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J. Compos. Sci., Volume 5, Issue 1 (January 2021) – 35 articles

Cover Story (view full-size image): Radiopaque shape memory polymer (SMP) foams were developed for neurovascular embolization applications. X-ray visibility is required in embolization devices to ensure safe delivery of the devices to the targeted aneurysm site using fluoroscopy. The X-ray visibility of the SMP foams could be enhanced by adding varying degrees of highly radio-dense tantalum microparticles to a previously reported triiodobenzene-containing SMP foam premix. The developed SMP foams showed clinically relevant thermal properties, full volume expansions, good cytocompatibility, good mechanical properties, and appropriate radiopacities at neurovascular device scales. Thus, radiopaque SMP foams are very promising materials for use as neurovascular embolization devices. View this paper.
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Open AccessArticle
Designing Sensing Devices Using Porous Composite Materials
J. Compos. Sci. 2021, 5(1), 35; https://doi.org/10.3390/jcs5010035 - 19 Jan 2021
Viewed by 431
Abstract
The need for portable and inexpensive analytical devices for various critical issues has led researchers to seek novel materials to construct them. Soft porous materials, such as paper and sponges, are ideal candidates for fabricating such devices due to their light weight and [...] Read more.
The need for portable and inexpensive analytical devices for various critical issues has led researchers to seek novel materials to construct them. Soft porous materials, such as paper and sponges, are ideal candidates for fabricating such devices due to their light weight and high availability. More importantly, their great compatibility toward modifications and add-ons allows them to be customized to match different objectives. As a result, porous material-based composites have been extensively used to construct sensing devices applied in various fields, such as point-of-care testing, environmental sensing, and human motion detection. In this article, we present fundamental thoughts on how to design a sensing device based on these interesting composite materials and provide correlated examples for reader’s references. First, a rundown of devices made with porous composite materials starting from their fabrication techniques and compatible detection methods is given. Thereafter, illustrations are provided on how device function and property improvements are achieved with a delicate use of composite materials. This includes extending device lifetime by using polymer films to protect the base material, while signal readout can be enhanced by a careful selection of protective cover and the application of advanced photo image analysis techniques. In addition to chemical sensors, mechanical responsive devices based on conductive composite materials are also discussed with a focus on base material selection and platform design. We hope the ideas and discussions presented in this article can help researchers interested in designing sensing devices understand the importance and usefulness of composite materials. Full article
(This article belongs to the Special Issue Feature Papers in Journal of Composites Science in 2021)
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Open AccessArticle
Study on the Propagation of Stress Waves in Natural Fiber Composite Strips
J. Compos. Sci. 2021, 5(1), 34; https://doi.org/10.3390/jcs5010034 - 19 Jan 2021
Viewed by 309
Abstract
The propagation of Lamb waves within the structure of natural fiber reinforced composite strips is investigated using a semi-analytical solution and a time domain spectral finite element numerical method. The need to monitor the structural health of natural fiber reinforced composites is becoming [...] Read more.
The propagation of Lamb waves within the structure of natural fiber reinforced composite strips is investigated using a semi-analytical solution and a time domain spectral finite element numerical method. The need to monitor the structural health of natural fiber reinforced composites is becoming greater, as these sustainable composites are being increasingly used in various industrial applications in automotive and marine structures. Three different types of flax fiber composites were studied and the fundamental wave modes were excited on the structure. Both methods under consideration were able to capture the symmetric and antisymmetric wave modes for all the material configurations. Especially the complex nature of a hybrid flax/glass fiber composite was studied and results were very promising for future damage investigation. Further to this, an attempt was made to excite the hybrid strip at higher frequency and the study revealed the potential to capture all the existing wave modes. Full article
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Open AccessArticle
Thermal Shock Behavior of Twill Woven Carbon Fiber Reinforced Polymer Composites
J. Compos. Sci. 2021, 5(1), 33; https://doi.org/10.3390/jcs5010033 - 18 Jan 2021
Viewed by 303
Abstract
In the current research, the effect of cyclic temperature variation on the mechanical and thermal properties of woven carbon-fiber-reinforced polymer (CFRP) composites was investigated. To this, carbon fiber textiles in twill 2/2 pattern were used as reinforced phase in epoxy, and CFRPs were [...] Read more.
In the current research, the effect of cyclic temperature variation on the mechanical and thermal properties of woven carbon-fiber-reinforced polymer (CFRP) composites was investigated. To this, carbon fiber textiles in twill 2/2 pattern were used as reinforced phase in epoxy, and CFRPs were fabricated by vacuum-assisted resin-infusion molding (VARIM) method. Thermal cycling process was carried out between −40 and +120 °C for 20, 40, 60 and 80 cycles, in order to evaluate the effect of thermal cycling on mechanical and thermal properties of CFRP specimens. In this regard, tensile, bending and short beam shear (SBS) experiments were carried out, to obtain modulus of elasticity, tensile strength, flexural modulus, flexural strength and inter-laminar shear strength (ILSS) at room temperature (RT), and then thermal treated composites were compared. A dynamic mechanical analysis (DMA) test was carried out to obtain thermal properties, and viscoelastic properties, such as storage modulus (E’), loss modulus (E”) and loss factors (tan δ), were evaluated. It was observed that the characteristics of composites were affected by thermal cycling due to post-curing at a high temperature. This process worked to crosslink and improve the composite behavior or degrade it due to the different coefficients of thermal expansion (CTEs) of composite components. The response of composites to the thermal cycling process was determined by the interaction of these phenomena. Based on SEM observations, the delamination, fiber pull-out and bundle breakage were the dominant fracture modes in tensile-tested specimens. Full article
(This article belongs to the Special Issue Carbon Fiber Composites)
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Open AccessArticle
Investigating the Effect of Interface Morphology in Adhesively Bonded Composite Wavy-Lap Joints
J. Compos. Sci. 2021, 5(1), 32; https://doi.org/10.3390/jcs5010032 - 17 Jan 2021
Viewed by 425
Abstract
Joints and interfaces are one of the key aspects of the design and production of composite structures. This paper investigates the effect of adhesive–adherend interface morphology on the mechanical behavior of wavy-lap joints with the aim to improve the mechanical performance. Intentional deviation [...] Read more.
Joints and interfaces are one of the key aspects of the design and production of composite structures. This paper investigates the effect of adhesive–adherend interface morphology on the mechanical behavior of wavy-lap joints with the aim to improve the mechanical performance. Intentional deviation from a flat joint plane was introduced in different bond angles (0°, 60°, 90° and 120°) and the joints were subjected to a quasi-static tensile load. Comparisons were made regarding the mechanical behavior of the conventional flat joint and the wavy joints. The visible failure modes that occurred within each of the joint configurations was also highlighted and explained. Load vs. displacement graphs were produced and compared, as well as the failure modes discussed both visually and qualitatively. It was observed that distinct interface morphologies result in variation in the load–displacement curve and damage types. The wavy-lap joints experience a considerably higher displacement due to the additional bending in the joint area, and the initial damage starts occurring at a higher displacement. However, the load level had its maximum value for the single-lap joints. Our findings provide insight for the development of different interface morphology angle variation to optimize the joints behavior, which is widely observed in some biological systems to improve their performance. Full article
(This article belongs to the Special Issue Feature Papers in Journal of Composites Science in 2021)
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Open AccessArticle
Mechanical Characterization of Two Dental Restorative Materials after Acidic Challenge
J. Compos. Sci. 2021, 5(1), 31; https://doi.org/10.3390/jcs5010031 - 16 Jan 2021
Viewed by 324
Abstract
The aim of this study was to determine the effect of acidic beverages on the mechanical characteristics of a nanofilled composite resin and of a glass ionomer. Thirty specimens of each restorative material were produced and were evaluated at three different time points: [...] Read more.
The aim of this study was to determine the effect of acidic beverages on the mechanical characteristics of a nanofilled composite resin and of a glass ionomer. Thirty specimens of each restorative material were produced and were evaluated at three different time points: before immersion (T0), after a 7 day immersion (T1) and after a 14 day immersion (T2) in water, beer and a soft drink. The studied parameters were microhardness and surface roughness. At T2, composite resin and glass ionomer specimens immersed in water, beer and the soft drink showed a statistically significant decrease in microhardness compared to T0 results. The surface roughness of composite resin specimens decreased between T0 and T1/T2 after immersion in beer and soft drink. A statistically significant increase was found between the roughness of glass ionomer specimens immersed in each one of the beverages at T0 and T1/T2. It is essential that clinicians are aware not only of available restorative materials, its characteristics and best handling techniques but also of the importance of performing an adequate assessment of patients’ dietary habits, thus making it possible to offer patients quality treatments with a predictable prognosis and longevity. Full article
(This article belongs to the Special Issue Composites: Biomaterials in Dental Fields)
Open AccessArticle
Development of A Nano-Apatite Based Composite Sealer for Endodontic Root Canal Filling
J. Compos. Sci. 2021, 5(1), 30; https://doi.org/10.3390/jcs5010030 - 16 Jan 2021
Viewed by 265
Abstract
Recently, endodontic sealers based on injectable bioactive materials were proposed to improve the filling of anatomical irregularities during root canal obturation. In this context, this preliminary work investigated the possibility of realizing a new calcium phosphate-based composite sealer for root canal filling with [...] Read more.
Recently, endodontic sealers based on injectable bioactive materials were proposed to improve the filling of anatomical irregularities during root canal obturation. In this context, this preliminary work investigated the possibility of realizing a new calcium phosphate-based composite sealer for root canal filling with an optimized composition on setting kinetics and dentin tubules occlusion. Several calcium phosphate/liquid phase mixtures were initially evaluated for their workability, finding two suitable formulations. Both of them contained 66 wt.% of a nano-apatite-based cement (solid powdered phase). The liquid phase (34 wt.%) comprised 13.6% propanediol and 20.4% PEG 1000 (formulation 1), and formulation 2 comprised 27.2% glycerin and 6.8% PEG 200 (formulation 2). Then, these formulations were tested by means of permeability measurements and observation by scanning electron microscopy of treated model dentin samples. Both formulations succeeded in occluding dentinal tubules: the first one was able to create a full-bodied layer on dentin surface and, moreover, to resist, at least to a large extent, against citric acid attack. The second one showed a lower effectiveness after citric acid exposure. The composite compound that better satisfied the overall required characteristics of use, workability and sealing capacity was formulation 1. Full article
(This article belongs to the Special Issue Polymer Composites: Fabrication and Applications)
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Open AccessReview
Fused Deposition Modelling of Fibre Reinforced Polymer Composites: A Parametric Review
J. Compos. Sci. 2021, 5(1), 29; https://doi.org/10.3390/jcs5010029 - 16 Jan 2021
Viewed by 366
Abstract
Fused deposition modelling (FDM) is a widely used additive layer manufacturing process that deposits thermoplastic material layer-by-layer to produce complex geometries within a short time. Increasingly, fibres are being used to reinforce thermoplastic filaments to improve mechanical performance. This paper reviews the available [...] Read more.
Fused deposition modelling (FDM) is a widely used additive layer manufacturing process that deposits thermoplastic material layer-by-layer to produce complex geometries within a short time. Increasingly, fibres are being used to reinforce thermoplastic filaments to improve mechanical performance. This paper reviews the available literature on fibre reinforced FDM to investigate how the mechanical, physical, and thermal properties of 3D-printed fibre reinforced thermoplastic composite materials are affected by printing parameters (e.g., printing speed, temperature, building principle, etc.) and constitutive materials properties, i.e., polymeric matrices, reinforcements, and additional materials. In particular, the reinforcement fibres are categorized in this review considering the different available types (e.g., carbon, glass, aramid, and natural), and obtainable architectures divided accordingly to the fibre length (nano, short, and continuous). The review attempts to distil the optimum processing parameters that could be deduced from across different studies by presenting graphically the relationship between process parameters and properties. This publication benefits the material developer who is investigating the process parameters to optimize the printing parameters of novel materials or looking for a good constituent combination to produce composite FDM filaments, thus helping to reduce material wastage and experimental time. Full article
(This article belongs to the Special Issue Advanced Fiber Reinforced Polymer Composites)
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Open AccessReview
Composite Material Recycling Technology—State-of-the-Art and Sustainable Development for the 2020s
J. Compos. Sci. 2021, 5(1), 28; https://doi.org/10.3390/jcs5010028 - 15 Jan 2021
Viewed by 702
Abstract
Recently, significant events took place that added immensely to the sociotechnical pressure for developing sustainable composite recycling solutions, namely (1) a ban on composite landfilling in Germany in 2009, (2) the first major wave of composite wind turbines reaching their End-of-Life (EoL) and [...] Read more.
Recently, significant events took place that added immensely to the sociotechnical pressure for developing sustainable composite recycling solutions, namely (1) a ban on composite landfilling in Germany in 2009, (2) the first major wave of composite wind turbines reaching their End-of-Life (EoL) and being decommissioned in 2019–2020, (3) the acceleration of aircraft decommissioning due to the COVID-19 pandemic, and (4) the increase of composites in mass production cars, thanks to the development of high volume technologies based on thermoplastic composites. Such sociotechnical pressure will only grow in the upcoming decade of 2020s as other countries are to follow Germany by limiting and banning landfill options, and by the ever-growing number of expired composites EoL waste. The recycling of fiber reinforced composite materials will therefore play an important role in the future, in particular for the wind energy, but also for aerospace, automotive, construction and marine sectors to reduce environmental impacts and to meet the demand. The scope of this manuscript is a clear and condensed yet full state-of-the-art overview of the available recycling technologies for fiber reinforced composites of both low and high Technology Readiness Levels (TRL). TRL is a framework that has been used in many variations across industries to provide a measurement of technology maturity from idea generation (basic principles) to commercialization. In other words, this work should be treated as a technology review providing guidelines for the sustainable development of the industry that will benefit the society. The authors propose that one of the key aspects for the development of sustainable recycling technology is to identify the optimal recycling methods for different types of fiber reinforced composites. Why is that the case can be answered with a simple price comparison of E-glass fibers (~2 $/kg) versus a typical carbon fiber on the market (~20 $/kg)—which of the two is more valuable to recover? However, the answer is more complicated than that—the glass fiber constitutes about 90% of the modern reinforcement market, and it is clear that different technologies are needed. Therefore, this work aims to provide clear guidelines for economically and environmentally sustainable End-of-Life (EoL) solutions and development of the fiber reinforced composite material recycling. Full article
(This article belongs to the Special Issue From Waste to Advance Composite Materials)
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Open AccessArticle
Evaluation of Single-Lap and Block Shear Test Methods in Adhesively Bonded Composite Joints
J. Compos. Sci. 2021, 5(1), 27; https://doi.org/10.3390/jcs5010027 - 15 Jan 2021
Viewed by 294
Abstract
Adhesive bonding is increasingly being used for composite structures, especially in aerospace and automotive industries. One common joint configuration used to test adhesive strength is the single-lap shear joint, which has been widely studied and shown to produce significant normal (peeling) stresses. When [...] Read more.
Adhesive bonding is increasingly being used for composite structures, especially in aerospace and automotive industries. One common joint configuration used to test adhesive strength is the single-lap shear joint, which has been widely studied and shown to produce significant normal (peeling) stresses. When bonding composite structures, the normal stresses are capable of causing delamination before the adhesive bond fails, providing inconclusive engineering data regarding the bonding strength. An alternative test is the block shear joint, which uses a shorter sample geometry and a compressive-shear loading to reduce normal stresses. Analytical models proposed by Goland and Reissner and Hart-Smith are used to compare the edge-bending moment for the two joint configurations. The stress distributions along the bondline are also compared using finite element analysis. Experimental tests are conducted to evaluate these analyses and the failure modes of each configuration are recorded. Block shear samples demonstrate a joint strength over 100% higher than single-lap shear specimen bonded with the same adhesive material. The lower joint strength measured in single-lap shear is found to be potentially misleading due to delamination of the composite adherend. Full article
(This article belongs to the Special Issue Feature Papers in Journal of Composites Science in 2021)
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Open AccessArticle
Coefficient of Thermal Expansion of Single-Wall Carbon Nanotube Reinforced Nanocomposites
J. Compos. Sci. 2021, 5(1), 26; https://doi.org/10.3390/jcs5010026 - 14 Jan 2021
Viewed by 322
Abstract
A study on the coefficient of thermal expansion (CTE) of single-wall carbon nanotube (SWCNT)-reinforced nanocomposites is presented in this paper. An interfacial adhesion factor (IAF) is introduced for the purpose of modelling the adhesion between SWCNTs and the matrix. The effective CTE and [...] Read more.
A study on the coefficient of thermal expansion (CTE) of single-wall carbon nanotube (SWCNT)-reinforced nanocomposites is presented in this paper. An interfacial adhesion factor (IAF) is introduced for the purpose of modelling the adhesion between SWCNTs and the matrix. The effective CTE and modulus of SWCNTs are derived using the IAF, and the effective CTE of the nanocomposite is derived by the Mori–Tanaka method. The developed model is validated against experimental data and good agreement is found. Full article
(This article belongs to the Special Issue Feature Papers in Journal of Composites Science in 2020)
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Open AccessArticle
Single Wall Carbon Nanotubes/Polypyrrole Composite Thin Film Electrodes: Investigation of Interfacial Ion Exchange Behavior
J. Compos. Sci. 2021, 5(1), 25; https://doi.org/10.3390/jcs5010025 - 14 Jan 2021
Viewed by 322
Abstract
Single-wall carbon nanotubes/polypyrrole (SWCNT/PPy) composite thin-film electrodes were prepared by electrodeposition of the pyrrole monomer on a porous network made of SWCNT bundles. Electrode/electrolyte interface, which is intimately related to the pseudocapacitive charge storage behavior, is investigated by using coupled electrogravimetric methods (electrochemical [...] Read more.
Single-wall carbon nanotubes/polypyrrole (SWCNT/PPy) composite thin-film electrodes were prepared by electrodeposition of the pyrrole monomer on a porous network made of SWCNT bundles. Electrode/electrolyte interface, which is intimately related to the pseudocapacitive charge storage behavior, is investigated by using coupled electrogravimetric methods (electrochemical quartz crystal microbalance (EQCM) and its coupling with electrochemical impedance spectroscopy, Ac-electrogravimetry), in a 0.5 M NaCl electrolyte (pH = 7). Our results show that the range of usable potential is greater for composite SWCNT/PPy films than for SWCNT films, which should allow a higher storage capacity to be obtained. This effect is also confirmed by mass variation measurements via EQCM. The mass change (corresponding to the amount of (co)electroadsorbed species) obtained with composite SWCNT/PPy films is four times greater than that observed for pristine SWCNT films if the same potential range is examined. The permselectivity is also greatly improved in the case of composite SWCNT/PPy films compared to SWCNT films; the former shows mainly cation exchange preference. The quantities of anions estimated by Ac-electrogravimetric measurements are much lower in the case of composites. This corroborates the better permselectivity of these composite SWCNT/PPy films even with a moderate amount of PPy. Full article
(This article belongs to the Special Issue Feature Papers in Journal of Composites Science in 2020)
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Open AccessArticle
Mechanical, Thermal, and Morphological Properties of Graphene Nanoplatelet-Reinforced Polypropylene Nanocomposites: Effects of Nanofiller Thickness
J. Compos. Sci. 2021, 5(1), 24; https://doi.org/10.3390/jcs5010024 - 14 Jan 2021
Viewed by 636
Abstract
In this work, polypropylene (PP) and graphene nanoplatelet (GNPs) composites are routed through twin screw mixing and injection moulding. Two types of GNPs with a fixed size of 25 µm with surface areas ranging from 50–80 m2/g (H25, average thickness 15 [...] Read more.
In this work, polypropylene (PP) and graphene nanoplatelet (GNPs) composites are routed through twin screw mixing and injection moulding. Two types of GNPs with a fixed size of 25 µm with surface areas ranging from 50–80 m2/g (H25, average thickness 15 nm) and 120–150 m2/g (M25, average thickness 6–8 nm) were blended with PP at loading rates of 1, 2, 3, 4, and 5 weight%. Mechanical properties such as tensile, flexural, and impact strengths and Young’s modulus (Ε) are determined. The X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), field emission scanning electron microscopy (FESEM), and polarised light microscopy (PLM) techniques are used to understand the crystallisation, thermal, dynamic mechanical, and structural behaviour of the prepared composites. The improvement of mechanical strength is observed with GNP loading for both grades. Decreasing the GNP thickness decreases the impact strength and on the other hand improves the tensile and flexural strengths and Young’s modulus. Maximum tensile (≈33 MPa) and flexural (≈58.81 MPa) strength is found for the composite carrying 5 wt% M25. However, maximum impact strength (0.197 J) is found for PP-5 wt% H25. XRD analysis confirms GNPs have an induction effect on PP’s β phase crystal structure. The PP-GNP composite exhibits better thermal stability based on determining the TD (degradation temperature), T10 (temperature at 10% weight loss), T50 (temperature at 50% weight loss), and TR (temperature at residual weight). Enhancement in melt (Tm) and crystallisation temperatures (Tc) is are observed due to a heterogeneous nucleation effect. The FESEM analysis concludes that the GNP thickness has a significant effect on the degree of dispersion and agglomeration. The smaller the thickness, the better is the dispersion and the lower is the agglomeration. Overall, the use of thinner GNPs is more advantageous in improving the polymer properties. Full article
(This article belongs to the Special Issue Carbon-Based Polymer Nanocomposites)
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Open AccessReview
Nanocomposites for Enhanced Osseointegration of Dental and Orthopedic Implants Revisited: Surface Functionalization by Carbon Nanomaterial Coatings
J. Compos. Sci. 2021, 5(1), 23; https://doi.org/10.3390/jcs5010023 - 14 Jan 2021
Viewed by 435
Abstract
Over the past few decades, carbon nanomaterials, including carbon nanofibers, nanocrystalline diamonds, fullerenes, carbon nanotubes, carbon nanodots, and graphene and its derivatives, have gained the attention of bioengineers and medical researchers as they possess extraordinary physicochemical, mechanical, thermal, and electrical properties. Recently, surface [...] Read more.
Over the past few decades, carbon nanomaterials, including carbon nanofibers, nanocrystalline diamonds, fullerenes, carbon nanotubes, carbon nanodots, and graphene and its derivatives, have gained the attention of bioengineers and medical researchers as they possess extraordinary physicochemical, mechanical, thermal, and electrical properties. Recently, surface functionalization with carbon nanomaterials in dental and orthopedic implants has emerged as a novel strategy for reinforcement and as a bioactive cue due to their potential for osseointegration. Numerous developments in fabrication and biological studies of carbon nanostructures have provided various novel opportunities to expand their application to hard tissue regeneration and restoration. In this minireview, the recent research trends in surface functionalization of orthopedic and dental implants with coating carbon nanomaterials are summarized. In addition, some seminal methodologies for physicomechanical and electrochemical coatings are discussed. In conclusion, it is shown that further development of surface functionalization with carbon nanomaterials may provide innovative results with clinical potential for improved osseointegration after implantation. Full article
(This article belongs to the Special Issue Feature Papers in Journal of Composites Science in 2021)
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Open AccessReview
Biomimetics and Composite Materials toward Efficient Mobility: A Review
J. Compos. Sci. 2021, 5(1), 22; https://doi.org/10.3390/jcs5010022 - 13 Jan 2021
Viewed by 484
Abstract
The development of new materials has always been strictly related to the rise of new technologies and progressively efficient systems. However, cutting-edge materials might not be enough to ensure the effectiveness of a given product if the design guidelines used do not favor [...] Read more.
The development of new materials has always been strictly related to the rise of new technologies and progressively efficient systems. However, cutting-edge materials might not be enough to ensure the effectiveness of a given product if the design guidelines used do not favor the specific advantages of this material. Polymeric composites are known for their excellent mechanical properties, but current manufacturing techniques and the relatively narrow expertise in the field amongst engineers impose the challenge to provide the most suitable designs to certain applications. Bio-inspired designs, supported by thousands of years of evolution of nature, have shown to be extremely profitable tools for the design of optimized yet structurally complex shapes in which the tailoring aspect of polymeric composites perfectly fit. Bearing in mind the current but old-fashioned designs of auto-parts and vehicles built with metals with little or no topological optimization, the present work addresses how biomimicry is being applied in the mobility industry nowadays to provide lightweight structures and efficient designs. A general overview of biomimicry is made regarding vehicles, approaching how the use of composite materials has already contributed to successful cases. Full article
(This article belongs to the Special Issue Feature Papers in Journal of Composites Science in 2021)
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Open AccessArticle
Ballistic Penetration Analysis of Soft Laminated Composites Using Sublaminate Mesoscale Modeling
J. Compos. Sci. 2021, 5(1), 21; https://doi.org/10.3390/jcs5010021 - 08 Jan 2021
Viewed by 376
Abstract
Ballistic impact mitigation requires the development of protective armor applications from composite material systems with good energy absorption and penetration resistance against threats, e.g., metallic projectiles. In this aim, high-strength and high-stiffness soft fibrous composite materials (such as ultra-high molecular weight polyethylene—UHMWPE) are [...] Read more.
Ballistic impact mitigation requires the development of protective armor applications from composite material systems with good energy absorption and penetration resistance against threats, e.g., metallic projectiles. In this aim, high-strength and high-stiffness soft fibrous composite materials (such as ultra-high molecular weight polyethylene—UHMWPE) are often used. The high specific strength feature is one of the main reasons for using these soft composite systems in ballistic impact applications. In the present investigation, experimental and computational finite element (FE) studies were carried out to investigate the ballistic behaviors of these soft layered composite targets. To this end, a new FE multi-scale analysis framework for ballistic simulations is offered. The proposed analysis presents a new meso-scale sublaminate material model, which is applied to Dyneema® cross-ply laminate in order to predict its behavior under ballistic impact. The sublaminate model is implemented within an explicit dynamic FE code to simulate the continuum response in each element. The sublaminate model assumes a through-thickness periodic stacking of repeated cross-ply configuration. In addition, a cohesive layer is introduced in the sublaminate model in order to simulate the delamination effect leading to the subsequent degradation and deletion of the elements. This new approach eliminates the widely used costly computational approach of using explicit cohesive elements installed at pre-specified potential delamination paths between the layers. Furthermore, in-plane damage modes (such as fiber tensile, and out-of-plane shearing) are also accounted for by employing failure criteria and strain-softening. The obtained quantitative results of ballistic impact simulations show good correlation when compared to a relatively wide range of experiments. Moreover, the simulations include evidence of capturing the main energy absorption mechanisms under high-velocity impact. The proposed modeling approach can be used as a useful armor design tool. Full article
(This article belongs to the Special Issue Feature Papers in Journal of Composites Science in 2020)
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Open AccessArticle
A Raman Spectroscopic Analysis of Polymer Membranes with Graphene Oxide and Reduced Graphene Oxide
J. Compos. Sci. 2021, 5(1), 20; https://doi.org/10.3390/jcs5010020 - 08 Jan 2021
Cited by 1 | Viewed by 465
Abstract
Nowadays, despite significant advances in the field of biomaterials for tissue engineering applications, novel bone substituents still need refinement so they can be successfully implemented into the medical treatment of bone fractures. Generally, a scaffold made of synthetic polymer blended with nanofillers was [...] Read more.
Nowadays, despite significant advances in the field of biomaterials for tissue engineering applications, novel bone substituents still need refinement so they can be successfully implemented into the medical treatment of bone fractures. Generally, a scaffold made of synthetic polymer blended with nanofillers was proven to be a very promising biomaterial for tissue engineering, however the choice of components for the said scaffold remains questionable. The objects of the presented study were novel composites consisting of poly(ε-caprolactone) (PCL) and two types of graphene materials: graphene oxide (GO) and partially reduced graphene oxide (rGO). The technique of choice, that was used to characterize the obtained composites, was Raman micro-spectroscopy. It revealed that the composite PCL/GO differs substantially from the PCL/rGO composite. The incorporation of the GO particles into the polymer influenced the structure organisation of the polymeric matrix more significantly than rGO. The crystallinity parameters confirmed that the level of crystallinity is generally higher in the PCL/GO membrane in comparison to PCL/rGO (and even in raw PCL) that leads to the conclusion that the GO acts as a nucleation agent enhancing the crystallization of PCL. Interestingly, the characteristics of the studied nanofillers, for example: the level of the organisation (D/G ratio) and the in-plane size of the nano-crystallites (La) almost do not differ. However, they have an ability to influence polymeric matrix differently. Full article
(This article belongs to the Special Issue Feature Papers in Journal of Composites Science in 2020)
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Open AccessReview
Modeling Strategies of Finite Element Simulation of Reinforced Concrete Beams Strengthened with FRP: A Review
J. Compos. Sci. 2021, 5(1), 19; https://doi.org/10.3390/jcs5010019 - 08 Jan 2021
Viewed by 327
Abstract
Fiber-reinforced polymer (FRP) composites do not only possess superior mechanical properties, but can also be easy to tailor, install, and maintain. As such, FRPs offer novel and attractive solutions to facilitate strengthening and/or retrofitting of aging, weakened, and upgraded structures. Despite the availability [...] Read more.
Fiber-reinforced polymer (FRP) composites do not only possess superior mechanical properties, but can also be easy to tailor, install, and maintain. As such, FRPs offer novel and attractive solutions to facilitate strengthening and/or retrofitting of aging, weakened, and upgraded structures. Despite the availability of general code provisions, the design and analysis of FRP-strengthened concrete structures is both tedious and complex—especially in scenarios associated with unique loading conditions. As such, designers often leverage advanced finite element (FE) simulation as a mean to understand and predict the performance of FRP-strengthened structures. In order to narrow this knowledge gap, this paper details suitable strategy for developing and carrying out advanced FE simulations on FRP-strengthened concrete structures. The paper also covers techniques related to simulating adhesives (bonding agents), material constitutive properties and plasticity (cracking/crushing of concrete, yielding of steel reinforcement, and delamination of FRP laminates), as well as different material types of FRP (CFRP, GFRP, and their hybrid combinations), and FRP strengthening systems (sheets, plates, NSM, and rods) under various loading conditions including ambient, earthquake, and fire. The principles, thumb rules, and findings of this work can be of interest to researchers, practitioners, and students. Full article
(This article belongs to the Special Issue Polymer Composites and Fibers)
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Open AccessArticle
The Structure and Crystallizing Process of NiAu Alloy: A Molecular Dynamics Simulation Method
J. Compos. Sci. 2021, 5(1), 18; https://doi.org/10.3390/jcs5010018 - 07 Jan 2021
Viewed by 342
Abstract
This paper studies the influence of factors such as heating rate, atomic number, temperature, and annealing time on the structure and the crystallization process of NiAu alloy. Increasing the heating rate leads to the moving process from the crystalline state to the amorphous [...] Read more.
This paper studies the influence of factors such as heating rate, atomic number, temperature, and annealing time on the structure and the crystallization process of NiAu alloy. Increasing the heating rate leads to the moving process from the crystalline state to the amorphous state; increasing the temperature (T) also leads to a changing process into the liquid state; when the atomic number (N), and t increase, it leads to an increased crystalline process. As a result, the dependence between size (l) and atomic number (N), the total energy of the system (Etot) with N as l~N−1/3, and −Etot always creates a linear function of N, glass temperature (Tg) of the NiAu alloy, which is Tg = 600 K. During the study, the number of the structural units was determined by the Common Neighborhood Analysis (CNA) method, radial distribution function (RDF), size (l), and Etot. The result shows that the influencing factors to the structure of NiAu alloy are considerable. Full article
(This article belongs to the Special Issue Multifunctional Composites)
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Open AccessArticle
Designing Hierarchical Honeycombs to Mimic the Mechanical Behaviour of Composites
J. Compos. Sci. 2021, 5(1), 17; https://doi.org/10.3390/jcs5010017 - 07 Jan 2021
Viewed by 334
Abstract
Honeycombs are used ubiquitously in engineering applications as they have excellent out-of-plane strength and stiffness properties with respect to weight. This paper considers the properties of honeycombs in the in-plane direction, a direction that is significantly weaker and less stiff than the out-of-plane [...] Read more.
Honeycombs are used ubiquitously in engineering applications as they have excellent out-of-plane strength and stiffness properties with respect to weight. This paper considers the properties of honeycombs in the in-plane direction, a direction that is significantly weaker and less stiff than the out-of-plane direction. We assess how judiciously locating structural hierarchy within a honeycomb array can be a geometric design principle with direct consequences on the mechanical behaviour of the honeycomb. Here, we use finite element methods to design reinforced honeycomb mechanical metamaterials that mimic the mechanical behaviour of unidirectional fibre reinforced composites. We specifically incorporate structural hierarchy within hollow honeycomb cells to create mechanical metamaterial pseudo-composites, where the hierarchical parts are pseudo-fibres, and the hollow parts are the pseudo-matrix. We find that pseudo-fibre contribution coefficients are higher than the fibre contribution coefficient of carbon fibre reinforced plastics (CFRP). We also find that the elastic modulus of unidirectional pseudo-composites can be predicted using the (Voigt model) rule of mixtures with a good level of accuracy. Full article
(This article belongs to the Special Issue Feature Papers in Journal of Composites Science in 2020)
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Open AccessArticle
Influence of SiC Addition on Mechanical Behavior of Thermal Barriers with the Aid of Acoustic Emission
J. Compos. Sci. 2021, 5(1), 16; https://doi.org/10.3390/jcs5010016 - 07 Jan 2021
Viewed by 299
Abstract
The improvement of high temperature materials with lower heat transfer coefficients lead to the development of thermal barrier coatings (TBCs). One of the most widely used materials for thermal barrier coatings is Y2O3 stabilized ZrO2 (Y-TZP) because of its [...] Read more.
The improvement of high temperature materials with lower heat transfer coefficients lead to the development of thermal barrier coatings (TBCs). One of the most widely used materials for thermal barrier coatings is Y2O3 stabilized ZrO2 (Y-TZP) because of its excellent shock resistance, low thermal conductivity, and relatively high coefficient of thermal expansion. The aim of this work is to study the TBCs mechanical behavior with the addition of SiC into the suspension of Y-TZP/Al2O3 by acoustic emission (AE). Additionally, a microstructural analysis and a finite elements model were carried out in order to compare results. The coatings were made by suspension plasma spray (SPS) on metal plates of 70 × 12 × 2 mm3. An intermetallic was deposited as a bond coating, followed by a coating of Y-TZP/Al2O3 with and without 15 wt.% SiC, with thicknesses between 87 and 161 μm. The AE becomes a fundamental tool in the study of the mechanical behavior of thermal barriers. The use of wavelet transforms streamlines the study and analysis of recorded sound spectra. The crack generation arises at very low stress levels. Full article
(This article belongs to the Special Issue Progress in Si-based Ceramic and Composites)
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Open AccessEditorial
Editorial for the Special Issue: Multifunctional Composites in the Journal of Composites Science
J. Compos. Sci. 2021, 5(1), 15; https://doi.org/10.3390/jcs5010015 - 07 Jan 2021
Viewed by 260
Abstract
With the progress in nanotechnology and production methods, composite materials are becoming lighter, cheaper, more durable, and more versatile [...] Full article
(This article belongs to the Special Issue Multifunctional Composites)
Open AccessArticle
Enhanced X-ray Visibility of Shape Memory Polymer Foam Using Iodine Motifs and Tantalum Microparticles
J. Compos. Sci. 2021, 5(1), 14; https://doi.org/10.3390/jcs5010014 - 06 Jan 2021
Viewed by 450
Abstract
Shape memory polymer (SMP) foams are porous materials with high surface area and large volumetric expansion capabilities that are well suited for endovascular occlusion applications, including brain aneurysm embolization. However, many polyurethane SMP foams are inherently radiolucent when X-ray visibility is required to [...] Read more.
Shape memory polymer (SMP) foams are porous materials with high surface area and large volumetric expansion capabilities that are well suited for endovascular occlusion applications, including brain aneurysm embolization. However, many polyurethane SMP foams are inherently radiolucent when X-ray visibility is required to ensure the safe delivery of the foam to the targeted aneurysm site using fluoroscopy. Here, highly radio-dense tantalum microparticles were added to a previously reported triiodobenzene-containing SMP foam (ATIPA foam) premix to fabricate ATIPA foam-tantalum composites (AT_T). The AT_T foams showed comparable glass transition temperatures, faster expansion profiles, increased X-ray visibility, good cytocompatibility, and faster oxidative degradation compared to the control ATIPA foam without tantalum. The mechanical properties were improved up to 4 vol% tantalum and the X-ray visibility was most appropriate for the 2 vol% (AT_2%T) and 4 vol% (AT_4%T) tantalum foams. E-beam sterilization did not impair the critical properties of the ATIPA foams. Overall, AT_2%T was the optimal foam composition for neurovascular prototypes due to its high oxidative stability in vitro compared to previous low-density SMP foams. The AT_T foams are very promising materials with high toughness and sufficient X-ray visibility for use as neurovascular embolization devices. Full article
(This article belongs to the Special Issue Feature Papers in Journal of Composites Science in 2020)
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Open AccessArticle
Droplet Spreading on Unidirectional Fiber Beds
J. Compos. Sci. 2021, 5(1), 13; https://doi.org/10.3390/jcs5010013 - 06 Jan 2021
Viewed by 363
Abstract
This study reports a method to analyze parametric effects on the spread flow kinetics of fluid droplets on unidirectional fiber beds. The investigation was undertaken in order to guide the design of droplet arrays for production of an out-of-autoclave (OoA) prepreg featuring discontinuous [...] Read more.
This study reports a method to analyze parametric effects on the spread flow kinetics of fluid droplets on unidirectional fiber beds. The investigation was undertaken in order to guide the design of droplet arrays for production of an out-of-autoclave (OoA) prepreg featuring discontinuous resin distribution, referred to here as semi-preg. Volume-controlled droplets of a resin facsimile fluid were deposited on carbon fiber beds and the flow behavior was recorded. The time to full sorption (after deposition) and the maximum droplet spread distance were measured. Experiments revealed that fluid viscosity dominated time to full sorption—doubling the viscosity resulted in an 8- to 20-fold increase in sorption time, whereas doubling fabric areal weight increased the time only by a factor of three. Droplet spread distance was nearly invariant with fiber bed architecture and fluid viscosity. A series of droplet arrays were designed, demonstrating how the results can be leveraged to achieve different resin distributions to produce semi-preg optimized for OoA cure. Full article
(This article belongs to the Special Issue Carbon Fiber Composites)
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Open AccessArticle
Moisture Adsorption and Desorption Behavior of Raw Materials for the T-RTM Process
J. Compos. Sci. 2021, 5(1), 12; https://doi.org/10.3390/jcs5010012 - 05 Jan 2021
Viewed by 341
Abstract
The use of fiber reinforced plastics (FRPs) has significant potential to reduce the weight of components. As regards the sustainability of these components, thermoplastic matrices offer more potential for recycling than thermoset ones. A possible manufacturing process for the production of thermoplastic FRPs [...] Read more.
The use of fiber reinforced plastics (FRPs) has significant potential to reduce the weight of components. As regards the sustainability of these components, thermoplastic matrices offer more potential for recycling than thermoset ones. A possible manufacturing process for the production of thermoplastic FRPs is thermoplastic resin transfer molding (T-RTM). In this very moisture-sensitive process, ε-caprolactam in addition to an activator and catalyst polymerizes anionically to polyamide 6 (aPA6). The anionic polymerization of aPA6 is slowed down or even completely blocked by the presence of water. This study analyses the sorption behavior of the matrix, fiber, binder and core materials for the production of anionic polyamide 6 composites, which are processed in the thermoplastic RTM process. Water vapor sorption measurements are used to determine the adsorption and desorption behavior of the materials. The maximum moisture loading of the materials provides information about the water adsorption capacity of the material. This knowledge is crucial for correct handling of the materials to achieve a fast process and good properties of the final product. Full article
(This article belongs to the Special Issue Advanced Fiber Reinforced Polymer Composites)
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Open AccessArticle
Nanocellulose from Unbleached Hemp Fibers as a Filler for Biobased Photocured Composites with Epoxidized Cardanol
J. Compos. Sci. 2021, 5(1), 11; https://doi.org/10.3390/jcs5010011 - 03 Jan 2021
Viewed by 514
Abstract
Biobased composites were successfully prepared using raw materials derived from biomass waste, i.e., an epoxy resin obtained from cardanol and nanocellulose from unbleached hemp fibers. The composites were prepared by solvent exchange and an impregnation of the cellulosic mat with the resin, followed [...] Read more.
Biobased composites were successfully prepared using raw materials derived from biomass waste, i.e., an epoxy resin obtained from cardanol and nanocellulose from unbleached hemp fibers. The composites were prepared by solvent exchange and an impregnation of the cellulosic mat with the resin, followed by photocuring. Quantitative conversion was obtained, despite the high amount of fibers (30 wt%) and their absorbance in the UV region of the light spectrum. X-ray diffraction confirmed that the crystalline structure of cellulose did not change during the impregnation and curing process. The cured composites were flexible, hydrophobic, water resistant, transparent with a yellow/brown color, and in the rubbery state at room temperature. Full article
(This article belongs to the Special Issue Advanced Fiber Reinforced Polymer Composites)
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Open AccessArticle
Hybrid Joining by Induction Heating of Basalt Fiber Reinforced Thermoplastic Laminates
J. Compos. Sci. 2021, 5(1), 10; https://doi.org/10.3390/jcs5010010 - 02 Jan 2021
Viewed by 365
Abstract
Induction heating was used to join basalt fiber reinforced polymer laminates (BFRPL) using the process called inductive contact joining (ICJ). Two other mechanical joining processes, nut and bolt (NB) and two-piece hollow riveting (2PR), were compared to ICJ. The obtained joints were evaluated [...] Read more.
Induction heating was used to join basalt fiber reinforced polymer laminates (BFRPL) using the process called inductive contact joining (ICJ). Two other mechanical joining processes, nut and bolt (NB) and two-piece hollow riveting (2PR), were compared to ICJ. The obtained joints were evaluated using tensile shear tests and by analyzing fractured surfaces. Furthermore, simulation of the ICJ process was used to estimate the effective parameters. Joints produced by ICJ had superior joint strength compared to joints manufactured by 2PR. In addition, during ICJ, the BFRPL fibers were not damaged and the strength of the base material was maintained. The tensile shear forces of the ICJ process exceeded 3.5 kN and 2.5 kN for a joined, sandblasted aluminum sheet with BFRPL and for joining BFRPL to itself, respectively. Further optimization potential of the ICJ process was discovered during the investigation, so that potentially higher joint strengths and shorter processing times can be expected, making the process interesting for future industrial applications. Full article
(This article belongs to the Special Issue Advanced Fiber Reinforced Polymer Composites)
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Open AccessArticle
Electrodeposition from a Graphene Bath: A Sustainable Copper Composite Alloy in a Graphene Matrix
J. Compos. Sci. 2021, 5(1), 9; https://doi.org/10.3390/jcs5010009 - 31 Dec 2020
Viewed by 404
Abstract
The leaching effect of metals has led to the introduction of government regulations for the safety of the environment and humans. This has led to the search for new alloys with long-lasting sustainability. Herein, we wish to report a new brass alloy containing [...] Read more.
The leaching effect of metals has led to the introduction of government regulations for the safety of the environment and humans. This has led to the search for new alloys with long-lasting sustainability. Herein, we wish to report a new brass alloy containing carbon with a remarkable sustainability produced by electrodeposition from a graphene quantum dots bath. The electrochemical measurements were carried out using cyclic voltammetry, potentiodynamic analysis, and Tafel measurements, and the deposits were characterized by X-ray fluorescence spectroscopy (XRF), Raman imaging, X-ray diffraction (XRD), atomic force microscopy (AFM), and scanning electron microscopy (SEM) to understand the surface morphology and elemental compositions. The current–time transients in the potential-step electrolysis were used to investigate the nucleation and growth mechanism. The smooth and compact deposit obtained at −0.60 V showed a composition of Cu = 24.33 wt %; Zn = 0.089 wt %; and C = 75.57 wt %. The SEM and energy dispersion X-ray analysis revealed a surface morphology with a uniform distribution of the particles and the presence of Cu, Zn, and C. The corrosion density of the material is very much lower than that of conventional brass, suggesting a higher sustainability. Full article
(This article belongs to the Special Issue Graphene Composites)
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Open AccessArticle
Preparation and Evaluation of the Tensile Characteristics of Carbon Fiber Rod Reinforced 3D Printed Thermoplastic Composites
J. Compos. Sci. 2021, 5(1), 8; https://doi.org/10.3390/jcs5010008 - 31 Dec 2020
Viewed by 543
Abstract
The most common method to fabricate both simple and complex structures in the additive manufacturing process is fused deposition modeling (FDM). Many researchers have studied the strengthening of FDM components by adding short carbon fibers (CF) or by reinforcing solid carbon fiber rods. [...] Read more.
The most common method to fabricate both simple and complex structures in the additive manufacturing process is fused deposition modeling (FDM). Many researchers have studied the strengthening of FDM components by adding short carbon fibers (CF) or by reinforcing solid carbon fiber rods. In the current research, we sought to enhance the mechanical properties of FDM components by adding bioinspired solid CF rods during the fabrication process. An effective bonding interface of bioinspired CF rods and polylactic acid (PLA) was achieved by triangular interlocking sutures and by employing synthetic glue as the binding agent. In particular, the tensile strength of solid CF rod reinforced PLA samples was studied. Critical parameters such as layer thickness, extruder temperature, extruder speed, and shell thickness were considered for optimization. Significant process parameters were identified through leverage plots using the response surface methodology (RSM). The optimum parameters were found to be layer thickness of 0.04 mm, extruder temperature of 215 °C, extruder speed of 60 mm/s, and shell thickness of 1.2 mm. The results revealed that the bioinspired solid CF rod reinforced PLA (CFRPLA) composite exhibited a tensile strength of 82.06 MPa, which was approximately three times higher than the pure PLA (28 MPa, 66% lower than CFRPLA), acrylonitrile butadiene styrene (ABS) (28 MPa, 66% lower than CFRPLA), polyethylene terephthalate glycol (PETG) (34 MPa, 60% lower than CFRPLA), and nylon (34 MPa, 60% lower than CFRPLA) samples. Full article
(This article belongs to the Special Issue Carbon Fiber Composites)
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Open AccessArticle
Nano-Structured Polyaniline as a Potential Adsorbent for Methylene Blue Dye Removal from Effluent
J. Compos. Sci. 2021, 5(1), 7; https://doi.org/10.3390/jcs5010007 - 31 Dec 2020
Cited by 1 | Viewed by 387
Abstract
The textile sector is one of the major culprits of water pollution, and demands immediate attention. The coloured textile effluent, loaded with toxic dyes, when mixed with waterbodies, may harm aquatic life, plants, animals, and humans. Although polyaniline in its different forms was [...] Read more.
The textile sector is one of the major culprits of water pollution, and demands immediate attention. The coloured textile effluent, loaded with toxic dyes, when mixed with waterbodies, may harm aquatic life, plants, animals, and humans. Although polyaniline in its different forms was utilised for the adsorption of different dyes, the pure nano-fibrous form of polyaniline, i.e., PANI nanofibers, have reportedly not been used for the removal of dyes from wastewater. The present study aimed to employ nano-structured polyaniline, in the form of polyaniline nanofibers (base; PNB—polyaniline nanofiber base) for the elimination of methylene blue (cationic dye; MB) dye from its solution. The polyaniline nanofiber base (PNB) was synthesised by an interfacial polymerisation technique using ammonium persulphate as the oxidant and toluene as the organic solvent, and was characterised by FTIR, SEM, BET, HRTEM and XRD techniques. The HRTEM and SEM results showed that the average size of the synthesised polyaniline nanofiber base (PNB) was about 60 nm. BET revealed the enhanced surface area of polyaniline nanofiber base (PNB), i.e., 48 m2g−1 in comparison to that of conventionally synthesised polyaniline, which is only 14 m2g−1. The electric conductivity of the polyaniline nanofiber base (PNB) was reportedly lesser (2.3 × 10−2 S/cm) than the salt form of the polyaniline, measured by four probe technique. The batch-wise adsorption of MB was conducted onto the polyaniline nanofiber base (PNB), and the influence of the preliminary dye concentration, duration of contact and polyaniline nanofiber base (PNB) dose, etc., were studied. The equilibrium values of these parameters are reported as 6 mg/L, 60 min and 2 g/L, respectively. The results revealed the 91% sorption of dye onto the polyaniline nanofiber base (PNB). The experimental data were best-fitted to Pseudo-second order (R2 = 0.99) and followed Freundlich isotherm model (R2 = 0.97). On desorption, about 86% of the absorbed dye was recovered and the regenerated adsorbent could be used efficiently for three more cycles. Full article
(This article belongs to the Special Issue Composite Materials for Water Purification)
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Open AccessArticle
Fire Protective Surface Coating Containing Nanoparticles for Marine Composite Laminates
J. Compos. Sci. 2021, 5(1), 6; https://doi.org/10.3390/jcs5010006 - 30 Dec 2020
Viewed by 484
Abstract
A poly(vinyl alcohol) (PVA)-based coating containing ammonium polyphosphate (APP) and sepiolite nanofillers (SP) and supported by a glass fabric was developed to fire-protect a glass-fiber-reinforced unsaturated-polyester-based (UP) polymer (GFRP). The fire behavior and thermal stability of the PVA coatings were characterized using thermogravimetric [...] Read more.
A poly(vinyl alcohol) (PVA)-based coating containing ammonium polyphosphate (APP) and sepiolite nanofillers (SP) and supported by a glass fabric was developed to fire-protect a glass-fiber-reinforced unsaturated-polyester-based (UP) polymer (GFRP). The fire behavior and thermal stability of the PVA coatings were characterized using thermogravimetric analysis (TGA) and a cone calorimeter. The coatings’ residues were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results from the cone calorimeter showed that the addition of sepiolite significantly improves the flame retardancy of PVA/APP/SP coatings. The addition of both additives promoted the formation of a cohesive layer composed of a silico-phosphate structure resulting from the reactivity between APP and SP. The fire resistance of the composite laminate protected by PVA coatings was evaluated using a cone calorimeter by measuring the temperature of the back face. Photogrammetry was used to assess the swelling of residues after heat exposure. The interaction between APP and SP in PVA coating leads to the formation of an effective thermal barrier layer. The presence of SP reduces the layer expansion but greatly decreases the backside temperature during the initial period of exposure. The effect was assigned to high thermal stability of the layer and its ability to dissipate heat by re-radiation. Full article
(This article belongs to the Special Issue Fire Safety of Structural Composites)
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