Lipophobic Quality
Physical properties that inhibit the penetration and migration of oils and fats through a substrate determine the suitability of paper for food contact. This grease resistance is achieved through mechanical refining of fibres to create a dense sheet or by applying chemical treatments and coatings. It prevents unsightly staining and preserves the structural integrity of the container when it holds oily contents.
Testing Methodology
Evaluation of this characteristic often employs the kit test or the turpentine test to measure the rate of oil absorption. During a kit test, drops of various mixtures of castor oil and solvents are applied to the surface to see which ones penetrate. Better grease resistance allows the paper to withstand more aggressive chemical mixtures without showing spots on the reverse side.
Results are typically expressed as a numerical value corresponding to the highest successful mixture.
Packaging Application
Fast food wraps and bakery boxes rely on these barriers to maintain a clean appearance for the consumer. If grease resistance is insufficient, the oil can soften the paper fibres and lead to the failure of the package or the transfer of oils to the hands and clothing of the user. Modern developments focus on using bio-based polymers to reach these performance levels without relying on fluorinated chemicals.
Maintaining this barrier during creasing and folding is a persistent challenge for converting operations.
