This Puraflex Permeation Modeller App (PPM) program is specific to the Puraflex Hydrocarbon and Chemical Resistant Environmental Barrier membrane.
If a challenge chemical is not in the database, please Email email@example.com with requests for the data of any additional chemicals.
Particularly appropriate for volatile hydrocarbons / Volatile Organic Compounds (VOCs).
|PHC Aliphatic EC 5-8||5000|
|PHC Aliphatic EC >8-10||5000|
|PHC Aliphatic EC >10-12||5000|
|PHC Aliphatic EC >12-16||5000|
|PHC Aromatic EC 5-8||5000|
|PHC Aromatic EC 8-16||5000|
Hydrocarbon Fractions are also recognised:
|Aliphatic (E)C>16-21||White Mineral Oil||8042-47-5|
|PHC Aliphatic EC >8-10||White Mineral Oil||8008-20-6|
When using these fractions you need to include in the name at least Aliph or Arom (i.e. Aliph or Aliph. or Aliphati... not case sensitive). You also have a lot of freedom for specifying the range: C5-C6 or C5 - C6 or EC5-EC6 or EC>5- EC6 etc. (Hence the 'E' in parentheses above). There must not be spaces between the C and the number. So C5 works but C 5 does not.
As there are a number of different standards for specifying general aliphatics and aromatics we have chosen the worst case (smallest) indicator.
Given the range of assumptions, entering a chemical as a Cresol rather than a specific (o-, m-, p-) Cresol, or just lumping together an o-,m-,p- mix as "Cresols" will give adequate accuracy.
After calculating, the Effective Soil Concentration, Permeation Rate, Permeated mg/kg/yr and Cumulative mg/kg/period values appear under Outputs.
Given a known level of contaminants in a soil, how effective will a barrier membrane be in keeping the soil on the
"clean" side safe from the contaminants?
That simple question itself raises three issues:
However good a practical barrier membrane is, some contaminant will permeate through. It is impossible to create a barrier to achieve "zero contaminant", however desirable. The question is whether the amount getting through is significant in terms of health and safety criteria.
The Partition Coefficient is important since soil moisture influences the effective concentration of chemical contaminant at the surface of the barrier membrane. For example, a soil concentration of Benzene at 250 mg/kg will have an effective concentration of 25,000 mg/kg at the surface of the barrier in wet soils.
PPM modeller is capable of using concentration-dependent diffusion coefficients which could be influenced by the total level of contaminants in the membrane. At concentrations above 1,000 ppm, an approximation to concentration dependant diffusion coefficients is used.
Similarly HSP can take into account mixed solvent effects whereby two bad solvents can make a good solvent. In principle there could be synergies at the outer surface. However, at low concentrations and, given the other complexities of the system, such synergies have been ignored.
The calculation of permeation via the vapour route is extremely complex. We have therefore used the simplifying assumption (commonly used in barrier literature) that the effective concentration at the surface of the membrane is the value expected from the water:membrane partition coefficient, modified by the Henry's constant.
For a permeant such as benzene this gives a reduction to 22% of the value expected from water:membrane, i.e. the dimensionless Henry's constant for benzene is 0.22.
There are two modes for calculating vapour phase permeation:
Vapour from soil concentrations.
For non-volatile permeants, or those with a large solubility in water the Henry's constant is effectively zero so there is no transmission via the vapour route. The calculated vapour concentration is shown in units of your choice. This uses the standard Henry's calculation modified by the soil partition coefficient, porous fraction etc.
So for benzene if at 0% Vapour the effective concentration is 100 then at 100% Vapour the effective concentration is 22 and at 50% it is 61. For a typical phenol the figures would be 0 and 50 respectively because the Henry's Constant for these phenols is effectively 0.
An examination of the literature on temperature dependence of Henry's constants shows that for a typical soil temperature range the variation in values is often less than the variation in published values at 25°C so no attempt is made to adjust for temperature.
Vapour phase data only.
If you have vapour phase data you must make sure that the input units are selected as Vapour g/cc or Vapour μg/m3. Rather than do a vapour-only calculation, which is outside the science of the program, a theoretical soil concentration is calculated (shown in the Max. Effect. Conc. column in μg/m/kg) from which the correct vapour concentration is predicted. From the theoretical soil concentration, and the above logic, the diffusion through the barrier is calculated.
In both cases, a Vapour Out value is calculated which is the vapour concentration in the soil on the "clean" side. The Vapour Out value is calculated via the same Henry's law calculation, using the cumulative soil concentration. Those who use the vapour calculation generally are using something like a Johnson and Ettinger model which assumes that the vapour is being transferred from the soil to the building. The cumulative calculations are deliberately pessimistic and assume that all the contaminant stays in the 1m of soil on the â€œcleanâ€ side. Therefore the Vapour Out calculations are likely to provide an over-estimate to the Johnson and Ettinger model.
With so many assumptions behind the vapour calculations it is clear that they cannot be hyper-precise. But because they use standard assumptions they offer useful guidance in a complex area and the Vapour Out data can be used in (e.g.) Johnson and Ettinger models which also have many complexities and also cannot be hyper-precise.
By nature of their molecular structure, mono-polymer membranes have specific chemical resistance spectrums. HDPE, PP, PVC, CR, CSPE, Butyl and EPDM are examples common mono-polymer membrane.
HDPE is the most common membrane and it is made of a Non-polar polymer which makes it more permeable to Nonpolar chemicals such as hydrocarbons.
Puraflex is a multi-layer barrier incorporating Polar and Non-Polar polymers. This therefore makes it a good barrier against both Polar and Non-Polar chemicals.
It is also important to note that doubling the thickness of monopolymer membranes (HDPE, PVC, Butyl Rubber etc.) only halves the permeation rate.
Soil Temp. 20 °C
Partition Coefficient None applied
Chemical Concentration 100 mg/kg
|Butyl benzyl phthalate||85-68-7||5.80E-03||4.92E+01||1.64E+02||1.31E+02||1.64E+02||1.64E+01||1.31E+02|
|Isopropyl Benzene (Cumene)||98-82-8||5.64E-05||1.57E+02||5.22E+02||4.18E+02||5.22E+02||5.23E+01||4.18E+02|
|Methyl Isopropyl Ketone (MIK)||563-80-4||9.43E+00||8.05E+02||2.68E+03||2.15E+03||2.68E+03||2.69E+02||2.15E+03|
|Polychlorinated biphenyl (PCB)||1336-36-3||1.77E-05||6.52E+01||2.17E+02||1.74E+02||2.17E+02||2.17E+01||1.74E+02|
For the latest technical information, please refer to the following publications which are available from our technical
department or in digital format from our website (Registration required):
Product information detailing relevant standards and test methods, our comprehensive chemical resistance testing programme, production and quality assurance
Puraflex Technical Data
Comprehensive test data for mechanical, hydraulic, thermal, durability and chemical resistance to BS, EN, ISO and ASTM test methods
Puraflex Design and Installation Details
Design considerations and best practice installation instructions for certified installation contractors
Puraflex Model Specification
Suggested specification to assist design engineers in the preparation of project documentation
Puraflex Safety Information
Control of Substances Hazardous to Health (COSHH) & Material Safety Data Sheets (MSDS)
Here are answers to some Frequently Asked Questions:
No. It is generally accepted that solids do not permeate.
PPM has been unable to match either by CAS# or chemical name or synonym.
Please look up the CAS number or use a different synonym.
For Hydrocarbon Fractions grouped by carbon numbers, please check that the correct protocol has been followed.
pH has no direct effect on the standard polymers used in membranes and therefore can have no effect on permeation rate on most chemicals. In general any pH which causes a neutral chemical to become charged (e.g. phenols at high pH, amines at low pH) will reduce the permeation rate through typical membrane polymers, so predictions from the software will be, if anything, pessimistic.
There is at present insufficient data to calculate permeation of charged molecules. So no attempt is made to estimate
the permeation of such species.
However, given that the outer layer of Puraflex is a hydrocarbon it is highly unlikely that significant quantities of charged species will be sufficiently soluble to be able to permeate at a significant rate.
Also the partition coefficient of charged species between a hydrocarbon film and a typical moist soil will be very much in favour of the soil - the charged species will generally prefer to be in an aqueous environment.
Although the general trends of permeation of gases can be modelled, it is not sensible to mix gas permeation (calculated in units of pressure) with chemical permeation (calculated in terms of concentration).
The effect of thickness is surprisingly small. Doubling the thickness, in the best case, only halves the permeation.
Doubling the thickness quadruples the "breakthrough time" but this merely means that a breakthrough in, say, 20 days will become a breakthrough in 80 days, which is not significant for a membrane intended to last for years.
The key here is not the time for permeation to stabilise but the rate of permeation.
With Puraflex the permeation rates will be very low. This will then automatically translate into low mg/kg over timescales of decades..
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The use of the software is done at your own discretion and risk and with agreement that you will be solely responsible for any damage to your computer system or loss of data that results from such activities. No advice or information, whether oral or written, obtained by you from ITP or from the ITP web site shall create any warranty for the software.
ITP emphasises that the data for the chemical resistance is based on data from multiple sources. ITP does not guarantee the accuracy and correctness of such data, and does not accept any responsibility for any loss or damage that result from the use by customers or by any third parties to whom such data may be transmitted. The user is required to carry out the appropriate tests to ensure the suitability and safety of the products for the use envisaged in accordance with all applicable regulations. No warranties or assurances of reliability, suitability or fitness for a particular purpose of specimens or data are offered. Final determination of the suitability of any information or material for the use contemplated and the manner of use is the sole responsibility of the user and the user must assume all risk and liability in connection therewith.
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Puraflex Permeation Modeller Software (PPM)
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