Filler Particles Research Articles

Hardening mechanism of waste polyolefin mixtures in the presence of modified bentonite clay

The aim of the work is to obtain and study polymer composite materials based on mixtures of secondary polyolefins and modified polydisperse bentonite clay. The formation features of the structure of mixtures of waste polyolefins in the presence of this-type filler are studied. The data on the changes in the mechanical strength of mixed composites, as well as the results of physico-chemical studies are presented. Mixtures based on waste polymers in the presence of highly dispersed particles of modified polydisperse bentonite are characterized by the improvement of the strength of composites due to increased interfacial interaction in them and by the formation of structure uniformity of the material. This to some extent compensates for the loss of cohesive strength of secondary polymers due to thermal degradation processes. The following conclusions are made: at the phase boundaries, the molecular mobility of polymer chains decreases, which leads to changing the crystallization conditions and to appearing a nonequilibrium stress state; introducing bentonite increases crystalline due to the initiation of physico-chemical interaction; the strength grows due to increased interfacial interaction and structure uniformity; the formation mechanism of a complex of properties of composites consists of two-level adsorption – a modifier on filler particles and active polymer groups on the modified filler surface.

High-performance flexible piezocomposites based on an enhanced interfacial polarization effect via BCZT@Ag heterostructure design

Flexible piezoelectric energy harvesters (FPEHs) can convert mechanical energy into electric energy in a manner that powers electronic equipment and systems. Structural design of piezoelectric fillers in organic–inorganic piezocomposites is means of enhancing the power generation performance of FPEHs. Herein, a design strategy of piezoelectric fillers is proposed: decorating Ag nanoparticles onto Ba0.85Ca0.15Ti0.9Zr0.1O3 (BCZT) particles, forming a BCZT@Ag heterostructure, thus obtaining BCZT@Ag/poly(vinylidene fluoride) (PVDF) piezocomposites. An extremely high piezoelectric constant d33 of 34 pC/N is achieved in the BCZT@Ag/PVDF sample, which is 2.6 times higher than that of the BCZT/PVDF sample. The greatly improved piezoelectric properties are attributable to enhanced interfacial polarization via BCZT@Ag heterostructure design. More poling electric voltage is applied to the piezoelectric filler particles, resulting in substantially improved poling efficiency. This composite approach of introducing metal particles is a generic design method and can be extended to other organic–inorganic piezocomposite systems.

Effect of Particle Size and Filler Content on Mechanical Properties of Avocado Wood Flour-Low Density Polyethylene Composite

Effect of Particle Size and Filler Content on Mechanical Properties of Avocado Wood Flour-Low Density Polyethylene Composite

3D Printing Technologies for Fabrication of Magnetic Materials Based on Metal-Polymer Composites: A Review.

Additive manufacturing is a very rapidly developing industrial field. It opens many possibilities for the fast fabrication of complex-shaped products and devices, including functional materials and smart structures. This paper presents an overview of polymer 3D printing technologies currently used to produce magnetic materials and devices based on them. Technologies such as filament-fused modeling (FDM), direct ink writing (DIW), stereolithography (SLA), and binder jetting (BJ) are discussed. Their technological features, such as the optimal concentration of the filler, the shape and size of the filler particles, printing modes, etc., are considered to obtain bulk products with a high degree of detail and with a high level of magnetic properties. The polymer 3D technologies are compared with conventional technologies for manufacturing polymer-bonded magnets and with metal 3D technologies. This paper shows prospective areas of application of 3D polymer technologies for fabricating the magnetic elements of complex shapes, such as shim elements with an optimized shape and topology; advanced transformer cores; sensors; and, in particular, the fabrication of soft robots with a fast response to magnetic stimuli and composites based on smart fillers.

A comparative study on the depth of cure, hardness and microleakage applied to primary teeth of different types of bulk-fill resins

Objective: To compare the depth of cure, surface hardness and microleakage applied to primary teeth of three types of bulk-fill resins, so as to provide reference for clinical application. Methods: Composite resin FiltekTM Z350 XT (group A) and giomer Beautifil Ⅱ (group B) were used as controls, high-viscosity bulk-fill resin FiltekTM Bulk Fill (group C), sonic-activated bulk-fill resin SonicFill 2 (group D) and flowable bulk-fill resin SDR® flow+(group E) were studied. The microstructure of each group was observed by scanning electron microscope (SEM). Specimens of each group were prepared (6 pieces per group), and the Vickers microhardness of the surface layer and different depths of each group were measured, and then the depths of cure were calculated. Twenty-five primary molars dentin were filled by resins of each group (5 teeth per group), sliced, then aged, slices of each group were developed by silver ion staining. SEM was used to observed the distribution of silver ions. Microleakage of each group were analyzed by Jonckheere-Terpstra rank sum test. Results: SEM showed that the filler particles in groups A and C were spherical and evenly distributed. The shape of the fillers in groups B, D and E were polygonal and unevenly distributed. The surface hardness of groups A, B, C, D and E were (84.97±6.30), (65.04±5.95), (57.80±1.18), (60.77±2.34), (33.32±1.83) MPa respectively. Group A had the highest hardness, while group E was the lowest, and the differences between the two groups and other groups was statistically significant (P<0.05). There were no statistically significant differences among groups B, C, and D (P>0.05). The curing depths of groups A, B, C, D and E were 2.6, 3.4, 5.8, 3.8 and 7.8 mm respectively. The largest microleakage was found in group E [2% (1/50) for grade 0, 22% (11/50) for grade 1, 30% (15/50) for grade 2, 24% (12/50) for grade 3, and 22% (11/50)for grade 4], which was statistically different from other groups (P<0.05). No statistically significant differences were found among other 3 groups (P>0.05). Conclusions: Both high-viscosity and sonic-activated bulk-fill resins have the greater depth of cure, the same hardness and microleakage as giomer, which might be an option for restoration in primary teeth.

Electrically conductive polymer composites based on elastic fiber

The possibility of obtaining electrically conductive composites by applying carbon suspensions to fibrous materials by aerosol spraying and screen printing, on printing equipment, which ensures high productivity, is shown. A manufacturing technology has been developed and the electromechanical properties of layered fibrous composites based on knitwear and graphite dispersion designed for the manufacture of strain and stress sensors used in "wearable electronics", robotics and medicine have been investigated. In an experimental study, it is shown that the conductive path, that is, the length of the chains of contacting filler particles decreases with tensile deformation due to the growth of microcracks in the material. The electrical resistance of growing microcracks has much higher values than the resistance of deformable piezoresistive material. Cracks can open and close in various ways during bending, torsion, stretching and compression deformation. The electrical conductivity of fibers and filaments significantly depends on the localization of electrically conductive particles on their surface or in volume. The location of the conductive chains on the surface or in the volume of the filaments determines the dependence of the electrical properties of composites on the state of the environment (composition, temperature, humidity). Preliminary studies of filaments with electrically conductive components of various chemical nature (metals, metal salts, carbon in various allotropic forms) show that changes in temperature and humidity significantly affect the resistivity of the conductive fiber. The paper presents data on the effect of temperature and humidity on the electromechanical properties of elastic fiber composites with graphite. When stretched to 15%, the calibration coefficient GF is reduced by 2 times at 100% humidity. The different influence of air temperature in the range of 100C-700C on the deformation and strain sensitivity during cyclic deformation up to 15% and 30% has been established. The presence of two ranges of deformation sensitivity is due to the difference in the mechanisms of elongation of knitwear due to straightening and stretching of threads. Different deformation and strain sensitivity of composites in the ranges of small and significant strains, at different temperatures and humidity of the air, has been established. The strain sensitivity reaches 130, and the strain sensitivity is 12 MPa -1, which is an order of magnitude higher than the stress sensitivity of known polymer composites with various electrically conductive fillers.

Improvement of thermo‐mechanical and dielectric properties of poly(lactic acid) and thermoplastic polyurethane blend composites using a graphene and BaTiO3 filler

AbstractThis study focuses on the development of composite materials using thermoplastic polyurethane (TPU) and poly(lactic acid) (PLA) with fillers such as barium titanate (BaTiO3) and graphene. Suitable surface treatment of filler particles is applied to activate the fillers to enhance the compatibility between the fillers and polymer matrix. Specifically, the BaTiO3 particles are hydroxylated and treated with glycidyl methacrylate (GMA), which acts as a compatibilizer between the two matrix polymers. On the other hand, the graphene particles are hydroxylated and treated with isophorone diisocyanate (IPDI), which reacts with the TPU soft segment chains during composite fabrication. The composite samples are fabricated via melt‐blending at 190°C, followed by mini molding at the same operating temperature for subsequent analysis. The results demonstrate a three‐fold improvement in the dielectric constant of 40 wt.% BaTiO3 and graphene–TPU–PLA blends composites relative to that of the neat TPU, along with an improved tensile strength. The tensile strength improvement is attributed to the support of the TPU matrix against the low ductility of the PLA. The thermal conductivity was doubled as compared with the neat TPU–PLA matrix for the 40 wt.% BaTiO3 and graphene–TPU–PLA blends.Highlights Composites of TPU–PLA–graphene and BaTiO3 filler particles were fabricated. The melt blending technique was employed to fabricate the composite. The dielectric constant was analyzed at both constant and variable frequencies. Thermal conductivity was doubled (40 [graphene + BaTiO3])

Functionalized Thiophosphate and Oxidic Filler Particles for Hybrid Solid Electrolytes

AbstractTo achieve the commercialization of solid‐state‐batteries (SSBs), solid electrolyte properties need to be further improved. The hybrid solid electrolyte (HSE) approach is expected to combine the favorable properties of different solid electrolyte classes and is therefore systematically investigated. Mixing low amounts of thiophosphate or oxide filler particles (FP) into a polyethylene oxide (PEO) polyethylene glycol (PEG) and lithium salt bis(trifluoromethane)sulfonimide (LiTFSI) matrix cannot improve the electrochemical properties. Silanization of the thiophosphate FPs significantly increases the ionic conductivity to 0.1 mS cm−1 at room temperature compared to 0.017 mS cm−1 for a pure PEO solid electrolyte. Moreover, a correlation between the intrinsic conductivity of the FPs and the resulting conductivity of the HSE is observed. Also, the functionalization is successfully transferred to oxide FPs. In addition to an equally significant increase in ionic conductivity, a strong influence of the crystallite size of the FPs on the resulting ionic conductivity of the HSE was found. The discovered effect of FP surface structure on overall HSE conductivity indicates a participation of the FP surface in ion transport and emphasizes the need for tailored filler design in HSE applications.

Comparative analysis of thermo-physical and mechanical properties of PALF/CF/epoxy resin with and without nano TiO2 filler

The performance of an engineering material depends on its potentiality and characterization under different mechanical and thermal test environments. The present research study has revealed the performance of a new class of hybrid composites, focused specially on the general trends observed in their impact of fabrication and its properties. To investigate how the mechanical and thermal qualities of the epoxy matrix may be improved, pineapple leaf fibre and carbon fibre were particularly chosen. By embedding the selected filler into the Pineapple leaf Fiber/Carbon Fiber(PALF/CF) reinforced epoxy resin, coordination effects, impact of embedding were achieved in the form of modified mechanical and thermal properties. The present research work is focused to perform the thermal and mechanical properties of pineapple leaf fiber/carbon fiber reinforced epoxy resin(ER) composites with and without particulate nano TiO2 fillers. The comparison of hybrid fibre (carbon and pineapple leaf fibre) reinforced epoxy composites with and without particulate nano TiO2 fillers was done. The results of the mechanical tests demonstrated that, in comparison to all other composites, the inclusion of nano fillers improved the tensile, flexural, and impact strengths. Nano particle reinforced with hybrid composite has a score of 23.4, whereas clean epoxy only gets a score of 4.5. It follows from this example that the presence of nanoparticles raises the residual values.

Conductive and self-cleaning composite membranes from corn husk nanofiber embedded with inorganic fillers (TiO2, CaO, and eggshell) by sol–gel and casting processes for smart membrane applications

Abstract The utilization of corn husk as a renewable bio-cellulose material for producing bio-composite membranes through wet chemical and sol–gel process offers numerous advantages. It is an abundant, inexpensive, nontoxic, and readily available agricultural waste product. To enhance the properties of bio-composite membranes, various particulate ionic fillers such as titanium dioxide, calcium oxide, and eggshell (as a source of calcium carbonate) are incorporated in different weight percentages (0, 1, and 5%). These fillers act as additives to the corn husk nanofiber mixed with polyvinyl alcohol during the formation of the biomembrane. The resulting biocomposite membranes exhibit several desirable characteristics. They are lightweight, easy to shape, biodegradable, nontoxic, and possess excellent physical, mechanical, thermal, and electrical properties. Moreover, the addition of 5 wt% of eggshell powder leads to an increase in the dielectric constant and electrical conductivity, reaching approximately 3.300 ± 0.508 and 1.986 × 103 (Ω·m)−1, respectively. These measurements were taken at a frequency of 500 Hz and a temperature of 27°C. Furthermore, these membranes demonstrate self-cleaning abilities due to a contact angle greater than 90°. The electrical properties of the biocomposite membrane improve with a higher percentage of inorganic filler, making them suitable for applications in smart membranes, as well as mechanical, electrical, and thermal systems.

The effect of extrusion and injection molding on physical, chemical, and biological properties of PLLA/HAp whiskers composites

This paper deals with physical, chemical and biological properties of polymer-ceramic composites based on poly(l-lactide) (PLLA) with the addition of 10, 20 or 30 % (by weight) of hydroxyapatite (HAp) whiskers, produced by a combination of twin-screw extrusion and injection molding techniques. The materials obtained were tested for morphology (scanning electron microscopy), chemical composition (energy dispersive x-ray spectroscopy, infrared spectroscopy), processing properties (melt flow rates and density), thermal properties (differential scanning calorimetry, thermogravimetry), strength (static tensile test, impact strength) and surface properties (optical profilometry, contact angle measurements). The biological evaluation was performed by in vitro assessment of the manufactured materials’ cytotoxicity, level of colonization by osteo- and fibroblasts and level of adhesion displayed by a microbial pathogen, referred to as the Staphylococcus aureus. The results indicate an influence of the applied processing path on the properties of the filler particles − the apatite whiskers were significantly shortened. On the other hand, we have demonstrated the possibility of obtaining PLLA/HAp composites with good strength parameters, precise geometric shape and slightly improved surface properties. The results of biological evaluation revealed that all of the materials obtained displayed low cytotoxicity and a high level of colonization, irrespective of the content of hydroxyapatite. The only exception was the composite containing 10 % HAp, for which we observed weaker fibroblast adhesion compared to other materials. In turn, the level of colonization by S.aureus grew with the increase in HAp content in polymers. Results of biological evaluation indicate that although obtained polymers display favorable properties in terms of eukaryotic cell adhesion/colonization, they may also provide advantageous surface conditions for bacterial development. Therefore, inclusion of antimicrobial to the materials obtained may be necessary and should be further investigated. Nevertheless, the results obtained certainly provide useful information from the point of view of designing and manufacturing of biocomposites for bone tissue engineering applications.

The effect of quaternary ammonium polyethylenimine nanoparticles on bacterial adherence, cytotoxicity, and physical and mechanical properties of experimental dental composites

A significant problem related to the functioning of resin-based composites for dental fillings is secondary or recurrent caries, which is the reason for the need for repeated treatment. The cross-linked quaternary ammonium polyethylenimine nanoparticles (QA-PEI-NPs) have been shown to be a promising antibacterial agent against different bacteria, including cariogenic ones. However, little is known about the properties of dental dimethacrylate polymer-based composites enriched with QA-PEI-NPs. This research was carried out on experimental composites based on bis-GMA/UDMA/TEGDMA matrix enriched with 0.5, 1, 1.5, 2 and 3 (wt%) QA-PEI-NPs and reinforced with two glass fillers. The cured composites were tested for their adherence of Streptococcus Mutans bacteria, cell viability (MTT assay) with 48 h and 10-days extracts , degree of conversion (DC), water sorption (WSO), and solubility (WSL), water contact angle (CA), flexural modulus (E), flexural strength (FS), compressive strength (CS), and Vickers microhardness (HV). The investigated materials have shown a complete reduction in bacteria adherence and satisfactory biocompatibility. The QA-PEI-NPs additive has no effect on the DC, VH, and E values. QA-PEI-NPs increased the CA (a favorable change), the WSO and WSL (unfavorable changes) and decreased flexural strength, and compressive strength (unfavorable changes). The changes mentioned were insignificant and acceptable for most composites, excluding the highest antibacterial filler content. Probably the reason for the deterioration of some properties was low compatibility between filler particles and the matrix; therefore, it is worth extending the research by surface modification of QA-PEI-NPs to achieve the optimum performance characteristics.

Effect of silicon carbide on kerf convergence and irregularity of the surface during abrasive water jet machining of fiber-metal hybrid composites

The traditional way to machine hybrid composites is hard because they tend to break, have a high retraction, have a high service temperature, and have an uneven surface irregularity. For high-strength fiber/metal composite constructions, alternative machining methods have drawn interest as a solution to these problems. Current research focuses on enhancing the Abrasive Water Jet Machining process by optimizing its variables using a composite material of epoxy reinforced with silicon carbide, stainless steel wire mesh, and Kevlar. The variables assessed are the Nozzle-to-substrate gap (S), the Abrasive discharge molding and different percentages of silicon carbide (SiC) filler (0%, 3%, and 6% by weight), three different types of hybrid laminates (H1, H2, and H3) were produced. The response surface method (RSM) was utilized in this learning, specifically on a central composite design, to calculate and optimize machining variables based on the Kerf convergence ratio (Kt) and Surface irregularity (Ra) as responses. According to the results, the traverse feed velocity, Abrasive discharge proportion, and Nozzle-to-substrate gap are the critical factors in determining Surface irregularity and Kerf convergence width (H1 laminate) for a fiber/metal laminate with 0%, 3% and 6% weight fraction. In the case of a 3% weight fraction H2 laminate, the traverse feed velocity was identified as the primary factor affecting the Kerf convergence ratio. In contrast, traverse feed velocity and Nozzle-to-substrate gap had the most significant influence on Surface irregularity. The findings also indicated that S, followed by Abrasive discharge proportion and traverse feed velocity, are the variables that have the most significant influence when cutting 6 wt% SiC filler particle fiber/metal laminate (H3 laminate). For Surface irregularity, the combination of traverse feed velocity and Nozzle-to-substrate gap had the most significant impact. To validate the optimization results, confirmatory tests was conducted, and the findings were very similar to the experimental values, indicating the accuracy and effectiveness of the optimization process. To better understand the manufacturing processes, a scanning electron microscope was used to examine the morphological features of the machined surfaces, such as delamination, fibre breakage, and fibre pull-out.

The effect of alkali treatment on the mechanical properties of date seed particulates waste polypropylene filled composites

Date seeds collected as waste were reduced to 63 µm particles and treated with NaOH (aq) at 1, 3, 5, 7 and 10 %. The extent of chemical modification was assessed using FTIR analysis. The waste polypropylene (wPP)/date seed particles (DSP) composites filled with untreated and treated particles at 20 % filler loadings were fabricated using compounding and compression moulding techniques by means of two rolls mill. Tensile, flexural, impact tests and hardness (HV) were conducted and evaluated. Subsequently, a morphological study of the fractured surface of the composites was achieved using SEM. The application of alkali treatment enhanced various properties of the composites at the optimal concentration of 10 % w/v. Specifically, the tensile strength, flexural strength, elongation at break, impact strength, and hardness were improved, resulting in values of 28.86 MPa, 140 MPa, 172.5 %, 0.92 J/m², and 23.8 Hv, respectively. While tensile and flexural moduli showed a decrease with increasing alkali concentration. The SEM of the fractured surface of the treated composite revealed a better dispersion of filler particles within the matrix with no cluster seen compared to the untreated.

Modifying dental composites to formulate novel methacrylate-based bone cements with improved polymerisation kinetics, and mechanical properties

ObjectivesThe aim was to develop bone composites with similar working times, faster polymerisation and higher final conversion in comparison to Cortoss™. Additionally, low shrinkage/heat generation and improved short and longer-term mechanical properties are desirable. MethodsFour urethane dimethacrylate based composites were prepared using tri-ethylene-glycol dimethacrylate (TEGDMA) or polypropylene dimethacrylate (PPGDMA) diluent and 0 or 20 wt% fibres in the glass filler particles. FTIR was used to determine reaction kinetics, final degrees of conversions, and polymerisation shrinkage/heat generation at 37 °C. Biaxial flexural strength, Young’s modulus and compressive strength were evaluated after 1 or 30 days in water. ResultsExperimental materials all had similar inhibition times to Cortoss™ (140 s) but subsequent maximum polymerisation rate was more than doubled. Average experimental composite final conversion (76%) was higher than that of Cortoss™ (58%) but with less heat generation and shrinkage. Replacement of TEGDMA by PPGDMA gave higher polymerisation rates and conversions while reducing shrinkage. Early and aged flexural strengths of Cortoss™ were 93 and 45 MPa respectively. Corresponding compressive strengths were 164 and 99 MPa. Early and lagged experimental composite flexural strengths were 164–186 and 240–274 MPa whilst compressive strengths were 240–274 MPa and 226–261 MPa. Young’s modulus for Cortoss™ was 3.3 and 2.2 GPa at 1 day and 1 month. Experimental material values were 3.4–4.8 and 3.0–4.1 GPa, respectively. PPGDMA and fibres marginally reduced strength but caused greater reduction in modulus. Fibres also made the composites quasi-ductile instead of brittle. SignificanceThe improved setting and higher strengths of the experimental materials compared to Cortoss™, could reduce monomer leakage from the injection site and material fracture, respectively. Lowering modulus may reduce stress shielding whilst quasi-ductile properties may improve fracture tolerance. The modified dental composites could therefore be a promising approach for future bone cements.

Thermal shock behavior and high-temperature oxidation performance of PDC-based environmental barrier coatings on AISI 441 stainless steel

The present work aimed to investigate the influence of different testing conditions on high-temperature oxidation performance of selected polymer-derived ceramic (PDC) environmental barrier coatings on AISI 441 stainless steel substrates. For this purpose, two types of double-layer PDC-based glass-ceramic coatings containing passive and glass fillers were fabricated using a combination of dip coating and spray coating processes. To evaluate the performance of the coatings in harsh environments simulating real applications, thermal cyclic tests in dry air, long-term static oxidation tests in humidified air, and thermal shock tests were performed. YAG, monoclinic ZrO2, cubic ZrO2, and a newly formed BaAl2Si2O8 phase were identified from XRD patterns of the tested PDC coatings. The SiO2 reflections, detected in the coatings after pyrolysis, were absent after both oxidation and thermal shock resistance tests. The SEM examination indicated that the performance of the studied PDC coatings was mainly affected by the microstructural modifications induced by differential sintering of the glass filler particles, leading to an expansion of existing pores, which represented preferential failure sites in the coating. In contrast, the existence of internal porosity relieved the residual stresses and reduced the driving force for crack extension, resulting in an increased thermal shock resistance. A combined scratch test based on the acoustic emission signal record along with the SEM observation of the resulting scratch tracks were also carried out. The most significant damage event in both tested PDC coatings was partial decohesion and surface chipping, which, however, did not translate into a critical adhesive failure. These findings confirm that the developed PDC coatings can be used for the protection of stainless steel in oxidizing environments up to 900 °C.

ZnO Quantum Photoinitiators as an All-in-One Solution for Multifunctional Photopolymer Nanocomposites.

Nanocomposites are constructed from a matrix material combined with dispersed nanosized filler particles. Such a combination yields a powerful ability to tailor the desired mechanical, optical, electrical, thermodynamic, and antimicrobial material properties. Colloidal semiconductor nanocrystals (SCNCs) are exciting potential fillers, as they display size-, shape-, and composition-controlled properties and are easily embedded in diverse matrices. Here we present their role as quantum photoinitiators (QPIs) in acrylate-based polymer, where they act as a catalytic radical initiator and endow the system with mechanical, photocatalytic, and antimicrobial properties. By utilizing ZnO nanorods (NRs) as QPIs, we were able to increase the tensile strength and elongation at break of poly(ethylene glycol) diacrylate (PEGDA) hydrogels by up to 85%, unlike the use of the same ZnO NRs acting merely as fillers. Simultaneously, we endowed the PEGDA hydrogels with post-polymerization photocatalytic and antimicrobial activities and showed their ability to decompose methylene blue and significantly eradicate antibiotic-resistant bacteria and viral pathogens. Moreover, we demonstrate two fabrication showcase methods, traditional molding and digital light processing printing, that can yield hydrogels with complex architectures. These results position SCNC-based systems as promising candidates to act as all-in-one photoinitiators and fillers in nanocomposites for diverse biomedical applications, where specific and purpose-oriented characteristics are required.

Data-driven rheological characterization of stress buildup and relaxation in thermal greases

Thermal greases, often used as thermal interface materials, are complex paste-like mixtures composed of a base polymer in which dense metallic (or ceramic) filler particles are dispersed to improve the heat transfer properties of the material. They have complex rheological properties that impact the performance of the thermal interface material over its lifetime. We perform rheological experiments on thermal greases and observe both stress relaxation and stress buildup regimes. This time-dependent rheological behavior of such complex fluid-like materials is not captured by steady shear-thinning models often used to describe these materials. We find that thixo-elasto-visco-plastic (TEVP) and nonlinear-elasto-visco-plastic (NEVP) constitutive models characterize the observed stress relaxation and buildup regimes, respectively. Specifically, we use the models within a data-driven approach based on physics-informed neural networks (PINNs). PINNs are used to solve the inverse problem of determining the rheological model parameters from the dynamic response in experiments. These training data are generated by startup flow experiments at different (constant) shear rates using a shear rheometer. We validate the “learned” models by comparing their predicted shear stress evolution to experiments under shear rates not used in the training datasets. We further validate the learned TEVP model by solving a forward problem numerically to determine the shear stress evolution for an input step-strain profile. Meanwhile, the NEVP model is further validated by comparison to a steady Herschel–Bulkley fit of the material’s flow curve.

Optimized regression model for microhardness of experimental dental composite resins with nano-hydroxyapatite filler particles

ABSTRACT Background: Bioactive materials produce a biological reaction such as stimulation of pulpal cells for dentinal repair and induction of the formation of hydroxyapatite. Aim: The study was conducted to evaluate the microhardness of experimental dental composite resins (EDCR) containing nano-hydroxyapatite, zirconia, and glass filler particles. Materials and Methods: The EDCR was prepared with varying concentrations of barium aluminum fluoride glass (5–20 nm), zirconia (4–11 nm), and hydroxyapatite (20–80 nm) filler particles added to the organic matrix. The L9 orthogonal array was used to prepare a sample size of 27 samples. Disc-shaped specimens of 10 mm diameter and 4 mm thickness were prepared using the American Society for Testing and Materials E384 standard for testing the microhardness. The Taguchi’s method of optimization was used to obtain a composite with optimum microhardness. A regression model was developed. Results: EDCR with 23.7% of zirconia, 27.5% of nano-hydroxyapatite, and 20% of glass filler particles gave the optimum microhardness of 222.67 HV. The confirmatory experimental test of EDCR gave a microhardness of 225 HV. The model developed with regression equation for the microhardness was 60–123 Z + 114 H + 17.8 G + 2.48 ZH − 0.02 HG + 0.97 Z2 − 3.40 H2. The difference between the R 2 (99.9) and adjusted R 2 values (99.4) is &lt;0.5, this shows that the model is acceptable. Conclusion: The EDCR developed after using Taguchi’s method of optimization had microhardness superior to that of the commercially available composite resins.

An Investigation on Filler Particle Size and Its Distribution in Glass-Epoxy Hybrid Composites Using Image Processing

Analysis of filler particle size and distribution plays a vital role in achieving a good balance of polymer composites’ electrical, thermal, and mechanical properties. Such assessments help understand the relationship between microstructure and the physical nature of polymer composites reinforced with fillers. In this investigation, glass epoxy composites with different nano and micro-sized fillers, namely SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> , MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , graphite and cenosphere, are fabricated by hand-lay technique with bagging. Particle analysis is carried out by employing image processing techniques using ImageJ. To understand the nature of hybrid filler size distribution, a comprehensive assessment of the micro and nanofiller particle distribution and the average shortest and longest separation distance between the nano and micron particles is estimated. From the particle size distribution analysis, it is observed that the micron particles are more evenly distributed than nanoparticles. The average distance between micron and nanofiller particles is observed depending on the type of filler used. The microparticles tend to surround the nanoparticles, which is desirable for decreasing the free space distances between the filler particles. Also, statistical analysis is carried out to study the experimental and estimated micron and nanofiller particle sizes used in the composites.