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Permeation Glossary

A

Accuracy
Degree of agreement of a measurement with an accepted reference level or value.

Ambient Temperature
Surrounding temperature; temperature encompassing on all sides.

Arrhenius Plot
In chemical kinetics, an Arrhenius plot displays the logarithm of a reaction rate constant, ln(k) plotted against reciprocal of the temperature 1/T. Arrhenius plots are often used to analyze the effect of temperature on the rates of chemical reactions. For a single rate-limited thermally activated process, an Arrhenius plot gives a straight line, from which the activation energy and the pre-exponential factor can both be determined.

Arrhenius Theory
The Arrhenius Theorem states that the permeation rate, transmission rate, diffusivity or solubility vary with the film temperature according to the following equation(s): P=P0 exp (-Ep/RT);  TR=TR0 exp (-ETR/RT);  D=D0 exp (-ED/RT);  S=S0 exp (-ES/RT) where P, TR, D and S are the measured properties, P0, TR0, D0, and S0 are the respective constants, E is the activation energy, R is the gas constant and T is the absolute temperature. The Arrhenius equation has been verified empirically to give the temperature behavior of the mass transfer properties within experimental accuracy over fairly large temperature ranges.

ASTM International
ASTM International is one of the largest voluntary standards developing organizations in the world. We are a not-for-profit organization that provides a forum for the development and publication of international voluntary consensus standards for materials, products, systems, and services. ASTM standards are used by individuals, companies and other institutions around the world. 

ASTM Standard
A standard is a document that has been developed and established through ASTM's consensus principles and which meets the requirements of our procedures and regulations. Full consensus standards are developed with the participation of stakeholders with an interest in their development and use.

ATM
Abbreviation for standard atmospheric pressure.


B

Bar
A unit of pressure. The bar is equal to 100,000 Pa (pascal), 750.062 mmHg, 29.53 InHg, 14.504 psi and 0.987 ATM (standard atmospheres). See SI units.

Barometric Pressure
Pressure of the atmosphere. This is usually expressed in terms of the height (in millimeters mmHg) of a column of mercury.

Barrier
Object or device, such as a polymer film, which is designed to restrict the free movement and mingling of populations or areas of higher and lower concentrations.

Barrier Plastics
Plastics that impede the passage of oxygen, water vapor, and other vapors and gasses.

Baseline Zero 
See zero.

Blister Pack
Package with multiple small compartments for individual products. Common with, but not exclusive to pharmaceutical capsules.

Bypass
No gas is being routed to the sensor from the test cells. The sensor is in a protected state.


C

Calibration
Procedure to adjust a quantitative measuring instrument to agree with an accepted reference. See Accuracy.

Carrier Gas
Picks up the permeant that passes through a test barrier and carries (transports) it to the detector to be quantified. Permeation analyzers use nitrogen gas for this function.

Cell
See Test Cell.

CFR 21 Part 11 compliant 
Code of Federal Regulations deals with the United States Food and Drug Administration (FDA) guidelines on electronic records and electronic signatures (ERES).

Conditioning
Period allowed for a film or package to acclimate to the conditions within the test cell or Package Environmental Chamber. Conditioning shortens the test time to reach a steady state increasing throughput.

Conditioning Time 
Number of hours, specified by the operator, during which a sample is conditioned.

Convergence Hours
Number of hours, specified by the operator, over which to compare transmission rate readings. The transmission rate readings are compared to determine whether the convergence criteria (i.e., equilibrium) has been reached.

Convergence Testing
Method by which the computer determines when a test material has reached equilibrium. Test materials' transmission rates are examined and compared on a timed basis.

Coulometric Sensor
Fuel cell that performs in accordance with Faraday's Law. When exposed to water vapor, the coulometric sensor generates an electrical current proportional to the amount of water vapor entering the sensor.

Coulox® coulometric sensor
MOCON’s patented sensor. Every O2 molecule that enters the cell is routed through the sensor to be consumed, thus generating an electrical current directly proportional to the number of O2 molecules. It is an absolute sensor and no calibration is required.

CO2TR (Carbon Dioxide Transmission Rate.)
Typically measured in cc/(m2×day). It is the rate of CO2 moves through a barrier.


D

Deactivate
Removing a module from the test rotation. Modules are deactivated by clicking on Control-Pause.

Desorb
To give up or release from a barrier.

Differential-Pressure Method
See Manometric Method

Diffusion
The process by which matter is transported from one part of a film to another as a result of random molecular motions. In a film each molecule behaves independently of the other. When collisions occur, molecules move towards regions of lower concentration and sometimes towards regions of higher concentration. Because the number of molecules on the test gas side of a film is higher than the number of molecules on the carrier side, the overall movement of molecules will be in the direction of the carrier gas. Diffusion is usually expressed in units of cm2/sec. Diffusion varies with temperature and sometimes with permeant concentration (see Fick's first law).

Diffusion Coefficient
A coefficient specific to a given barrier and permeant that describes the relationship between the permeant mass flux and the permeant mass concentration change across the barrier. The diffusion coefficient (D) is defined by Fick's law and is usually expressed in terms of cm2/sec. Other terms are m2/day, cm2/day, m2/in, in2/sec and in2/min.

Driving Force 
Substances naturally tend to move from a higher chemical potential to a lower one. It prompts a molecule to diffuse within a polymer.

Dual-Film Test Cartridge
A removable Test Cell that can hold two film samples to be tested in a High Through-Put Film Permeation Analyzer.


E

Equilibrium
Point at which the amount of permeant passing through a test material has stabilized at a steady rate. The computer reports equilibrium value as the material's final transmission rate.

Equal-Pressure Method
See Iso-Static Method


F

Fickian Behavior
Simply a material that exhibits a linear relationship between the driving force and the transmission rate. Fickian behavior is observed when a given permeant diffuses through a given polymer film according to the mathematical equations governed by Fick's First and Second Laws. In the case of an isostatic transmission rate test, the equilibrium values of the permeation rate, transmission rate, solubility and diffusion rate of a polymer-permeant pair exhibiting Fickian curve behavior can be predicted according to Pasternak's solution of Fick's law. NOTE: Many organic permeants react with polymeric materials causing non-Fickian behavior and prevent the prediction of equilibrium values.

Fick's First Law
The mathematical equation adopted by Fick in 1855 which correlates diffusion to heat conduction. The mathematical theory of diffusion in a substance is therefore based on the hypothesis that the rate of transfer of a diffusing substance through a unit area of a section is proportional to the concentration gradient measured normal to the section, i.e., F=-D ∂C/∂x Where F is the rate of transfer per unit area of section, C the concentration of diffusing substance, x the space coordinate measured normal to the section, and D is the diffusion coefficient.

Fick's Second Law
Fick's Second Law is the fundamental differential equation of diffusion in a medium. It states that: ∂C/∂t=D∂2C/∂x2 where C is the concentration of diffusing substance, x the space coordinate measured normal to the section and D is the diffusion coefficient. This assumes there is a concentration gradient in only the x-direction.

Film Test Cartridge
Removable test cell assembly for permeation testing of barrier films

Flow Rate
The volumetric rate at which gas is traveling through the module.

Flux
The rate of flow or transfer of permeant. The term is normally used to denote the quantity of permeant that crosses a unit area of a given surface in a unit of time.

Foil Mask
Reduces the exposed area of a film sample (most commonly with a low barrier) or supports a fragile sample in the test cell.


G

Gas Flow Rate
See Flow Rate.

Gas Pressure
Pounds per square inch (psi) of the test and carrier gasses. Used to regulate relative humidity via the module-mounted pressure regulator knobs.

Glass Transition Temperature (Tg)
The temperature at which an amorphous material (such as glass or polymer) changes from a brittle glass-like state to a plastic state. Many polymers such as acrylics and their derivatives have this transition point which is related to the number of carbon atoms in the ester group. The Tg of glass depends on its composition and extent of annealing. Example: The Tg of PET is about 70C.

Gravimetric Method
Also known as cup test – measuring moisture loss or gain by weight.

GTR
Gas transmission rate.


H

High Vacuum Grease
Highly refined grease that is used to seal a test material in the test cell and to lubricate parts of the module.

Homogenous Material
Barrier material that has the same basic characteristics throughout the thickness of the barrier.

Hydrophilic
Refers to substances that absorb water. A hydrophilic substance will bond, on a molecular level with water.

Hydrophobic Material
Refers to materials that will repel water.

Hygroscopic Material
Refers to the ability of a material to absorb humidity from the air. A hygroscopic substance will actively attract and absorb water, without bonding.

HPLC-grade Water
High purity distilled water (sometimes called triple-distilled water). HPLC-grade water prevents the formation of scale, which can obstruct the plumbing. It is used in the humidifier where its high purity is needed for accurate RH results. It is the only recommended water source for the reservoirs within any MOCON permeation instrument. HPLC is an acronym for high-pressure liquid chromatography.


I

Individual Zero
Method by which more accurate results are achieved for high barriers. The computer sends nitrogen through both halves of the test cell, then routes it to the sensor to determine the amount of permeant vapor it is carrying. Because the carrier gas obtained this permeant vapor due to edge leaks or other factors, the computer subtracts that amount from the transmission rate obtained during testing. This provides a very accurate actual transmission rate. Essentially this corresponds to the innate leak of an individual test cell and the loaded sample.

Integrated Package Test Cartridge
Package permeation test cartridge that does not require adhesive or epoxy to mount the test sample.

IQ/OQ/PQ
Verification of machinery and equipment usually consists of installation qualification (IQ), operational qualification (OQ), and performance qualification (PQ).

ISO
International Organization of Standards - An international standard-setting body composed of representatives from various national standards organizations to promote worldwide proprietary, industrial and commercial standards.  Headquartered in Geneva, Switzerland works in 164 countries.

Isostatic Test Method
A test procedure during which a test film is clamped in a permeation cell. The test divides the cell into two chambers. A test gas flows continually through the high concentration cell chamber, and an inert carrier gas flows through the low concentration cell chamber. The partial pressure gradient of the penetrant provides a driving force for the penetrant permeating through to the low concentration cell chamber, where the penetrant can be conveyed to a detector for quantification. Steady state is reached when the transmission rate, monitored continually, remains constant under constant conditions of temperature and permeant vapor pressure.


J

JIS
Japanese Institute of Standards


K

Kelvin (SI Symbol - K)
The Kelvin is the SI base unit of the absolute thermodynamic temperature scale where absolute zero is -273.15C and which uses the Celsius temperature interval.


L

Leak Rate
Amount of permeant vapor entering the carrier gas through edge leaks or other factors. This value is determined during individual zeroing operations and is later subtracted from the apparent transmission rate to determine the actual transmission rate.


M

Manometric Method (aka Differential-Pressure Method)
Universal testing method applicable to nearly all gases for determining gas transmission rate through flat plastic materials like films, sheeting, laminates, co-extruded or coated materials under a differential pressure.

Micron
Unit of thickness measurement One micron is equal to 3.93 x10-5 inches (1x10-6 meter).

mil
Unit of thickness measurement. One mil is equal to 1 x 10-3 inches.

mmHg
Millimeters of mercury. A unit of atmospheric pressure. Standard atmospheric pressure at sea level is 760 mmHg. 1 mmHg = .0193371 psi.

Module
Modules contain the environment in which films and packages are tested.

Mol
Abbreviation for mole, the International System of Units (Système international d' unités, abbreviated “SI”) base unit for quantity of matter. A mol is numerically equal to molecular weight; 1 mol = 6.023 x 1023 atoms. See Mole.



N

N2  
Chemical abbreviation for the nitrogen molecule. Two nitrogen atoms make a nitrogen molecule. See Nitrogen.

Nitrogen
Main constituent in the Permeation instrument carrier gas. It carries the permeant gas that passes through a film or package into the instrument sensor for quantification.

Nitrogen Purge
Process by which nitrogen (carrier gas) is used to expel residual water vapor from a cell, package, or sensor.

 

O

OTR (Oxygen Transmission Rate)
Typically measured in cc/ (m2×day). Is the steady state rate at which oxygen gas permeates through a film at specified conditions of temperature and relative humidity. 

 

P

Package Adapter Cartridge
Cartridge with fittings for carrier gas used for mounting packages, used on package testing instruments or PackRack.

Package Mounting Foils
Single use foils to mount packages to package test cartridges.

Package Test Cartridge
Apparatus for mounting packages for permeation testing.

PackRack Fixture
Fixture that enables use of package test cartridges with a film permeation analyzer and remote testing cartridge adapter.

Pascal
The Si unit for pressure. One pascal is equal to .9869233 x 10-5 atmospheres. See SI units.

Perm
A unit of measurement for permeance. One metric perm is equal to 1 gm/(m2•day•mmHg); one perm in the foot-pound system is equal to 1 grain/(in2•h•inHg).

Permeability Coefficient
Product of the permeance and the thickness of a barrier. For example, water vapor permeability is measured in SI units as mol•mm/(m2•s•Pa), and in metric units as gm•cm /(m2•day•mmHg). Permeability is a property of a homogenous material.

Permeance
Ratio of a barrier's transmission rate to the partial vapor pressure differential across the barrier. Water vapor permeance is measured in SI units as mol/(m2•s•Pa), and in metric units as gm/ (m2• day•mmHg) (also called a metric perm).

Permeant
Gas, vapor, or other physical entity that passes through a barrier.

Permeation
Permeation is the penetration of a permeant (such as a liquid, gas, or vapor) through a solid. It is directly related to the concentration gradient of the permeate, a material's intrinsic permeability, and the materials' mass diffusivity. Permeation is modeled by equations such as Fick's laws of diffusion.

Permeation Rate
The transmission rate normalized to thickness. Permeation Rate is usually expressed as a (gm or cc) of (gas or vapor) at 1 (cm or mil) per unit area of material (m2 or 100in2) in a discreet unit of time (day or sec) and usually is normalized to one atmosphere (760 mmHg or atm). If the material is homogeneous, Permeation Rate can be converted to Transmission Rate of any thickness. Transmission Rate is inversely proportional to thickness (TR = P/x).

Porous Packaging Material
A material used in medical packaging which is intended to provide an environmental and biological barrier, while allowing sufficient air flow to be used in gaseous sterilization methods (e.g., medical-grade papers and Tyvek®)

Precision
Degree of mutual agreement among individual measurements. Relative to a method of test, precision is the degree of mutual agreement among individual measurements made under prescribed like conditions.

Pressure
See gas pressure.

P = SD Equation
Permeation through a polymer film or sheet is a measure of the steady-state transfer rate of the permeant, which is normally expressed as the permeability constant P. The permeability constant is the product of two fundamental mass-transfer parameters: the diffusion and solubility coefficients. The diffusion coefficient D is a measure of how rapidly penetrant molecules are going through the barrier, in the direction of lower concentration or partial pressure. The solubility coefficient S describes the amount of the transferring molecules retained or dissolved in the film at equilibrium conditions. This equation is applicable only for situation where D is independent of permeant concentration and S follows Henry's law of solubility.

psi
Abbreviation for pounds per square inch (pressure).

psig
Abbreviation for pounds per square inch (gauge).


Q

Quality Assurance (QA)
Consists of that “part of quality management focused on providing confidence that quality requirements will be fulfilled.” Relates to how a process is performed or how a product is made. The confidence provided by quality assurance is twofold—internally to management and externally to customers, government agencies, regulators, certifiers, and third parties.

Quality Control (QC)
Is that “part of quality management focused on fulfilling quality requirements.” The inspection aspect of quality management, usually directed at a packages ability to provide the protection required to achieve the calculated shelf life.

 

R

RH
See Relative Humidity.

Relative Humidity (RH)
Ratio of the quantity of water vapor in air to the maximum capacity of the air at a specific temperature and pressure. The transmission rate of many barrier plastics is dependent on the RH at which the transmission rate is tested.

Remote Film Test Cell
Independent film test cell for use in thermal chambers connected to remote test cartridge adaptor via tubing.

Remote Testing Cartridge Adapter
Cartridge with fittings for carrier gas used for connecting packages or remote test cells and accessories, used for a film instrument

Repeatability
Measure of the accuracy of a system and the testing method used. A highly repeatable system will provide very consistent results. That is, if the same test is run twice on a test material, the results should be very nearly the same.

Resolution
Minimum discernible difference in the change of output signal of an instrument.

Re-Zero
Method for minimizing the effects of environmental or other factors that should not be included in test data. The operator-entered value in, Re-Zero, tells the computer when to perform Re-Zero. The Re-zero value "resets" the test parameter baseline. No test cell data may be obtained until the Re-zero baseline value is known, as this value is subtracted from every sample data point. The Re-zero baseline is a transient value that is regularly determined to provide the most accurate test values.

 

S

Sccm
Abbreviation for standard cubic centimeters per minute.

Sensitivity
Degree to which an instrument responds to a defined incoming quantity of the phenomenon being detected. A very sensitive instrument will detect very small changes in the area being measured.

Shelf Life
Period of time a product can be stored and remain suitable for use. Information obtained when testing for water vapor, oxygen, or carbon dioxide transmission rates, can help determine a product's shelf life using a particular barrier film or package.

Single Cell Testing
Testing conducted in one cell of a module.

Solubility
The equilibrium amount of permeant absorbed into a material per unit volume of material. Solubility is measured assuming a constant vapor pressure and temperature. Units are usually (gm or cc) of permeant per unit of volume (cc) of material at a set vapor pressure i.e. (gm/cc). Units of solubility can also be normalized to vapor pressure i.e., gm/(cc.mmHg). Solubility varies with temperature and permeant condition.

Solubility Coefficient
The volume of a gas that can be dissolved by a unit volume of solvent at a specified pressure and temperature.

 

T

Test Cartridge
Removable Test Cell.

Test Cartridge Bottom
Bottom-half of Film Test Cell Cartridge.

Test Cartridge Top
Top half of Film Test Cell Cartridge.

Test Cartridge Tray or Tray
Drawer that holds Film Test Cartridge in the instrument

Test Cell (or Test Cell Fixture)
Cell or station containing a test gas chamber and a carrier gas chamber for permeation testing of barriers.

Test Gas
Gas species that is being detected. For example, the AQUATRAN uses water vapor as the test gas.

Test Gradient
The partial vapor pressure difference on each side of the test film.

Transmission
Passing of a gas or vapor through a barrier, normally by absorption of the gas into the barrier, the diffusion of the gas through the barrier, and the desorption of the gas on the opposite side of the barrier.

Transmission Rate
Quantity of a gas or vapor that will cross a unit of a barrier in a unit of time by diffusion.

TruSeal® Technology
MOCON’s patented TruSeal flush ring at the perimeter of the test cell ensures to sweep away any ambient moisture or air entering the cell between the film sample and the cell, so that only test gas entering the cell via permeation through the film is measured.

U

N/A

 

V

Vapor Pressure
The pressure (usually expressed in mmHg) characteristic of a liquid or solid at any given temperature, in equilibrium with its vapor.

 

W

Water Reservoir
A water source within a permeation instrument for generating relative humidity when a test is to be conducted at preset RH condition.

Water Vapor Transmission Rate (WVTR)
Typically measured in g/(m2
×day). The standard measurement by which films are compared for their ability to resist moisture. Lower values indicate better moisture protection. Only values reported at the same temperature and humidity can be compared, because transmission rates are affected by both parameters. Also known as Moisture Vapor Transmission Rate (MVTR)

 

X

N/A

 

Y

N/A

 

Z

Zeroing
Operation that provides a new "zero point” (baseline) for the permeation module. Zeroing gives the computer a reference point to use when generating transmission data. This value is subtracted from all test cell data.

Zero Foils
Impermeable barrier used to run baseline individual zero.