The integration of civilian nitrocellulose in propellant with highly improved mechanical property and thermal stability, and study on its combustion behavior

The consumption of ammunition resources in information warfare has increased exponentially due to its shorter duration and accelerated processes, thus the timely and accurate supply of ammunition plays a critical role in winning the war [1], [2], [3]. Research into raw material sources and production has important implications for ammunition preparation and supply. Nitrocellulose (NC), also known as nitrocotton made from refined cotton, is one of the basic raw materials used in ammunition production, particularly in the manufacture of conventional propellants and high-energy mixing explosives. Gun propellants in service include single, double, and triple base propellants and others, of which nitrocotton as a binder is the basic component [4,5]. Of these, the maximum nitrocotton content in single-base propellants could be 98 %, while the content of nitrocellulose in triple base propellants is smaller at 30 % [6]. Therefore, the supply ability of nitrocotton determins the production capacity of gun propellants.

In the search for binders to replace nitrocotton in solid propellants, various new polymer binder propellants have been developed in recent decades to satisfy the requirements of safety, energy, and process for propellant [7,8]. Generally, it can be divided into energetic binders and non-energetic binders. Non-energetic binders have been commonly studied in composite propellant systems for rocket engines, such as the hydroxyl‑terminated polybutadiene (HTPB) system [9,10], the polyurethane (PU) system [11,12], the nitrated bacterial cellulose system [13,14], and so forth. The addition of a non-energetic binder, on the other hand, reduces the energy level of the gun propellant. Notably, the way of enhancing the energy of propellant by adding huge volumes of energetic explosives, will not only diminish the mechanical strength of the propellant but will also promote barrel ablation and drastically reduce the weapon's service life [15,16]. Therefore, the research about non-energetic binders focused on applying composite propellants in rocket motors. Energetic binders, which contain energetic groups in the main or side chains, such as nitro (-NO₂), nitrate (-ONO₂), and azido (-N₃), are also mainly used in the field of rocket propellants and explosives. At present, the application of energy-containing thermoplastic elastomers (ETPE) [17], [18], [19], glycidyl azide polymers (GAP) [20], and poly glycidyl nitrate (PGN) [21,22] in gun propellant has been reported. However, most of these energetic binders are used in small quantities as additives in formulations, and some processing problems prevent them from being used in large quantities as the base material for gun propellants. Thus, nitrocotton, or a mixture of nitrocotton and a polymer, was still the main binder for solid propellants.

Nitrocellulose derived from cotton fibers is widely used for the production of propellants owing to its high purity and ease processing. However, the propellant prepared with NC derived from cotton fibers faces two main problems:(a) There are nearly no other raw fibers except cotton, while the use of other plant fibers requires the replacement of the corresponding production equipment and the adjustment of process conditions. (b) It has fewer production lines and a lower level of capacity efficiency. Civilian Nitrocellulose (CNC) is a type of nitrocellulose created from wood, bamboo pulp, cotton and other plant fiber sources, and it is primarily used in civilian products such as paint, nail polish, film, and varnish [23], [24], [25]. It has the same spatial network structure and composition as NC. Furthermore, beneficial from the excellent production technology and equipment, CNC has high purity, a wide range of viscosities, and good mechanical qualities, and its production and consumption are much higher than that of military NC.As a potential propellant binder that can be supplied in large quantities and at short notice in certain cases, CNC could be an excellent alternative to military nitrocellulose to overcome the shortfall in military NC production. Moreover, a study of the nitrogen content characteristics of nitrocellulose revealed that increasing its nitrogen content improved the overall stiffness of the propellant system while decreasing the mechanical properties. The application of CNC with 12N% nitrogen content and excellent mechanical properties in propellant formulation means that the mechanical properties of gun propellants can be satisfied while adding more energetic components to increase the energy, which provides a new way to achieve a balance between the energetic and mechanical properties of artillery propellants [15]. Additionally, due to their excellent performance characteristics and relatively simple and economical manufacture and use, modern solid propellants have been applied in a variety of civil applications, including signaling and fireworks, various special devices in the automotive and aeronautical industries, and the destruction of hazardous biological or chemical agents and persistent pollutants [26]. Hence, the utilization of CNC as a binder for solid propellants may also lead to developments in some civil applications.

Herein, a kind of novel CNC-based propellants were prepared by the traditional solvent method. The effect of CNC on the processability, morphology, mechanical properties, thermal stability, and combustion behavior and energy performance of the gun propellant was investigated. To the best knowledge of us, the use of CNC in gun propellant has not been reported before. Therefore, this study will provide a new strategy of selecting a gun propellant binder, controlling production costs, and developing engineering applications.