DSC and TGA characterization of free and surface water of colloidal unimolecular polymer (CUP) particles for coatings ap
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DSC and TGA characterization of free and surface water of colloidal unimolecular polymer (CUP) particles for coatings applications Peng Geng, Sagar Vijay Gade, Michael Roy Van De Mark
Ó American Coatings Association 2020 Abstract Colloidal unimolecular polymer (CUP) particles are spheroidal nano-scale and 3–9 nm that can be easily designed and controlled. The formation of CUP involves simple synthesis and water reduction. These nanoparticles have charged hydrophilic groups on the surface and are surrounded by a layer of surface water that does not freeze until very low temperature. CUPs have very high surface area per gram, which gives them a high nonfreezing water content. The CUP system is free of surfactant and has zero VOC, exhibiting great potential for coatings applications. The amount and thickness of the surface water were determined by differential scanning calorimetry (DSC) using the heat of fusion. The solution density and knowledge of the resin density and the composition of the CUP solution were used to determine the density of surface water. The evaporation rate of free water and surface water in CUP solutions were investigated by thermogravimetric analysis (TGA) and showed the effect of CUP on the evaporation rate. CUP as an additive to give freeze thaw stability, wet edge retention and open time improvements were explored. Excellent performance in freeze thaw, wet edge time improvement and more open time was found. The CUP system offers an excellent alternative to form zero VOC waterborne coatings. Keywords Colloidal unimolecular polymer (CUP), Nano-scale, Surface water, Freeze thaw stability, Wet edge retention
P. Geng, S. V. Gade, M. R. Van De Mark (&) Department of Chemistry, Missouri S&T Coatings Institute, Missouri University of Science and Technology, Rolla, MO 65409, USA e-mail: [email protected]
Introduction In recent years, due to the capacity of nanotechnology to have enhanced physical and chemical properties, application of nanotechnology has become more and more important. The term nano commonly refers to anything smaller than 1000 nm and nanoparticles with particle size smaller than 10 nm. These nanoparticles often exhibit significant increases in properties due to the ultra-small particle size or higher surface area per gram.1 Most existing nanoparticles smaller than 10 nm are inorganic nanoparticles. It is difficult to make polymeric nanoparticles with particle size less than 10 nm. Colloidal unimolecular polymer (CUP) particles are a new type of spheroidal nano-scale material (3–9 nm). The polymer can be simply synthesized and made into CUP through a water reduction process,2 which is shown in Fig. 1. The process of CUP formation for the carboxylate example was as follows. The polymers were dissolved in THF, and the solvent must be low boiling and water miscible and then neutralized to pH 8.5 based on the acid number using a peristaltic pump. It is critical that the polymer concentration be low enough to avoid chain entanglement at the point of collapse. The carboxylate groups repe
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