Self-healing Polymer Composites Research Articles

Silver Nanoparticle-Assisted Electrochemically Exfoliated Graphene Inks Coated on PVA-Based Self-Healing Polymer Composites for Soft Electronics.

Smart sensors with self-healing capabilities have recently aroused increasing interest in applications in soft electronics. However, challenges remain in balancing the sensors' self-healing and compatibility between their sensing and substrate layers. This study evaluated several self-healing polymer substrates and graphene ink-based strain-sensing coatings. The optimum electrochemically exfoliated graphene (e-graphene)/silver nanoparticle-coated tannic acid (TA)/superabsorbent polymer/graphene oxide (GO) blended poly(vinyl alcohol) polymer composites exhibited improvements of 47.1 and 39.2%, respectively, for the healing efficiency in a substrate crack area and in the graphene-based sensing layer due to conductive layer adhesion. While TA was found to improve healing efficiency on the coating surface by forming hydrogen bonds between the sensing and polymer layers, GO healed the polymer surface due to its ability to form bonds in the polymer matrix. The superabsorbent polymer was found to absorb excess water in e-graphene dispersion due to its host-guest interaction, while also reducing the coating thickness.

Bio-based conductive polyurethane composites derived from renewable castor oil with enhanced self-healing ability for flexible supercapacitors

To alleviate the pressure on the petrochemical industry and address environmental concerns, the utilization of polyurethane (PU) derived from castor oil (CO) (as an ester polyol replacement of petrochemical-based materials) has garnered significant attention in recent decades. Extending the service life of materials requires imparting self-healing properties to vegetable oil-based polymers, an aspect that has received limited attention in current studies. However, low self-healing efficiency still poses a significant challenge, and non-conductivity also remains an obstacle in current research, crucial for their application in electronic devices. In this work, we present the first series of electrically self-healing biopolymer composites constructed by incorporating carbon nanotube (CNT) networks into crosslinked castor oil-based polyurethane (BPU) through a simple curing process. These materials address the challenges mentioned above and exhibit improved mechanical, electrical, and self-healing capabilities compared to other bio-based self-healing materials. The resulting BPU/CNT composite demonstrated exceptional repeated self-healing capacity, restoring both mechanical properties and electrical performance even after experiencing severe mechanical damage. Notably, this composite served as a conductive substrate in flexible solid-state supercapacitor (FSSC) devices. Consequently, the FSSC derived from the composite conductive substrate achieved an impressive 92.4 % self-healing efficiency even after undergoing 7 cutting/healing cycles. The device remained virtually unchanged even after being bent at a 180° angle with a bending radius of 1.6 mm, indicating excellent repeatability and durability. The exceptional self-healing ability, with ∼98 % electrical recovery at 100 °C for 70 s and 93 % at 80 °C after 6 min, of these composites was attributed to the synergistic interactions of the dynamic exchange reactions of disulfide bonds and dense hydrogen bonds within the BPU matrix, which provide a reversible dynamic polymer network. The healing efficiency of these dynamic bonds was evaluated by adjusting the composition ratio of the long linear chain of pTHF in hybrid polyols of the crosslinked polymer network. Overall, this work highlights a series of green, simple, and highly efficient self-healing polymer composites derived from renewable castor oil, and it establishes an essential framework for future sustainable polymer composite design.

A micromechanical damage-healing model for encapsulation-based self-healing polymer composites under tensile loading

In this study, a novel micromechanics-based damage model is proposed for the damage evolution of a two-component microencapsulated-based self-healing polymer composite. In this way, a representative volume element (RVE) including an epoxy matrix with randomly distributed poly(methyl methacrylate) (PMMA) microcapsules is modeled in DigimatTM software and analyzed in Abaqus®. A new technique is developed to investigate the progressive damage by pre-inserted cohesive elements along all element boundaries of the epoxy matrix, PMMA shell, and capsule-matrix interfaces with the bilinear traction–separation law. Moreover, the impact of interface bonding strength, interface fracture energy, and PMMA microcapsules volume fraction on the load-carrying capacity of the RVEs under uniaxial tension loading was studied. The results indicated that the tensile strength of the self-healing polymer composite increased as the interfacial strength and fracture energy increased from 10 to 60 MPa and 100 to 1000 J/m2, respectively. Furthermore, the higher volume fraction of 5% PMMA microcapsules results in a lower load-carrying capacity of self-healing polymer composite with a strength of 4.9 N. A similar trend of Young’s modulus was observed for microcapsule-loaded epoxy composite compared to the pristine epoxy matrix. The micromechanical model has proper accuracy in predicting the tension behavior of self-healing composite in comparison to experimental results. Finally, two healing strategies are considered for the damaged RVE.

Synergistic Effect of Cation Composition Engineering of Hybrid Cs1−xFAxPbBr3 Nanocrystals for Self‐Healing Electronics Application (Adv. Mater. 9/2023)

Self-Healing Nanophotonics In article number 2207617, Fang-Cheng Liang, Takayuki Chiba, Junji Kido, Chi-Ching Kuo, and co-workers present novel post-synthesis Cs/FA mixed-cation perovskite nanocrystals possessing high structural and optoelectronic properties for integration in self-healing polymer composites. The entropy-driven self-healing not only enhances the white backlight display performance but also sustains the shattered–repaired glass substrate laser working performance, thereby representing potentially major advances in optoelectronics and photonics applications.

富山県立大学 工学部 機械システム工学科 材料設計加工学講座 真田研究室

The objective of our laboratory is development of new polymer composites with superior performance and reliability using experimental and analytical approaches. Nowadays, we have been working on three research themes for new polymer composites: self-healing polymer composites, high thermal conductive polymer composites, and polymer composites with cellulose nanofibers. This article introduces research facilities and outline of three research themes in our laboratory.

Multi-factor analysis of the effects of graphene oxide nanoplatelets on self-healing polymer composites based on micromechanical FE simulation

To investigate the effects of graphene oxide (GO) nanoplatelets and mixed self-healing microcapsules on the mechanical properties of polymer nanocomposites, a multi-factor analysis was made based on numerical experimental results, which comprehensively reveals the influences of structural parameters (including the volume fraction, aspect ratio, orientation of GO and the content of self-healing microcapsules). A series of micromechanical FE models of nanocomposites containing randomly-distributed nanoplatelets were established and validated by experimental data. The competing failure mechanisms of matrix damage and interface debonding have been fully considered in the simulation. The significance levels of the nanocomposite’s structural parameters were quantitatively determined finally, and it was found that the volume fraction is the most significant factor and the aspect ratio is the next (the weights are 46.1% and 21.7%, respectively). The work would provide effective theoretical instructions in the material design and optimization of GO-reinforced self-healing polymer nanocomposites.

A Comprehensive Review of Self-Healing Polymer, Metal, and Ceramic Matrix Composites and Their Modeling Aspects for Aerospace Applications.

Composites can be divided into three groups based on their matrix materials, namely polymer, metal and ceramic. Composite materials fail due to micro cracks. Repairing is complex and almost impossible if cracks appear on the surface and interior, which minimizes reliability and material life. In order to save the material from failure and prolong its lifetime without compromising mechanical properties, self-healing is one of the emerging and best techniques. The studies to address the advantages and challenges of self-healing properties of different matrix materials are very limited; however, this review addresses all three different groups of composites. Self-healing composites are fabricated to heal cracks, prevent any obstructed failure, and improve the lifetime of structures. They can self-diagnose their structure after being affected by external forces and repair damages and cracks to a certain degree. This review aims to provide information on the recent developments and prospects of self-healing composites and their applications in various fields such as aerospace, automobiles etc. Fabrication and characterization techniques as well as intrinsic and extrinsic self-healing techniques are discussed based on the latest achievements, including microcapsule embedment, fibers embedment, and vascular networks self-healing.

Simultaneously optimized healing efficiency and mechanical strength in polymer composites reinforced by ultrahigh loading fillers based on interfacial energy and dynamic disulfide bonds

In general, ultrahigh loading fillers can increase the hardness and hinder the interfacial healing progress in polymer composites. Therefore, the healing ability and mechanical strength of polymer composites with ultrahigh filler loading are contradictory properties and are difficult to optimize simultaneously. Herein, self-healing hard polymer composites consisting of 72.4 vol% fillers and self-healing thermoplastic elastomers based on surface energy and disulfide bonds were fabricated. The results showed that in the case that of ultrahigh filler loading, polymer composites not only obtained a high mechanical strength of ∼3.21 MPa and a high self-healing efficiency of ∼92.8%, but also possessed the strong reshape ability. Besides, a physical model was used to describe the self-healing mechanism. The adhesion effectively closed cracks and the surface energy driven the movement of polymer chains as well as disulfide bonds reconstructed new polymer chains at the interfaces, resulting in recovering heal mechanical property. • Self-healable polymer composites with ultrahigh loading fillers were prepared. • The maximum healing efficiency and mechanical strength reached 92.8% and 3.21 MPa. • The physical model was used to describe healing mechanism in detail.

Wear in-situ self-healing polymer composites incorporated with bifunctional microcapsules

Self-lubricating materials inevitably suffered mechanical damage such as wear, micro-scratch and cracks, which will shorten the service life of materials. The highlight of this work is to improve the wear resistance of the material by coupling self-lubricating and self-healing. Herein, we investigated the ability of a polymer composite incorporated with bifunctional microcapsules to heal mechanical damage. Thermally robust microcapsules containing organic solvent dibutyl phthalate (DBP) and linseed oil (LO) were synthesized by in situ polymerization of urea and formaldehyde in an oil-in-water emulsion. The microcapsules were filled in an epoxy (EP) resin matrix and cured to form composite materials. Multiple characterization methods such as 3D scratch instrument, UMT-5 machine and Atomic Force Microscope (AFM) were adopted to investigate the healing performance and healing mechanism of materials. The composite materials incorporated with bifunctional microcapsules presented excellent scratch self-healing ability (the self-healing efficiency was higher than 96% by volume) and wear resistance (the friction coefficient has been reduced by 92% and the wear rate has been reduced by three orders of magnitude). It was demonstrated that the combination of lubrication enhancement and wear scar self-healing could greatly prolong the service life of lubricating materials.

Mechanically robust, shape memory, self-healing and 3D printable thermoreversible cross-linked polymer composites toward conductive and biomimetic skin devices applications

The current work demonstrates excellent thermal, mechanical, shape memory, and self-healing properties of 3D printable, thermoreversible, cross-linked network composites. The thermoreversible cross-linked networks are composed of Diels-Alder (DA) reversible covalent and transient cross-links, which are formed by thermoplastic polyurethane (TPU) and poly(ε-caprolactone) (PCL). Also, cellulose nanocrystalline (CNC) is utilized as a cross-linking agent. The incorporated CNC, modified with furan (CNC-FA) and maleic anhydride groups (CNC-MAH), exhibits excellent compatibility with TPU/PCL matrix, forming physical and chemical cross-linking structures in the composites. Also, the mechanical properties, thermal stability, and self-healing properties are significantly improved after the addition of modified CNC. In addition, the mechanism of performance enhancement is further analyzed by molecular dynamics simulations. One should note that the mechanically robust and 3D printable self-healing composites enable the fabrication of durable conductive devices and biomimetic skin devices with high mechanical integrity, excellent electrical healing and superior strain-induced fluorescence properties, showing promise in next-generation flexible electronics, encryption devices and electronic skins, and may broaden the variety and applications of 3D-printable materials. • The thermoreversible composites are composed of DA reversible covalent and transient crosslinks. • The CNC modified with furan and maleic anhydride groups, exhibit compatibility with polymer matrix. • The mechanism of performance enhancement is further analyzed by molecular dynamics simulations. • The damage could be healed due to the good self-healing capability, thanks to the shape memory effect.

INVESTIGATION ON FLEXURAL AND IMPACT STRENGTH OF HOLLOW GLASS FABRIC AND E-GLASS FIBER-REINFORCED SELF-HEALING POLYMER COMPOSITES

The present study investigates the self-healing functionality of e-glass unidirectional fiber-reinforced epoxy resin, based on a hollow glass fiber approach under flexural and impact loading. The planned self-healing fiber-reinforced composite constitutes epoxy resin (Lapox ARL-125 + AH-367), e-glass fibers with 0° orientation, embedded hollow glass fabric (HGF) filled with a curing agent (Lapox L-552/K-552), which provides a self-healing functionality. The developed composite is tested on the virgin, damaged, and healed conditions for the various healing periods (1, 2, and 3 days), and recovered flexural, impact strength and subsequent healing efficiency are studied. On day three, the optimum flexural strength achieved is 851.17 N/mm<sup>2</sup>, with a healing efficiency of 74.53% when subjected to quasi-static load. Similarly, the optimum impact energy absorbed is 4439.26 J/m, and impact strength achieved is 445.88 kJ/m<sup>2</sup>, with a healing efficiency of 55.58% when subjected to impact load. The results show that developed self-healing composites may provide excellent flexural and impact properties for marine structural applications.

HEALING CARBON FIBER COMPOSITES WITH THERMOPLASTIC POLYMERS

Self-healing materials are materials that automatically and independently heal or repair damage caused by any cause, without outside intervention. Self-healing polymeric materials are in the class of smart materials. Research on self-healing polymers and polymer composites using this effect has increased rapidly in recent years due to the advantages such as cost reduction and less labor that this new topic will provide. In this review, first of all, a brief information about the self-healing mechanisms used in composites will be given in the light of the studies in the literature, then the use of the stitch method in composites and self-healing composites and finally the test methods of self-healing composites will be mentioned.

Numerical study of the heating effects of high intensity focused ultrasound on shape memory polymer fiber reinforced self-healing polymer composite

In polymer composites, constrained shape recovery, either by shape memory polymer (SMP) matrix or embedded SMP fibers, is utilized to close wide-opened cracks, followed by molecular scale healing either extrinsically or intrinsically, the so-called close-then-heal strategy. The most popular means to trigger shape recovery and healing is by heating. In this study, the potential for using high intensity focused ultrasound as a trigger for shape memory effect and self-healing of an SMP fiber-reinforced thermosetting polymer composite was explored. The objectives of the study were achieved via a finite element simulation in COMSOL Multiphysics. Simulation results showed that for an 8 mm thick, 18 mm long model composite with 5.8% SMP fiber volume fraction, a temperature rise of up to 5.6 K was obtained in the embedded SMP fiber after 2 s with only 1 s of the insonation. It was found that heat generation occurred at the fiber–matrix interfaces; however, subsequent temperature rise within the embedded fibers was achieved via conventional thermal conduction from the high-temperature interfacial regions into the fibers. The effect of specimen length, thickness, and fiber volume fraction on temperature rising was also evaluated. This study provides a better understanding of using ultrasound to trigger self-healing of SMP fiber-reinforced polymer composites.

A Literature Review on the Extensive Study of Multi-functional Self-healing Polymer Composites(SHPC)

A Literature Review on the Extensive Study of Multi-functional Self-healing Polymer Composites(SHPC)

Fracture resistance of in-situ healed CFRP composite using thermoplastic healants

In this study, macro fiber composite (MFC) assisted in-situ healing of unidirectional fiber reinforced polymer (FRP) composite was investigated and characterized by the double cantilever beam (DCB) tests. Biomimetic healing of delamination damage in carbon fiber reinforced composite (CFRP) was achieved by using a blend of biphasic healant: polycaprolactone (PCL) and polyurethane shape memory polymer (SMP). When the damage initiated at the fiber matrix interface or through the matrix, the thermoplastic SMP/PCL blend closed the crack due to localized stimulus (heat) provided by MFC. Crack closure was followed by healing via PCL healant using the same stimulus. Protocol for characterizing the healing efficiency of CFRP composite was established. The experimental results demonstrated that the localized healing method not only enables the in situ healing but also outperforms conventional healing methods in terms of healing efficiency. The MFC actuated healing yielded up to ∼160 % recovery of virgin interlaminar fracture property and ∼70 % flexure property recovery for seven healing cycles. This novel healing system can thus provide efficient in-situ healing in aerospace structures using MFC sensors as self-healing actuators, and bridge the gap between the laboratory scale and large-scale industrial application of self-healing polymer composite.

Hydrogen bonding derived self-healing polymer composites reinforced with amidation carbon fibers

Self-healing polymer materials (SHPM) have aroused great interests in recent years. Ideal SHPM should have not only simple operations, but also high elongations at break, tensile strain and self-healing properties at room temperature. Herein, the amidated carbon fibers (CFs) reinforced self-healing polymer composites were designed by hydrogen bonding interaction between functionalized CFs and hyperbranched polymers. The amidated CFs were prepared by transformation of hydroxyl to acylamino through a one-step amidation. By introducing amidated CFs, amidated CFs self-healing polymer composites (called AD-CF) exhibited many desirable characteristics compared to pure polymer composites, such as a better elasticity, lower healing temperatures, and higher self-healing efficiencies. The stress–strain test was selected to carefully study the self-healing property of the AD-CF. The observed same recovery condition, i.e. without any mechanical breakdown after the 10 sequential cycles of cutting and healing indicates no aging of the AD-CF. The ability of AD-CF to exhibit a soft state and rapid self-healing at room temperature makes it possible for much wider applications.

Toughening and self-healing fiber-reinforced polymer composites using carbon nanotube modified poly (ethylene-co-methacrylic acid) sandwich membrane

This paper proposes a sandwich membrane with a carbon nanotube (CNT) buckypaper as core and two poly (ethylene-co-methacrylic acid) (EMAA) meshes as face-layers. Mode I interlaminar fracture toughness (GIC) is determined to evaluate the toughening and self-healing effect of CNT/EMAA and contrastive neat EMAA membranes on a glass fiber reinforced laminate. Results show that CNT/EMAA could enhance the GIC by 34.6% and show self-healing efficiencies of 115.3% for the first healing and 129.4% for the second healing. Comparatively, neat EMAA significantly improves the GIC by 121.1%, and the obtained 1st and 2nd healing efficiencies can also achieve 108.4% and 118.6%, respectively. Moreover, compared with neat EMAA, CNT/EMAA shows less negative effect on the interlaminar shear strength and flexural strength of the laminates. Therefore, this research reveals that CNT/EMAA membrane possesses better multi-functionality, i.e. notable self-healing and moderate toughening capability and less negative effect on the strengths of the laminates.

Self-Healing Polymer Composites Based on Hydrogen Bond Reinforced with Graphene Oxide

Self-Healing Polymer Composites Based on Hydrogen Bond Reinforced with Graphene Oxide

Healing efficiency characterization of self-repairing polymer composites based on damage continuum mechanics

Self-healing polymer composites are part of a class of materials which have the capability to repair themselves when damaged. They are often tested by inflicting damage onto them and then performing a mechanical test to initiate and measure self-healing. Self-healing efficiency is commonly defined as the ratio of a recovered property value to its original value. Applying this in practice can be challenging as most self-healing experiments are idealized scenarios. In this work, microcapsules containing epoxy and mercaptan self-healing agents were incorporated into ±45° composite weaves that were subjected to cyclic tensile loading and unloading. A damage mechanics theory was applied to quantify the change in stiffness and determine self-healing effectiveness. As this method did not enable a direct comparison between the damaged and healed states of the material, a new methodology was developed to take into account the energy levels of the material in order to quantify self-healing performance.

Cure kinetics of poly (5-ethylidene-2-norbornene) with 2nd generation Hoveyda-Grubbs’ catalyst for self-healing applications

Self-healing polymer composites based on ring-opening metathesis polymerization (ROMP) incorporating second generation Hoveyda-Grubbs’ (HG2) catalyst as polymerization initiator and 5-ethylidene-2-norbornene (5E2N) as healing monomer are promising for self-healing applications. This is particularly true at low temperatures that may persist in the internal environment of an operating space vehicle. By using a systematic micro-Raman spectroscopic analysis and a detailed methodology specifically implemented for the investigation of 5E2N and HG2 reactants, we studied the progression of the ROMP reaction over time from room temperature down to −30 °C. The analysis is based on measuring the changes in peak intensity and integrated area of Raman phonons related to the characteristic (CC) functional groups indicating the progression of the reaction with time. The cure kinetic reaction of the 5E2N/HG2 system at low temperatures is found to follow an Arrhenius behavior showing the temperature dependence of the reaction rates. On this basis, the activation energy of the reaction is measured to be 64 (±3) kJ mol−1 (0.663 eV), a value that is about 40% higher than the data reported for similar materials.