Conventional Composites Research Articles

A step toward bio-inspired dental composites

This feasibility study aimed to develop a new composite material of aligned glass flakes in a polymer resin matrix inspired by the biological composite nacre. The experimental composite was processed by an adapted method of pressing a glass flake and resin monomer system. By pressing and allowing the excess monomer to flow out, the long axis of the flakes was aligned. The resultant anisotropic composite with silanized and non-silanized glass flakes were subjected to fracture toughness tests. We observed increasing fracture toughness with increasing crack extension (Δa) known as resistance curve (R-curve) behavior. Silanized specimens had higher stress intensity KR-Δa over non-silanized specimens, whereas non-silanized specimens had a much lower Young’s modulus, and higher nonlinear plastic-elastic JR-Δa R-curve. In comparison with conventional composites, flake-reinforced composites can sustain continued crack growth for more significant extensions. The primary toughening mechanism seen in flake-reinforced composites was crack deviation and crack branching. We produced an anisotropic model of glass flake-reinforced composite showing elevated toughening potential and a prominent R-curve effect. The feasibility of flake reinforcement of dental composites has been shown using a relatively efficient method. The use of a biomimetic, nacre-inspired reinforcement concept might guide further research toward improvement of dental restorative materials.

Nature-inspired energy dissipation sandwich composites reinforced with high-friction graphene

Although extensive studies have confirmed that adding graphene can improve the damping properties of polymer composites, to date, some critical issues, including aggregation, and mediocre surface friction force of graphene, remain unimproved. In this study, nature-inspired sandwich composites are designed and prepared for vibration suppression, where the conventional blended composites and pure epoxy resin specimens are also prepared as a reference. Dynamic mechanical analysis and vibration test results confirm that the damping properties of sandwich composites are superior compared to those of blended composites and pure epoxy, where the loss factor of pure epoxy is 0.067, and those of conventional blended and sandwich composites with the mass fraction of 0.75 wt‰ are increased to 0.067 and 0.0942, respectively. The energy dissipation mechanism of competitive behavior is then proposed to interpret the bell-shaped damping variation of sandwich composites with the increasing thickness of core layer. Moreover, polydopamine (PDA) is used to modify reduced graphene oxide (rGO) to enlarge the surface friction force, which improves the damping enhancing capability of rGO. To be specific, the damping ratio of PDA modified rGO reinforced composites with a mass fraction of 0.5 wt‰ is 42.2% higher than that of rGO reinforced composites with the same mass fraction. The modification of rGO and the successful preparation of sandwich composites provide a charming strategy for vibration energy dissipation and damping enhancement.

Color Stability of Polymer-Based Composite CAD/CAM Blocks: A Systematic Review.

This systematic review aims to evaluate the color stability of resin composite CAD/CAM blocks (CCB) when submitted to staining solutions. A systematic search was performed on different databases (Embase, Medline, Scopus, Web of Science). Search terms were: 'polymer infiltrated', 'polymer-based', 'resin nanoceramic', 'resin ceramic', 'hybrid composite', 'hybrid ceramic', 'composite ceramic', 'resin infiltrated', 'CAD-CAM', 'CAD/CAM', 'color stability', 'staining', 'staining susceptibility', 'color change', 'color difference'. in vitro articles published in the English language until 18 September 2022 without initial time restriction evaluating the color stability of CCB when submitted to staining solutions. studies investigating color change induced by smoke or whitening treatments; studies not including a clinical evaluation of the results using the thresholds for color perceptibility and acceptability. Risk of bias assessment using the QUIN tool. Out of the 378 initially retrieved articles, 19 were included in this review. They investigated 17 different CCBs and different artificial staining by liquid protocols, including coffee, red wine, tea, and cola. CCBs exceeded clinical acceptability thresholds for color shift in 18 out of 19 studies, with a significantly higher color stability than conventional hybrid resin-based composites (RBCs), and a significantly lower color stability than ceramic materials. The identified differences in CCBs in color stability can be attributed to the material's composition, but also to the heterogeneity of staining procedures. Interpretation and clinical implication: Clinicians should be aware that, although to a lower degree when compared to RBCs used in direct or indirect procedures, CCBs undergo color changes to a higher degree in comparison to ceramic materials.

How Flexible Is the Concept of Local Thermodynamic Equilibrium?

It has been demonstrated by using generalized phenomenological irreversible thermodynamic theory (GPITT) that by replacing the conventional composition variables {xk} by the quantum level composition variables {x˜k,j} corresponding to the nonequilibrium population of the quantum states, the resultant description remains well within the local thermodynamic equilibrium (LTE) domain. The next attempt is to replace the quantum level composition variables by their respective macroscopic manifestations as variables. For example, these manifestations are, say, the observance of fluorescence and phosphorescence, existence of physical fluxes, and ability to register various spectra (microwave, IR, UV-VIS, ESR, NMR, etc.). This exercise results in a framework that resembles with the thermodynamics with internal variables (TIV), which too is obtained as a framework within the LTE domain. This TIV-type framework is easily transformed to an extended irreversible thermodynamics (EIT) type framework, which uses physical fluxes as additional variables. The GPITT in EIT version is also obtained well within the LTE domain. Thus, GPITT becomes a complete version of classical irreversible thermodynamics (CIT). It is demonstrated that LTE is much more flexible than what CIT impresses upon. This conclusion is based on the realization that the spatial uniformity for each tiny pocket (cell) of a spatially non-uniform system remains intact while developing GPITT and obviously in its other versions.

Improvement of Electrical and Mechanical Properties of PLA/PBAT Composites Using Coconut Shell Biochar for Antistatic Applications

Biochar-based environment-friendly polymer composites are suitable substitutes for conventional non-biodegradable polymer composites. In this work, we developed polylactic acid (PLA)/polybutylene adipate-co-terephthalate (PBAT)/biochar (BC) composites with improved mechanical and electrical properties for antistatic applications. Coconut shell biochar was obtained through the pyrolysis of coconut shell in an inert atmosphere, and characterised using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), to investigate the morphology and structural properties. The biochar was converted to powder form, sieved to reduce the particle size (≤30 μm diameters), and melt-mixed with PLA and PBAT to form composites. The composites were extruded to produce 3D printing filaments and, eventually, 3D-printed tensile specimens. The tensile strength and tensile modulus of the 3D-printed PLA/PBAT/BC (79/20/1) composite with 1 wt% of biochar improved by 45% and 18%, respectively, compared to those of PLA/PBAT (80/20). The interfacial interaction between the biochar and polymer matrix was strong, and the biochar particles improved the compatibility of the PLA and PBAT in the composites, improving the tensile strength. Additionally, the electrical resistivity of the composite did reduce with the addition of biochar, and PLA/PBAT/BC (70/20/10) showed the surface resistivity of ~1011 Ω/sq, making it a suitable material for antistatic applications.

Digital Anthropometry: A Systematic Review on Precision, Reliability and Accuracy of Most Popular Existing Technologies.

Digital anthropometry (DA) has been recently developed for body composition evaluation and for postural analysis. The aims of this review are to examine the current state of DA technology, as well as to verify the methods for identifying the best technology to be used in the field of DA by evaluating the reliability and accuracy of the available technologies on the market, and lay the groundwork for future technological developments. A literature search was performed and 28 studies met the inclusion criteria. The reliability and accuracy of DA was high in most studies, especially in the assessment of patients with obesity, although they varied according to the technology used; a good correlation was found between DA and conventional anthropometry (CA) and body composition estimates. DA is less time-consuming and less expensive and could be used as a screening tool before more expensive imaging techniques or as an alternative to other less affordable techniques. At present, DA could be useful in clinical practice, but the heterogeneity of the available studies (different devices used, laser technologies, population examined, etc.) necessitates caution in the interpretation of the obtained results. Furthermore, the need to develop integrated technologies for analyzing body composition according to multi-compartmental models is increasingly evident.

Ultrafast-responsive carbon nanotube-grafted fibre textiles

Direct grafting of carbon nanotubes (CNTs) on fibre textiles is a promising strategy to functionalize conventional fibre-reinforced polymer composites with extra merits such as integrated sensing capability. In this study, CNTs are in situ grafted on glass fibre (GF) via chemical vapor deposition at a low synthesis temperature (500 °C). By regulating the mass fractions of CNTs, the quantum tunnelling effect can be triggered among CNT nanoparticles, with which the CNT-grafted GF textiles manifest high sensitivity to structure-guided ultrasonic waves in a frequency regime from 175 to 375 kHz. With ignorable degradation in mechanical attributes due to this direct grafting processing as affirmed by ASTM-complied tests (ASTM C1557 and D3039), the CNT-grafted GF textiles demonstrate the great potential in developing hybrid functional composites.

Dry sliding wear characteristics of natural fibre reinforced poly-lactic acid composites for engineering applications: Fabrication, properties and characterizations

Natural fibre composites have emerged as a viable alternative to conventional polymer composites, after environmental concerns gain popularity. In recent years, a tremendous growth in the applications of natural fibre composites have been observed, particularly in the field of construction, as well as aerospace and automotive industries. The present study investigates the feasibility of developing a novel tribo-material by reinforcing biopolymer with easily accessible and inexpensive plant fibres from the surroundings. The fibres were treated chemically prior to fabrication. The injection molding process was used to fabricate laminated composites by incorporating three different kinds of fibres (sisal, banana, and bagasse) into Poly-lactic acid (PLA) matrix at 10% and 20% fibre concentrations. Wear properties of fabricated composites were studied on a digital display controlled pin-on-disc test rig. The test parameters under dry sliding conditions were sliding distance (1000–3000 m), sliding speed (2,4 and 6 m/s) and applied load (10 N). The experimental results depict that the incorporation of natural fibres improved tribological properties of neat PLA matrix. The worn surfaces of developed composites were examined using a scanning electron microscope to study the wear mechanism.

Mechanical and Biomimetic Characteristics of Bulk-Fill Resin Dental Composites Following Exposure in a Simulated Acidic Oral Environment

During the last 10 years, various companies have marketed different "bulk-fill" resin dental composites for the restoration of posterior stress-bearing teeth; however, the impact of acidic conditions on these relatively newer materials has not been thoroughly investigated. Therefore, an attempt was made to evaluate the effect of acidic beverages on the mechanical biomimetic characteristics of four bulk-fill and one conventional nanohybrid resin-based dental composites (RBCs). The specimens of each RBC were stored in two acidic beverages namely 'Orange Juice' and 'Coca-Cola', whereas 'dry' and 'distilled water' storage of specimens served as controls. After 1 week of storage, flexural and surface hardness properties of specimens were determined using a universal testing machine and Vickers hardness tester, respectively. In general, the 'Coca-Cola' beverage caused the greatest degradation of flexural strength, flexural modulus, and surface hardness characteristics in all RBCs in contrast to the 'dry', 'distilled water' controls and 'Orange Juice' storage conditions. However, the overall mechanical biomimetic performance of nanohybrid RBCs was relatively better than all other bulk-fill RBCs and may, therefore, be considered a suitable candidate for the restoration of posterior stress-bearing permanent dentition.

A novel approach to fabricate WC reinforced W[sbnd]Cu composites via MSC and infiltration method

WC reinforced WCu composites have excellent wear resistance and high-temperature strength, and can replace conventional WCu composites in special applications. In this work, WCu composites with WC@W core-shell structure are fabricated through a novel microwave-heating salt-bath carbonization (MSC) and infiltration method, using graphite as the carbon source. The MSC behavior of W particles and the influence of the graphite content on the microstructure and properties of the WCu composites are investigated. The results show that WC is successfully coated on the surface of W particles by the MSC method. The addition of an appropriate amount of graphite to W powders can improve the high-temperature mechanical properties and wear resistance of the WCu composites. Compared with conventional WCu composites, the WCu composites with 0.9 wt% graphite have higher thermal conductivity (245 W/(m·K)), higher hardness (293.8 HV), higher bending strength (1089.4 MPa), and higher compressive strength (410 MPa|600°C). The addition of graphite also significantly improved the wear resistance of the WCu composites. The average coefficient of friction (CoF) and wear rates (WR) of WCu9 composites are 0.51 and 5.37 × 10−6 mm3 N−1 m−1, respectively. The WC reinforced WCu composites prepared in this work provide an excellent approach to improve the wear resistance and high-temperature properties of guide plates in guide devices.

Çeşitli Kompozit Rezinlere Uygulanan Farklı Yüzey Pürüzlendirme Yöntemlerinin Porselen Bağlanma Dayanımına Etkisi: İn Vitro Çalışma

Objective: This study compares different surface conditioning methods applied to various composite surfaces in order to investigate the possible effects on composite-ceramic bond strength. It was aimed to increase the bond strength between flowable composite which is frequently used in the immediate dentin sealing procedure and ceramic surfaces. Material and Methods: Eighty flowable composite and eighty conventional composite discs were prepared with five different surface conditioning methods applied to the discs. The folllowing treatments were applied to the discs: orthophosphoric acid, air-flow, bur conditioning, Er:YAG laser irradition and an unconditioned control group. The composite disc surface roughness was measured with a profilometer. Composite and ceramic (Glass-ceramic blocks, e.max CAD, Ivoclar Vivadent AG, Liechtenstein) discs were then bonded with an adhesive resin cement. The shear bonding test was performed with an universal tester. Results: There was no statistical difference between the conditioning methods applied to flowable composites in terms of bond strength (p>0.05). However, a statistically significant difference was found between the conditioning methods applied to conventional composites regarding bond strength (p<0.05). The highest mean bond strength value was observed with ER:YAG laser conditioned conventional composites and was significantly higher than laser irradiated flowable composite groups. Conclusion: Our data shows that similar bond strength values are obtained when using either flowable or conventional composite resins. In addition, both conventional and flowable composite resins require surface conditioning to achieve reliable adhesion to porcelain material.

Comparative Color Stability Assessment of One- Shaded Structurally-Colored and Conventional Multi-Shaded Resin Composites

Purpose: To assess the color stability of one- shaded structurally- colored resin composite compared to conventional multi- shaded one. Subjects and methods: Thirty- two disc- like specimens from one- shaded structurally- colored resin composite (Omnichroma, Tokuyama Dental); Group I, or conventional resin composite (Filtek Z350, 3M ESPE); Group II were prepared, with equal allocation ratio (i.e.: n= 16). Samples were left in coffee then by using spectrophotometry, colors for all specimens were assessed in (CIE) Lab values; before (baseline) and 30 days later. Substitution in the (after - before) equation was performed to obtain the color change (ΔE); to detect color change for each specimen. Data was tabulated & statistically analyzed. Results: One- shaded structurally- colored resin composite (Omnichroma) showed statistically significant (p ≤ 0.05) color stability in comparison to conventional resin composite (Filtek Z350). Conclusion: One- shaded structurally- colored resin composite (Omnichroma) proved better than conventional resin composite (Filtek Z350) regarding color stability. Esthetic color matching, therefore, could be easily obtained and maintained.

Clinical Evaluation of Class I Posterior Restorations Restored with Smart Dentin Replacement Flowable Bulk-fill Composite Material in Bulk-fill and Incremental Technique – One-year Randomized Clinical Trial

ABSTRACT Aim and Objective: The aim and objective of this in vivo study are to evaluate the clinical performance of smart dentin replacement (SDR) flowable bulk-fill composite in class I restorations with incremental technique and bulk-fill technique. Materials and Methods Fifty patients with at least two class 1 cavities in the age group of 18–40 years were recruited. In all cavities, Xeno Vplus self-etch adhesive was applied. In one of the cavities, SDR was placed in bulk increments up to 4 mm as needed to fill the cavity 2-mm short of the occlusal surface. The occlusal part was placed with SureFil nanohybrid composite, and the other cavity was placed by incremental technique. The restorations were evaluated using FDI criteria. Results: Data were subjected to statistical analysis and analyzed using Chi-square test. After 1 year, all restorations received clinically excellent and clinically good scorings for each criterion. Conclusion: There is no statistically significant difference between the bulk-fill technique and the incremental technique using SDR after 1-year follow-up. CLINICAL RELEVANCE TO INTERDISCIPLINARY DENTISTRY The smart dentin replacement bulk-fill resin composites demonstrated good clinical durability as equal as conventional composites. It provides an advantage of less clinical time for placement in deep posterior cavities.

Marginal Sealing Ability of Bulk-Fill vs Conventional Composites; A Systematic Review

Marginal Sealing Ability of Bulk-Fill vs Conventional Composites; A Systematic Review

Electric Vehicle Charging Capacity of Distribution Network Considering Conventional Load Composition

At present, the large-scale access to electric vehicles (EVs) is exerting considerable pressure on the distribution network. Hence, it is particularly important to analyze the capacity of the distribution network to accommodate EVs. To this end, we propose a method for analyzing the EV capacity of the distribution network by considering the composition of the conventional load. First, the analysis and pretreatment methods for the distribution network architecture and conventional load are proposed. Second, the charging behavior of an EV is simulated by combining the Monte Carlo method and the trip chain theory. After obtaining the temporal and spatial distribution of the EV charging load, the method of distribution according to the proportion of the same type of conventional load among the nodes is adopted to integrate the EV charging load with the conventional load of the distribution network. By adjusting the EV ownership, the EV capacity in the distribution network is analyzed and solved on the basis of the following indices: node voltage, branch current, and transformer capacity. Finally, by considering the 10-kV distribution network in some areas of an actual city as an example, we show that the proposed analysis method can obtain a more reasonable number of EVs to be accommodated in the distribution network.

Effect of Exogenous Neutral Protease Fermentation on Cigar Leaf Quality

In order to reveal the effect of exogenous neutral protease addition on the quality of cigar tobacco leaves during fermentation. Taking Sichuan Shifang cigar tobacco leaves as the research object, the changes of conventional chemical composition, amino acid content, organic acids and other substances in tobacco leaves after natural fermentation and fermentation with exogenous enzyme preparations were investigated, and the changes of sensory quality of cigar tobacco leaves before and after fermentation were also investigated. The results show that: 1) After fermentation, the content of total sugar, reducing sugar, total nitrogen, chlorogenic acid and rutin in tobacco leaves decreased, and the content of reducing sugar fermented with enzyme preparation decreased more. 2) After fermentation, the total amount of free amino acids in tobacco leaves increased. With the increase of exogenous neutral protease, the content of amino acids first increased and then decreased. 3) After fermentation, the content of organic acids in tobacco leaves increased. When the amount of enzyme added was 2.5g/kg leaves, the increase of organic acid content was greater than that of natural fermentation, and the other additions of enzyme were close to that of natural fermentation. 4) After fermentation, the content of plastid pigment in tobacco leaves decreased slightly. With the increase of neutral protease, the content of plastid pigment increased. 5) After the fermentation of exogenous enzyme preparation, the sensory quality of tobacco leaves is improved, but too much protease will produce bitter taste.

Fabrication of green composites by waste coconut shells as partial replacement of coarse aggregates in concrete and determination of its acoustic behaviour

Nowadays, natural materials have been frequently used for sound absorption in constructions and buildings. This paper has characterised the acoustic behaviour of coconut shell reinforced concrete composite with partial substitution of coarse aggregates in terms of sound absorption at octave frequency signals (32 Hz-16 kHz). Composites have been prepared in different weight percentages (5%, 10%, 15%, and 20%) of partial substitution of coarse aggregates. The acoustic test has been conducted in a 3.5 mm thick glass box without and with samples by point method of sound power measurement. The results have demonstrated that the value of the sound pressure level has decreased at different points with the increased percentage of coconut shells in composite, hence increasing the sound absorption coefficient of the concrete. The results have also been compared with conventional concrete composite. Additionally, the results have indicated that these concrete blocks can significantly absorb sound in the mid-frequency range. Generally, a sound absorption coefficient greater than 0.2 for any material qualifies it as a sound-absorbing material, and a sound absorption coefficient greater than 0.6 for any material is known as the best sound absorber. Therefore, developing such green composites can be an eco-friendly approach to the acoustic community.

Thermo-mechanical characterization of sea water immersed GO based GRE hybrid composite

The present work is aimed to investigate the durability of graphene oxide (GO) dispersed GFRP hybrid polymer composite subject to exposure in natural sea water for 4 weeks. Conventional GFRP and GO (0.5 wt%) based GFRP were fabricated by taking 12 layers of woven E-glass fibre as reinforcement and epoxy thermosetting polymer as matrix. GO was synthesized in laboratory by modified Hummer’s method. Synthesis of GO was confirmed through XRD and Raman spectroscopy. Short beam shear (SBS) specimens of all types (both conventional and hybrid) of as-cured composites in desired dimension were immersed in natural sea water for various lengths of duration (maximum up to 4 weeks). All the sea water treated composite samples were characterized through 3-point bend test to reveal inter laminar shear strength (ILSS). About 35 % decrease in ILSS was reported for conventional GRE composite after 4 week of sea water immersion. Decrease in ILSS for GO reinforced GFRP composite was found to be 24.8 %, which is lesser than that compared to conventional GFRP composite. Low temperature Differential scanning calorimetry (DSC) test was conducted to access the glass transition temperature (Tg) of sea water immersed composite samples. After 4 weeks of sea water immersion, conventional GRE and GO-GRE composite exhibited 16% and 15.2% of decrease in Tg. Mechanism of bonding across fibre–matrix interface embedded with GO filler was investigated through the fractographic images, as obtained by scanning electron microscope (SEM).

Physico-Mechanical Characteristics of Ormocer and Bulk Fill Composite Resin Restorative Materials: An in-vitro Study

Introduction: Bulk Fill (BF) resins and Ormocers are recently introduced composite restorative materials in order to overcome the disadvantage of polymerisation shrinkage exhibited by most of the conventional resin-based composites. Aim: To evaluate the physical and mechanical properties of Organically Modified Ceramics (Ormocers) in comparison with BF composite resin restorative material. Materials and Methods: In this in-vitro study, 20 human extracted premolars were allocated into two groups of 10 each. ORM (Group-1 Admira fusion, n=10) and BF (Group-2 Filtek BF, n=10) composite materials were used to prepare and restore Class-V cavities. The teeth were subjected to thermocycling and immersed in 1% methylene blue dye solution. Along the lateral walls of each sectioned specimen, depth of dye penetration was measured under the stereo microscope. A total of 20 rectangular (25x2x2 mm) and 20 disc (10x2 mm) shaped specimens of the above-mentioned materials were fabricated. Specimens of Flexural Strength (FS) were tested with the universal testing machine and Vickers hardness tester used for Surface Hardness (SH) evaluation. The data was statistically analysed using an unpaired t-test. Results: Total of 20 extracted premolars were analysed. On inter-group comparison, it was observed that mean dye penetration was lowest for Group-1 (0.6±0.69) compared to Group-2 (2±0.81) and the difference observed was statistically significant (p=0.001). BF exhibited a lower FS of 211.69±43.9 compared to Ormocer 326.19±90.3, the difference is statistically significant (p=0.001). However, BF exhibited a higher SH of 38.3±0.15 compared to Ormocer 33.70±0.86, and the difference is statistically significant (p-value&lt;0.001). Conclusion: Ormocer exhibited improved marginal integrity and also higher FS compared to BF resin restorative materials. However, BF exhibited higher SH values compared to Ormocer.

Surfactant Assisted One-Pot Method for Preparation of Polyethylene-Clay Nanocomposites (PECN) and Study of their Viscoelastic Behaviour

This work demonstrates a one-pot soft template-assisted technique for developing polyethylene clay nanocomposite (PECN) using cetyltrimethylammonium bromide (CTAB) micelle as structure directing agent. Linear and shear viscosities of the composite were studied in the oscillatory and rotational modes. The effect of clay content, temperature and gallery space on the storage modulus and steady-state viscosities were analyzed. The composite exhibited enhanced storage modulus over the pristine polymer, confirming strong interaction between the clay platelet and polymer molecules. The prepared PECN showed superior thermal stability, phase transition temperature, flame retardancy and mechanical properties as compared to the conventional composite. Morphological studies using SEM and TEM also confirmed the formation of the nanocomposite. This one step surfactant-assisted emulsion method offers a broad scope in designing polymer clay nanocomposites with exciting properties and consequent applications.