Thermal protective and hydrophobic coating on polyimide resin matrix composites surface for improved aging resistance

Polyimide composites are easily degraded in high temperature and high humidity environments for long service, which reduces their reliability and stability in aerospace, electronic components, weapons, and other fields. In this paper, the inorganic and organic multiphase double-layer coating was prepared. The insulating layer was made of vinyl polysilazane resin as the base material and hollow glass microspheres as the filler. The hydrophobic layer consisted of polydimethylsiloxane as the base material, hollow phenolic microspheres, and nano-TiO2 as the filler. The heat resistance, hydrophobic properties, and aging resistance of the coated polyimide resin matrix composites were studied. The results showed that the thickness of the double-layer coating was about 200 mu m. Under the 200 degrees C thermal insulation test, the maximum temperature drop can be achieved at 59.7 degrees C. After adding 5 wt% TiO2, the static contact angle of composites was increased from 86.2 degrees to 127.7 degrees. Significantly, the hydrophobic performance was improved by 48.1%, which was due to the construction of micro-nano structures in the surface layer coating. In the accelerated hydrothermal aging tests, the bending properties of coated composite materials can be improved by 8.5%, 3.2%, and 8.7% in water, alkali, and acid environments, respectively. The moisture absorption of glass fiber and the pyrolysis of polyimide led to the degradation of the mechanical properties. The existence of heat-resistant and hydrophobic coating could effectively eliminate this adverse effect, which was of great significance for polyimide composites to cope with various service environments.Highlights A novel coating consisting of thermal insulating and hydrophobic layers was developed on glass fiber reinforced polyimide composites (G/PI) composites. The maximum temperature drop of coating can be achieved at 59.7 degrees C. The static contact angle of coated G/PI composites was increased from 86.2 degrees to 127.7 degrees. In the aging tests, the protective effect of the coating resulted in improved mechanical strengths of G/PI composites. The microscopic damage morphology was performed to analyze the anti-aging properties of the coating. In this work, a novel double-layer coating was prepared at ultralow temperature for enhanced thermal protection of glass fiber-reinforced polyimide (G/PI) composites. The bottom heat-insulating layer consisted of vinyl-polysilazane (PSZ) and hollow glass microspheres (HGMs). Nano-TiO2 and surface-modified hollow phenolic resin microspheres (HPRs) were selected as fillers in the surface hydrophobic layer, and polydimethylsiloxane (PDMS) was used as the adhesive. The double-layer coating possessed good hydrophobic properties and excellent thermal protection. The results of the hygrothermal aging test demonstrated the existence of coating can effectively improve the anti-aging properties of G/PI composites. By observing the changes of microstructure and composition, the protective mechanism of the coating was further revealed. image