A trojan horse approach for biopolymer based barrier paper coatings

 
Barrier-coatings are important for a number of applications of different paper-grades used e.g. in packaging. Using natural polymer resources, such as cellulose-esters or polymers derived from hydroxypropyl-cellulose, such macromolecules can be used to coat the surface of paper substrates and render these surfaces hydrophobic and even superhydrophobic. Although such surfaces repel water in a fashion well-known as "Lotus-effect", they still are permeable for gases, including water vapor. In this talk an extension of such known studies towards understanding barrier coatings that eventually can restore ("self-repair") a superhydrophobic property, even after mechanical or thermal impacts, will be outlined. I will explain distinct examples, where we have fundamentally studied functional barrier coatings on paper substrates, which consist of a pre-layer made from fiber immobilized alkyl keten dimer (AKD) and a top layer consisting of cellulose- and hydroxipropyl cellulose-ester respectively. The procedure of polymer preparation, paper coating as well as extensive characterization of such superhydrophobic coatings, exhibiting flower-like architectures on paper will be shown. The structure-guiding motif, which drives the formation of fractal structures on top of the paper fibers, is hidden in the immobilized AKD on the paper fiber - similar to a trojan horse approach. We show that the thermal restoration of superhydrophobic properties can be achieved multiple times, even if the layers are treated by mechanical impacts. Because any kind of coating method for both layers can be employed, this approach is also beneficial for a number of technological important applications.