|Re: Diffusion through PVC foil (0.2 mm)|
Posted by Dave on January 22, 2004 at 08:22:20:
In Reply to: Re: Diffusion through PVC foil (0.2 mm) posted by Diffusion Platform on January 17, 2004 at 18:13:50:
Hi Platform contributers,
What is the amount (weight/volume percent)
of plasticizers / poly vinyl chloride (pvc) used in these sorts of plastic bags?
: Thank you for your interesting case.
: Based on experience the following diffusion parameters can be
: estimated for normal pure PVC (without plastizers) and water in
: atmospheric conditions and at 25 degrees Celsius:
: Water density: 10^6 gram/m3
: Water solubility: 0,003 volume fraction liquid (=0,3%) -> very low volume fraction: case 1 diffusion (Fick's law)
: Water diffusion coefficient: 10^-12 m2/s(amorphous polymer)
: Permeability is: [10^6 gram/m3] x [0,003] x [10^-12 m2/s ] =3 x 10^-9 gram m /s in the stationary
: Based on a wall of thickness of 0.2 mm, stationary state is reached after 4 hours.
: The amount of water that diffuses through in the stationary state is [Permeability
: Figure] divided by [wall thickness], resulting in 0,05 gram /m2 hour = 0.5 kg / m2 year.
: Based on the information above the following can be stated:
: The figure you got of 16 kg / m2 year would indeed by high for 'pure' PVC, like it
: is used for building pipelines, however the Polyvinylchloride you got may be plasticed with a
: plasticizer that has relative strong affinity for water that may cause swelling, leading
: to a larger permeability. However when you compare your figure with the figure
: for a polyester resin and water (as it is used for building boats) - 5 kg/ m2 year - the
: performance of your PVC bag is not so bad - of course depending on your application.
: Mind that the air humidity plays a role in the total amount that diffuses through. If
: You got water on one side and air with relative humidity of e.g. 70% on the other side,
: The total trough put from the liquid side - in stationary state - would be 16 kg / m2 year x (1-70%) = 5 kg /m2 year.
: best regards,
: Diffusion in Polymers Platform