Bulletin of Materials Science最新文献

Poly(ethylene-co-vinyl acetate) is used in numerous industries due to its versatility and increasing development of reinforced foams with a variety of fillers as well as the method of expansion, impacting the properties of foams. By varying the type and content of the incorporated filler as well as the expansion method, it is possible to obtain different cell morphologies even with low filler content in the polymer matrix. On this basis, this study reports the development of EVA foams reinforced with small amounts of micronized graphite and expanded by two expansion methods, namely thermocompression with chemical blowing agents (CBA) and expansion in an autoclave with CO₂ in supercritical state as physical blowing agent (PBA). The main results show that the presence of a small amount of graphite reduces the density of foam, significantly increases the size of cells, and consequently, reduces the number of cells per unit area. The CBA foams had a lower density than PBA foams; however, the PBA foams exhibited a more homogeneous morphological structure.

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Graphene oxide–cobalt ferrite magnetic nanocomposite (M-GOC) was efficiently synthesised by microwave-assisted method for water remediation. The graphene oxide (GO) was synthesized by improved Hummers’ method, while cobalt ferrite (CoFe₂O₄) was synthesized by microwave-assisted combustion method. X-ray diffractograms indicated high phase-pure M-GOC with an average crystallite size of 18.5 nm. An enhancement in the absorbance was observed in the range of 220–280 nm due to the presence of additional π–π* transition of aromatic C–C bonds of GO. Appearance of a peak around 584 cm⁻¹ corresponds to the stretching vibration of Co–O bond. Corrugated GO sheets were observed in SEM and HRTEM images with agglomerated spherical CoFe₂O₄ nanoparticles intercalated between the GO sheets. A particle size distribution curve was plotted that indicated an average particle size of ~11 nm of the CoFe₂O₄ nanoparticles. Raman spectra of GO confirmed the synthesis of pure GO sheets. Vibrating sample magnetometer was employed to investigate the magnetic behaviour of M-GOC, which showed a M_r/M_s ratio of 0.278. The adsorption study was performed, in which M-GOC nanocomposite exhibited an excellent adsorption capacity of 2229.9 mg g⁻¹ for heavy metal i.e., cadmium ions (Cd⁺²).

Yttria-stabilised zirconia is used as a thermal barrier coating material and is widely applied in the thermal protection field. However, its tendency to undergo phase transformation at high temperatures poses a significant challenge to the durability of these coatings. An alternative material with superior high-temperature phase stability and a high coefficient of thermal expansion is thus desirable. Rare earth zirconate, such as Gadolinium zirconate (Gd₂Zr₂O₇), has emerged as a promising candidate due to its inherent properties. High-entropy ceramics have attracted much attention due to their excellent properties. Leveraging the design principles of high-entropy systems, the structural configuration of Gd₂Zr₂O₇ has been optimised to enhance its properties. In this work, A-, B- and AB-sites of Gd₂Zr₂O₇ were designed by regulating the configurational entropy. Based on this strategy, seven types of high-entropy powders and ceramic blocks were prepared successfully. The structure and thermal properties of the as-prepared samples were investigated. The results indicate that the configurational entropy within the system and the size disorder parameter are pivotal in determining the thermal stability and thermal conductivity of the as-prepared high-entropy ceramic materials. Notably, the dual-phase high-entropy Gd₂(Ce_0.2Zr_0.2Hf_0.2Sn_0.2Ti_0.2)₂O₇ ceramic exhibits good thermal stability. The large size and mass difference between the elements results in a reduced mean free path of phonons, thereby reducing the thermal conductivity significantly. The Gd₂(Ce_0.2Zr_0.2Hf_0.2Sn_0.2Ti_0.2)₂O₇ ceramic demonstrates thermal conductivity that is substantially lower than that of Gd₂Zr₂O₇ and other high-entropy ceramics, which is as low as 0.927–0.850 W m⁻¹ K⁻¹ at 200–800°C. These results indicate that the high-entropy Gd₂(Ce_0.2Zr_0.2Hf_0.2Sn_0.2Ti_0.2)₂O₇ is an outstanding candidate for application in thermal barrier technology and related fields.

Aim of this work is to study the effect of pectin content on the physicochemical, morphological, swelling and releasing properties of composite hydrogel beads based on pectin and sodium metasilicate (SM). Synthesis of pectin–silica composite beads was carried out using the ionotropic gelation method and sol–gel reaction of SM as a silica precursor. The entrapment efficiency of mesalazine (66–88%) and gel strength (0.86–2.10 N) increased in the pectin–silica hydrogels compared to pectin–Ca hydrogels. These parameters increased with the increase in concentration of pectin. Energy-dispersive X-ray analysis showed that the silicon content was higher in the beads with an increased SM/pectin ratio (2:1). Fourier transform infrared spectroscopy revealed the formation of an organic/inorganic composite, the presence of H–bonds in pectin–silica hydrogel and the loading of mesalazine into the composite gel. Composite hydrogels with the lowest amount of pectin (an organic component) showed the highest thermal stability. Pectin–silica hydrogels were less sensitive to the adsorption of gastrointestinal fluids and released mesalazine very slowly compared to pectin–Ca gels. Mesalazine release from composite gels decreased with the increase in pectin concentration and gel strength. The gel formulations with high gel strength and a low SM/pectin ratio had the lowest mesalazine release rate in the gastrointestinal environment. Mesalazine was released slowly in gastrointestinal fluids and more rapidly in colonic fluid. Synthesized pectin–silica hydrogels based on callus culture pectin, appear to be a promising composite system for targeted drug delivery to the colon.

The interface between matrix and reinforcement plays a vital role in determining the mechanical properties of the composite. The surface of reinforcement can be modified to enhance the interfacial bonding. In the present work, Kenaf fiber (KF) was used as a reinforcement, while polypropylene (PP) acted as a matrix. KF was chemically treated to remove the amorphous phases thereby improving its interaction with the matrix. Further, fibres were coated with magnesium hydroxide (MH) particles. Fibre to particle ratio varied in the ratio of 100:1, 50:1, 20:1 and 10:1. For the fabrication of composites, 10 wt.% KF was used and specimens were injection moulded. Particles were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The moulded specimens were subjected to tensile test, impact test, water absorption test, and thermal analysis. Enhancement in mechanical properties has been observed due to improvement in interfacial bonding. Using the MH coated fibres, tensile strength and impact strength were increased by 13% and 31%, respectively.

Today, economic consumption of biodegradable polymers is significant in many applications. Thermoplastic starch (TPS) and polylactic acid (PLA) are two bio-based and biodegradable polymers that are increasingly being used to replace the petrochemical-based polymers. Adding TPS into a PLA matrix can also decrease material cost and increase its biodegradation rate. This work tested the printability of TPS/PLA films. For this purpose, TPS was first prepared by the addition of sorbitol and glycerol as softeners using an internal mixer at 140°C. Then, it was added to the PLA in internal mixer at 180°C. To analyse the data, design of the experiment was done according to Box–Behnken design (BBD) method for three variables in three levels by using Design-Expert software, which led to the preparation of 15 samples. Individual and interactive effects of wt% of PLA in TPS/PLA mixture, the wt% of starch in TPS, and the ratio of sorbitol to glycerol on the tensile properties, thermal properties and printing properties (optical density) were investigated. Solvent-based flexographic ink was applied to test printability of the films. It has been found that the PLA can be successfully printed with flexographic solvent inks to achieve a quality comparable to that of common packaging films.

To deepen the fundamental knowledge on the effect of titanium diboride (TiB₂) particle interface on thermal conductivity of three different composites with polyethylene matrices (HDPE/TiB₂, MDPE/TiB₂ and LDPE/TiB₂), this paper is devoted to a theoretical approach on the analysis of thermal behaviour of polymer-based composites. This study is based on the Hashin and Shtrikman model, which allows us to determine the thermal conductivity considering an idealized interface between the reinforcing molecules. In addition, the Hasselman and Johnson model is used to evaluate thermal conductivity with an imperfect interface. We mainly discuss the difference between two types of interfaces with the aim of improving the thermal conductivity within the composite material used in this study without altering the mechanical and thermal behaviours. This approach creates new opportunities, especially in manufacturing, to use high-quality composite materials at low-cost and non-destructive. To this end, we have investigated the variations in the effective thermal conductivity of different composites, λ_eff as a function of volume fraction of the reinforcement (TiB₂). In particular, we have emphasized the study on the effective thermal conductivity of the composite, taking into account interactions at the interface between the particles and matrix. Definitely, the random dispersion of spherical particles and cylindrical particles oriented perpendicular to the heat flow is considered. The main conclusion is that the form of particles and the type of interface of the reinforcement drastically affect thermal conductivity of the system under consideration.

In the present study, we have confined the smallest water clusters namely, monomer and dimer under various carbon nanotubes and fullerenes using quantum mechanics/molecular mechanics methods. We observed the change in their structural, vibrational, optical and electronic properties as compared to each other as well as against the free monomer and dimer. For monomer, the confinement effect was found to be the greatest for carbon nanotube CNT(7,0) followed by C-60 and then by C-78. However, in the case of the dimer, there was a change in its structure, thus exhibiting different confining effects in each geometry. We also note that, as the diameter of the CNT goes on increasing, the confining effects over the monomer and the dimer go on decreasing. We have also confined a monomer by placing it over one C-60 fullerene, and between two and three C-60 fullerenes at various sites—the hexagon, pentagon and the vertex at different distances from the surface, and compared the extent of confinement. In the vibrational spectra, for short-range interactions, a redshift was observed, whereas a blueshift was seen in the case of long-range interactions as we went from hexagon to pentagon to vertex sites. We have also confirmed the results obtained by studying their structural, vibrational, electronic and optical properties.

A structural study of the transformation of 6√3 reconstruction on the surface of a 4H–SiC substrate into quasi-free epitaxial graphene was carried out by the reflection high-energy electron diffraction (RHEED) method. The conversion was carried out via hydrogen intercalation between the reconstructed layer and the adjacent top layer of SiC. The initial 6√3 reconstruction was obtained during short sublimation annealing of the 4H–SiC substrate in an argon medium. A slight violation of the 6√3 reconstruction layer formation uniformity was found. The results of the study of the crystal structure of quasi-free-standing graphene and single-layer graphene comprising a buffer layer formed on 4H–SiC in the traditional way in an Ar atmosphere without intercalation were compared.

Cotton gauze (CG) is the most commonly used primary wound dressing to protect wounds from the external environment. However, it is highly susceptible to fouling due to the adhesion of bacteria present on the wound surface. Bacterial colonization of the dressing is detrimental as it aids in wound infection and delays wound healing. To mitigate this issue, the objective of this study was to transform the inert CG into a fouling-resistant wound dressing that can actively resist bacterial adhesion and also prevent biofilm formation on the surface of cotton. In this work, a facile method of modifying commercial CG using oxidized dextran (Odex) was developed. Odex was derived from dextran via periodate oxidation reaction and then coated over the CG using mussel-inspired chemistry. The resultant Odex-modified CG demonstrated a substantial reduction in bacterial adhesion after 4 h of incubation in bacterial suspension. The modified gauze suppressed biofilm formation, achieving ~83% reduction in viable bacterial count as compared to unmodified CG after 48 h of incubation in the bacterial suspension. In addition, the modified CG also showed good breathability, wettability and moisture retention properties. The results suggest a promising approach of transforming inert CG into a potential fouling-resistant wound dressing for the management of wound infections.