Thermal spraying of polymers

Thermally sprayed polymer coatings are gaining significant attention from many industries, including the petrochemical, automotive, and aircraft industries. They are being used for surface protection against humidity, corrosion, and aggressive chemical environments, as low friction and stable electrical insulation coatings,. and as coatings with tailored electrical and magnetic properties. Thermal spraying is a unique, environmentally compliant, technique for the application of polymers and polymer composites because it overcomes processing limitations of other polymer coating techniques. Materials are processed in powder form and therefore the need for solvents is eliminated. Processing is not limited by melt viscosity and/or thermal conductivity of the substrate material. It is an effective method to produce coatings with a large range of thicknesses on a variety of substrate materials. Coating applications are not restricted by the size of the part being coated and coatings can be readily applied in the field, which is an important consideration for industrial use. Spraying is a one step process, with no additional cure time needed. Thermoplastic coatings can be repaired by remelting and applying additional material to the desired location. Many polymers can be applied in high humidity conditions as well as at temperatures below freezing. Successful deposition of polymer coatings by thermal spraying involves careful consideration of material limitations and the capabilities of individual thermal spray processes. Coating performance is strongly influenced by processing parameters and the subsequent coating microstructure that develops. Carefully designed processing conditions are necessary to obtain optimal heat input into the powder and to prevent polymer degradation. Sufficient heat input, optimal substrate preparation, and material changes during deposition must be carefully balanced so that the polymer deforms and adheres well to the substrate. Various thermal spraying techniques available for spraying polymers, and their attributes, are described. Heat transfer and its effects on changes in physical properties of polymers due to spraying are presented. Through the experimental results obtained by various researchers, process-structure-property relationships are discussed. Size, distribution, and filler content effects on polymer composite coatings are introduced. Current and potential fields of application of thermally sprayed polymer coatings are reviewed.