Search Results (32)

The development of sustainable flame-retardant polymer composites is important for expanding the practical use of bio-based plastics while reducing reliance on petroleum-derived and halogenated materials. In this work, biodegradable polylactic acid (PLA) composites were prepared using raw wood-derived biochar as a degradable carbon-based filler and magnesium hydroxide (MH) as a halogen-free flame-retardant additive. PLA/Biochar/MH composites were prepared by melt compounding and compression molding, followed by systematic evaluation of their structural, thermal, flame-retardant, mechanical, and stability-related properties. The flame-retardant performance, evaluated by limiting oxygen index (LOI) and UL-94 (UL: Underwriters Laboratories) vertical burning tests, was significantly enhanced by the combined biochar/MH system. Biochar alone slightly increased the LOI of PLA, while MH-containing composites exceeded the practical 21% LOI threshold, with PLA/Biochar20/MH20 achieving the highest LOI value of 26.2%. This improvement was attributed to char formation, heat absorption, gas dilution, and magnesium oxide-supported barrier formation. The composites also maintained reasonable dimensional stability after accelerated aging with thickness changes below 1%. Overall, this study demonstrates that combining biodegradable PLA with degradable biochar and halogen-free MH provides a promising sustainable strategy for developing flame-retardant PLA-based composites with improved residue formation and dimensional stability. Full article

A composite meeting the UL94 V-0 rating was produced by adding 30 wt% epoxy silane-modified aluminum trihydrate (EPATH) to a 60/40 epoxy/benzoxazine matrix. Various bimodal and trimodal composites containing 20–40 wt% of three types of ceramic fillers, i.e., aluminum oxide (Al₂O₃), boron nitride (BN), and magnesium oxide (MgO), were prepared to simultaneously achieve flame-retardant and thermal conductive properties. The bimodal composites with 40 wt% of Al₂O₃ and MgO exhibited thermal conductivities of 1.22 W/m∙K and 1.29 W/m∙K, respectively, which were superior to that of the composite containing the same amount of ATH (1.0 W/m∙K). In contrast, both the coefficient of thermal expansion (CTE) and shear strength decreased with increasing ceramic filler content. For agglomerated BN, the filler loading was constrained above 30 wt% because its high specific volume caused a significant rise in the viscosity. In the trimodal composites with a total filler content of 40 wt% of Al₂O₃ and BN, a BN fraction of 7.5 wt% yielded the highest thermal conductivity of 1.64 W/m∙K and the lowest water absorption of 0.69%. When the trimodal composites were exposed to −55 °C and 150 °C for 1000 h, they exhibited a reduction in shear strength of less than 30% compared to their initial values. Full article

Coal combustion residues are often useful components for the cement industry. This study represents a material characterization and screening analysis by focusing on the mineralogical, physicochemical, and petrographic compositions of fly and bottom ash samples from four Greek power plants in order to evaluate their suitability and potential in industrial applications, especially as fillers in cement manufacturing. Proximate analysis revealed LOI values exceeding ASTM C618-22 limits. The sum of SiO₂, CaO, and Al₂O₃ classifies the studied samples as Class C except one. Iron and magnesium oxides are among the major components, while S, Ni, and Sr are also contained in significant amounts. Calcite, quartz, and plagioclases dominate, corresponding to their geochemical profile, while secondary mineral phases (i.e., neo-formed minerals during coal combustion) such as natrolite and gehlenite, were also identified. Relatively high amounts of carbonized organic matter and unburnt organic particles point to the incomplete combustion process, revealing the risk of slagging into the combustion chamber; this is confirmed through the high slagging and fouling indices. The amount of the magnetic fraction is low; magnetic spherules with complex surface structures and a wide range of spherule sizes were observed. While the pozzolanic character of the samples is strong, high values of LOI, S content, and carbonized organic material make them suitable for the cement industry after further treatment only. Full article

We report on the study of the immobilization process of non-radioactive rhenium (Re), a chemical analogue of technetium-99 (⁹⁹Tc), in compounds based on magnesium potassium phosphate (MKP), as well as the possibility of enhancing their properties with iron-bearing additives/fillers. Powdered Re₂O₇ was used as the initial Re-containing source. Because of the solubility and high leachability of Tc (VII), which is also volatile at high temperatures, its immobilization for long-term storage and disposal poses a serious challenge to researchers. Taking this into account, low-temperature stabilization technology based on MKP, a cementitious material, is currently considered promising. We prepared experimental specimens based on Re-incorporated MKP matrices and analyzed their microstructure in detail using analytical methods of X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Considering that iron-bearing substances can reduce Tc (VII) to the lower-valence form Tc (IV), which is more stable, attention was also paid to evaluate the effect of fillers (Fe₂O₃, Fe₃O₄, Fe, FeS and blast furnace slag (BFS)) on strength, oxidation state, and water resistance (expressed as leaching cumulative concentration). The addition of fillers ensures the formation of denser compounds based on MKP after 28 days of curing under ambient conditions and increases their mechanical strength. The oxidation state of Re and the reduction from Re (VII) to Re (IV) was estimated using X-ray-absorption near-edge structure (XANES) analysis. Considering the Re leaching concentrations from tests using the ANS-16.1 standard in water, enhanced leachability indices (LI) for Re from MKP matrices were determined with the addition of iron-bearing fillers. Overall, the average LI values were greater than the minimum limit, indicating their acceptance for disposal recommended by the U.S. Nuclear Regulatory Commission. Full article

Halogenated flame retardants have been amongst the most widely used and effective solutions for enhancing fire resistance. However, their use is currently strictly regulated due to serious health and environmental concerns. In this context, phosphorus-based and mineral flame retardants have emerged as promising alternatives. Despite this, their combined use is neither straightforward nor guaranteed to be effective. This study scrutinizes the interactions between these two classes of flame retardants (FR) through a systematic analysis aimed at elucidating the antagonistic pathways that arise from their coexistence. Specifically, this study focuses on two inorganic fillers, mineral huntite and chemically precipitated magnesium hydroxide, both of which produce basic oxides upon thermal decomposition. These fillers were incorporated into a poly(butylene terephthalate) (PBT) matrix to be utilized as advanced-mattress FR coating fabric and were subjected to a series of flammability tests. The pyrolysis products of the prepared polymeric composite compounds were isolated and thoroughly characterized using a combination of analytical techniques. Thermogravimetric analysis (TGA) and differential thermogravimetric analysis (dTGA) were employed to monitor decomposition behavior, while the char residues collected at different pyrolysis stages were examined spectroscopically, using FTIR-ATR and Raman spectroscopy, to identify their structure and the chemical reactions that led to their formation. X-ray diffraction (XRD) experiments were also conducted to complement the spectroscopic findings in the chemical composition of the resulting char residues and to pinpoint the different species that constitute them. The morphological changes of the char’s structure were monitored by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS). Finally, the Limited Oxygen Index (LOI) and UL94 (vertical sample mode) methods were used to assess the relative flammability of the samples, revealing a significant drop in flame retardancy when both types of flame retardants are present. This reduction is attributed to the neutralization of acidic phosphorus species by the basic oxides generated during the decomposition of the basic inorganic fillers, as confirmed by the characterization techniques employed. These findings underscore the challenge of combining organophosphorus with popular flame-retardant classes such as mineral or basic metal flame retardants, offering insight into a key difficulty in formulating next-generation halogen-free flame-retardant composite coatings. Full article

In order to explore the influence of steel slag on the road performance of asphalt mastic and its mixtures, steel slag powder (SSP) and steel slag aggregate (SSA) were used to replace limestone mineral powder filler (MF) and natural limestone aggregate (LA) respectively to prepare asphalt mastic and mixture. A series of standardized tests including penetration, softening point, ductility, viscosity, pull-off strength, dynamic shear rheometer (DSR), and bending beam rheometer (BBR) were carried out to evaluate the performance of asphalt mastics with SSP. Meanwhile, high- and low-temperature performance, moisture stability, volumetric stability, and fatigue resistance were evaluated by wheel tracking, uniaxial penetration strength, Hamburg, three-point bending, freeze–thaw splitting, immersed Marshall stability, water immersion expansion, and two-point bending trapezoidal beam fatigue tests. The results show that compared to the asphalt mastic with MF, enhanced high-temperature deformation resistance and reduced low-temperature cracking resistance of asphalt mastic with SSP were observed, as well as superior aging resistance. The improvements in high-temperature stability, moisture resistance, and fatigue performance were confirmed for asphalt mixtures with SSP/SSA. Additionally, compromised volumetric stability and low-temperature crack resistance were found when SSP/SSA was used in mixtures. Although asphalt mixtures with SSA exhibited 257.79%–424.60% higher expansion rate after 21-day immersion than those with LA, the 3-day immersion expansion rates complied with specification limits (<1.5% per JTG F40-2004). Critical volume expansion control measures should be adopted for full-component applications of steel slag powder/aggregates due to the hydration potential of free lime (f-CaO) and magnesium oxide (MgO) in steel slag under moisture exposure. Full article

This study presents a comprehensive assessment of the fresh state, rheological, and mechanical properties of alkali-activated mortars (AAMs) developed by incorporating magnesium oxide (MgO) and nanomaterials. A total of 24 AAM mixes with varying content of MgO, multi-walled carbon nanotube (MWCNT), and reduced graphene oxide (rGO) were developed following the one-part dry mix technique using powder-based activators/reagents. The effects of the types/combinations of source materials (binary or ternary)/reagents, MgO (0 to 5%), MWCNT (0 to 0.6%), and rGO (0 to 0.6%) were evaluated in terms of the mini-slump flow, setting times, viscosity, yield stress, compressive strength, ultrasonic pulse velocity (UPV), and microstructural properties. The results showed that the addition of finer MgO/nano-fillers produced a higher viscosity and yield stress accompanied by a lower slump flow and setting times. The addition of 5% MgO resulted in the lowest slump flow of 80 mm, 2–2.5 times higher viscosity, and the reduction in the initial and final setting times of about 21% and 16%, respectively. Mixes with MWCNT showed about 5–10% higher viscosity whereas for mixes with rGO, the values were noted to be 8% higher, on average, than the mixes with no MWCNT or rGO. All the developed AAMs exhibited shear-thinning behavior. The 28-day compressive strength of the AAMs ranged from 37 MPa to 49 MPa with 5% MgO and up to a 0.3% MWCNT/rGO addition increased the compressive strength. Correlations among the fresh state, rheological, and mechanical properties such as the viscosity, slump flow, setting time, compressive strength, and UPV are also described. Full article

This study investigated the effects of substituting magnesium oxide (MgO) with dolomitic limestone (DL) on the mechanical and physical properties of magnesium oxysulfate (MOS) cement. Additionally, the hydration formation phases and the influence of the molar ratio on the MOS cement’s performance were examined. The corresponding action mechanisms were identified and explored by compressive strength tests, scanning electron microscopy (SEM), X-ray diffraction (XRD), isothermal calorimetry, and a thermogravimetric analysis (TGA). The results showed that replacing MgO with DL decreased the reaction speed and heat release rate generated in the hydration process of the MOS cement. This substitution also reduced the quantity of non-hydrated MgO particles and delayed the formation of Mg(OH)₂. The diminished formation of Mg(OH)₂ contributed to an increase in the apparent porosity of pastes containing DL, thus alleviating internal stresses induced by Mg(OH)₂ formation and enhancing their mechanical strength after 28 days of curing. Conversely, the increased porosity improved the CO₂ diffusion within the structure, promoting the formation of magnesium carbonates (MgCO₃). Through the characterization of the cement matrix (XRD and TGA), it was possible to identify phases, such as the brucite, periclase, and 318 phases. The obtained results revealed the potential of incorporating mineral fillers like limestone as a promising approach to producing MOS cement with a reduced environmental impact and better properties at higher curing ages. Full article

The objective of this research was to develop highly effective conductive polymer composite (CPC) materials for flexible piezoresistive sensors, utilizing hollow three-dimensional graphitic shells as a highly conductive particulate component. Polystyrene (PS), a cost-effective and robust polymer widely used in various applications such as household appliances, electronics, automotive parts, packaging, and thermal insulation materials, was chosen as the polymer matrix. The hollow spherical three-dimensional graphitic shells (GS) were synthesized through chemical vapor deposition (CVD) with magnesium oxide (MgO) nanoparticles serving as a support, which was removed post-synthesis and employed as the conductive filler. Commercial multi-walled carbon nanotubes (CNTs) were used as a reference one-dimensional graphene material. The main focus of this study was to investigate the impact of the GS on the piezoresistive response of carbon/polymer composite thin films. The distribution and arrangement of GS and CNTs in the polymer matrix were analyzed using techniques such as X-ray diffraction and scanning electron microscopy, while the electrical, thermal, and mechanical properties of the composites were also evaluated. The results revealed that the PS composite films filled with GS exhibited a more pronounced piezoresistive response as compared to the CNT-based composites, despite their lower mechanical and thermal performance. Full article

The radiological protection has the purpose of safeguarding the physical well-being of the user, preventing exposure to detrimental levels of ionizing radiation. This study introduces a novel, cost-effective category of lead-free elastomeric material designed for radiation shielding. The filler compounds utilized are notably lighter than conventional lead-based materials, enhancing user ergonomics during application. They comprise of a blend of barium sulfate combined or not with magnesium oxide with addition-cure liquid silicone rubber. To ensure the effectiveness of the radiation shielding, X-ray transmission measurements were performed for the different thicknesses of the materials and the results compared with Monte Carlo simulations. Additionally, the physical properties of the new materials, such as density, homogeneity, tensile strength, viscosity, and wettability, were also evaluated. The findings indicate that both materials fulfill the requirement for application in radiation protection garments. Full article

Hardystonite-based (HT) bioceramic foams were easily obtained via thermal treatment of silicone resins and reactive oxide fillers in air. By using a commercial silicone, incorporating strontium oxide and magnesium oxide precursors (as well as CaO and ZnO), and treating it at 1100 °C, a complex solid solution (Ca_1.4Sr_0.6Zn_0.85Mg_0.15Si₂O₇) that has superior biocompatibility and bioactivity properties compared to pure hardystonite (Ca₂ZnSi₂O₇) can be obtained. Proteolytic-resistant adhesive peptide mapped on vitronectin (D2HVP), was selectively grafted to Sr/Mg-doped HT foams using two different strategies. Unfortunately, the first method (via protected peptide) was unsuitable for acid-sensitive materials such as Sr/Mg-doped HT, resulting in the release of cytotoxic levels of Zinc over time, with consequent negative cellular response. To overcome this unexpected result, a novel functionalization strategy requiring aqueous solution and mild conditions was designed. Sr/Mg-doped HT functionalized with this second strategy (via aldehyde peptide) showed a dramatic increase in human osteoblast proliferation at 6 days compared to only silanized or non-functionalized samples. Furthermore, we demonstrated that the functionalization treatment does not induce any cytotoxicity. Functionalized foams enhanced mRNA-specific transcript levels coding IBSP, VTN, RUNX2, and SPP1 at 2 days post-seeding. In conclusion, the second functionalization strategy proved to be appropriate for this specific biomaterial and was effective at enhancing the material’s bioactivity. Full article

Carbon dioxide (CO₂) concentration is now 50% higher than in the preindustrial period and efforts to reduce CO₂ emission through carbon capture and utilization (CCU) are blooming. Membranes are one of the attractive alternatives for such application. In this study, a rubbery polymer polydimethylsiloxane (PDMS) membrane is incorporated with magnesium oxide (MgO) with a hierarchically two-dimensional (2D) nanosheet shape for CO₂ separation. The average thickness of the synthesized MgO nanosheet in this study is 35.3 ± 1.5 nm. Based on the pure gas separation performance, the optimal loading obtained is at 1 wt.% where there is no observable significant agglomeration. CO₂ permeability was reduced from 2382 Barrer to 1929 Barrer while CO₂/N₂ selectivity increased from only 11.4 to 12.7, and CO₂/CH₄ remained relatively constant when the MMM was operated at 2 bar and 25 °C. Sedimentation of the filler was observed when the loading was further increased to 5 wt.%, forming interfacial defects on the bottom side of the membrane and causing increased CO₂ gas permeability from 1929 Barrer to 2104 Barrer as compared to filler loading at 1 wt.%, whereas the CO₂/N₂ ideal selectivity increased from 12.1 to 15.0. Additionally, this study shows that there was no significant impact of pressure on separation performance. There was a linear decline of CO₂ permeability with increasing upstream pressure while there were no changes to the CO₂/N₂ and CO₂/CH₄ selectivity. Full article

Herein, we present a mussel-inspired supramolecular polymer coating to improve the an-ti-corrosion and self-healing properties of an AZ31B magnesium alloy. A self-assembled coating of polyethyleneimine (PEI) and polyacrylic acid (PAA) is a supramolecular aggregate that takes advantage of the weak interaction of non-covalent bonds between molecules. The cerium-based conversion layers overcome the corrosion problem between the coating and the substrate. Catechol mimics mussel proteins to form adherent polymer coatings. Chains of PEI and PAA interact electrostatically at high density, forming a dynamic binding that causes strand entanglement, enabling the rapid self-healing properties of a supramolecular polymer. The addition of graphene oxide (GO) as an anti-corrosive filler gives the supramolecular polymer coating a superior barrier and impermeability properties. The results of EIS revealed that a direct coating of PEI and PAA accelerates the corrosion of magnesium alloys; the impedance modulus of a PEI and PAA coating is only 7.4 × 10³ Ω·cm², and the corrosion current of a 72 h immersion in a 3.5 wt% NaCl solution is 1.401 × 10⁻⁶ Ω·cm². The impedance modulus of the addition of a catechol and graphene oxide supramolecular polymer coating is up to 3.4 × 10⁴ Ω·cm², outperforming the substrate by a factor of two. After soaking in a 3.5 wt% NaCl solution for 72 h, the corrosion current is 0.942 × 10⁻⁶ A/cm², which is superior to other coatings in this work. Furthermore, it was found that 10-micron scratches were completely healed in all coatings within 20 min, in the presence of water. The supramolecular polymer offers a new technique for the prevention of metal corrosion. Full article

Composite fillers are often used to improve the protective properties of coatings. To obtain a high protective performance of epoxy coatings for magnesium alloys, polyaniline (PANI) and graphene oxide (GO) composite powders were selected because of their corrosion inhibition and barrier performance, respectively. The paper mainly focuses on the effect of the preparation methods of the composite powders on the protective performance. PANI and GO composite powders were prepared by in situ polymerization and blending, respectively. First, the composite powder was characterized by X-ray diffractometer, Fourier transform infrared spectroscopy, and scanning electron microscopy. Then, the different composite powders and pure PANI powder were dispersed uniformly in epoxy resin, and the coating was prepared on the surface of the AZ91D magnesium alloy and studied by an electrochemical impedance test, adhesion strength test and physical properties test. The results show that the impedance value of the coating with the added PANI and GO composite powders by in situ polymerization was 4 × 10⁹ Ω·cm² and higher than that with the added pure PANI (4 × 10⁹ Ω·cm²) and PANI and GO mixed powders (1 × 10⁹ Ω·cm²) after 2400 h immersion in a 3.5% NaCl solution; the former also had better flexibility, ss impact resistance, and adhesion strength. Compared with the direct blending method, the PANI and GO polymerization powders can exert the shielding effect of GO and PANI corrosion inhibition better and achieve a better protective effect on the magnesium alloy. Full article

Rare earth oxide particles have received important attention in recent years, and due to the wide diversity of promising applications, the need for this kind of material is predicted to expand as the requirements to use the current resources become more demanding. In this work, cerium oxide (CeO₂) was introduced into ethylene-vinyl acetate (EVA)/magnesium hydroxide (MDH) composites for enhancing the flame retardancy, mechanical properties and anti-ultraviolet aging performance. The target EVA/MDH/CeO₂ composites were prepared by extrusion and injection molding, and the effects of the addition of the CeO₂ were explored by thermogravimetric analysis (TGA), Differential Scanning Calorimetry (DSC), X-ray Diffraction (XRD), limiting oxygen index (LOI), UL-94, cone calorimetry test, and anti-ultraviolet aging test. Typically, the incorporation of the CeO₂ allows a significant increase of the elongation at break and Young’s modulus compared with EVA/MDH by 52.25% and 6.85%, respectively. The pHRR remarkably decreased from 490.6 kW/m² for EVA/MDH to 354.4 kW/m² for EVA/MDH/CeO₂ composite. It was found that the CeO₂ presents excellent synergism with MDH in the composites for the anti-UV properties in terms of mechanical properties preservation. Notably, the combination of CeO₂ with MDH is a novel and simple method to improve the filler–polymer interaction and dispersion, which resulted in the improvement of the mechanical properties, flame retardancy and the anti-ultraviolet aging performance of the composites. Full article