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The development of natural fiber (NFr) composites for a variety of applications is on the rise. The optimization of the interfacial bonding (IFB) between the reinforcing NFr and polymer matrix is perhaps the single most critical aspect in the development of natural fibre polymer composites (NFPCs) with high mechanical performance. While the IFB is critical in determining the mechanical properties of the NFPCs, such as stress transfer, it is one of the least understood components. This article offers a summary of IFB mechanisms, different modification approaches targeted at lowering incompatibility and improving IFB, and evaluation of the impact of IFB. It has been found that 1) In general, interdiffusion, electrostatic adhesion, chemical reactions, and mechanical interlocking are accountable for the IFB; 2) the incompatibility of the fibre and matrix, which results in poor dispersion of the fiber, weak IFB, and ultimately worse composite quality, may be addressed through strategic modifications; and 3) Interfacial interactions between polymers and nanoparticles (NPs) are significantly improving their performance in areas like thermal, mechanical, robust IFB, and moisture absorption. As a result, this review study could be an important resource for scholars interested in coating and treating NFr to further enhance their surface characteristics.

HighlightsA nanofiber composite reinforced organohydrogel with multifunctionality is prepared.The composite organohydrogel possesses multiple interfacial bondings and multi-level strengthening and toughening mechanism is proposed.The composite organohydrogel exhibits long-term strain sensing stability and can be used for high performance electromagnetic interference shielding. Composite organohydrogels have been widely used in wearable electronics. However, it remains a great challenge to develop mechanically robust and multifunctional composite organohydrogels with good dispersion of nanofillers and strong interfacial interactions. Here, multifunctional nanofiber composite reinforced organohydrogels (NCROs) are prepared. The NCRO with a sandwich-like structure possesses excellent multi-level interfacial bonding. Simultaneously, the synergistic strengthening and toughening mechanism at three different length scales endow the NCRO with outstanding mechanical properties with a tensile strength (up to 7.38 ± 0.24 MPa), fracture strain (up to 941 ± 17%), toughness (up to 31.59 ± 1.53 MJ m−3) and fracture energy (up to 5.41 ± 0.63 kJ m−2). Moreover, the NCRO can be used for high performance electromagnetic interference shielding and strain sensing due to its high conductivity and excellent environmental tolerance such as anti-freezing performance. Remarkably, owing to the organohydrogel stabilized conductive network, the NCRO exhibits superior long-term sensing stability and durability compared to the nanofiber composite itself. This work provides new ideas for the design of high-strength, tough, stretchable, anti-freezing and conductive organohydrogels with potential applications in multifunctional and wearable electronics.

This paper investigates the bond failure performance between precast normal concrete (NC) and cast-in situ ultra-high performance concrete (UHPC), emphasizing the influence of interfacial roughness. The interfacial bonding behavior under tension and under shear was investigated based on 72 groups of pull-off tests and 36 groups of bi-shear tests, considering six different interface treatment methods and two different NC strength levels. The results demonstrate that certain interfacial roughness is essential to gain a reliable bond connection between NC and UHPC. Its enhancement on the tensile bond performance could be described by the positive linear relationship between the mean roughness and the pull-off strength. However, further research is required to determine the characterization method of its influence on the shear bond performance. The higher strength of the base concrete is beneficial to the bond performance. Though this effect is evident in the pull-off tests under tension, the influence on the shear interfacial performance could be offset by that of the interface morphology in the case with high interfacial roughness.

In the current study, we proposed a method of differential temperature rolling with electromagnetic induction heating to prepare Ti/Al composite plates in a protective atmosphere to realize the homogeneous deformation of Ti/Al bonding rolling and improve the interfacial bonding strength of the composite plates. The temperature field required for homogeneous deformation rolling of titanium and aluminum was constructed using finite element simulation by adjusting the parameters of electromagnetic induction heating, which made a temperature difference of about 632 °C between titanium and aluminum, and the temperature of each plate was relatively uniform. The induction heating experiment was designed based on the finite element simulation, and the experiment verified the accuracy of the simulation results. The effects of rolling temperature and reduction rate of homogeneous deformation and bonding strength of Ti/Al composite plates were evaluated by rolling experiments. With the increase of rolling temperature and reduction rate of titanium, when the heating temperature of the Ti plate is 750–850 °C, and the reduction rate is 30%–48%, the reduction rate of Ti plate and Al plate gradually tend to be the same. When the titanium plate and aluminum plate temperature is 850 °C and 188 °C, respectively, with a rolling reduction rate of 48%, the deformation rate of Ti plate and Al plate is 46.8% and 48.6%, respectively. Moreover, the bonding strength of the composite plate reaches 77MPa.

To investigate the interfacial bonding performance between high-early-strength high-ductility concrete (HES-HDC) and existing concrete, 108 bonding specimens were used to study the effects of concrete substrate roughness, the content of silica fume, hydroxypropyl methylcellulose (HPMC), and polyethylene (PE) fiber in HES-HDC, as well as curing age and testing methods on the interface failure mode, load-slip curve, and interfacial bonding strength between HES-HDC and concrete. The results show that the interfacial bonding strength at 2 h of all bonding specimens exceeded 1.2 MPa, with the interfacial bonding strength at 1 day reaching 60% of that at 28 days, demonstrating significant high-early-strength properties, meeting the requirements for rapid repairs. The concrete substrate roughness significantly influenced the interface failure mode and the characteristics of the shear load-slip curve. The interfacial shear strength increases with increasing concrete substrate roughness, HPMC content, fiber content, and curing age. HES-HDC with 6% silica fume exhibits higher interfacial shear strength with existing concrete. Based on the experimental results, a formula for the interfacial bonding strength between HES-HDC and concrete was proposed, considering interface properties and material strength, which could be applicable for predicting bonding strength using different interface testing methods.

This article is aimed at discussing the combined effect of mineral admixture and servicing temperature, especially in cold environment, on the properties of magnesium phosphate repair mortar (MPM). The influence mechanism of fly ash content on the microstructure and performance of MPM were firstly investigated, and then the evolution rules in properties of fly ash modified MPM cured at − 20 °C, 0 °C, 20 °C and 40 °C were further revealed. The results show that the incorporation of fly ash has no significant effect on the setting time and fluidity of MPM. When MPM is modified with 10 wt% and 15 wt% fly ash, its mechanical properties, adhesive strength, water resistance, and volume stability are effectively improved. Fly ash reduces the crystallinity and continuity of struvite enriched in hardened MPM, and its particles are embedded among struvite and unreacted MgO. The compressive strength of MPM-10 cured for various ages increases with the elevating of curing temperature, while the flexural strength, interfacial bonding strength, strength retention and linear shrinkage exhibits the opposite laws. When cured at 0 °C and − 20 °C, MPM-10 still has good early strength, water resistance and interfacial bonding properties, which indicates that MPM-10 provides with an ability of emergency repair of cracked components served in cold environments.

Traditional concrete bridge decks often incorporate steel mesh to ensure connection and prevent cracking. However, the cracking in the connecting layer, low bond strength, misalignment of steel mesh, and settling at the bottom often appear. In this study, fiber-reinforced concrete was used for the bridge deck overlay, and a horseshoe-shaped shear key was employed to connect it with the beam body, forming a robust composite bridge deck system. By optimizing the concrete composition and interface bonding methods within the system, a comprehensive investigation was conducted into the compressive and splitting tensile strengths of different composite systems. The findings showed that the horseshoe-shaped shear key enhances the splitting tensile strength of the composite structural system while maintaining its compressive strength, ensuring a certain level of structural integrity during failure. As the strength grade of the steel fiber-reinforced concrete in the deck overlay increases, the compressive and splitting tensile strengths of the composite system initially rise and then stabilize, with C40 being the optimal strength grade for the deck overlay concrete. Furthermore, the overall performance of the deck overlay concrete with steel fibers is superior to that with the POM and PP fibers. The application of the YJ-302 interface bonding agent at the connection between the deck overlay and the beam body concrete further enhances the mechanical properties of the composite system.

To efficiently heal large-aperture cracks in the sandstone cultural relics, a microbially induced magnesia carbonation (MIMC) method was introduced in combination with sandstone grains. A series of MIMC samples and sandstone–MIMC composite samples were meticulously prepared, incorporating different initial water content and magnesia content variations. The mechanical behavior was evaluated by three-point bending test. The results showed that fractures consistently occurred on the MIMC side of the sandstone–MIMC samples, indicating superior bonding compatibility with sandstone. The interfacial bonding strength of sandstone–MIMC samples had a maximum value of 675 kPa, while MIMC samples had a maximum value of 1200 kPa. X-Ray diffraction (XRD) analysis confirmed that brucite with low crystallinity was the predominant cementing product at the interface, and the degree of carbonation showed a stepwise increase with distance from the interface. The bonding between MIMC and sandstone can be attributed to mechanical interlocking of hydration/carbonation products with the sandstone surface and the chemical reaction between brucite and silica. Microstructural examination revealed that there were layered structures near the interface namely interfacial transition zone (ITZ), including the diffusion layer, strong bonding layer and weak bonding layer. The diffusion and strong bonding layers positively enhanced the bonding strength, while numerous microcracks in the weak bonding layer provided a negative effect. This study provides valuable insights into the bonding mechanism of the interface, contributing to the understanding of how MIMC interacts with rock in the context of healing large-aperture cracks in sandstone cultural relics.HighlightsMicrobially-induced magnesia carbonation (MIMC) is a promissing biomineralization technology for sandstone cultural relics ceack healing.The interfacial bonding strength of MIMC to sandstone is up to 675 kPa.Low-crystallinity brucite is the predominant cementing product at the interface.There is a layered structure in the interfacial transition zone near the interface.Weak bonding layer is the zone where failure occurs.

Fiber-reinforced resin composites (FRRCs) are widely used in several fields such as construction, automotive, aerospace, and power. Basalt fiber (BF) has been increasingly used to replace artificial fibers such as glass fiber and carbon fiber in the production of BF-reinforced resin matrix composites (BFRRCs). This preference stems from its superior properties, including high temperature resistance, chemical stability, ease of manufacturing, cost-effectiveness, non-toxicity, and its natural, environmentally friendly characteristics. However, the chemical inertness of BF endows it with poor compatibility, adhesion, and dispersion in a resin matrix, leading to poor adhesion and a weak BF–resin interface. The interfacial bonding strength between BF and resin is an important parameter that determines the service performance of BFRRC. Therefore, the interfacial bonding strength between them can be improved through fiber modification, resin–matrix modification, mixed enhancers, etc., which consequently upgrade the mechanical properties, thermodynamic properties, and durability of BFRRC. In this review, first, the production process and properties of BFs are presented. Second, the mechanical properties, thermodynamic properties, and durability of BFRRC are introduced. Third, the modification effect of the non-destructive surface-modification technology of BF on BFRRC is presented herein. Finally, based on the current research status, the future research direction of BFRRC is proposed, including the development of high-performance composite materials, green manufacturing processes, and intelligent applications.

Recycled carbon fiber, as a novel type of solid waste, possesses high tensile strength, structural stability, and low utilization rates. Recycling carbon fiber for use in cementitious materials presents an efficient solution. However, achieving good interfacial bonding between recycled carbon fiber and cementitious materials is crucial for its high-performance application in such materials. This study first characterizes the properties of recycled carbon fiber and, for the first time, tests the interfacial parameters between recycled carbon fiber and cement matrix through single-fiber pull-out tests. The results show that the surface of recycled carbon fiber, lacking active functional groups and being relatively smooth, leads to poorer interfacial bonding with the cement matrix compared to virgin carbon fiber. The interfacial bonding strength, interfacial friction bonding strength, and chemical debonding energy are 0.65 MPa, 0.47 MPa, and 0.36 J/m2, respectively. Next, based on the theoretical model of interfacial mechanics, a single-fiber pull-out model was used to predict the bridging stress curve of recycled carbon fiber. The calculations show that the bridging stress of recycled carbon fiber at volume fractions of 0.16%, 0.3%, and 0.47% are 1.25 MPa, 2.18 MPa, and 3.40 MPa, respectively. Finally, tensile tests were conducted to investigate the tensile properties of cementitious materials reinforced with recycled carbon fiber. At various fiber contents, the recycled carbon fibers provided corresponding bridging stresses at crack sites, enhancing the tensile strength of the cementitious materials by 8.8~35.48%.