POLİ-o-FENİLENDİAMİN/CdO NANOKOMPOZİTLERİNİN SENTEZİ VE KARAKTERİZASYONU

In this study, the poly-o-phenylenediamine (POPD) and POPD/CdO nanocomposites with different mole rates of CdO nanoparticles were synthesized in aqueous diethylene glycol solution via chemical oxidative polymerization. As synthesized polymer and nanocomposites were analyzed by fourier transform infrared spectroscopy, differential scanning calorimetry, UV-Vis spectroscopy and scanning electron microscopy for structural on morphological characterization and electrical conductivity of the samples was measured by four-point AC conductivity method. It is suggested that the POPD/CdO nanocomposites, synthesized in the presence of CdO nanoparticles by chemical polymerization of OPD, are not an ordinary mixture. There are strong interactions between CdO nanoparticles and POPD which affect conjugation and electron density and the corresponding interactions lead to increase electrical conductivity of POPD due to increasing CdO nanoparticle amount. Furthermore, the thermal behavior of POPD/CdO nanocomposites was affected by CdO nanoparticle amount and maximum thermal stability occurred when OPD/CdO rate was equal to 2/1. Scanning electron microscope investigations revealed that spherical shaped CdO nanoparticles were surrounded by POPD homopolymer.Bu çalışmada, poli-o-fenilendiamin polimeri (POPD) ve farklı mol oranlarında CdO nanoparçacıkları içeren POPD/CdO nanokompozitleri sulu dietilen glikol çözeltisi ortamında kimyasal polimerizasyon yöntemi ile sentezlenmiştir. Sentezlenen polimer ile nanokompozitler Fourier transform infrared spektroskopi, diferansiyel taramalı kalorimetre, UV-Görünür bölge spektroskopisi, taramalı elektron mikroskobu analizleri ile yapısal ve morfolojik olarak incelenmiş ve dört nokta yöntemi ile elektriksel iletkenlik ölçümleri yapılmıştır. Nanoparçacık varlığındaki kimyasal polimerizasyon ile elde edilen yapıların polimer ile nanoparçacığın basit bir karışımı olmadığı, polimer ile nanoparçacıklar arasında konjügasyonun ve elektron yoğunluğunun değişmesine neden olacak kuvvetli etkileşimlerin söz konusu olduğu nanokompozit yapıların sentezlendiği ve nanokompozitlerin iletkenlik değerlerinin polimerin iletkenliğinden daha yüksek olduğu belirlenmiştir. Ayrıca nanokompozitin sentezlenmesi sırasında kullanılan OPD/CdO oranlarına bağlı olarak termal kararlılığın değiştiği, bu oranın 2/1 olması ile maksimum termal kararlılığın elde edildiği görülmüştür. Taramalı elektron mikroskobu ile yapılan morfolojik incelemeler, POPD homopolimerinin küresel yapıya sahip CdO nanoparçacıkların etrafında birikerek nanoparçacıkları kapladığını göstermektedir

Chemical, mineralogical and structural features of native and expanded perlite from Macedonia

The physico-mechanical, chemical and mineralogical characteristics of volcanic glass (perlite) from the Mariovo region (Macedonia) as well as the mineralogical changes that occur during its thermal treatment were investigated to demonstrate its utilization for industrial use. The native perlite was characterized by chemical analysis, X-ray powder diffraction (XRPD), infrared (IR) spectroscopy, thermal analysis (TGA/DTA), scanning electron microscopy (SEM-EDX), transmission electron microscopy (TEM), and solid- state NMR. The chemical examination suggests that the perlite represents an acidic volcanic rock with a high percentage of SiO2 (72.45%), high in alkali metal oxides (4.21 wt.% K2O, 3.56 wt.% Na2O), with a loss of ignition 3.54 wt.%. Results from the XRPD indicated major amorphous behaviour, with low amounts of feldspars, quartz, and cristobalite. SEM examinations revealed glassy structure with presence of certain pores (dimensions ranging from 50–100 μm). The determined expansion coefficient was 20 times its original volume. XRPD of expanded perlite compared to the native perlite depicted new intensive peaks of cristobalite. SEM and TEM revealed irregular morphology with broken or ragged edges. On the basis of the chemical and mineralogical composition, the studied perlite is classified as an appropriate material suitable as ceramic flux to lower the sintering temperature.</p

Coating graphene nanoplatelets onto carbon fabric with controlled thickness for improved mechanical performance and EMI shielding effectiveness of carbon/epoxy composites

Coating nanostructures on fiber reinforcement is a facile and scalable technique to manufacture next-generation fiber-reinforced polymer composites with tailored physical properties. Optimizing the nanomaterial coating thickness on fibers is vital in tailoring the multifunctionality of fiber-reinforced composites without sacrificing the mechanical performance since it relies on the fiber–matrix interface, where interlaminar and other physical properties are governed. This paper investigates the impact of graphene nanoparticle (GNP) coating thickness on the mechanical properties, fracture behavior, thermo-mechanical, and electromagnetic interference (EMI) shielding effectiveness (SE) of composite structures. We grafted GNPs on carbon fabrics using a solution coating method with various thicknesses (10, 20, and 30 µm), and GNPs grafted fabrics were impregnated with an epoxy resin. The 20 µm GNPs coating thickness exhibited the highest mechanical performance, increasing the tensile and interlaminar shear strength by 32% and 26%, respectively, compared to pristine samples. Storage modulus and transition (Tg) temperature values increased by 18.6% and 13.6% for 20 µm coating thickness, respectively. Besides, the unstable crack growth at the fiber–matrix interface was stabilized when the GNPs coating thickness reached 20 µm according to delamination toughness tests. While mode-I fracture toughness increased up to 22%, an improvement of 13.5% was obtained in mode-II fracture toughness. The underlying toughening mechanisms at the interfacial region were identified using scanning electron microscopy. The EMI-SE was slightly increased by the GNPs grafting, whereas thinner GNPs coatings exhibited higher shielding efficiency

Hybrid nanoparticles embedded polyvinyl butyral nanocomposites for improved mechanical, thermal and microwave absorption performance

WOS:000684693100001Polymer-based nanocomposites have been broadly investigated to improve its specific properties such as thermal and mechanical properties to use in different application areas. In this study, we aimed to ameliorate the desired physical properties of polyvinyl butyral (PVB) by introducing various amounts of silver (Ag) and cobalt (Co) nanoparticles (NPs) in the polymer matrix. The arc-discharge method submerged in liquid nitrogen was performed to synthesize the metal NPs. To produce hybrid nanocomposites, we demonstrated embedding Ag:Co nanoparticles in the PVB matrix via easy/low-cost solution casting process without any additional materials. In the results of analysis for nanocomposites, it was observed that there were improvements in thermal, mechanical and microwave absorption characteristics of the PVB polymer with interaction of NPs with the polymer. As a result of these interactions, the hybridization of PVB with the metal NPs resulted in the improved thermal stability since the glass transition temperature was increased from 45.6 to 55.1 °C. Besides, while the tensile strength (σ) of the bare PVB film was calculated as 20.52 MPa, the strength of the corresponding tensile strength (σ) of 1.0 wt.% Ag:Co nanocomposite film was improved to 43.41 MPa. Moreover, in order to determine the effect of these changes on the radar absorption feature of nanocomposites, one-dimensional A-Scan measurements were performed on 2–18 GHz frequency band. In the results, it was observed that 1.0%.wt Ag:Co nanocomposite film absorbed approximately 90% of the incoming energy. The characterization results revealed that a positive synergetic effect raised in the case of the modification of the PVB matrix with both Ag and Co NPs. In the light of these data, it was understood that the characteristics of PVB were improved with the NPs combining, and the usage area of that will also increase thanks to this improvement. These regenerated properties made the hybrid nanocomposite a promising substrate material with considerable potential applications for various transparent, flexible, and portable surface coatings

Multi-walled carbon nanotube grafted 3D spacer multi-scale composites for electromagnetic interference shielding

The development of structural fiber reinforced polymer composites with various additional functionalities is becoming a hot research area to achieve the application of multi-functional composites in the aerospace and automotive industries. An innovative material solution is 3D spacer composites with distinctive anisotropic structural characteristics. Herein, we report the manufacturing of multi-walled carbon nanotubes (MWCNTs) grafted of 3D spacer glass/epoxy multi-scale composites and their electromagnetic interference shielding efficiencies (EMSE). To manufacture multi-scale composites, we utilized dip coating, vacuum filtering, and vacuum infusion methods to introduce MWCNTs of the woven fabric, while we also modified the epoxy resin with MWCNTs to increase electrical conductivity of intrinsic insulator epoxy resin. Owing to the rectangular-shaped channel structure, which is beneficial for multiple reflection and scattering between top and bottom face sheets, the resultant 3D spacer multi-scale composite represented a good EMSE performance of −18.3 dB in the frequency range of 8.2–12.4 GHz with an increase of 107% comparing the corresponding neat composite counterpart. Moreover, we measured the in-plane conductivity as 1.89E-2 S/m after MWCNTs grafting, while the out-of-plane conductivity remained three times lower than the in-plane conductivity. Dynamic mechanical analysis revealed that the storage modulus increased almost three times with the MWCNTs grafting, while glass transition temperature shifted to higher temperatures (from 77.5 to 89.7°C). Therefore, we anticipate that our study will expand the use of 3D spacer composites in the aviation and automotive industries

Effect of long-term stress aging on aluminum-BFRP hybrid adhesive joint's mechanical performance: static and dynamic loading scenarios

Composite-aluminum hybrid adhesive joints represent an ideal solution for designing lightweight structures for the marine industry. However, seawater aging is a serious concern, limiting the safe service life of the joint. Notably, efforts to understand the impact of aging have largely focused on the short-term periods without considering actual operating conditions. Here, we report the mechanical performance of hybrid joints subjected to the long-term stress aging. Besides, we modified the epoxy adhesive with halloysite nanotubes (HNTs) to limit the aging driven adhesive degradation and improve the adhesive's rigidity. We evaluated mechanical performances of hybrid joints by performing tensile, flexural, and drop-weight impact tests. While we increased the load-carrying capacity by over 25% with the HNTs modification before the stress aging process, modified adhesive withstood almost 55% higher tensile load than the neat epoxy adhesive after six-month stress aging. The modified adhesive also absorbed 41% less impact energy, indicating the efficiency of HNTs on limiting the degradation due to the stress aging. Furthermore, the damage mode transformed from adhesion to cohesion, thanks to the improved adhesive-composite interface performance. We envisage that these exciting results will pave the way for designing robust hybrid joints for the marine industry

Fracture and dynamic mechanical analysis of seawater aged aluminum-BFRP hybrid adhesive joints

Adhesively bonded hybrid FRP-aluminium structures have recently become an efficient solution for marine engineering applications. However, polymer adhesives' bond performance is sensitive to the marine environment due to polymer and interfacial degradation. This study aims to develop mode I, mode II delamination toughness, and Tg data as a comprehensive design guideline for hybrid BFRP-aluminum modified-adhesively bonded joints subjected to seawater aging. The hybrid joints were exposed to long-term seawater aging (for 6 months) to reveal their fracture and thermomechanical performances. Besides, the adhesive was reinforced with HNTs to increase fracture resistance with additional nano-scale toughening mechanisms and to delay the water absorption. After the long-term aging, reinforced adhesively bonded joints exhibited ∼36% higher fracture toughness than neat adhesively bonded joints. Moreover, DMA was conducted on miniaturized SLJ samples, which revealed that HNT modified adhesive joints showed ∼11.5 °C higher Tg. The calculated aging rates also proved the effectiveness of HNTs modification on the epoxy adhesive's aging performance since the HNT reinforced adhesive represented 43% lower aging rates in terms of storage modulus. It is considered that experimental results will help comprehend long-term aging influences on the composite-aluminum hybrid designs’ fracture and thermomechanical performances. These exciting findings will pave the way for the safe use of high stiffness and cost-effective aluminum-BFRP hybrid structures for the marine industry