Filler-matrix Interface Research Articles

Epoxy resin reinforced with carbonized chicken feathers: An innovative composite material with sustainable potentials

This article explores a novel method for enhancing the mechanical properties of epoxy resin composites by incorporating carbonized chicken feathers as a filler material. The fabrication process involves carbonizing chicken feathers at 600°C and incorporating 5-10 wt% of the fillers into an epoxy matrix. The composites showed enhanced mechanical properties and samples containing 10 wt% filler exhibit the best properties. The performance corresponds to 49% increase in tensile strength, 16% rise in Young’s modulus, 40% improvement in flexural modulus, and 57% in flexural strength. X-ray diffraction and scanning electron microscopy with energy dispersive spectroscopy were employed to characterize the filler. This characterization provides valuable insights into the structure and chemical composition of the pulverized carbonized chicken feathers that contributed to the attained improvement in composites’ properties. Microstructural examination of the developed composite under scanning electron microscope also provides insights into matrix-filler interface and dispersion of the fillers within the composite matrix. The study not only highlights the unique combination of carbonized feathers’ inherent strength and compatibility with the epoxy matrix but also underscores the eco-friendly nature of utilizing agricultural waste. The findings suggest promising applications in industries demanding lightweight, high-strength materials, which can contribute to sustainable engineering solutions.

The Development of Sustainable Polyoxymethylene (POM)-Based Composites by the Introduction of Natural Fillers and Melt Blending with Poly(lactic acid)-PLA

The conducted study was focused on the development of a new type of technical blend reinforced with natural fillers. The study was divided into two parts, where, in the first stage of the research, unmodified POM was reinforced with different types of natural fillers: cellulose, wood flour, and husk particles. In order to select the type of filler intended for further modification, the mechanical characteristics were assessed. The 20% wood flour (WF) filler system was selected as the reinforcement. The second stage of research involved the use of a combination of polyoxymethylene POM and poly(lactic acid) PLA. The POM/PLA blend (ratio 50/50%) was modified with an elastomeric compound (EBA) and chain extender as the compatibilized reactive (CE). The microscopic analysis revealed that for the POM/PLA system, the filler–matrix interface is characterized by better wettability, which might suggest higher adhesion. The mechanical performance revealed that for POM/PLA-based composites, the properties were very close to the results for POM-WF composites; however, there is still a significant difference in thermal resistance in favor of POM-based materials. The increase in thermomechanical properties for POM/PLA composites occurs after heat treatment. The increasing crystallinity of the PLA phase allows for a significant increase in the heat deflection temperature (HDT), even above 125 °C.

Polyethyleneimine NH2-UiO-66 nanofiller-based mixed matrix membranes for natural gas purification

Effective separation of CO2 from CH4 is crucial for the purification of natural gas, which requires membrane materials with high permeability, selectivity, and stability of under high pressures. In this work, a high CO2-affinity MOF-based nanofiller (Pin@NH2-UiO-66) was prepared and integrated in polyetherimide (PEI) to prepare mixed matrix membranes (MMMs) for enhanced CO2/CH4 separation capabilities. The Pin@NH2-UiO-66 nanofiller comprised an in situ-formed polyethyleneimine-NH2-UiO-66 composite prepared via a one-pot synthesis. The polyethyleneimine was covalently attached to the H2BDC-NH2 ligand allowing for a stronger integration within the PEI matrix. The polyethyleneimine affects the nucleation of MOF, leading to miniaturization of the MOF particles. The smaller-sized filler is beneficial for improved interaction at the filler-matrix interface. The numerous amino functionalities grafted onto the NH2-UiO-66 increased the CO2 adsorption sites, thereby enhancing the affinity for CO2. Owing to the improved interaction, the elevated CO2 attraction, and the inherent properties of the porous NH2-UiO-66, the fabricated MMMs preformed superior in separating CO2/CH4. The 30-Pin@NH2-UiO-66-PEI membrane (containing 30 wt% nanofiller) exhibited a CO2/CH4 selectivity of 27.7 and a CO2 permeability of 2498.9 Barrer. The CO2 permeability was 21 times greater than that of the pristine PEI membrane, and 4 times higher compared to P@NH2-UiO-66 MMM with polyethyleneimine modified MOF filler prepared by a traditional wet impregnation method. Additionally, the novel MMM demonstrates excellent separation stability under conditions that mimic industrial settings, demonstrating its potential application for natural gas purification.

Promoting Cross-Link Reaction of Polymers by the Matrix-Filler Interface Effect: Role of Coupling Agents and Intermediate Linkers.

The matrix-filler interface effect plays an important role in determining the structural stability and mechanical properties of polymer composite materials, which remain ambiguous and need to be studied. The network-forming dynamics of poly(3,3-bis (azidomethyl) oxetane-tetrahydrofuran) (PBT) at the ammonium perchlorate (AP) surface was studied by using atomistic molecular dynamics simulation, considering the additives of curing agent toluene diisocyanate (TDI), cross-linker trimethylolpropane (TMP), and coupling agent triethanolamine (TEA). The presence of the AP surface promotes chain cross-link reaction, which is attributed to the increased production of intermediate linkers formed by TDI, TMP, and TEA. The intermediate linker has three reactive sites that can react with PBT main chains to form a cross-linked structure. Owing to the strong interaction with the AP surface, the coupling agent TEA plays a dominant role in forming the intermediate linker. At the early stage of network forming (reaction ratio r < 30%), the AP surface adsorbs TEA, which leads to a maximum contact density to PBT. As r increases to 60%, the density of intermediate linkers near the AP surface reaches a maximum value. Consequently, the chain cross-link reactions between the intermediate linker and PBT main chains are enhanced as r > 60%. This work explains the micromechanism of the promotion of chain cross-link reaction by the interface effect and provides important insights on designing polymer materials with high mechanical properties.

Functional and ultrastretchable thermoplastic elastomeric materials: Influence of carbon dots on fluorescence, dielectric and mechanical properties

AbstractCarbon dots (CDs) are an interesting nanomaterial due to their tunable photoluminescence and other functional properties. Herein, by introducing amine‐functionalized CDs nanoparticles onto macromolecular chains of maleic anhydride grafted styrene‐ethylene‐butylene‐styrene (SEBS‐g‐MA) via a possible ring‐opening reaction of anhydride with amine, a mechanically robust and ultrastretchable thermoplastic elastomeric materials with fluorescence and dielectric functionality was developed. The amine‐functionalized CDs nanoparticles were synthesized from pyrene precursor by hydrothermal treatment. The transmission electron micrograph, Raman, Fourier transform infrared, and x‐ray photoelectron spectra confirmed the formation of highly crystalline graphitized structure of the CDs nanoparticles. Fluorescence and UV–Vis spectroscopy were used to evaluate the optical properties of the developed materials. The developed CDs/SEBS‐g‐MA nanocomposites exhibited strong intense green fluorescence compared with the pure SEBS‐g‐MA film. The thermal stability of the developed nanocomposites was improved by an increase of the Tmax by about 18°C. In addition, the developed composite showed high stretchability (strain at break ~1000%), good mechanical strength, and dielectric properties (room temperature dielectric constant ~5.2). The enhanced dielectric property of the developed composites may be due to the space charge accumulation and induced interfacial polarization at the filler–matrix interface.

Development of Polylactic Acid Films with Alkali- and Acetylation-Treated Flax and Hemp Fillers via Solution Casting Technique.

This study aims to enhance value addition to agricultural byproducts to produce composites by the solution casting technique. It is well known that PLA is moisture-sensitive and deforms at high temperatures, which limits its use in some applications. When blending with plant-based fibers, the weak point is the poor filler-matrix interface. For this reason, surface modification was carried out on hemp and flax fibers via acetylation and alkaline treatments. The fibers were milled to obtain two particle sizes of <75 μm and 149-210 μm and were blended with poly (lactic) acid at different loadings (0, 2.5%, 5%, 10%, 20%, and 30%) to form a composite film The films were characterized for their spectroscopy, physical, and mechanical properties. All the film specimens showed C-O/O-H groups and the π-π interaction in untreated flax fillers showed lignin phenolic rings in the films. It was noticed that the maximum degradation temperature occurred at 362.5 °C. The highest WVPs for untreated, alkali-treated, and acetylation-treated composites were 20 × 10-7 g·m/m2 Pa·s (PLA/hemp30), 7.0 × 10-7 g·m/m2 Pa·s (PLA/hemp30), and 22 × 10-7 g·m/m2 Pa·s (PLA/hemp30), respectively. Increasing the filler content caused an increase in the color difference of the composite film compared with that of the neat PLA. Alkali-treated PLA/flax composites showed significant improvement in their tensile strength, elongation at break, and Young's modulus at a 2.5 or 5% filler loading. An increase in the filler loadings caused a significant increase in the moisture absorbed, whereas the water contact angle decreased with an increasing filler concentration. Flax- and hemp-induced PLA-based composite films with 5 wt.% loadings showed a more stable compromise in all the examined properties and are expected to provide unique industrial applications with satisfactory performance.

Construction of silver-epoxy adhesive with suppressed silver migration rate based on thiol-silver interaction

The silver migration limits the application of silver based conductive adhesives in wet environment. The existing methods for inhibiting silver migration in epoxy conductive silver adhesives involve one or more issues such as cost, complexity, and inhibition of conductivity. Moreover, there is currently a lack of strategies that can suppress the silver migration effect while ensuring good dispersion of silver fillers in the matrix and constructing a good filler matrix interface. Herein, a facile method was reported suppressing the silver migration in silver-epoxy conductive adhesive. Tetrafunctional thiopentaerythritol tetramercaptoacetate (PERTMA) was introduced into 1,4-cyclohexanedimethanol diglycidyl ether (CHDMGE) epoxy resin as the curing agent. This method utilized the strong interaction between silver and thiols, including coordination and covalent bonding, to achieve good compatibility between filler and matrix. By tightly combining silver with the resin system, the content of free silver atoms was reduced, capturing and inhibiting the hydrolysis of silver atoms and their migration with current, and the conductivity of the conductive silver adhesive was not greatly degraded due to the silver-thiol interaction. At the same time, the introducing of PERTMA was able to reduce the surface hydrophilicity of epoxy resin, which also helped suppressing the silver migration effect under humid circumstances. The interaction between silver and thiol was characterized, and the influence of silver content on the curing behavior, material mechanical performance, conductivity, resistivity on silver migration and flexibility was explored. The CHDMGE/PERTMA/Ag conductive adhesive based on strong thiol-silver interaction had excellent resistance to silver migration, which occurred after 3500s, which was 10.67 times longer than the control group. In addition, the silver filler enhanced the tensile strength of the matrix resin by this thiol-silver interaction. This study will provide new ideas for the design and development of silver migration resistant conductive adhesives based on matrix filler interaction.

Pyroelectricity in poled all-organic polar polynorbornene/polydimethylsiloxane-based stretchable electrets.

Pyroelectricity in a recently developed all-organic composite electret with a polar polynorbornene-based filler and polydimethylsiloxane (PDMS) matrix has been studied with the help of thermal and dielectric techniques. Measurement of the pyroelectric p coefficient using a quasi-static periodic temperature variation at RT shows a non-linear dependence with the applied poling field, which is uncharacteristic of amorphous materials. Dielectric relaxation spectroscopy (DRS) and the thermally stimulated depolarization current (TSDC) technique reveal that this behaviour can be attributed to Maxwell-Wagner interface (MWI) polarization that occurs at the filler-matrix interface. These charges released during the onset of dipolar α and β relaxations of the filler particles contribute majorly to the observed pyroelectricity at RT. The saturation of both MWI TSDC shoulders and spontaneous polarization at higher electric fields correlates with the p coefficient value reaching a plateau at these applied fields. A maximum p coefficient of 0.54 μC m-2 K-1 is calculated for a poling field of 30 V μm-1.

Mesoscopic Modeling and Experimental Validation of Thermal and Mechanical Properties of Polypropylene Nanocomposites Reinforced By Graphene-Based Fillers.

The development of nanocomposites relies on structure-property relations, which necessitate multiscale modeling approaches. This study presents a modeling framework that exploits mesoscopic models to predict the thermal and mechanical properties of nanocomposites starting from their molecular structure. In detail, mesoscopic models of polypropylene (PP)- and graphene-based nanofillers (graphene (Gr), graphene oxide (GO), and reduced graphene oxide (rGO)) are considered. The newly developed mesoscopic model for the PP/Gr nanocomposite provides mechanistic information on the thermal and mechanical properties at the filler-matrix interface, which can then be exploited to enhance the prediction accuracy of traditional continuum simulations by calibrating the thermal and mechanical properties of the filler-matrix interface. Once validated through a dedicated experimental campaign, this multiscale model demonstrates that with the modest addition of nanofillers (up to 2 wt %), the Young's modulus and thermal conductivity show up to 35 and 25% enhancement, respectively, whereas the Poisson's ratio slightly decreases. Among the different combinations tested, the PP/Gr nanocomposite shows the best mechanical properties, whereas PP/rGO demonstrates the best thermal conductivity. This validated mesoscopic model can contribute to the development of smart materials with enhanced mechanical and thermal properties based on polypropylene, especially for mechanical, energy storage, and sensing applications.

Reducing residual stress in photopolymerized composites by grafting high-mobility polymer chains onto the filler-matrix interface

3D/4D printing of thermosets, composites and hydrogels, lithographic procedures and dental resins are important examples of applications that rely on light-driven polymerization supported on substrates. Adhesion between the polymer and substrate during photopolymerization (and even between printed layers) can restrict the usual polymerization shrinkage, leading to the generation of residual stresses. These residual stresses can result in poor-quality products due to the presence of cracks and occurrence of warpage. In this work, silica nanoparticles were incorporated into photopolymerizable dimethacrylate based networks. These nanoparticles had their surface modified by grafting polymer chains with high mobility at usual room temperatures (low glass transition temperature polymer) and with high affinity towards the polymer matrix in order to test the hypothesis that these high-mobility chains could be helpful in dissipating stress and energy generated during photopolymerization in conditions in which the polymerization shrinkage is restricted. The nanoparticles and composites were analyzed via: electron microscopy (SEM), thermal analysis and mechanical bending tests. The evolution of the monomer-to-polymer conversion during photopolymerization was monitored using real-time infrared (FTIR) spectroscopy. To determine the residual stress generated by the polymerization at restricted contraction conditions, a universal mechanical testing machine was adapted and used. The results showed that silica nanoparticles with grafted high-mobility polymer chains that were able to interpenetrate and interact with the dimethacrylate based networks led to the production of composites having higher mechanical properties and lower polymerization stresses than composites containing only silanized nanoparticles and nanoparticles having immiscible polymer grafts towards the dimethacrylate based network. Results indicate that the modifications of the interface of composites developed in this work can be useful in the formulation of materials with improved mechanical properties and stability regarding polymerization shrinkage and residual stress that can lead to higher-quality products obtained in processes that employ light-driven polymerization supported on substrates or that occur on sequential polymerized layers, such as 3D/4D printing, lithography and in dental applications.

AIN particles/BN whiskers co-doped epoxy composites modified with polydopamine with high thermal conductivity

In this work, aluminum nitride particles (AlN) and boron nitride whiskers (BNw) were surface-functionalized by polydopamine, and then novel composites were prepared by co-doping. By observing with transmission electron microscopy, we clearly saw that the surfaces of AlN and BNw were successfully coated with a thin polydopamine coating. This is beneficial to enhance the filler-matrix interface interaction and the filler dispersion. The co-doping of the two thermally conductive fillers increases the chance of contact between the filler and the filler, and reduces the interfacial thermal resistance, thereby forming a thermal conduction network more efficiently. The results show that at a frequency of 1 MHz at room temperature, the dielectric constant of 30 wt%AlN@PDA/6 wt%BNw@PDA/EP composites is 4.74 and the dielectric loss tangent is 0.0171. Its thermal conductivity is 0.40 W/(m·K), the glass transition temperature reaches 250.2°C, the impact strength reaches 6.89 kJ m−2, and the breakdown field is 10.93 kV/mm.

Modified poly(phenylene oxide)/(CaSr)TiO3 composites with ultrahigh permittivity and low loss for microwave substrates

Polymer/ceramic composites used as microwave dielectric combine the excellent dielectric properties of ceramic with the toughness of polymer. The properties of composites are not only determined by the properties of components but also influenced by the polymer-ceramic interface. In this work, we conducted experiments and simulations on the dielectric properties and thermal conductivity of modified poly(phenylene oxide)/(CaSr)TiO3 (mPPO/CST) composites. A comparison of composites filled with different sizes (2.5, 11, and 20 µm) of CST fillers demonstrates that smaller particle (more filler-matrix interface) is beneficial to mechanical properties but detrimental to dielectric properties and heat transfer. The finite element simulation results are in good agreement with the experimental values, which is of significance for guiding future experiments. The composite filled with 80 wt. % CST20 has a high relative density of 97%, an ultrahigh εr of ∼20, and a low tan δ of 0.0019 at 10 GHz. Meanwhile, the mPPO/CST composites are eco-friendly and suitable for mass production and are promising candidates for automotive and aerospace applications.

Novel Latent Heat Storage Systems Based on Liquid Metal Matrices with Suspended Phase Change Material Microparticles.

Phase change materials (PCMs) are considered useful tools for efficient thermal management and thermal energy utilization in various application fields. In this study, a colloidal PCM-in-liquid metal (LM) system is demonstrated as a novel platform composite with excellent latent heat storage capability, high thermal and electrical conductivities, and unique viscoelastic properties. In the proposed formulation, eutectic Ga-In is utilized as a high-thermal-conductivity and high-fluidity liquid matrix in which paraffinic PCM microparticles with various solid-liquid phase transition temperatures are suspended as fillers. Good compatibility between the fillers and matrix is achieved by the nanosized inorganic oxides (titania) adsorbed at the filler-matrix interface; thus, the composite is produced via simple vortex mixing without tedious pre- or post-processing. The composite shows unique trade-off effects among various properties, i.e., elastic modulus, yield stress, density, thermal conductivity, and melting or crystallization enthalpy, which can be easily controlled by varying the contents of the suspended fillers. A Joule heating device incorporating the composite exhibits improved electrothermal performance owing to the synergy between the high electrical conductivity and latent heat storage capability of the composite. The proposed platform may be exploited for the rational design and facile manufacture of high-performance form-factor-free latent heat storage systems for various potential applications such as battery thermal management and flexible heaters.

Effect of neutral polymeric bonding agent on tensile mechanical properties and damage evolution of NEPE propellant

Introducing Neutral Polymeric bonding agents (NPBA) into the Nitrate Ester Plasticized Polyether (NEPE) propellant could improve the adhesion between filler/matrix interface, thereby contributing to the development of new generations of the NEPE propellant with better mechanical properties. Therefore, understanding the effects of NPBA on the deformation and damage evolution of the NEPE propellant is fundamental to material design and applications. This paper studies the uniaxial tensile and stress relaxation responses of the NEPE propellant with different amounts of NPBA. The damage evolution in terms of interface debonding is further investigated using a cohesive-zone model (CZM). Experimental results show that the initial modulus and strength of the NEPE propellant increase with the increasing amount of NPBA while the elongation decreases. Meanwhile, the relaxation rate slows down and a higher long-term equilibrium modulus is reached. Experimental and numerical analyses indicate that interface debonding and crack propagation along filler–matrix interface are the dominant damage mechanism for the samples with a low amount of NPBA, while damage localization and crack advancement through the matrix are predominant for the ones with a high amount of NPBA. Finally, crosslinking density tests and simulation results also show that the effect of the bonding agent is interfacial rather than due to the overall crosslinking density change of the binder.

Structural effects of TiO2 nanoparticles in photocurable ladder-like polysilsesquioxane nanocomposites

AbstractLadder-like polysilsesquioxanes (LPSQs) are characterized by a double-stranded siloxane backbone, whose chemical and structural properties depend on both the synthesis parameters and the nature of the organic side-chains. In the case of ladder-like (methacryloxypropyl) polysilsesquioxanes (LPMASQ), polymer matrices can be produced by exploiting the presence of photocurable methacrylate groups. Consequently, they can be used to prepare functional nanocomposites (NCs), either by blending with organic polymers such as polybutadiene or exploiting the inorganic fillers’ dispersion. Since the properties of LPMASQ-based NCs are strongly related to their structure, the structural changes of polymerized LPMASQ were investigated upon addition of low loadings of TiO2 nanoparticles (up to 3 wt%) by solid state nuclear magnetic resonance and X-ray diffraction. The filler addition leads to the reduction of the polymerization capacity of the LPMASQ organic side-chains. Moreover, a different organization of ladder chains has been highlighted, ascribable to the increase in fully condensed linear ladder units at the expenses of folded chains and defective structures. The methodological approach here adopted can be extended to other composite systems and may help to describe the properties at the filler-matrix interface, offering valuable hints for a better design of these materials. Graphical Abstract

New Reinforcing Approach for Biobased UV-Curing Resins: Hybrid Lignocellulose Fillers with Improved Synergy and Wood Structure Mimics

Lignocellulosic fillers have been widely investigated for various polymer resin applications since they have great potential for using wood biomass and recycled plastics. However, besides cellulose nanocrystals (CNC) and nanofibrils (CNF), not much of the other lignocellulose has been used for UV-curing resins. Even more so, none has been used in hybrid lignocellulose combination compositions. In the present work, the effects of hybrid lignocellulose fillers such as lignin (LN)/CNC/CNF/hemicellulose (HC) with ratio-varying compositions on UV-curing biobased resins have been investigated for wood-mimic material coating applications. The hybrid filler effects on the macromolecular chain network, surface morphology, thermomechanical properties, and thermostability were carefully studied. A combination of scanning electron microscopy, DMA Cole–Cole plot, contact angle, etc., allowed getting a sense of hybrid filler distribution and interaction within the polymer matrix. It was identified that an increase in the HC content of up to 38% contributes to more even particle distribution and achieves a maximum double bond conversion rate of about 80%. HC also contributes to porous surface structure, while CNC smooths surface morphology, and, in turn, CNF increases defects. Thermomechanical testing revealed the unique benefit of hybrid reinforcement, showing higher results than single-filler compositions despite the general decrease after incorporation of 5 wt % LN. The storage modulus showed a fourfold increase for 5 wt % LN composition. The observed enormous property enhancement has been attributed to the benefits of hybrid fillers, which mitigate characteristic radical scavenging properties of LN and strongly reduce general filler aggregation, allowing more even filler dispersion while also improving filler–matrix interface synergy. Seventeen different compositions clearly, in comparison to single fillers, show the benefit of hybrid lignocellulosic reinforcement and testify to the ability to precisely tune up material performance and achieve wood structure-mimicking coating materials.

Interfacial interactions in rubber-based composites

ABSTRACT The interfacial region of nitrile butadiene rubber matrix composites filled with magnetite and carbon black particles was studied. Raman spectroscopy was used as an alternative to study the filler-matrix interface behaviour. It was found that the amount of magnetite and its size (nano or micro) induce variations in the stress transfer between the fillers and the matrix. Stress propagation altered the graphitic domains of the carbon black that fill the matrix and induced shifts in position, changes in width, and intensity of the D and G bands. The XPS high-resolution spectra corresponding to the Fe2p, C1s, and S2p regions of the composites confirmed chemical interactions at the interface of the nanosized magnetite-filled composites. Fe-C and Fe-S bonds were identified in those regions between the fillers and the NBR matrix. No chemical bonds were found at the interface of the composites filled with microsized magnetite.

Surface grafting of Poly (ether ether ketone) on silica particles as novel filler for dental composites: Physico-chemical characterization

This study aimed to describe the fabrication of a novel dental composite by surface modification of silica fillers with polyether ether ketone (PEEK) and assess surface coverage of fillers and the effect of different concentration of modified fillers on degree of conversion, flexural strength, polymerization shrinkage, water sorption and solubility, viscosity and thermal expansion of the formulated composites. In this experimental study, aminosilane derivative of PEEK was synthesized and grafted to the silica filler surface, then evaluated using a fourier transform infrared spectroscopy (FTIR), and thermo-gravimetric analysis (TGA). Silica-PEEK fillers were then mixed with Bis-GMA/TEGDMA resin base in 10, 30, and 50 wt%. The most relevant physico-chemical properties were evaluated and compared with a control composite resin group containing conventional 3-(methacryloxypropyl) trimethoxysilane (γ-MPS) modified fillers. Data were analyzed by ANOVA and Tukey’s HSD test. (α = 5%). The experimental composite with 30% modified fillers showed highest flexural strength and degree of conversion (DC) ( p &lt; 0.05), and comparable polymerization shrinkage and viscosity to the control composites ( p &gt; 0.05). After thermocycling, the composite with 30% modified fillers showed the lowest solubility and water sorption ( p &lt; 0.05). Surface modification of silica fillers with PEEK polymer significantly increases the resistance of the filler–matrix interface to hydrolysis. The above mentioned intervention can improve mechanical properties of the composite and may be considered as a promising protocol to reduce the failure of dental composites.

A Comparative Study on the Microscale and Macroscale Mechanical Properties of Dental Resin Composites.

Dental resin composites are universal restorative materials, and various kinds of fillers are used to reinforce their mechanical properties. However, a combined study on the microscale and macroscale mechanical properties of dental resin composites is missing, and the reinforcing mechanism of the composites is still not fully clarified. In this work, the effects of the nano-silica particle on the mechanical properties of dental resin composites were studied by combined dynamic nanoindentation tests and macroscale tensile tests. The reinforcing mechanism of the composites was explored by combining near-infrared spectroscopy, scanning electron microscope, and atomic force microscope characterizations. It was found that the tensile modulus increased from 2.47 GPa to 3.17 GPa, and the ultimate tensile strength increased from 36.22 MPa to 51.75 MPa, with the particle contents increasing from 0% to 10%. From the nanoindentation tests, the storage modulus and hardness of the composites increased by 36.27% and 40.90%, respectively. The storage modulus and hardness were also found to increase by 44.11% and 46.46% when the testing frequency increased from 1 Hz to 210 Hz. Moreover, based on a modulus mapping technique, we found a boundary layer in which the modulus gradually decreased from the edge of the nanoparticle to the resin matrix. Finite element modeling was adopted to illustrate the role of this gradient boundary layer in alleviating the shear stress concentration on the filler-matrix interface. The present study validates mechanical reinforcement and provides a potential new insight for understanding the reinforcing mechanism of dental resin composites.

Cytotoxic, Elastic-Plastic and Viscoelastic Behavior of Aged, Modern Resin-Based Dental Composites

The development of resin-based composites (RBCs) is a delicate balance of antagonistic properties with direct clinical implications. The clear trend toward reducing filler size in modern RBCs solves esthetic deficiencies but reduces mechanical properties due to lower filler content and increases susceptibility to degradation due to larger filler-matrix interface. We evaluated a range of nano- and nano-hybrid RBCs, along with materials attempting to address shrinkage stress issues by implementing an Ormocer matrix or pre-polymerized fillers, and materials aiming to provide caries-protective benefit by incorporating bioactive fillers. The cytotoxic response of human gingival fibroblast (HGF) cells after exposure to the RBC eluates, which were collected for up to six months, was analyzed using a WST-1 assay. The microstructural features were characterized using a scanning electron microscopy and were related to the macroscopic and microscopic mechanical behaviors. The elastic-plastic and viscoelastic material behaviors were evaluated at the macroscopic and microscopic levels. The data were supplemented with fractography, Weibull analysis, and aging behavioral analysis. The results indicate that all RBCs are non-cytotoxic at adequate exposure. The amount of inorganic filler affects the elastic modulus, while only to a limited extent the flexural strength, and is well below the theoretical estimates. The nanoparticles and the agglomeration of nanoparticles in the RBCs help generate good mechanical properties and excellent reliability, but they are more prone to deterioration with aging. The pre-polymerized fillers lower the initial mechanical properties but are less sensitive to aging. Only the Ormocer retains its damping ability after aging. The strength and modulus of elasticity on the one hand and the damping capacity on the other are mutually exclusive and indicate the direction in which the RBCs should be further developed.