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Natural Rubber Composites for Paper Coating Applications
* 1 , 2 , 2
1  University Hasselt, Institute for Materials Research, Applied and Analytical Chemistry, Agoralaan Gebouw D, B-3590 Diepenbeek, Belgium
2  Topchim N.V. (a Solenis International LCC Company), Nijverheidsstraat 98, B-2160 Wommelgem, Belgium


Natural rubbers are characterized by extremely high molecular weight that might be beneficial in the formation of a protective barrier layer on paper substrates, providing good cohesive properties but limited adhesion. In parallel, the thermal properties of natural rubber with extremely low glass transition temperature might give the opportunity for good sealability. Therefore, natural rubbers can be good candidates to serve as an alternative ecological binder in paper coatings for water and grease barrier resistance. In order to be able to tune the surface properties of the paper coating, the effect of different additives are evaluated on rheological properties, thermo-mechanical properties and final surface properties of a paper coating. The additives are selected in parallel with common practice for paper industry, including talc, kaolinite clay and a type of organic nanoparticles, which are all added in the range of 5 to 20 wt.-%. Depending on the selected type of natural rubber, the dispersibility range (i.e., dispersive and distributive mixing) of the additives in the latex phase highly varies and is mainly determined by the molecular weight profile of the rubber. However, an optimum selection of viscosity range allows to obtain homogeneous mixtures without the need of surface modification of the additives. After bar-coating the latex mixtures on paper substrates, the drying properties of the composite coatings are followed by thermo-analytical evaluation and spectroscopy illustrating the influences of selected additives on the vulcanization process of the coating. In particular, the latter most efficiently improves in presence of nanoparticle fillers and highly increases the mechanical properties of the coating: the coating hydrophobicity can be successfully increased while in parallel reducing the adhesive surface properties.

Keywords: paper; natural rubber; additives