ABSTRACT Aramid fibers are extensively utilized in personal protective equipment owing to their lightweight and superior properties. This study proposes a novel composite structure comprising aramid fabric, EVA hotmelt films, and graphene‐clay nanostructured HDPE laminate, totalizing 20 repeated layers (aramid/EVA/HDPE/EVA/aramid). The composites were hot‐pressed molded, showing thickness differences of up to 8% among all composites studied. V50 impact test showed values that lie within the range 343–368 m/s for 9 mm and 355–379 m/s for 0.357 Magnum. For both conditions, the values were lower than the ones found in literature (450–550 m/s for 9 mm and 420–500 m/s for 0.357 Magnum). Backface Signature (BFS) showed values lower than 21.5 mm for HDPE and all composites studied (a value of 13.58 mm was found for composites containing 1.50 wt% graphene). To avoid lethal or severe trauma, values lower than 44 mm are recommended, according to NIJ 0101.06 standard. Other mechanical tests, such as Izod impact, short‐beam, flexural strength, and Split‐Hopkinson pressure bar (SHPB), were also studied.
ABSTRACT Poly(vinylidene fluoride) (PVDF)/BaTiO 3 composites combine polymer flexibility with ceramic polarizability, while their dielectric, thermal, and interfacial responses depend strongly on filler loading and processing history. This study investigates PVDF/BaTiO 3 composites containing 0, 5, 10, 20, and 30 vol% BaTiO 3 before and after post‐fabrication atmospheric dielectric‐barrier‐discharge (DBD) plasma treatment. The same composition series was characterized by differential scanning calorimetry, Fourier‐transform infrared spectroscopy, X‐ray diffraction, scanning electron microscopy, atomic force microscopy, contact‐angle/surface‐free‐energy measurements, and dielectric spectroscopy. Mass‐fraction‐corrected PVDF crystallinity in the untreated series increased from 39.2% for neat PVDF to 45.2% at 5 vol% BaTiO 3 and then decreased to 35.9% at 30 vol%. Quantitative composition‐dependent results are based on three independently fabricated specimens per composition and treatment state ( n = 3) and are reported as mean ± standard deviation (SD). At 1 MHz, plasma treatment changed the real permittivity by 2.6%–39.4% in magnitude. Full‐frequency analysis over 20 Hz–1 MHz showed that tanδ and ε ″ decrease with increasing frequency for all compositions, whereas the loss‐derived AC conductivity, σac = 2πf ε ₀ ε ″, increases with frequency. Across the measured range, DBD treatment lowers σac for the 0, 10, 20, and 30 vol% compositions but increases it for the anomalous 5 vol% composition, demonstrating a composition‐dependent rather than uniform conductivity response. XRD and FTIR show no evidence of a new bulk crystalline phase or major bulk chemical transformation. In contrast, water contact angle decreased from 81° to 93° in untreated specimens to 44°–57° after DBD treatment, while total surface free energy increased from 29.2–37.0 mJ m −2 to 53.5–63.3 mJ m −2 , providing direct evidence of altered surface wettability. SEM and AFM further indicate composition‐dependent near‐surface morphological changes. An archived auxiliary instrument‐response channel is retained only as a relative observation because its absolute calibration could not be reconstructed and it is not interpreted as conductivity. The present results therefore support composition‐dependent dielectric, thermal, and surface modulation by DBD treatment. Surface‐/trap‐sensitive validation remains necessary before mechanism‐specific generalization, while direct breakdown testing would be required for explicit insulation‐performance claims.
ABSTRACT Fiber‐reinforced thermoplastics have great potential as anti‐impact materials, especially polyetherketoneketone (PEKK) with damping properties and carbon nanotube (CNT) with energy dissipation capacity. However, high melt viscosity and poor solubility of PEKK limit its processability, and inter‐tube van der Waals forces lead to CNT agglomeration when used as reinforcement. Therefore, this study developed CNT/PEKK composites by introducing a co‐protonation strategy. Owing to the PEKK dissolvability and the CNT dispersion in superacids, the co‐protonation‐based pre‐composition can be achieved. Meanwhile, the protonation makes it possible to load high‐content CNTs (20 wt%) into composites. The full pre‐composition between CNT and PEKK, complete CNT dispersion, and uniform CNT distribution lead to great performance improvement. The flowability of composite powders promotes the processability and structural stability of hot‐pressed beams. When the content of CNTs reached 10 wt%, the flexural strength and elongation at break of the CNT/PEKK composite beams could reach 294.8 MPa and 10.8%, respectively, and the energy absorption per unit thickness could reach 15.3 J mm −1 . In addition, the high‐CNT‐content CNT/PEKK composite powders can also be used as masterbatches to develop new materials. Based on these advantages, combined with good electrical conductivity and thermal stability, the CNT/PEKK composites obtained are expected to be used as an anti‐impact material.
ABSTRACT Carbon fiber (CF) exhibits inherent chemical inertness and a non‐polar surface, resulting in poor interfacial compatibility with polyether ether ketone (PEEK) matrix and limited mechanical performance of CF/PEEK composites. Herein, a fluorinated poly(aryl ether ketone) containing chalcone moieties (ChF‐PAEK), previously reported as a fluorinated polymer structure, was employed as a structurally compatible sizing agent for CF/PEEK interface modification. The influence of ChF‐PAEK concentration on the interfacial properties is systematically investigated. Results indicate that the ChF‐PAEK sizing at an appropriate concentration forms a uniform and PEEK‐compatible interphase, enhancing interfacial compatibility through multiple proposed interactions, including π – π interactions, van der Waals forces, and macromolecular entanglement with the PEEK matrix. The composite 0.5 wt% ChF‐PAEK shows the best mechanical properties with interlaminar shear strength (ILSS) of 103.5 MPa and flexural strength of 286.1 MPa. The ILSS is improved by 66.4% compared with that of desized CF/PEEK composite. Thermal behavior, crystallization analysis, mechanical testing, and fracture morphology reveal that the ChF‐PAEK sizing agent improves interfacial compatibility, accelerates resin infiltration, and promotes stress transfer. This work provides a facile and effective molecular‐design strategy to improve the interfacial compatibility of CF/PEEK and other carbon fiber–reinforced thermoplastic composites.
ABSTRACT This study investigates the effects of short‐fiber geometry, fiber content, and curing system on the compressive yield and postyield behavior of epoxy resins. Short carbon fibers (CFs) and short aramid fibers (AFs) were incorporated into two anhydride‐cured epoxy systems based on maleic anhydride (MA) and methyl tetrahydrophthalic anhydride (MTHPA, denoted as MT). Compressive yield strength, elastic modulus, and postyield load‐retention behavior were evaluated, together with macroscopic failure and SEM observations. CFs showed greater potential for enhancing strength and stiffness. Within the investigated range up to 80 phr, the maximum compressive yield strength increased by 32.4% and 25.3% in the MA and MT systems, respectively, while the corresponding maximum increases in elastic modulus were 40% and 37%. MT‐CF‐L3‐80 phr exhibited the highest compressive yield strength and elastic modulus, reaching 142.31 MPa and 3.24 GPa. AFs produced smaller increases in strength and stiffness but exhibited a more gradual postyield response. At 40 phr and an additional postyield displacement of 7 mm, the minimum load‐retention ratio among the investigated fiber‐length groups remained 0.945. At high fiber contents, longer fibers tended to overlap, entangle, or agglomerate, thereby reducing dispersion uniformity and interfacial load transfer. SEM observations showed fiber fracture, pull‐out, interfacial debonding, and crack deflection in CF‐modified systems, whereas AF‐modified systems mainly exhibited matrix peeling, shear tearing, localized pull‐out, and interfacial debonding. Overall, fiber geometry, content, and curing system exerted distinct effects on compressive yielding, stiffness, and postyield load‐retention behavior.
