To investigate the microscopic mechanism of aging-induced “dewetting” at the matrix/filler interface in Nitrate Ester Plasticized Polyether (NEPE) propellant, this study decoupled the aging process into two factors: crosslinking density evolution and nitrate ester decomposition. Molecular dynamics (MD) simulations were employed to construct all-component matrix models and matrix/filler interface models with varying aging extents. Key parameters including crosslinking density, mechanical properties, free volume fraction, diffusion coefficients of the matrix, as well as interfacial binding energy and radial distribution function (RDF) were calculated to analyze the effects of both aging factors on “debonding”. The results indicate the following: 1. Increased crosslinking density enhances matrix rigidity, suppresses molecular mobility, and causes interfacial binding energy to initially rise then decline, peaking at 40% crosslinking degree. 2. Progressive nitrate ester decomposition expands free volume within the matrix, improves binder system mobility, and weakens nitrate ester-induced interfacial damage, thereby strengthening hydrogen bonding and van der Waals interactions at the interface. 3. The addition of a small amount of bonding agent improved the interfacial bonding energy but did not change the trend of the bonding energy with aging.

The matrix and particle interface of hydroxyl-terminated polybutadiene (HTPB) propellant is the weakest part of its mechanical properties, making it prone to dewetting damage and destroying the structural integrity of the propellant. This article uses nano-indentation, gas cluster ion beam etching, and X-ray photoelectron spectroscopy experimental analyses to study the physicochemical properties of the interface and subsequently construct a microscopic model for the HTPB matrix and ammonium perchlorate particle interface. The model fully considers the existing forms of curing agent toluene diisocyanate, bonding agent Tris (2-methyl-aziridine) phosphine oxide (MAPO), and the aging products of the propellant in the interface structure. Meanwhile, the physicochemical properties, mechanical properties, and adhesive properties of the interface under different tensile loading conditions were analyzed. The results indicate that the bonding agent MAPO significantly enhances the mechanical and adhesive properties of the interface. The interface is sensitive to changes in temperature and tensile rate, and the aged interface is more fragile.

To clarify the evolution of dewetting during the aging of NEPE propellant during long-term storage and more intuitively reveal the impact of aging on dewetting behavior, we used micro-CT to scan NEPE propellant samples subjected to 20% constant strain at different points during aging. After image processing, the internal pores of the samples were extracted, porosity was calculated, and the law of the variation in dewetting behavior at the matrix/filler interface during aging was analyzed. Additionally, we used SEM technology to scan the tensile fracture surfaces of the NEPE propellant samples, observing the aging evolution of the matrix and matrix/filler interface on the fracture surfaces. Along with conducting a micro-CT test, we further explored the changes in bonding performance at the matrix/filler interface during aging. The micro-CT scanning results indicated that dewetting was evident in unaged samples under constant-strain loading, resulting in numerous petal-shaped pores with a significant volume. As aging progressed, the number of petal-shaped pores gradually decreased, and porosity dropped significantly. The SEM scanning results show that the matrix gradually softened during aging, encapsulating solid particles more tightly. Based on all the experimental results, debonding in the NEPE propellants became progressively less pronounced with aging, and interfacial adhesion between the matrix and filler improved. These results provide support for enhancing NEPE propellants’ matrix/filler interfacial bonding strength and, consequently, improving their mechanical properties.