Novel polyurethane-based binders, specifically designed for environmentally responsible rocket propellant composites, were obtained by employing the polyester-polyols that resulted from the degradation of polyethylene terephthalate waste. A new class of “greener” rocket propellants, comprising polyurethanes (based on recycled PET) as the binder, phase stabilized ammonium nitrate (PSAN) as the eco-friendly oxidizer, and triethylene glycol dinitrate (TEGDN) as the energetic plasticizer, together with aluminum as fuel and Fe₂O₃ as the catalyst, is herein reported. The components of the energetic mixtures were investigated (individually and as composite materials) through specific analytical tools: ¹H-NMR, FT-IR, SEM-EDX, DTA and TGA, tensile and compression tests, DMA, and micro-CT. Moreover, the feasibility of this innovative solution is sustained by the ballistic performances exhibited by these composite materials in a subscale rocket motor, proving that these new formulations are suitable for rocket propellant applications.

Shear thickening fluids (STFs) have garnered attention as potential enhancers of protective capabilities and for the optimization of Kevlar^® armor design. To assess the possible shear thickening properties and potential application in ballistic protection, ten formulations were developed by employing polyethylene glycol (PEG) or polypropylene glycol (PPG), along with fumed silica or Aerosil HDK^®. Rheological characterization facilitated the identification of formulations displaying shear thickening behavior. The potential integration of the selected shear thickening fluids (STFs) into Kevlar^®-based composites was investigated by studying the impact resistance of Kevlar^® soft armor structures. Also, high-velocity impact testing revealed that the distance between aramid layers plays a crucial role in the impact resistance effectiveness of Kevlar^®–STF composite structures and that there is a very narrow domain between optimal and undesired scenarios in which STF could facilitate the penetration of Kevlar. The introduction of STF between the Kevlar sheets disrupted this packing and the energy absorption capacity of the material was not improved. Only one formulation (PEG400, Aerosil 27 wt.%) led to a less profound traumatic imprint and stopped the bullet when it was placed between layers no.1 and no.2 from a total of 11 layers of Kevlar XP. These experimental findings align with the modeling and simulation of Kevlar^®–STF composites using Ansys simulation software (Ansys® AutoDyn 2022 R2).

The aim of the current study is to investigate the mechanical properties and ballistic performance of HARDOX 450 steel for defense applications in different conditions: uncoated, alumina-coated, and LINE X polyurea-coated. Tensile tests and Vickers microhardness measurements were conducted, along with fracture surface analysis using stereomicroscopy, scanning electron microscopy, and computed tomography. Experimental results showed that uncoated HARDOX 450 steel exhibited the highest strength and hardness, with ductile fracture features. Polyurea-coated HARDOX 450 steel samples retained good mechanical properties and demonstrated effective ballistic protection, including the containment of fragments. In contrast, alumina-coated HARDOX 450 steel samples exhibited reduced strength and ballistic resistance, attributed to the microstructural changes in HARDOX 450 steel caused by the high-temperature deposition process of alumina. Numerical simulations performed with the 5.56 × 45 mm bullet used in the simulation, along with its ballistic impact interaction with the Hardox 450 target model, aligned well with experimental ballistic impact results for all the samples. Overall, LINE X polyurea coating on HARDOX 450 steel proved to be the more suitable coating for applications requiring a balance of mechanical strength and ballistic impact resistance.

Lightweight materials, valued for their mechanical strength and efficiency, are widely applied in aerospace, automotive, civil, electronic, and biomedical fields. Recent advances in defense and high-speed communication technologies have intensified interest in their use for electromagnetic interference (EMI) shielding. This study explores the synthesis and characterization of flexible polyurethane (PUR) films embedded with reactive poly(methyl methacrylate-co-hydroxypropyl methacrylate)microparticles containing Mo₂Ti₂AlC₃ (MXenes). The poly(MMA-co-HPMA)@Mo₂Ti₂AlC₃ microparticles were prepared via suspension polymerization, utilizing the surface hydroxyl functionality to react with isophorone diisocyanate (IPDI) during PUR formation. This ensured uniform dispersion and stable incorporation of MXenes within the matrix. Characterization included FT-IR spectroscopy, SEM, XRD, DMA, mechanical testing, and EMI shielding evaluation. FT-IR confirmed successful copolymerization with complete monomer conversion. SEM revealed the microparticles as a well-dispersed phase within the PUR matrix, while XRD validated the intact MAX phase with minimal delamination. PUR films exhibited high flexibility and tensile resilience, reaching 0.7 MPa at ∼85% strain. EMI shielding improved with increasing microparticle concentration, with 2 wt% composites achieving 3 dB attenuation and reflecting 50% more power than lower-loaded samples in the 8.2–12.4 GHz range.

Pyrotechnic generation of functional aerosols remains a key technological approach for atmospheric intervention because it enables rapid particle production, efficient dispersion, and compatibility...