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Self-healing polymeric materials: A review of recent developments
Abstract
The development and characterization of self-healing synthetic polymeric materials have been inspired by biological systems in which damage triggers an autonomic healing response. This is an emerging and fascinating area of research that could significantly extend the working life and safety of the polymeric components for a broad range of applications. An overview of various self-healing concepts for polymeric materials published over the last 15 years is presented in this paper. Fracture mechanics of polymeric materials and traditional methods of repairing damages in these materials are described to provide context for the topic. This paper also examines the different approaches proposed to prepare and characterize the self-healing systems, the different methods for evaluating self-healing efficiencies, and the applicability of these concepts to composites and structural components. Finally, the challenges and future research opportunities are highlighted.
... Burada R, σ, ε, E ve I sırasıyla kırılma gerilmesi, kopma uzaması, kırılma enerjisi ve moleküler parametrelere ilişkin geri kazanım oranlarını ifade etmektedir [17]. ...
... Potansiyel bir avantaj sağlayan tersinir sistemler, malzemenin geri dönüşümüne izin verir. Bu durum tersinir sistemlerin araştırılmasında artan bir ilgiye dönüşmüştür [17]. ...
... Termosetlerden termoplastiklere ve elastomerlere kadar tüm polimer sınıfları kendi kendine iyileşme potansiyeline sahiptir. Termoplastik ve termoset malzemelerin kendi kendini iyileştirmesi için hem moleküler hem de yapısal yaklaşımların araştırıldığı, ancak araştırma ilgisinin son yıllarda termoset bazlı sistemlere kaydığı görülmektedir [17]. ...
Sevgili okuyucular, Hayatta kullandığımız her ürün bir malzemeden üretilmekte ve günümüz teknolojileri ile birlikte kompozit malzemeler hayatımızda önemli bir yer tutmaktadır. Bu kitap, kompozit alanındaki bilimsel çalışmaları farklı mühendislik perspektiflerinden incelemektedir. Kompozit malzemeler üzerinde çeşitli malzemeler kullanarak yeni ürünler ve yenilikçi teknolojiler geliştirmek ve sürdürülebilir çözümler sağlamak için bu çalışmaları farklı mühendislik yaklaşımlarıyla incelemek önemlidir ve bu kitapta kompozit malzemeler bu bakış açısıyla incelenmiştir. Okuyucular, günümüzde kompozit alanında yapılan çeşitli çalışmalara erişebilecekler. Kitapta ayrıca farklı matris ve takviye elemanları kullanılarak polimer, seramik ve elastomer matrisli kompozit malzemeler üzerinde yapılan çalışmalar hakkında bilgiler yer almaktadır. Bu kitap akademisyenler, mühendisler, araştırmacılar ve öğrenciler için bir kaynak olarak tasarlanmıştır. İleride kompozit malzemeler üzerine yapacağınız araştırma ve çalışmalara büyük fayda sağlayacağına inanıyorum. Saygılarımla.
... Burada R, σ, ε, E ve I sırasıyla kırılma gerilmesi, kopma uzaması, kırılma enerjisi ve moleküler parametrelere ilişkin geri kazanım oranlarını ifade etmektedir [17]. ...
... Potansiyel bir avantaj sağlayan tersinir sistemler, malzemenin geri dönüşümüne izin verir. Bu durum tersinir sistemlerin araştırılmasında artan bir ilgiye dönüşmüştür [17]. ...
... Termosetlerden termoplastiklere ve elastomerlere kadar tüm polimer sınıfları kendi kendine iyileşme potansiyeline sahiptir. Termoplastik ve termoset malzemelerin kendi kendini iyileştirmesi için hem moleküler hem de yapısal yaklaşımların araştırıldığı, ancak araştırma ilgisinin son yıllarda termoset bazlı sistemlere kaydığı görülmektedir [17]. ...
Sevgili okuyucular, Hayatta kullandığımız her ürün bir malzemeden üretilmekte ve günümüz teknolojileri ile birlikte kompozit malzemeler hayatımızda önemli bir yer tutmaktadır. Bu kitap, kompozit alanındaki bilimsel çalışmaları farklı mühendislik perspektiflerinden incelemektedir. Kompozit malzemeler üzerinde çeşitli malzemeler kullanarak yeni ürünler ve yenilikçi teknolojiler geliştirmek ve sürdürülebilir çözümler sağlamak için bu çalışmaları farklı mühendislik yaklaşımlarıyla incelemek önemlidir ve bu kitapta kompozit malzemeler bu bakış açısıyla incelenmiştir. Okuyucular, günümüzde kompozit alanında yapılan çeşitli çalışmalara erişebilecekler. Kitapta ayrıca farklı matris ve takviye elemanları kullanılarak polimer, seramik ve elastomer matrisli kompozit malzemeler üzerinde yapılan çalışmalar hakkında bilgiler yer almaktadır. Bu kitap akademisyenler, mühendisler, araştırmacılar ve öğrenciler için bir kaynak olarak tasarlanmıştır. İleride kompozit malzemeler üzerine yapacağınız araştırma ve çalışmalara büyük fayda sağlayacağına inanıyorum. Saygılarımla.
... Reproduced with permission. [9] Copyright 2008, Elsevier. d) Recombination of reversible dynamic interactions during healing of intrinsic self-healing polymers. ...
... [ self-healing in service. [9,34] The following subsections report on experimental efforts to identify promising polymer chains that meet these criteria, including polydimethylsiloxane, polybutadiene, and poly(vinylidene fluoride-co-hexafluoropropylene). ...
... [67] Compared to PDMS and PB chains, the T g value of PVDF-co-HFP is relatively higher (≈ −10°C), implying a longer time scale is required for autonomous self-healing at room temperature according to the time-temperature equivalence principle. [9] To overcome this, plasticizers are often used in the PVDF-co-HFP system to increase chain mobility for efficient and fast self-healing performance. Wang and his team proposed the first example, incorporating hydrophobic dibutyl phthalate (DBP) plasticizers into the PVDF-co-HFP matrix. ...
Polymeric materials capable of spontaneously healing physical damages and restoring various functions have been attracting growing interest. Among these, the category of water‐insensitive self‐healing materials emerges as a promising research focus due to their reliable self‐healing and stable mechanical properties in high‐humidity environments and even underwater. In this review, an update on the significant advancements in the design of water‐insensitive self‐healing polymers is presented, which are based on various unique chains. Their advantages and limitations are discussed. Additionally, a series of typical dynamic interactions that are used to enable autonomous self‐healing in underwater environments is highlighted. Moving beyond these fundamental designs, the diverse opportunities to leverage recent synthetic advancements in water‐insensitive self‐healing materials for the progression of soft electronic applications are systematically discussed. Ultimately, the significant challenges and remaining opportunities to present a comprehensive view of the future development of water‐insensitive self‐healing materials are highlighted. This review aims to stimulate further innovation in this burgeoning and emerging field of intrinsic healable materials, interfacing with dynamic chemistry and soft electronics.
... Figure 11 illustrates the textiles used in the facades of the Muhammad Ali Center MAC in Kentucky, USA, designed by Beyer Belle in 2005, which contributed to improving its surrounding environment and reducing pollution levels [18] (Figs. 11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26, 27,28). ...
... In the basement and ground floor, there are administrative areas, workshops, and spatial laboratories. The first floor houses all the lecture halls, classrooms, and laboratories for the preparatory level [22]. The second and third floors accommodate the educational spaces for the Civil Engineering and Electronic Engineering departments, respectively. ...
Considering the significant growth of the global population, several severe issues have emerged, including pollution, economic challenges, and environmental problems. To tackle these ecological issues, many construction experts are actively seeking new flexible techniques. Among these, Nano-technology stands out as a crucial field aiming to enhance the efficiency of the built environment and play a vital role in addressing future challenges. This study aims to examine the effectiveness of integrating Nano-technology techniques in construction to harness the acquired properties of materials and their impact on the interior thermal environment. The paper is divided into three main parts, each providing a detailed and scientific depiction of the study. The first part begins by shedding light on the concept of sustainability in architecture and the evaluation of sustainable buildings. Additionally, it explores the definition of Nano-technology and its substantial impact on the field of architecture by discussing various architectural terms associated with Nano-technology. The emergence of Nano-architecture is seen as a significant advancement in scientific research, representing a fusion between architecture and Nano-technology. Moving on to the second part of the thesis, it focuses on how Nano-technology techniques influence the work of architects. Nowadays, architects consider the properties of construction materials, construction methods, and energy consumption. These factors are essential in achieving an ideal design that is defined as sustainable. The second part also examines the effect of Nano-technology on the thermal environment, analyzing both national and international projects that have implemented this technique.
... Though the planning of the intervention for many historical structures is significant the execution area still lacks. This is due to improper evaluation of the site; lack of resilience in our restoration materials, incapability of repairs to regulate more deterioration and an absence of lucrative placement technologies [3,5]. This is well-curtained that the efficiency of mortar repairs depends on the quality and behaviour of the interface between the repair material and the substrate material in existing structures. ...
... This is well-curtained that the efficiency of mortar repairs depends on the quality and behaviour of the interface between the repair material and the substrate material in existing structures. Therefore, the researchers are significantly working on the reparation materials to understand their behaviours to carry out restoration and repair [4,5]. Though the literature shows that the basic techniques and materials of masonry have remained untouched through the ages still there exists a dilemma in employing proper methods to repair them [6]. ...
Masonry infrastructure repair is a daunting challenge. The short intervention and limited resources have led to the loss of novel rendering and finishing materials. In the present study, the bibliometric analysis is conducted for period 2003 to 2022. Co-cited reference analysis, keywords, cluster, and temporal evolution were used for analysis using Citespace software. Additionally, summary of suitable content showed that major challenges in this field are disparities in the properties of old mortar and new materials and the lack of documents to understand nature and methodology of construction. Based on the analysis and content review, a suggestive technique is proposed inculcating four aspects: Finite element analysis, preparing numerical models, improvised techniques for bonding mechanisms and understanding mechanical attributes.
... The damage and destroying are natural consequences of the application of materials. Engineering research is focused mostly on the development of more stable and advantageous materials [4]. ...
... Each of these types differs according to the mechanism used -i.e. isolation and detention of healing agent to the moment of demolition [4]. ...
... Wu et al. [21] defined healing as when two identical materials are above the glass transition temperature, the contact interface gradually disappears, and the crack healing caused by molecular diffusion at the interface will increase the mechanical strength at the interface. The definition explicitly points out one of the essential conditions for healing-temperature, which must be higher than the material's glass transition temperature. ...
... Wu et al. [21] defined healing as when two identical materials are above the glass transition temperature, the contact interface gradually disappears, and the crack healing caused by molecular diffusion at the interface will increase the mechanical strength at the interface. The definition explicitly points out one of the essential conditions for healingtemperature, which must be higher than the material's glass transition temperature. ...
In order to study the self-healing performance of macroscopic fractures of asphalt mixtures, semicircular bending (SCB) tests were used to test 90# base asphalt mixtures, SBS (Styrene–Butadiene–Styrene) modified asphalt mixtures, and SBS + CR (Chloroprene Rubber) composite modified asphalt mixtures. The F-H-F (the asphalt mixture specimen was fatigued for a certain number of times, then healed under certain conditions, and then fatigued until destroyed) test was carried out, and the fatigue life recovery rate of the fatigue test before and after healing was defined as the healing index (HI). The gray correlation analysis method was used to judge the influence degree of influencing factors on fatigue–healing according to the correlation index. The results show the type of asphalt has the most significant influence on the healing ability of the asphalt mixture. In the case of complete healing, the fatigue–healing performance of the SBS + CR composite modified asphalt mixture was the best, followed by the SBS-modified asphalt mixture, and 90# base asphalt. When the healing temperature is close to the softening point of asphalt, the healing performance of 90# base asphalt is better when the healing temperature is low. When the healing time is longer, the healing performance is better, and there is an optimal healing time. The healing index decreased with the increase in the degree of damage. When the degree of damage is too large, the asphalt mixture will be difficult to heal.
... However, there is not a real repair without reactivating and re-establishing the material continuity. In fact, the self-healing effect refers to the ability of the material to be repaired automatically or by external stimuli after being damaged or cracked [9,10]. In this light, the addition of self-healing functionality through the addition of suitable SH materials is essential to complete the repairing action. ...
... PUF/DCPD plays the role of a healing agent, and the healing efficiency seems to have a great amount of around 0.5 wt% of microcapsule content. 9. Micrographs make it possible to distinguish the presence and breakage of the microcapsules and the repair action of broken cells. ...
In this study, Polyurea/Formaldehyde (PUF) microcapsules containing Dicyclopentadiene (DCPD) as a healing substance were fabricated in situ and mixed at relatively low concentrations (<2 wt%) with a thermosetting polyurethane (PU) foam used in turn as the core of a sandwich structure. The shape memory (SM) effect depended on the combination of the behavior of the PU foam core and the shape memory polymer composite (SMPC) laminate skins. SMPC laminates were manufactured by moulding commercial carbon fiber-reinforced (CFR) prepregs with a SM polymer interlayer. At first, PU foam samples, with and without microcapsules, were mechanically tested. After, PU foam was inserted into the SMPC sandwich structure. Damage tests were carried out by compression and bending to deform and break the PU foam cells, and then assess the structure selfhealing (SH) and recovery capabilities. Both SM and SH responses were rapid and thermally activated (120 ◦C). The CFR-SMPC skins and the PU foam core enable the sandwich to exhibit excellent SM properties with a shape recovery ratio up to 99% (initial configuration recovery). Moreover, the integration of microcapsules (0.5 wt%) enables SH functionality with a structural restoration up to 98%. This simple process makes this sandwich structure ideal for different industrial applications
... The rapid initial self-healing process is attributed to the elastic recovery of the supramolecular elastomer near the damaged area. However, it is followed by a slower electrical recovery (after 40 h), which may be due to surface rearrangement and diffusion of the polymer chains 31,32 . For the narrower damage width at 1 μm, the resistance was initially reduced to the 10 2 Ω level and fully recovered to its initial value after 24 h. ...
Skin-like field-effect transistors are key elements of bio-integrated devices for future user-interactive electronic-skin applications. Despite recent rapid developments in skin-like stretchable transistors, imparting self-healing ability while maintaining necessary electrical performance to these transistors remains a challenge. Herein, we describe a stretchable polymer transistor capable of autonomous self-healing. The active material consists of a blend of an electrically insulating supramolecular polymer with either semiconducting polymers or vapor-deposited metal nanoclusters. A key feature is to employ the same supramolecular self-healing polymer matrix for all active layers, i.e., conductor/semiconductor/dielectric layers, in the skin-like transistor. This provides adhesion and intimate contact between layers, which facilitates effective charge injection and transport under strain after self-healing. Finally, we fabricate skin-like self-healing circuits, including NAND and NOR gates and inverters, both of which are critical components of arithmetic logic units. This work greatly advances practical self-healing skin electronics.
... Calculations of healing efficiency manifest variations in material properties such as fracture toughness (K IC ), strength ( X ), strain energy (U), stiffness (k), and Young's modulus (E). [78][79][80] Often, for ease of measurement and comparison, researchers evaluate Young's modulus. This fundamental property determines the stiffness of materials and their resistance to deformation under external stress. ...
This review addresses the self‐healing effects in perovskite solar cells (PSCs), emphasizing the significance of chemical and physical bonding as core mechanisms. Polymeric additives play a vital role in inducing self‐healing phenomena along with the intrinsic properties of perovskite materials, both of which are discussed herein. As a relatively underexplored area, the self‐healing effect induced by polymeric additives in PSCs is reviewed from a chemical perspective. The chemical bonds involved in self‐healing include isocyanate, disulfide, and carboxylic acid groups. The physical bonds related to self‐healing effects are primarily hydrogen bonding and chelation. Self‐healing in flexible perovskite devices extends their lifespan and improves their mechanical robustness against environmental and mechanical stressors. This discussion delves into the initiation methods for self‐healing, the conditions required, and the recovery‐rate profiles. This review not only catalogs various approaches to self‐healing, but also considers the fundamental limitations and potential of this phenomenon in PSCs. In addition, insights and an outlook on self‐healing in perovskite‐based optoelectronics are provided, offering guidance for future research and applications.
... [35][36][37][38] Self-healing polymers (SHPs) are representative examples of ''smart'' materials that can repair cracks or fractures by themselves. [39][40][41][42][43][44][45] The most important advantages of using light to trigger molecular processes inside materials are that remote activation is easily doable since light can travel a long distance; spatially controlled activation is possible as the light beam (often a laser) can be delivered to selected areas; and lighttriggered processes can be halted and resumed ''on-demand'' by turning off or turning on the excitation light. ...
Smart materials with dual functionalities demonstrate considerable potential in various applications. Designing and synthesizing hydrogels with excellent stimuli‐responsive self‐healing and high mechanical strength is extremely challenging. The present study initiates the development of a new generation of smart materials with selective superadsorption capacity. Here, we introduce a novel anthracene‐modified poly (amido amine) (PAMAM)‐N‐isopropyl acrylamide hydrogel (PAMNG). The hydrogel becomes hybrid as we incorporate the silica nanoparticle. PAMAM dendrimer‐based organic/inorganic hybrid silica nanoparticles (PAMAGN) have been characterized using nuclear magnetic resonance (NMR), Fourier‐transform infrared spectroscopy (FT‐IR), scanning electron microscopy (SEM), transmission electrone microscopy (TEM) and rheology. The developed hybrid gel exhibited excellent near‐infrared (IR) responsive self‐healing character. The hybrid gel had excellent mechanical strength, which was as high as 10⁶ Pa. Further, the gel was used for superadsorption studies and showed selective adsorption of methyl orange from water. The adsorption was 96 %, which is remarkable. The results taken together suggest that the PMNG gel can be a promising candidate for developing multifunctional smart materials. In the future, we aim to explore how this self‐healing mechanism applies to biological applications.
... Intrinsic materials do not require any intervention and the healing is based on forming chemical bonds and physical interactions between damage ends, whereas extrinsic selfrepair needs external recovery agents. A typical example of this process is the addition of microcapsules containing healing agents with a catalyst in matrix polymers (van der Zwaag 2007, Carvalho et al. 2019, Rodrigues et al. 2019, Carrara et al. 2023, which causes microcapsules to rupture when suffering damage events and consequent release of healing agent, in turn advancing to completely or partially seal damage, as illustrated in Figure 1 (Dry et al. 1992, Brown et al. 2002, Wu et al. 2008. ...
This study describes a methodology to prepare and characterize PUF [poly(urea formaldehyde)] microcapsules containing 5-ethylidene-2-norbornene (ENB) as self-healing agent, as well as the compatibility evaluation of ENB in the presence of Grubb's catalyst with an epoxy matrix. First, the results of an adhesion assay by lap shear proved chemical compatibility between the epoxy matrix and self-healing agent in the presence of Grubb's catalyst. After evaluating the chemical compatibility, microcapsules with ENB were synthesized in an oil-in-water emulsion system. Thereafter, the microcapsules were morphologically, chemically and thermally characterized in which a granulometric dispersion between 30-140 μm and an average size of 69.8 ± 4.9 μm were observed. The SEM (scanning electron microscope) results showed that the average thickness of microcapsules shell was 3.6 ± 0.4 μm. The thermogravimetric analysis (TGA) showed that microcapsules are susceptible to rupture and consequent ENB release in temperatures greater than 230 °C, demonstrating that microcapsules are suitable for applications in materials with self-healing capacity.
... The rapid initial selfhealing process is attributed to the elastic recovery of the supramolecular elastomer near the damaged area. However, it is followed by a slower electrical recovery (after 40 h), which may be due to surface rearrangement and diffusion of the polymer chains 32,33 . For the narrower damage width at 1 µm, the resistance was initially reduced to the 10 2 Ω level and fully recovered to its initial value after 24 h. ...
Skin-like field-effect transistors are key elements of bio-integrated devices for future user-interactive electronic-skin applications. Despite recent rapid developments in skin-like stretchable transistors, imparting self-healing ability while maintaining necessary electrical performance to these transistors remains a challenge. Herein, we describe a stretchable polymer transistor capable of autonomous self-healing. The active material consists of a blend of an electrically insulating supramolecular polymer with either semiconducting polymers or vapor-deposited metal nanoclusters. A key feature is to employ the same supramolecular self-healing polymer matrix for all active layers, i.e., conductor/semiconductor/dielectric layers, in the skin-like transistor. This provides adhesion and intimate contact between layers, which facilitates effective charge injection and transport under strain after self-healing. Finally, we fabricate skin-like self-healing circuits, including NAND and NOR gates and inverters, both of which are critical components of arithmetic logic units. This work greatly advances practical self-healing skin electronics.
... The specific approach employed during this stage may differ, depending on the chosen healing mechanism, to facilitate the repair process. Three different categories of self-healing materials can be made: intrinsic, vascular, and capsule-based [8]. ...
The present work provides a comprehensive discussion on various factors that need to be considered when utilizing smart polymer coatings. The term "smart coating" refers to coatings that possess the ability to sense their environment and respond accordingly to external stimuli. Significant efforts have been made towards the development of multifunctional coatings capable of detecting corrosion, pressure, and temperature. We explored the application and limitations of self-healing principles in polymer coatings. Furthermore, this chapter delves into the extensive range of current approaches and technologies encompassing antibacterial polymer coatings and the utilization of low molecular weight antibacterial agents. Additionally, an overview is presented regarding a novel approach that incorporates diverse catalytic mechanisms for decontamination, which are employed in self-cleaning coatings. Lastly, the concentration and spectral distribution of optical sources can be effectively controlled through the implementation of optical components and filtering optical projection systems, which encompass filters, mirrors, lenses, and optical fibers.
... The ability to inherently repair damage without external intervention has gained significant interest in the scientific community, resulting in an emerging class of smart materials with higher endurance limits and prolonged service-life through self-healing functionalities [1][2][3][4]. Functional polymers and fillers present several advantages for producing self-healing nanocomposites due to their ease of processability and wide range of combinations available in the material design space, enabling simultaneous tailoring of application-specific properties (e.g., mechanical, thermal, and electrical properties) as well as responses to different external stimuli, such as heat, light, or electricity, to activate self-healing mechanisms. For instance, the incorporation of conductive nanofillers in thermoplastic matrices has been reported as a common approach for introducing selfhealing functionality, as the formation of interconnected pathways of randomly dispersed C 2023, 9,111 2 of 19 filler material introduces a percolation network that provides resistive heat generation upon passage of an electric current [5][6][7]. ...
In the present study, a series of carbon-based nanocomposites based on recycled thermoplastic polyurethane (TPU) matrix and MWCNT fillers synthesized in a laboratory environment were prepared at various loadings and assessed in terms of their functional thermal, dielectric, and rheological properties, as well as their ohmic heating capability, for self-healing applications in extrusion-based 3D printing technologies. The synthesis of nanomaterials focused on the production of two different types of carbon nanotubes (CNTs) via the chemical vapor deposition (CVD) method. A comparative assessment and benchmarking were conducted with nanocomposite filaments obtained from commercial nanomaterials and masterbatches with MWCNTs. For all the polymer nanocomposites, samples were prepared at additive contents up to 15 wt.% and filament feedstock was produced via the melt-extrusion process for 3D printing; these were previously characterized by rheological tests. The measurements of thermal and electrical conductivity resulted in a selected composition with promising ohmic heating capability. As a preliminary assessment of the self-healing ability of the above samples, artificial cracks were introduced on the surface of the samples and SEM analysis took place at the crack location before and after applying voltage as a measure of the effectiveness of the material remelting due to the Joule effect. Results indicate a promising material response with a partial restoration of artificial cracks.
... Nanoparticles have the possibility to modify the asphalt mixture at the molecular level, with a high self-healing capacity [17][18][19][20]. Self-healing by nanoparticles has been described by stretching and extending of the polymer chains near to the nanoparticles [21]. To understand the properties of nanoparticles in asphalt pavement, scientists incorporate nanomaterials in deferent applications, to improve rheological, fatigue and aging performances of asphalt. ...
Ageing and cracking are the main failure forms of the distresses in asphalt
pavements. These issues occur due to the impact of factors such as heavy traffic
and weather. Asphalt pavement is a self-healing material that can fix itself because it has the ability to restore its properties by closing micro-cracks. To make
asphalt roads better at fixing themselves, numerous successful technologies are
investigated. One of these techniques is called microencapsulation which represents nowadays a promising approach that could help make asphalt pavement
last longer. In general, self-healing microcapsules will be incorporated into asphalt pavements before they are activated to release the rejuvenator, requiring
them to be stable for years. Thereby, excessive thermal and mechanical properties
in terms of asphalt pavements are necessary, because of how they are mixed and
compacted. This paper aims to present an overview of new research on microencapsulation technologies, focusing on the durability of microcapsules embedded
in asphalt pavement. Furthermore, some recommendations of future solutions to
improve the mechanical stability of microcapsules will be proposed.
... Blends prepared by melt mixing of ENR and Na/Zn-ionomers showed good selfhealing efficiency. 17,18 Thermal and structural analysis exhibited that both the functionalities of ENR and the ion content of ionomer have a marked impact on the self-mending behavior of the blends. The interaction of a rubbery phase with the ionomer phase and the mobility of the rubbery phase were considered as factors to change the healing abilities of materials. ...
We report the development of novel self‐healing binary thermoplastic elastomeric blends of Zn²⁺‐neutralized poly[ethylene‐co‐(methacrylic acid)] (Zn‐ionomer) and styrene–butadiene–styrene block copolymer (SBS). Zn‐ionomer/SBS blends were prepared by the melt‐blending technique using a twin‐screw extruder with three mass ratios of 75/25, 50/50 and 25/75. Structure, phase morphology and thermal as well as tensile properties of the samples were characterized. Fourier transform infrared spectroscopy results indicated the presence of two types of polymeric materials and their interactions. Scanning electron microscopy images confirmed the miscibility of blend components which remarkably influenced the properties of the blends. The optimum peak degradation temperature of Zn‐ionomer/SBS (75/25 wt%) blend was observed to be 484 °C. The ratio of the tensile strength of the healed specimens to that of the original specimens was implemented to quantitatively evaluate the self‐healing efficiency of the materials. The self‐healing efficiencies were calculated to be 55.42%, 58.36% and 60.75% for Zn‐ionomer samples healed for 4, 8 and 16 h, respectively. All of the blend samples exhibited self‐healing behavior and the self‐healing efficiency was more than that of virgin Zn‐ionomer which may be credited to the high mobility of SBS segments in the blends. The healing efficiency was increased with an increase of SBS content in the blends and also heat energy facilitated the healing process. The self‐healing efficiencies of Zn‐ionomer/SBS (25/75 wt%) blend sample were calculated to be 75.09%, 80.27% and 80.87%, respectively, for 4, 8 and 16 h of healing time at 100 °C. A comparison of optical micrographs of the cut area of samples (before healing and after the healing process) was also made and self‐healing of the blend materials was observed. © 2023 Society of Industrial Chemistry.
... They recommended that nanoparticles are better than larger particles for healing because they diffuse faster than the larger ones. (Wu et al., 2008). ...
... Self-healing ability of materials has been a promising approach to overcome this issue and many researchers have reported various self-healing techniques by incorporating them into the polymer systems to show healing abilities [11][12][13][14][15][16]. The self-healing method mimics biological systems by varying extents to incorporate healing ability into the system. ...
Self-healing polymeric materials has created an extensive interest among researchers due to their autonomic healing ability and potential applications in wide range of industries. Herein, we report an intrinsic self-healing method, by using a novel isocyanate based self-healing curator for polyurethane formation which exhibits excellent self-healing capability via disulfide metathesis. Exchange of disulfide bonds between polymeric chains at the damaged area leads to self-healing. Density Functional Theory [DFT/B3LYP/6-311++G (d, p)] calculations were done to examine the optimized molecular geometry, vibrational frequencies, 1H and 13C NMR chemical shifts, HOMO–LUMO energies and molecular electrostatic potential (MEP) map of the compound. The theoretical results were also closely matched with the experimental data. The concept of self-healing-cum-curing agent in polyurethane matrix has not been explored so far.
... Besides, it can also detect the presence of reversible bonds in rubber systems because the breakage of these dynamic bonds requires energy which shows an endothermic peak in the DSC curves. 122 Many researchers have involved DSC analysis in their studies to investigate the thermal behaviour of self-healing rubbers, especially those with intrinsic self-healing systems 56,70,123 This is because the reversibility of this system allows the material to heal under repeated cycles, allowing the material to be heated and cooled repeatedly during DSC analysis to analyse the thermal behaviour of the material. 124 For instance, Jia et al. 70 used DSC to monitor the Diels-Alder (DA) chemistry in the self-healable EPDM/silica composites. ...
The emerging self-healing concept in rubber materials appears to be a good option for reducing rubber waste since it can enhance the longevity of the product's structure in conjunction with standard development goals to ensure sustainable consumption and efficient use of resources. Self-healing elastomers are fabricated to heal cracks and damage both at the micro and macroscopic levels to restrict failure by incorporating healing agents extrinsically or intrinsically. The major successful techniques to fabricate self-healing rubber were reviewed. The review also focuses on testing and analysis methods to understand the healing phenomena and quantification methods to measure the healing performance. The review also includes an overview of the self-healing elastomers for tyre applications.
... However, conventional rubber vulcanization is non-reversible cross-linking, where the rubber network chains are neither dissolved nor melted the vulcanization of traditional rubber is irreversible crosslinking, and the rubber network chain is insoluble and infusible. Once the rubber structure is destroyed, it cannot be reused, which limits its service life [1][2][3][4][5]. Not only that, once the rubber is scrapped, its using value will be lost, and subsequent processing is also very difficult, and it is difficult to recycle and reuse. ...
As the second largest synthetic rubber after styrene butadiene rubber, cis-butadiene rubber (BR) is one of the important raw materials for automobile tires and cold-resistant products. Herein, a traditional rubber preparation process was used to introduce dynamic reversible bonds into BR based on an “imitative” click reaction. Compared with traditional complex self-healing techniques, this method is undoubtedly simpler and more efficient. Dynamic reversible bonds are able to break and recombine under the stimulation of external conditions, which endow rubber with self-healing properties. We use the small biological molecule lipoic acid (LA) as a cross-linking agent and cross-link LA and BR through mechanical compounding and hot press vulcanization to obtain self-healing butadiene rubber (BLA). In addition, BLA-(Zn ²⁺ ) was further prepared by introducing Zn ²⁺ to form metal-oxygen coordination bonds with carboxyl groups. And systematically studied the effect of Zn ²⁺ on the mechanical properties and self-healing properties of cross-linked BR. Through the combined action of disulfide bonds, hydrogen bonds and Zn ²⁺ -O coordination bonds, BLA-(Zn ²⁺ ) has better properties than BLA, the tensile strength can reach 3.76 MPa, and the repair efficiency is about 82 %. This simple preparation process is certainly more cost effective.
... This has motivated the development of artificial materials with healing functions to prolong their service life and reliability, which is important in fields of intelligent architecture, aerospace engineering, and the automotive industry. In contrast to the traditional recovery mechanism [53], selfassembly or migration of the PDMS-based polymer occurs after the coating is worn because of its low surface energy. Water contact angle (CA) was used to monitor the self-recovery of MEPC-W. ...
Protective materials are essential for personal, electronic, and military defenses owing to their efficient impact-resistant and energy-absorbing properties. Inspired by the bottom-up fabrication process and energy dissipation mechanism of natural organisms with hierarchical structures, we demonstrated a self-wrinkled photo-curing coating as a new protective material for enhancing the anti-impact property of the substrates. Owing to the self-assembly of polydimethylsiloxane (PDMS) containing polymeric photoinitiator on the surface, the liquid coating formulation was photo-cured by one-step UV irradiation with simultaneous generation of self-wrinkled surface morphology and a gradient cross-linked architecture. The maximum impact resistance height (hmax) of the glass substrate coated with plain coating increased from 120 to 180 cm when coated with wrinkled gradient coating. Furthermore, the Young's modulus, fracture stress, and toughness of the wrinkled gradient coating film improved from 39.6 MPa, 2.4 MPa, and 74.1 MJ/cm3 to 235.0 MPa (∼5× increase), 18.5 MPa (∼6.6× increase), and 845.0 MJ/cm3 (∼10.8× increase) compared to the pure coating film as reference. The theoretical simulation and experimental results proved that the surface self-wrinkled morphology and intrinsic hierarchical architecture contribute to the energy dissipation and impact resistance of the cured coating. The photo-curing process, a bottom-up strategy, is conducted in a non-contact mode compared with nano-printing and lithography, enabling bulk materials to be engineered.
The unique properties of hydroxyl-terminated polybutadiene (HTPB) make it suitable for use in various fields. Because it is impossible to use external factors to repair the damage caused by HTPB polymer in all places, it is very useful to create intrinsic self-healing properties. In this study, HTPB polymer became intrinsically self-healing during three stages of hydrobromination, amination, and the addition of 2-ureido-4-pyrimidinone groups. ATR and NMR analysis confirmed the formation of intermediates and the final self-healing compound. Also, DSC analysis showed that the glass transition temperature of the resin, which is its most important feature, has not changed. After self-healing HTPB was synthesized, this resin was mixed with isophorone diisocyanate and coated on a glass slide. The cured polyurethane coating was scratched, and an optical microscope monitored the healing process for 24 h. The corrosion test of metal plates confirmed the creation of self-healing properties in the resin. The places of scratches created on the control sample were rusted in the sodium chloride solution, while the plates with modified resin coating did not show this issue.
HTPB polymer becomes intrinsically self-healing during three stages of hydrobromination, amination, and the addition of 2-ureido-4-pyrimidinone groups. These groups have a great tendency to form hydrogen bonds and give intrinsic self-healing properties to the resin. Self-healing HTPB can repair damage without the need for an external agent.
Polymers incorporating double‐decker‐shaped phenyl‐substituted silsesquioxane (DDSQ) into the main chain are expected to exhibit excellent thermal stability and significantly reduced dynamics of the polymer segments. In this study, thiol‐ene polymerization at 25 °C for 5 min under 365 nm irradiation was applied for 3,13‐divinyl‐DDSQ ( E1 ) with oxybis(2,1‐ethanediyloxy‐2,1‐ethanediyl) bis(3‐sulfanylpropanoate) ( T1 ) as a bithiol monomer for linear and 2,2‐bis{[(3‐sulfanylpropanoyl)oxy]methyl}butyl 3‐sulfanylpropanoate ( T2 ) as a trithiol monomer for soluble cross‐linked poly(thioether)s. All the resulting poly(thioether)s yielded colorless and transparent films by casting tetrahydrofuran solutions onto glass substrates. These polymers showed a higher decomposition temperature of 5 wt% loss over 350 °C. The films exhibited glass transition temperatures below 25 °C. Scratch scars were made on the surface of the cast films, and the self‐healing behavior was observed after heating at 40 °C. These results suggest that the DDSQ unit suppresses the molecular motion of the polymers and contributes to their self‐healing behavior.
In lithium‐ion batteries, the polymer electrolyte was susceptible to mechanical damage from external stimuli or internal expansion caused, which in turn affected the performances of the batteries. The thermally reversible self‐healing gel polymer electrolyte (DASHPE) based on the Diels–Alder reaction was prepared to solve the above problems. The DASHPE electrolytes exhibited good flexibility and self‐healing ability, achieving self‐healing at 80°C for 30 min. Furthermore, the DASHPE electrolyte exhibited excellent thermal stability and could withstand temperatures above 300°C. Additionally, it had a wide electrochemical window (about 5 V) and good electrochemical performances. Serving as the electrolyte in lithium‐ion batteries, DASHPE‐2 showed an initial specific capacity of 133.11 mAh g ⁻¹ at 0.1 C. The DASHPE electrolyte was expected to be a candidate material for self‐healing battery.
This study compares the impact damage response and self-healing potential of unstitched and stitched glass/polypropylene (PP) fiber reinforced thermoset composite structures. The novelty of this study is weaving preforms with an intra-ply hybridization of glass and thermoplastic PP fibers and stitching these preforms with a unique stitching pattern by considering the effect of stitching fiber types (PP, Kevlar ® , Dyneema ® , carbon and silk) on impact damage response and self-healing potential of composites. The mechanical properties of the stitching fiber influenced the composite’s behavior against impact and compressive loads. The unstitched composite deflected more than stitched composites under the same impact energy levels due to delaying of delamination via stitching process. The stitching process reduced the damage areas of composites subjected to 30 J and 60 J impact energies by 57 and 86%, respectively. Structural healing significantly decreased the damaged areas of both unstitched and stitched composite structures up to 87%, while it was more effective on stitched composites. The polypropylene melted and accumulated along the path of the stitch pattern, regardless of whether the stitching fiber was thermoplastic. Due to the reduced impacted area, compression after impact (CAI) strength retention of the stitched composite materials increased by up to 94%.
PEMA [poly (ethylene-co-methacrylic acid)] ionomer is a cost-effective, commercially important class of random copolymer of ethylene and methacrylic acid (3–15 mol %) where 15–80% of the acid groups are neutralized to form metal salts. Such PEMA ionomers carry great potential for use in a wide variety of unique applications such as shape memory, packaging materials, compatibilizers, toughening agent, and effective water vapor barrier material in organic devices and photovoltaic applications. Besides, due to their ‘self-healing’ property after impact, these materials have attracted special attention to the material scientists and technologists for their use in armour applications. The potential of self-healing materials to enable them damage-tolerant and also the load-bearing capability are promising aspects to develop lightweight functional structures to meet aerospace application requirements. This review introduces the state-of-the-art discussion of such novel ionomeric materials and their applications, especially on self-healing and shape memory materials. Indeed, this review first enlightens a deep understanding of the fundamentals of this class of materials with its electrostatic interactions within such ionic polymeric materials as well as highlights their extended functional applications.
Solid composites used in material extrusion additive manufacturing have experienced considerable expansion over the past 5 years, incorporating functional properties into 3D‐printed objects. This paper presents a systematic review that aims to: (I) analyze the current state of development in the field; (II) quantify and categorize the adopted polymeric matrices, reinforcing materials, feedstock shapes, characterization strategies, and extrusion mechanisms; and (III) identify the applications, limitations, and trends for future research. The PRISMA statement was followed and the databases Scopus, Web of Science, and PubMed were consulted. Among the 116 included studies, the use of customized filaments surpassed the commercially available ones, with particulate matter being the most common form of filler when melt‐mixed with the polymer. Polyamide is the most widely adopted matrix (30.3%), followed by PLA (22.0%) and ABS (17.4%). In terms of reinforcements, carbon fiber (32.4%), glass fiber (12.5%), and ceramics (12.5%) compose the podium as the most frequently used, with nanofillers receiving increasing attention. In the conducted analysis, no standardized protocols were identified that clearly encompassed the entire process from feedstock formulation to technical prototype fabrication. At last, recycling, exploration of biodegradable materials, and 4D printing were identified as the main opportunities for future research.
Highlights
Reinforced polymers enable the enhancement of properties for 3D‐printed parts.
Composite feedstock is usually formulated and mixed before printing.
3D printers with filament‐ or screw‐based extrusion mechanisms have been used.
Mechanical and morphological analyses are common in material characterization.
No identified applications were employed in real‐world scenarios.
Hydrogen bonds facilitate self-healing of polymers. However, free and associated hydrogen bonds have different effects on mechanical properties and self-healing performance. Here, both unmodified nano-silica (nano-SiO2) and nano-SiO2 modified by...
“Self-healing” has emerged as a concept to increase the functional stability and durability of polymer materials in applications and thus to benefit the sustainability of polymer-based technologies. Recently, van der Waals (vdW)-driven “self-healing” of sequence-controlled acrylate-based copolymers due to “key-and-lock”- or “ring-and-lock”-type interactions has generated considerable interest as a viable route toward engineering polymers with “self-healing” ability. This contribution systematically evaluates the time, temperature, and composition dependence of the mechanical recovery of acrylate-based copolymer and homopolymer systems subject to cut-and-adhere testing. “Self-healing” in n-butyl acrylate/methyl methacrylate (BA/MMA)- or n-butyl acrylate/styrene (BA/Sty)-based copolymers with varying composition and sequence is found to correlate with the bulk viscoelastic properties of materials and to follow a similar trend as other tested acrylate-based homo- and copolymers. This suggests that “self-healing” in this class of materials is more related to the chain dynamics of bulk materials rather than composition- or sequence-dependent specific interactions.
Covalent adaptive networks (CANs) crosslinked with dynamic covalent bonds, particularly hindered urea bonds (HUBs) have gained significant efforts in the development of advanced materials exhibiting self-healability and reprocessability for various...
In materials science and engineering, self-healing polymers, a breakthrough class of materials with built-in abilities to automatically repair damage, are becoming increasingly important. The purpose of this in-depth review article is to present a thorough investigation of self-healing polymers, providing a complete understanding of their principles, development, uses, and prospects for the future. An overview of the fundamental theories and mechanisms of self-healing polymers opens the paper. It explores the contrast between intrinsic and extrinsic healing mechanisms, illuminating how these materials imitate the regeneration functions of nature. Self-healing polymers come in a variety of shapes and sizes depending on how they repair themselves. This review organises and clarifies the mechanisms, which include shape-memory polymers, vascular networks, supramolecular interactions, and microencapsulated systems. The distinct advantages of each type are thoroughly discussed. To give readers a complete picture of the state-of-the-art in this sector, recent developments and new trends in self-healing polymers are highlighted. The discussion emphasises the dynamic nature of this topic by highlighting current research orientations and intriguing areas for investigation. Self-healing polymers have numerous uses in a variety of fields, including aerospace, automotive, electronics, healthcare, and environmental protection. This review focuses on the influence on various areas of practical implementatioAlthough self-healing polymers have a lot of potential, they are also constrained. Some of the problems that need to be solved involve scalability, affordability, and long-term durability. In this context, we examine potential remedies and future research possibilities in great detail.
Click reactions, with remarkable merits including high efficiency, atom economy, mild reaction conditions, good functionality tolerance, simple isolation process, and regio‐ and/or stereoselectivity, have drawn intense attention of polymer chemists and found widespread applications in polymer synthesis. Besides the famous Cu(I)‐catalyzed azide–alkyne click reaction, plentiful click reactions, such as Diels–Alder, thiol‐based, nonaldol carbonyl, amino‐yne, hydroxyl–yne, and sulfur(VI) fluoride‐exchange click reactions, have also been introduced into the field of polymer chemistry. With these efficient click reactions in hand, diverse functional groups can be readily incorporated into polymer chains to endow them with desired functionalities. Copolymers with complex structures, such as block, graft, star, and cyclic polymers, can be synthesized using click reaction as polymer conjugation method. These click reactions have also been developed into facile polymerization techniques, that is, click polymerization, for the direct synthesis of linear, hyperbranched, and cross‐linked polymers with various properties. This article intends to give a brief summary of click reactions applied in polymer synthesis, including preparation of polymers and postpolymerization modification of preformed polymers.
Cracking, due to loading, is a major problem in materials durability because the cracks increase permeability. The sensing of cracking or corrosion of a settable material by a chemical or physical sensor which, in the process of sensing, starts the activation of a remedial process is the topic of this research. Specifically, materials containing various types of hollow porous fibers filled with a chemical which release into the matrix at appropriate times, or over time, are designed to address some issues of material brittleness and durability; i.e. cracking and corrosion.
Active smart electrorheological fluids in building materials are expensive,
need to be widely dispersed, and require large amounts of electricity. These
practical considerations led to the consideration of ways of having similar effects
in a matrix but using different materials. Tuneable fibers is an inexpensive
dispersed passive system, requiring no electricity. The modulus of elasticity of
a solid filled fibers is very different from a liquid or gas-filled fiber or a hollow
fiber. The ability to empty and fill fibers with a material which could change
phase in the fiber or in the matrix in response to some stimulus or signal from
the environment is promising. In the laboratory we have used filled fibers which
empty their contents into the matrix in response to a change in the environment.
In this case as a Bubstitute for ER fluid, a blast, vibration, or shaking motion
could release a catalyst from flexed fibers. It would cross-link with a resin either
in the porous fiber or in the matrix. Passive tuneable fibers could also be used
for nonbuilding applications such as radar evasion due to changing modulus
profile.
The subject of this research is the sensing of damage such as cracking or corrosion in a settable material by a chemical or physical sensor which, in the process of sensing, starts the activation of a remedial or prevention process. It is a distributed system in which sensing and actuation repair occur when and where they are needed. Materials containing various types of hollow fibers filled with a chemical which releases into the matrix at appropriate times, or over time, are designed to address some of the major issues of material performance.
The yielding and fracture behaviour of epoxy/glass microballoon composites has been studied as a function of filler content, temperature and strain rate. No increase in elastic modulus, yield stress and fracture toughness was observed. The compressive yield stress of the composites showed strain rate dependence with more than one rate-activated yielding process. The fracture toughness parameters Gc and Kc were found to be temperature insensitive. The variations in the measured mechanical quantities are discussed in terms of the observed morphology and thermal behaviour of the epoxy composites.
Repairing broken thermoset pieces is often carried out, although optimization of the technique may not have been achieved. A new way is investigated using a thermoset based on an unsaturated polyester resin allowing the final product to exhibit good mechanical properties. The procedure described here consists of two stages: putting some pure resin on the surface of the broken thermoset piece over a given a period of time, then putting this pre-treated piece in the mould with fresh uncured thermoset (made of pure resin with fibreglass and filler) necessary to fill the mould, and curing this system. The pre-treatment with the pure resin is made on the surface of the broken thermoset piece which will be in contact with the fresh uncured thermoset. The mechanical properties in elongation and flexion of the final material are measured. It appears that not only the diffusion of pure resin into the broken thermoset is responsible for an increase in these mechanical properties, but also that the time of diffusion is of interest, 24 h being better then 4 h. With a time of diffusion of 24 h, the mechanical properties are nearly similar to those obtained with the original non broken thermoset piece.
Incorporation of chemicals into the internal matrix of cement or concrete, with later release occurring upon stimulation, alters the matrix parameters from those at initial set. Permeability is reduced and therefore durability may be enhanced. The advantages of the designs are the ability to reduce maintenance and repair costs in the
initial building design and to delay the time of eventual repair. Also the components and the structure can take greater environmental abuse. Corrosion damage is reduced by the timed release of calcium nitrite near the rebars from hollow, porous fibers upon freezing. Permeability can be reduced by release of a polymer from wax-coated, porous fibers upon heating to temperature of polymerization. Freeze/thaw damage is reduced by the timed release of linseed oil or antifreeze due to the freezing action itself from porous aggregates. These three designs all gave superior durability performance when compared to conventional treatments for durability or environmental distress. Concerns that significant strength reduction would occur due to fiber loading were unfounded. An adequate amount of wetting could be obtained with 2.75% volume of fibers, above which the fibers do reduce the strength. The internal release of chemicals gave superior performance in reduction of permeability and freeze/thaw damage. Fiber filling, aggregate manufacture, storage, and placement need to be researched and assessed for cost. Design of components using only targeted areas for release as well as fiber reinforced cement laminates should be evaluated.
Methods for the fusion bonding repair of thermoplastic resin composites are discussed. Depending on the damage modes, thermoplastic resin composites may be repaired by welding on a patch or by thermal reforming. The merits and shortcomings of patching by fusion bonding are discussed and compared to those of adhesive patching. Resistance heating and induction heating with susceptors are considered to be suitable for patching type repair. The processing parameters and critical problems for the field repair application of these methods are investigated. Healing type repair, or thermal reforming, is based on the concept of crack healing of polymers. This technique is particularly interesting for repair of delamination. However, healing type repair requires relatively high pressure which can be achieved generally only at well equipped repair depots.
Inspired by biological systems, in which damage triggers an autonomous healing response, a polymer composite material that can heal itself when cracked has been developed. The material consists of an epoxy matrix composite, which utilizes embedded microcapsules to store a healing agent and an embedded catalyst. This paper investigates issues of fracture and fatigue consequential to the development and optimization of this new class of materials. When damage occurs, the propagating crack ruptures the microcapsules, which releases healing agent into the crack plane. Polymerization of the healing agent is triggered by contact with exposed catalyst, which bonds the crack faces closed. The efficiency of crack healing is defined as the ability of a healed sample to recover fracture toughness. Healing efficiencies of over 90% have been achieved. Embedded microcapsules significantly increase the fracture toughness and reduce the fatigue crack propagation rate of epoxy. Fracture mechanisms for neat epoxy and epoxy with embedded microcapsules are presented.
The general behavior of self-healing materials is modeled including both irreversible and healing processes. A constitutive model, based on a continuum thermodynamic framework, is proposed to predict the general response of self-healing materials. The self-healing materials’ response produces a reduction in size of microcracks and voids, opposite to damage. The constitutive model, developed in the mesoscale, is based on the proposed Continuum Damage-Healing Mechanics (CDHM) cast in a consistent thermodynamic framework that automatically satisfies the thermodynamic restrictions. The degradation and healing evolution variables are obtained introducing proper dissipation potentials, which are motivated by physically based assumptions. An efficient three-step operator slip algorithm, including healing variables, is discussed in order to accurately integrate the coupled elastoplastic-damage-healing constitutive equations. Material parameters are identified by means of simple and effective analytical procedures. Results are shown in order to demonstrate the numerical modeling of healing behavior for damaged polymer-matrix composites. Healed and not healed cases are discussed in order to show the model capability and to describe the main governing characteristics concerning the evolution of healed systems.
Ni-Ti shape memory alloy fiber-reinforced denture base resin matrix smart composites were developed as a new denture base material for a "smart denture". Composite plate specimens were produced, and changes in their shape and strength after repair were evaluated. The shape recovery process for repair was carried out smartly by a simple process of heating at 80 °C for 10 min. The shape change of the composite after "smart repair" was not significantly different from that of the resin specimen repaired on a planar plate. Because the shape change of the resin should be minimized, the shape change of the composite after smart repair was evaluated to be quite small. The strength of the composite after repair was also not significantly different from that of the resin. These results indicated that the smart repair process of smart dentures is effective for easy and accurate repair.
A microscopic theory of thermally induced crack healing in poly(methyl methacrylate) is presented. Both laser-induced cylindrical cracks and knife-induced surface cracks were analyzed. For a given temperature, the crack closure rate was constant for both types of cracks. However, the crack closure rate was lower for samples with cylindrical cracks than for those with surface cracks. The former exhibited higher activation energy for crack closure than the latter, because the knife-induced cracks had sharper crack tips. Fracture stress was proportional to surface crack healing time to the one-fourth power for thermal healing at a given temperature. Based on the reptation model of polymer chains, the activation energy of chain diffusion was calculated. The healing process was monitored via fractography and crack closure was confirmed. The results were compared with solvent healing and thermal healing in the literature.
Materials containing various types of hollow porous fibers filled with a chemical that is released into the matrix at appropriate times, or over time, are designed to address some issues of material performance, namely, cracking, corrosion, energy absorption and change in dynamic modulus (Dry, 1991a, 1991b). The sensing of the cracking or corrosion of a settable material by a chemical or physical sensor starts the activation of a remedial process. It is a distributed system in which sensing and repair occur when and where they are needed. In the process, the dynamic modulus is changed, a phenomenon that could be utilized for acoustic or radar evasion (Dry, 1991b).
Joining of thermoplastic composites is an important step in the manufacturing of aerospace thermoplastic composite structures. Therefore, several joining methods for thermoplastic composite components have been under investigation and development. In general, joining of thermoplastic composites can be categorized into mechanical fastening, adhesive bonding, solvent bonding, co-consolidation, and fusion bonding or welding. Fusion bonding or welding has great potential for the joining, assembly, and repair of thermoplastic composite components and also offers many advantages over other joining techniques. The process of fusion-bonding involves heating and melting the polymer on the bond surfaces of the components and then pressing these surfaces together for polymer solidification and consolidation. The focus of this paper is to review the different fusion-bonding methods for thermoplastic composite components and present recent developments in this area. The various welding techniques and the corresponding manufacturing methodologies, the required equipment, the effects of processing parameters on weld performance and quality, the advantages/disadvantages of each technique, and the applications are described.
A different type of self-organization in a hydrogel is described. In this self-organization, a cylindrical piece of gel transforms into a completely hollow spherical or ellipsoidal object in the presence of specific transition metal ions. It is shown that only certain gels, which have a critical balance of hydrophilic and hydrophobic groups in their chemical structure, demonstrate the self-organization from solid cylinder to hollow sphere.
Two sets of organotin compounds, that is, one having dibutyl and the other dioctyl groups each with a varying length of a carboxyl group attached to a tin atom, were studied as catalysts for the polycondensation of room temperature vulcanization of hydroxyfunctional polydimethylsiloxane (HOPDMS). The experiments were carried out with the help of a simple and inexpensive piece of equipment called the vibrating needle curemeter (VNC). It has been found that an increase in the length of the carboxyl, as well as the alkyl group bonded to the tin atom, decreases the activity of organotin compounds as catalysts for the polycondensation of HOPDMS. A threshold limit for the difference in catalytic activity of organotin compounds for curing HOPDMS has, for the first time, been established. It has been worked out that when the total number of carbon atoms in the ester and alkyl groups in organotin compounds exceeds 30, then the difference in their catalytic activity reaches a nonmeasurable level by VNC. (C) 1998 John Wiley & Sons, Inc.
Repairing old thermoset pieces could be an interesting challenge instead of replacing them by new ones. This repair procedure necessitates the following stages: adding fresh uncured resin in the place of the broken part of the thermoset piece, and curing the two parts in a heated mould. The process of cure is studied in the two parts of the thermoset piece and especially at their interface by placing emphasis on the heat transfer and state of cure. Of course a higher state of cure is obtained in the old part, leading to a heterogeneity in the system. Nevertheless, the mechanical properties in elongation of the two part-system are not so bad, being of the same order of magnitude as the old thermoset piece. The state of cure is evaluated in the curing system by taking into account the heat transfer by conduction through the resin and the kinetics of heat evolved during the cure reaction.
Polyurethane microcapsules containing functional oil (citronella oil) were successfully prepared by conventional interfacial polymerization of tolulene 2,4-diisocyanate (TDI) and ethylene glycol (EG) and charaterized by Fourier transform (FT-IR) spectroscopy, Ultraviolet spectroscopy, particle size analysis, thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). The effects of polymerization variables, such as surfactant concentration and agitation speed, on the particle size and particle size distribution were investigated. FT-IR spectroscopic data showed that citronella oil was successfully encapsulated in the microcapsule. Thermogravimetric analysis data showed that the microcapsule was thermally stable up to 220°C. The controlled release of the citronella oil present in the microcapsule core in a methanol medium was demonstrated by ultraviolet spectroscopy, showing that the amount of released citronella oil was increased with increasing time. It was observed that the amount of released citronella oil was increased with increasing stirring speed and emulsifier concentration in the microcapsule preparation step. Polyurethane microcapsules containing citronella oil showed excellent anti-moth property.
In this paper the possible role of chain entanglements in stress transfer is discussed. By the new method of crack healing, chain diffusion coefficients down to 1 multiplied by 10** minus **2**2 m**2/s have been determined. On the basis of these results it can be estimated that the full short-time stresses are transferred across an interface in PMMA and SAN (of M//w equals 130 000) once the molecular coils have penetrated by about 10 nm into the opposite matrix. A description of the healing process is also given in terms of the reptation model, leading to a tube diffusion coefficient of D//t(390 K) equals 32. 5 multiplied by 10** minus **2 **0 m**2 s and to curvilinear diffusion distances of 200 nm at the moment of full apparent crack healing.
A self-repairing polyester matrix composite material is described which utilizes embedded polyoxymethylene urea (PMU) microspheres to store a crack filling agent to be released into the crack and rebond the crack faces. The developed repair mechanism uses naturally occurring functional sites in the polyester matrix network to trigger the repair action. The repair agent is mostly composed of styrene monomers and high molecular weight polystyrene. Microscopic observations of the microsphere/crack interaction are presented. Of particular interest is the process with which the microspheres break and release their content when encountered by a crack. The effects of the microspheres on the stiffness and toughness of the polyester resin are also studied. Using standard tensile samples, the composite elastic modulus has been found to decrease with the volume fraction of microspheres, while the fracture toughness of tapered double cantilever beam (TDCB) specimens is shown to reach a maximum value at approximately 10% volume fraction. Examinations of the fracture surfaces show tails extending from the microspheres, indicating crack pinning and crack front bowing as the primary toughening mechanisms. An enhanced level of adhesion between the microsphere and matrix has been found to decrease the composite fracture toughness and increase the incidence of sphere breakage on the fracture surface.
The preparation of polyurethane capsules by interfacial reaction of di- and multiisocyanates (dissolved in toluene) and different di- and triols (dissolved in the aqueous phase) is investigated. Particular attention was paid to obtaining high yields and good mechanical resistance. The experimental conditions were chosen in order to obtain large capsules in the diameter range 50-400 μm since it is expected that for microcapsules prepared according to the same procedure, the mechanical resistance will be still higher. Observations by optical and electronic microscope demonstrate that the wall structure is of the same type as for polyamide microcapsules with an internal dense layer of thickness about 0.6 μm at the water side and a porous layer of about 2 μm at the organic side. The results show that the kinetics of capsule formation are strongly dependent on the temperature reaction. Clean and supple capsules presenting a smooth external surface are obtained when using moderate amounts of crosslinking agents and short poly(ethylene glycol)s as diol. In these conditions, the porous structure of the wall is finer and more homogenous and the capsules are sufficiently supple to allow deformation without breakage.
Five different methods of joining graphite-reinforced polyetheretherketone (PEEK) thermoplastic composite material were investigated, including adhesive bonding, riveting, vibration welding, graphite resistance welding, and induction welding. ICI APC-2/PEEK graphite reinforced thermoplastic composite was used to fabricate 2.54×10.16 cm (1×4 inch) coupons for joining and lap shear testing. Joints were successfully fabricated in accordance with ASTM D1002 using the adhesive bonding, vibration welding, and graphite resistance welding techniques. Both the vibration welding and graphite resistance welding resulted in joint strengths higher than that of adhesive bonds. The choice of joining method depends on the application. The adhesive bonding method was easiest but weakest; vibration welding is strong but not suitable for large parts; and resistance welding could be useful but requires more development.
Inspired by biological systems in which damage triggers an autonomic healing response, a polymer composite material that can heal itself when cracked has been developed. In this paper we summarize the self-healing concept for polymeric composite materials and we investigate fracture mechanics issues consequential to the development nd optimization of this new class of material. The self-healing material under investigation is an epoxy matrix composite, which incorporates a microencapsulated healing agent that is released upon crack intrusion. Polymerization of the healing agent is triggered by contact with an embedded catalyst. The effects of size and concentration of the catalyst and microcapsules on fracture toughness and healing efficiency are investigated. In all cases, the addition of microcapsules significantly toughens the neat epoxy. Once healed, the self-healing polymer exhibits the ability to recover as much as 90 percent of its virgin fracture toughness.
Hollow particle filled epoxy composites are fabricated by an ordinary molding technique. Young's modulus, tensile strength, fracture toughness and dielectric constant are measured as a function of density of the composites (i.e. wall thickness of the hollow particles). Specific strength is almost flat irrespective of the density, while specific modulus and the dielectric constant increase, and the fracture toughness simultaneously decreases with the decrease in the density. Fracture path varies from fracture particles in the case of particles with thinner shell to interfacial debonding in the case of thicker shell in the fracture toughness tests, while particle fracture is predominant in the tensile tests. In-situ observation of the material tests and finite element analyses are utilized to interpret the deformation and fracture behaviors and also to estimate the in-situ strength of silica. It is clarified by the observation that particles larger than 30 μm in diameter are predominantly damaged and smaller particles less than 15 μm are never fractured. Premature fracture of such coarse particles in early stage of loading is attributable to the strength properties. The in-situ strength of silica increases with the decrease in the particle diameter. According to the result of the finite element analysis, stress concentrates near inner surface along an equator under uni-axial loading, and this tendency becomes remarkable with the decrease in the wall thickness. On the other hand, interfacial stress decreases rapidly with the decrease in the wall thickness. The stress concentration along the equator is relaxed under multi-axial loading which is possible in the fracture toughness tests. All of these results indicate that elimination of the coarse particles is essential to improve the tensile properties, and that interfacial modification is effective only for toughness enhancement. SiCp reinforced Al2O3 and SiCp reinforced aluminum composites are also analyzed numerically to evaluate the efficiency of introducing hollow particles into ceramics and polymer materials.
The stereoselective synthesis of a spiropiperidine through a diastereoselective tandem ring closing metathesis (RCM) reaction is reported. The efficient relay of stereochemistry from a pentyl chain to the newly formed spirocentre three carbon atoms away was found to be particularly dependant on the nature of the Ru-catalyst employed - 1st generation Grubbs catalyst was found to be significantly more selective than the more active 2nd generation carbene complexes.
The self-repairing reaction of polymer chains cleaved due to degradation was elucidated through the use of degradation poly phenylene-ether (PPE) related polymer composites. In the case where the cleavage of main chain partially occurred, a spontaneous re-bonding reaction proceeded at the chain ends with copper/amine complex added as a catalyst. The relative value of molecular weight was determined as a criterion of the self-repairing reaction, This reaction was also found to proceed as a redox mechanism for supplying oxygen continuously into the system. Through these processes, the oxidation state of copper was changed from a mono-valent state to a di-valent state that was active for the re-combination reaction between chain ends in polymer. Moreover, blending several kinds of plasticizers with PPE enabled the increase of its molecular weight because of recombination between chain ends that had been cleaved by degradation. During the re-polymerization, water discharge was detected, and the correlation between the ratio of yielded water and increase of molecular weight was clarified. From these results, we concluded that the concept of the self-repairing mechanism could be applied to a wide range of industrial materials and that it had a strong potential to overcome environmental and resource problem in the near future.
The concept of micron scale two-phase self-healing process is dissected. The limits imposed on the self-healing formulation by the rough conditions of the space environment are scrupulously discussed. The possibility to add such capabilities to materials relevant to space exploration is analyzed in detail. The encapsulation of dicyclopentadiene in polyureaformaldehyde is illustrated. The preparation of styrene-isoprene-styrene block copolymers with self-healing properties is described, together with preliminary experimental data obtained by microscopy, spectroscopic techniques (FTIR and Raman), and mechanical testing. Copyright © 2006 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
Recent publications on the thermal decomposition behaviour of polycarbonates have reached divergent conclusions regarding mechanism. The conflicting explanations are considered in relation to the differences in degradation conditions and methods of determining the nature of the reaction products. Criticisms made of the homolytic routes which have been proposed for the thermal degradation of some polycarbonates (notably bisphenol A polycarbonate) are answered.
Predictive methods/computer codes for the computational simulation of acoustic fatigue resistance of hot composite structures subjected to acoustic excitation emanating from an adjacent vibrating component are discussed. Select codes developed over the past two decades at the NASA Lewis Research Center are used. The codes include computation of acoustic noise generated from a vibrating component, degradation in material properties of a composite laminate at use temperature, dynamic response of acoustically excited hot multilayered composite structure, degradation in the first ply strength of the excited structure due to acoustic loading, and acoustic fatigue resistance of the excited structure, including the propulsion environment. Effects of the laminate lay-up and environment on the acoustic fatigue life are evaluated. The results show that, by keeping the angled plies on the outer surface of the laminate, a substantial increase in the acoustic fatigue life is obtained. The effect of environment (temperature and moisture) is to relieve the residual stresses leading to an increase in the acoustic fatigue life of the excited panel.
This comprehensive, accessible resource abridges the ``Polymeric Materials Encyclopedia'', presenting more than 1,100 articles and featuring contributions from more than 1,800 scientists from all over the world. The text discusses a vast array of subjects related to the: (1) synthesis, properties, and applications of polymeric materials; (2) development of modern catalysts in preparing new or modified polymers; (3) modification of existing polymers by chemical and physical processes; and (4) biologically oriented polymers.
We report the first measurements of self-healing polymers with embedded shape memory alloy (SMA) wires. Improvements of healed peak loads by up to a factor of two are observed, approaching the performance of the virgin material. Moreover, the repairs can be effected with reduced amounts of healing agent. The improvements in performance of self-healing polymers with SMA wires are due to three effects: i) crack closure, which reduces the crack volume, ii) heating of the curing agent during polymerisation, which improves the cross-linking, and iii) mechanical registration of the two crack faces, which results in a reduced crack volume on closure.
The activation parameters for the ring-opening metathesis polymerization (ROMP) of endo- (1) and exo-dicyclopentadiene (2), endo-1,2-dihydrodicylopentadiene (3), and norbornene (4) in the presence of Grubbs' catalyst were determined using in situ NMR. The exo isomer of DCP was found to be more than an order of magnitude more reactive than the endo isomer. endo-DCP was found to have reactivity similar to its partially saturated counterpart 3, suggesting that the cause of the rate difference between the two isomers of DCP is primarily steric in nature. This interaction is shown to be predominantly entropic and is suspected to originate from an interaction of the penultimate repeat unit and the incoming monomer. Additionally, the alkylidene generated during the polymerization of endo-DCP was found to form an intramolecular complex, but this complex only affects the rate slightly.
Over the past decade, olefin metathesis has emerged as a powerful method for the formation of carbon-carbon double bonds [1].
In particular, two ruthenium-based catalysts- (PCy3)2(Cl)2Ru=CHPh (1)
Ring-opening metathesis polymerization (ROMP), ring-closing metathesis (RCM) and ring-opening cross metathesis (RO/CM) are
interesting methods to synthesize polymers with attractive mechanical and electrical properties, and specialty chemicals.
Ruthenium and osmium based catalysts are water stable and possess a remarkable tolerance towards most functional groups. Whereas
the first generation of well defined ruthenium based ROMP catalysts, cationic complexes like Ru(H2O)6tos2 (tos=toluene-4-sulfonate) and Ru(arene)2tos2 (activated by UV-irradiation) showed much lower reactivities as compared to “activated” early transition metal catalysts,
Ru-phosphine complexes like RuCl2(p-MeC6H4CHMe2)(PCy3) (1, Cy=cyclohexyl) developed by Ciba SC and later Ru-phoshine-carbenes, developed by Grubbs et al. and Ciba SC are able to polymerize
a large range of cycloolefins including DCPD (in technical quality and in mixtures with additives and fillers) very efficiently.
The new classes of ruthenium carbene complexes are accessible by a novel synthesis which avoids the use of hydrogen gas and
is therefore easy to scale up. Catalyst reactivities in ROMP of different monomers (characterized in terms of their turn-over
frequencies (TOF) and compared with other catalysts for olefin polymerization), in RCM and RO/CM are very much dependent on
the ligand sphere and the type of monomer used. Polymerizations were conducted in bulk, solution and dispersion with a large
range of non-functionalized and functionalized 2-norbornene derivatives to obtain linear and crosslinked homo- and copolymers
(block and random) which may find useful applications in the near future.
This paper contains the results of an investigation to determine the effectiveness of primers in promoting adhesion and improving the environmental durability of epoxy adhesive bonds on grit-blasted aluminum substrates. The control for this study consisted of phosphoric acid anodization of substrates followed by the application of EC 3924 B primer. The following primers were evaluated on grit-blasted substrates: (1) EC 3924 B; (2) Metlbond 6726; (3) Dow Corning Z-6040; and (4) EA 9203. In addition, grit blasting followed by Alodine application was compared with the other primers. Studies include shear strength evaluations of each primer/adhesive system at 23 and 105°C. In order to assess the relative durability of each system, shear strength testing at 93°C of samples exposed for 2 weeks to a 93°C/condensing humidity environment and wedge crack extension testing of samples exposed for a 2-week period to a 60°C/condensing humidity environment were performed. The peel strengths of the systems were determined by conducting floating roller peel studies at -55, 23, and 105°C. Statistical analysis of the data revealed that the level of performance provided by EC 3924 B, solvent-borne, corrosion inhibiting control primer on phosphoric acid-anodized surfaces exceeded that of all the primers on grit-blasted substrates. However, when comparing the primers applied after only a grit-blast treatment, y-glycidoxypropyltrimethoxysilane primer showed statistically better results than the other primer systems.
Several poly(ethylene-co-methacrylic acid) copolymers have shown the unique ability to self-heal following projectile puncture, with the punctured site subsequently holding pressures in excess of 3 MPa. Four specific materials (ionomers and non-ionomer copolymers) were examined to determine if ionic interactions are responsible for puncture reversal. A range of novel experiments including peel, projectile, and quantitative post-puncture testing were used to determine that ionic content is not necessary for the healing response. Mechanistically, it was concluded that healing occurs through at least a two-stage process of melt elastic recovery followed by sealing and polymer chain interdiffusion at the damaged site.
Chemicals, especially in the liquid state, can enter thermosetting polymers. Thus, the process of absorption of styrene by cured unsaturated polyester is found to be controlled by transient diffusion with a constant diffusivity. Moreover, the amount of styrene absorbed, around 3%, is so low that it is not responsible for a change in dimensions of the solid. The rate of absorption is so high at the beginning of the process that the coefficient of transfer at the surface can be considered infinite, meaning that the concentration at equilibrium on the surface is attained as soon as the process starts. Thus, mathematical treatment is feasible, leading to equations expressing the kinetics of absorption in good agreement with experiments, and also the profiles of concentration of styrene as they should develop through the thin plates of resin. Evaluation of the profiles is attempted for the viscous uncured unsaturated polyester by following a law found in the literature connecting the diffusivity of the substance with its molecular weight. Finally, this knowledge on the diffusion of both these materials has been used to explain the efficiency of a new method developed for repairing a broken thermoset piece. This method consists of two steps: the one with the absorption of the viscous uncured polyester system with styrene in it by the previously cured resin over a given time, the other with the cure of the broken thermoset piece in a mould with the fresh uncured resin necessary to fill the mould previously used for curing the original thermoset piece. This study on diffusion was of help for determining the right time necessary for achieving the first stage, this time being of several hours.
This paper presents an experimental investigation on the residual mechanical behaviour of patch-repaired composite pultruded structures initially submitted to low-velocity impact loading. It reports detailed results about static, fatigue and impact tests performed on different glass/polyester impact-damaged structures repaired by low-cost and manual techniques. All the tests were conducted at room temperature. It appears that, firstly, for all the studied structures, the initial static strength is completely recovered. Secondly, for two types of pultruded structures, the fatigue crack-growth life does not recover its initial values but compared with the damaged specimen, the lifetime is significantly enhanced. Residual performances of both undamaged and repaired specimens seemed to be influenced by the profile geometry (in fatigue bending tests) and especially by the open/closed characteristic of the structures. Carefully designed, external scarf patch repairs can recover more than 85% of the undamaged mechanical behaviour, depending on the type of residual applied loading.
Since the discovery of olefin metathesis in the mid-1950s, there has been great interest in using this versatile reaction to synthesize macromolecular materials. More recently, living ring-opening metathesis polymerization (ROMP), a variation of the olefin metathesis reaction, has emerged as a particularly powerful method for synthesizing polymers with tunable sizes, shapes, and functions. The technique has found tremendous utility in preparing materials with interesting biological, electronic, and mechanical properties. This review covers the fundamental aspects of living ROMP and briefly traces its historical development from a catalyst-design perspective. Highlights from the recent literature are used to illustrate the utility of living ROMP in the preparation of macromolecular materials with advanced structures and functions. A discussion on the current status of state-of-the-art catalysts for use in living ROMP reactions as well as opportunities for the future concludes this review.
The characteristics of networks formed in cured ‘reworkable’ epoxy thermosets capable of controlled thermal degradation were studied. Dynamic mechanical thermal analysis, swelling measurements, and glass transition temperature measurements were used to obtain information regarding the time and temperature dependence of the crosslink densities of these materials. By applying isothermal conditions, networks containing up to 36mol% non-degradable components could be completely degraded, i.e. progress from a network of infinite molecular weight to a finite one with zero crosslink density. Percolation theory was used to facilitate the interpretation of these results. The degradation behavior of the reworkable thermosets were well-described by gel degradation theory, i.e. the reverse of the gelation process, and the experimental results were in good agreement with calculated values obtained by replacing the extent of reaction, p, in Macosko and Miller's branching theory with the extent of degradation, 1−p.