can make two
materials. For example, the relationship betweensides of the specimen have a very stable
water vapor permeance of hydrophilic polymerpressure difference with small fluctuation. The
cellophane and the humidity difference does notmore precision the temperature and humidity
present a liner relationship, which is the mostcontrolling is, the more beneficial it is to test data.
obvious difference of water vapor and commonField data repeatability of TSY-W3 is very good in
inorganic gases in terms of permeation withinthe whole test range. In addition, test period of
polymers.this instrument is shorter than that of cup
3 the Difference of Cup method and Sensormethod instruments. It presents an obvious
Methodadvantage in testing materials with lower water
At present, test methods employed by watervapor permeability. This kind of instruments is not
vapor permeability are either cup method orsensitive to the environmental shaking; and has
sensor method. These methods are based oneffectively avoided the influence of environment
different test principles; and the structure of teston test efficiency.
instruments also varies significantly.5 Conclusions
In cup method, the cup with specimen sealedHumidity and temperature of test environment
inside is put in constant temperature and humidityare two important factors that influence the data
atmosphere. Relative humidity on two sides ofof water vapor permeability testing. Therefore, an
the specimen is controlled by desiccant oreffective controlling of the two factors can
saturated saline solution inside the cup and by theimprove precision and repeatability of test data.
constant temperature and humidity atmosphere.Comprehensively speaking, Labthink TSY-W3
Water vapor permeability can be calculated withpresents strong test advantages in aspects of
the measured weight increase or decrease of thetemperature and humidity controlling.
cup. Test atmosphere of this method is provided 
by constant temperature and humidity. TheLabthink Instruments Co., Ltd.
humidity is the difference of inside cup humidityNo. 144 Wuyingshan Road, Jinan 250031, China
and atmospheric humidity. Since operations of theTracy Bao  info@labthink.