Molecular Simulation of Improved Mechanical Properties and Thermal Stability of Insulation Paper Cellulose by Modification with Silane-Coupling-Agent-Grafted Nano-SiO2

Abstract

Cellulose is an important part of transformer insulation paper. Thermal aging of cellulose occurs in long-term operation of transformers, which deteriorates the mechanical properties and thermal stability of cellulose, resulting in a decrease in the transformer life. Therefore, improvement of the mechanical properties and thermal stability of cellulose has become a research hotspot. In this study, the effects of different silane coupling agents on the mechanical properties and thermal stability of modified cellulose were studied. The simulation results showed that the mechanical parameters of cellulose are only slightly improved by KH560 (γ-glycidyl ether oxypropyl trimethoxysilane) and KH570 (γ-methylacrylloxy propyl trimethoxy silane) modified nano-SiO2, while the mechanical parameters of cellulose are greatly improved by KH550 (γ-aminopropyl triethoxy silane) and KH792 (N-(2-aminoethyl)-3-amino propyl trimethoxy silane) modified nano-SiO2. The glass-transition temperature of the composite model is 24 K higher than that of the unmodified model. The mechanism of the change of the glass-transition temperature was analyzed from the point of view of free-volume theory. The main reason for the change of the glass-transition temperature is that the free volume abruptly changes, which increases the space for movement of the cellulose chain and accelerates the whole movement of the molecular chain. Therefore, modifying cellulose with KH792-modified nano-SiO2 can significantly enhance the thermal stability of cellulose.

Investigation of physical, mechanical, and thermal properties of glass fiber reinforced polymer composites strengthened with KH550 and KH570 silane-coated silicon dioxide nanoparticles

“…The increase in T g values can be attributed to the delays of molecular chain transitions due to the silane coatings. 28,30 The higher T g can be associated with the well-bound establishment of the kinematic chains by the silane-coated SiO 2 nanoparticles dispersed into the epoxy matrix. The energy requirement for the molecular motion of polymer was increased, which contributed to the curing behavior of the composites.…”

“…29 Silanization can also be applied to avoid agglomerations of the particles within the polymer matrix by reducing surface energy of the SiO 2 nanoparticles. 25,30 Wu et al 3 functionalized the SiO 2 with a KH550 type silane coupling agent and achieved a good dispersion with a slight agglomeration up to 5 wt.% of nano SiO 2 addition within the epoxy matrix. Mallakpour and Madani 31 improved the compatibility of zinc oxide (ZnO) nanoparticles within the poly (amide-imide) (PAI) matrix with KH550 and KH570 type silane coatings, which contributed to both the fine dispersion of ZnO particles and thermal stability of the developed nanocomposites.…”

“…This is due to the improved adhesion between the reinforcements and the matrix. Zhang et al 30 functionalized the nano SiO 2 particles with different silane coupling agents like KH550, KH560, KH570, and KH792 and compared the results. While KH560 and KH570 silane coupling agents slightly improved the mechanical and thermal performance of the modified SiO 2 , KH550 and KH792 provided better enhancements.…”

“…KH550 is finely grafted to the surface of SiO 2, and so it provides more hydrogen bonds between the SiO 2 and the polymer molecules. 30 Wang et al 27 grafted several silane coupling agents (KH550, KH560, and KH570) on the surface of SiO 2 nanoparticles and obtained better thermodynamical properties with KH550 coated SiO 2 /cellulose composites compared to the others due to the more hydrogen bonds in the case of KH550 grafting. Bahramnia et al 32 functionalized the SiO 2 nanoparticles with 3-glycidoloxypropyl trimethoxy silane (GPTMS), containing glycidyl functional group, and then hybridized with multiwalled carbon nanotubes (MWCNTs) within the epoxy, which provided covalent bonds between MWCNTs and polymer chains.…”

“…When the literature was scrutinized, it is clear that silane treatments can overcome some disadvantages of nano SiO 2 filled polymer matrix. The recent literature 30,38 has evidently shown that the combined effect of silane treatment and pure nano SiO 2 particle addition into the polymer matrix has a favorable impact on the interfacial strength leading to better structural performance. The present study investigates the effects of both KH550 and KH570 silane-coated nano SiO 2 addition at different ratios, as a secondary reinforcement, on the physical, mechanical, and thermal properties of glass/epoxy composites.…”