Journal of Composites Science — Open Access Journal

This study aims to evaluate the synergical effects of SiO₂ nanoparticles (nano-SiO₂) and organic photostabilizers (Tinuvin 384 (T384) and Tinuvin 292 (T292)) on the weathering resistance of acrylic polyurethane coating. Data obtained from infrared (IR), field emission scanning electron microscopy (FESEM), and weight loss of coatings (before and after aging test), suggest that the SiO₂ nanoparticles play a dual role, as both reinforcer and UV absorber, thus improving effectively both the mechanical properties and the weathering resistance of polyurethane acrylic coatings. The nanocomposite coating containing 2 wt % nano-SiO₂, 2 wt % T384, and 1 wt % T292 exhibits excellent weathering and abrasion resistances, offering a durable outdoor application. Full article

Due to increasing costs and growing environmental concerns pertaining to the construction of structures, an alternative form of reinforcement has been proposed through our studies; through a new beam design methodology, referred to as triple composite beams, glass can be used as a cost-competitive and more environmentally friendly macro-scale compressive reinforcement. The cost competitiveness of glasses derives from their large compressive strength (in general 1000 MPa; >1100 MPa for fused quartz). To support the triple composite design architecture, equations have been developed using Euler–Bernoulli beam theory and the method of transformed sections and compared against finite element modeling determined stresses. Our results show that the average stress was more accurate but less precise than fully considering binder, assuming the binder did not contribute to the cross-section of the beam. The paper concludes by presenting a flexural reinforcement utilization ratio (R), which predicts the ability of a reinforcement-binder combination to utilize the reinforcement to maximum stress effectively while ignoring bonding strength. This R ratio suggests that while concrete is a low cost, it cannot be used in a glass-reinforced beam as the concrete is too stiff compared to the glass. Full article

Moisture absorption of composites with nanoscale carbon additives such as carbon nanotubes, carbon nanofibers, graphite nanoplatelets, and carbon black is investigated using thermogravimetric data and a non-Fickian hindered diffusion (Langmuir-type) model. The moisture absorption parameters are determined using this model for six different types of carbon/epoxy nanocomposites. The absorption behaviors obtained at different humidity levels and thermal environments are recovered by minimizing the error between the experimental data and model predictions, thus enabling the accurate determination of the moisture equilibrium level. The absorption behavior and the weight gain of all nanocomposites are shown to be accurately represented by this model over the entire absorption period. The presence of carbon nanomaterials is found to induce varying levels of non-Fickian behavior, governed by the nondimensional hindrance coefficient. This behavior is enhanced with the nanomaterial content and separate from the slight non-Fickian behavior of all neat epoxy samples. The molecular bonding during diffusion, as well as the interfacial moisture storage, could be among the reasons for non-Fickian behavior and should be included in the absorption models for accurate characterization of carbon/epoxy nanocomposites. Full article

The oxygen reduction reaction is an essential reaction in several energy conversion devices such as fuel cells and batteries. So far, the best performance is obtained by using platinum-based electrocatalysts, which make the devices really expensive, and thus, new and more affordable materials should be designed. Biomass-derived carbons were prepared by hydrothermal carbonization in the presence of carbon nanotubes with different oxygen surface functionalities to evaluate their effect on the final properties. Additionally, nitrogen functional groups were also introduced by ball milling the carbon composite together with melamine. The oxygen groups on the surface of the carbon nanotubes favor their dispersion into the precursor mixture and the formation of a more homogenous carbon structure with higher mechanical strength. This type of structure partially avoids the crushing of the nanotubes and the carbon spheres during the ball milling, resulting in a carbon composite with enhanced electrical conductivity. Undoped and N-doped composites were used as electrocatalysts for the oxygen reduction reaction. The onset potential increases by 20% due to the incorporation of carbon nanotubes (CNTs) and nitrogen, which increases the number of active sites and improves the chemical reactivity, while the limiting current density increases by 47% due to the higher electrical conductivity. Full article

In the present study, Ni₅₀Ti₅₀ (NiTi) particle reinforced aluminum nanocomposites were fabricated using microwave sintering and subsequently hot extrusion. The effect of NiTi (0, 0.5, 1.0, and 1.5 vol %) content on the microstructural, mechanical, thermal, and damping properties of the extruded Al-NiTi nanocomposites was studied. Compared to the unreinforced aluminum, hardness, ultimate compression/tensile strength and yield strength increased by 105%, 46%, 45%, and 41% while elongation and coefficient of thermal expansion (CTE) decreased by 49% and 22%, respectively. The fabricated Al-1.5 NiTi nanocomposite exhibited significantly higher damping capacity (3.23 × 10⁻⁴) and elastic modulus (78.48 ± 0.008 GPa) when compared to pure Al. Full article

This work focused on a mutual comparison and characterization of the physicochemical properties of three-component polymer composites. Binary polyaniline–chitosan (PANI–CHT) composites were synthesized by in situ polymerization of PANI onto CHT. Ternary composites were prepared by blending with a third component, polyvinyl alcohol (PVA). Composites with variable PANI:CHT (25:75, 50:50 and 75:25) weight ratios were prepared whilst fixing the composition of PVA. The structure and physicochemical properties of the composites were evaluated using thermal analysis (thermogravimetric analysis (TGA), differential scanning calorimetry (DSC)) and spectroscopic methods (infrared (IR), nuclear magnetic resonance (NMR)). The equilibrium and dynamic adsorption properties of composites were evaluated by solvent swelling in water, water vapour adsorption and dye adsorption isotherms. The electrical conductivity was estimated using current–voltage curves. The mechanical properties of the samples were evaluated using dynamic mechanical analysis (DMA) and correlated with the structural parameters of the composites. The adsorption and swelling properties paralleled the change in the electrical and mechanical properties of the materials. In most cases, samples with higher content of chitosan exhibit higher adsorption and mechanical properties, and lower conductivity. Acid-doped samples showed much higher adsorption, swelling, and electrical conductivity than their undoped analogues. Full article

In this paper, the influence of layer thickness (LT), infill percentage (IP), and extruder temperature (ET) on the maximum failure load, thickness, and build time of bronze polylactic acid (Br-PLA) composites 3D printed by the fused deposition modeling (FDM) was investigated via an optimization method. PLA is a thermoplastic aliphatic polyester obtained from renewable sources, such as fermented plant starch, especially made by corn starch. The design of experiment (DOE) approach was used for optimization parameters, and 3D printings were optimized according to the applied statistical analyses to reach the best features. The maximum value of failure load and minimum value of the build time were considered as optimization criteria. Analysis of variance results identified the layer thickness as the main controlled variable for all responses. Optimum solutions were examined by experimental preparation to assess the efficiency of the optimization method. There was a superb compromise among experimental outcomes and predictions of the response surface method, confirming the reliability of predictive models. The optimum setting for fulfilling the first criterion could result in a sample with more than 1021 N maximum failure load. Finally, a comparison of maximum failure from PLA with Br-PLA was studied. Full article

In recent years, there has been increasing interest in developing green biocomposite for industrial wastewater treatment. In this study, prawn-shell-derived chitosan (CHT) and kaolinite rich modified clay (MC) were used to fabricate biocomposite beads with different compositions. Prepared composite beads were characterized by FTIR, and XRD, and SEM. The possible application of the beads was evaluated primarily by measuring the adsorption efficiency in standard models of lead (II) and methylene blue (MB) dye solution, and the results show a promising removal efficiency. In addition, the composites were used to remove Cr (VI), Pb (II), and MB from real industrial effluents. From tannery effluent, 50.90% of chromium and 39.50% of lead ions were removed by composites rich in chitosan and 31.50% of MB was removed from textile effluent by a composite rich in clay. Moreover, the composite beads were found to be activated in both acidic and basic media depending on their composition, which gives a scope to their universal application in dye and heavy metal removal from wastewater from various industries. Full article

Pelletized biomaterial composites that contain chitosan (C) and torrefied wheat straw (S) at variable weight composition (C:S) were prepared using a facile blending process. The fractional content of the wheat straw was studied to elucidate the role of biomass on the pelletized product and effects of S-content on the physicochemical properties relevant to adsorption phenomena. Chitosan pellets (with and without S) were characterized by spectroscopic (FT-IR and ¹³C NMR) and thermal (TGA and DSC) techniques to provide support for their respective C:S composition. Confocal microscopy using fluorescein (FL) as a dye probe revealed the presence and an increase in the accessibility of the active sites for the composite pellets according to the S-content (wt %). Equilibrium and kinetic sorption studies using FL and reactive black (RB) dyes revealed an incremental adsorption affinity of the pellets with anionic dyes in variable charge states (FL and RB). The trend for dye adsorption parallels the incremental S-content (wt %) in the composite pellets. This study reports a first-example of a low-cost, facile, and sustainable approach for the valorization of straw and chitosan suitable for sorption-based applications in aqueous media. Full article

This study describes the application of multi-walled carbon nanotubes that were nitrogen-doped during their synthesis (N-MWCNTs) in melt-mixed polypropylene (PP) composites. Different types of N-MWCNTs, synthesized using different methods, were used and compared. Four of the five MWCNT grades showed negative Seebeck coefficients (S), indicating n-type charge carrier behavior. All prepared composites (with a concentration between 2 and 7.5 wt% N-MWCNTs) also showed negative S values, which in most cases had a higher negative value than the corresponding nanotubes. The S values achieved were between 1.0 μV/K and −13.8 μV/K for the N-MWCNT buckypapers or powders and between −4.7 μV/K and −22.8 μV/K for the corresponding composites. With a higher content of N-MWCNTs, the increase in electrical conductivity led to increasing values of the power factor (PF) despite the unstable behavior of the Seebeck coefficient. The highest power factor was achieved with 4 wt% N-MWCNT, where a suitable combination of high electrical conductivity and acceptable Seebeck coefficient led to a PF value of 6.1 × 10⁻³ µW/(m·K²). First experiments have shown that transient absorption spectroscopy (TAS) is a useful tool to study the carrier transfer process in CNTs in composites and to correlate it with the Seebeck coefficient. Full article

Condition-based maintenance refers to the installation of permanent sensors on a structure/system. By means of early fault detection, severe damage can be avoided, allowing efficient timing of maintenance works and avoiding unnecessary inspections at the same time. These are the goals for structural health monitoring (SHM). The changes caused by incipient damage on raw data collected by sensors are quite small, and are usually contaminated by noise and varying environmental factors, so the algorithms used to extract information from sensor data need to focus on sensitive damage features. The developments of SHM techniques over the last 20 years have been more related to algorithm improvements than to sensor progress, which essentially have been maintained without major conceptual changes (with regards to accelerometers, piezoelectric wafers, and fiber optic sensors). The main different SHM systems (vibration methods, strain-based fiber optics methods, guided waves, acoustic emission, and nanoparticle-doped resins) are reviewed, and the main issues to be solved are identified. Reliability is the key question, and can only be demonstrated through a probability of detection (POD) analysis. Attention has only been paid to this issue over the last ten years, but now it is a growing trend. Simulation of the SHM system is needed in order to reduce the number of experiments. Full article

The present article introduces a dimensionless number devised to assist composite engineers in the fabrication of continuous fiber composites by Liquid Composite Molding (LCM), i.e., by injecting a liquid polymer resin through a fibrous reinforcement contained in a closed mold. This dimensionless number is calculated by integrating the ratio of the injection pressure to the liquid viscosity over the cavity filling time. It is hereby called the “injectability number” and provides an evaluation of the difficulty to inject a liquid into a porous material for a given part geometry, permeability distribution, and position of the inlet gate. The theoretical aspects behind this new concept are analyzed in Part I of the article, which demonstrates the invariance of the injectability number with respect to process parameters like constant and varying injection pressure or flow rate. Part I also details how process engineers can use the injectability number to address challenges in composite fabrication, such as process selection, mold design, and parameter optimization. Thanks to the injectability number, the optimal position of the inlet gate can be assessed and injection parameters scaled to speed up mold design. Part II of the article completes the demonstration of the novel concept by applying it to a series of LCM process examples of increasing complexity. Full article

The dimensionless “injectability number” was devised to assist composite engineers in the fabrication of continuous fiber composites by Liquid Composite Molding (LCM), i.e., by injecting a liquid polymer resin through a fibrous reinforcement contained in a mold cavity. Part I of this article introduced the injectability number as the integral of the ratio of the injection pressure to the resin viscosity over the cavity filling time and analyzed the theoretical aspects behind this new concept. For a given mold configuration and reinforcement material characteristics, the invariance of the injectability number with regard to process parameters was demonstrated, and an initial verification in unidirectional injection cases was conducted. Part II completes the analysis by evaluating the injectability number in more complex application cases, confirming its invariance properties. The investigation, which was carried out using numerical simulations of different LCM processes and injection strategies, examined the fabrication of various composite parts: a rectangular laminate, a hood for automotive applications, a reservoir box and a fuselage section for the aerospace industry. The results indicate that more efficient injection strategies lead to lower values of the injectability number, thus enabling the use of this dimensionless number as a tool to assess the difficulty to manufacture a given part by LCM as well as to guide process selection and compare different mold configurations. Full article

A suitable polymer matrix and well dispersed conducting fillers forming an electrically conducting network are the prime requisites for modern age electromagnetic shield designing. An effective polymer-based shield material is designed that can attenuate 99.9% of incident electromagnetic (EM) radiation at a minimum thickness of <0.5 mm. This is accomplished by the choice of a suitable partially crystalline polymer matrix while comparing non-polar polypropylene (PP) with polar polyvinylidene fluoride (PVDF) and a best suited filler nanomaterial by comparing different types of carbon nanotubes such as; branched, single-walled and multi-walled carbon nanotubes, which were added in only 2 wt %. Different types of interactions (polar-polar and CH-π and donor-acceptor) make b-MWCNT more dispersible in the PVDF matrix, which together with high crystallinity resulted in the best electrical conductivity and electromagnetic shielding ability of this composite. This investigation additionally conceals the issues related to the thickness of the shield material just by stacking individual thin nanocomposite layers containing different carbon nanotube (CNT) types with 0.3 mm thickness in a simple manner and finally achieves 99.999% shielding efficiency at just 0.9 mm thickness when using a suitable order of the different PVDF based nanocomposites. Full article

The reaction kinetics of anionic polymerization for the production of anionic polyamide 6 (aPA6) are widely understood. It is also known that this reaction is very sensitive to external influences such as water. This paper analyzes and quantifies the influence of water on the reaction of ε-caprolactam to anionic polyamide 6. A kinetic model is developed in which the reactive molecules of the activator and catalyst are defined as variables and the concentrations of activator and catalyst as well as water content are considered. A model for the calculation of the reaction kinetics is established and validated with experimental data. The developed model can be used to predict the influence and compensation of water by addition of surplus activator and catalyst during the polymerization of ε-caprolactam. Full article

The activated anionic ring opening polymerization of ε-caprolactam to polyamide 6 is highly sensitive to external influences such as water. Based on an initial theory, preliminary reaction kinetic tests are carried out with the aim of compensating the influence of the water by increasing the activator and catalyst concentration. Different formulations of activator and catalyst were studied to understand the influence of water on the concentration of activator and catalyst. It was found that the compensation of added water with activator and catalyst restores the original reaction time. The test plates produced are examined with regard to their mechanical characteristics and the polymer properties. The results of the mechanical characterization show no significant impairment after compensation of the added water. The physical properties of the matrix show degradation with repeated compensation. However, the residual ε-caprolactam content remains below the critical value of 1% for three of the four investigated formulations. Full article

Experimental studies are presented on quasi-static tensile and compressive loading of composites hybridised at two levels: intraply and interply. Consistent reinforcements in the form of novel unidirectional fabrics were developed using T700SC carbon and E-CR glass fibres. Composites were manufactured using Resin Transfer Moulding process with epoxy resin and characterised to ensure consistency and comparability, further enabling easier understanding and confirmation of hybrid effect in a reliable way. Failure strain in tension for interply hybrid revealed a positive hybrid effect of +7.4%, while interply hybrid showed a negative hybrid effect of −6.4% in compression. Intraply hybrid with three carbon and three glass tows blocked together demonstrated the best mechanical performance among all hybrids; synergistic effects of +17.8% and +39.6% in tensile and compressive strength, respectively, was observed for this hybrid configuration. The results show that different hybridisation strategies can be exploited to balance cost and performance of composites for structural and lightweight applications. Full article

In this research, three kinds of carbon fiber (CF) with lengths of 1, 3, and 25 mm were prepared for processing composite. The effect of submicron glass fiber addition (sGF) on mechanical properties of composites with different CF lengths was investigated and compared throughout static tests (i.e., bending, tensile, and impact), as well as the tension-tension fatigue test. The strengths of composites increased with the increase of CF length. However, there was a significant improvement when the fiber length changed from 1 to 3 mm. The mechanical performance of 3 and 25 mm was almost the same when having an equal volume fraction, except for the impact resistance. Comparing the static strengths when varying the sGF content, an improvement of bending strength was confirmed when sGF was added into 1 mm composite due to toughened matrix. However, when longer fiber was used and fiber concentration was high, mechanical properties of composite were almost dependent on the CF. Therefore, the modification effect of matrix due to sGF addition disappeared. In contrast to the static strengths, the fatigue durability of composites increased proportionally to the content of glass fiber in the matrix, regardless to CF length. Full article