Self-healing Composite Materials Research Articles

Polyetherimide copolymer film with room-temperature self-healing properties and high breakdown field strength

With the waste of resources caused by human activities, it has gradually become an increasingly prominent social problem. The development of self-healing polymers in the field of insulation has attracted widespread attention. Develop polymer matrices with efficient healing efficiency and sound insulation properties to achieve green and sustainable resource conservation. In addition, improving the dielectric properties of intrinsic self-healing matrices has been a hot topic. In this work, we developed a new PEI matrix-modified self-healing polymer substrate that provides a breakdown field strength of 240 kV/mm and self-healing properties at room temperature, this has significantly improved the dielectric properties over other previously reported self-healing polymers. In addition to the abovementioned performance, we found significant differences in thermodynamic behavior in the synthesized end-modified polymers. By dielectric characterization (LCR), the breakdown composite can be left at room temperature for 60 min, and the material can recover 80 % of the initial properties without external intervention(This is demonstrated by the fact that its DC conductivity at 60 min of autonomous healing was significantly changed from that of the freshly electrically pierced DC conductivity and remained around 5.38 × 10−11 S/cm for a longer period of time thereafter). The microscopic morphology of the modified PEI matrix was observed by scanning electron microscopy (SEM) and EDS surface elemental analysis, which further supports the existence of metal coordination structures. These findings can further deepen the thinking of self-healing dielectric composites. The work inspired by this may break the limits and take self-healing composite dielectric materials to a new height.

Tensile and Compressive Properties of Woven Fabric Carbon Fiber-Reinforced Polymer Laminates Containing Three-Dimensional Microvascular Channels.

Microvascular self-healing composite materials have significant potential for application and their mechanical properties need in-depth investigation. In this paper, the tensile and compressive properties of woven fabric carbon fiber-reinforced polymer (CFRP) laminates containing three-dimensional microvascular channels were investigated experimentally. Several detailed finite element (FE) models were established to simulate the mechanical behavior of the laminate and the effectiveness of different models was examined. The damage propagation process of the microvascular laminates and the influence of microvascular parameters were studied by the validated models. The results show that microvascular channels arranged along the thickness direction (z-direction) of the laminates are critical locations under the loads. The channels have minimal effect on the stiffness of the laminates but cause a certain reduction in strength, which varies approximately linearly with the z-direction channel diameter within its common design range of 0.1~1 mm. It is necessary to consider the resin-rich region formed around microvascular channels in the warp and weft fiber yarns of the woven fabric composite when establishing the FE model. The layers in the model should be assigned with equivalent unidirectional ply material in order to calculate the mechanical properties of laminates correctly.

New recyclable and self-healing elastomer composites using waste from toner cartridges

Product recycling reintroduces what is discarded as waste and minimizes the environmental impact on our society. Among the different types of waste from electrical and electronic equipment, toner recycling often falls short, downcycling plastic components. This study introduces an innovative approach in which waste parts from toner cartridges are valorized to develop (recyclable and) self-healing elastomeric composite materials. The synergy between carboxylated nitrile rubber (XNBR) as the elastomeric phase and high-impact poly (styrene) (HIPS) as the thermoplastic phase derived from toner cartridge waste was explored and optimized. This combination resulted in the creation of a thermoplastic elastomer exhibiting robust mechanical properties and self-healing capabilities with a tensile strength of 6.6 ± 0.2 MPa and a temperature-driven mechanical recovery of 100%. Furthermore, the capacity of toner powder, an integral component of waste, to act as a reinforcing filler was confirmed, with a 50% increase in mechanical strength compared with the unfilled composite. Moreover, an increase in toner content (up to 20 phr) resulted in an optimal balance between tensile strength and self-healing capacity, surpassing the traditional antagonism between these properties. As a result, this research opens a new pathway in the field of self-healing composites and suggests a practical and environmentally friendly approach for managing electronic waste, effectively supporting the principles of Circular Economy.

Constitutive model and damage of self-healing 3D braided composites with microcapsules

In this paper, a constitutive model and damage of self-healing three-dimensional (3D) braided composites with microcapsules are investigated. First, a constitutive model that takes into account the impact of microcapsules is established to study the stress distribution in self-healing composite materials. Second, a 3D multiscale finite element (FE) model of the 3D braided self-healing composites with microcapsules is developed to assess the self-healing impact of the microcapsules on fiber-matrix debonding damage. Finally, the effects of microcapsule position and the presence of several microcapsules on stress distribution and healing effectiveness are further examined. The findings demonstrate that the proposed constitutive model is adaptive to the design and improvement of the current self-healing smart composites.

Simulation of the mechanical behavior of self-healing composite materials

PurposeThe purpose of this study is the investigation of self-healing materials containing encapsulated healing agents embedded in a polymer matrix with dispersed catalysts. In recent years, the high performance and design flexibility of composite materials have led to their widespread use in the aeronautics, space, automotive and marine fields. Simultaneously, as the need for advanced material properties has increased, many studies have been conducted on multifunctional materials, focusing on different fields of their desired capabilities.Design/methodology/approachA multiscale model was developed to simulate the effect of microcapsules on the mechanical behavior of the polymer matrix. Furthermore, the effects of microcapsule diameter and microcapsule concentration on the mechanical behavior of the composite were studied. Digimat and Ansys software were used to simulate the self-healing composites.FindingsThere is a trade-off between the efficiency of the microcapsules and the degradation of the properties of the composite material.Originality/valueThe generated model simulated an encapsulated healing agent in a polymeric matrix.

Self-Healing Materials for Electronics Applications.

Self-healing materials have been attracting the attention of the scientists over the past few decades because of their effectiveness in detecting damage and their autonomic healing response. Self-healing materials are an evolving and intriguing field of study that could lead to a substantial increase in the lifespan of materials, improve the reliability of materials, increase product safety, and lower product replacement costs. Within the past few years, various autonomic and non-autonomic self-healing systems have been developed using various approaches for a variety of applications. The inclusion of appropriate functionalities into these materials by various chemistries has enhanced their repair mechanisms activated by crack formation. This review article summarizes various self-healing techniques that are currently being explored and the associated chemistries that are involved in the preparation of self-healing composite materials. This paper further surveys the electronic applications of self-healing materials in the fields of energy harvesting devices, energy storage devices, and sensors. We expect this article to provide the reader with a far deeper understanding of self-healing materials and their healing mechanisms in various electronics applications.

Progress and challenges in self-healing composite materials

Self-healing methods.

A new generation self-healing composite materials

Self-healing is a certain type of unique physicochemical property, by which the material can be able to repair automatically the damage or fracture part of our tissue due to accident and used successfully at the time of operation. This damage may be due to accidents or by ageing processes. This self-healing concept is a blessing to medical science. Now-a-days extensive work is carried out with the self-healing materials. The mechanism of self-healing is of two kinds, the first one is autonomic systems, which requires no stimulus and the second one is non-autonomic system, which requires external stimulus such as heat or light for repairing damaged tissue. Self-healing materials behaves like elastomers and have a number of important applications in commercial and industrial sectors. The self-healing composite act as a significant healing agent and create an external trigger by initiating the process. Self-healing material is a novel sustainable material and can be successfully applied in many fields especially in tissue engineering.

Prospects and Future Directions of Self-Healing Fiber-Reinforced Composite Materials.

In this paper, the anticipated challenges and future applications of self-healing composite materials are outlined. The progress made, from the classical literature to the most recent approaches, is summarized as follows: general history of current self-healing engineering materials, self-healing of structural composite materials, and self-healing under extreme conditions. Finally, the next stage of research on self-healing composites is discussed.

(Invited) Creating “Double Network” Composites Via Macroscale Reinforcement

The double network concept has been revolutionary in its ability to turn soft, brittle hydrogels into tough, robust materials with mechanical properties that match the best synthetic elastomers. Double network hydrogels consist of two interpenetrating networks, where each network has a specific mechanical response: the “first network” acts as a sacrificial network, consisting of a rigid, extended network with relatively low loading percentage, and the “second network” is a globally percolated, stretchable network. When a double network hydrogel is stretched, covalent bonds of the first network break, dissipating energy; this process continues with increasing strain, until the sacrificial network is completely broken and the second network ruptures. Here, we will utilize this concept to develop materials with analogous fracture properties at the macroscale. Like double network hydrogels, our systems consist of rigid “first networks” embedded in global, soft and stretchable “second networks.” As a control system, 3d printed polyurethane/polyacrylate composite grids were utilized with a synthetic rubber. We found that when the strength of the matrix exceeds the strength of the grid, local fracture occurs in the grid, and stretching is isolated to the rubber in the fractured region. As stretching increases, the force increases, and when the force exceeds the strength of the grid, fracture will occur elsewhere in the composite. This process continues sequentially throughout the sample until all grid fracture sites are exhausted, and the matrix ruptures. By tuning the stiffness of the grid, we can independently control the yield strength and fracture strain of the composite, until a point where the grid strength exceeds the matrix strength, and the multiple fracture process no longer occurs. At an optimized grid:matrix strength ratio, we can then vary the number of fracture sites in the grid, maximizing toughness for a given component combination. The macroscale double network technique enables us to create composites with unique properties. Previously it has been difficult to create composites with hydrogels, because they undergo swelling which results in buckling or delamination in composite samples. We have created new hydrogel composites by incorporating low-melting point alloy (LMA) grids to alleviate this problem. A hydrogel is polymerized around the LMA frame, and the composite structure is submerged in water until the equilibrium swelling conditions are achieved. The sample is then heated to allow the LMA frame to melt, relieving the swelling stress in the composite sample. This LMA frame has been specifically designed based on the macroscale double network criteria to undergo multiple fracture events during stretching. Furthermore, utilizing an LMA frame allows us to stretch the sample up to 250%, fracturing the frame to dissipate energy, return the composite to its original shape, and then “heal” the structure in hot water. These samples can be then annealed in cold water, and retested, with 100% repeatability and healing efficiency. This process introduces new avenues to create self-healing composite hydrogel materials. Figure 1

Review of research and developments in self healing composite materials

Self-healing materials are artificial or synthetically created substances that have the built-in ability to automatically repair damage to themselves without any external diagnosis of the problem or human intervention. This article presents the current research and developments in self-healing composite materials. A detailed study is conducted on various types of self-healing composites with their self-healing mechanisms. The applications of self-healing materials in various fields including space sector is also discussed. Economics and Future outlooks for self-healing smart materials is highlighted at the end of the article. This research article will be useful to manufacturers, policy makers and researchers widely.

Research progress of self-healing intelligent composite materials

Self-healing composite material is an important intelligent composite material. In this paper, according to the recent research progress of the self-healing of composite materials, introduced the two kinds of typical extrinsic self-healing methods, which are microcapsule self-healing and hollow fiber self-healing, the paper expounds the repair mechanism of the two methods of self-healing, self-healing system characteristics and research status. This paper introduces some problems existing in the field of self-healing, and looks forward to the application prospect and development direction of self-repairing intelligent composite materials.

Continuum-Micromechanical Modeling of Microcapsules-Based Composites

Microcapsules are used in a wide range of applications, especially in self-healing composite materials and phase change materials. There is a growing body of literature that recognizes the importance of reinforcement on the mechanical properties of composites, however the effect of microcapsules during service needs to be further investigated. In this study, numerical investigations were conducted to examine the effects of the various geometric parameters on the mechanical behavior of microcapsules-based composites. The effective Young’s modulus and Poisson’s ratio of core-shell microcapsules distributed in a continuous matrix were predicted. A detailed three-dimensional finite element modeling (FEM) was presented. The numerical results were compared with a hierarchical proposed analytical model for three-constituent composites. Good agreements were achieved.

Synthesis of epoxy-loaded poly(melamine-formaldehyde) microcapsules: Effect of pH regulation method and emulsifier selection

In this work, epoxy-loaded microcapsules were successfully synthesized by in situ polymerization in oil-in-water emulsion with poly(melamine-formaldehyde) as shell material and diglycidyl ether of bisphenol F resin as liquid core substance. Two synthesis methods were deeply studied and optimized. For each method, different reaction conditions were analyzed by changing the following parameters: emulsifier type (single or binary) and concentration, emulsification conditions and pH adjustment during the polymerization reaction. The morphology, chemical structure, composition and thermal properties were characterized by Scanning Electron Microscopy and Optical Microscopy, Fourier Transform Infrared Spectroscopy, Thermogravimetric Analysis and Differential Scanning Calorimetry.It was found that the quality, size and surface morphology of the microcapsules depended strongly on the pH adjustment during the in situ polymerization. Moreover, the optimal type and concentration of emulsifier depended on the stage in which the acid pH was adjusted. Spherical microcapsules with different sizes and distributions, improved thermal stability and high core content were obtained by the optimization of reaction parameters and remained stable under more than one year at ambient laboratory conditions. Results indicate that the microcapsules are suitable for the development of self-healing composite materials.

Modeling microcapsule-enabled self-healing cementitious composite materials using discrete element method

Concrete with a micro-encapsulated healing agent is appealing due to its self-healing capacity. The discrete element method (DEM) is emerging as an increasingly used approach for investigating the damage phenomenon of materials at the microscale. It provides a promising way to study the microcapsule-enabled self-healing concrete. Based on the experimental observation and DEM, a three-dimensional damage-healing numerical model of microcapsule-enabled self-healing cementitious materials under compressive loading is proposed. The local healing effect can be simulated in our model, as well as the stress concentration effect and the partial healing effect. The healing variable of the DEM model is developed to describe the healing process. We examine the dependence of the mechanical properties of the microcapsule-enabled self-healing material on (a) the stiffness of the solidified healing agent, (b) the strength of the solidified healing agent, (c) the initial damage of specimens, and (d) the partial healing effect. In particular, the proposed numerical damage-healing model demonstrates the potential capability to explain and simulate the physical behavior of microcapsule-enabled self-healing materials on the microscale.

Robust synthesis of epoxy resin-filled microcapsules for application to self-healing materials

Mechanically and thermally robust microcapsules containing diglycidyl ether bisphenol A-based epoxy resin and a high-boiling-point organic solvent were synthesized in high yield using in situ polymerization of urea and formaldehyde in an oil-in-water emulsion. Microcapsules were characterized in terms of their size and size distribution, shell surface morphology and thermal resistance to the curing cycles of commercially used epoxy polymers. The size distribution of the capsules and characteristics such as shell thickness can be controlled by the specific parameters of microencapsulation, including concentrations of reagents, stirrer speed and sonication. Selected microcapsules, and separated core and shell materials, were analysed using thermogravimetric analysis and differential scanning calorimetry. It is demonstrated that capsules lose minimal 2.5 wt% at temperatures no higher than 120°C. These microcapsules can be applied to self-healing carbon fibre composite structural materials, with preliminary results showing promising performance.

Characterisation of Dicyclopentadiene Filled Microcapsules for Self-Healing Composite Materials

Self-healing composite materials possess healing agent which fills up the crack when ruptured and heals the crack by becoming a tough polymer when stimulated by a catalyst. Dicyclopentadiene (DCPD) in its monomer form is microencapsulated in the shell of Urea Formaldehyde (UF) under different agitation rates to acquire microcapsules of different diameters. The distribution of particle size, surface morphology and the presence of various chemical constituents in the microcapsules were analysed using optical microscopy, SEM and EDAX respectively. An agitation rate of 300 rpm, yielded capsules of diameters ranging from 800μm to 1700μm and at 900rpm the diameters were less than 300μm. Spherical shaped free flowing microcapsules were obtained through insitu polymerisation of dicyclopentadiene in Urea Formaldehyde.

Development of Composites with a Self-Healing Function

This research aimed to realize experimentally the facilevascular self-healing system in epoxy glass fibre reinforced composite. Using flexiblepolytetrafluoroethylene tubes as removable preforms, the channels were embeddedinto both neat epoxy resin and unidirectional glass-fibre reinforced epoxy laminate.Room temperature curable epoxy resin with a surfactant and an amine-basedhardener were the components of the binary healing agent. The specimens oftapered double cantilever beam geometry were subjected to Mode I fracture tests.Fracture of specimens released the healing agent from channels and triggeredself-healing process of the crack. Tested neat epoxy resin specimensdemonstrated recovery of fracture toughness ca. 70 % after 24 h of self-healingat 50°C. Unidirectional laminate specimens (250×23×1.2 mm) were made by vacuuminfusion method from two layers of glass yarns with 5 embedded channels aligningto reinforcing fibers. The channels were alternately filled with components of thehealing agent and then sealed. It was revealed that the embedded vascularchannels in specimens had very little effect on their elastic modulus. Theexperimental program included multiple three-point bending tests of specimensfor their initial damage and self-healing of specimens during their heat treatmentand following exposure at room temperature. Static and dynamic flexural moduli ofelasticity were determined by three-point bending and cantilever beam vibrationat all stages of the test program. The healing efficiency was evaluated as a relativechange of elastic modulus. The efficiency ca. 30 % was reached during 24 h at50°C and additionally increased up ca. 40 % after more than 3 weeks of roomtemperature exposure. The sealed healing agent was capable of maintaining thecapacity for self-healing for at least six months. The research resultsdemonstrated capacity of the macro-channel approach for self-healing realizationin multifunctional polymer composite materials. DOI: http://dx.doi.org/10.5755/j01.ms.21.1.5354

Highly flexible transparent self-healing composite based on electrospun core-shell nanofibers produced by coaxial electrospinning for anti-corrosion and electrical insulation.

Coaxial electrospinning was used to fabricate two types of core-shell fibers: the first type with liquid resin monomer in the core and polyacrylonitrile in the shell, and the second type with liquid curing agent in the core and polyacrylonitrile in the shell. These two types of core-shell fibers were mutually entangled and embedded into two flexible transparent matrices thus forming transparent flexible self-healing composite materials. Such materials could be formed before only using emulsion electrospinning, rather than coaxial electrospinning. The self-healing properties of such materials are associated with release of healing agents (resin monomer and cure) from nanofiber cores in damaged locations with the subsequent polymerization reaction filing the micro-crack with polydimethylsiloxane. Transparency of these materials is measured and the anti-corrosive protection provided by them is demonstrated in electrochemical experiments.

The Self-Healing Capability of Carbon Fibre Composite Structures Subjected to Hypervelocity Impacts Simulating Orbital Space Debris

The presence in the space of micrometeoroids and orbital debris, particularly in the lower earth orbit, presents a continuous hazard to orbiting satellites, spacecrafts, and the international space station. Space debris includes all nonfunctional, man-made objects and fragments. As the population of debris continues to grow, the probability of collisions that could lead to potential damage will consequently increase. This work addresses a short review of the space debris “challenge” and reports on our recent results obtained on the application of self-healing composite materials on impacted composite structures used in space. Self healing materials were blends of microcapsules containing mainly various combinations of a 5-ethylidene-2-norbornene (5E2N) and dicyclopentadiene (DCPD) monomers, reacted with ruthenium Grubbs' catalyst. The self healing materials were then mixed with a resin epoxy and single-walled carbon nanotubes (SWNTs) using vacuum centrifuging technique. The obtained nanocomposites were infused into the layers of woven carbon fibers reinforced polymer (CFRP). The CFRP specimens were then subjected to hypervelocity impact conditions—prevailing in the space environment—using a home-made implosion-driven hypervelocity launcher. The different self-healing capabilities were determined and the SWNT contribution was discussed with respect to the experimental parameters.