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

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

Assessment of microcapsule—catalyst particles healing system in high performance fibre reinforced polymer composite

Autonomous self-healing in carbon fibre reinforced polymer (CFRP) is demonstrated using epoxy resin filled microcapsules and a solid-state catalyst. Microcapsules filled with oligomeric epoxy resin (20–450 μm) and particles of Sc(OTf)3 are embedded in an interleave region of a unidirectional CFRP laminate and tested under mode I loading. Double cantilever beam (DCB) test specimens containing variable concentrations of microcapsules and catalyst were prepared, tested and compared to those healed by manual injection with corresponding healing resin formulation. The healing efficiency was evaluated by comparing the maximum peak load recorded on load–displacement curves for pristine and healed specimens. A 44% maximum recovery was observed for specimens containing 10 wt% of solid phase catalyst and 11 wt% of epoxy microcapsules. However, a significant (80%) decrease in initial strain energy release rate (G IC) was observed for specimens with the embedded healing chemistries

Taguchi and ANOVA analysis for the optimization of the microencapsulation of a volatile phase change material

The microencapsulation of volatile phase change materials is an important and challenging area for low-temperature thermal energy storage. Our previous studies have effectively addressed the challenge of long-term volatile core retention and also indicated that the quality of the obtained poly(urea-formaldehyde) microcapsules is highly affected by various process parameters, including reaction temperature, initial pH, reaction time, and homogenization speed. In this paper, the Taguchi orthogonal array has been employed to optimise controllable process parameters to identify the most synergistic combination, in order to maximise the payload, yield, and encapsulation efficiency. The Taguchi signal-to-noise ratio results substantiated that the most efficient combination of parameters was 3 h reaction time, pH 3.5, 55 °C reaction temperature, and 1200 rpm homogenization speed. With this combination of parameters, microcapsules with superbly high payload of 95.2%, as well as a yield of 30.5% and encapsulation efficiency of 71.1% were amalgamated. In addition, Analysis of Variance (ANOVA) was also utilised to demonstrate the mean response magnitudes (% contribution) of each of the four controllable process parameters, in terms of contribution for the payload, yield, and encapsulation efficiency. Overall, it was indicated that the temperature is the most influential parameter at 83.1% contribution, followed by pH at 6.8%, reaction time at 5.2%, and homogenization speed at 4.9%. Such findings in this work postulate the fundamental insights into maximising the output of the formulation conditions, which in turn is aimed to minimise the time and cost of production of the microcapsules

Progress in Self-Healing Fiber-Reinforced Polymer Composites

This paper sets out to review the current state of the art in applying self-healing/self-repair to high-performing advanced fiber-reinforced polymer composite materials (FRPs). A significant proportion of self-healing studies have focused so far on developing and assessing healing efficiency of bulk polymer systems, applied to particulate composites or low-volume fraction fiber-reinforced materials. Only limited research is undertaken on self-healing in advanced structural FRP composite materials. This review focuses on what is achieved to date, the ongoing challenges which have arisen in implementing self-healing into FRPs, how considerations for industrialization and large-scale manufacture must be considered from the outset, where self-healing may provide most benefits, and how a functionality like self-healing can be validated for application in real structures. Systems are compared in terms of process parameters, resulting mechanical properties, methods of healing assessment, as well as values of healing quantification. Guidelines are further given for a concerted effort to drive toward standardization of tests and the use of specific reinforcement architectures in order to allow reliable comparison between the available healing systems in structural composites

GIG economy and sustainable development: bibliometric analysis and identification of future research directions

Purpose: The aim of this article is to identify the most common fields of study undertaken by researchers in scientific papers covering simultaneously the gig economy and sustainable development. Design/methodology/approach: The research study used a structured literature review method. The structured bibliometric query Q1 allowed for the exploration of the Scopus database. As a result, 48 scientific studies from the period 2017-2023 were selected for analysis, which simultaneously addressed the issues of the gig economy and sustainable development. Findings: The analyses carried out showed that the issue of sustainable development is addressed in the context of the gig economy. This is a relatively new research area, as shown, for example, by the generated database of studies used for the bibliometric analyses conducted. The issues of sharing economy and decent work are important areas addressed in the context of the gig economy. It was noticed that there was a lack of author keywords covering 'green' issues. Research limitations/implications: Research results based on other databases (e.g. Web of Science) may lead to different results. It should be noted that the different bibliometric databases do not overlap, which is related to the indexing of scientific journals or publications in the databases. Nonetheless, a universal query was used in the study, which can be used in the various bibliometric databases once it has been adapted to their respective query form. In addition, the various databases are constantly being supplemented with new scientific papers, which also depends on the publishing process. Hence, the content of the Q1 query can in future be used for comparison purposes with the results obtained, or to compare different bibliometric databases with each other. Originality/value: In the discussion that followed, attention was drawn to the issues of green jobs and green self-employment. In the authors' opinion, such research directions, although not yet visible in the authors' keywords, will be developed soon in the context of studies covering the issues of the gig economy and sustainable development considering the green transformation of the economy taking place. This article is addressed to all those who are interested in the issues of the gig economy and sustainable development

Exposing greenwashing: a catalyst for green economy development

Purpose: Two closely related research objectives have been constructed, aimed at exploring scientific studies dealing simultaneously with the issues of greenwashing and the green economy. The first objective is to identify the most frequently undertaken research areas in the indicated area. While the second objective of the study is to identify the green research areas highlighted by researchers through the author's keywords. Design/methodology/approach: The study used two research methods (systematic literature review and classical literature review). The bibliometric queries created allowed the exploration of two databases (Scopus and Web of Science). The result of the exploration carried out in the research procedure was the selection for analysis of 37 scientific papers that simultaneously dealt with the issues of greenwashing and the green economy. Findings: The analyses carried out showed that the issue addressed is a relatively new research area, and thus further development of research in this area can be expected in the future. Conclusions of the analysis lead to the conclusion that greenwashing is a very unfavorable phenomenon that contributes to the problem of correct verification of the scale of greening the economy. Hence the need to expose this type of practice. Research limitations/implications: Conducting research based on other databases can lead to different results in terms of the green research areas identified. This issue is because the various bibliometric databases do not overlap. The indicated aspect is shown in the article by presenting the issue of Scopus and Web of Science databases. In the study, however, universal bibliometric queries were used. They can be applied to various bibliometric databases after their proper syntactic adjustment. The queries used (Q1 and Q2) can be reused in the future for comparative purposes of changes over time. Originality/value: Promising future research directions around greenwashing and the green economy were identified. Such areas could be, especially, the question of the impact of greenwashing practices on the creation of quality green jobs, or the issue of the green skills gap. The article is aimed primarily at researchers addressing the issues of greenwashing and the green economy in their deliberations

Mikrokapsułki mocznikowo-formaldehydowe – synteza oraz wpływ prędkości mieszania na rozrzut wymiaru

Microcapsules from commercially available epoxy resin (Epidian® 52) and an organic solvent (ethylphenylacetate, EPA), for application to self-healing epoxides, were prepared. Poly(urea-formaldehyde) microcapsules containing the active ingredients were prepared using in situ polymerization in an oil-in-water emulsion. The prepared capsules were characterized by scanning electron microscope (SEM) for their surface morphology and size distribution. Thermogravimetric analysis (TGA) has been carried out to determine their thermal stability and maximum processing temperature. Moreover, the influence of stirring speed on their size distribution was investigated in predefined conditions. It is demonstrated that microcapsules can be easily prepared using the literature methodology and that the urea-formaldehyde polymer is a good barrier for the enclosed epoxy resin–organic solvent. Performed experiments suggest that size of microcapsules can be controlled by the stirring speed of the emulsion and that the capsules are thermally stable up to 140 °C for 24 hours. Additional studies showed that microcapsules exhibit excellent interface with a commercial epoxy resin matrix cured at elevated temperatures what is desired in their further application.Otrzymano polimerowe mikrokapsułki zawierające mieszaninę żywicy epoksydowej (Epidian®52) i rozpuszczalnika organicznego (fenylooctan etylu, EPA) przeznaczone do zastosowań w samonaprawiających się materiałach epoksydowych. Kapsułki przygotowano z wykorzystaniem techniki polikondensacji mocznika i formaldehydu w emulsji oleju w wodzie. Metodą skaningowej mikroskopii elektronowej (SEM) analizowano morfologię powierzchni wytworzonych kapsułek i określano rozrzut ich wymiarów. Stabilność kapsułek w podwyższonej temperaturze oraz maksymalną temperaturę przetwórstwa wyznaczano termograwimetrycznie (TGA). Badano też wpływ szybkości mieszania wyjściowej mieszaniny surowców na rozrzut wymiarów otrzymanych kapsułek. Stwierdzono, że stosowana żywica mocznikowo-formaldehydowa stanowi warstwę barierową (ścianę kapsułki) dla inkludowanych mieszanin epoksydów z rozpuszczalnikiem organicznym. Wykazano, że zastosowanie odpowiedniej prędkości mieszania składników podczas emulsyfikacji pozwala na zmniejszenie rozrzutu wymiarów kapsułek. Otrzymane kapsułki są termicznie stabilne do temperatury 140 °C w ciągu 24 h. Stwierdzono też, że warstwa powierzchniowa kapsułek jest silnie związana z żywicą epoksydową usieciowaną w podwyższonej temperaturze, co jest korzystne w ich dalszych zastosowaniach

15-minute city: identifying current and setting future research directions

Purpose: The main aim of the research was to identify the most common research areas in scientific publications addressing the issue of the 15-minute city, which were expressed by researchers of the concept through the author's keywords. An additional aim of the analyses undertaken was to identify key green research areas in the scientific studies analyzed. Design/methodology/approach: The study was planned and conducted from November 2023 to May 2024. To achieve the aims of the study, the method of systematic literature review and classical literature review was used. 126 scientific publications were analyzed. Findings: The analyses conducted showed that the issue of the 15-minute city is a relatively new and still area-evolving research concept. Numerous research threads are raised around this issue. Nonetheless, the most frequently discussed issue is the proximity and accessibility to city residents of facilities with social functions, which are defined as essential or basic. Even though green issues have been discussed in most of the scientific publications analyzed (mainly the issue of green spaces, green areas, and green zones), issues that can be directly linked to the issue of the green economy have been a marginal research thread. Research limitations/implications: The study is limited by the choice of the database for bibliometric analysis (Scopus database) and the content of the bibliometric query. Hence, the same study based on a different database may result in different results (a problem further described in the article). The Q1 bibliometric query can be repeated in the future or applied to other databases (provided the record is adjusted). Thus, the study is reproducible and can provide a point of comparison for other researchers of the 15-minute city in the future. Originality/value: Directions for future research at the intersection of the 15-minute city concept and green economy issues were proposed. In terms of this issue, among other things, the research issue of green jobs (one of the key pillars of the green labor market) was highlighted. In addition, it was pointed out that the concept of the 15-minute city applied in practice can stimulate the formation of a green business ecosystem in cities. The article is addressed to anyone interested in the issues of the 15-minute city

Lamb-Wave-Based Method in the Evaluation of Self-Healing Efficiency

The aim of this research is a feasibility study of self-healing process monitoring in composite laminates. A novel nondestructive method based on the full wavefield of Lamb wave processing is proposed. Experimental verification is presented for glass-fiber-reinforced polymer plate with embedded self-healing function in the form of a dry microcapsule powder. After impacting the specimen to create barely visible impact damage, a series of laser vibrometer full wavefield measurements were carried out and processed to assess self-healing efficiency.</jats:p

Lamb-Wave-Based Method in the Evaluation of Self-Healing Efficiency

The aim of this research is a feasibility study of self-healing process monitoring in composite laminates. A novel nondestructive method based on the full wavefield of Lamb wave processing is proposed. Experimental verification is presented for glass-fiber-reinforced polymer plate with embedded self-healing function in the form of a dry microcapsule powder. After impacting the specimen to create barely visible impact damage, a series of laser vibrometer full wavefield measurements were carried out and processed to assess self-healing efficiency