Effect of Moisture on Mechanical Properties and Thermal Stability of Meta-Aramid Fiber Used in Insulating Paper

Abstract

Seven composite models of meta-aramid fibers with different moisture contents were studied using molecular dynamics simulation. The effects of moisture on the thermal stability and mechanical properties of the fibers and their mechanisms were analyzed, considering characteristics such as hydrogen bonding, free volume, mean square displacement, and mechanical parameters. The simulation results showed that the large number of hydrogen bonds between water molecules and meta-aramid fibers destroyed the original hydrogen-bond network. Hydrogen bonds between the molecular chains of meta-aramid fibers were first destroyed, and their number decreased with increasing moisture content. The free volume of the fibers thereby increased, the interactions between fiber chains weakened with increasing moisture content, and the fiber chain movement intensified accordingly. The ratio of diffusion coefficients of the water molecules to moisture contents of the composite models increased linearly, and the water molecule diffusion increased, which accelerated the rate of damage to the original hydrogen-bond network of the meta-aramid fibers and further reduced their thermal stability. In general, the mechanical properties of the composites were negatively related to their moisture content.

Molecular Simulation on the Thermal Stability of Meta-Aramid Insulation Paper Fiber at Transformer Operating Temperature

“…In addition, the intramolecular distance can no longer meet the conditions for the formation of a hydrogen bond; therefore, the hydrogen bond number decreases slightly. The hydrogen bond number is similar for the different simulations using the model for the amorphous regions, which is consistent with reported results [50].…”

“…In contrast, the arrangement of molecular chains inside the amorphous regions is irregular, and the long chains are easily deformed, bent, and even folded; therefore, both intermolecular and intramolecular hydrogen bonds can form in the amorphous regions. The number of intermolecular hydrogen bonds was greater than that of intramolecular hydrogen bonds [50]. An N–H···O-type hydrogen bond can form when an O atom is close to an –NH radical group, and an N–H···N-type hydrogen bond can form when an N atom is close enough to an –NH radical group; these two types of hydrogen bond can be intermolecular or intramolecular.…”

Molecular Dynamics Simulations on the Thermal Decomposition of Meta-Aramid Fibers

“…However, these experimental methods cannot be used to explain the complex phenomena of microreactions and the microscopic mechanisms. As a scientific calculation method, the molecular dynamics method can be used to clarify these previously unexplainable mechanisms [30,31,32,33,34,35,36]. Further investigation of the degradation mechanism and thermal decomposition of meta-aramid fiber at the micro-level using molecular simulation is needed.…”

Investigating the effects aviation fluids have on the flatwise compressive strength of Nomex® honeycomb core material

“…Semple et al [4] showed that paper honeycomb losses its flexural stiffness, shear strength, and compressive strength significantly in high humidity (95% RH) compared to normal humidity (65% RH). Allred and Roylance [22] and Yin et al [23] reported that degradation of mechanical property of Nomex V R honeycomb core is caused by water molecules which destroy hydrogen bond network of the aramid fiber. If a composite structure absorbs moisture, the polymer matrix can be plasticized which degrades the structure (physical aging).…”