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Preparation and application of polysulfone microcapsules containing tung oil in self-healing and self-lubricating epoxy coating
Abstract
Polysulfone microcapsules containing tung oil were synthesized by a solvent evaporation method. The mean diameter and wall thickness of the synthesized microcapsules were approximately 130 μm and 9 μm, respectively. High thermal stability of the microcapsules with a thermal degradation onset temperature of 350 °C was obtained. The multi-functional coating was fabricated by incorporating the microcapsules containing tung oil into an epoxy matrix. The self-healing and self-lubricating functions were evaluated by corrosion and tribology test. 10 wt% microcapsules embedded in epoxy coating offered optimum results. The microcapsules showed excellent anticorrosion performance in scratched coatings, which was attributed to the formation of a cross-linked polymer film after tung oil was released from the damaged microcapsules. The frictional coefficient and wear rate of the self-lubricating coating decreased significantly as compared to the neat epoxy. The formation of a transfer film from releasing tung oil and the entrapment of wear particles in the cavities left by the ruptured microcapsules were the major antifriction mechanism.
... Among them, microcapsules containing lubricating oil are well known as a novel core-shell additive that enables the incorporation of lubricating oil into polymer matrices. Many related studies have reported that microcapsules have amazing effects in enhancing the tribological properties of polymers, such as epoxy [37, 38], polyamide 6 [39, 40] and polypropylene [41]. In self-lubricating composites, as the solid matrix wears, the liquid lubricant is released to the friction surface without external intervention or maintenance, resulting in a signi cant reduction in matrix wear [37][38][39]. ...
... Many related studies have reported that microcapsules have amazing effects in enhancing the tribological properties of polymers, such as epoxy [37, 38], polyamide 6 [39, 40] and polypropylene [41]. In self-lubricating composites, as the solid matrix wears, the liquid lubricant is released to the friction surface without external intervention or maintenance, resulting in a signi cant reduction in matrix wear [37][38][39]. Considering the low processing temperature of PVDF, microcapsules can be used as reinforcing llers to improve the self-lubricating properties of PVDF and expand the application of PVDF in the eld of tribology. ...
... PSF coated PAO microcapsules (PAO@PSF) were prepared by the solvent evaporation method [37]. PSF (0.9 g) and PAO (0.9 g) were dissolved into 33 mL of DCM, and the continuous phase was prepared. ...
In the study, the waste polyvinylidene fluoride (PVDF) membranes were recovered and the micropowders of this polymer were obtained by solvent recovery method. Moreover, the new direction for applying waste PVDF membranes to the field of tribology were developed. Thus, a novel PVDF-based tribological composite (PAO@PSF/PVDF) was fabricated with recycled PVDF micropowders acted as the matrix polymer and PAO@PSF microcapsules with the configuration of polysulfone (PSF) capsuling lubricant oil (PAO) served as the filler. The self-lubricating and wear properties of PAO@PSF/PVDF composite were tested under dry sliding condition using a ball-on-disc configuration. In particular, this kind of composite with the inclusion of 20 wt% PAO@PSF microcapsules exhibited the best tribological properties, i.e., the lowest friction coefficient (0.077) and the smallest wear rate (2.34×10 ⁻¹⁵ m ³ /Nm). The filling of PAO@PSF microcapsules greatly improved the antifriction and wear resistance of PVDF, guaranteeing the self-lubricating feature of this polymer. The tribological properties of PAO@PSF/PVDF composite can reach close to those under the condition of dripping lubricating oil, and the prepared PAO@PSF/PVDF self-lubricating composite can be applied to a large range of friction conditions. Furthermore, without any doubt, it will facilitate the reutilization of waste polymers.
... SEM and FE-SEM are used to provide sweeping images at high resolution, 1 nm, which yields topographical, morphological, and compositional data gathered from different detectors, making them useful for various scientific and industrial purposes [55]. Accordingly, researchers have extensively employed this method to investigate healing performance in coatings, healing agent release from microcapsules and fibers along with investigation of morphologies of micro/nanocapsules as well as micro/nanofibers containing healing agent (Fig. 4a-e) [56][57][58]. Moreover, other strategies such as nanogel swelling and migration of nanoparticles ( Fig. 4f and g) [59] and intrinsic healing in the coatings leading to crack healing can also be investigated by this method. ...
... Recently, researchers have been employing SKP mapping to monitor Fig. 4. SEM micrographs of a) the core-shell nanofiber, b) the release of the healing agent from the capsules when ruptured by mechanical scribing and c) the crosssection of ascribed self-healing coating on a substrate, reproduced with permission from Ref. [57]. d) SEM images of microcapsules and e) ruptured microcapsule which shows the thickness of the shell, reproduced with permission from Ref. [56]. f) The SEM image of nanogel composite swelling and g) the healing of the cracks, reproduced with permission from Ref. [59]. ...
Self-healing coatings have attracted a great deal of interest because of their ability to prevent or control the corrosion process, which is a serious challenge in almost all industries. Despite the fact that there are various methods for the evaluation of self-healing performance in coatings, there are still no standard and established methods for these assessments. This article reviewed the characterization methods for evaluating the self-healing behavior in polymeric coatings and highlighted the significant benefits and drawbacks of each method. Accordingly, all the methods assessing self-healing performance and self-healing efficiency in polymeric coatings that have been utilized in the most recent studies are described. These methods are classified into visualization and quantitative methods, and the equations for the determination of self-healing efficiency are introduced and the terms are defined. This review aims to provide a comprehensive overview of the characterization methods used in evaluating self-healing in polymeric coatings. Its objective is to pave the way for the development and industrial application of self-healing coatings by offering insights into the mechanisms of self-healing and identifying quantitative methods for its determination.
... The part left in the matrix will not have a great impact on the original properties of the matrix because the liquid content is very little. Therefore, microcapsules were recommended to be incorporated into the self-lubricating liner to prolong its service life under the high-frequency swing conditions where thermostable polysulfone (PSF) was also selected as a shell with the consideration of generated friction heat [27][28][29][30]. Additionally, poly α-alkene oil 40# (PAO-40#) has good lubrication performance and good temperature resistance [31,32]. ...
... The decomposition of microcapsules is divided into three stages, namely the first stage for the decomposition of PAO-40#; (a temperature range of 260-410 ℃), the second stage of decomposition transition from PAO-40# to PSF (a temperature range of 410-500 ℃), as well as the third stage of decomposition of PSF between 500 ℃ and 700 ℃. The initial decomposition temperature of microcapsules was detected to be higher than that of PAO-40#, indicating a certain protective effect of shell PSF on the decomposition of PAO-40# core [29]. The PAO-40# content in the microcapsules was determined to be 43 wt % based on TGA results. ...
To extend the service life of the self-lubricating bearing, polysulfone/poly α-alkene oil 40# microcapsules were added to polytetrafluoroethylene (PTFE)/aramid fiber composite liner for the first time. The modified composite liner with 9 wt% contain-oil microcapsules achieved the best tribological properties in plane friction tests, as evidenced by decreasing of the average friction coefficient and wear rate by 26.8% and 27.8% respectively.
Service life of modified composite liner under a simulated self-lubricating bearing test appeared to be significantly increased from 450 h for the pure liner to 1000 h at 35 Hz swing frequency. More promisingly, it has been confirmed that microcapsules modification resulted in two-fold prolongation on the service life of conventional
liners.
... The core materials of the microcapsules could be freely selected such as poly alpha olefin (PAO), silicone oils, liquid wax, and ionic liquid [9][10][11][12][13]. However, due to the limitation of preparation principles, shell materials were mostly polymers such as polysulfone (PSF), polyurethane (PU), poly(urea-formaldehyde) (PUF), poly(melamine-formaldehyde) (PMF), and polystyrene (PS) [14][15][16][17][18][19]. In order to investigate the lubricating effect of microcapsules, they were implanted into polymers to prepare polymer composites [11,20]. ...
... The COF and wear rate of epoxy composites were decreased by 75.4% (from 0.61 to 0.15) and 98.6 % (from 86.0× 10 −14 to 1.2×10 −14 m 3 /(N·m)), respectively. Although microcapsules have been proven to possess excellent lubricating properties, most of previous studies [5,6,14,15] on the lubrication performance of microcapsules were tested in EP matrices because the mild molding environment used for EP subjected to curing at room temperature and without pressure will not damage the fragile microcapsules. However, well-known engineering materials almost have to undergo a series of harsh environments in the molding including the dispersion of additives in organic solvents, and the process of melting and curing the matrices under continuous high temperature or high temperature/ pressure. ...
Novel Ni-PSF@PAO40 microcapsules (NPPMS) with high stability were prepared by using a combined processing method of electroless nickel plating and solvent volatilization. The results indicate that Ni is completely assembled on the surfaces of PSF/PAO40 microcapsules with the encapsulation capacity of NPPMS achieved at 50%. Organic solvents immersion shows that NPPMS have an excellent chemical stability. Macro thermal stability tests reveal that the softening temperature of NPPMS is increased up to over 400 °C while it becomes lower than 200 °C for PSF/PAO40 microcapsules. Furthermore, NPPMS were embedded into polyamide 6 (PA6) to prepare PA6/NPPMS composites. The cross-sectional morphology shows that NPPMS are intact in PA6 matrices. The microhardness of PA6 is effectively improved with the incorporation of NPPMS. As compared with neat PA6, the coefficient of friction (COF) for PA6/NPPMS composites with 10% NPPMS could be reduced by 87.7% (from 0.49 to 0.06) and the wear rate could be decreased by 96.8% (from 1.29×10−5 to 4.15×10−7 mm3/(N·m)). Further studies confirmed that increasing test loads and test temperatures was beneficial to improve the lubrication performance of NPPMS despite the opposite trend occurred when increasing the sliding speeds. It has been demonstrated that synergistic effects between PAO40 and Ni layer play an important role in improving the tribological properties of PA6. Therefore, NPPMS significantly improve the ability of microcapsules to resist a harsh environment, which has important scientific significance for expanding the use of microcapsules more practically in self-lubricating composites.
... This process, facilitated by the unsaturated fatty acids (primarily alphaeleostearic acid) in tung oil, results in a cross-linked polymeric network. These unique molecular characteristics endow tung oil with exceptional water resistance and durability, making it an ideal candidate for enhancing the protective qualities of polyurea coatings in dental applications [4,5]. The intrinsic properties of tung oil present a multifaceted solution to the challenges encountered by polyurea coatings within the dental environment. ...
Within the realm of dental material innovation, this study pioneers the incorporation of tung oil into polyurea coatings, setting a new precedent for enhancing self-healing functionality and durability. Originating from an ancient practice, tung oil is distinguished by its outstanding water resistance and microbial barrier efficacy. By synergizing it with polyurea, we developed coatings that unite mechanical strength with biological compatibility. The study notably quantifies self-healing efficiency, highlighting the coatings' exceptional capacity to mend physical damages and thwart microbial incursions. Findings confirm that tung oil markedly enhances the self-repair capabilities of polyurea, leading to improved wear resistance and the inhibition of microbial growth, particularly against Streptococcus mutans, a principal dental caries pathogen. These advancements not only signify a leap forward in dental material science but also suggest a potential redefinition of dental restorative practices aimed at prolonging the lifespan of restorations and optimizing patient outcomes. Although this study lays a substantial foundation for the utilization of natural oils in the development of medical-grade materials, it also identifies the critical need for comprehensive cytotoxicity assays. Such evaluations are essential to thoroughly assess the biocompatibility and the safety profile of these innovative materials for clinical application. Future research will concentrate on this aspect, ensuring that the safety and efficacy of the materials align with clinical expectations for dental restorations.
... Liquid lubricants such as paraffin [13][14][15], lube base oil [16], ionic liquids [17], and diisocyanates [18] are usually used as the core material of microcapsules. Materials such as PUF [19,20], polysulfone [21], and polystyrene [22] are used as wall materials. Ionic liquids are salts composed of organic cations and polyatomic anions, which are liquid at room temperature and have the advantages of high dipolarity, nonvolatility, chemical stability, and non-combustibility [23][24][25][26]. ...
Thermosetting epoxy resins are widely used as bearings, gears, gaskets, and other components. The tribological properties of epoxy resins play an important role in ensuring the life and reliability of the components. A novel self-lubricating microcapsule was synthesized in this study by in situ polymerization using ionic liquid as the core material and polyurea formaldehyde (PUF) as the wall material. The effects of the ionic liquid microcapsule content on the coefficient of friction, wear rate, and surface morphology of the epoxy resin composites were investigated under dry friction conditions. The results showed that the incorporation of self-lubricating microcapsules significantly improved the friction and wear properties of the composites, and the 5 wt.% microcapsule/epoxy composites had the best tribological properties, with the coefficient of friction decreasing from 0.634 to 0.062 and the wear rate decreasing from 6.64 × 10–4 mm³/(N m) to 1.64 × 10–5 mm³/(N m). Compared with the pure epoxy resin, the friction coefficient of the composites was reduced by 90.22% and the wear rate was reduced by 97.53%. The wear mechanism of epoxy resin changes from severe fatigue wear and adhesive wear to slight abrasive wear. This is because after friction destroys the composite, the embedded microcapsules rupture, releasing the lubricant and forming a transfer film that lubricates the friction surface. At the same time, the addition of microcapsules enhances the tensile strength and hardness of the epoxy resin. This study would provide the experimental basis for the design and performance enhancement of epoxy composites with high self-lubricating properties. The prepared epoxy composites are expected to be applied to self-lubricating spherical plain bearings and other mechanical parts.
... Additionally, organic wall materials comprise polysulfone, polystyrene, polyurea, urea-formaldehyde resin, and melamine resin [16,17]. Microcapsules for self-lubrication can be added to polymeric materials like nylon 6 and epoxy resin [18][19][20][21]. There is a trend to apply microcapsules to fiber composite liners. ...
Polyaryl ether sulfone/polymethylphenlsiloxane (PES/PMPS) microcapsules were prepared and added to a polytetrafluoroethylene (PTFE)/aramid fiber composite liner for the first time to improve the tribological properties of self-lubricating fiber liners under high-temperature environments. Compared with the virgin liner, the friction coefficient and wear rate of the liner containing 9 wt% PES/PMPS microcapsules are reduced by
48.5% and 21.6%, respectively. At the microscopic and atomic scale, lubricant PMPS changes the interaction energy between PTFE and the Fe layer to weaken the adhesion of PTFE to the friction couple, further reducing the adhesive wear of the liner. Under the action of lubricating phases PMPS and PTFE, the tribological properties of the liner are significantly improved.
... It was observed that the degradation of tung oil begins at approximately 350 °C. The high decomposition temperature of tung oil is due to its thermally stable structure [38]. MF microcapsules (empty) and tung oil filled MF microcapsules demonstrated almost similar thermal behaviour. ...
In this study microcapsules were prepared by in-situ polymerization route with melamine formaldehyde as a shell material and tung oil as core material. Melamine formaldehyde (MF), a thermosetting polymer, is one of the most widely used monomers in microencapsulation due to its superior mechanical strength and thermal stability. Tung oil contains unsaturated double bonds that can be oxidized to form a film in air. Tung oil is fast drying and biodegradable, besides it is low cost and does not pollute the environment. Most importantly, tung oil is a versatile substance in industry. Therefore, tung oil is a good choice as core material. The chemical structure of microcapsules were characterized by Fourier Transform Infrared (FTIR) spectroscopy. The surface morphology and particle size and distribution were evaluated by Scanning Electron Microscopy (SEM). The thermal behavior of microcapsules and tung oil were studied by thermogravimetric analysis (TGA). The results showed that the spherical microcapsules (particle size of mostly 4-5 μm) were produced with a filling content of 15.64 wt.%, and a yield of 49.78 wt.%. The microcapsules exhibit a good thermal stability
... Strong vibrations in the spectra at 831, 850, and 871 cm −1 are due to aromatic C-H bending [42]. [43,44]. ...
Commercial polymer membranes are largely utilized to separate oil/water mixtures; however, membrane fouling, flux decline, and short lifetime often inhibit their high performance. In order to resolve these drawbacks of the commercial membranes, we introduce a surface modification strategy following the electrospinning method. Electrospun fibers of polysulfone (PSf)/iron oxide (FeO)/halloysite nanotubes (HNT) nanocomposite are applied to modify the polyether sulfone (PES) standard membrane support surface for developing highly efficient oil/water emulsion separating membranes. This facile and simple spinning process for shorter periods ensures nanocomposite coatings on the standard PES membranes and allows a better oil/water separation. We analyze the structural and morphological characteristics of the modified membrane surface using scanning electron microscopy, Fourier transformation infrared spectroscopy, and X-ray diffraction studies and hydrophilicity from contact angle studies. FeO nanoparticles of 2–5 nm and HNTs of < 50 nm size mixed in PSf produce fibers of 531 ± 162 nm average diameter at a relatively lower applied electrical voltage of 14.5 kV, compared to PSf. Underwater and under-oil contact angle values are used to prove the surface characteristics of the membranes and total organic content (TOC) values for the emulsion separation performance. From PES support to PSf and PSf/HNT-FeO, the TOC values respectively change from 67 to 75 and 79%. We find moderately hydrophilic membranes (PSf/HNT-FeO) resulting in a higher permeate flux (28,447 Lm⁻²·h⁻¹) and quicker separation performance. We believe this study provides a notable solution to modify the surface of commercial membranes for better emulsion separation performance.
... 15,16 Meanwhile, microcapsules containing oil also enable to significantly improve tribological properties of polymers. [17][18][19] Li et al. [20][21][22] prepared microcapsules with lubricating or tung oil as a core material and PSF or PSF/SiO 2 as a wall material by solvent volatilization and sol-gel methods respectively. The microcapsules were added to low-density linear polyethylene or epoxy resin in order to modify their tribological properties. ...
In this study, three different methods based on vacuum adsorption, solvent volatilization, and Pickering emulsion were utilized to prepare microcapsules with the core material of PAO40 and the wall materials of SiO 2 , polysulfone (PSF), and PSF/SiO 2 composites, respectively. PTFE/Kevlar fabric liners were modified by PAO40/SiO 2 microcapsules (PSMS), PAO40/PSF microcapsules (PPMS), and PAO40/PSF/SiO 2 microcapsules (PPSMS). The effect of microcapsules based on different wall materials on the tribological properties of liners was investigated by friction and wear tester under low‐speed and heavy‐load conditions. The anti‐friction and anti‐wear mechanisms of several microcapsule types on the liners were systematically investigated. The results showed that PPMS induced the most significant enhancement in anti‐friction properties of liners when compared to pure liner resulting in a 19.4% reduction in coefficient of friction (COF). PSMS was found to reveal much better wear resistance of liners, as evidenced by 75% increase in wear rate. PSMS and PPSMS not only release lubricating oil after the break of microcapsules under the friction action to lubricate, but also generate a cavity to store abrasive debris for liner wear reduction. Nonetheless, PPMS only released the oil onto the friction surfaces for lubrication. PSF as the microcapsule wall material could not contribute to the formation and promote wear resistance of transfer films. SiO 2 as a microcapsule wall material participates in the formation and enhances the wear resistance of transfer films. The findings obtained are anticipated to improve the reliability and broaden the range of applications of liners in aerospace and other industrial fields.
Highlights
Three microcapsules all improve the tribological properties of the liners.
Anti‐friction and wear‐resisting mechanism of three microcapsules in liners.
SiO 2 as wall material can increase the wear resistance of transfer films.
PAO40 in microcapsules has antifriction effect at the friction interface.
... The band during 579-635 cm -1 can possibly correspond to the vibration of the Fe-O bonds. The characteristic absorption peaks of the pristine HNT, such as the O-H stretching of inner hydroxyl groups at 3625 cm -1 , O-H deformation of water at 1631 cm -1 , O-H bending of inner hydroxyl groups at 906 cm -1 and Si-O stretching at 1004 cm -1[43,44]. ...
Commercial polymer membranes are largely utilized to separate oil/water mixtures, however membrane fouling, flux decline and short lifetime often inhibit their high performance. In order to resolve these drawbacks of the commercial membranes, we introduce a surface modification strategy following the electrospinning method. Electrospun fibers of polysulfone (PSf)/iron oxide (FeO)/halloysite nanotubes (HNT) nanocomposite is applied to modify the polyether sulfone (PES) standard membrane support surface for developing highly efficient oil/water emulsion separating membranes. This facile and simple spinning process for shorter periods ensures nanocomposite coatings on the standard PES membranes and allows better oil/water separation process. We analyze the structural and morphological characteristics of the modified membrane surface in addition to the hydrophilicity from contact angle studies. FeO nanoparticles of 2-5 nm and HNTs of <50 nm size mixed in PSf produce fibers of 531 ± 162 nm average diameter at a relatively lower applied electrical voltage 14.5 kV, compared to PSf. Under water and under oil contact angle values are used to prove the surface characteristics of the membranes and TOC values for the emulsion separation performance. From PES support to PSf and to PSf/HNT-FeO, the TOC values respectively change from 67 % to 75 % and to 79 %. We find the moderately hydrophilic membranes resulting in the higher permeate flux and quicker separation performance. We believe this study provides a notable solution to modify the surface of commercial membranes for better emulsion separation performance.
... Therefore, self-healing materials without catalyst, non-toxic and environmental protection have attracted great attention from researchers [21][22][23]. Tung oil is a kind of dry plant oil natural film forming material, it contains 80% tung acid, the rest is linolenic acid, linoleic acid and oleic acid, these substances contain unsaturated double bonds, can be oxidized into film in air [24,25]. The structural formula of tung oil is shown in Fig. 2. Due to the good biodegradability of tung oil, the self-healing coating prepared by tung oil as restorer not only meets the requirements of environmental protection, but also reduces the cost. ...
In this study, Pickering emulsion template method and interfacial polymerization method are used to prepare microcapsules containing tung oil with Polyvinyl alcohol (PVA) as stabilizer, PUA as wall material and tung oil as core material. Microcapsules are structured and spherical, with uniform size distribution. The prepared microcapsules were dispersed in epoxy resin to form a self-healing epoxy coating. The effect of brine soaking time on the corrosion resistance of the self-healing epoxy coating was studied. EIS results showed that the self-healing epoxy coating with microcapsules had better corrosion resistance than pure epoxy resin. The mechanical properties of the self-healing epoxy coating with microcapsule content were studied by measuring the tensile strength, tensile shear strength and coating hardness. When the microcapsule content was 3%, the tensile strength increased to 84.71 MPa, which was 35.53% higher than that of pure epoxy resin. The hardness of self-healing epoxy coating is 22.46 HV, which is 0.18% lower than that of pure epoxy coating. The experimental results show that a small amount of microcapsules can improve the mechanical properties of the self-healing coating.
... On the other hand, the incorporation of additives such as graphene [12], rate earth [13], WS 2 [14], SiC [15], etc. can significantly improve wear resistance of the liners. In recent years, various material-processing techniques have been employed including solvent volatilization [16,17], in-situ polymerization [18], vacuum adsorption [19] and so on in order to manufacture microcapsules in which solid materials work as coated wall materials using liquid lubricants. Polymeric modification enables to substantially improve tribological properties with the aid of solid-liquid synergetic effect of microcapsules. ...
Self-lubricating liners are considered as critical bearing components, which show the primary applications in the
aerospace field in a typical operation between -50–163℃ to significantly influence the service life of liners. Therefore, the effect of ambient temperature (-40 to 160℃) on tribological properties of liners with 6 wt% PAO40/SiO2 microcapsules friction chromium-plated shaft under 240 MPa was investigated. The results indicate that elevated temperature enhanced the formation of transfer films and associated tribochemical reaction that
nonetheless could be restrained at the low temperature level. Wear depth and friction coefficient (COF) of the liner reached 0.052 mm and 0.039 respectively at 80 ℃, mainly due to the synergistic effect of friction reaction, high wear resistance of SiO2 and uniform density of the transfer film.
... In the future, self-healing polymer/nanocarbon nanocomposites can be developed for damage sensing in aerospace structures [186,187]. In aerospace, self-healing materials can be beneficial for desirable electronic components such as batteries, circuits, sensors, supercapacitors, etc. [188,189]. Novel healing agents based on nanocapsules and nanocarbon nanoparticles need to be designed with superior self-healing efficiency under high temperature, pressure and impact conditions. Such materials may enhance the durability of future space structures [190]. ...
Self-healing polymers and nanocomposites form an important class of responsive materials. These materials have the capability to reversibly heal their damage. For aerospace applications, thermosets and thermoplastic polymers have been reinforced with nanocarbon nanoparticles for self-healing of structural damage. This review comprehends the use of self-healing nanocomposites in the aerospace sector. The self-healing behavior of the nanocomposites depends on factors such as microphase separation, matrix–nanofiller interactions and inter-diffusion of polymer–nanofiller. Moreover, self-healing can be achieved through healing agents such as nanocapsules and nanocarbon nanoparticles. The mechanism of self-healing has been found to operate via physical or chemical interactions. Self-healing nanocomposites have been used to design structural components, panels, laminates, membranes, coatings, etc., to recover the damage to space materials. Future research must emphasize the design of new high-performance self-healing polymeric nanocomposites for aerospace structures.
... The release of friction-sensitive microcapsules is generally triggered by matrix wearing out [98]. The process of deformation and release is similar to pressure-sensitive microcapsules [99][100][101]. ...
... Tung oil is a non-edible oil, mainly grown in China, which primarily contain unsaturated fatty acids with the following average molar distribution, 77.2% α-eleostearic acid, 7.6% linoleic acid, 5.9% oleic acid, 4.2% palmitic acid, 2.3% stearic acid, and 0.4% linolenic acid. As an excellent drying oil, tung oil has long fatty acid chains and polar groups, and this amphiphilicity enables them to have a good film/force relationship, which can act as a boundary lubricant [23][24][25][26]. However, due to the high degree of unsaturation and low oxidation stability of tung oil, it is not suitable for direct use as lubricating oil [27]. ...
... A completely different strategy to enhance the durability of coatings is the development of self-healing materials. Li et al. [132] developed a multi-functional coating made of microcapsules containing tung oil incorporated into an epoxy matrix. Through the release of tung oil, the broken microcapsules decreased the wear rate and friction coefficient due to a tribo-film formation and self-healing property. ...
Sustainability has become of paramount importance, as evidenced by the increasing number of norms and regulations concerning various sectors. Due to its intrinsic trans-sectorial nature, tribology has drawn the attention of the supporters of sustainability. This discipline allows the environmental, economic, and social impacts to be decreased in a wide range of applications following the same strategies. In 2010, Nosonovsky and Bhushan drew up 12 approaches based on the 12 principles of green chemistry and the 12 principles of green engineering, defining the “12 principles of green tribology.” This review exploits the 12 principles of green tribology to fathom the developed research related to sustainability and tribology. Different approaches and innovative studies have been proposed in this short selection as references to consider for further development, pursuing the efforts of the scientific community for a sustainable future through the contribution also of tribosystems. The manuscript aims to provide practical examples of materials, lubricants, strategies, and technologies that have contributed to the overall progress of tribology, decreasing wear and friction and increasing efficiency, and at the same time promoting sustainable development, lowering toxicity, waste production, and loss of energy and resources.
... da Cunha et al. 27 studied the dual-functional poly(urea formaldehyde) microcapsules, and they were used with linseed oil and benzotriazole (BTA). Li et al. 28 encapsulated tung oil into polysulfone successfully. Li 29 studied that self-healing microcapsules were prepared by the solvent evaporation method with polysulfone (PSF) as the shell and tung oil as core materials because PSF has relatively stable chemical properties and high thermal stability. ...
Propane-1,2,3-triol-loaded polysulfone (PSF) microcapsules were prepared by the solvent evaporation method. The particle size of the microcapsules is about 140 μm. The shell wall thickness is about 17 μm approximately. The microcapsules have high thermal stability and antiwear performance. The self-healing coating was prepared by adding the prepared capsule into the epoxy resin coating. After electrochemical and corrosion immersion experiments, the resistance modulus of the coating added to the microcapsules was higher than the others in a 3.5 wt % NaCl corrosion solution, and it had the lowest corrosion current density, so the self-healing microcapsule coatings showed excellent healing ability and corrosion inhibition function for microcracks. This was attributed to the formation of a hydrophobic film after propane-1,2,3-triol was released from the damaged microcapsules.
... Drying (or semi-drying) oils have been used in industrial applications, such as coatings and paints. In particular, several studies have been reported on the application of drying oils (for example, linseed oil, soybean oil, or tung oil) to microcapsule-type self-healing protective coatings [14][15][16][17][18][19][20][21][22]. ...
Generally, microcapsule-based self-healing materials have the limitation of single local self-healing. A few studies have reported repeatable self-healing in these microcapsular materials, but there is a challenge to develop multi-cycle self-healing materials that have the advantages of easier preparation and a more efficient operation. In this work, a mixture of two vegetable oils, soybean and olive oil, was used as a healing agent. The atmospheric oxygen-induced reaction behavior (in the presence of a catalyst) was investigated for various compositions of the vegetable oil mixtures; infrared spectroscopy, recovery testing, and viscoelasticity measurement were performed to find an optimum composition of the healing agent. Microcapsules loaded with soybean oil and catalyst-containing olive oil were separately prepared and used to prepare a dual-capsule self-healing coating. It was demonstrated through optical and scanning electron microscopy that, upon scribing the self-healing coating, the vegetable oils flowed out from microcapsules to self-heal the damaged area. When the healed area of the self-healing coating was re-scribed, self-healing was repeated, which was confirmed by scanning electron microscopy (SEM) and anticorrosion and electrochemical testing. Our new repeatable self-healing coating provides the merits of easy preparation, no need for external intervention such as light irradiation, and an environmentally-friendly nature.
... While self-healing is highly attractive in many applications because it equips coatings in longer protection and lasting appearance, corrosion inhibition is important in protecting a variety of substrates [14]. In many applications mechanical forces imposed on coatings may lead to premature wear and embedded self-lubricants alleviate this process [15]. Self-reporting stimuli-responsive functions are also desirable because their presence will detect excessive mechanical or thermal stresses [16,17]. ...
Continuous interests in stimuli-responsive macromolecules significantly impacted new developments in polymeric coatings. Responsiveness to bacterial attacks, ice or fog formation, anti-fouling properties, autonomous self-cleaning and self-healing, or drug delivery systems, are just a few examples of modern functions of macromolecules and other components utilized in polymeric coatings. These autonomous responses to various external stimuli combined with the suitable protection and appearance are particularly attractive functions. This review outlines recent advances in the development of novel stimulus-responsive polymeric coatings in the context of current and future trends. A combination of stimuli-responsiveness, protection and durability, appearance, and other “smart” functions make polymeric coatings particularly attractive as integral components of future engineered systems. This review consists of four sections, (1) stimulus-responsive protection, (2) stimulus-responsive appearance, (3) smart functions, and (4) future trends and opportunities. The purpose of this monograph is not to list all stimuli and responsiveness utilized in polymeric coatings, but address favorable and unpropitious, in our view, scientific advances and technological opportunities in the development of a new generations of “smart” coatings that still maintain traditional functions of protection and appearance.
This work reports polymer/metal double‐shell microcapsules with polysulfone (PSF) and copper as walls for application in self‐lubricating polymer. First, polyalphaolefin 40 (PAO40) was selected as lubricant oil, and PAO@PSF single shell microcapsules were prepared. A critical issue for the formation of copper layer is the sensitization of PSF shell, which can affect not only the adhesion between PSF shell and copper layer, but also the density of copper layer. The sensitization conditions were discussed in detail, and the corresponding effect on the formation of copper layer was evaluated. PAO@PSF/Cu microcapsules obtained under optimal sensitization condition were characterized by scanning electron microscopy (SEM), thermogravimetric analyzer (TGA), x‐ray energy dispersive spectrometer (EDS) and fourier transform infrared spectroscopy (FTIR). A uniform and compact copper layer improved the thermal properties of microcapsules. PSF/Cu microcapsules maintained relatively complete spherical shape when were heated to 300°C, while the PSF microcapsule softened and deformed at 200°C. The self‐lubricating polyamide 6(PA6) composites containing PAO@PSF/Cu microcapsules were fabricated at 230°C, microcapsules maintained complete structure and uniform distributed in the polymer matrix. Coefficient of friction (COF) and wear rate of PA6 composites were tested under different friction conditions. Compared with pure PA6, 15 wt.% PAO@PSF/Cu microcapsules could reduce the COF by 79.5%, and the wear rate was decreased by 98.3% under 300 rpm sliding speed and 50 N friction load.
Highlights
PSF/Cu double‐shell oil‐loaded microcapsules were designed and prepared.
The copper layer effectively improved the thermal properties of microcapsules.
The self‐lubricating PA6 composite exhibited excellent tribological properties.
Cured epoxy resins have poor abrasion resistance, which shortens the service life of the material. This work aims to improve the tribological properties of epoxy resins by coupling self‐lubrication and auto‐healing. In this study, linseed oil microcapsules with an average particle size of 38.57 μm and good thermal stability were successfully prepared by in situ polymerization. The effects of microcapsule content on the tribological, mechanical, and self‐healing properties of the composite coatings were studied. It was demonstrated that the composite coating has outstanding self‐lubricating properties. The coefficient of friction reduced from 0.634 (pure epoxy resin) to 0.0459 (epoxy resin with 10 wt.% linseed oil microcapsules). Wear rate reduced from 7.16 × 10 ⁻⁴ mm ³ /(N m) to 1.74 × 10 ⁻⁵ mm ³ /(N m). The self‐lubricating mechanism of the coating was investigated by SEM and EDS, which indicated that the formation of uniform and continuous lubricating film on the surface of the friction pairs was the key to improving the wear resistance of the material. In addition, the linseed oil released after the microcapsules rupture can repair the abrasion marks by reacting with oxygen during the friction process. The dual‐functional effect of linseed oil microcapsules prolongs the life of epoxy resin coating and expands its application range.
This work focuses on the preparation and characterization of an anti-bacterial self-healing polymeric coating by linseed oil encapsulated in a poly (urea-formaldehyde) shell with CuO addition. The synthesized microcapsules (MCs) were characterized using scanning electron microscope (SEM) and Fourier Transform Infrared Spectroscopy (FTIR) analysis. The corrosion properties of the prepared coatings were investigated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization examinations in 3.5 wt% NaCl solution. The results indicated that the corrosion performance of the coating was improved demonstrating that the most elevated corrosion resistance (Icorr =49.5 μA/cm2, Ecorr = −0.56 V) is gotten by adding 15 wt% MCs, and by increasing the MCs concentration improves the corrosion rate while the mechanical properties decrease. In addition, self-healing coatings exhibited efficient antibacterial functioning against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) due to the release of CuO nanoparticles in the damaged areas. The samples with 4 g/lit of CuO in the healing agent completely inhibited antibacterial activity. Moreover, the copper oxide nanoparticles were more effective against S. aureus bacteria than E. coli
Herein, novel microcapsules were designed and synthesized by emulsion polymerization and used for self-healing coating for magnesium alloy. Polyaniline (PANI) was used directly as a capsule shell, and thermoplastic acrylic resin was used as the core material. Polymerization processes of microcapsules were observed by optical microscopy, and some key polymerization parameters were discussed. Composite microcapsules were analyzed by scanning electron microscopy, infrared spectroscopy, and thermogravimetric analysis. The corrosion protection performance of microcapsule and epoxy varnish coatings with defect was tested by electrochemical impedance spectroscopy. Results showed that the microcapsule coating had a higher corrosion protection than epoxy varnish coating because capsule core acrylic resin could significantly improve the shield performance of the defect coating and capsule shell PANI could inhibit the corrosion reaction of magnesium alloy.
In the study, the waste polyvinylidene fluoride (PVDF) membranes were recovered and the obtained resin powders by a solvent recovery method were employed for the fabrication of a novel PVDF‐based tribological composite. Herein, a new strategy was developed for applying the waste PVDF membranes to fabricate a self‐lubricant composite, where the recycled PVDF powders acted as the polymer matrix and microcapsules with the configuration of polysulfone (PSF) capsuling lubricant oil (PAO) served as the filler. The morphologies, crystal phases, chemical components and groups as well as thermal stabilities of fabricated PAO@PSF/PVDF composites were characterized, and the self‐lubricating and wear properties of fabricated composites were tested under the dry sliding condition using a ball‐on‐disc configuration. Experimental results suggest that the PAO@PSF/PVDF composite with an addition of 20 wt% PAO@PSF microcapsules exhibits the best tribological properties, in view of the lowest friction coefficient (0.077) and the smallest wear rate (2.34 × 10 ⁻¹⁵ m ³ /Nm). The incorporation of PAO@PSF microcapsules greatly reduces the friction coefficient of PVDF polymer. The tribological properties of fabricated PAO@PSF/PVDF composite will be expectable to that of the PVDF polymer with the dripping presence of lubricating oil.
This study proposed a tung-oil based magnetic targeted delivery microcapsules (MDTMs) to enhance the efficiency of self-healing coatings (SHC). Magnetic particles were used as function particles and emulsifier in synthesis of microcapsules (MC). DSC, OM, SEM, TEM, VSM, NSS, EIS and SKP were used to characterize the compounds, structure, healing behavior and anti-corrosion performance. Results indicate that magnetically driven SHC (MD-SHC) reduces 50% migration path of the released tung oil, and increases the release rate of tung oil after the coating is mechanically damaged. SKP and EIS results suggest that the healing part has impressive anti-corrosion performance, scratches were filled with a large amount of tung oil in a short time, and the released tung oil had formed a complete oil film on scratches at 24 h with higher polarization resistance (Rp). Rp of MD-SHC (2.5 × 105–3.6 × 105 Ω cm2) is 2.0–2.8 times of that the SHC (1.1 × 105–1.8 × 105 Ω cm2). The enrichment in MD-SHC at the interface decreases bonding strength from 7 to 4.5 MPa as the mass additive of microcapsules reaches 15 wt.%. The current work proves the effectiveness of MD-SHC in improving self-healing ability.
As a significant method to inhibit metal corrosion by blocking the diffusion of corrosive mediums to the metal surface, the anticorrosion coating with a self-healing function can actively repair a damaged structure and improve the anticorrosion performance to better meet actual needs. In this study, “external aid” and “intrinsic triggering” self-healing coatings have been introduced in detail, including the preparation method, healing mechanism and practical applications. The healing of “external aid” is based on the addition components such as microcapsules containing healing agents and functional nanoparticles, whose ability of self-healing shows the independence with the coating resin. But the finitely additive amount may limit the sustainable use of “external aid” components, and the abundant fillers also change the basic physical properties of the coating. On the contrary, the “intrinsic triggering” resins can form the cover layer in the defects owing to the physical or chemical reactions between the polymer chains, along with the unlimited cycles theoretically. By contrast, the small defects or gaps can be repaired gradually through chain reactions, but the large areas of damage may need the quick release of healing additives in “external aid” coating. In this review, the advances of two kinds of self-healing coatings were analyzed to discuss the advantages and disadvantages of various healing technologies, and the challenges of development and prospects were also forecasted to provide useful ideas.
According to one of the currently developed mechanisms of self-healing of epoxy protective coatings, an important role in the process is played by the diffusion migration stage of the composition components to the crack network defects, on the one hand, by swelling of the pore walls, on the other hand, and by their adhesive interaction, on the third. PART 3.1; 3.2, and 3.3 of this chapter summarize the results of our investigations performed at the Laboratory of Structural and Morphological Research of the Institute of Physical Chemistry of the Russian Academy of Sciences concerning the translational mobility of epoxy oligomers, epoxy-amine adducts as model systems for investigation of curing processes of epoxy oligomers and phase equilibrium and structure formation during curing of epoxy compositions. It seems that the presented experimental and methodological material will make it possible to significantly advance our understanding of the details of the self-curing mechanism.
Self-healing materials, which can increase the lifespan of various types of products, have been researched quite intensively in recent decades. In general, self-healing polymers and composites are classified based on their mechanisms of action. While extrinsic systems depend on an external healing agent, the process takes place through reversible bonds or supramolecular interactions in intrinsic systems. In this chapter, the main mechanisms of self-healing epoxy systems, involving extrinsic and intrinsic approaches, autonomous and non-autonomous, are presented and discussed. Since the development of the first extrinsic self-healing epoxy systems, based on microcapsules and vascular networks, which are still the most studied approaches for coatings and composites, many new possibilities have been researched, especially systems involving intrinsic mechanisms. Among them, mechanisms of dynamic covalent networks based on thermally activated reversible Diels–Alder reactions and disulfide bonds, and photoreversible cross-linking have been considered. Furthermore, new trends in self-healing processes concerning vitrimers, non-covalent supramolecular systems, shape memory-assisted self-healing, and bio-based epoxy materials are introduced, looking forward to a wider range of possible applications.
Low alloy steels are widely used in bridges, construction, chemical and various equipment and metal components due to their low cost and excellent mechanical strength. Information in the literature related to the preparation, advantages and disadvantages, and applications along with research progress of various types of protective coatings suitable for low-alloy steel surfaces is reviewed, while a conclusive and comparative analysis is also afforded to the numerous factors influencing the protective ability of coatings. The characteristics of coatings drawn from the latest published literature are discussed and suggest that the modification of traditional metal coatings and the development of new organic coatings under the consideration of environmental protection, low cost, simplicity and large-scale industrial application are simultaneously proceeding, which holds promise for improving the understanding of corrosion protection in related fields and helps to address some of the limitations identified with more conventional coating techniques.
Although microcapsules can remarkably diminish the friction coefficient and wear rate of the composites, most of the superior tribological properties are achieved under small contact areas and low loads. To enhance the tribological performance of microcapsule-containing composites at large contact areas and high loads, the PTFE is introduced to construct PTFE/microcapsule/epoxy composites. The resulted composites maintain a low coefficient of friction (COF) of 0.057 and a wear rate of 1.45✕10⁻⁷ mm³/Nm against PH13–8Mo Steel in ring-on-ring test configuration at 1500 N (12.7 MPa), where the microcapsule/epoxy composite fails to ensure constant and adequate lubrication. The effect of the PTFE content on the mechanical and tribological properties has been methodically examined and discussed in some detail. The analysis results provide evidence that the island-like transfer film associated with the PTFE is essential for the intense enhancement of tribological properties, in which composition is confirmed by exhaustive analysis. The transfer film tends to lessen the solid friction resulting from the direct contact of asperities in mixing or boundary lubrication while the reducing lubricant film failure is essentially caused by high flash temperature. Additionally, the oleophobic properties of the PTFE promote oil lubrication under a limited oil supply. This work aims to extend service conditions and promote applications of microcapsule/epoxy composites in mechanical components.
Epoxy resin (EP) is prone to brittle fracture during friction due to internal stress after curing, resulting in fatigue wear and cracking. Adding carbon fillers is considered as one of the great potential solutions to solve the serious dry wear of EP. Herein, we develop a novel carbon capsule composite filler (CNC‐IL) filled with ionic liquid (IL) in carbon nanocages (CNC) using the vacuum principle to address these concerns. Compared with pure EP, the friction coefficient (0.10) and wear rate (1.712 × 10−6 mm3 Nm−1) of the optimized CNC‐IL/EP were reduced by 74.62% and 88.14%, respectively. Such excellent tribological properties can be attributed to the solid–liquid lubricating film formed by the IL released from the broken CNC during friction. A low‐shear‐resistance slip layer can be formed between the CNC‐IL in the film due to the repulsion of the isoelectric ions adsorbed on the surface of the CNC; it effectively integrates the self‐lubricating functions of CNC and the liquid lubrication functions of ILs. This work provides a valuable idea for designing C/EP composites with good antifriction properties. A novel carbon capsule composite filler (CNC‐IL) using carbon nanocage (CNC) stuffed with ionic liquid (IL) is first constructed to solve the fatigue, creep and adhesive wear problems of epoxy resin (EP). It presents a stable low‐friction performance for the optimized carbon/epoxy composites.
Metal corrosion causes huge economic losses, environmental pollution and industrial disasters. Application of smart self-healing coatings for the active corrosion protection of metal substrate has attracted substantial interest in recent years. The self-healing function can be achieved through either the intrinsic or extrinsic method. The intrinsic self-healing coatings mainly make use of the reversible physical and chemical interactions between molecules, whose self-healing effect is permanent. While the extrinsic method is mainly caused by embedding the micro/nanocontainers in the coatings, which can sense the micro-environmental changes and give rapid feedback to repair the micro cracked zones on the coating surface, the self-healing performance is temporary after the encapsulated active substances are fully consumed. Furthermore, inspired by these intelligent behaviors, more and more multi-functional coatings are designed and widely used in different fields. In this review, we summarized the research development of different stimuli-responsive self-healing coatings based on micro/nanocontainer techniques in recent years. Different types of micro/nanocontainers, as well as their synthesis or encapsulation technologies, are exampled to clarify the recent achievements. Meanwhile, the single stimulus-responsive systems are gradually evolved into the multi-stimulus-responsive system that endows the coatings with more sensitivity and intelligence. The stimuli-responsive self-healing coatings with different functions, such as self-reporting, anti-microbial, anti-fouling and self-lubrication functions, etc., are also explored, which enriches the application ranges of these smart coatings. This review investigated the research progress of the micro/nanocontainers-based self-healing coatings over the past few years and provided a unique insight into the future development of such smart coatings.
When marine stern shafts operate under low speed and heavy load conditions, the metal shaft and water-lubricated bearing will be in a state of boundary lubrication or even dry friction. Poor lubrication can cause severe wear and friction-induced vibration, endangering the stealth performance of underwater vehicles. In this study, several typical liquid lubricants, including liquid paraffin, tung oil (TO), dimethyl silicone oil (DSO), ionic liquid (IL), and hexamethylene diisocyanate (HDI) were selected as the surface coatings for nitrile butadiene rubber (NBR). Using a tribological test machine with a high-precision vibration acceleration sensor, as well as scanning electron microscopy (SEM) and other techniques, the tribological performance and mechanisms of the NBR samples coated with different lubricants were studied under various working conditions. The results showed that the liquid lubricant significantly reduced the coefficient of friction of the NBR at high rotational speeds by over 92.2%. The sample coated with HDI showed obvious tribochemical wear, and coating with the rest of the liquid lubricants decreased the specific wear rate of NBR. According to the friction-induced vibration signals, we found that an increase in loading aggravated friction-induced vibrations, and the vibrational energy was mainly concentrated in the low frequency range. The liquid paraffin and TO coatings barely changed the vibration characteristics of the NBR, while the other three lubricants produced more friction-induced self-oscillations. In conclusion, compared to the other liquid lubricants, TO exhibited the best tribological performance. The finding of this study further our understanding of the friction and vibration behaviours of polymer materials, providing a reliable basis for designing composite materials with good lubrication and vibration damping performance.
Benzotriazole-loaded polydopamine/polyaniline ([email protected]/PANI) microcapsules are prepared vis the combination of a hard template method and in-situ polymerization. The PDA/PANI hollow microspheres are first prepared using SiO2 as a hard template and etching them with hydrofluoric acid. The BTA corrosion inhibitor is then loaded into the PDA/PANI hollow microspheres to obtain the [email protected]/PANI microcapsules. The mean particle size and shell thickness of the synthesized microcapsules are 8.3 and 2.1 µm, respectively. The load capacity of BTA is above 20 wt.%. The corrosion resistance of epoxy coatings with different contents and types of microcapsules is compared by saline immersion and electrochemical impedance tests. A scratched coating with 1 wt.% [email protected]/PANI microcapsules has the best anti-corrosion effect. The synergistic anticorrosion mechanism of BTA, PDA and PANI is revealed and confirmed.
The self-healing eutectogels with multifunctionality have attracted much attention in soft materials owing to their high conductivity and non-volatility. However, obtaining eutectogels with complete recovery of mechanical properties is still challenging. Herein, we developed a series of halogenated dibenzylidene-D-sorbitol (X-DBS) gelators. The X-DBS could form eutectogels in deep eutectic solvents obtained from choline chloride combined with alcohols or urea, which exhibit self-healing, complete recovery, load-bearing, and injectability. Fourier transform infrared, ¹⁹F nuclear magnetic resonance, and molecular dynamics simulations showed that the hydrogen bond between the C-F bond and the solvent molecule is key to the self-healing property of the eutectogels. Interestingly, the high ionic conductivity and self-healing property of our eutectogel make it potentially useful in a smart ionic conductor. Moreover, the self-healing eutectogels with corrosion resistance showed good lubricating performances on steel interfaces. In addition, the eutectogels showed excellent dye adsorption, effectively removing dyes from aqueous solutions. Thus, the efficient DBS-based eutectogels with self-healing properties are excellent candidates for conductive materials, interfacial lubrication, dye adsorption, and other applications.
In recent years corrosion-resistant self-healing coatings have witnessed strong growth and their successful laboratory design and synthesis categorises them in the family of smart/multi-functional materials. Among various approaches for achieving self-healing, microcapsule embedment through the material matrix is the main one for self-healing ability in coatings. The present work focuses on optimizing the process parameters for developing microcapsules by in-situ polymerization of linseed oil as core and urea-formaldehyde as shell material. Characteristics of these microcapsules with respect to change in processing parameters such as stirring rate and reaction time were studied by using optical microscopy (OM), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). The effectiveness of these microcapsules in coatings was characterized by studying their adhesion, performance, and mechanical properties.
The effects of wax lubricant filled microcapsule content on the tribological properties of epoxy composites without or with 8 wt.% short carbon fibers (SCFs) were systematically investigated. The core percentage of the microcapsules used in this study was about 70 wt.%. The tribological results clearly showed that the friction and wear of the epoxy composites without or with SCFs tested against a 6mm steel ball significantly decreased with increased microcapsule content from 2.5 to 10 wt.% as a result of the increased amount of released wax lubricant to lubricate rubbing surfaces. The epoxy composites with 8 wt.% SCFs exhibited the lower friction and wear than the ones without SCFs due to the combined lubricating effects of SCFs and released wax lubricant and the improved mechanical strength of the composites. It can be concluded that the higher microcapsule content gives rise to the lower friction and wear of the epoxy composites as the epoxy composites with 8 wt.% SCFs have the better tribological performance than the ones without SCFs.
Core–shell microcapsules of urea-resorcinol-formaldehyde shell and linseed oil (LO) core material as paint additives for self-healing coatings were prepared. The capsules contained LO either with or without Co-octoate as drier material and/or octadecylamine (ODA) as corrosion inhibitor. The microcapsules embedded in a commercial paint were applied on sandblasted mild steel sheets. After scratching the coated surface, the inhibition efficiency of core–shell microcapsule-containing coat, dipped into corrosive media, was followed visually and evaluated numerically by electrochemical impedance spectroscopy (EIS). In separate experiments, to optimize for the self-healing process, the composition of the core material, the effect of the drier and/or the inhibitor ODA on drying process of LO films were monitored by infrared spectroscopy. Pure LO needed 6–7 days to dry completely. The drying period could be shortened (to 5 h) via application of a dryer, but the addition of the corrosion inhibitor alone increased significantly the time needed for solifidication. To minimize the drying period we have found the proper combination of the ODA and the dryer of the LO.
The EIS measurements, in accordance with the drying tests, resulted in the next order of self-healing ability: LO < LO(+ODA) < LO(+Co-octoate) < LO(+ODA+Co-octoate).
We develop a new smart light responsive coating by incorporating hollow nanocontainers with azobenzene-based molecular switch into a water-based alkyd coating. The functionalized nanocontainers were obtained by immobilizing photoresponsive azobenzene molecular switches in the mesopore inner walls of hollow mesoporous silica nanoparticles. This nanoplatform permits encapsulation of active molecules within the hollow cavity under visible light but releases them exposure to UV irradiation. In addition, the expulsion of benzotriazole from the hollow nanocontainers can be started and stopped at will, which provides an effective approach to avoid side effects caused by excess release of active materials after the corrosion healing. The organic coatings containing functionalized nanocontainers exhibit continuous self-healing property sensitive to light, meanwhile, improve the long-term performance of aluminum alloy. The results of scanning vibrating electrode technique demonstrate that the incorporation of azobenzene-modified hollow mesoporous silica nanocontainers endows the organic hybrid coatings with an excellent continuous self-healing performance.
The effects of wax lubricant filled microcapsule content on the tribological properties of epoxy composites without or with 8 wt.% short carbon fibers (SCFs) were systematically investigated. The core percentage of the microcapsules used in this study was about 70 wt.%. The tribological results clearly showed that the friction and wear of the epoxy composites without or with SCFs tested against a 6 mm steel ball significantly decreased with increased microcapsule content from 2.5 to 10 wt.% as a result of the increased amount of released wax lubricant to lubricate rubbing surfaces. The epoxy composites with 8 wt.% SCFs exhibited the lower friction and wear than the ones without SCFs due to the combined lubricating effects of SCFs and released wax lubricant and the improved mechanical strength of the composites. It can be concluded that the higher microcapsule content gives rise to the lower friction and wear of the epoxy composites as the epoxy composites with 8 wt.% SCFs have the better tribological performance than the ones without SCFs. [DOI: 10.1115/1.4028752]
UV-induced self-repairing polydimethylsiloxane–polyurethane (PDMS–PUR) crosslinked networks capable of repairing mechanical damage upon UV exposure were developed. Induced by the presence of the copper chloride (CuCl2) catalyst, the network remodeling and bond reformation are achieved by the formation of Cu–O coordination complexes, covalent Si–O–Si hydrolysis with subsequent bond reformation. Upon UV exposure, Cu–O complexes undergo tetrahedral-to-distorted tetrahedral rearrangements which parallel the Si–O bond reformation. When PDMS was substituted with OH-terminated polyethylene glycol (PEG) to form PEG–PUR crosslinked networks, square planar-to-tetrahedral rearrangements occur during the damage–repair cycle. Alkyl backbone distortions and segmental motions induced by the local Cu–O symmetry changes result in volume changes of the metal–ligand complex center. These studies show that a combination of supramolecular and covalent bonds facilitates self-repairing.
Self-lubricating and wear resistant epoxy composites were developed via incorporation of wax-containing microcapsules. The effects of microcapsule size and content and working parameters on the tribological properties of epoxy composites were systematically investigated. The incorporation of microcapsules dramatically decreased the friction and wear of the composites than those of the epoxy. The increased microcapsule content or the incorporation of larger microcapsules decreased the friction and wear of the epoxy composites due to the larger amount of released wax lubricant via the rupture of microcapsules during wear test. The friction of the composites decreased with increased normal load as results of the promoted wear of the composites and the more release of the wax lubricant.
Self-lubricated coatings have been a major topic of interest in thermal spray in the last decades. Self-lubricated coatings obtained by thermal spray are exclusively based on solid lubricants (PTFE, h-BN, graphite, MoS2, etc.) embedded in the matrix. Production of thermal spray coatings containing liquid lubricants has not yet been achieved because of the complexity of keeping a liquid in a solid matrix during the spraying process. In the present article, the first liquid-solid self-lubricating thermal spray coatings are presented. The coatings are produced by inserting lubricant-filled capsules inside a polymeric matrix. The goal of the coating is to release lubricant to the system when needed. The first produced coatings consisted solely of capsules for confirming the feasibility of the process. For obtaining such a coating, the liquid-filled capsules were injected in the thermal spray flame without any other feedstock material. Once the concept and the idea were proven, a polymer was co-sprayed together with the capsules to obtain a coating containing the lubricant-filled capsules distributed in the solid polymeric matrix. The coatings and the self-lubricated properties have been investigated by means of optical microscopy, Scanning Electron Microscopy, and tribological tests.
a b s t r a c t The effect of wax-containing microcapsules incorporated in silicone composite coatings deposited on aluminum (Al) alloy substrates on the tribological performance of the coatings was systematically investigated. The wax-containing microcapsules were prepared via in situ polymerization. The tribological behavior of the composite coatings was evaluated using ball-on-disk tribological test. It was found that the increase in microcapsule concentration in the composite coatings apparently reduced the friction coefficient of the coatings because the lubricant released from the broken microcapsules during the tribological test of the coatings lubricated the rubbing surfaces. The results showed that the silicone composite coatings rubbed by a smaller Cr6 steel ball (3 mm diameter) under a lower normal load (100 mN) produced higher friction coefficients via reduced complication of their underlying strong substrates compared to the same coatings tested against a larger Cr6 steel ball (6 mm diameter) under a higher normal load (1 N). & 2012 Elsevier B.V. All rights reserved.
Structural polymers are susceptible to damage in the form of cracks, which form deep within the structure where detection is difficult and repair is almost impossible. Cracking leads to mechanical degradation of fibre-reinforced polymer composites; in microelectronic polymeric components it can also lead to electrical failure. Microcracking induced by thermal and mechanical fatigue is also a long-standing problem in polymer adhesives. Regardless of the application, once cracks have formed within polymeric materials, the integrity of the structure is significantly compromised. Experiments exploring the concept of self-repair have been previously reported, but the only successful crack-healing methods that have been reported so far require some form of manual intervention. Here we report a structural polymeric material with the ability to autonomically heal cracks. The material incorporates a microencapsulated healing agent that is released upon crack intrusion. Polymerization of the healing agent is then triggered by contact with an embedded catalyst, bonding the crack faces. Our fracture experiments yield as much as 75% recovery in toughness, and we expect that our approach will be applicable to other brittle materials systems (including ceramics and glasses).
Microcapsules containing an ionic liquid (IL) are potential candidate materials for preparing in situ self-lubricating composites with excellent tribological properties. 1-ethyl-3-methylimidazolium bis[(trifluoromethyl) sulfonyl]imide ([EMIm]NTf2) IL encapsulated polysulphone microcapsules are synthesized. The mean diameter and wall thickness are about 128 μm and 10 μm, respectively. Microcapsules have excellent thermal stability, with a thermal degradation onset temperature of 440 °C compared to traditional lubricants-loaded microcapsules. In situ self-lubricating composites are prepared by incorporating the IL-encapsulated microcapsules into epoxy matrix. When the concentration of the IL microcapsules is 20 wt%, the frictional coefficient and specific wear rate of composites are reduced by 66.7% and 64.9% under low sliding velocity and middling applied load conditions, respectively, as compared to the neat epoxy. The tribological behavior of the self-lubricating composites is further assessed in different applied load and sliding velocity conditions. The in situ self-lubricating mechanism of composites is proposed.
Polysulfone (PSF) microcapsules containing lubricant oil have been successfully prepared using solvent evaporation method. The results show that lubricant oil was successfully encapsulated and the encapsulation capacity of about 56.0 wt.% was achieved. The uniform microcapsules have nearly spherical shape and quite smooth outer surface. The mean diameter is approximately 156 and 169 μm by using different dispersant solutions. The wall material is porous in structure with wall thickness of about 20 μm. The initial decomposition temperature of PSF is 480 °C. It is higher than traditional poly(urea-formaldehyde) (PUF) and poly(melamine-formaldehyde) (PMF) wall materials with 245 °C and 260 °C initial decomposition temperature, respectively. High thermal stability of PSF microcapsules can be considered as additives in high temperature resistant polymer materials. The frictional coefficient and wear rate of epoxy composites decreased significantly by incorporating microcapsules containing lubricant oil into epoxy. When the concentration of microcapsules was 25 wt.%, the frictional coefficient and specific wear rate were reduced by 2.3 and 18.3 times, respectively, as compared to the neat epoxy.
The effects of compositional modifications on the sliding friction and wear against bearing steel were investigated for newly-developed binary and ternary epoxy composites. Some of the new materials included hexamethylene diisocyanate (HDI) filled microcapsules and wax filled microcapsules, and others used HDI filled microcapsules, wax filled microcapsules and short carbon fibers (SCFs) at different ratios. The hardness of the binary and ternary epoxy composites decreased with increased content of wax filled microcapsules. The wax filled microcapsules were larger than the HDI filled microcapsules. Due to the rigidity of the SCFs, the hardness of the epoxy composites with 8 wt% SCFs was higher than that of the composites without SCFs. Pin-on-disc, sliding friction and wear performance for the binary and ternary epoxy composites tested against a 100Cr6 steel ball, was improved as the content of wax filled microcapsules increased. This was due to their effective lubricating effects. It was proposed that the addition of 8 wt% SCFs, which lowered the friction and wear of the epoxy composites, promoted solid lubrication by free-rolling SCFs.
Pentasulfid bis(2, 2, 4-trimethyl) pentyl (RC2540)-melamine-formaldehyde resin microcapsules was synthesized by in-situ polymerization method with sulfureted fatty additive RC2540 as core materials and melamine-formaldehyde resin (MF resin) as shell materials. FTIR, thermo-gravimetric analysis and SEM measurements were used to characterize these microcapsules. The friction and wear properties of RC2540-MF resin microcapsules were investigated with four-ball testing machine using polyethyleneglycol as base fluid. The experimental results reveal that the friction coefficient can be as low as 0.04 under the lubrication of the base oil with 3% mass fraction of RC2540-MF resin microcapsules in 314 N load, the wear diameter under 314 N load(with 5% mass fraction of RC2540-MF resin microcapsules) is 0.54 mm, the experimental load can be increased to 1000 N above. The effect of RC2540-MF resin microcapsules in reducing friction and wear may be attributed to the physical and chemical adsorption on the friction surface, and to the tribochemical reaction film by active sulfides released from broken RC2540-MF resin microcapsules, leading to anti-friction, good extreme pressure and anti-wear property.
The applications of polysulfone (PSf) microcapsules have been increasing in the last years. The main reason for using PSf as a capsule shell is due to the high chemical and physical stability that this material possesses. In addition, it is a well-known polymer, broadly used by industries and moreover, it is a non-toxic and biocompatible functional material that may be employed for medical and biological applications. Polysulfone microcapsules preparation may be carried out easily by phase inversion precipitation technique that is a well-established technique in which capsule formation takes place in few seconds. Phase inversion precipitation allows obtaining different polymer shapes, it does not produce toxic products and it does not require high temperatures. The present review collects and describes several investigations focused on the use of PSf as polymer system for microencapsulation and its applications.
In this work, a PTFE-based self-lubricating coating containing microencapsulated [HMIM][NTf2] ionic liquid (IL) lubricant is reported. The microcapsules, made of polysulphone, are prepared by solvent evaporation. In order to allow incorporation in the thin PTFE coating layer, which is applied by spraying, the capsules were produced with small sizes (below 10 μm). Their physico-chemical characterization is presented in terms of SEM/EDS, TGA, FTIR and particle size distribution analysis. It is shown that both the encapsulant material and the IL lubricant are able to withstand the high-temperature curing conditions necessary for the coating system used (380 °C during 30 min). Crossed-cylinders tribological testing of the applied coatings showed that incorporation of IL-containing capsules yields a reduction in coefficient of friction of up to 12 % when compared to the baseline formulation and a reduction of up to 70 % in wear rate under high load and low sliding speed conditions. The tribological behaviour of the modified coating is further assessed in different load and speed (P.V) combinations.
Silica gel shell microcapsules containing ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate ([Bmim][PF6]) have been successfully synthesized through an interfacial self-assembly process and solgel reaction. They are further developed as filler to improve the tribological property of polyurethane composite coatings. The tribological behaviors of the polyurethane composite coatings filled with microcapsules have been systematically investigated using ball-on-disk tribological test. The results showed that the polyurethane composite coating filled with microcapsules displayed much lower friction coefficient and wear, compared with that of unfilled one. It is demonstrated that the ionic liquid released from the broken microcapsules during the friction process lubricates the rubbing surfaces and prevents a direct contact between steel ball and coating, leading to a lower friction coefficient and a lower wear width and depth.
The self-repairing polymer coating based on microencapsulated epoxy resin agent and catalyst was prepared. Defects in the coating were successfully healed when epoxy resin was released from the microcapsules, which were ruptured under simulated mechanical action. Polymer healed area was found to prevent corrosion of the substrate, which was analysed by scanning electron microscopy. The healing efficiency was determined using electrochemical impedance spectroscopy. The local corrosion activity of the damaged coating on the carbon steel was evaluated. The impedance spectroscopy of the self- healing coating showed measurable improvements of anticorrosion performance after defect creation.
Double-layered polyurea microcapsules containing hexamethylene diisocyanate (HDI) with outstanding shell tightness have been successfully synthesized via interfacial polymerization reaction in an oil-in-water emulsion. The resultant capsules were systematically characterized by scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR). The reaction parameters including reaction temperature (40°C, 50°C, 60°C), reaction duration (1h, 1.5h, 2h and 2.5h), the amount of Suprasec 2644 (2.4g, 3g and 3.6g) and emulsification time (15 min, 45 min and 75 min) were investigated and evaluated in terms of core fraction and quality of microcapsules. The core fraction of microcapsules was reduced with the increase of reaction temperature, reaction duration, the mass of Suprasec 2644 and emulsification time, while the quality of microcapsules fluctuated. The thermal and organic solvents resistances were assessed by using TGA and titration. The results showed that the microcapsules had 1.6 % weight loss compared with pure HDI with 90 % weight loss after 60 min isothermal treatment at 100 °C. After immersion in various solvents for 24 days, the microcapsules released as low as ~3% of core in weakly polar solvents (i.e. hexane and xylene), about 5% - 60% core in polar aprotic solvents (i.e. ethyl acetate, acetone, DMF and DMSO), and 60% - 90% in water and polar protic solvents (i.e. isopropanol and ethylene glycol). Both fresh and hexane treated HDI-capsules showed excellent anticorrosion performance in the scratched coatings via self-healing functionality, indicating promising practical application in industrial coating and paint systems.
For the production of polysulfone microcapsules, a process was proposed, which allowed the obtaining of capsules with different wall morphology. A polysulfone solution was projected to a precipitation bath. Three solvents were assessed: N,N-dimethylformamide, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone. Precipitation baths were composed by water, pure or mixed with solvent. Surfaces and cross–sections of different preparations were observed by Scanning Electron Microscopy. The study was focused on capsules of 30 ± 10 µm of diameter. Microcapsules surfaces were porous and two different structures were distinguished in the cross-section: macrovoids and sponge-like structures. High concentration of solvent in the precipitation bath reduced the porosity of the surface and the macrovoids of the wall, thus favoring sponge-like structures. The present work set some bases for a better control of polysulfone microcapsules morphology. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013
We report the preparation and characterization of light-healable nanocomposites based on cellulose nanocrystals (CNCs) and a metallosupramolecular polymer (MSP) assembled from a telechelic poly(ethylene-co-butylene) that was end-functionalized with 2,6-bis(1′-methylbenzimidazolyl) pyridine (Mebip) ligands and Zn(NTf2)2. The polymer absorbs incident ultraviolet (UV) radiation and converts it into heat, which causes dissociation of the metal–ligand motifs. This process liquefies the material, and small defects are readily filled. When the UV light is switched off, the MSP reassembles and the original properties are restored. The introduction of CNCs into the MSP matrix leads to a significant increase of the stiffness and strength, from 52 and 1.7 MPa for the neat polymer to 135 and 5.6 MPa upon introduction of 10% w/w CNCs. The Zn2+ ions bind to the CNCs which means the metal:ligand ratio of the MSP must be adjusted accordingly. In nanocomposites thus made, deliberately introduced defects can be efficiently healed.
A self-healing polymer for coating application was developed based on thermoreversible Diels–Alder (DA) reactions. The polymer network is formed by reacting a mixture of trifunctional and difunctional furanized resins (3F and 2F) with a bismaleimide (2M). The DA reaction occurs at temperature above 50 °C whilst retro-DA reaction occurs at about 120 °C. FTIR spectra were taken in order to monitor the reaction progress, and the thermal reversibility of the reaction was proved by DSC and DMA tests. A significant improvement of both the mechanical properties and the self-healing behaviour was achieved by introduction of small amount of a suitable plasticizer like benzyl alcohol. Self-healing properties of the plasticized polymer resulted in complete scratch recovery after retro-DA and DA reaction, whilst tensile testing reveals a 48% restoring of the pristine mechanical strength.
In this study, urea-formaldehyde based microcapsules containing linseed oil were prepared via in situ polymerization method. Microcapsules with a regular spherical shape, 10-300 mu m diameter and an oil content of 63-77 wt% were synthesized in various core:shell ratios and different mixing speeds. The effect of core:shell ratio and mixing speed on the size and morphology of the microcapsule were studied using optical microscopy, SEM and particle size analysis. Epoxy-based coatings containing various amounts of microcapsules were prepared and the effect of microcapsule size and loading on the mechanical properties and healing performance were evaluated by measuring the tensile properties and corrosion performance of the coatings. The amount of the oil released in the scratched coating was determined both practically and theoretically and the results were compared. The results showed that the addition of microcapsules reduces the tensile properties of the coating, the extent of which depends on the microcapsule size and loading wt%. For instance, sample containing 3 wt% of the microcapsules with an average particle size of 53 mu m showed 8.6% reduction in tensile modulus. Optical microscopy of the scratched sample revealed that with increasing microcapsules' size and loading, the crack was filled more effectively and this led to an improved corrosion performance. Finally, the optimum combination of self-healing and mechanical properties was found to be for the coating containing 5 wt% of microcapsules, with an average particle size of 53 mu m.
Hydrolysable organic silane, i.e. 1H,1H,2H,2H-perfluorooctyl triethoxysilane (POTS), was carefully selected and microencapsulated as healing agent via in situ polymerization in an oil-in-water emulsion. The microcapsule size was adjustable via changing agitation rate for various coating systems. POTS microcapsules were incorporated into epoxy resin and coated on a steel substrate to form a corrosion resistant organic coating. The corrosion test in the salt solution demonstrated the good corrosion resis-tance of the self-healing coating compared to the control sample. Additional analysis revealed that the corrosion prohibition functionality was realised by an autonomous self-healing mechanism of the encap-sulated POTS hydrolysed with water upon scratch.
Organic coatings based on inhibitor loaded inorganic containers for smart corrosion inhibition are presented. The overall coating performance is strongly influenced by the containers as well as their inhibitor capacity, compatibility with the coating matrix, and size. The important effect of container size is described for the first time in this work by investigating two types of mesoporous silica containers of different diameters: 80 and 700 nm. The coating physical properties (thickness and adhesion) are comparable for both container types. In contrast, the coating barrier properties are strongly influenced by the container size as assessed with electrochemical impedance spectroscopy (EIS). The incorporation of bigger containers reduces the coating resistance by a factor of two. Surprisingly, despite the similar amounts (20 wt%) of loaded inhibitor (2-mercaptobenzothiazole), different active inhibition ability is detected with the scanning vibrating electrode technique (SVET). Therefore, it is found that coatings with smaller containers exhibit better self-healing performance.
Novel continuously aligned carbon nanotubes (ACNTs) were synthesized by a floating catalyst Chemical Vapor Deposition (CVD) process. The ACNTs reinforced epoxy (EP) composites were prepared by a capillary-induced moistening method. The tribological properties of pure EP and ACNTs/EP composites in water were comparatively investigated in terms of loads and velocities. Results indicated that both the wear rate and the friction coefficient of ACNTs/EP composites were lower than those of pure EP. ACNTs/EP composites displayed outstanding anti-wear properties, which reduced the wear rate by 219 times as compared to pure EP. Superior performances of ACNTs/EP composites were also observed in rigorous condition (4.0 MPa). The worn and counterpart surfaces were studied by scanning electron microscopy (SEM). SEM observations revealed a slightly abrasive wear behavior for ACNTs/EP composites, while fatigue and abrasive wear behavior for pure EP. In particular, owing to the obstruction of ACNTs tips, part of the debris of epoxy adhered to the worn surface of ACNTs/EP composites. This debris reinsertion behavior further improved the wear resistance of ACNTs/EP composites. Besides, the effect of water on the tribological behaviors of ACNTs/EP composites was discussed as well.
In this paper, epoxy microcapsules were prepared by interfacial polymerization of epoxy resin droplets with ethylenediamine (EDA), and the capsules were characterized by scanning electron microscope (SEM). Then, the coatings containing epoxy microcapsules were applied on carbon steels, and their behavior and self-healing effect were investigated by electrochemical impedance spectroscopy (EIS) technique and SEM observation. The experimental results demonstrate that the artificial scratches were successfully healed in about 4-h after made. Furthermore, coating prepared from 20 wt.% epoxy microcapsules shows the best performance among all the prepared coatings.
Cinnamide moiety-containing polydimethylsiloxane (CA-PDMS) was prepared and used as a healing agent. The photo-cross-linking behavior of CA-PDMS was investigated by UV-vis and Fourier transform infrared (FT-IR) spectroscopy. Upon photo-irradiation, CA-PDMS generates viscoelastic substances which have intrinsic recoating (or self-healing) capability when scribed with a cutter blade. CA-PDMS was microencapsulated with a urea-formaldehyde polymer, and the mean diameter and size distribution of the microcapsules could be controlled by the agitation rate. The prepared microcapsules were integrated into a commercial enamel paint to create a self-healing coating. It was confirmed by optical microscopy and scanning electron microscopy (SEM) that, when the self-healing coating is scribed, the healing agent is released from ruptured microcapsules and fills the scribed region. The scribed self-healing coating was photo-irradiated to induce photo-cross-linking of the released CA-PDMS. SEM imaging provided visual evidence that, when the scribed and healed region is re-scribed, repeated self-healing is accomplished. It was successfully demonstrated by anticorrosion and electrochemical tests that the CA-PDMS-based self-healing coating system has repeatable self-healing capability. Our self-healing coating is the first example of microcapsule-type repeatable self-healing system, and offers the advantages of simple, inexpensive, practical healing.
In the present work, epoxy based quaternary composites were produced by filling lubricant oil-loaded microcapsules, surface grafted nano-SiO2 and discontinuous carbon fibers. Through orthographic tests, the optimal contents of the fillers were determined for achieving significantly improved tribological properties. The lowest specific wear rate and friction coefficient of the composite can be 9.8×10−7mm3/Nm and 0.12, respectively, much lower than those of unfilled epoxy, i.e. 1.3×10−4mm3/Nm and 0.56. In addition, mechanical properties, especially the maximal loading ability, of the quaternary composite were evidently higher than those of the binary composite with oil-loaded microcapsules. The oil released from the broken microcapsules during sliding wear mainly accounted for the lubrication, while nano-SiO2 and carbon fibers serve as both solid lubricant and reinforcement. As a result, positive synergetic effect appeared and the proposed quaternary composites might be applicable in practice.
The incorporation of microcapsules containing lubricant oil into epoxy composites leads to materials with ultra‐low friction and wear performance. During sliding wear tests, the capsules are damaged by the asperities of the counterface, releasing the oil to the contact area. The lubrication effect of the released oil and the entrapment of wear particles in the cavities left by the ruptured capsules leads to a significant reduction of both the frictional coefficient and the specific wear rate. The approach provides the merits of fluid lubrication but excludes the drawbacks of external lubrication. A minute amount of lubricant oil is sufficient to improve the tribological properties significantly.
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The self-healing anticorrosion effect of layer-by-layer (LbL) assembled nano-reservoirs (polyelectrolyte-coated nanoparticles) embedded in a hybrid coating deposited onto an Al alloy is investigated (see figure). The corrosion inhibitor, benzotriazole, is entrapped in the polyelectrolyte at the LbL assembly step; its release is initiated by local pH changes near the corrosion-damaged zones in the alloy. The nanoreservoirs increase long-term corrosion protection of the substrate and provide effective inhibitor storage and its prolonged release on demand.
Effectiveness of linseed oil filled microcapsules was investigated for healing of cracks generated in paint/coatings. Microcapsules were prepared by in situ polymerization of urea–formaldehyde resin to form shell over linseed oil droplets. Characteristics of these capsules were studied by FTIR, TGA/DSC, scanning electron microscope (SEM) and particle size analyzer. Mechanical stability was determined by stirring microcapsules in different solvents and resin solutions. Cracks in a paint film were successfully healed when linseed oil was released from microcapsules ruptured under simulated mechanical action. Linseed oil healed area was found to prevent corrosion of the substrate.
Smart/self-healing micro-capsulated inhibitor incorporated in epoxy primer before painting on a steel surface was evaluated for its corrosion protection effectiveness on exposure to ASTM D 5894 electrolyte in laboratory and natural tropical sea-shore environment. The “healant” inhibitor was industrial custom-made and non-chromate organic-based microcapsules which were mixed into the primer before applying a polyurethane topcoat layer on steel surface. The results indicate that the active components in ruptured embedded inhibitor microcapsules were released into an inflicted scribe primer and topcoat film on steel surface on exposure to inhibit development of an electrochemical cell. Undamaged surface film of the test and control specimens exposed in the environments demonstrated excellent corrosion-inhibition performance as reflected by both visual inspection and electrochemical impedance spectroscopy experimental data. The results obtained on the performance of self-healing inhibitors should provide an understanding of the fundamental material-property relationships of smart inhibitor coatings. And, thus, should facilitate the development of optimized paint compositions in order to extend the useful service life of steel-infrastructure applications.
The efficacy of a “self-healing” corrosion protection coating system for use on steel enclosures for outdoor equipment has been investigated using urea formaldehyde microcapsules (50–150 μm in diameter) containing several types of film forming compounds (healants) and corrosion inhibitors mixed into commercially available coatings systems. Five different types of inhibitors/film formers were tested, and three different techniques for application of the coatings with microcapsules were evaluated. Laboratory tests showed that when the coating system was damaged by abrasion, the microcapsules released the film forming and corrosion inhibiting compounds. Steel substrates coated with these self-healing systems were scribed and laboratory tested according to ASTM D 5894. Undercutting at the scribe (ASTM D 1654) was reduced by using microcapsules containing self-healing compounds. Growth of coating damage at the scribe was arrested in self-healing coatings with all microcapsule formulations compared to control samples. The performance of some microcapsules evaluated in this study was found to be dependent on the method of application.
The capability of the encapsulated Tung oil was investigated as a scratch healing agent for self-healing coatings. Encapsulation of Tung oil with urea–formaldehyde shell was carried out by in situ polymerization. Before the mechanical agitation of microcapsules into epoxy resin, their characteristics were evaluated by scanning electron microscope (SEM) and Fourier transform infrared spectroscopy (FTIR). Released Tung oil from ruptured microcapsules healed the artificial scratch in the coating matrix successfully. Corrosion resistance of healed area was evaluated by electrochemical impedance spectroscopy (EIS) and immersion test; and the results were compared with neat epoxy coating.
Keywords
Tung Oil; Self-Healing Coating; Epoxy Coating; In situ polymerization
Layer-by-layer assembled nanocontainers for self-healing corrosion protection
- D G Shchukin
- M Zheludkevich
- K Yasakau
- S Lamaka
- M G S Ferreira
- H Mohwald
D.G. Shchukin, M. Zheludkevich, K. Yasakau, S. Lamaka, M.G.S. Ferreira, H.
Mohwald, Layer-by-layer assembled nanocontainers for self-healing
corrosion protection, Adv. Mater. 18 (2006) 1672-1678.