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Water Permeability of materials

Water Permeability of materials

Water Permeability of materials

Hey guys,

Hope all is well! I'm running into an issue of mold growth in an aqueous-filled pouch that we have. The film material that houses this pouch is TPU. We also have a pouch that is houses by a PVC film, but this does not have the mold issue. Does anyone know why these two materials behave so much differently? I can't find distinctive evidence between the difference in water permeability between PVC and TPU. Is moisture absorption the same thing? Please advise.

Thank you so much!


RE: Water Permeability of materials

Is the mold on the pouch or inside? If it's on the inside and both are filled with water then water permeability is not the issue.

If the mold is on the outside then the main difference could be what the mold is feeding on. The plasticizer in the PU or PVC could be different and the mold sees the additives in the TPU as viable food and those in the PVC as not viable food. For example, PVC is often stabilized with calcium zinc salts where the zinc is anti-microbial and may even help prevent mold growth.

We would need to know more to help more.

Chris DeArmitt PhD
President - Phantom Plastics LLC

Consulting, ideas and training on plastic materials

RE: Water Permeability of materials

The mold was ON the pouch, not inside. The pouches were from the polybags that they are shipped in and individually immersed them in sterile bags and added the extractant (Fluid D). The outside analysis firm says it seems unlikely that organisms could escape from within but all they really tested was the exterior.

The materials that the gel is made up of are:

EDTA, Powder

Methyl Paraben, Powder

Deionized Water)


Quadrol Polyol (Medical Grade

Do you think that the mold could be feeding off any of these ingredients that could potentially be secreted through the TPU bag?

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