Enhanced mechanical properties and thermal stability of cellulose insulation paper achieved by doping with melamine-grafted nano-SiO₂

In the long-term operation of power transformer, the traditional cellulose insulation paper undergoes aging phenomena, making it difficult for this type of paper to meet severe insulation requirements. In this study, cellulose is modified by doping with melamine-grafted nano-SiO₂, and cellulose/water (C–H2O), nano-SiO₂-modified cellulose/water (CN–H2O) and melamine-grafted nano-SiO₂-modified cellulose/water (CAN–H2O) models are developed. The results show that the mechanical properties of CN–H2O and CAN–H2O are improved relative to those of C–H2O and that CAN–H2O exhibits the best mechanical properties. Furthermore, the glass transition temperatures of CN–H2O and CAN–H2O are, respectively, 39 and 69 K, higher than that of C–H2O. Near the glass transition temperature, the mean square displacement of the water molecules changes considerably. Therefore, increasing the glass transition temperature and thus the thermal stability of cellulose can be achieved by modifying cellulose with melamine-grafted SiO₂ nanoparticles. Experimental studies show that with an increase in the aging time, the moisture content in the modified insulation paper will be less than that in the unmodified insulation paper, while the tensile strength, degree of polymerization (DP) and breakdown strength were greater than that in the unmodified insulation paper. In particular, the melamine-grafted nano-SiO₂-modified insulation paper has the lowest moisture content and highest tensile strength DP and breakdown strength during the entire aging time. Thus, this study shows that the thermal stability and electrical characteristics of the melamine-grafted nano-SiO₂-modified insulation paper is the highest at both the microscopic and macroscopic levels, indicating that this insulation paper could meet the insulation performance requirements of large transformers under high-temperature and high-pressure conditions.