Polymers 2020 , 12 , 173
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situation causes a strong adhesion and blade vibrations, which in turn generates non-uniform creping and profile of the paper, blade wear, and damage to the surface of the drying cylinder [5]. On the other hand, the most common release agents usually have the combination of fatty alcohols, glycerol, and non-ionic emulsifying agents such as lecithin [6,7].
Figure1. Scheme of the creping process using a coating-release agent in the yankee dryer.
The main limitation is that all the components must be completely emulsified along with the coating in the yankee’s surface during application since the hardness and adhesiveness should be equilibrated depending on the needs [7,8]. The previous requirement implies that during the application the emulsions must be stable and homogeneous, which normally does not occur when the most common release agents are used [8]. In general, these types of emulsions are easily separated and their application in the yankee leads, for example, to non-homogeneous coating, which is traumatic for the drying process a ff ecting the formation of the tissue paper rolls and also yankee’s surface could be deteriorated [5,7]. The shelf-life of the doctor creping blade could be reduced and the di ff erent adherence intensity to the paper sheet deteriorates its creping process and the final quality of the paper [5,7]. Therefore, there is a great demand for a crepe coating-release couple that remains soft and re-wettable under the drying conditions found in creping [1,7]. It is necessary that produces high creping e ffi ciency while generating a high-quality paper [9], less creping blade wear, and greater protection for the yankee to generate a uniform release of the paper and that does not produce bursting problems on paper rolls [7]. Promising coatings that seems to accomplish these requirements are the polyamine-based resins. These resins show charge density and structures related to the fibers of the pulp which generates lower dry strength in the paper than the classical PAE [10,11]. In addition, they have less adhesion and hardness properties, controllable during the polymerization process [12] in order to have properties required by the yankee [5]. At the same time, release agents based on vegetal oil surfactants present stable emulsions that control this type of coatings once they are applied to the yankee [13,14], which inspire us for the present development. For this reason, a new coating (Polycoat 38 ® ) was designed based on a diamine and epichlorohydrin [15] to generate a cationic polyamine whose structure, viscosity, percentage of solids, charge density, and tensile measures indicates a greater adhesion-release balance. Therefore, greater rewetting properties together with the interaction of a mineral oil-based release agent (Disprosol 17 ® ), allows a more stable coating on the yankee [1], with high resistance, greater smoothness, and a better absorbency of the paper while the creping took place at a paper mill of a tissue production plant [5,7,8].
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