Enhancing simultaneously the flame retardancy and mechanical properties of polymer materials is a good expectation but always a tough challenge. In this work, two multifunctional compounds: phosphaphenanthrene/vinylsiloxane (DDVS) and phosphaphenanthrene/phenylsiloxane (DDPS) were synthesized, and both effectively improved the flame-retardant properties, toughness and UV shielding performance of epoxy resins (EPs) with high transparency. It was further found that the flame retardancy and toughness of EPs were greatly affected by simply changing the substituents from phenyl to vinyl groups on Si atom. Compared with DDPS, DDVS with vinyl group on Si showed more efficiency in improving flame retardancy (higher LOI value), self-extinguishing properties (higher UL 94 grade) and higher quality retention (more carbon residue) in EP. For example, DDVS was added in two-thirds of the amount of DDPS to make EPs achieve UL94 V-0 rating. This attributed to the high-temperature self-crosslinking of unsaturated carbon-carbon double bonds in DDVS, which can increase the charring ability of EPs and form more high-temperature stable char residues. Meantime, this also inhibited the release of volatile phosphorus-containing pieces from DDVS decomposition and retained more P in condense phase, thus improving the compactness and graphitization degree of char layers. The introduction of unsaturated bonds strengthened the condense-phase flame-retardant function of DDVS in EP, while retaining the original gas-phase flame-retardant actions of DOPO groups. The mechanism of gas-phase and condensed-phase mechanisms cooperated with each other, obtaining better flame retardant effect. Meanwhile, DDVS possessed greater efficiency than DDPS in increasing the fracture toughness of matrix due to the difference of steric hindrance between the substituents on silicon. Furthermore, the introduction of DDVS and DDPS did not significantly affect the transparency of EPs and the high visual transparency of materials was still maintained. In brief, the coordination design of phosphaphenanthrene and vinylsiloxane groups provided a theoretical basis to simultaneously improve the flame retardancy and toughening of EPs without losing glass transition temperature, while maintaining the high visual transparency of EPs with good UV shielding performance.

This study investigates the viscoelastic performance of additively manufactured (AM) nylon and nylon-matrix composites reinforced with short and continuous fibres with three different fibre orientations: longitudinal, transverse, and quasi-isotropic. Dynamic mechanical analysis under a frequency sweep of 1–100 Hz along with tensile tests used to determine the Young's modulus and X-ray micro-CT for evaluation of microstructural porosity were employed to fully describe the viscoelastic behaviour of the composites. Generally, the addition of fibres increased the storage modulus of most composites. The composites revealed increased porosity and fractography using a scanning electron microscope on the tensile specimens demonstrated poor fibre-matrix bonding. These factors, along with the fibre orientation, had a complex effect on the loss modulus of the composite structures. Overall, the addition of fibres reduced the damping factor of the composite specimens compared to pure AM nylon samples. The quantified parameters, including those of the Prony series, can be used in numerical simulations supporting the design and optimisation of AM components.

In this paper, ternary BiOBr/Bi/CoWO4 composites with high sonocatalysis activity were prepared by the chemical precipitation method. Numerous techniques were used to analyze the physicochemical characteristics of composites made of BiOBr/Bi/CoWO4. The degradation of tetracycline (TC) was used to assess the sonocatalysis activity of the produced composites. The findings revealed that the sonocatalysis degradation efficiency of 1 g/L BiOBr/Bi/CoWO4 composite and 30 mg/L TC solution reached 91.58% under ultrasonic radiation (500 W) for 120 min. The degradation effect of BiOBr/Bi/CoWO4 sonocatalyst on TC is better than that of pure CoWO4. Four recycling experiments fully proved the good stability and recyclability of BiOBr/Bi/CoWO4. The scavenger experiment showed that hydroxyl radical (·OH) played a major role in the process of sonocatalysis degradation of TC. The potential sonodegradation mechanism based on the sonocatalysis reaction demonstrated that the recombination of BiOBr and Bi can enhance the efficiency of electron-hole pair (e−-h+) separation. This article confirms the great potentiality of BiOBr/Bi/CoWO4 composites in wastewater treatment and they can be used as an ideal alternative material for toxic organic pollutants, which provides a valuable reference for synthesizing and using composite sonocatalysts.

This paper presents a micromechanical high cycle fatigue damage model for short fiber reinforced composite materials. Because the damage processes within such materials are influenced strongly by their microstructure, we use a mean field homogenization framework to compute the macroscopic behavior of the composite as well as the microscopic stresses and strains in the constituent phases. This allows us to account for damage phenomena related to both the fiber phase as well as in the matrix material. Fiber and fiber-interface damage is modeled using a Tsai–Wu and Weibull-based approach and the progressive damage due to cyclic loading is described by a progressive matrix damage model. The latter includes a novel coupling term in which the matrix damage progression is linked to the damage state of the reinforcing fibers. A cycle-based numerical formulation is used to overcome the computational limits of such load cases in the time domain. While the approaches are in principle applicable to different types of fiber–matrix composite, a short glass fiber reinforced polyamide 6.6 is used as an example material, for which microstructural analyses as well as tensile and fatigue tests are reported. The model’s capabilities with regard to complex fiber orientations and different fiber fractions are studied using different grades of this material class. Furthermore, the model is analyzed via benchmarks of the numerical schemes and by parameter sensitivity studies. The results show that the approach is capable of modeling the complex and microstructure-dependent fatigue damage and fatigue limits for the different material grades with limitations only becoming visible at very high fiber fractions.

Mechanical response of short fibre composites is varying locally with respect to the microstructural constitution of the material, which in turn is a consequence of flow conditions during manufacturing. This local constitution is described by local fibre volume content, local fibre orientation distribution and local fibre length distribution. For short fibre reinforced plastics, both distributions are affected by flow conditions during an injection moulding process. Current material models for predicting the homogenised material response account for the local volume fraction and local fibre orientation distribution. Fibre length distribution, however, is usually approximated with a single average fibre length. To investigate the effects of fibre length distribution on the elasto-plastic response of short fibre composites, a micromechanical Orientation Averaging model has been extended. Two methods are presented in this work. In the first method, an additional averaging scheme over the fibre length distribution is included. In the second method, a novel representative fibre length is presented based on a stiffness-weighted average. The predictionsobtained from these methods are then compared and evaluated against experimental results of uniaxial tensile tests taken from literature. Good agreements are found using both methods. However, for the investigated behaviour, using a representative fibre length is still beneficial due to the superior computational performance.

This work investigates the interplay between viscoelasticity and instabilities in soft particulate composites undergoing finite deformation. The composite is subjected to in-plane deformation at various constant strain rates, and experiences microstructural buckling upon exceeding the critical strain level. We characterize the dependence of the critical strain and wavelength on the applied strain rate through our numerical analysis.In the simulations, we employ the single and multiple-branch visco-hyperelastic models. We find that the critical strain and wavelength – characterized by the single-branch model – show a non-monotonic dependence on the strain rate, reaching a maximum at a specific strain rate. Remarkably, different buckling patterns (with different critical wavelengths) can be activated by changing strain rates. The space of admissible buckling modes widens in composites with higher instantaneous shear modulus. In the composites characterized by the multiple-branch model, the critical strain function exhibit multiple local maxima following a superposition of the single-branch responses. Typically, the branch with a larger relaxation time has a more significant effect on the critical strain. Moreover, the local maximum (of the critical strain function) is amplified by increasing the strain–energy factor of the corresponding branch term.Finally, we perform the experiments on the 3D-printed particulate soft composite characterized by a broad spectrum of relaxation times. The comparison of the experimental and simulation results demonstrates the ability of the numerical model to predict the critical buckling characteristics.

Fabrication of polymer films with superb mechanical properties is far from mature compared to that of fibers, hampering the further engineering applications of lightweight polymer materials. Herein, high density polyethylene (HDPE) films reinforced with re-dispersed or refined reduced graphene oxide (rGO) are prepared via a facile melt-stretching strategy. The incorporation of only 0.2 wt% rGO is demonstrated to endow the melt-stretched film (80× stretch ratio) with ultrahigh Young's modulus of 2.9 GPa and tensile strength of 162.2 MPa, which are comparable to many engineering plastics and also significantly superior to the existing HDPE/graphene composites. More importantly, these modulus and strength values are increased by 71 and 65% compared to the neat PE (80×), respectively, far more than the theoretical prediction with the mixing rule. Experimental characterizations indicate that the high-efficient mechanical enhancement is attributed to the strong synergy of melt stretching-driven crystallization and rGO re-dispersion or refinement in constructing the compact and robust shish-kebabs crystal network. Such microstructural characteristics greatly promote the load transfer along the covalently bonded molecular chains, and also from polymer to rigid fillers under loading. Furthermore, the excellent puncture resistance and thermo-mechanical properties of PE/rGO films have been demonstrated. This work provides a feasible way towards scalable manufacturing of high-performance polymer nanocomposite films from general plastics and carbonaceous nanomaterials.

Honeycombs are engineered cellular materials that often show superior specific strength, stiffness and energy absorption compared to solid materials. As a consequence they have found numerous applications across engineering fields. The development of additive manufacturing (AM) technologies has initiated an abundance of studies into novel honeycombs as historic manufacturing constraints are lifted. Investigations have been focused on improving or tailoring a given property but very few have focused on isotropy, and little has been done to bring together different patterns under the same manufacturing and experimental conditions. In this study, AM has been used to manufacture nominally identical honeycombs based on differing unit cells, in a range of orientations and densities. Elastic and plastic properties for the hexagon, triangle, square, re-entrant and double-V honeycombs have been obtained through mechanical testing. The elastic properties of these honeycombs have been modelled for all possible in-plane loading directions using minimal computational resources. The effect of orientation and density has been presented, confirming the level of in-plane isotropy for dense honeycombs with regards to Young’s modulus, Poisson’s ratio, yield strength and compressive strength. Insights have also been gained into how these properties vary with relative density. These results provide a basis for comparison with future work on honeycombs.

Bone marrow stem cells (BMSCs)-loaded injectable hydrogels are promising vehicles for the restoration of articular cartilage defect (ACD), while was limited with insufficient chondrogenic capacity and poor maintenance of chondrogenic phenotype. Herein, we reported a dual-drug delivering sulfated hyaluronic acid (SHA) hydrogel with injectable capacity to promote ACD repairment. Two precursor solutions were initial prepared: the HA-CHO-SO3 solution loaded with Kartogenin (KGN), β-cyclodextrin-CHO (β-CD-CHO) and BMSCs, and the HA-NHNH2-SO3 loaded with transforming growth factor β1 (TGF-β1) and BMSCs. The HA-CHO-SO3 could adsorb TGF-β1 through sulfonic acid group, and β-CD-CHO could preabsorb KGN through a hydrophobic cavity on β-CD. The aldehyde group on β-CD-CHO could react directly with the acylhydrazide to load KGN onto the HA-NHNH2-SO3 network. The mixture of two solutions resulted in the formation of a SHA@KGN/TGF-β1 hydrogel through reversible dynamic Schiff-based cross-linking between hydrazide and aldehyde groups. The SHA@KGN/TGF-β1 hydrogel had the benefits of injectability, rapid gelation, self-healing, and firm adhesion to the host tissue due to the reaction between the amine group on the host tissue and the aldehyde group on the SHA. Additionally, it could simultaneously load both TGF-β1 and KGN through electrostatic reaction and host-guest reaction, respectively, providing sustained release kinetics for both drugs. The dual-loaded drugs in the SHA@KGN/TGF-β1 hydrogel could synergistically enhance chondrogenic differentiation and suppress the hypertrophy of BMSCs, effectively promoting cartilage regeneration at both in vitro and in vivo circumstance. The one-step construction of this hydrogel system via mixing injection endowed facile arthroscopic ACD restoration and may significantly promote clinical application.

It remains a great challenge to enhance entitative activity and make more active sites visible with non-noble metal electrocatalysts. Herein, we ingeniously design Mo-doped Mott-Schottky heterostructure by combining metallic MXene and n-type semiconductor NiCoP (defined as Mo–NiCoP@MXene/NF). With the strategy the catalyst electron redistribution is caused by the self-driven transfer of heterojunction charges and reduces the adsorption energy of H and O reaction intermediates (H*, OH*, O*, OOH*). Density functional theory calculation (DFT) further proves the above conjecture. As expected, the synthesized 3D “triangle plum” flower structure Mo–NiCoP@MXene/NF exhibits outstanding hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performance. Overpotential (η) only at low levels of 1.56 V is required to drive the water splitting current densities of 10 mA cm−2 apart from the superb electrolytic stability in a two-electrode configuration. It allows for the development of other new, highly efficient catalysts based on the same design concept.

The dual interface-enhanced sizing agents are prepared to simultaneously exhibit high surface roughness and high interfacial wettability through self-assembled nano-polymers. Five self-assembled nano-polymer modified water-based sizing agents (NPSAs) with various cross-linking structures are synthesized in this paper. It is demonstrated strong characteristics of homogeneous particle size in the 90–200 nm range and heat stability below 200 °C. NPSAs significantly improve the CF surface properties of both surface roughness and surface energy, with reached high values of 13.89 nm and 40.22 mN m-1. Notably, the interlaminar shear strength (ILSS), flexural strength, and fracture toughness (KIC) of CF/ER composites sized by NPSAs are enhanced to 70%, 51%, and 120% compared with the unoptimized composite, respectively. The NPSA reinforcing mechanism, enhancing interfacial properties of CF/ER composites in the interfacial interlocking and adhesion ability, was clarified by the coefficient of thermal expansion (CTE1). Additionally, NPSAs have the advantage of being applicable for simple one-pot synthesis methods, and secondly, no toxic solvents were used.

Aircraft, automotive industries and the increasing numbers of wind turbine blade lead to a huge amount of carbon fiber reinforced polymers requiring to be recycled and/or reused in a closed loop supply chain or circularity of materials. Herein, we have designed and synthesized a tetra-epoxidized imidazolium ionic liquid (Tetra-IL) monomer containing ester-cleavable groups. This monomer was incorporated as a molecular brick platform into conventional epoxy-amine networks in order to tailor the physical properties as well as the end-of-life of the resulting networks. Thus, the introduction of only 10% of IL-based comonomers significantly reduced the gel time by 85% opening perspectives in the field of fast-cure epoxy resins. Overall, all the networks designed in this work presented high thermal stability (>350 °C), higher Tg included between 180 and 230 °C combined with hydrophobic behavior. Increasing the amount of IL monomer in the networks improved the homogeneity of thermosets and wettability of the epoxy resins with the carbon fibers (CF). Most importantly, the use of Tetra-IL led to the development of degradable networks under mild conditions within a brief timeframe (4.5 h) and allowing to recover the carbon fibers. In summary, this study highlighted the great potential of IL-based comonomers as molecular brick into conventional epoxy thermosets as a promising strategy to tailor the physical properties versus sustainability/degradability for the development of high-performance thermosets and composites.

A new strategy to establish a large number of interfacial coherence in nanocrystalline multi-phase composites was proposed. The route consisting of amorphization, crystallization and in-situ reaction was demonstrated using WC-Co composites as a typical example. Characteristics of crystal nucleation, growth crystallography, and phase transformation were studied in detail on the atomic scale for the ceramic grains. Mechanisms for the formation of specific interfacial coherence in the prepared nanocrystalline ceramic-metal composites were disclosed. Assisted by the interfacial coherence, the continuity of local deformation is maintained from metal to ceramic phase, resulting in a uniform strain extension instead of stress concentration at the interfaces. The present nanocrystalline composite achieved outstanding mechanical properties with simultaneously high hardness and fracture toughness. The findings in this work provide new insights to tailor grain structure and interface relationship in cermet composites for superior comprehensive mechanical performance.

Porosity represents a critical issue in composite manufacturing often leading to parts rejection. The aim of this work was to develop a multiphysic model capable to predict the conditions leading to porosity generated by water in composite parts processed by autoclave lamination. The developed model does not aim to assess the void growth phenomenon, as other models in the literature, but it enables the prediction of the thermodynamic conditions for water-generated porosity, where they could occur and how to prevent their presence by suitably modifying the process parameters. The potential of this multiphysic model was proved on epoxy matrix carbon fiber reinforced laminates cured after their exposition to a moist environment. The model was also applied to modify the curing cycle suggested by the prepreg provider in order to avoid favorable conditions for porosity development.

Three-dimensional (3D) bioprinting provides a new possibility for personal customization of cartilage tissues. Although biocompatible, most natural biopolymer inks have poor mechanical strength to bear repeated extrusion, incomparable with load-bearing cartilage. By utilizing a heteropolysaccharide called flaxseed gum (FG), a strong photo-crosslinked methacrylated FG (FGMA) bioink was synthetized and integrated with stem cells for cartilage defect therapy. As a hybrid bioink, FGMA has favorable 3D printability and shown to exhibit high mechanical strength and superior fatigue resistant ability. 4% FGMA2 (MA substitution = 8.1%) has the modulus of about 41 times of GelMA and could maintain its structure integrity under 60% deformation after 2000 cycles. FGMA2 has a degradation period of about 66 days, similar to that of GelMA. In vitro study shows that FGMA2 has excellent biocompatibility with stem cells and chondrogenic potential, both beneficial to cartilage regeneration in the cartilage lesion model. More importantly, in vivo study demonstrated that the regenerated neo-cartilage tissue by FGMA2 displayed the similar morphology and matchable mechanical strength to the natural cartilage after 8 weeks. In conclusion, FGMA has demonstrated this potential as a high-performance bioink for 3D printing for tissue/organ regeneration.

While phase change materials (PCMs) have great potential for use in solar energy storage, they suffer from a lack of shape stability and energy conversion ability. In this study, proper amination of melamine sponge (MS) was designed to construct an integrated MXene and reduced graphene oxide (rGO) structure. The MXene/rGO layer is sufficiently robust to endure the capillary pressure caused by solvent evaporation during the airdrying process. In addition, the reduction of GO using oleylamine (OA) contributes to the protection of MXene from oxidation by preventing the surface of MXene nanosheets from being exposed to oxygen and moisture. The as-designed MXene/rGO sponges have been shown to effectively enhance the thermophysical and photo absorption properties of paraffin wax (PW) in the composite PCM. The composite with the highest amount of MXene/rGO maintained 93.3% of the latent heat of pure PW. The photothermal storage efficiency can reach as high as 93.0% at an MXene content of around 1%. A thermal conductivity enhancement of 66.9% can be achieved compared to the pure MS/PW composite. Therefore, this study presents a new approach for designing of high-performance phase change composites for waste-heat recovery and solar thermal energy storage applications.

The interest in sustainable materials and technologies has increased significantly due to environmental issues triggered by using plastics and their associated wastes. Every year more than 400 million metric tons (Mt) of plastic production takes place globally, out of which 350 Mt plastic convert into plastic waste. Plastic waste mostly consists of polyolefin and their contribution to plastic waste is approximately 50%. Therefore, this review is focused on upcycling polyolefin waste by manufacturing natural/sustainable filler-based biocomposites. This is the novelty of the present review as a detailed review of the manufacturing of polyolefin waste-based biocomposites and their 3D printing suitability is not available in the literature. Natural filler-based biocomposites reduce the use of synthetic filler and help to move towards sustainability goals. This review starts with an overview of plastic waste generation and recycling techniques. A detailed discussion has been done on manufacturing waste polyolefin-based biocomposites and the effect of various fillers and compatibilizers on different properties. These biocomposites are found to be used for trays, packaging boxes, reusable bags, false ceilings, flooring, boundary walls, tiles, cabinets, chairs, tables, doors, designer pots, and automotive interior applications. In the later section, the scope of additive manufacturing of recycled polyolefin waste-based biocomposites along with their associated problems and their solution is also discussed. This review is concluded with the future potential of polyolefin waste upcycling in the sustainable filler-based biocomposites manufacturing sector.

The synergistic corrosion resistance microcapsules (SCRMs) were synthesized by utilizing CaAl–NO2 LDH (NO2-LDH) as chloride trigger and high-performance corrosion inhibitor to hybridize self-healing microcapsules. The morphology, chemical structure and self-healing performance of the microcapsules were characterized. The chloride triggering and corrosion resistance property of the SCRMs were evaluated. The interaction of hybrid wall, NO2-LDH and chloride ion was calculated by first-principles. The findings revealed that the microcapsules show regular spherical with obvious core-wall structure. EDS and chemical structure measurements confirmed that NO2-LDH was successfully embedded within the microcapsule wall. The SCRMs showed excellent corrosion resistance property in simulated chloride-contaminated concrete pore solution (SCPS), and the highest inhibition efficiency was 97.85%. The microcapsule wall was hybridized by NO2-LDH species through chemical pathways. The first-principles calculation results confirmed that Ca and Al species are the main factors for chloride ion immobilization of hybrid wall. The ion exchange process of microcapsules destroys the molecular force of NO2-LDH@ethyl cellulose hybrid wall and improves the mechanical triggering efficiency of microcapsules in cement-based composites.

Transition metal carbonitrides (MXene) with two-dimensional layered structures are a recent research topic in the field of supercapacitors. However, because MXene can easily self-stack, its capacitance performance is affected. To this end, one-dimensional cellulose nanofibers (CNF) and carboxylic single-walled carbon nanotubes (SWCNT) were used to intercalate MXene to obtain well-dispersed MXene/SWCNT/CNF aqueous suspensions and their hybrid hydrogels, and to obtain hybrid aerogels through supercritical drying. CNF gives aerogel excellent porosity, a high specific surface area (301.03 m2 g−1), good electrolyte infiltration, and gentle mechanical flexibility, while SWCNT imparts high conductivity to aerogel film. We assembled a symmetrical all-solid-state flexible supercapacitor and interdigitated micro-supercapacitors using an aerogel film as a flexible electrode. The area specific capacity of the above electrode reaches 746.68 mF cm−2 and 244.50 mF cm−2, respectively. This study provides a fabrication method of polymer–inorganic hybrid nanocomposite aerogel film electrodes for flexible supercapacitors.

MXenes, are an emerging class of 2D materials which have attracted growing interest among the scientific research community due to their unique properties, making them suitable for a wide variety of applications. Different transition metal-based MXenes have been investigated, being derived from the pristine MAX phase by selective etching of the “A” layer. MXene-based composite materials have shown great potential in electromagnetic interference (EMI) shielding and microwave (MW) absorption applications due to their conductivity, high specific surface area, highly active surface sites, and multi-layered structure. In this critical review article, we discuss the synthesis of 2D layered MXenes. We start by first introducing the MAX phase preparation, and the morphologies of different MXenes. We then examine the various approaches for MXene synthesis. The exfoliation and detachment of layers from bulk MXene into few layers, and the availability of functional groups in MXene materials are then discussed. We finish the review by covering the latest advances in 2D MXene-based composite materials for use in EMI shielding applications, also discussing the current challenges, new opportunities and prospects for MXene materials.