Polymer Coating over Solid Particles with In Situ Thermal Curing
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Solid particles coated by cross-linked polymer layers find applications in many areas, including hydraulic fracturing operations. In this study, a hot-melt resin coating process for solid particles is developed and optimized for hydraulic fracturing applications. Phenolic resin is used to coat the particles above its melting point and is subsequently cured in situ by hexamethylenetetramine (HMTA). The coating quality is then characterized by the surface morphology, acid solubility, and crush resistance of the resin-coated particles. The effects of various operating parameters on the coating performance are systematically studied. Among them, temperature is shown to play an especially important role. The coating process involves intricate coupling between resin rheology, HMTA mass transfer, and curing kinetics, all of which are profoundly influenced by temperature. Different constant temperature levels as well as controlled temperature ramps are investigated, and the results show a complex dependence. Higher temperature leads to stronger coating layers with better barrier properties, whereas lower temperature is preferable for better surface morphology. These two trends can be partially reconciled with ramping temperature profiles; the improvement is, however, eventually limited by the rate of heat transfer. This study not only provides insight into the physical and chemical processes underlying the resin coating operation, it also demonstrates a generalizable strategy suitable for various particle coating processes.