scholarly journals Healing Efficiency of CNTs-Modified-UF Microcapsules That Provide Higher Electrical Conductivity and EMI Shielding Properties

Polymers ◽  
2021 ◽  
Vol 13 (16) ◽  
pp. 2753
Author(s):  
Maria Kosarli ◽  
Anastasia Polymerou ◽  
Georgios Foteinidis ◽  
Christos Vazouras ◽  
Alkiviadis S. Paipetis
Keyword(s):  
Thermal Stability ◽  
Electrical Conductivity ◽  
Electrical Properties ◽  
Electromagnetic Interference ◽  
Urea Formaldehyde ◽  
Conductive Network ◽  
Self Healing ◽  
Shell Wall ◽  
Healing Efficiency ◽  
Emi Se

In this study, the effect of the addition of multi-walled carbon nanotubes (MWCNTs), at three percentages, into the urea-formaldehyde (UF) shell-wall of microcapsules on the healing efficiency is reported. The modified shell-wall created a conductive network in semi-conductive epoxies, which led to an improvement of the electromagnetic interference shielding effectiveness (EMI SE); utilizing the excellent electrical properties of the CNTs. The microcapsule’s mean diameter and shell wall were examined via scanning electron microscopy (SEM). Thermal stability was evaluated via thermogravimetric analysis (TGA). The healing efficiency was assessed in terms of fracture toughness, while the electrical properties were measured using impedance spectroscopy. The measurements of the EMI SE were carried out in the frequency range of 7–9 GHz. The derived results indicated that the incorporation of the CNTs resulted in a decrease in the mean size of the microcapsules, while the thermal stability remained unchanged. In particular, the introduction of 0.5% w/v CNTs did not affect the healing efficiency, while it increased the initial mechanical properties of the epoxy after the incorporation of the self-healing system by 27%. At the same time, it led to the formation of a conductive network, providing electrical conductivity to the epoxies. The experimental results showed that the SE increased on average 5 dB or more after introducing conductive microcapsules.

scholarly journals Interface Engineered Microcellular Magnetic Conductive Polyurethane Nanocomposite Foams for Electromagnetic Interference Shielding

2021 ◽  
Vol 13 (1) ◽  
Author(s):  
Guolong Sang ◽  
Pei Xu ◽  
Tong Yan ◽  
Vignesh Murugadoss ◽  
Nithesh Naik ◽  
...  
Keyword(s):  
Electromagnetic Interference ◽  
Magnetic Loss ◽  
Interfacial Polarization ◽  
Conductive Network ◽  
Shielding Effectiveness ◽  
Electromagnetic Interference Shielding ◽  
Multiple Reflections ◽  
Conduction Loss ◽  
Composite Foams ◽  
Emi Se

Abstract Lightweight microcellular polyurethane (TPU)/carbon nanotubes (CNTs)/ nickel-coated CNTs (Ni@CNTs)/polymerizable ionic liquid copolymer (PIL) composite foams are prepared by non-solvent induced phase separation (NIPS). CNTs and Ni@CNTs modified by PIL provide more heterogeneous nucleation sites and inhibit the aggregation and combination of microcellular structure. Compared with TPU/CNTs, the TPU/CNTs/PIL and TPU/CNTs/Ni@CNTs/PIL composite foams with smaller microcellular structures have a high electromagnetic interference shielding effectiveness (EMI SE). The evaporate time regulates the microcellular structure, improves the conductive network of composite foams and reduces the microcellular size, which strengthens the multiple reflections of electromagnetic wave. The TPU/10CNTs/10Ni@CNTs/PIL foam exhibits slightly higher SE values (69.9 dB) compared with TPU/20CNTs/PIL foam (53.3 dB). The highest specific EMI SE of TPU/20CNTs/PIL and TPU/10CNTs/10Ni@CNTs/PIL reaches up to 187.2 and 211.5 dB/(g cm−3), respectively. The polarization losses caused by interfacial polarization between TPU substrates and conductive fillers, conduction loss caused by conductive network of fillers and magnetic loss caused by Ni@CNT synergistically attenuate the microwave energy.

Temperature Profile of Microencapsulation for Self-Healing Application

2010 ◽  
Vol 143-144 ◽  
pp. 353-357
Author(s):  
Ting Ting Li ◽  
Xing Liu ◽  
Rui Wang
Keyword(s):  
Temperature Profile ◽  
Shell Thickness ◽  
Urea Formaldehyde ◽  
Life Time ◽  
Self Healing ◽  
Time Service ◽  
Healing Efficiency ◽  
Performance Surface ◽  
The Relationship

Healing agents significantly affect the efficiency of healing microcracks, which produced from life-time service in composites. And microencapsulating 5-ethylidene-2-norbornene (ENB) with Melamine-Urea-Formaldehyde (MUF) shell possessing higher self-healing efficiency is sensitive to the manufacture temperature profile which is difficult to control but crucial to the microcapsule performance and thus the reproducibility. In this paper, we studied the relationship between heating curve (rate, steps and time) and microcapsule performance (surface morphology, thermal stability and shell thickness). It shows that fast-slower heating stage produces the best quality of microcapsule with proper outer and inner surface which can endure 285°C, and the particle size is about 100m with 400-700nm shell thickness.

scholarly journals Carbonization of Graphene-Doped Isocyanate-Based Polyimide Foams to Achieve Carbon Foams with Excellent Electromagnetic Interference Shielding Performance

Materials ◽  
2021 ◽  
Vol 14 (24) ◽  
pp. 7551
Author(s):  
Hui Jing ◽  
Zongnan Miao ◽  
Zhong Zeng ◽  
Hui Liu ◽  
Shengtai Zhou ◽  
...  
Keyword(s):  
Electrical Conductivity ◽  
Electromagnetic Interference ◽  
Carbonization Temperature ◽  
Shielding Effectiveness ◽  
Emi Shielding ◽  
Emi Shielding Effectiveness ◽  
Graphitization Degree ◽  
Carbon Foams ◽  
Potential Applications ◽  
Emi Se

Lightweight carbon foams with excellent electromagnetic interference (EMI) shielding performance were prepared by carbonization process, using isocyanate-based polyimide foams as carbon precursors. The influence of carbonization temperature and graphene-doping on the morphological, electrical and EMI shielding effectiveness (SE) of corresponding carbon foams was studied in detail. Results showed that the addition of graphene was beneficial to the improvement of electrical conductivity and EMI shielding performance of carbon foams. The electrical conductivity of carbon foams increased with the carbonization temperature which was related to the increase of graphitization degree. Collapse of foam cells was observed at higher carbonization temperatures, which was detrimental to the overall EMI SE. The optimal carbonization temperature was found at 1100 °C and the carbon foams obtained from 0.5 wt% graphene-doped foams exhibited a specific EMI SE of 2886 dB/(g/cm3), which shows potential applications in fields such as aerospace, aeronautics and electronics.

scholarly journals Self-Healing EPDM Rubbers with Highly Stable and Mechanically-Enhanced Urea-Formaldehyde (UF) Microcapsules Prepared by Multi-Step In Situ Polymerization

Polymers ◽  
2020 ◽  
Vol 12 (9) ◽  
pp. 1918 ◽  
Author(s):  
Hyeong-Jun Jeoung ◽  
Kun Won Kim ◽  
Yong Jun Chang ◽  
Yong Chae Jung ◽  
Hyunchul Ku ◽  
...  
Keyword(s):  
Mechanical Stability ◽  
In Situ Polymerization ◽  
Urea Formaldehyde ◽  
Testing Machine ◽  
Optical Microscope ◽  
The Self ◽  
Self Healing ◽  
Grubbs Catalyst ◽  
Healing Efficiency

The mechanically-enhanced urea-formaldehyde (UF) microcapsules are developed through a multi-step in situ polymerization method. Optical microscope (OM) and field emission scanning electron microscope (FE-SEM) prove that the microcapsules, 147.4 μm in diameter with a shell thickness of 600 nm, are well-formed. From 1H-nuclear magnetic resonance (1H-NMR) analysis, we found that dicyclopentadiene (DCPD), a self-healing agent encapsulated by the microcapsules, occupies ca. 40.3 %(v/v) of the internal volume of a single capsule. These microcapsules are mixed with EPDM (ethylene-propylene-diene-monomer) and Grubbs’ catalyst via a solution mixing method, and universal testing machine (UTM) tests show that the composites with mechanically-enhanced microcapsules has ca. 47% higher toughness than the composites with conventionally prepared UF microcapsules, which is attributed to the improved mechanical stability of the microcapsule. When the EPDM/microcapsule rubber composites are notched, Fourier-transform infrared (FT-IR) spectroscopy shows that DCPD leaks from the broken microcapsule to the damaged site and flows to fill the notched valley, and self-heals as it is cured by Grubbs’ catalyst. The self-healing efficiency depends on the capsule concentration in the EPDM matrix. However, the self-healed EPDM/microcapsule rubber composite with over 15 wt% microcapsule shows an almost full recovery of the mechanical strength and 100% healing efficiency.

scholarly journals Mechanical Properties Assessment of Low-Content Capsule-Based Self-Healing Structural Composites

2020 ◽  
Vol 10 (17) ◽  
pp. 5739
Author(s):  
Xenia Tsilimigkra ◽  
Dimitrios Bekas ◽  
Maria Kosarli ◽  
Stavros Tsantzalis ◽  
Alkiviadis Paipetis ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Fracture Toughness ◽  
Flexural Strength ◽  
Mechanical Performance ◽  
Urea Formaldehyde ◽  
Healing Process ◽  
Experimental Results ◽  
Self Healing ◽  
Healing Efficiency ◽  
A Minor

Microcapsule-based carbon fiber reinforced composites were manufactured by wet layup, in order to assess their mechanical properties and determine their healing efficiency. Microcapsules at 10%wt. containing bisphenol-A epoxy, encapsulated in a urea formaldehyde (UF) shell, were employed with Scandium (III) Triflate (Sc (OTf)3) as the catalyst. The investigation was deployed with two main directions. The first monitored changes to the mechanical performance due to the presence of the healing agent within the composite. More precisely, a minor decrease in interlaminar fracture toughness (GIIC) (−14%), flexural strength (−12%) and modulus (−4%) compared to the reference material was reported. The second direction evaluated the healing efficiency. The experimental results showed significant recovery in fracture toughness up to 84% after the healing process, while flexural strength and modulus healing rates reached up to 14% and 23%, respectively. The Acoustic Emission technique was used to support the experimental results by the onsite monitoring.

scholarly journals Microencapsulated Bio-Based Rejuvenators for the Self-Healing of Bituminous Materials

Materials ◽  
2020 ◽  
Vol 13 (6) ◽  
pp. 1446 ◽  
Author(s):  
Jose Norambuena-Contreras ◽  
Luis E. Arteaga-Perez ◽  
Andrea Y. Guadarrama-Lezama ◽  
Rodrigo Briones ◽  
Juan F. Vivanco ◽  
...  
Keyword(s):  
Thermal Stability ◽  
Chemical Properties ◽  
The Self ◽  
Asphalt Pavements ◽  
Self Healing ◽  
Biomass Waste ◽  
Good Thermal Stability ◽  
Bituminous Materials ◽  
Healing Efficiency ◽  
Indentation Tests

Asphalt self-healing by encapsulated rejuvenating agents is considered a revolutionary technology for the autonomic crack-healing of aged asphalt pavements. This paper aims to explore the use of Bio-Oil (BO) obtained from liquefied agricultural biomass waste as a bio-based encapsulated rejuvenating agent for self-healing of bituminous materials. Novel BO capsules were synthesized using two simple dripping methods through dropping funnel and syringe pump devices, where the BO agent was microencapsulated by external ionic gelation in a biopolymer matrix of sodium alginate. Size, surface aspect, and elemental composition of the BO capsules were characterized by optical and scanning electron microscopy and energy-dispersive X-ray spectroscopy. Thermal stability and chemical properties of BO capsules and their components were assessed through thermogravimetric analysis (TGA-DTG) and Fourier-Transform Infrared spectroscopy (FTIR-ATR). The mechanical behavior of the capsules was evaluated by compressive and low-load micro-indentation tests. The self-healing efficiency over time of BO as a rejuvenating agent in cracked bitumen samples was quantified by fluorescence microscopy. Main results showed that the BO capsules presented an adequate morphology for the asphalt self-healing application, with good thermal stability and physical-chemical properties. It was also proven that the BO can diffuse in the bitumen reducing the viscosity and consequently self-healing the open microcracks.

Recovery of Fracture Toughness on Self-Healing Epoxies Using Ternary Nanomodified Microcapsules: A Parametric Study

2019 ◽  
Vol 827 ◽  
pp. 258-262 ◽  
Author(s):  
Maria Kosarli ◽  
Kyriaki Tsirka ◽  
Stella Chalari ◽  
Antigoni Palantza ◽  
Alkiviadis S. Paipetis
Keyword(s):  
Electron Microscopy ◽  
Thermal Stability ◽  
Parametric Study ◽  
External Surface ◽  
Self Healing ◽  
Healing Efficiency ◽  
Mean Diameter ◽  
Healing Agent ◽  
The Mean ◽  
Scanning Electron

This study is focused on the effect of the nanomodification of the microcapsules healing agent on the healing efficiency. In detail, nanomodified epoxy resin with both carbon nanotubes (CNTs) and carbon black (CB) diluted with a non-toxic solvent was encapsulated into UF capsules. The morphology of the external surface and the mean diameter was investigated via Scanning Electron Microscopy (SEM). In addition, the thermal stability was estimated with Thermogravimetric analysis and healing efficiency was evaluated for the polymer epoxy matrix. A parametric study was performed at various solvent percentages and catalyst percentages. Results indicated an increase of the healing efficiency with nanomodified capsules against of the use of conventional microcapsules.

Synthesis of Self-Healing Microcapsules via Different Heating Profiles

2010 ◽  
Vol 148-149 ◽  
pp. 1486-1490
Author(s):  
Ting Ting Li ◽  
Rui Wang ◽  
Xing Liu
Keyword(s):  
Shell Thickness ◽  
Urea Formaldehyde ◽  
Self Healing ◽  
Heating Method ◽  
Temperature Resistance ◽  
Healing Efficiency ◽  
Higher Temperature ◽  
The Mean ◽  
Heating Profiles

Self-healing by microcapsules is one of methods to stop and heal crack propagation in time. Microcapsule containing 5-ethylidene-2-norbornene (ENB) core and Melamine-Urea -Formaldehyde (MUF) shell with possibly higher healing efficiency was synthesized via three different heating histories including different heating rate and heating steps, which significantly affect microcapsule surface morphology, thermal stability, and yield, thus the reproducibility. Finally, it is demonstrated that the best quality of microcapsule was obtained from fast-slower heating method with proper outer surface and shell thickness, as well as 285 higher temperature resistance. The mean particle size is about 100m.

Synthesis of Self-Healing Thermosetting Resin Based Capsules and their Related Complexities

2015 ◽  
Vol 1119 ◽  
pp. 428-432 ◽  
Author(s):  
Ikbal Choudhury ◽  
Sudipta Halder ◽  
Abhinav Mathur ◽  
Writuparna Nath ◽  
Aniruddha Phukan
Keyword(s):  
Emulsion Polymerization ◽  
Process Parameters ◽  
Urea Formaldehyde ◽  
Solvent Evaporation ◽  
Preparation Process ◽  
Self Healing ◽  
Thermosetting Resin ◽  
Shell Wall ◽  
Bioinspired Materials ◽  
The Difference

Microencapsulation forms an integral part in synthesizing bioinspired materials. This paper focuses on elaborating the problems faced in encapsulation of DGEBA microcapsules in PMMA and urea formaldehyde shell wall. The preparation process and the process parameters affecting the microcapsule property are discussed. The difference between the microcapsules prepared using emulsion polymerization and that by solvent evaporation has been discussed. The size, shape and morphology of the microcapsules was characterized using FESEM technique. It was observed that the agglomeration of the microcapsules can be prevented by changing the concentration of the emulsifier. However, in case of urea formaldehyde encapsulation chunks of pre-polymer resulted in agglomeration of the nanosized capsules even if higher concentration of emulsifier was implemented.

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