In this paper, thermal and mechanical properties of ablative thermal protective material (TPM) as inhibitors for a free-standing propellant grain based on phenolic resin (PR) and acrylonitrile butadiene rubber (NBR) were investigated. NBR elastomerized PR composite, reinforced with chopped carbon fibers (CFs) (PR/NBR/CF), was prepared by homogenization of 90 parts by weight (PBW) PR in 100 PBW NBR (28 wt.% of acrylonitrile content). PR/NBR/CF composite was blended in two-roller open and closed mixers and in a twin-screw extruder. Carbon black, aluminum(III)-oxide, and fumed silica were added as promoters of thermal and mechanical properties of PR/NBR/CF. The structural analysis was studied using Fourier transform infrared spectroscopy (FT-IR). Thermal properties of the prepared PR/NBR/CF composite inhibitor were studied by ablation and firing tests, while a morphological analysis of the char layer formed after the ablation test was conducted via scanning electron microscopy (SEM). A low erosion rate of 2.00 × 10⁻⁴ m·s⁻¹ and high tensile strength and elongation at break of 6.7 MPa and 419.92%, respectively, indicate that the developed materials can be applied as a thermal insulation/inhibitor of free-standing rocket propellant grains. Bond strength between PR/NBR/CF composite and aluminized composite rocket propellant (ACRP), determined via a standard peel test, showed higher adhesion forces between the PR/NBR/CF composite and the ACRP compared to the cohesion between the ACRP molecular chains.

Conventional black powder typically consists of charcoal, sulfur and potassium nitrate (KNO3). The use of other carbon-based substances instead of charcoal has been less common. Following the development of time delay pyrotechnic compositions in this research, the pyrotechnic properties of other carbon-based substances, particularly carbon black were studied. The use of charcoal has been widely spread due to its unique chemical composition and superior combustion properties. However, due to the specific production process and the selection of materials for producing charcoal, it is difficult to achieve the same quality, i.e., chemical composition of charcoal. The use of other carbon-based substances may suppress those problems. Quaternary compositions containing charcoal or carbon black as a fuel and KNO3, sulfur and phenol-formaldehyde resin were prepared and tested. Commercially available charcoal and carbon black were obtained for this initial research. The as-received materials, charcoal and carbon black, were characterized by SEM, EDS and particle size analyzer. SEM and EDS analysis were used to obtain information about morphology and semi-quantitative determination of the chemical composition and particle size analyzer for obtaining information about particle size and its distribution. The experimental values of heat of reaction and linear burning rate were compared. The average linear burning rate for pyrotechnic composition with carbon black of 7.33mm/s showed increase of 28.5% comparing to pyrotechnic composition with charcoal. Observed behavior suggests that this compound may be useful for a variety of pyrotechnic applications.