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Article
Publication date: 6 April 2021

Raj Kumar Pittala, Satish Ben B., Syam Kumar Chokka and Niranjan Prasad

Microcapsule-embedded autonomic healing materials have the ability to repair microcracks when they come into contact with the crack by releasing the healing agent. The…

Abstract

Purpose

Microcapsule-embedded autonomic healing materials have the ability to repair microcracks when they come into contact with the crack by releasing the healing agent. The microcapsules with specific shape and thickness effect in releasing healing agent to the cracked surfaces. Thus, the purpose of this paper is to know the load bearing capacity of the self-healing microcapsules and the stresses developed in the material.

Design/methodology/approach

In the present study, self-healing microcapsule is modelled and integrated with the polymer matrix composite. The aim of the present study is to investigate failure criteria of Poly (methyl methacrylate) microcapsules by varying the shell thickness, capsule diameter and loading conditions. The strength of the capsule is evaluated by keeping the shell thickness as constant and varying the capsule diameter. Uniformly distributed pressure loads were applied on the capsule-reinforced polymer matrix composite to assess the failure strength of capsules and composite.

Findings

It is observed from the results that the load required to break the capsules is increasing with the increase in capsule diameter. The failure strength of microcapsule with 100 µm diameter and 5 µm thickness is observed as 255 MPa. For an applied load range of 40–160 N/mm2 on the capsules embedded composite, the maximum stress developed in the capsules is observed as 308 MPa.

Originality/value

Failure strengths of microcapsules and stresses developed in the microcapsule-reinforced polymer composites were evaluated.

Details

World Journal of Engineering, vol. 18 no. 3
Type: Research Article
ISSN: 1708-5284

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Article
Publication date: 11 September 2009

J. Hu, Z. Zheng, F. Wang, W. Tu and L. Lin

The purpose of this paper is to synthesise and characterise novel thermally expandable microcapsules having poly (acrylonitrile (AN)‐methyl methacrylate (MMA)‐butyl…

Abstract

Purpose

The purpose of this paper is to synthesise and characterise novel thermally expandable microcapsules having poly (acrylonitrile (AN)‐methyl methacrylate (MMA)‐butyl acrylate (BA)) copolymer shells and p‐toluenesulphonylhydrazide (TSH) cores.

Design/methodology/approach

The novel thermally expandable microcapsules are synthesised by suspension polymerisation. The effects of various parameters including monomers and surfactant compositions on thermal expandability and stability, and particle size and size distributions of the microcapsules obtained are studied. Fourier transform infrared (FTIR) and scanning electronic microscopy (SEM) analyses are employed to characterise the chemical structure and morphology of the microcapsules obtained.

Findings

Suspension polymerisation with the monomers composition of 70 per cent AN/20 per cent MMA/10 per cent BA can yield microcapsules having a good expansion property and heat stability at 150°C. The paper also finds that when the amount of the incorporated PA reaches 20 per cent, the shells of microcapsules obtained will adhere together and some shells rupture resulting in the collapse of many of the expanded microcapsules. During the course of polymerisation, high‐molecular surfactant styrene – maleic acid copolymer sodium salt can help to achieve microcapsules with more uniform size distribution. FTIR and SEM characterisation show that the chemical structure of microcapsules contain core material and copolymeric shell and the morphology of microcapsules is very well defined, core‐shell type, respectively.

Research limitations/implications

The shell copolymer in the present context is synthesised from acrylonitrile‐methyl methacrylate‐ and butyl acrylate. Besides, it can be synthesised from other monomers also. In addition, the expansion efficiency of microcapsules can be studied.

Practical implications

The learning gained through this paper can be applied to the synthesis and application of other microcapsule or even nano‐capsule systems.

Originality/value

The method for preparation of TSH microcapsules by suspension polymerisation is novel and the microcapsules could find applications in water‐based intumescent and flame retardant wood coatings.

Details

Pigment & Resin Technology, vol. 38 no. 5
Type: Research Article
ISSN: 0369-9420

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Article
Publication date: 7 March 2016

Pooneh Kardar

– The purpose of this work was to prepare a catalyst-free microcapsules as self-healing agent in an automotive clearcoat to improve the scratch resistance of coatings.

Abstract

Purpose

The purpose of this work was to prepare a catalyst-free microcapsules as self-healing agent in an automotive clearcoat to improve the scratch resistance of coatings.

Design/methodology/approach

In this research, microcapsule with isophorone diisocyanate (IDPI) core and polyurethane shell were prepared and used in self-healing coatings. Microcapsules synthesised were characterised by thermal gravimeter and infrared spectra. The microcapsules were dispersed in an acrylic-melamine clearcoat, and the scratch resistance was evaluated.

Findings

The triplex product and the formed polyurethane bonds were confirmed by thermal gravimeter and infrared spectra. In addition, smooth spherical particles with a diameter of 1.5 to 1.7 micronmeters were observed by a scanning electron microscope. The microcapsules dispersed in an acrylic-melamine clearcoat increased the scratch resistance of coatings. Also, the self-healing feature of those coatings was proved.

Research limitations/implications

The size of microcapsules can affect its dispersion in the clearcoat and consequently affect the properties of the cured films.

Practical implications

The self-healing coatings are interested for many industries such as building and automotive industries. The reported data can be used by the formulators working in the R & D departments.

Social implications

Self-healing systems are considered as one of the smart coatings. Therefore, the developing of its knowledge can help to extend its usage to different applications.

Originality/value

The application of microcapsules in the coating as healing agents is a great challenge, which has been hardly investigated so far. In the current research, the effect of polyurethane-IDPI microcapsules in an automotive clearcoat as a self-healing coating was investigated.

Details

Pigment & Resin Technology, vol. 45 no. 2
Type: Research Article
ISSN: 0369-9420

Keywords

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Article
Publication date: 27 March 2020

Min Ji, Shuhai Liu and Huaping Xiao

The purpose of this paper is to study the tribology behavior of steel–steel contact under the lubrication of water-based drilling mud with different oleic acid-filled…

Abstract

Purpose

The purpose of this paper is to study the tribology behavior of steel–steel contact under the lubrication of water-based drilling mud with different oleic acid-filled microcapsules as lubricant additives.

Design/methodology/approach

A ball-on-disc tribometer was used to evaluate the lubrication properties of the steel–steel contact. The wear tracks of the worn surfaces were observed by a scanning electron microscope.

Findings

Results show that the dependence of both friction and wear on the category of additives shares a consistent pattern. In contrast to oleic acid and empty microcapsules, oleic acid-filled microcapsules achieve the best tribological performance which is related to the lubricant effect of oleic acid and the isolation and rolling abilities of microcapsules.

Practical implications

This study provides a helpful method of encapsulated lubricant additives to prolong lubrication performance for steel–steel contact.

Originality/value

This study has applied microcapsules to improve the tribological properties of drilling mud.

Peer review

The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-08-2019-0320/

Details

Industrial Lubrication and Tribology, vol. 72 no. 7
Type: Research Article
ISSN: 0036-8792

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Article
Publication date: 3 July 2017

Amir Khalaj Asadi, Morteza Ebrahimi and Mohsen Mohseni

The purpose of this work was to express a facile method to fabricate microcapsules containing linseed oil with melamine-urea-formaldehyde (MUF) shell in the presence of…

Abstract

Purpose

The purpose of this work was to express a facile method to fabricate microcapsules containing linseed oil with melamine-urea-formaldehyde (MUF) shell in the presence of polyvinylpyrrolidone (PVP) as an emulsifier. These microcapsules may be used in self-healing coating formulations.

Design/methodology/approach

In this work, different types of PVP (i.e., PVP with different molecular weights or K values) were used as emulsifiers and colloid protectors to encapsulate linseed oil in an MUF shell. Moreover, the effect of agitation rate on the morphology of the microcapsules was investigated. Microcapsule morphology and particle size distribution were evaluated using optical microscopy and scanning electron microscopy. Thermal studies were performed using a thermo-gravimetric analysis technique and chemical structure of materials was characterized by using Fourier transform infrared analysis.

Findings

In this work, microcapsules with a regular spherical shape and a shell thickness of about 330 nm were fabricated. The results revealed that the use of PVP in the fabrication of MUF could facilitate the synthesis process by eliminating the necessity of pH control during the reaction. In fact, the pH of the reaction media must be precisely controlled in conventional processes. The yield of microencapsulation was found to be 86.5 per cent when a high molecular weight of PVP (PVP K-90) was used. It was also found that the surface morphology of microcapsules became smoother when PVP K-90 was used. The results showed that the surface roughness and the average particle size decreased with an increase in stirring intensity. Mean diameter of the prepared microcapsules ranged from 34 to 346 μmin for various synthesis conditions.

Research limitations/implications

This work is limited to the encapsulation of a hydrophobic liquid (such as linseed oil) by an in situ polymerisation of amino resins.

Practical implications

The presented results can be used by researchers (in academia and industry) who are working in the field of fabrication microcapsules, in various applications such as pharmaceuticals, electrophoretic displays, textiles, carbonless copy papers, cosmetics, printing and self-healing materials.

Social implications

PVP is considered as an environmentally friendly emulsifier. Therefore, this process is less harmful to the environment. In addition, the prepared microcapsules may be used in self-healing coatings, which helps in reducing maintenance costs for buildings and steel structures.

Originality/value

Ethylene maleic anhydride and styrene maleic anhydride are usually used as emulsifiers in conventional methods for the preparation of amino resin microcapsules. These methods require an intensive and precise pH control to obtain favourable microcapsules, while in the present research, a facile method was used to fabricate MUF microcapsules containing linseed oil without needing any pH control during the reaction.

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Article
Publication date: 6 March 2017

Mehdi Shahidi Zandi and Majdeh Hasanzadeh

The aim of this work is to investigate the self-healing performance of epoxy coatings containing microcapsules. The microcapsule-based coatings were applied on AA6061 Al…

Abstract

Purpose

The aim of this work is to investigate the self-healing performance of epoxy coatings containing microcapsules. The microcapsule-based coatings were applied on AA6061 Al alloy and immersed in 3.5 per cent NaCl solution.

Design/methodology/approach

Microcapsules with urea–formaldehyde as the shell and linseed oil as the healing agent were prepared by in situ polymerization in an oil-in-water emulsion. For the sake of an optimum self-healing system, some coating samples were prepared by using different microcapsule concentrations: 0, 5, 10 and 20 Wt.%. The scratch-filling efficiency as the theoretical estimate of the self-healing performance was calculated for the coating samples with different microcapsule concentrations. The scratch-sealing efficiency (SSE) as a particularly crucial parameter in the self-healing evaluation of coatings was measured by both electrochemical impedance spectroscopy (EIS) and electrochemical noise (EN) techniques.

Findings

According to EIS and EN results, the coating samples containing 5 and 10 per cent microcapsules provided the insignificant self-healing performance, while the coating sample containing 20 per cent microcapsules exhibited the acceptable self-healing performance to AA6061 alloy in the NaCl solution. The measured SSE values confirmed the good agreement of EN data with electrochemical parameters obtained from the EIS technique.

Originality/value

This work is an attempt to evaluate the self-healing performance of microcapsule-based epoxy coatings applied on AA6061 Al alloy in sea water.

Details

Anti-Corrosion Methods and Materials, vol. 64 no. 2
Type: Research Article
ISSN: 0003-5599

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Article
Publication date: 20 February 2019

Rui Wang, Mengxuan Li, Xing Liu and Yanli Sun

This study aims to elaborate on the microencapsulation of the plant extract (PE, from Camellia sinensis leaf, clover flower and cocoa flower) and the preparation of a…

Abstract

Purpose

This study aims to elaborate on the microencapsulation of the plant extract (PE, from Camellia sinensis leaf, clover flower and cocoa flower) and the preparation of a slow-release lining fabric loading the PE microcapsule.

Design/methodology/approach

PE was microencapsulated into polyvinyl alcohol (PVA) shells through interfacial polymerization. The morphology, thermal stability, slow-release property and drug loading ratio of the PVA/PE microcapsules were characterized to ensure the availability in coating finishing. To find the optimum parameters, the composite fabrics were prepared from non-woven fabrics coated by calcium alginate hydrogel, which glued mass fractions of microcapsules and dried in different ways. To evaluate the effectiveness, a lipase enzyme activity test was conducted.

Findings

Under optimal conditions, the PVA/PE microcapsules with smooth surface have an average particle size of 14.5 um, and they are expected to reach a loading ratio of 38.5 per cent while remaining stable under 220°C. Given a microcapsule of 4 per cent (of the mass), the composite fabric has a good hand feeling, being prepared through calcium chloride coating. It is shown that the inhibition ratios of the microcapsules and composite fabrics on lipase are 31.3 and 21.0 per cent, respectively.

Research limitations/implications

The composite fabric could be prepared through the other finishing methods such as padding and printing. In addition, the release mechanism of the composite could be studied.

Practical implications

This study provided a simple and effective way to prolong the duration of PE. This way was conductive to protect environmental sensitive PEs from being destroyed in compositing processes.

Originality/value

Preparing composite fabrics for transdermal delivery system was novel and other kind of plant extracts could be used in this way.

Details

Pigment & Resin Technology, vol. 48 no. 3
Type: Research Article
ISSN: 0369-9420

Keywords

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Article
Publication date: 19 November 2018

Ruhan Altun-Anayurt, Sennur Alay-Aksoy, Cemil Alkan, Sena Demirbag and M. Selda Tözüm

The purpose of this paper is to prepare microencapsulated phase change materials (PCMs) and apply them to cotton and wool fabrics for developing thermo-regulating fabrics.

Abstract

Purpose

The purpose of this paper is to prepare microencapsulated phase change materials (PCMs) and apply them to cotton and wool fabrics for developing thermo-regulating fabrics.

Design/methodology/approach

Microencapsulated n-hexadecane and n-octadecane with poly(methylmethacrylate-co-2-hydroxy ethyl methacrylate) shell was prepared. Microcapsules were fabricated using oil-in-water emulsion polymerization method. Their chemical structure, microstructure, thermal energy storage properties and thermal stability were analyzed by Fourier-transform infrared spectroscopy, polarized light microscope, differential scanning calorimeter and thermogravimetric analyzer, respectively. The mean particle size was tested by a particle sized instrument. The microcapsules were applied to the wool and cotton fabrics using pad-dry-cure method. The thermo-regulating property of the fabrics was evaluated using the T-History test. The distribution and durability of the microcapsules on the fabrics was investigated with scanning electron microscopy.

Findings

Spherical microcapsules with p(MMA-co-HEMA) shell and n-alkane core have been produced successfully. n-hexadecane in microcapsule solidifies at 14.8−15.6°C with the latent heat of 65.6−129.8 J/g and melts at 16.7−16.9°C with the latent heat of 67.6−136.9 J/g. Microencapsulated n-octadecane solidifies at 25.8−26.3°C with the latent heat of 74.1−106.2 J/g and melts at 26.8−27.4°C with the latent heat of 80.3−113.4 J/g. The microcapsules have enough thermal stability to the temperature of 150°C that was applied during the fixation of microcapsules on the fabric. The thermo-regulating effect of the microcapsule-incorporated fabrics has been proved by the T-history test.

Originality/value

PCM microcapsules with p(MMA-co-HEMA) shell and n-hexadecane and n-octadecane core have been produced and their usage to produce thermo-regulating textiles have been proved. To determine the thermo-regulating property of the fabrics treated with these new PCM microcapsules, a T-History system has been designed.

Details

International Journal of Clothing Science and Technology, vol. 31 no. 1
Type: Research Article
ISSN: 0955-6222

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Article
Publication date: 8 May 2018

Amir Khalaj Asadi, Morteza Ebrahimi and Mohsen Mohseni

The purpose of this investigation is to develop a facile method to encapsulate a sunlight-curable silicone-based resin into a melamine–urea–formaldehyde (MUF) shell in the…

Abstract

Purpose

The purpose of this investigation is to develop a facile method to encapsulate a sunlight-curable silicone-based resin into a melamine–urea–formaldehyde (MUF) shell in the presence of polyvinylpyrrolidone (PVP) as an emulsifier. These microcapsules can be used in self-healing coating formulations.

Design/methodology/approach

MUF microcapsules containing a sunlight-curable core (methacryloxypropyl-terminated polydimethylsiloxane, MAT-PDMS) have been fabricated by means of in situ polymerisation of an oil-in-water emulsion using PVP as an efficient and environmentally advantageous stabiliser. The effects of agitation rate and PVP concentration on the microencapsulation process have been investigated using optical microscopy (OM) and scanning electron microscopy (SEM). The chemical structure and thermal stability of the microcapsules have been studied using Fourier transform infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA). The solvent resistance of the microcapsules has been determined as well.

Findings

It has been revealed that the pH of the reaction mixture remained almost constant during the reaction, which simplified the process. It has also been observed that the microencapsulation yield improved and the microcapsules’ surface morphology became smoother when a high PVP content was used. With an increase in stirring rate from 600 to 1,200 rpm, the surface roughness and the average particle size decreased. The mean diameter of the prepared microcapsules ranged from 32.1 to 327.1 µm depending on the synthesis conditions. It was demonstrated that the microcapsules had a high capacity for MAT-PDMS encapsulation (more than 88 Wt.%). The solvent stability of the microcapsules against different polar, semi-polar and non-polar solvents was also evaluated.

Research limitations/implications

This research is limited to the encapsulation of a hydrophobic and sunlight curable liquid (such as MAT-PDMS) by means of in situ polymerisation of amino resins.

Practical implications

The results can be used by researchers working on the fabrication of microcapsules for applications such as drugs, electrophoretic inks, electrophoretic displays, intumescent fire-retardant coatings and self-healing materials.

Social implications

In self-healing coatings, healing agents which can be cured by UV irradiation or sunlight are envisaged attractive because they are catalyst-free, environmentally friendly and relatively inexpensive. PVP is an environmentally friendly emulsifier. The prepared microcapsules can be used in self-healing coatings to help in reducing maintenance costs for buildings and steel structures.

Originality/value

The novel aspect of this work is the development of a sunlight-curable silicone-based resin that was encapsulated in a MUF shell in the presence of PVP. A simple method was used to fabricate MUF microcapsules containing MAT-PDMS without the need to control pH during the reaction. Conventional methods for the preparation of amino resin microcapsules require an intensive and precise pH control to obtain favourable microcapsules. MAT-PDMS can be cured by sunlight and is catalyst-free, environmentally friendly and relatively inexpensive.

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Article
Publication date: 11 August 2020

Mingqi Gu, Wei Zhang, Shang Hao, Xiaochen Liu, Zichao Zhang and Fenjuan Shao

This study aims to explore the infrared imaging effect of fabrics coated with phase change material microcapsules (PCM-MCs), which are prepared by the initiation of…

Abstract

Purpose

This study aims to explore the infrared imaging effect of fabrics coated with phase change material microcapsules (PCM-MCs), which are prepared by the initiation of ultraviolet (UV) light.

Design/methodology/approach

PCM-MCs were prepared by UV polymerization using paraffin (PA) as core material, polymethyl methacrylate as wall material and ferric chloride as photoinitiator. The effects of emulsifier dosage and emulsification temperature on the properties of PA emulsion were investigated. Scanning electron microscopy, particle size analysis, infrared spectroscopy, differential scanning calorimetry and infrared imaging test were used to characterize the properties of microcapsules.

Findings

The PCM-MCs with good morphology and particle size were prepared with 25 cm of the distance between light source and the liquid. The average particle size was 1.066 µm and the latent heat of phase transition was 19.96 J/g. After 100 accelerated thermal cycles, the latent heat only decreased by 1.8%. It had good heat storage stability and thermal stability. The fabric coated by the microcapsules exhibited a variable temperature hysteresis effect when placed in the sun, and presented a color close to the infrared images of the human palm under the external environment temperature close to the human body temperature.

Research limitations/implications

The PCM-MCs prepared based on UV light initiation showed good thermal properties and its coated fabrics had an infrared decoy effect below the temperature of the human body.

Practical implications

This study explored the application of microcapsules in textiles.

Originality/value

The microcapsules had a certain application potential in infrared decoy effect.

Details

Pigment & Resin Technology, vol. 50 no. 2
Type: Research Article
ISSN: 0369-9420

Keywords

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