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J. Compos. Sci., Volume 3, Issue 3 (September 2019)

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Open AccessArticle
Comparison of the Processing of Epoxy Resins in Pultrusion with Open Bath Impregnation and Closed-Injection Pultrusion
J. Compos. Sci. 2019, 3(3), 87; https://doi.org/10.3390/jcs3030087 (registering DOI)
Received: 30 June 2019 / Revised: 2 August 2019 / Accepted: 13 August 2019 / Published: 23 August 2019
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Abstract
In this study, the influence of the open bath and closed-injection pultrusion (CIP) processing methods of epoxy resins on the quality of glass fiber composites was investigated. In addition to the state-of-the-art epoxy resin system with long pot life, new resin systems with [...] Read more.
In this study, the influence of the open bath and closed-injection pultrusion (CIP) processing methods of epoxy resins on the quality of glass fiber composites was investigated. In addition to the state-of-the-art epoxy resin system with long pot life, new resin systems with short pot life have recently been developed. These systems require processing by closed-injection pultrusion. The epoxies with long pot life allow both processing variants. The experimental work was carried out with two types of injection and impregnation chambers (ii_chamber), namely with a conical and a teardrop design. Fully impregnated composites, which were used for further analyses, could be produced by using the conical ii_chamber. The composite properties of the open bath and the conical ii_chamber impregnation methods were compared. No significant influence on the bending stress could be determined; the interlaminar shear strength was up to 10% better with open bath impregnation than with ii_chamber. For the composites investigated, it was shown that the open bath and ii_chamber impregnation methods can be used to produce parts with partially comparable properties, as demonstrated for the epoxy formulation with long pot life. These results indicate that processing of epoxy systems with a short pot life is also possible by closed-injection pultrusion. Furthermore, the influence on the composite properties of the time interval between the mixing of an epoxy resin and processing in an open bath was investigated. No significant effect on the bending stress and interlaminar shear strength could be determined. Full article
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Open AccessDiscussion
Research and Development in Carbon Fibers and Advanced High-Performance Composites Supply Chain in Europe: A Roadmap for Challenges and the Industrial Uptake
J. Compos. Sci. 2019, 3(3), 86; https://doi.org/10.3390/jcs3030086 (registering DOI)
Received: 30 June 2019 / Revised: 5 August 2019 / Accepted: 19 August 2019 / Published: 22 August 2019
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Abstract
Structural materials, typically based on metal, have been gradually substituted by high-performance composites based on carbon fibers, embedded in a polymer matrix, due to their potential to provide lighter, stronger, and more durable solutions. In the last decades, the composites industry has witnessed [...] Read more.
Structural materials, typically based on metal, have been gradually substituted by high-performance composites based on carbon fibers, embedded in a polymer matrix, due to their potential to provide lighter, stronger, and more durable solutions. In the last decades, the composites industry has witnessed a sustained growth, especially due to diffusion of these materials in key markets, such as the construction, wind energy, aeronautics, and automobile sectors. Carbon fibers are, by far, the most widely used fiber in high-performance applications. This important technology has huge potential for the future and it is expected to have a significant impact in the manufacturing industry within Europe and, therefore, coordination and strategic roadmapping actions are required. To lead a further drive to develop the potential of composites into new sectors, it is important to establish strategic roadmapping actions, including the development of business and cost models, supply chains implementation, and development, suitability for high volume markets and addressing technology management. Europe already has a vibrant and competitive composites industry that is supported by several research centers, but for its positioning in a forefront position in this technology, further challenges are still required to be addressed. Full article
(This article belongs to the Special Issue Feature Papers in Journal of Composites Science in 2019)
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Open AccessArticle
Effects of Nano Organoclay and Wax on the Machining Temperature and Mechanical Properties of Carbon Fiber Reinforced Plastics (CFRP)
J. Compos. Sci. 2019, 3(3), 85; https://doi.org/10.3390/jcs3030085
Received: 25 June 2019 / Revised: 8 August 2019 / Accepted: 13 August 2019 / Published: 20 August 2019
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Abstract
Carbon fiber reinforced plastics (CFRP) are appreciated for their high mechanical properties and lightness. Due to their heterogeneous nature, CFRP machining remains delicate. Damages are caused on the material and early tool wear occurs. The present study aims to evaluate the effects of [...] Read more.
Carbon fiber reinforced plastics (CFRP) are appreciated for their high mechanical properties and lightness. Due to their heterogeneous nature, CFRP machining remains delicate. Damages are caused on the material and early tool wear occurs. The present study aims to evaluate the effects of fillers on CFRP machinability and mechanical behavior. CFRP laminates were fabricated by the vacuum assisted resin transfer molding (VARTM) process, using a modified epoxy resin. Three fillers (organoclay, hydrocarbon wax, and wetting agent) were mixed with the resin prior to the laminate infusion. Milling tests were performed with polycrystalline diamond (PCD) tools, equipped with thermocouples on their teeth. Machinability was then studied through the cutting temperatures and forces. Tensile, flexural, and short-beam tests were carried out on all samples to investigate the effects of fillers on mechanical properties. Fillers, especially wax, allowed us to observe an improvement in machinability. The best improvement was observed with 1% wax and 2% organoclay, which allowed a significant decrease in the cutting forces and the temperatures, and no deteriorations were seen on mechanical properties. These results demonstrate that upgrades to CFRP machining through the addition of nanoclays and wax is a path to explore. Full article
(This article belongs to the Special Issue Feature Papers in Journal of Composites Science in 2019)
Open AccessArticle
Chitosan Hydrogels Crosslinked by Genipin and Reinforced with Cellulose Nanocrystals: Production and Characterization
J. Compos. Sci. 2019, 3(3), 84; https://doi.org/10.3390/jcs3030084
Received: 28 June 2019 / Revised: 5 August 2019 / Accepted: 6 August 2019 / Published: 13 August 2019
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Abstract
In this work, chitosan hydrogels crosslinked with genipin and reinforced with cellulose nanocrystals (CNC) were developed and characterized with the aim of future biomedical applications. CNC was produced by acid hydrolysis and characterized by atomic force microscopy (AFM). Chitosan/CNC nanocomposite hydrogels were produced [...] Read more.
In this work, chitosan hydrogels crosslinked with genipin and reinforced with cellulose nanocrystals (CNC) were developed and characterized with the aim of future biomedical applications. CNC was produced by acid hydrolysis and characterized by atomic force microscopy (AFM). Chitosan/CNC nanocomposite hydrogels were produced with different CNC concentrations (w/w): 0%, 2%, 4%, and 6%. The genipin was used as a crosslinking agent in a genipin/chitosan molar proportion of 1:8. The hydrogels were characterized by porosity measurements, scanning electron microscopy (SEM), swelling test, and mechanical compression test. No significant differences were observed concerning the porosity of the hydrogels; however, a trend of decreasing porosity was observed with increasing CNC content. The SEM images showed a better pore structure as the CNC concentration increased. A decrease in the swelling degree with increasing CNC content in the chitosan/CNC nanocomposite hydrogel was verified in the swelling tests. An increase in the CNC concentration in the chitosan/CNC nanocomposite hydrogel caused a gradual increase in the maximum stress and maximum strain as observed in the compression tests, showing a significant difference between chitosan/CNC 6 wt % and neat chitosan hydrogel. Full article
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Open AccessArticle
Structural Nanocomposite Fabrication from Self-Assembled Choline Chloride Modified Kaolinite into Poly(Methylmethacrylate)
J. Compos. Sci. 2019, 3(3), 83; https://doi.org/10.3390/jcs3030083
Received: 28 June 2019 / Revised: 3 August 2019 / Accepted: 6 August 2019 / Published: 13 August 2019
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Abstract
Composite materials produced from indigenous nanoscale particles and synthetic polymers have created demand in the field of nanoscience and technology. Layered silicates are potential candidates for reinforcing the properties of composites. Here, we report the fabrication of nanocomposites using poly(methylmethacrylate) (PMMA) as the [...] Read more.
Composite materials produced from indigenous nanoscale particles and synthetic polymers have created demand in the field of nanoscience and technology. Layered silicates are potential candidates for reinforcing the properties of composites. Here, we report the fabrication of nanocomposites using poly(methylmethacrylate) (PMMA) as the matrix and the Bijoypur clay of Bangladesh known as kaolinite (200–250 nm) as the filler via solution casting. Kaolinite was first modified using choline chloride to prepare core-shell particles through a precipitation technique and was used for self-assembled nanocomposite films preparation. A series of nanocomposites films using 0, 1, 3, 5 and 10% (w/w) modified kaolinite was prepared. The neat PMMA and nanocomposite films were characterized by attenuated total reflection infra-red (ATR-IR) spectroscopy and X-ray diffraction (XRD) techniques. The mechanical properties, thermal stability, and morphology of the films were investigated using a universal testing machine (UTM), a thermal gravimetric analyzer (TGA), and a scanning electron microscope (SEM). The nanocomposite films exhibited better mechanical properties and thermal stability than neat PMMA film. Development of such structural nanocomposite materials using naturally occurring nanoscale particles would play a crucial role in the field of materials science for packaging applications and separation technology. Full article
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Open AccessArticle
Increasing the Impact Toughness of Cellulose Fiber Reinforced Polypropylene Composites—Influence of Different Impact Modifiers and Production Scales
J. Compos. Sci. 2019, 3(3), 82; https://doi.org/10.3390/jcs3030082
Received: 29 June 2019 / Revised: 24 July 2019 / Accepted: 4 August 2019 / Published: 8 August 2019
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Abstract
While cellulose fiber reinforced polypropylene (PP) composites typically offer good stiffness and strength in combination with ecological benefits and a high potential for lightweight construction, they often require measures taken to improve their impact performance. In this work, the influence of different types [...] Read more.
While cellulose fiber reinforced polypropylene (PP) composites typically offer good stiffness and strength in combination with ecological benefits and a high potential for lightweight construction, they often require measures taken to improve their impact performance. In this work, the influence of different types of impact modifier on the mechanical performance of a PP–cellulose composite was systematically investigated, with a particular focus on the improvement of the notched impact strength and the accompanying loss of stiffness. Among the tested impact modifiers, ethylene-octene copolymers appeared to be the most suitable class to achieve a good overall performance. A high modifier viscosity increased its potential to improve the notched impact strength of the composite. Additionally, composite production on a larger scale improved the impact performance without significantly affecting the tensile properties. Several composites from this study surpassed the overall mechanical performance of a benchmark commercial PP–cellulose composite. While the impact strength of commercial high-impact PP–talc composites could not be reached, the considerably lower density of the PP–cellulose composites is worth mentioning. Full article
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Open AccessArticle
Correlation of Rh Particle Size with CO Chemisorption: Effect on the Catalytic Oxidation of MTBE
J. Compos. Sci. 2019, 3(3), 81; https://doi.org/10.3390/jcs3030081
Received: 28 June 2019 / Revised: 31 July 2019 / Accepted: 1 August 2019 / Published: 7 August 2019
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Abstract
This study was conducted to identify the correlation between the CO chemisorption (linear interaction and gem dicarbonyl) and the specific size of rhodium particles, and further to determine the influence of this relationship on the catalytic oxidation reaction of methyl tert-butyl ether (MTBE). [...] Read more.
This study was conducted to identify the correlation between the CO chemisorption (linear interaction and gem dicarbonyl) and the specific size of rhodium particles, and further to determine the influence of this relationship on the catalytic oxidation reaction of methyl tert-butyl ether (MTBE). During the synthesis, first, TiO2 was developed by the sol-gel method under acidic conditions. Second, Rh was deposited (1 wt %) by the incipient wetness impregnation method. Later, with the aim of controlling the particle size, the Rh/TiO2 materials were crystallized at different reduction conditions during 3 h heat treatment. The results obtained by TEM micrographs indicated that the average particle size varies between 1.0 and 8.1 nm, depending on the conditions of heat treatment. From the histogram analysis of each TEM micrograph, two correlations were made: (i) the gem-dicarbonyl interaction was typical of Rh particles ≤ 1.5 nm, and (ii) a linear interaction, bridged interaction and dentate interaction were observed in particles ≥ 1.6 nm. The gem-dicarbonyl interaction (particle size ≤ 1.5 nm) was the most active in the oxidation reaction of MTBE. Full article
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Open AccessArticle
Gas and Solution Uptake Properties of Graphene Oxide-Based Composite Materials: Organic vs. Inorganic Cross-Linkers
J. Compos. Sci. 2019, 3(3), 80; https://doi.org/10.3390/jcs3030080
Received: 1 July 2019 / Revised: 15 July 2019 / Accepted: 25 July 2019 / Published: 1 August 2019
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Abstract
This study focused on a comparison of the adsorption properties of graphene oxide (GO) and its composites that were prepared via cross-linking with chitosan (CTS) or Al3+ species, respectively. Comparative material characterization was achieved by several complementary methods: SEM, NMR spectroscopy, zeta-potential, [...] Read more.
This study focused on a comparison of the adsorption properties of graphene oxide (GO) and its composites that were prepared via cross-linking with chitosan (CTS) or Al3+ species, respectively. Comparative material characterization was achieved by several complementary methods: SEM, NMR spectroscopy, zeta-potential, dye-based adsorption, and gas adsorption at equilibrium and dynamic conditions. SEM, solids NMR, and zeta-potential results provided supporting evidence for cross-linking between GO and the respective cross-linker units. The zeta-potential of GO composites decreased upon cross-linking due to electrostatic interactions and charge neutralization. Equilibrium and kinetic adsorption profiles of the GO composites with methylene blue (MB) in aqueous media revealed superior uptake over pristine GO. The monolayer adsorption capacity (mg g−1) of MB are listed in descending order for each material: GO–CTS (408.6) > GO–Al (351.4) > GO (267.1). The gas adsorption results showed parallel trends, where the surface area and pore structure of the composites exceeded that for GO due to pillaring effects upon cross-linking. The green strategy reported herein for the preparation of tunable GO-based composites revealed versatile adsorption properties for diverse heterogeneous adsorption processes. Full article
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Open AccessArticle
Sandwich Panels Bond with Advanced Adhesive Films
J. Compos. Sci. 2019, 3(3), 79; https://doi.org/10.3390/jcs3030079
Received: 25 June 2019 / Revised: 16 July 2019 / Accepted: 25 July 2019 / Published: 1 August 2019
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Abstract
Sandwich structures present several advantages, being used in many industries such as the aeronautical industry. In this study, an automated laminating line is employed to manufacture sandwich panels for boards. This work focus on an innovative solution, employing an advanced adhesive film to [...] Read more.
Sandwich structures present several advantages, being used in many industries such as the aeronautical industry. In this study, an automated laminating line is employed to manufacture sandwich panels for boards. This work focus on an innovative solution, employing an advanced adhesive film to increase the bonding strength of sandwich structures used for this application. This was used to bond ceramic steel sheets to honeycomb‐cored structures, creating an innovative solution for the board industry. Bending tests were carried to evaluate the performance of the new sandwich solutions and to compare it against a typical one available on the market. Full article
Open AccessArticle
Statistical-Probabilistic Approach to the Lifetime and Strength Degradation of E-Glass Filaments and Bundles under Constant Tensile Loading in Water
J. Compos. Sci. 2019, 3(3), 78; https://doi.org/10.3390/jcs3030078
Received: 31 May 2019 / Revised: 8 July 2019 / Accepted: 11 July 2019 / Published: 1 August 2019
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Abstract
The present paper discusses the statistical features of static fatigue for E-glass multifilament tows in water. In such an aggressive environment, the glass fibres are sensitive to slow crack propagation from micron-sized flaws. Rupture and interrupted static fatigue tests under constant deformation in [...] Read more.
The present paper discusses the statistical features of static fatigue for E-glass multifilament tows in water. In such an aggressive environment, the glass fibres are sensitive to slow crack propagation from micron-sized flaws. Rupture and interrupted static fatigue tests under constant deformation in water, as well as tensile tests in inert environments on tows after fatigue were carried out on E-glass fibre tows that comprised around 2000 single filaments. The slow crack growth constants and the fast fracture statistical parameters for filaments were extracted from the outcome of experiments on tows, i.e., the load relaxation curves during fatigue and stress-strain curves during the tensile tests. These parameters provide a pertinent data base for the prediction of several characteristics in various conditions of fatigue for filaments and tows including statistical distributions of lifetimes and residual strengths, strength degradation during fatigue, size effects on lifetime and tow residual behaviour. Equations for calculation of filament lifetime and residual strength, and tow tensile behaviour were based on the model of slow crack growth and Weibull statistical distribution. Calculations using strength-probability-time relations provided insight into static fatigue behaviour of tows in water. Validity of the approach was assessed by the comparison of experimental and predicted tow residual behaviours. Full article
(This article belongs to the Special Issue Durability of Composites Under Severe Environmental Conditions)
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Open AccessArticle
Facile Synthesis and Surface Characterization of Titania-Incorporated Mesoporous Organosilica Materials
J. Compos. Sci. 2019, 3(3), 77; https://doi.org/10.3390/jcs3030077
Received: 4 June 2019 / Revised: 5 July 2019 / Accepted: 15 July 2019 / Published: 1 August 2019
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Abstract
Titania-incorporated organosilica-mesostructures (Ti-MO) were synthesized using tris [3-(trimethoxysilyl)propyl]isocyanurate, tetraethylorthosilicate as silica precursors, and titanium isopropoxide as the titanium precursor via a co-condensation method in the presence of the triblock copolymer, Pluronic P123. The triblock copolymer was completely removed by extraction with a 95% [...] Read more.
Titania-incorporated organosilica-mesostructures (Ti-MO) were synthesized using tris [3-(trimethoxysilyl)propyl]isocyanurate, tetraethylorthosilicate as silica precursors, and titanium isopropoxide as the titanium precursor via a co-condensation method in the presence of the triblock copolymer, Pluronic P123. The triblock copolymer was completely removed by extraction with a 95% ethanol solution, followed by a thermal treatment at 350 °C under flowing nitrogen without decomposing isocyanurate bridging groups. The molar ratio of titanium to silica in the mesostructures was gradually changed by increasing the amount of tetraethylorthosilicate in the initial reaction mixture. Our synthesis strategy also allowed us to tailor both adsorption and structural properties, including a well-developed specific surface area, high microporosity, and large pore volume. A portion of the samples was thermally treated at 600 °C to remove both the block copolymer and bridging groups. The thermal treatment at 600 °C was used to convert the amorphous titania into a crystalline anatase form. The Ti-MO materials were characterized using a N2 adsorption desorption analysis, thermogravimetric analysis (TGA), solid state nuclear magnetic resonance (NMR), transmission electron microscope (TEM), and X-ray powder diffraction (XRD). CO2 adsorption studies were also conducted to determine the basicity of the Ti-MO materials. The effect of the surface properties on the CO2 sorption was also identified. Full article
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Open AccessArticle
An Impedance Measurement Technique for Composite Materials Moisture Level Detection Devoted to Health Monitoring in Aeronautics
J. Compos. Sci. 2019, 3(3), 76; https://doi.org/10.3390/jcs3030076
Received: 8 January 2019 / Revised: 12 July 2019 / Accepted: 15 July 2019 / Published: 1 August 2019
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Abstract
The current design practice of composite material aeronautical structures imposes the use of knock-down structural material allowables to take into account the high sensitivity to environmental exposure (i.e., moisture, temperature, damages). The “moisture derating factor” comes from specific mechanical test campaign and drastically [...] Read more.
The current design practice of composite material aeronautical structures imposes the use of knock-down structural material allowables to take into account the high sensitivity to environmental exposure (i.e., moisture, temperature, damages). The “moisture derating factor” comes from specific mechanical test campaign and drastically reduces the advantage of using such materials; but the continuous monitoring of the moisture content of the structure could enable the use of higher design allowables. In the framework of FUSIMCO (Work developed within the frame of the Project FUSIMCO-FUSoliera Ibrida Metallo COmposito-co-financed by MIUR-Italian Ministry of Research with DAC-Campania Aerospace District as beneficiary and Leonardo Company-Aerostructure Division as “prime” partner) project, the aim of this study is to verify the effectiveness of the impedance measurement method as a health-monitoring tool to evaluate the moisture quantity absorbed by an aeronautical composite structure. The method is based on the idea that a composite laminate can be associated with an equivalent electric circuit (EEC). Some electrical characteristics of this EEC can be associated to the moisture content of the laminate. A simple EEC model, mainly capacitive, was used. A frequency sweep was the electric stimulus signal of some electrodes, glued onto the specimens to investigate the EEC parameters variation with respect to the induced moisture content variation (gravimetrically determined). The study confirmed the possibility of effectively using the impedance measurement method as a health-monitoring tool for moisture content evaluation of a composite laminate. Full article
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Open AccessArticle
A C-Doped TiO2/Fe3O4 Nanocomposite for Photocatalytic Dye Degradation under Natural Sunlight Irradiation
J. Compos. Sci. 2019, 3(3), 75; https://doi.org/10.3390/jcs3030075
Received: 11 June 2019 / Revised: 4 July 2019 / Accepted: 16 July 2019 / Published: 22 July 2019
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Abstract
Magnetically recyclable C-doped TiO2/Fe3O4 (C-TiO2/Fe3O4) nanocomposite was successfully synthesized via a sol–gel method. The synthesized samples were characterized using SEM, energy-dispersive X-ray spectroscopy (EDS), FTIR, and UV-VIS diffuse reflectance spectroscopy (DRS) techniques. [...] Read more.
Magnetically recyclable C-doped TiO2/Fe3O4 (C-TiO2/Fe3O4) nanocomposite was successfully synthesized via a sol–gel method. The synthesized samples were characterized using SEM, energy-dispersive X-ray spectroscopy (EDS), FTIR, and UV-VIS diffuse reflectance spectroscopy (DRS) techniques. The results clearly showed that a C-TiO2/Fe3O4 nanocomposite was produced. The photocatalytic activities of the prepared pristine (TiO2), C-doped TiO2 (C-TiO2) and C-TiO2/Fe3O4 were evaluated by the photodegradation of methyl orange (MO) under natural sunlight. The effect of catalyst loading and MO concentration were studied and optimized. The C-TiO2/Fe3O4 nanocomposite exhibited an excellent photocatalytic activity (99.68%) that was higher than the TiO2 (55.41%) and C-TiO2 (70%) photocatalysts within 150 min. The magnetic nanocomposite could be easily recovered from the treated solution by applying external magnetic field. The C-TiO2/Fe3O4 composite showed excellent photocatalytic performance for four consecutive photocatalytic reactions. Thus, this work could provide a simple method for the mass production of highly photoactive and stable C-TiO2/Fe3O4 photocatalyst for environmental remediation. Full article
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Open AccessArticle
Water Uptake in PHBV/Wollastonite Scaffolds: A Kinetics Study
J. Compos. Sci. 2019, 3(3), 74; https://doi.org/10.3390/jcs3030074
Received: 29 May 2019 / Revised: 26 June 2019 / Accepted: 10 July 2019 / Published: 16 July 2019
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Abstract
Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) is a widely studied polymer and it has been found that porous PHBV materials are suitable for substrates for cell cultures. A crucial factor for scaffolds designed for tissue engineering is the water uptake. This property influences the transport [...] Read more.
Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) is a widely studied polymer and it has been found that porous PHBV materials are suitable for substrates for cell cultures. A crucial factor for scaffolds designed for tissue engineering is the water uptake. This property influences the transport of water and nutrients into the scaffold, which promotes cell growth. PHBV has significant hydrophobicity, which can harm the production of cells. Thus, the addition of α-wollastonite (WOL) can modify the PHBV scaffold’s water uptake. To our knowledge, a kinetics study of water uptake of α-wollastonite phase powder and the PHBV matrix has not been reported. In this work, PHBV and WOL, (PHBV/WOL) films were produced with 0, 5, 10, and 20 wt % of WOL. Films were characterized, and the best concentrations were chosen to produce PHBV/WOL scaffolds. The addition of WOL in concentrations up to 10 wt % increased the cell viability of the films. MTT analysis showed that PHBV/5%WOL and PHBV/10%WOL obtained cell viability of 80% and 98%, respectively. Therefore, scaffolds with 0, 5 and 10 wt % of WOL were fabricated by thermally induced phase separation (TIPS). Scaffolds were characterized with respect to morphology and water uptake in assay for 65 days. The scaffold with 10 wt % of WOL absorbed 44.1% more water than neat PHBV scaffold, and also presented a different kinetic mechanism when compared to other samples. Accordingly, PHBV/WOL scaffolds were shown to be potential candidates for biological applications. Full article
(This article belongs to the Special Issue Nanocomposites for Biomedical Implants and Tissue Engineering)
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Open AccessReview
Progress in Experimental and Theoretical Evaluation Methods for Textile Permeability
J. Compos. Sci. 2019, 3(3), 73; https://doi.org/10.3390/jcs3030073
Received: 9 May 2019 / Revised: 30 June 2019 / Accepted: 2 July 2019 / Published: 10 July 2019
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Abstract
A great amount of attention has been given to the evaluation of the permeability tensor and several methods have been implemented for this purpose: experimental methods, as well as numerical and analytical methods. Numerical simulation tools are being seriously developed to cover the [...] Read more.
A great amount of attention has been given to the evaluation of the permeability tensor and several methods have been implemented for this purpose: experimental methods, as well as numerical and analytical methods. Numerical simulation tools are being seriously developed to cover the evaluation of permeability. However, the results are still far from matching reality. On the other hand, many problems still intervene in the experimental measurement of permeability, since it depends on several parameters including personal performance, preparation of specimens, equipment accuracy, and measurement techniques. Errors encountered in these parameters may explain why inconsistent measurements are obtained which result in unreliable experimental evaluation of permeability. However, good progress was done in the second international Benchmark, wherein a method to measure the in-plane permeability was agreed on by 12 institutes and universities. Critical researchers’ work was done in the field of analytical methods, and thus different empirical and analytical models have emerged, but most of those models need to be improved. Some of which are based on Cozeny-Karman equation. Others depend on numerical simulation or experiment to predict the macroscopic permeability. Also, the modeling of permeability of unidirectional fiber beds have taken the greater load of concern, whereas that of fiber bundle permeability prediction remain limited. This paper presents a review on available methods for evaluating unidirectional fiber bundles and engineering fabric permeability. The progress of each method is shown in order to clear things up. Full article
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Open AccessArticle
How the Mix Factors Affect the Dynamic Modulus of Hot-Mix Asphalt
J. Compos. Sci. 2019, 3(3), 72; https://doi.org/10.3390/jcs3030072
Received: 8 June 2019 / Revised: 30 June 2019 / Accepted: 2 July 2019 / Published: 10 July 2019
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Abstract
Hot-mix asphalt (HMA) is a composite material consisting of stone-aggregates, sand, asphalt binder and additives. The properties of this combined material are dependent on the volumetric parameters used in the mix design. This study investigates the effects of volumetric mix factors on the [...] Read more.
Hot-mix asphalt (HMA) is a composite material consisting of stone-aggregates, sand, asphalt binder and additives. The properties of this combined material are dependent on the volumetric parameters used in the mix design. This study investigates the effects of volumetric mix factors on the dynamic moduli (E*) of eleven categories of HMAs. For each category of asphalt mixture, the variations in dynamic modulus for different contractors, binder types, effective binder content (Vbe), air void (Va), voids-in-mineral aggregates (VMA), voids-filled-with asphalt (VFA) and asphalt content (AC) are assessed statistically. Results show that the S(100) mixture (nominal size of 19 mm, 100 gyrations) with the Performance Grade (PG) binder of PG 64-22 has the highest value of E* at low temperature or high reduced frequency. At high temperature or lower reduced frequency, S(100) PG 76-28 has the highest E* value. The SX(75) mixture (nominal size of 12.5 mm, 75 gyrations) with the binder of PG 64-28 has the lowest E* value at high temperature or lower reduced frequency. At low temperature or high reduced frequency, SX(75) PG 58-34 has the lowest E* value. The Stone Mix Asphalt (SMA) mix has a lower E* compared to S(100) and SX(100) mixes ((nominal size of 12.5 mm, 100 gyrations) with the Performance Grade (PG) binder of) at low temperature. The E* increases with an increase in Vbe, Va, and VFA, and decreases with an increase in VMA and AC. The E* of a mix can vary from 200 ksi (1380 MPa) to about 1000 ksi (6900 MPa) for a particular frequency (10 Hz) and temperature (21.1 °C), even if samples are from the same contractor. Full article
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Open AccessArticle
An Experimental Investigation of Combined Symmetric-Asymmetric Composite Laminates
J. Compos. Sci. 2019, 3(3), 71; https://doi.org/10.3390/jcs3030071
Received: 11 April 2019 / Revised: 10 June 2019 / Accepted: 3 July 2019 / Published: 10 July 2019
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Abstract
It has been found that certain asymmetric composite laminates exhibit bistability, where the composite laminate exhibits multiple stable static equilibrium states. If the bistable composite is actuated, it will snap to its secondary equilibrium state and then remain there without further actuation. This [...] Read more.
It has been found that certain asymmetric composite laminates exhibit bistability, where the composite laminate exhibits multiple stable static equilibrium states. If the bistable composite is actuated, it will snap to its secondary equilibrium state and then remain there without further actuation. This study investigates how the amount of symmetry in a combined symmetric asymmetric rectangular laminate under an imposed clamped edge boundary condition affects the bistability and the curvature of the laminate. Laminates with varying amounts of asymmetry were fabricated and then measured using a profilometer to capture the curvatures of the equilibrium shapes. The results showed that up to 20% symmetry can be introduced in the laminate without a substantial loss in snap through curvature, and that up to 83% symmetry can be introduced in the laminate before bistability is lost. Finite element simulations were conducted in Abaqus and showed good correlation with the experimental results. Full article
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Open AccessArticle
Al/Niobium Diboride Nanocomposite’s Effect on the Portevin-Le Chatelier Phenomenon in Al-Mg Alloys
J. Compos. Sci. 2019, 3(3), 70; https://doi.org/10.3390/jcs3030070
Received: 3 June 2019 / Revised: 18 June 2019 / Accepted: 7 July 2019 / Published: 10 July 2019
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Abstract
In Al-Mg alloys, the Portevin-Le Chatelier phenomenon, or dynamic strain aging, reveals itself as serrations upon plastic tensile deformation. This research evaluates this phenomenon when Al/NbB2 nanocomposite pellets are added to a magnesium-supersaturated Al matrix. A ball-milled 90 wt % Al and [...] Read more.
In Al-Mg alloys, the Portevin-Le Chatelier phenomenon, or dynamic strain aging, reveals itself as serrations upon plastic tensile deformation. This research evaluates this phenomenon when Al/NbB2 nanocomposite pellets are added to a magnesium-supersaturated Al matrix. A ball-milled 90 wt % Al and 10 wt % NbB2 nanocomposite helped inoculate an Al-Mg melt to incorporate the nanoparticles effectively. The melt was cast into rods that were cold-rolled into 1 mm diameter wires. Two sets were prepared: The first group was an as-cast set of samples, for comparison purposes, whereas the second was a solution-treated set. The solution treatment consisted of annealing followed by ice-water quenching. The results corroborating that the phenomenon was observable only in the specimens bearing the solution treatment, were used as the research baseline. Said treated alloy was compared to one containing the nanoparticles, which proved that the NbB2 particles caused a reduction of the serrated signal amplitude. Full article
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Open AccessFeature PaperArticle
Evaluation of Critical Parameters in Tensile Strength Measurement of Single Fibres
J. Compos. Sci. 2019, 3(3), 69; https://doi.org/10.3390/jcs3030069
Received: 8 May 2019 / Revised: 25 June 2019 / Accepted: 7 July 2019 / Published: 9 July 2019
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Abstract
Mechanical properties of fibre reinforced composites are primarily dependent on those of fibres. Fibre properties are used for estimating the damage and strength behaviour of composite materials and structures. Tensile strength of fibres is commonly determined by single fibre tensile tests, which is [...] Read more.
Mechanical properties of fibre reinforced composites are primarily dependent on those of fibres. Fibre properties are used for estimating the damage and strength behaviour of composite materials and structures. Tensile strength of fibres is commonly determined by single fibre tensile tests, which is challenging and is prone to measurement errors. In this study, different possible sources of errors due to experimental limitations in the fibre testing process were identified. Their effect on fibre tensile strength was analytically modelled. This model was used to evaluate the uncertainty in experimentally determined fibre strength. A sensitivity analysis was conducted to rank the relative significance of input quantities on the calculated fibre strength. Since composite models require fibre properties determined at very small gauge lengths, the results of the sensitivity analysis were extrapolated to determine critical parameters for tests done at those small gauge lengths of a few millimetres. It was shown that, for sufficiently long fibres, their strength depends mainly on the diameter and failure force; however, for shorter gauge lengths, the effects of misalignment become very significant. The knowledge of uncertainty would be useful in estimating the reliability of the predictions made by composite strength models on the damage and failure behaviour of composite materials and structures. Minimising the influence of critical parameters on fibre strength would help in designing improved single fibre testing systems capable of determining fibre strength more accurately. Full article
(This article belongs to the Special Issue Feature Papers in Journal of Composites Science in 2019)
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Open AccessFeature PaperArticle
Effect of Different Types of Block Copolymers on Morphology, Mechanical Properties, and Fracture Mechanisms of Bisphenol-F Based Epoxy System
J. Compos. Sci. 2019, 3(3), 68; https://doi.org/10.3390/jcs3030068
Received: 31 May 2019 / Revised: 19 June 2019 / Accepted: 1 July 2019 / Published: 4 July 2019
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Abstract
The effect of adding different types of soft block copolymer on the tensile properties, fracture mechanic properties, and thermo-mechanical properties of bisphenol F based epoxy resin were studied. Two different self-assembling block copolymers, (a) constituting of a center block of poly (butyl acrylate) [...] Read more.
The effect of adding different types of soft block copolymer on the tensile properties, fracture mechanic properties, and thermo-mechanical properties of bisphenol F based epoxy resin were studied. Two different self-assembling block copolymers, (a) constituting of a center block of poly (butyl acrylate) and two side blocks of poly (methyl) methacrylate-co-polar co-monomer (BCP 1) and (b) poly(ethylene oxide)-b-poly(butylene oxide) (PEO-PBO) diblock copolymer (BCP 2), were used with an epoxy-hardener system. The maximum fracture toughness and fracture energy were measured as KIc = 2.75 MPa·m1/2 and GIc = 2.37 kJ/m2 for the 10 wt % of BCP 1 modified system, which were 366% and 2270% higher in comparison to reference epoxy system, and a 63% reduction in tensile strength was also observed. Similarly, for BCP2 modified systems, the maximum value of KIc = 1.65 MPa·m1/2 and GIc = 1.10 kJ/m2 was obtained for epoxy modified with 12 wt % of BCP2 and a reduction of 32% in tensile strength. The fracture toughness and fracture energy were co-related to the plastic zone size for all the modified systems. Finally, the analysis of the fracture surfaces revealed the toughening micro-mechanisms of the nanocomposites. Full article
(This article belongs to the Special Issue Feature Papers in Journal of Composites Science in 2019)
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Open AccessFeature PaperArticle
Analysis and Evaluation of Fiber Orientation Reconstruction Methods
J. Compos. Sci. 2019, 3(3), 67; https://doi.org/10.3390/jcs3030067
Received: 24 May 2019 / Revised: 14 June 2019 / Accepted: 1 July 2019 / Published: 4 July 2019
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Abstract
The calculation of the fiber orientation of short fiber-reinforced plastics with the Fokker–Planck equation requires a considerable numerical effort, which is practically not feasible for injection molding simulations. Therefore, only the fiber orientation tensors are determined, i.e., by the Folgar–Tucker equation, which requires [...] Read more.
The calculation of the fiber orientation of short fiber-reinforced plastics with the Fokker–Planck equation requires a considerable numerical effort, which is practically not feasible for injection molding simulations. Therefore, only the fiber orientation tensors are determined, i.e., by the Folgar–Tucker equation, which requires much less computational effort. However, spatial fiber orientation must be reconstructed from the fiber orientation tensors in advance for structural simulations. In this contribution, two reconstruction methods were investigated and evaluated using generated test scenarios and experimentally measured fiber orientation. The reconstruction methods include spherical harmonics up to the 8th order and the method of maximum entropy, with which a Bingham distribution is reconstructed. It is shown that the quality of the reconstruction depends massively on the original fiber orientation to be reconstructed. If the original distribution can be regarded as a Bingham distribution in good approximation, the method of maximum entropy is superior to spherical harmonics. If there is no Bingham distribution, spherical harmonics is more suitable due to its greater flexibility, but only if sufficiently high orders of the fiber orientation tensor can be determined exactly. Full article
(This article belongs to the Special Issue Feature Papers in Journal of Composites Science in 2019)
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Open AccessArticle
On the Role of Bonding Time on Microstructure and Mechanical Properties of TLP Bonded Al/Mg2Si Composite
J. Compos. Sci. 2019, 3(3), 66; https://doi.org/10.3390/jcs3030066
Received: 21 May 2019 / Revised: 18 June 2019 / Accepted: 28 June 2019 / Published: 1 July 2019
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Abstract
Transient liquid phase diffusion bonding of an aluminum metal matrix composite with 15 wt.% Mg2Si reinforcement particles using Cu powder interlayer at 560 °C for different bonding times has been studied. Three different zones were identified at the bonding line: athermally [...] Read more.
Transient liquid phase diffusion bonding of an aluminum metal matrix composite with 15 wt.% Mg2Si reinforcement particles using Cu powder interlayer at 560 °C for different bonding times has been studied. Three different zones were identified at the bonding line: athermally solidified zone, isothermally solidified zone and base metal. By increasing the bonding time, due to the diffusion of copper to the substrate, the width of the athermally solidified zone decreased, became more homogenous and the amount of intermetallic phase (CuAl2) decreased. Therefore, the shear strength increased to a maximum of 60 MPa for the samples with a holding time of 5 h at the bonding temperature. Full article
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Open AccessArticle
Optimum Design of Carbon/Epoxy Composite Pressure Vessels Including Moisture Effects
J. Compos. Sci. 2019, 3(3), 65; https://doi.org/10.3390/jcs3030065
Received: 28 May 2019 / Revised: 14 June 2019 / Accepted: 24 June 2019 / Published: 1 July 2019
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Abstract
The main target of the present study is to preserve the structural integrity of the composite pressure vessels (PVs) used in the seawater reverse osmosis (SWRO) desalination plants under internal pressure loading when moisture effects are taken into consideration. Different composite material lay-ups [...] Read more.
The main target of the present study is to preserve the structural integrity of the composite pressure vessels (PVs) used in the seawater reverse osmosis (SWRO) desalination plants under internal pressure loading when moisture effects are taken into consideration. Different composite material lay-ups and fiber orientations are considered. In each case, the optimum safe thickness of the PV is found based on the appropriate failure criterion. The PVs are made of carbon/epoxy C/E IM7/977-3 with (±θ)ns lay-up. For verification purposes, PVs made from stainless steel SST 316L and carbon/epoxy C/E AS4/3501-6 are considered and their available results are compared with the predictions of the MATLAB code developed in this study. The study consists of three main cases. The first case considered the PVs materials SST 316L steel and C/E AS4/3501-6 carbon/epoxy composite, without moisturizing effect, with the purpose to verify the results of the developed MATLAB code by comparing with results from the available literature. The second case is concerned with the composite material C/E IM7/977-3, without moisture effects, while the third case included moisture effects on the same material (C/E IM7/977-3). The optimum angles found for C/E AS4/3501-6 is (±55.1)ns and for C/E IM7/977-3 with and without moisture are (±55.8)ns and (±54.0)ns, respectively. The best weight saving of the composite PV, when compared to the steel PV, reached 95.2%. Full article
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Open AccessFeature PaperArticle
The Role of Multiwalled Carbon Nanotubes in the Mechanical, Thermal, Rheological, and Electrical Properties of PP/PLA/MWCNTs Nanocomposites
J. Compos. Sci. 2019, 3(3), 64; https://doi.org/10.3390/jcs3030064
Received: 9 June 2019 / Revised: 23 June 2019 / Accepted: 25 June 2019 / Published: 1 July 2019
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Abstract
Polypropylene/polylactic acid (PP/PLA) blend (10–40% of PLA) and PP/PLA/MWCNTs nanocomposites (0.5, 1, and 2 wt% of MWCNTs) were prepared via melt compounding. Scanning electron microscopy revealed a co-continuous PLA phase in the PP/PLA blends with high PLA content. Moreover, the addition of 2 [...] Read more.
Polypropylene/polylactic acid (PP/PLA) blend (10–40% of PLA) and PP/PLA/MWCNTs nanocomposites (0.5, 1, and 2 wt% of MWCNTs) were prepared via melt compounding. Scanning electron microscopy revealed a co-continuous PLA phase in the PP/PLA blends with high PLA content. Moreover, the addition of 2 wt% multi-walled carbon nanotubes (MWCNTs) increased the tensile modulus and tensile strength of the PP/PLA40% by 60% and 95%, respectively. A conductive network was found with the addition of 2 wt% MWCNTs, where the electrical conductivity of the PP/PLA increased by nine orders of magnitude. At 2 wt% MWCNTs, a solid network within the composite was characterized by rheological assessment, where the composite turned from nonterminal to terminal behavior. Soil burial testing of the PP/PLA blend within 30 days in natural humus compost soil featured suitable biodegradation, which indicates the PP/PLA blend is as an appropriate candidate for food packing applications. Full article
(This article belongs to the Special Issue Feature Papers in Journal of Composites Science in 2019)
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Open AccessArticle
Constituents Phase Reconstruction through Applied Machine Learning in Nanoindentation Mapping Data of Mortar Surface
J. Compos. Sci. 2019, 3(3), 63; https://doi.org/10.3390/jcs3030063
Received: 30 May 2019 / Revised: 12 June 2019 / Accepted: 14 June 2019 / Published: 26 June 2019
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Abstract
In the present study, data generated from nanoindentation were used in order to reconstruct the surface constituent phases of mortar grids through machine learning algorithms. Specifically, the K-Means algorithm (unsupervised learning) was applied to two 49 measurement (7 × 7) datasets with information [...] Read more.
In the present study, data generated from nanoindentation were used in order to reconstruct the surface constituent phases of mortar grids through machine learning algorithms. Specifically, the K-Means algorithm (unsupervised learning) was applied to two 49 measurement (7 × 7) datasets with information about the modulus (E) and hardness (H) in order to discover the underlying structure of the data. The resulting clusters from K-Means were then evaluated and values range assigned so as to signify the various constituent phases of the mortar. Furthermore, another dataset from nanoindentation containing information about E, H, and the surface colour of the measured area (obtained from an optical microscope) was used as the training set in order to develop a random forests model (supervised learning), which predicts the surface colour from the E and H values. Colour predictions on the two 7 × 7 mortar grids were made and then possible correlations between the clusters, signifying constituent phases, and the predicted colours were examined. The groupings of data in the clusters (phases) corresponded to a unique surface colour. Finally, the constituent phases of the mortar grids were reconstructed in contour plots by assigning the corresponding cluster of the K-Means algorithm to each measurement (position in the grid). Full article
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