Concept of a Novel Glass Ionomer Restorative Material with Improved Mechanical Properties

The objective of this study was to transfer the concept of ductile particle reinforcement to restorative dentistry and to introduce an innovative glass ionomer material that is based on the dispersion of PEG-PU micelles. It was hypothesized that reinforcing a conventional glass ionomer in this way increases the flexural strength and fracture toughness of the material. Flexural strength and fracture toughness tests were performed with the novel reinforced and a control glass ionomer material (DMG, Hamburg, Germany) to investigate the influence of the dispersed micelles on the mechanical performance. Transmission electron microscopy was used to identify the dispersed micelles. Fracture toughness and flexural strength were measured in a 3-point-bending setup using a universal testing machine. Before performing both tests, the specimens were stored in water at 37 °C for 23 h. The fracture toughness (MPa∙m0.5) of the novel glass ionomer material (median: 0.92, IQR: 0.89-0.94) was significantly higher than that of the control material (0.77, 0.75-0.86, p = 0.0078). Significant differences were also found in the flexural strength (MPa) between the reinforced (49.7, 45.2-57.8) and control material (41.8, 40.6-43.5, p = 0.0011). Reinforcing a conventional glass ionomer with PEG-PU micelles improved the mechanical properties and may expand clinical applicability of this material class in restorative dentistry.

Microstructural Understanding of Hydroxyapatite Addition on Age Hardening, Internal Friction, and Mechanical and Electrochemical Response of Resorbable Magnesium Alloys with Good Cytocompatibility

The present work aims to assess the age hardening of microalloyed Mg-Zn-Mn alloy reinforced with Ca₁₀(PO₄)₆(OH)₂ (hydroxyapatite, HAp) particles to impart mechanical strength without deteriorating their degradation and biocompatibility behavior for their suitability toward resorbable fixation devices. The hydroxyapatite powder was synthesized with high purity. Mg-Zn-Mn (ZM31) and Mg-Zn-Mn/HAp (ZM31/HAp) were stir-cast, homogenized, and solution-treated to achieve uniform dissolution. Further, they were given a range of aging treatments (175 °C for 0, 5, 10, 25, 50, and 100 h), and the age hardening was measured as Vickers microhardness. The solution-treated and peak-aged (175 °C × 50 h) samples were further investigated using optical and electron microscopy, tensile testing, electrochemical corrosion testing, dynamic mechanical analysis, and biocompatibility. The peak-aged ZM31 sample revealed the highest ultimate strength (134.09 ± 5.46 MPa). The aging treatment resulted in notable improvement in ductility in ZM31 (8.72 ± 1.38%) and yield strength in ZM31/HAp (82.50 ± 1.43 MPa). The rapid strain-hardening behavior was distinctly visible in peak-aged samples in the initial stage of deformation. The amplitude-dependent internal friction confirmed the active solute and age-hardening mechanisms in agreement with the Granato-Lücke model. All samples displayed favorable cell viability (>80%) and cell adhesion behavior; however, their hemocompatibility and biodegradation need further consideration.

Development of Cork Biocomposites Enriched with Chitosan Targeting Antibacterial and Antifouling Properties

The demand for bio-based and safer composite materials is increasing due to the growth of the industry, human population, and environmental concerns. In this framework, sustainable and safer cork-polymer composites (CPC), based on green low-density polyethylene (LDPE) were developed using melt-based technologies. Chitosan and polyethylene-graft-maleic anhydride (PE-g-MA) were employed to enhance the CPC's properties. The morphology, wettability, mechanical, thermal, and antibacterial properties of the CPC against Pseudomonas putida (P. putida) and Staphylococcus aureus (S. aureus) were examined. The CPC showed improved stiffness when compared with that of the LDPE matrix, preferably when combined with chitosan and PE-g-MA (5 wt. %), reinforcing the stiffness (58.8%) and the strength (66.7%). Chitosan also increased the composite stiffness and strength, as well as reduced the surface hydrophilicity. The CPCs' antibacterial activity revealed that cork significantly reduces the biofilm on the polymer matrix. The highest biofilm reduction was found with CPC containing cork and 5 wt. % chitosan for both P. putida (54% reduction) and S. aureus (36% reduction), confirming their potential to extend the lifespan of products for packaging and healthcare, among other applications. This work leads to the understanding of the factors that influence biofilm formation in cork composites and provides a strategy to reinforce their behavior using chitosan.

Enhancement of Impact Abrasion Resistance Performances of White Cast Iron Utilizing Ti3AlC2

Al-Ti-C master alloy agent is currently the most promising grain refiner. This work investigates the influence of Ti₃AlC₂ addition (1.0-3.0 wt.%) on the microstructure of a hypoeutectic cast iron (4.7 wt.% Cr, 2.3 wt.% C). Microstructures of the samples were examined by SEM (scanning electron microscope). It was demonstrated that the added Ti₃AlC₂ did reduce the size of coarse primary carbides. The XRD (X-ray diffraction) pattern shows that Ti₃AlC₂ is decomposed into TiC in the alloy substrate. The EDS (energy dispersive spectrometer) interfacial element analysis shows that TiC combines well with the matrix interface. As the Ti₃AlC₂ amount was increased, the finest microstructure was achieved. When 2 wt.% Ti₃AlC₂ was added, the wear-resistance property of the material improved and became two times harder than the former. However, when 3% Ti₃AlC₂ was added, TiC gathered at the crystal boundary, which caused a decrease in the wear resistance of the material.

Numerical homogenization of thermal conductivity of particle-filled thermal interface material by fast Fourier transform method

Thermal interface material (TIM) is pivotal for the heat dissipation between layers of high-density electronic packaging. The most widely used TIMs are particle-filled composite materials, in which highly conductive particulate fillers are added into the polymer matrix to promote heat conduction. The numerical simulation of heat transfer in the composites is essential for the design of TIMs; however, the widely used finite element method (FEM) requires large memory and presents limited computational time for the composites with dense particles. In this work, a numerical homogenization algorithm based on fast Fourier transform was adopted to estimate the thermal conductivity of composites with randomly dispersed particles in 3D space. The unit cell problem is solved by means of a polarization-based iterative scheme, which can accelerate the convergence procedure regardless of the contrast between various components. The algorithm shows good precision and requires dramatically reduced computation time and cost compared with FEM. Moreover, the effect of the particle volume fraction, interface thermal resistance between particles (R-PP), interface thermal resistance between particle and matrix (R-PM), and particle size have been estimated. It turns out that the effective conductivity of the particulate composites increases sharply at a critical filler volume fraction, after which it is sensitive to the variation of filler loading. We can observe that the effective thermal conductivity of the composites with low filler volume fraction is sensitive to R-PM, whereas the it is governed by R-PP for the composites with high filler content. The algorithm presents excellent efficiency and accuracy, showing potential for the future design of highly thermally conductive TIMs.

Injection Molding of Highly Filled Polypropylene-based Biocomposites. Buckwheat Husk and Wood Flour Filler: A Comparison of Agricultural and Wood Industry Waste Utilization

The study presents a comparative analysis for two types of polymer fillers used during the processing of polypropylene by the injection molding technique. The aim of the study was to assess the usefulness of buckwheat husk waste as an alternative to the widely used wood fiber fillers. For this purpose, we prepared composite samples containing 10, 30 and 50 wt % of the filler, which were subjected to mechanical tests, thermal analysis, and structural observations in order to evaluate and compare their properties. Additionally, we evaluated the effectiveness of the composite system's compatibility by using maleic anhydride grafted polypropylene (PP-g-MA). The results of mechanical tests confirmed a more effective reinforcement mechanism for wood fibers; however, with the addition of PP-g-MA compatibilizer, these differences were significantly reduced: we observed a 14% drop for tensile modulus and 5% for strength. This suggests high susceptibility to this type of adhesion promoter, also confirmed by SEM observations. The paper also discusses rheological measurements conducted on a rotational rheometer, which allowed to confirm more favorable flow characteristics for composites based on buckwheat husks.

Electrical Current Map and Bulk Conductivity of Carbon Fiber-Reinforced Nanocomposites

A suitably modified resin film infusion (RFI) process was used for manufacturing carbon fiber-reinforced composites (CFRCs) impregnated with a resin containing nanocages of glycidyl polyhedral oligomeric silsesquioxane (GPOSS) for enhancing flame resistance and multi-wall carbon nanotubes (MWCNTs) to contrast the electrical insulating properties of the epoxy resin. The effects of the different numbers (7, 14 and 24) of the plies on the equivalent direct current (DC) and alternating current (AC) electrical conductivity were evaluated. All the manufactured panels manifest very high values in electrical conductivity. Besides, for the first time, CFRC strings were analyzed by tunneling atomic force microscopy (TUNA) technique. The electrical current maps highlight electrically conductive three-dimensional networks incorporated in the resin through the plies of the panels. The highest equivalent bulk conductivity is shown by the seven-ply panel characterized by the parallel (σ_//0°) in-plane conductivity of 16.19 kS/m. Electrical tests also evidence that the presence of GPOSS preserves the AC electrical stability of the panels.

Tailoring Material Stiffness by Filler Particle Organization

In the context of emerging methods to control particle organization in particle-matrix composite materials, we explore, using finite element analysis, how to modulate the material bulk mechanical stiffness. Compared to a composite containing randomly distributed particles, material stiffness is enhanced 100-fold when filler particles are aligned into linear chains lying parallel to the loading direction. In contrast, chains aligned perpendicular to that direction produce negligible stiffness change. These outcomes reveal how zigzag chains, which provide intermediate results, can modulate stiffness. The stiffness decreases gradually with increasing zigzag angle θ over a range spanning 2 orders of magnitude.

Functionalized Carbon Nanotubes with Phosphorus- and Nitrogen-Containing Agents: Effective Reinforcer for Thermal, Mechanical, and Flame-Retardant Properties of Polystyrene Nanocomposites

Aminated multiwalled carbon nanotubes (A-MWCNT) were reacted with diphenylphosphinic chloride (DPP-Cl) to prepare the functionalized MWCNT (DPPA-MWCNT). A-MWCNT and DPPA-MWCNT were respectively mixed with polystyrene (PS) to obtain composites through the melt compounding method. SEM observations demonstrated that the DPPA-MWCNT nanofillers were more uniformly distributed within the PS matrix than A-MWCNT. PS/DPPA-MWCNT showed improved thermal stability, glass transition temperature, and tensile strength in comparison with PS/A-MWCNT, resulting from good dispersion and interfacial interactions between DPPA-MWCNT and PS matrix. The incorporation of DPPA-MWCNT to PS significantly reduced peak heat release rate, smoke production rate, and carbon monoxide and carbon dioxide release in cone calorimeter tests. The enhanced fire-retardant properties should be ascribed to the barrier effect of carbon nanotubes, which could provide enough time for DPPA-MWCNT and its functionalized groups to trap the degrading polymer radicals to catalyze char formation. The char layer served as an efficient insulating barrier to reduce the exposure of polymer matrix to an external heat source as well as retarding the flammable gases from feeding the flame.

Finite element analysis of the effect of an interphase on toughening of a particle reinforced polymer composite

A numerical method was used to study the interaction between a crack and the filler phase in a particle-reinforced polymer composite. The simulation was achieved by implementing a progressive damage-and-failure material model and element-removal technique through finite element analysis, providing a framework for the quantitative prediction of the deformation and fracture response of the composite. The effect of an interphase on composite toughness was also studied. Results show that a thin and high strength interphase results in efficient stress transfer between particle and matrix and causes the crack to deflect and propagate within the matrix. Alternatively, a thick and low strength interphase results in crack propagation within the interphase layer, and crack blunting. Further analysis of the effect of volume fraction and particle-particle interactions on fracture toughness as well as prediction of the fracture toughness can also be achieved within this framework.