Back in history 1855, to understand the shelf life of food packaging

calculation of OTR and WVTR, WVTR transmission rate of plastic, shelf life of packaging material, shelf life of food packaging,

We understand, the packaging materials formed from glass, paper, or metal. The shelf life of packaging material is a valuable physical property for many food manufacturing and bio-medical applications.

The packaging made from plastics is permeable to varying degrees to small particles such as gases, moisture, acidic vapors, and other low molecular weight compounds. For example, plastic with low permeability, i.e., high barrier properties, is required for food packaging applications to prevent degradation of quality, aroma, color, and to increase shelf life.
Understand the shelf life of food packaging
The permeate of gases and liquids through polymer or plastic films is started by either a pressure or temperature gradient, or by an external force field and a concentration gradient.
The shelf life of food, pharmaceuticals, and other perishable items is defined with one of the factors, i.e., permeability or flux. The wall thickness and grade of the plastic depends on how much air, moisture, and organic vapor can diffuse through the packaging material. 
Every packaging engineer | technologist should know the calculation of diffusion to estimate the shelf life of packaging material. And also, it assists in finding the shelf life of the food product. So, the awareness of the classifications of deteriorative reactions that affect food quality is the first step in developing food packaging. And it will minimize undesirable changes in quality and maximize the development and preservation of desirable properties.
For the pharmaceutical business, it has to comply with the packaging material’s testing and retesting just because to ensure the packaging material complies with the diffusion limit standard – The limitation as per the required standard (defined by FDA regulations).
The shelf life of packaging material depends on the calculation of OTR and WVTR by diffusion law – Fick’s first Law (1855)
Source: Wikipedia

Q – the quantity of gas or vapor permeating a polymer of thickness X
A – surface area
t – time
p1 – pressure gradient on one side
p2 – pressure gradient on another side
*where p1 > p2
D – Constant diffusion coefficient
S – solubility coefficient of the permeant; the product DS referred to as the permeability coefficient (or constant) or permeation coefficient, or merely the permeability, and expressed by the symbol P. 
The permeability of gases and moisture in a polymer can be different for different polymers and permeants.

Best explained in videos: Fick’s first law

Calculator of OTR & WVTR transmission rate of plastic
I am recommending a free tool that helps you to estimate the calculation of OTR and WVTR transmission rate of plastic without any instrument. The calculating guides estimates of the O2 (oxygen), Water Vapour, and CO2 Transmission Rate of many plastics packaging materials like PP, PE, PET, PA, and EVOH.

Standards and accreditation
  • Oxygen permeability testing – ASTM D-3985, ASTM F-1927, and ASTM F-1307, DIN 53380-3, or JIS K 7126.
  • Water vapor permeability testing – ASTM F1249, BS 7406 (method A), ISO 9932:1990, and TAPPI T557.



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