Polymer Film Micro Fracture Mechanisms under High Strain Shear in Folding Boxboard Creases
High strain shear during boxboard creasing causes polymer film micro fractures when local elongation exceeds film yield capacity along the outer bend radius.
Gas Transmission Rate
Permeation Metric
Food preservation packaging requires precise barrier metrics to protect contents from atmospheric oxygen or carbon dioxide exchange. The metric known as gas transmission rate defines the volume of gas passing through a unit area of paperboard or polymer barrier film over a specified time frame under controlled temperature and partial pressure gradient conditions. Packaging engineers utilize this parameter to evaluate modified atmosphere packaging performance and project product shelf life.
Measurement Protocol
Standardized testing procedures employ coulometric sensors or manometric pressure differentials to quantify gas flux through planar substrates. Determining the gas transmission rate follows standards such as ASTM D3985 for oxygen, measuring gas volumes in cubic centimeters passing per square meter over twenty-four hours. Relative humidity significantly impacts paperboard substrates, as moisture absorption swells cellulose fibres and alters the morphology of polymer barrier coatings.
Testing must take place at defined environmental conditions, typically twenty-three degrees Celsius and zero or fifty percent relative humidity, to ensure comparable dataset values across barrier formulations. Converting processes like creasing, heat sealing, and lamination are tested to evaluate barrier degradation in finished packaging structures.
Barrier Limit
Gas transmission rates increase rapidly when physical pinholes, micro-cracks, or polymer degradation compromise the barrier layer. High ambient moisture levels cause hydro-sensitive barrier materials to lose gas protection capability.