Polymer fiber composites are increasingly being used in many industries, including the defense industry. However, for protective applications, in addition to high specific strength and stiffness, polymer composites are also required to have a high energy absorption capacity. To improve the performance of fiber-reinforced composites, many researchers have modified them using multiple methods, such as the introduction of nanofillers into the polymer matrix, the modification of fibers with nanofillers, the impregnation of fabrics using a shear thickening fluid (STF) or a shear thickening gel (STG), or a combination of these techniques. In addition, the physical structures of composites have been modified through reinforcement hybridization; the appropriate design of roving, weave, and cross-orientation of fabric layers; and the development of 3D structures. This review focuses on the effects of modifying composites on their impact energy absorption capacity and other mechanical properties. It highlights the technologies used and their effectiveness for the three main fiber types: glass, carbon, and aramid. In addition, basic design considerations related to fabric selection and orientation are indicated. Evaluation of the literature data showed that the highest energy absorption capacities are obtained by using an STF or STG and an appropriate fiber reinforcement structure, while modifications using nanomaterials allow other strength parameters to be improved, such as flexural strength, tensile strength, or shear strength.

As part of the present work, polymer composites used in 3D printing technology, especially in Melted and Extruded Manufacturing (MEM) technology, were obtained. The influence of modified fillers such as alumina modified silica, quaternary ammonium bentonite, lignin/silicon dioxide hybrid filler and unmodified multiwalled carbon nanotubes on the properties of polycarbonate (PC) composites was investigated. In the first part of the work, the polymer and its composites containing 0.5–3 wt.% filler were used to obtain a filament using the proprietary technological line. The moldings for testing functional properties were obtained with the use of 3D printing and injection molding techniques. In the next part of the work, the rheological properties—mass flow rate (MFR) and mechanical properties—Rockwell hardness, Charpy impact strength and static tensile strength with Young’s modulus were examined. The structure of the obtained composites was also described and determined using scanning electron microscopy (SEM). The porosity, roughness and dimensional stability of samples obtained by 3D printing were also determined. On the other hand, the physicochemical properties were presented on the basis of the research results using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), wide angle X-ray scattering analysis (WAXS) and Fourier Transform infrared spectroscopy (FT-IR). Additionally, the electrical conductivity of the obtained composites was investigated. On the basis of the obtained results, it was found that both the amount and the type of filler significantly affected the functional properties of the composites tested in the study.

This paper presents ways to modify epoxy resin matrix composites to increase their electrical conductivity. Good electrical properties are particularly important for materials used in the construction of vehicles (cars, trains, airplanes) and other objects exposed to lightning (e.g., wind turbines). When the hull plating is made of an electrical conductor (e.g., metal alloys) it acts as a Faraday cage and upon lightning discharge the electrical charge does not cause damage to the structure. Epoxy-resin-based composites have recently been frequently used to reduce the weight of structures, but due to the insulating properties of the resin, various modifications must be applied to improve the conductivity of the composite. The methods to improve the conductivity have been categorized into three groups: modification of the matrix with conductive fillers, modification of the composite reinforcement, and addition of layers with increased electrical conductivity to the composite.

As part of the work, new polymer materials were used in 3D printing, which can be used in three technologies depending on the apparatus used: Fused Filament Fabrication (FFF), Melted and Extruded Manufacturing (MEM), Melt Extrusion Polymers (MEP). As part of the work, the properties of obtained polymer composites were examined. Polylactide (PLA) was used as the matrix, and powdered natural ground fillers were used as fillers: bamboo dust (PB), cork dust (PK) and wood dust (PD). In the first part of the work, filaments were received from the tested composites using the filament preparation line made by METACHEM in Torun for use in 3D printers. Samples for mechanical tests were obtained from the filaments thus received by means of an MEP printer and after granulation by injection molding. In the next part of the work, rheological, mechanical and structural properties of obtained composites were examined. It was found that the addition of natural fillers increased the fluidity of the obtained polymeric materials in the case of composite with addition of PK even by 48.73% compared to unfilled PLA. It was also observed that the composites obtained had lower Charpy impact strength, Rockwell hardness and tensile strength. Observation of the microstructure of the composites using SEM confirmed the even distribution of natural fillers in the polymer matrix, which proves well-chosen parameters of their homogenization in the polymer matrix.

Additive manufacturing is still the fastest-developing technology in the modern world. Three-dimensional printing has become popular due to the method’s numerous advantages, such as its short time and low cost, compared to conventional methods such as injection molding. Therefore, the demand for new materials and material systems that will be characterized by the desired functional properties is clearly growing. As part of this work, work was carried out on the development and preparation of new polymer composites dedicated to 3D printing applications, especially in FDM/FFF/MEM technologies. The influence of the content and amount of fillers, such as silica modified with alumina (S) and bentonite modified with a quaternary ammonium salt (B), on the functional properties of a commercially available fiber made of traditional plastic, such as polycarbonate, obtained in the form of a filament (PCF), was determined. It was found that the addition of B significantly increased the fluidity of the polymer, the introduction of a filler in the amount of 1.5% allowed to obtain a result that was 6% higher compared to PCF (16.8 g/10 min), while the amount of 3% was 20% higher. The obtained mass melt flow rate (MFR) results were confirmed by determining the viscosity of the produced polymer composites. Satisfactory results of mechanical properties were obtained, including the following: it was found that the introduced modified fillers increased the elasticity of the material. The introduction of modified silica resulted in a reduction in Young’s modulus by 10.02% at the content of 0.5% S and at 1% S by 8.64% compared to the polymer. The introduced modified filler S significantly increased the thermostability of polycarbonate (T_5% equal to 449 °C) by 23 °C for PCF/0.5% S and 14 °C for PCF/1% S, respectively. The SEM and WAXS results confirmed the appropriate dispersion of the fillers in the polymer matrix, which indicates well-selected conditions for the homogenization process of the components and the subsequent production of samples. Detailed characterization of the influence of selected fillers on the functional properties of the polymer matrix-polycarbonate allowed for an increase in the range of polymer composites and their use in rapid prototyping technologies, as well as supplementing the literature on databases regarding the characteristics of the obtained materials.

As part of the work, polymer composites dedicated to rapid prototyping were developed, especially for 3D printing using the material extrusion technique. For this purpose, a polymer matrix was selected, which was an acrylonitrile-butadiene-styrene (ABS) terpolymer and a flame retardant, which was tetrakis (2,6-dimethylphenyl)-m-phenylenebisphosphate, commercially known as PX200. The effect of the presence and amount (5, 10, 15 and 20 wt.%) of the introduced additive on the rheological properties, structural properties, flammability (limiting oxygen index, LOI; UL94) and flame retardant properties (microcone calorimeter, MLC) of ABS-based composites was investigated. In addition, the mechanism of thermal degradation and flame resistance was investigated using thermogravimetric analysis, TGA and Fourier transform infrared spectroscopy, FT-IR of the residue after the MLC test. In the first part of the work, using the author’s technological line, filaments were obtained from unfilled ABS and its composites. Samples for testing were obtained by 3D printing in Fused Deposition Modeling (FDM) technology. In order to determine the quantitative and qualitative spread of fire and the effectiveness of the phosphorus flame retardant PX200 in the produced composites, the Maximum Average Rate of Heat Emission (MARHE); Fire Growth Rate Index (FIGRA); Fire Potential Index (FPI) and Flame Retardancy Index (FRI) were determined. Based on the obtained results, it was found that the aryl biphosphate used in this work exhibits activity in the gas phase, which was confirmed by quantitative assessment using data from a microcone calorimeter and non-residues after combustion and thermolysis at 700 °C. As a result, the flammability class did not change (HB40), and the LOI slightly increased to 20% for the composite with 20% flame retardant content. Moreover, this composite was characterized by the following flammability indices: pHRR = 482.9 kW/m² (−40.3%), MARHE = 234 kW/m² (−40.7%), FIGRA = 3.1 kW/m²·s (−56.3%), FPI = 0.061 m²·s/kW (+64.9%), FRI = 2.068 (+106.8%).