Meaning
Microstructural characteristic defined as the space within a macromolecular material not occupied by the constituent atoms themselves. Theory of molecular packing suggests that this unoccupied space allows for the movement of polymer chains and the diffusion of small molecules. The polymer free volume directly influences properties such as the glass transition temperature and the rate of gas permeability.
In packaging applications, controlling this volume is necessary for maintaining the shelf life of food or chemical products.
Barrier Property
Materials with a high amount of internal space are more likely to allow oxygen or moisture to pass through. Suppliers of barrier films must optimize the polymer free volume to meet the strict oxygen transmission rate requirements in supply contracts. Increasing the crystallinity of the plastic is one way to reduce this volume and improve protection.
Thermal Sensitivity
Expansion of the free volume occurs as temperature rises, making the material softer and more permeable. This change can affect the mechanical stability of a container during high-temperature sterilization. Understanding these shifts is necessary for manufacturers who ship goods through different climate zones.
Diffusion Rate
Mobility of additives like plasticizers or dyes depends on the available space. This affects the leaching behavior.
