High-gravity-assisted emulsification for continuous preparation of waterborne polyurethane nanodispersion with high soli
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RESEARCH ARTICLE
High-gravity-assisted emulsification for continuous preparation of waterborne polyurethane nanodispersion with high solids content Weihong Zhang1,2, Dan Wang (✉)1, Jie-Xin Wang1,2, Yuan Pu (✉)2, Jian-Feng Chen1,2 1 State Key Laboratory of Organic-Inorganic Composites, Beijing University of Chemical Technology, Beijing 100029, China 2 Research Centre of the Ministry of Education for High Gravity Engineering and Technology, Beijing University of Chemical Technology, Beijing 100029, China
© Higher Education Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract In this work, we developed a continuous preparation strategy for the production of high-solidscontent waterborne polyurethane (WPU) emulsions via high-gravity-assisted emulsification in a rotating packed bed (RPB) reactor. By adjusting the experimental parameters and formula, WPU emulsions with a high solids content of 55% and a low viscosity were prepared. Preliminary applications of the high-solids-content WPU as a thermally insulating material were demonstrated. RPB emulsification is an economical and environmentally friendly production strategy because of the low energy consumption, short emulsification time, and effective devolatilization. This study demonstrated an effective method for preparation of high-solids-content WPU, moving toward commercialization and industrialization. Keywords waterborne polyurethane, rotating packed bed, emulsification, nanodispersion, high solids content
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Introduction
In the previous decade, various products consisting of volatile organic compound-free polymers, which are considered a class of green materials, have been created for use in coatings [1], adhesives [2], multi-functional materials [3], and others [4,5]. Waterborne polyurethane (WPU) dispersions have recently attracted increased attention because of their excellent chemical and mechanical properties and their suitability with respect to environmental requirements and human health [6]. It is Received July 21, 2019; accepted August 22, 2019 E-mails: [email protected] (Wang D), [email protected] (Pu Y)
noteworthy that hydrophilic monomers, include carboxylate, sulfonate, quaternary ammonium salts, or non-ionic groups, are usually embedded into the molecular chain to obtain self-emulsification and good stability of the dispersions in water [7]. To date, anionic WPUs are commercially predominant and carboxylates, especially dimethyl propionic acid (DMPA), are the most common products reported in the literature [8–11]. However, commercial WPU products generally exhibit low solids contents, which lead to a slow drying rate, high latent heat consumption, and high transport costs; therefore, the preparation of high-solids-content WPU is of industrial significance [12]. The key point for preparation of WPU with high solids content is to effectively disperse polyurethane pre-polymers into water to form a stable colloidal dispersion. However, a high solids content and high viscosity often occur simultaneously. As the solid
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