The emptying behavior of highly viscous liquids. Part I: Polymeric surfaces and plasma coatings
Residues of fill goods on the inner side of packages are a problem not only from the economical point of view but also from an ecological perspective. For example, the cost of recycling increases with increasing amount of residues. Another point is the consumer satisfaction that declines when too much product remains in the package. The compositions of products as well as the packaging material have been optimized to provide specific characteristics, e. g., a particular taste or temperature resistance in case of viands, and, e. g., mechanical properties in case of packages. To achieve good anti-adhesive quality between such optimized systems one possible approach is to minimize adhesion forces between the inner side of the package and the fill good. This can be achieved by modifying the packages surfaces, e. g., by the use of plasma enhanced chemical vapor deposition (PECVD) with which deposition of defined nano-scale layers is possible. In this work plasma polymer coatings are compared with standard packaging material (PET) and typical anti-adhesive materials like PTFE with regard to emptying properties, surface free energy and work of adhesion. It will be shown that a low surface free energy is important for minimizing the residue. These low energetic surfaces can be designed by PECVD using two different chemical classes (PTFE-and silicone-analogous). The results show that besides surface free energy other physical-chemical characteristics of the packaged system influence the macroscopic amount of adhered fill goods.