Search Results (196)

In order to address vibration and noise challenges in modern industry while satisfying the lightweighting requirements for aerospace and transportation applications, the development of polymer elastomers integrating both lightweight and high-damping properties holds substantial significance. This study developed polyurethane (PU) with optimized damping and mechanical properties at room temperature through monomer composition optimization. Hollow glass microspheres (HGMs) were introduced into the PU matrix to increase stiffness and reduce density, though this resulted in decreased tensile strength (Rm) and loss factor (tanδ). To further improve mechanical and damping properties, we applied a carbon coating to the surface of the HGMs to optimize the interface between the HGMs and the PU matrix, and systematically investigated the energy dissipation and load-bearing behavior of PU composites. The effect of enhanced interface damping of HGM@C/PU resulted in broadening of the effective damping temperature range (tanδ ≥ 0.3) and higher maximum loss factor (tanδ_max) compared to HGM/PU at equivalent filler loading. The tensile and dynamic properties significantly improved due to optimized interfacial adhesion. In PU composites reinforced with 10 wt% HGM and HGM@C, a 46.8% improvement in Rm and 11.0% improvement in tanδ_max occurred after carbon coating. According to acoustic testing, average transmission loss of HGM/PU and HGM@C/PU with the same filler content showed a difference of 0.3–0.5 dB in 500–6300 Hz, confirming that the hollow structure of the HGMs was preserved during carbon coating. Full article

Tracheal defects have been the focus of research since the 19th century, but reconstructing this complex structure remains challenging. Identifying a safe, effective tracheal substitute is a key goal of surgery. This integrative review explores current tracheal substitutes and tissue engineering techniques. Data were collected from June 2024 to March 2025 from electronically available databases. Articles published between 2015 and 2025 were selected using the individualized protocol for each database. After screening 190 articles, 82 were excluded, and 108 were reviewed, with 100 meeting the final inclusion criteria. Recent substitutes include three-dimensional synthetic grafts made from polycaprolactone and copolyamide with thermoplastic elastomer, thermoplastic polyurethane and polylactic acid. Additionally, models using decellularized and recellularized tracheal matrix scaffolds and bioprinting techniques are being developed. Comparative studies of synthetic grafts and tracheal scaffolds, as well as cell self-aggregation methods to create tracheal analogues, are discussed. Advances in hybrid approaches combining synthetic polymers with extracellular matrix components aim to improve biocompatibility and functional integration. The importance of selecting appropriate preclinical animal models, such as goats, is also highlighted for translational relevance. Further research is required to refine protocols, overcome challenges related to vascularization and immune response, and ensure the development of clinically viable, long-lasting tracheal substitutes. Full article

Lignin, an abundant and renewable biopolymer, has gained significant attention as a sustainable modifier and building block in polymeric materials. Recent advancements highlight its potential to tailor mechanical, thermal, and barrier properties of polymers while offering a greener alternative to petroleum-based additives. This review provides an updated perspective on the incorporation of lignin into various polymer matrices, focusing on lignin modification techniques, structure–property relationships, and emerging applications. Special emphasis is given to recent innovations in lignin functionalization and its role in developing high-performance, biodegradable, and recyclable materials such as polyurethanes, epoxy resins, phenol-formaldehyde resins, lignin-modified composites, and lignin-based films, coatings, elastomers, and adhesives. These lignin-based materials are gaining attention for potential applications in construction, automated industries, packaging, textiles, wastewater treatment, footwear, supporting goods, automobiles, printing rollers, sealants, and binders. Full article

This study investigates the elastic properties of thermoplastic polyurethane (TPU) produced through Multi Jet Fusion (MJF) (HP Inc., Palo Alto, CA, USA) additive technology. TPU specimens of varying thicknesses (0.5 mm to 1.0 mm) and orientations (horizontal, diagonal, vertical) were tested. Results show anisotropic behavior, with diagonally oriented specimens exhibiting the highest elastic properties. The study emphasizes the importance of specifying the method for determining elastic properties in TPU filaments for accurate material selection in applications. The findings highlight that a single-value Young’s modulus is insufficient to describe TPU’s elastic behavior, emphasizing the need for more detailed methodological specification in material datasheets. Additionally, SEM (Thermo Fisher Scientific, Waltham, MA, USA). analysis reveals that build orientation significantly affects failure modes in MJF-printed TPU: vertical prints tend to fracture in a brittle-like manner due to interlayer delamination, whereas horizontal and diagonal orientations promote ductile failure with better layer cohesion. These insights are critical for both accurate material selection and for optimizing TPU parts in functional applications, particularly where mechanical performance under tension is essential. Full article

Integrating strong mechanical properties and excellent optical properties for self-healing materials is challenging in both academia and industry. Robust self-healing polyurethane elastomers are expected to have superior mechanical properties, transparency, remarkable healing capability, and shape-memory performance via the adjustment of chemical and microphase separation structure. Herein, a robust transparent self-healable 4,4′-diphenylmethane diisocyanate (MDI)-based polyurethane elastomer containing disulfide bonds and branched structure (MPUE-SS) was synthesized. The chemical and topological structures, compatibility of soft–hard phases, and hard domain size of polyurethane could be adjusted via branched structure and mixed chain extender containing disulfide bonds and 1,4-butanediol (BDO), leading to enhanced self-healing, transparency, and mechanical properties. MPUE-SS exhibited a maximal tensile strength of 40 MPa. The microphase separation structure and reduced crystallinity led to a high transparency of about 91%, close to that of alicyclic polyurethane elastomers. After cutting in half and splicing, the MPUE-SS film recovered more than 95% of the original mechanical properties in 24 h. The shape recovery ratio at 40 °C and shape fixity ratio at −20 °C of MPUE-SS were 96.0% and 99.6%, respectively, higher than those of MPUE without disulfide bonds. Therefore, the chemical, topological structures, and microphase separation of polyurethane could be adjusted to achieve desired self-healing, transparency, shape-memory, and mechanical properties. Full article

The leather tanning industry generates a substantial quantity of solid waste, which, in part, is discarded in the environment in landfills or incinerated. One alternative end-of-life solution is to manufacture engineered materials by forming composites with a thermoplastic polymer/binder. In this work, leather fibres (LFs) were melt-compounded into partially bio-based thermoplastic polyurethane (TPU), at leather fibre contents between 10 and 30% (TPU/LF), followed by compression moulding or 3D printing. The results showed that the incorporation of LF into the polymer matrix produced materials with a Young’s modulus comparable to that of leather. The melt extrusion processing influenced the polymer chain orientation and the resulting mechanical performance. The cyclic stress softening and abrasion resistance of the TPU/LF materials were evaluated to understand the potential of this material to be used in the footwear industry. The level of LF incorporation could be tailored to produce the specific targeted mechanical properties. This work demonstrates that LF could be used to produce materials with a high potential to be used in the fashion industry. Full article

This study investigated the mechanical energy absorption properties of polymeric lattice structures fabricated using additive manufacturing. Existing studies have primarily focused on rigid or single-use materials, with limited attention given to flexible polymers and their behaviour under repeated compressive loading. Addressing this gap, the structures investigated in this study are manufactured using three flexible polymers—polyether block amide, thermoplastic polyurethane, and thermoplastic copolyester elastomer—to enhance the reusability performance. Two high-performance designs were analysed, namely honeycomb structures (inspired by pomelo peel and simply hexagonal arrangements) and 3D triply periodic minimal surface structure of the type FRD. The primary objective was to evaluate their energy absorption capacity and reusability using three repeated compression tests. These tests revealed that thermoplastic copolyester elastomer exhibited the highest energy absorption in initial impact conditions, but lower values for the following compressions. However, polyether block amide demonstrated superior reusability, maintaining a consistent energy absorption efficiency of 56.1% over multiple compression cycles. The study confirms that modifying triply periodic minimal surface structures along the z-axis enhances their absorption efficiency, with even-numbered z-parameter structures outperforming odd-numbered ones due to their complete cell structure. These findings highlight the critical role of structural geometry and material selection to optimise polymeric lattice structures for lightweight reusable energy absorption applications, such as automotive safety and impact protection. Full article

To improve the issue of the decreased toughness and electrical performance of epoxy resin (EP) in thermal shock environments, we prepared thermoplastic polyurethane elastomer (TPU)-filled modified EP composites. We also studied the mechanical and electrical performance of these composites, which had different TPU filling contents, under thermal shock conditions. The results indicated that after 240 h of thermal cycling between −15 °C and 100 °C, the TPU/epoxy composites, when compared to unmodified EP, exhibited a 10.1% enhancement in their elastic modulus, a 15.3% increase in their elongation at break, a 22.3% improvement in their tensile strength, and a 47.8% increase in their impact strength. Moreover, their volume resistivity increased by 10.5% and their AC breakdown strength improved by 52.1%. In contrast, their dielectric constant and dielectric loss experienced reductions of 40.2% and 7.5%, respectively. This study demonstrates that introducing flexible TPU molecular chains into the resin significantly enhances the toughness of EP structures. Additionally, the new cross-linked structures formed within the TPU/EP composites improve their insulation performance under thermal shock conditions. Full article

In recent years, a series of studies have examined the effects of blast loads on structures and proposed new materials to enhance or retrofit the resistance of conventional materials, such as steel or concrete. Polymeric materials, including foams and elastomers, play a significant role in this field due to their low density and favorable mechanical properties under dynamic loads. This study investigates the use of polyurethane elastomer to improve the mechanical properties of 2 mm A36 steel sheets. The efficiency of this material in steel structures has not yet been studied in the scientific literature through blast tests. A total of 18 near-field blast tests were conducted at standoff distances of 300 mm and 500 mm. The explosive charges consisted of 334 g of bare Composition B in a spherical shape. The steel sheets were fixed to rigid supports and exposed to the blast either bare or covered with different layers of commercial Shore A 60 or 90 polyurethane elastomer, with thicknesses varying from 2 to 6 mm. The maximum displacement of the steel sheets was measured using a high-speed camera and the results were compared. The elastomer retrofitted sheets exhibited a reduction in maximum displacement ranging from 5% to 20% when compared to the sheet without the elastomer. Full article

Recently, there has been an increasing emphasis on improving the performance of metal components across various industries, such as automotive, aerospace, electronics, medical devices, and military applications. However, the challenges related to efficient heat generation and transfer in equipment and devices are becoming increasingly critical. A solution to these issues involves the adoption of a metal–composite hybrid structure, designed to efficiently manage heat, while substituting conventional metal components with polymer–carbon composites. In this study, nanopores were formed on the metal surface using an anodization process, serving as the basis for creating 3D-printed polymer/metal hybrid constructions. Various surface treatments, including plasma treatment, mixed electrolyte anodization, and etching, were applied to the metal surface to enhance the bonding strength between the 3D-printed polymer and the aluminum alloy. These processes were essential for developing lightweight polymer/metal hybrid structures utilizing a range of 3D-printed polymer filaments, such as polylactic acid, thermoplastic polyurethane, acrylonitrile butadiene styrene, polypropylene, thermoplastic polyester elastomer, and composite materials composed of polymer and carbon. In particular, the hybrid structures employing polymer–carbon composite materials demonstrated excellent heat dissipation characteristics, attributed to the remarkable conductive properties of carbon fibers. These technologies have the potential to effectively address the device heat problem by facilitating the development of lightweight hybrid structures applicable across various fields, including automotive, mobile electronics, medical devices, and military applications. Full article

The primary challenges in the tissue engineering of small-diameter artificial blood vessels include inadequate mechanical properties and insufficient anticoagulation capabilities. To address these challenges, urea-pyrimidone (Upy)-based polyurethane elastomers (PIIU-B) were synthesized by incorporating quadruple hydrogen bonding within the polymer backbone. The synthesis process employed poly(L-lactide-ε-caprolactone) (PLCL) as the soft segment, while di-(isophorone diisocyanate)-Ureido pyrimidinone (IUI) and isophorone diisocyanate (IPDI) were utilized as the hard segment. The resulting PIIU-B small-diameter artificial blood vessel with a diameter of 4 mm was fabricated using the electrospinning technique, achieving an optimized IUI/IPDI composition ratio of 1:1. Enhanced by multiple hydrogen bonds, the vessels exhibited a robust elastic modulus of 12.45 MPa, an extracellular matrix (ECM)-mimetic nanofiber morphology, and a high porosity of 41.31%. Subsequently, the PIIU-B vessel underwent dual-functionalization with low-molecular-weight heparin and gelatin via ultraviolet (UV) crosslinking (designated as PIIU-B@LHep/Gel), which conferred superior biocompatibility and exceptional anticoagulation properties. The study revealed improved anti-platelet adhesion characteristics as well as a prolonged activated partial thromboplastin time (APTT) of 157.2 s and thrombin time (TT) of 64.2 s in vitro. Following a seven-day subcutaneous implantation, the PIIU-B@LHep/Gel vessel exhibited excellent biocompatibility, evidenced by complete integration with the surrounding peri-implant tissue, significant cell infiltration, and collagen formation in vivo. Consequently, polyurethane-based artificial blood vessels, reinforced by multiple hydrogen bonds and dual-functionalized with heparin and gelatin, present as promising candidates for vascular tissue engineering. Full article

Syntactic foams are a promising candidate for applications in marine, oil and gas industries in underwater cables and pipelines due to their excellent insulation properties. The effective transmission of electrical energy through cables requires insulation materials with a low loss factor and low dielectric constant. Similarly, in transporting fluid through pipelines, thermal insulation is crucial. However, both applications are susceptible to potential environmental degradation from moisture exposure, which can significantly impact the material’s properties. This study addresses the knowledge gap by examining the implications of prolonged moisture exposure on thermoplastic polyurethane elastomer (TPU) and TPU-derived syntactic foam via various multi-scale material characterization methods. This research investigates a flexible syntactic foam composed of TPU and glass microballoons (GMBs) fabricated through selective laser sintering. The study specifically examines the effects of moisture exposure over periods of 90 and 160 days, in conjunction with varying GMB volume fractions of 0%, 20%, and 40%. It aims to elucidate the resulting microphase morphological changes, their underlying mechanisms, and the subsequent impact on thermal transport and dielectric properties, all in comparison to unaged samples of the same material. Our findings reveal that increasing the volume fraction of GMB in TPU-based syntactic foam reduces its thermal conductivity and specific heat capacity. However, moisture exposure did not significantly affect the foam’s thermal conductivity. Additionally, we found that the dielectric constant of the syntactic foams decreases with increasing volume fraction of GMB and decreasing frequency of the applied field, which is due to limited molecular orientation in response to the field. Finally, moisture exposure affects the dielectric loss factor of TPU-based syntactic foams with GMBs, possibly due to the distribution morphology of hard and soft segments in TPU. Full article

Copolymers of glycidyl azide polymer (GAP) and poly (caprolactone) (PCL) were obtained by introducing PCL molecular chains at both ends or side groups of GAP molecular chains, respectively. GAP/PCL elastomers were prepared via polyurethane curing reaction and compared with GAP/PCL elastomers prepared by physical blending, in order to clarify the relationship between microstructure and macroscopic properties. The results showed that no GAP and PCL phase separation was observed in the chemically bonded GAP/PCL elastomers. The elongation at break of the thermosetting GAP/PCL block copolymer elastomer increased significantly from 268% to 300% due to the increase in molecular weight between crosslinking points. The GAP/PCL graft copolymer, with its longer PCL segment length and higher segment mobility, formed microcrystalline domains within the elastomer, resulting in a significant improvement in tensile strength from 0.32 MPa to 1.07 MPa. In addition, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) revealed that the glass transition temperature of the GAP/PCL elastomer was 2.6 °C lower than that of the pure GAP elastomer, and the thermal stability was also enhanced. Full article

Dielectric elastomer generators (DEGs) are electrostatic transducers capable of harvesting electrical energy from oscillating mechanical parts and storing it in a battery or supercapacitor. The energy conversion element typically consists of a flexible capacitor with a variable capacitance that depends on the applied stress cycle and requires an external voltage source (bias voltage). In designing an energy harvesting device from human gait, we propose integrating two components: a dielectric elastomer fabricated using a nanocomposite polyurethane (TPU-CaCu₃Ti₄O₁₂) and an electret serving as a bias voltage source. In this work, we report on the electret fabrication and long-term charge retention properties using corona charging. The manufactured electrets are tested in coupling with the dielectric elastomer and allowed us to harvest an energy amount of 62 µJ/cycle (3.1 µJ/cm²) on a resistive load of 450 MΩ during motion cycles at a frequency of 0.5 Hz. Given the materials used, this approach is well suited to harvesting energy from human gait and holds promise for powering wearable devices. Full article

The mechanical properties of rubber-like materials, such as their high flexibility and durability, make them widely applicable across different industrial fields, from aerospace to healthcare and, most notably, the automotive sector. In operative conditions, these materials experience large deformations and repeated loadings, which may result in inelastic and dissipative phenomena. The aim of this study is to investigate the mechanical properties of two thermoplastic elastomeric materials manufactured with the Fused Filament Fabrication (FFF) technique: unfilled thermoplastic polyurethane (TPU) and TPU reinforced with carbon nanotubes (CNTs). Several experimental tests were performed to assess the response of both materials under monotonic and cyclic loadings. The addition of CNTs led to improved stiffness and strength without compromising elasticity. Under repeated loadings, both materials were characterized by the Mullins and viscous effects. However, the presence of CNTs was found to slightly amplify these inelastic phenomena. The integration of additive manufacturing technologies, combined with the use of innovative fillers, can offer design and performance optimization to all those components that strongly rely on elastomers. Full article