Rheological behaviors of step ladder-structured nitrocellulose in solution and gelatinization process

Step ladder-structured nitrocellulose (LNC) is a novel energetic binder prepared by chemically modifying nitrocellulose (NC) with the introduction of flexible polyethylene glycol (PEG-400) chain segments, with a regular structure and good performance of bonding. The step ladder-structured addresses critical limitations of NC-based propellants, including low-temperature brittleness and high sensitivity, while enhancing process safety. Although the structural, thermal, and other properties of LNC have been investigated in our previous research, there is a lack of systematic studies on the rheological properties during solution and gelatinization. The study of the relationship between the structural features and rheological properties of LNC is a key factor in guiding its gelatinization and improving the properties of LNC-based propellants. Steady-state rheology flow experiments revealed that LNC exhibited shear thinning in different solutions, which decreased with increasing concentration. It has desirable solubility and dispersion in N, N-dimethylformamide (DMF) solvent. The effect of solvents on the entanglement or orientation of LNC molecular chains may be reduced. These results can be quantitatively demonstrated using the Herschel-Bulkley model. Dynamic viscoelastic studies identified a critical point of concentration-frequency of 2.5 rad/s. This particular frequency point is a turning point in the law of the effect of concentration on the loss factor (tan δ ). For gelatinized systems, increasing the solvent content reduces the temperature sensitivity of the gelatinized materials. The viscosity-temperature correlation based on the Arrhenius equation allowed the optimization of the solvent content through the derived equilibrium relationship. These structure-rheological performance relationships establish basic guidelines for the precision gelatinization of LNC-based propellant, provide theoretical support for the replacement of conventional NC by LNC, and guide the gelatinization process to improve the performance of gun propellants.