Self-healing materials can increase the lifetime of products and improve their sustainability. However, the detection of damage in an early stage is essential to avoid damage progression and ensure a successful self-healing process. In this study, self-healing sensor composite strips were developed with the embedding of a thermoplastic styrene-based co-polymer (TPS) sensor in a self-healing matrix. Piezoresistive TPS sensor fibers composites (SFCs) and 3D printed sensor element composites (SECs) were fabricated and embedded in a self-healing matrix by lamination process to detect damage. In both cases, the value of the initial resistance was used to detect the presence of damage and monitor the efficiency of healing. A higher elongation at fracture could be achieved with the extruded sensor fibers. However, for the composite strips the SECs could achieve a higher elongation at fracture. Mechano-electrical analysis revealed that the strips maintained a monotonic, reproducible response after the healing of the matrix. The SFCs had significantly lower drift of the sensor signal during cyclic mechanical analysis. Nevertheless, on a tendon-based soft robotic actuator, the SECs obtained a drift below 1%. This was explained by the lower deformation (e.g.) strain in comparison to the tensile test experiments.

Electrospinning is a relatively simple technique for producing continuous fibers of various sizes and morphologies. In this study, an intrinsically hydrophilic poly(3-hydroxybutarate-co-3-hydroxyvalerate) (PHBV) biopolymer strain was electrospun from a solution under optimal processing conditions to produce bilayers of beadless micro-fibers and beaded nano-fibers. The fibrous mats produced from the pure PHBV solution exhibited hydrophilicity with complete wetting. Incorporation of polydimethylsiloxane (PDMS) treated silica into the electrospinning solutions resulted in a non-wetting state with increased fiber roughness and enhanced porosity; however, the fiber mats displayed high water droplet-adhesion. The SiO2–incorporated fibrous mats were then treated with stearic acid at an activation temperature of 80 °C. This treatment caused fiber surface plasticization, creating a tertiary hierarchical roughness owing to the interaction of PHBV chains with the polar carboxyl groups of the stearic acid. Scanning electron microscopy was used to assess the influence of the electrospinning process parameters and the incorporation of nanoparticles on surface morphology of the fibers; energy dispersive X-ray spectroscopy confirmed the presence of SiO2 nanoparticles. Fourier transform infrared spectroscopy was performed to study the incorporation of SiO2 and the interaction of stearic acid with PHBV at various concentrations. The chemical interaction between stearic acid and PHBV was confirmed, while SiO2 nanoparticles were successfully incorporated into the PHBV fibers at concentrations up to 4.5% by weight. The incorporation of nanoparticles and plasticization altered the thermal properties of PHBV and a decrease in crystalline fraction was observed. The stearic acid modified bilayers produced from the micro-nano-fibrous composites showed very low water droplet sticking, a roll off angle of approximately 4° and a high static contact angle of approximately 155° were achieved.

The focus of this research was to study the effect of combining nanofillers with different geometry and surface chemistry on the structure and properties of biopolymers as an alternative to traditional plastics. How the inclusion of 2D graphene oxide (GO) or reduced GO (rGO) combined with 1D sepiolite (SPT) or cellulose nanocrystals (CNCs) affect the structure and properties of chitosan and chitosan/carboxymethyl cellulose (CMC) materials was investigated. A 3D interconnected microstructure formed, composed of GO and SPT due to the strong interactions between these hydrophilic nanofillers. The chitosan/CMC/GO/SPT composite had the highest tensile strength (77.5 ± 1.2 MPa) and Young’s modulus (1925.9 ± 120.7 MPa). For the un-plasticised matrices, hydrophobic rGO nanosheets generally hindered the interaction of SPT or CNCs with the polysaccharides (chitosan and CMC) and consequently, composite properties were mainly determined by the rGO. However, for the chitosan matrix plasticised by 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]), rGO + CNCs or rGO + SPT disrupted polymer chain interactions more effectively than the nanofillers when added alone and resulted in the chitosan being more plasticised, as shown by increased chain mobility, ductility, and surface hydrophilicity. For the [C2mim][OAc]-plasticised chitosan/CMC matrix, the advantages of including hybrid fillers, rGO + CNCs or rGO + SPT, were also obtained, resulting in higher thermal stability and surface hydrophobicity.

This paper focuses on the physicochemical changes that happen in cold mix asphalts during curing, and more specifically, while and after transitioning to different simulated seasons. Several tests were carried out in order to better grasp the influence of the weather (temperature and humidity) on the curing of such materials. The mechanical behaviour of the mix was assessed using oedometer tests. The physicochemical evolutions of extracted binders, such as oxidation and rheology, were evaluated. The results show stiffening of the mix and ageing of the binder linked to a higher temperature and a lower humidity. A low temperature and high moisture seem to slow down these evolutions. However the binder behaviour does not explain the whole mix behaviour as the kinetics between them are not always similar. Thus other mechanisms are yet to be found and taken into account to fully understand cold mix asphalts behaviour.

The aim of this study was to identify the effect of material type (matrix and reinforcement) and process parameters, on the mechanical properties of 3D Printed long-fibre reinforced polymer composites manufactured using a commercial 3D Printer (Mark Two). The effect of matrix material (Onyx or polyamide), reinforcement type (Carbon, Kevlar®, and HSHT glass), volume of reinforcement, and reinforcement lay-up orientation on both Ultimate Tensile Strength (UTS) and Flexural Modulus were investigated. For Onyx, carbon fibre reinforcement offered the largest increase in both UTS and Flexural Modulus over unreinforced material (1228 ± 19% and 1114 ± 6% respectively). Kevlar® and HSHT also provided improvements but these were less significant. Similarly, for Nylon, the UTS and Flexural Modulus were increased by 1431 ± 56% and 1924 ± 5% by the addition of carbon fibre reinforcement. Statistical analysis indicated that changing the number of layers of reinforcement had the largest impact on both UTS and Flexural Strength, and all parameters were statistically significant.

Biodegradable films based on thermoplastic corn starch (TPS) and copper particles with antimicrobial capacity were developed. Copper nanoparticles (Cu) and silica coated copper microparticles (Si-Cu) in the range of 0.25 to 5% were used. Composite films were obtained by melt-mixing and subsequent thermo-compression. Particles distribution within TPS matrix and the presence of some pores and cracks, induced by Si-Cu particles, was evaluated by SEM. The presence of both fillers gave composite films a brown pigmentation and decreased their transparency; these effects were more pronounced at higher particles concentrations. Regarding mechanical properties, copper particles at 1 and 5% acted as reinforcing agents increasing the maximum tensile strength but their presence lead to a decrease in elongation at break, affecting films ductility. Composites inhibited the growth of Gram+ and Gram- bacteria, demonstrating their antimicrobial capacity. Copper effectively migrated to a simulant of aqueous foods and naked particles concentration in the simulant medium resulted higher than the minimum inhibitory concentration for bacteria. The characteristics and properties of developed composite films make them an interesting material for food primary packaging, mainly for meat fresh products.

We report the chemical synthesis of poly(aniline-co-aniline-2,5-disulfonic acid)) and its composite containing L-hexuronic acid and metallic Ag/SiO2 nanoparticles as a new thermally stable anionic polyelectrolyte for removing safranin dye. The composite was characterized by IR, UV, cyclic voltammetry, SEM, TEM, TGA, DSC, EDXS and elemental analyses. Microscopic images exhibited intensified spherical particles dispersed over almost the entire surface. The XRD exhibited peaks of the partially crystalline material at many 2θ values, and their interatomic spacing and sizes were calculated. The cyclic voltammograms exhibited characteristic redox peaks relative to the quinoid ring transition states. The uptake rates up to 82.5% adsorption were completed within 75 min and the equilibrium time was 45 min. The isotherm of dye adsorption interprets the interaction with the adsorbent and explain the relationship between the dye removal capacity and the initial dye concentration. In the current, the Langmuir isotherm model was the optimum to interpret both the dye/copolymer and the dye/composite interactions. The uptake of safranin by copolymer/SiO2@Ag nanocomposite was well defined by pseudo second order model with rate constant K2 = 0.03 g− 1 mg− 1 min− 1 for 19 mg safranin. A comparison of safranin adsorption efficiency of the synthesized material with other reported material in the same domain suggested that the present composite has a higher adsorption rate and capacity. The ongoing research is devoted to improving the removal percentage of the dye by using 1,3,5-triazine based sulfonated polyaniline/Ag@ SiO2 nanocomposite.

Graphene enhanced thermoplastic composites offer the possibility of conductive aerospace structures suitable for applications from electrostatic dissipation, to lightning strike protection and heat dissipation. Spray deposition of liquid phase exfoliated (LPE) aqueous graphene suspensions are highly scalable rapid manufacturing methods suitable to automated manufacturing processes. The effects of residual surfactant and water from LPE on thin films for interlaminar prepreg composite enhancement remain unknown. This work investigates the effect of heat treatment on graphene thin films spray deposited onto carbon fibre/polyether ether ketone (CF/PEEK) composites for reduced void content. Graphene thin films deposited onto CF/PEEK prepreg tapes had an RMS roughness of 1.99 μm and an average contact angle of 11°. After heat treatment the roughness increased to 2.52 μm with an average contact angle of 82°. The SEM images, contact angle, and surface roughness measurements correlated suggesting successful removal of excess surfactant and moisture with heat treatment. Raman spectroscopy was used to characterise the chemical quality of the consolidated graphene interlayer. Spectral data concluded the graphene was 3–4 layered with predominantly edge defects suggesting high quality graphene suitable for electrical enhancement. Conductive-AFM measurements observed an increase in conductive network density in the interlaminar region after the removal of surfactant from the thin film. Heat treatment of the Control sample successfully reduced void content from 4.2 vol% to 0.4 vol%, resulting in a 149% increase in compressive shear strength. Comparatively, heat treatment of graphene enhanced samples (~ 1 wt%) reduced void content from 5.1 vol% to 2.8 vol%. Although a 25% reduction in shear strength was measured, the improved electrical conductivity of the interlaminar region extends the potential applications of fibre reinforced thermoplastic composites. The heat treatment process proves effective in reducing surfactant and thus void content while improving electrical conductivity of the interlayer in a scalable manner. Further investigations into graphene loading effects on conductive enhancement, and void formation is needed.

A study on electrical conduction of carbon/epoxy laminates has so far been conducted in an ad hoc nature without a standardised method, involving many extrinsic factors. How these factors affect electrical conduction of carbon/epoxy laminates has not been well established. The objectives of this work are to ascertain the effects of electrical currents, temperatures, and clamping torques on the anisotropic electrical conduction of carbon/epoxy laminates. Two-probe method with solid electrodes was developed with machined carbon/epoxy laminate specimens of various dimensions. The contributions of elevated temperatures and clamping pressures to electrical conduction were investigated. Various contact conditions with or without conductive paint were examined. The relationship of electrical resistance correlating with temperature and clamping pressure was developed to aid an analysis of data trends. From the average test results of 18 groups, aided with qualitative predictions, the milliampere-to-ampere increases of current led to significant reductions in electrical conductivities in both in-plane and through-the-thickness directions. The rises of temperatures resulted in the similar reductions in electrical conductivity due to the increased resistance. The increase in clamping torque increased the electrical conductivity values in both directions. Applying conductive paint to the contact faces did not appear to affect the contact resistance. Thus, the enhanced values of electrical conductivity from the painted specimens were attributed to their lower body temperatures, as the conductive paint at the contact faces soaked up the substantial amount of the electrical energies.

Aluminium matrix composites (AMC) do combine a high lightweight potential with a wide range of specific mechanical or thermal properties, depending on their material composition or the content of reinforcement particles, respectively. Currently, the three main production technologies for manufacturing such AMC are powder metallurgy, semi-solid processes and casting. Here, the AMC´s reinforcement proportion that can be processed depends on the chosen manufacturing strategy and is therefore often limited to a maximum value of 30 vol. %, due to agglomeration and porosity problems. In this context, the main objective is to understand the fundamental mixing behaviour of powder mixtures for AMC green body production having reinforcement contents of up to 50 vol.% SiCp. For this purpose, powder mixtures of monomodal AlSi7Mg0.6 and different SiCp fractions were prepared with different mixing times and speeds to investigate the influence of these mixing parameters on the homogeneity of the particle distribution. Afterwards, the influence of powder size on the mixing process was investigated. The results showed that a slower mixing speed resulted in faster homogenisation as well as a larger particle size can be faster mixed. Furthermore, a regression model was developed using mixing time, speed and particle loading, to determine sufficient mixing parameters.

Styrene–butadiene–Rubber, SBR, is most often used in tread compounds in order to improve the Rolling Resistance (RR). The functionalized SBRs are used to increase the polymer–filler interaction in the compound to improve RR. In this study, the effect of different types of functional groups in SBR was investigated. Several types of functionalized S–SBR’s were synthesized by anionic polymerization: (i) SBR with an amine group at one end of the polymer chain, (ii) SBR with an alkoxy silane group at one end (iii) SBR with an amine group at one end and an alkoxy silane group at the other end of the polymer chain. A model reaction of silanization was conducted in a solvent to estimate how the amine functional group affects the silanization. Silica filled compounds were prepared with these SBR types. Payne effect and bound rubber measurement were done. The model silanization reaction of TESPT (Bis(triethoxysilylpropyl)tetrasulfide) with silica in the presence of amine shows that a higher amount of ethanol (EtOH) is released from TESPT compared to the amine free system. This result indicates that the silanization reaction can be accelerated by the presence of an amine functional group at the SBR polymer chain used in silica–filled compounds. The amine functionalized SBR and the alkoxy silane functionalized SBR show less Payne effect of the compounds which indicates that both functional groups can decrease the filler–filler interaction. More chemical bound rubber was obtained in branched SBRs compared to the corresponding linear SBRs. A branched polymer chain has a higher molecular weight compared to the linear type. Therefore, when one branched polymer chain reacts with silica or creates a silica–silane–polymer bond, more bound rubber can be obtained for the branched than for the linear type. The compound of the SBR with the alkoxy–silane functional group shows lower tan δ compared to the non–functionalized SBR and the amine functionalized SBR compounds. The influence of the type of functionalization of the SBR on tan δ at 70 °C was more significant in branched SBRs than in linear SBRs, due to the before–mentioned effect of the functional group on silanization and bound rubber.

The performance of electric sensors is continuously improving due to the demands of modern vehicles and electronic devices. Magnetic sensors are used in a wide field of applications. However, handling and mounting the typical high-performance rare earth permanent magnets are challenging due to their brittleness. A constant magnetic flux is a key property of the magnetic setup in many devices. State-of-the-art adhesive bonding of magnets in devices can cause problems due to the low durability and viscous behaviour of adhesive polymers, as the magnet may change its position and hence, the magnetic flux distribution in the magnetic setup changes. Ultrasonic welding is a powerful technique to join hybrid material systems quickly and reliably, providing high joint strength, even for brittle materials such as glasses, ceramics and rare earth permanent magnets. The latter is being investigated in this work for the first time. The ultrasonic welding process was adapted to join 316L stainless steel, representing potential components of magnetic devices, to Ni/Cu/Ni-coated Nd2Fe14B. In addition to directly joined steel/magnet-hybrids, ductile aluminium and nickel interlayers were used in order to enhance the joint strength. Process parameters were developed and evaluated considering the resulting shear strength of the joints. The highest shear strength of 35 MPa was achieved for 316L/Nd2Fe14B and 316L/Al/Nd2Fe14B, which is more than twice the shear strength of adhesively bonded joints of up to 20 MPa, according to the literature. The functional performance of the hybrid material systems, evaluated by the magnetic flux density of the hybrid material systems was the highest for directly bonded joints, and those with a nickel interlayer, which did not show any losses in comparison to the single magnet in its initial state. Joints with an aluminium interlayer showed losses of 3% and adhesively bonded joints showed losses of 7% of the magnetic flux density. In summary, the results of this work indicate that ultrasonic welding is a suitable technique to improve the production process and performance of magnetic devices.

The aim of this work is to characterize the moisture-dependent actuation behavior of bioinspired and additively manufactured hygromorphs based by following deductive and inductive design approaches. Fused Filament Fabrication (FFF) is employed to print bilayered structures consisting of swellable active layers and rigid passive layers. The active layer is composed of a polylactic acid (PLA) matrix filled with different hygroscopic cellulosic materials (native and modified) up to a filler content of 50 m%. Acrylonitrile Butadiene Styrene (ABS) is used for the passive layer. The FFF process allows the generation of desired differential swelling properties in the composites upon moisture absorption. The moisture dependent actuation strain of the printed bilayers was determined by video analyses. Some influencing geometrical factors which contribute to the actuation were deduced from x-ray diffraction (XRD) and micro computed tomography (μCT). The investigation of the mean cellulose microfibril orientation on the surface of the active layer suggested a preferential orientation with respect to printing direction. Furthermore, a gradient of cellulosic material within a single printed layer was observed, which indicates fiber sedimentation. Comparison with the thermomechanical model derived from Timoshenko (1925) shows that the computational prediction of the moisture dependent actuation is considerably accurate for most selected cellulosic materials and filler contents.

Silica is the rubber industry’s most essential and cost-effective reinforcing filler after carbon black. The silica reinforcement mechanism with a non-polar elastomer is complicated by the presence of polar functional groups on the silica surface. This polar nature of silica causes filler-to-filler interaction by forming hydrogen bonds. Therefore, sizeable non-dispersed silica clusters remain in a non-polar rubber matrix. To avoid these strong filler-filler interactions and improve rubber/silica compatibility, the silica surface needs to be modified. This can be done using a coupling agent which has functional groups capable of linking both the rubber and silica. It has been discovered that when silica/silane coupling agents are present, the critical properties like rolling resistance and wet grip in the magic triangle of tire tread balance out better than carbon black formulations, bringing the system closer to the green tire goal. In this review article, the efforts made by both the rubber formulation development and chemistry to fully exploit the potential of silica/silane reinforcement for automotive tires are retrospected. Highlights on how compounding ingredients, process technology, functionalized elastomer, novel silanes, and the variant of silicas can enhance the magic triangle and silica-silane reaction mechanism are provided. In addition, the kinetics of silanization and measurements for the degree of silanization is also highlighted. Future research directions in this area are also touched upon. Hopefully, this review can stimulate future silica/silane scientific and technology developments for both academic and industrial-oriented requirements.

The mechanical behavior of braided carbon nanotube yarns (CNTYs) on an elastomeric core to produce stretchable conductive materials were theoretically modeled and experimentally studied under tension. The elastomeric core served as the stretchable spring and the CNTYs braiding, with shape changing capabilities, as the conductive shell. A variety of samples were produced having various braiding angles on an elastomeric core and subsequently loaded in tension, and their stress–strain behavior was characterized. The model predicts the stress–strain behavior of the composite as a function of the initial braiding angle and the number of pitches. The innovative aspect was included in the model related to the friction between the braid and the core. Results indicated good agreement between the theoretical simulations and the experimental results which was not discussed in previous studies. Since the rate of the diameter decrease of the CNTYs braid was higher than that of the elastomeric core diameter, squeezing out of the core through the braid inter yarn space occurred. This limited the maximum potential extension of the braid. Thus, a critical strain was defined where the braid came into contact with the core. The addition of the friction stresses made a significant contribution to the overall stresses and the accuracy of the theoretical simulation, and its agreement with the experimental results. An apparent friction coefficient was proposed to account for the effect of the elastomer core/braid interactive restriction and squeezing out of the elastomer through the braiding, as observed in experimental results. As the CNTYs are conductive, a stretchable conductive composite was obtained having a resistivity of 9.05 × 10–4 Ohm*cm, which remained constant throughout the tensile loading until failure and under cyclic loading.

The exploration of a noble-metal-free and nitrogen-doped carbon (M–N/C) composite electrocatalyst for the oxygen reduction reaction (ORR) remains a great challenge. The activities of the M–N/C composite electrocatalysts are mainly affected by the metal active sites, pyridinic nitrogen, and graphitic nitrogen. In the present work, the iron-coordinated self-assembly is proposed for the preparation of iron-chelating pyridine nitrogen-rich coordinated nanosheet (IPNCN) composites as electrocatalysts. Due to the highly conjugated structure of the IPNCN precursor, the pyridine nitrogen elements at both ends of the tetrapyrido [3,2-a:2',3'-c:3'',2''-h:2''',3'''-j] phenazine (TP) provide the multiple ligands, and the coordination interactions between the irons and the pyridine nitrogen further improve the thermodynamic stability, where the metal active sites and nitrogen elements are uniformly distributed in the whole structure. The resultant IPNCN composites exhibit excellent ORR performance with an onset potential of 0.93 V and a half potential of 0.84 V. Furthermore, the IPNCN composite electrocatalysts show the higher methanol resistance and electrochemical durability than the commercial Pt/C catalysts. It could be convinced that the as-designed IPNCN composite catalysts would be a promising alternative to the noble metal Pt-based catalysts in the practical applications.

Fusion assembly is a highly promising technique for joining thermoplastic composite to thermoset composites, enabling the use of both the most affordable composite material and process for each substructure. However, some major challenges need to be addressed such as functionalizing the thermoset composite surface through co-curing with an appropriate thermoplastic interlayer or realizing a fast and robust welding process that meets all quality and mechanical requirements. In this paper, we investigated the potential of polyetheretherketone (PEEK) and its amorphous (PEEK A) and semicristalline (PEEK SC) states as interlayer materials, co-cured onto thermoset composites. A surface preparation involving the atmospheric plasma process demonstrated that both PEEK state materials can be used as interlayer with favorable adhesion properties. The influence of the plasma treatment on surface properties and morphology was also experimentally characterized.

Conventional carbon fibre laminates are known to be moderately electrically conductive in-plane, but have a poor through-thickness conductivity. This poses a problem for functionality aspects that are of increasing importance to industry, such as sensing, current collection, inductive/resistive heating, electromagnetic interference (EMI) shielding, etc. This restriction is of course more pronounced for non-conductive composite reinforcements such as glass, organic or natural fibres. Among various solutions to boost through-thickness electrical conductivity, tufting with hybrid micro-braided metal-carbon fibre yarns is one of the most promising. As a well-characterised method of through thickness reinforcement, tufting is easily implementable in a manufacturing environment. The hybridisation of materials in the braid promotes the resilience and integrity of yarns, while integrating metal wires opens up a wide range of multifunctional applications. Many configurations can be produced by varying braid patterns and the constituting yarns/wires. A predictive design tool is therefore necessary to select the right material configuration for the desired functional and structural performance. This paper suggests a fast and robust method for generating finite-element models of the braids, validates the prediction of micro-architecture and electrical conductivity, and demonstrates successful manufacturing of composites enhanced with braided tufts.

Epoxy is widely used material, but epoxy has limitations in terms of brittleness in failure, and thus researchers explore toughening and strengthening options such as adding a second phase or using electromagnetic fields to tailor toughness and strength, on demand and nearly instantaneously. Such approach falls into the category of active toughening but has not been extensively investigated. In this research, Si-BaTiO3 nanoparticles were used to modify the electro-mechanical properties of a high-performance aerospace-grade epoxy so as to study its response to electric fields, specifically low field strengths. To promote uniform dispersion and distribution, the Si-BaTiO3 nanoparticles were functionalised with silane coupling agents and mixed in the epoxy Araldite LY1564 at different content loads (1, 5, 10 wt%), which was then associated with its curing agent Aradur 3487. Real-time measurements were conducted using Raman spectroscopy while applying electric fields to the nanocomposite specimens. The Raman data showed a consistent trend of increasing intensity and peak broadening under the increasing electric field strength and Si-BaTiO3 contents. This was attributed to the BaTiO3 particles’ dipolar displacement in the high-content nanocomposites (i.e., 5 wt% and 10 wt%). The study offers valuable insights on how electric field stimulation can actively enhance the mechanical properties in epoxy composites, specifically in relatively low fields and thin, high-aspect-ratio composite layers which would require in-situ mechanical testing equipped with electric field application, an ongoing investigation of the current research.

Functional composite materials in principle advance the field of composites beyond their specific structural properties. The intrinsically heterogeneous nature of composite materials allows additional material phases to be introduced, with specific added properties such as electrical conductivity, magnetic properties, or integrated surface functions. While significant progress has been made on these hybrid material systems, a complete understanding of their properties is necessary to tailor their functions for a given application. Specific challenges and opportunities fuel this dynamic research area.This special collection in Functional Composite Materials highlights the diversity in contributions, class of materials, emerging areas, cross-disciplinary applications, specific challenges, and opportunities in this emerging. The collection features a subset of papers originally selected to be presented at the 19th European Conference on Composite Materials (ECCM19) in June 2020 in Nantes, France, which was cancelled as a result of the COVID-19 pandemic.The field of functional composites is very broad as it consists in bringing several functions to composites to satisfy complex specifications. This great diversity is illustrated in this collection, where various technologies and constitutive materials are employed to bring the desired properties to composites. As a result, this collection by no means pretends to fully cover the field, but instead to bring to light some interesting materials related aspects in this vibrant field.One approach to reach functional composite materials consists of hybridizing materials featuring complementary functional properties. In [1], the in-plane and transverse electrical conductivities of Carbon-Fiber-PEEK composites are significantly improved by nanomaterial functionalization via spray deposition of exfoliated graphene nanosuspensions. Adding only a few wt% graphene in the interlayers of structural CF-PEEK composites by this technique led to more than 60% increase in transverse electrical properties, and much more in plane.In [2], a more macroscopic approach was followed to improve the longitudinal electrical conductivity of structural composites, by braiding carbon and metallic fibers, while the through-thickness conductivity was achieved by tufting conductive fibers into the braided fibrous structure, bringing both functional and structural benefits for through thickness properties. This approach was modelled by Finite Element techniques to provide a guide to evaluate the functional performance of the braided hybrid materials.The tufting technology was also used in [3] to improve the through-thickness mechanical strength of flax fibre reinforced green bio composites, using glass fibers. This study confirms that the mechanical functionalization of a laminated structure results in the search for a compromise between improvement in the thickness direction and the reduction in performance in the planar direction.Combining dissimilar materials sometimes also involves the addition of an interlayer to ensure chemical compatibility in novel welding techniques. This point is illustrated in [4] for the fusion welding of thermoset to thermoplastic polymer composites. The thermoset side needs to be functionalised through co-curing with a thin thermoplastic interlayer, and so several grades of PEEK and PEI were evaluated, in addition with a prior plasma treatment. The main remaining challenge is the fine tuning of the Infra-red welding parameters, to avoid degradation in final properties as compared to more conventional welding techniques.The functionalization of materials allows the development of sensors adapted to numerous applications. The structural health of polymer composites was monitored in [5] by inserting carbon fibre rovings into glass non-crimp fabrics. It was shown that the capacitance decrease is highly correlated to the crack formation, as the permittivity of air gaps is lower than that of the composite. This method is promising for crack detection in structures, as it does not compromise the structural properties of the glass laminates, and it can be implemented in critical locations.The development of more reliable magnetic sensors was investigated in [6]. Permanent magnets are usually bonded to metal substrates, which limits their lifetime and operating temperature. The authors show that it is possible to develop more reliable sensors by torsional ultrasonic welding of the magnets to stainless steel substrates.In parallel, there is a growing interest in the use of natural materials in composite structures, in response to environmental issues. In [7], the mechanical and hygroscopic properties of thermoformed Chemi-Thermo-Mechanical Pulp were analysed as a function of manufacturing parameters. These functional properties are key for packaging applications. Results showed that a careful optimisation of the process parameters led to a lower water uptake of the material, with better retention of mechanical properties even after moisture exposure. Scholz et al [8] investigated application-oriented adaptive elements based on cellulose Cottonid capable of complex, passive, moisture-induced shape changes with adjustable amplitude. For construction-related applications, solar radiation was studied as an environmental trigger on this cellulose-based humidity-sensing material. In conclusion, promising tailor made natural material sensors can be produced.Finally, in [9], the influence of the temperature and humidity of various seasons on the curing cold mix asphalts was studied. Cold mix asphalts are better in terms of environmental impact as they do not require high temperature to be processed and produce less fumes. However, their mechanical performance over time is still not fully understood, and results of the presented study showed that warm and dry temperatures tend to increase the material stiffness as well as the ageing of the binder material.1.Christopher Leow, Peter B. Kreider, Christian Notthoff, Patrick Kluth, Antonio Tricoli and Paul Compston. A graphene film interlayer for enhanced electrical conductivity in a carbon-fibre/PEEK composite. Functional Composite Materials 2:1 (2021).2.Caroline O’Keeffe, Laura Rhian Pickard, Juan Cao, Giuliano Allegri, Ivana K. Partridge and Dmitry S. Ivanov. Multi-material braids for multifunctional laminates: conductive through-thickness reinforcement. Functional Composite Materials 2:5 (2021).3.M. Rashid, J. L. Hanus, K. Chetehouna, K. Khellil, Z. Aboura and N. Gascoin. Investigation of the effect of tufts contribution on the in-plane mechanical properties of flax fibre reinforced green biocomposite. Functional Composite Materials 2:11 (2021).4.Henri Perrin, Grégory Mertz, Noha-Lys Senoussaoui, Loïc Borghini, Sébastien Klein and Régis Vaudemont. Surface functionalization of thermoset composite for infrared hybrid welding. Functional Composite Materials 2:10 (2021).5.Christina Buggisch, Abedin Gagani and Bodo Fiedle. Capacitance measurements on integrated conductors for detection of matrix cracks in GFRP. Functional Composite Materials 2:2 (2021).6.Moritz Liesegang and Tilmann Beck. Ultrasonic welding of magnetic hybrid material systems –316L stainless steel to Ni/Cu/Ni-coated Nd2Fe14B magnets. Functional Composite Materials 2:6 (2021).7.Claire Dislaire, Yves Grohens, Bastien Seantier and Marion Muzy. The impact of molded pulp product process on the mechanical properties of molded Bleached Chemi-Thermo-Mechanical Pulp. Functional Composite Materials 2:7 (2021).8.R. Scholz, M. Langhansl, M. Hemmerich, J. Meyer, C. Zollfrank and F. Walther. Impact of solar radiation on chemical structure and micromechanical properties of cellulose-based humidity-sensing material Cottonid. Functional Composite Materials 2:9 (2021).9.Amélie Thiriet, Vincent Gaudefroy, Emmanuel Chailleux, Jean-Michel Piau, Frédéric Delfosse and Christine Leroy. Effects of curing on emulsion cold mix asphalts and their extracted binder. Functional Composite Materials 2:12 (2021).Download referencesAffiliationsÉcole Centrale de Nantes, Research Institute in Civil Engineering and Mechanics (GeM), UMR CNRS 6183, 44321, Nantes Cedex 3, FranceChristophe BinetruyHead of Laboratory for Processing of Advanced Composites (LPAC), MXH145, Station 12, Ecole Polytechnique Fédérale de Lausanne (EPFL), 1015, Lausanne, CH, SwitzerlandVéronique MichaudAuthorsChristophe BinetruyView author publicationsYou can also search for this author in PubMed Google ScholarVéronique MichaudView author publicationsYou can also search for this author in PubMed Google ScholarContributionsThe guest-editors would like to express their gratitude to the editor-in-chief Tony McNally for his support throughout the whole editorial process. We also want to thank all contributors to this special collection for their trust and flexibility, the reviewers for improving the quality of the manuscripts, and the editorial staff for their help in the production of this special collection. The author(s) read and approved the final manuscript.Corresponding authorCorrespondence to Christophe Binetruy.Competing interests The authors declare that they have no competing interests.Publisher’s NoteSpringer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. Reprints and PermissionsCite this articleBinetruy, C., Michaud, V. Emerging, hybrid & smart composites. Functional Composite Mater 2, 16 (2021). http://doi.org/10.1186/s42252-021-00028-yDownload citationReceived: 12 November 2021Accepted: 16 November 2021Published: 31 December 2021DOI: http://doi.org/10.1186/s42252-021-00028-yShare this articleAnyone you share the following link with will be able to read this content:Get shareable linkSorry, a shareable link is not currently available for this article.Copy to clipboard Provided by the Springer Nature SharedIt content-sharing initiative