All issues / Volume 15 (2021) / Issue 9 (September)
This is an editorial article. It has no abstract.
In this article, we investigate the use of laser processing to create effective surface contacts on multi-wall carbon nanotube (MWCNT)/polyethylene composites. Due to the photothermal conversion effect induced by laser radiation, MWCNTs can enhance thermal destruction and removal of the polymer from the composite surface. The structure of pristine and lasermodified composites is characterized by Raman spectroscopy, optical and scanning electron microscopy. It was found that in pristine composites only a small part of MWCNTs is located directly on the surface of the film, which is associated with the high work of polymer adhesion to the nanotube surface and the surface tension forces of the polymer matrix melt. Scanning electron microscopy (SEM) and Raman scattering demonstrate that in the surface contacts formed under the action of laser radiation, the polymer matrix is removed from the near-surface layer. The presence of MWCNTs with an unchanged structure and a small amount of amorphous carbon material was confirmed by Raman spectroscopy. The conductivity of pristine and modified composites was characterized by a series of current-voltage characteristic measurements with the through-plane 4-point probe. It was found that laser treatment of the composite surface leads to an increase in the measured volume conductivity by 1–2 orders of magnitude, depending on the content of MWCNTs. At the same time, the removal of the near-surface layer of the polymer by laser treatment makes it possible to reduce the contribution of the contact resistance to the resistance of the composite measured by 2-point probe from 55–77 to 0.18–5.3% for composites with an MWCNT content of 2.5–4 wt%.
This paper presents a novel investigation on the robustness of Acoustic Emission (AE) technique on the characterization of indentation-induced Damage Mechanisms (DMs) in scaled laminated composites. AE is used to monitor a comprehensive series of scaled Quasi-Static Indentation (QSI) tests performed on Quasi-Isotropic (QI) S-glass/8552 epoxy composite plates, with in-plane and intra-plane scaling. A detailed assessment of the damage evolution is carried out through clustering of the monitored AE signals. The AE results indicated the existence of different DMs such as delamination, matrix cracking and fiber breakage. Ultrasonic C-scan and visual observations were also used to verify the AE based results. It was observed that both in-plane and intra-plane scaling alter the induced DMs, and the AE analysis was able to accurately identify and quantify the DMs in each case. However, the AE features (frequency, energy and count) were found to be dependent on different variables such as size, geometry and stacking sequence of the investigated samples. This research highlights the potential and challenges to develop AE as a reliable structural health monitoring system for impact/indentation damage monitoring of composite plates over a range of sizes and complexities.
In the present study, a new method for the synthesis of the open-cell soft polyurethane foam (PUF) is developed. Silver nanoparticles are synthesized on the surface of ultrafine grain (100–500 nm) natural zeolite particles and this zeolite is than placed as a filler in the polyurethane. The Ag content of natural zeolite and PUF is about 5 wt%, and 1500 ppm, respectively. Most of the zeolite particles are partially or fully covered in the polyurethane cell wall which is favorable for long-term storage. However, as soon as the foam comes into contact with water or human sweat, the montmorillonite content of the zeolite swells and breaking through the cell wall of the foam structure. Indeed, particles of the zeolite protrude from the polyurethane matrix with the nano-silver particles showing a favourable biocide effect. The antibacterial effect of the natural zeolite containing Ag nanoparticles was examined against Escherichia coli (Gram-negative), and Micrococcus luteus (Gram-positive) strains in a 24 and 72 h interval. The results show that the natural zeolite containing Ag nanoparticles filler has an antibacterial effect, especially against Gram-positive bacteria.
In this work, the open-cell material has been prepared by phase separation-sol-gel method, where trans-polyisoprene (TPI) is used as the raw material. Dichloromethane (DCM) has been used as a good solvent for TPI, and anhydrous ethanol as a poor solvent to achieve the phase separation. The formation of pores has been tuned and studied by adjusting the quantity of anhydrous ethanol. It has been determined that the best ratio of raw materials, good solvents and poor solvents is 1:12:1.5. On this basis, the preparation process has been improved, and an open cell superhydrophobic composite material with good electromagnetic interference shielding effectiveness (EMI SE) and self-cleaning functions has been prepared. Multiwalled carbon nanotubes (MWCNTs) filler can form an effective 3D conductive network, and the material can be regarded as a disorderly accumulation of countless petal-like TPI flake particles with 1–10 µm size, forming interconnected and scattered cells through free overlap. The structure can make the composite material rough and form a multi-scale rough surface. The prepared TPI/MWCNTs open-cell composites (TMOCs) material has a low density of 0.27 g/cm3 and a water contact angle (CA) of 153.5° (in line with super-hydrophobic characteristics) and the EMI SE can be up to 26 dB at a thickness of 5 mm and the corresponding specific EMI SE has been achieved as high as 95.6 dB/(g/cm3), which is far exceeding that of many carbon-based composite materials with similar density. This simple and inexpensive preparation process with excellent self-cleaning property and EMI SE of the materials can promote the practical application of such materials.
We explored a simple approach to grow needle-like polyphosphazene nanotubes (PZSNT) on carbon fibers (CFPZSNT) via in-situ polycondensation under mild reaction conditions, to form a PZSNT-based multiscale reinforcement. PZSNT with abundant free hydroxyl groups can significantly change the chemical surface and increase the specific surface area of carbon fibers. A significant improvement of interfacial shear strength was obtained from 39.7 MPa for the virgin CF/polyamide 6 composites to 69.6 MPa for the CF-PZSNT/polyamide 6 composites.
In this paper, phenolic resin hollow microspheres (PHM) were prepared using in-situ polymerization and used as flame-retardants for TPU. The structure and composition of PHM were characterized by Scanning Electron Microscope (SEM). The potential of PHM as flame retardant was verified by thermogravimetric analysis (TG). Then, the flame retardancy and toxicity reduction of PHM in TPU/PHM composites were verified by cone calorimeter test (CCT) and Thermogravimetric Analysis-infrared Spectrometry (TG-IR). It has been found that comparing TPU/PHM-4 sample containing 4.0 wt% PHM with pure TPU, the peak heat release rate (pHRR) was reduced by 61.6%, the total smoke release (TSR) by 23.2%, and the CO production by 86.2%, respectively. The SEM, Laser Raman Spectroscopy Test (LRS), and other tests were carried out to test the char residues after CCT, and the mechanism of PHM in the process of flame retardant TPU was reasonably deduced. In a word, PHM is very effective as a flame retardant of TPU.
In this study, modified natural rubber (MNR) was used as a solid adsorbent for carbon dioxide (CO2) capture. The chemical structure of the NR latex was modified by diallylamine. Moreover, the silica particles were modified by (3-aminopropyl)trimethoxysilane, N-[(3-trimethoxysilyl)propyl]ethylenediamine, or N-[(3-trimethoxysilyl)propyl]diethylenetriamine (mono-, di- and tri-amines) to improve the CO2 capture ability of the MNR. The CO2 adsorption capacity of the MNR foam composite was increased 3- to 5-fold after filling with unmodified or modified silica particles. The mechanism for CO2 adsorption of the MNR composite was a combination of physisorption and chemisorption. At 100 °C, the highest CO2 adsorption capacity of MNR foam composite (10.35 mg/g of adsorbent) was obtained by adding tri-amine-modified silica particles. Finally, the MNR foam composite material could be regenerated process for more than 20 CO2 adsorption cycles.