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A mountain bike carbon reinforced polymeric frame failed in two pieces during cycling over a grass meadow at a speed of about 25 km/h. This has caused the shoulder dislocation of the driver, also last author of this paper. Here, we demonstrate evidence of macroscopic numerous pre‐existing and propagating defects, such as wrinkles, voids and delaminations, resulting in low mechanical properties of this frame. Numerical dynamic simulations conclude the paper and suggest a further cause of frame weakening, due to defect‐resonance interaction. The paper suggests that the design of carbon fiber reinforced plastic frame for mountain bikes may require new scientific and technological advancements for the safety of the riders, at least today carefully eliminating pre‐existing defects and tomorrow proposing bioinspired flaw tolerant solutions. [ABSTRACT FROM AUTHOR]

Graphene nanoplatelets (xGnP), expanded graphite (EG), multiwall carbon nanotubes (MWCNTs), and carbon black (CB) were dispersed in various amounts in a thermosetting polyurethane (PU) matrix derived from castor oil and composite plaques were obtained by compression molding. The electrical percolation threshold was found to be 0.1 vol% for MWCNT, 0.5 vol% for xGnP, 2.8 vol% for CB, and 2.7 vol% for EG‐filled systems. The relation between electrical conductivity, morphology, and electromagnetic interference shielding effectiveness (EMI SE) of the resulting composites was studied to understand how the EMI SE is influenced by morphology and electrical conductivity of each filler. The composites display significantly distinct EMI SE values, depending on the type of carbon filler and its volume fraction. Composite based in PU/EG and PU/xGnP exhibited the highest EMI SE values (70 and 47 −dB, respectively); however, PU/MWCNT composites showed higher EMI SE (24 −dB) value at the same filler content (3 vol%) than the other composite system. POLYM. COMPOS., 40:E78–E87, 2019. © 2017 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

Novel polyvinyl alcohol (PVOH) based biodegradable composites were prepared by a hand lay‐up process using ultrathin beech laminae cut by a specialized planer machine, and the resulting materials were thermo‐mechanically characterized. Density measured showed how the adopted procedure led to laminates having a high porosity degree (about 50% by volume) and an elevated wood concentration (about 80% by weight). In fact, because the wood fibers were perfectly cut (not pressed and abraded), wood porosity was partially filled by the PVOH resin, as documented by field emission scanning electron microscope (FESEM) micrographs. The occlusion of wood porosity by the PVOH matrix resulted to be beneficial for the tensile mechanical properties of the composites. In fact, quasi‐static tensile tests and DMTA analysis revealed how the stiffness (E, E′) and strength (σb) values of the composites both along longitudinal and transversal directions were considerably higher than those of the constituents. On the other hand, the values of the specific energy adsorbed under impact conditions by the composites samples were rather low, if compared to the neat matrix. POLYM. COMPOS., 39:1116–1124, 2018. © 2016 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

The main focus of this study is to characterize the interfacial interactions between silica nanoparticles and polypropylene and to investigate how the surface properties and morphology of the silica nanoparticles affect the elastic response of the silica-polypropylene composites. The composites were prepared by melt compounding and injection molding. Both non-functionalized and dimethyldichlorosilane-functionalized silica nanoparticles were used. Three-component composites were also prepared by including selected formulations of both poly(propylene- g-maleic anhydride) copolymer (PPgMA) and different types of silica. It was found that both silica types are nucleating agents for PP and significantly alter its crystallization behavior. A strong correlation between the glass transition temperature ( Tg) and the tensile modulus in silica-PP nanocomposites indicated the presence of a secondary reinforcing mechanism that is the pinning of the polymer chains on the silica surface. The presence of a complex constrained phase, represented by immobilized amorphous and transcrystalline phases, forming at the filler surface, was assessed by modulated differential scanning calorimetry and dynamic mechanical analysis. Finally, the interfacial interactions were correlated to the tensile and viscoelastic properties using the theoretical models proposed by Pukanszky and Sumita et al., respectively, and comparing the predictions of the models to experimental results. POLYM. COMPOS., 37:2018-2026, 2016. © 2015 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

Linear low-density polyethylene (LLDPE)-based composites were prepared through melt compounding and hot pressing using both untreated and treated halloysite nanotubes (HNT) up to filler contents of 8 wt% to assess the role of the filler exfoliation and surface treatment on the thermal, mechanical, and rheological properties of the resulting composites. The addition of treated nanoparticles resulted in a better dispersion of the filler within the matrix, as confirmed by observations conducted at scanning and transmission electron microscopies. A decrease in both complex viscosity and shear storage modulus was recorded for all LLDPE-HNT nanocomposites in the molten state. Differential scanning calorimetry analysis evidenced that HNT addition produced an increase of the crystallization peak temperature, while thermogravimetric analysis showed a remarkable improvement of the thermal stability with the nanofiller content. The addition of treated HNT nanoparticles induced better improvements in elastic modulus and tensile properties at break without significant loss in ductility. The fracture toughness, evaluated by the essential work of fracture approach, showed remarkable improvements (up to a factor of 2) with addition of treated HNT. Conversely, incorporation of untreated HNT produced an adverse effect on the fracture toughness when considering the nanocomposite filled with 8 wt% HNT. Both creep tests and dynamic mechanical analyses showed an overall enhancement of the viscoelastic properties due to addition of HNT, revealing higher improvements in nanocomposites added with treated HNT. POLYM. COMPOS., 36:869-883, 2015. © 2014 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

Highlights In fiber reinforced composite materials, the interfacial strength between the fibers and the matrix plays a key role in controlling the stress transfer and damage mechanisms of the composite. In this study, CO2 laser surface treatment of the fibers was investigated as a potential sustainable substitute for conventional chemical treatments, that can be costly and have negative environmental effects. The influence of the laser treatment on basalt fiber fabric was comprehensively investigated. The fibers were subjected to different laser power levels and characterized from a morphological and mechanical point of view. From optical and scanning electron microscopy, it was observed that the treated fibers manifested increased surface roughness along with spots of fused and bonded fibers. Individual treated fibers exhibited improved tensile properties with increased values of scale parameter (by about 21%) in the case of a laser power equal to 1.04 W/mm2, and no substantial changes in Young's modulus. The treated fibers were subsequently used in the preparation of epoxy‐based microcomposites, and microdebonding tests revealed an increase in the interfacial shear strength (IFSS) up to 8%. Therefore, this work proved that a laser surface treatment of basalt fibers is a valid alternative to conventional fiber surface modification to enhance the mechanical compatibility between fibers and matrix, and therefore to improve the mechanical performances of basalt fiber composites. Failure in composites due to weak interfacial adhesion with epoxy. CO2 laser treatment of basalt fibers to enhance interfacial adhesion. Treated fibers exhibit improved tensile properties. Treated fibers manifested improved interfacial shear strength (IFSS, +8%). [ABSTRACT FROM AUTHOR]

In this work, for the first time, carbon fibers (CFs) were coated with nanosized‐polycaprolactone (PCL) particles to obtain a functionalized self‐healable interphase, capable to fully recover the pristine interfacial shear strength with a debonded epoxy matrix. PCL nanoparticles were initially water‐dispersed at different concentrations and deposited on CFs by electrophoretic deposition. The application of various voltage levels resulted in different morphologies of the coating. Epoxy microdroplets were deposited and cured on neat and PCL‐coated fibers. After complete interfacial debonding by microdebonding tests, an electric current was applied on CFs to activate a thermal interfacial healing by Joule effect. The healing efficiency was estimated as the ratio of interfacial shear strength measured before and after healing. An outstanding repairing efficiency was obtained upon thermal mending with a complete recovery of the original interfacial shear strength, thus indicating a strong potential of the PCL nanocoating as interfacial healing agent for composite structures. Highlights: CFs were coated with nanosized‐PCL particles to obtain a functionalized self‐healable interphase.Electrophoretic deposition was employed for the fiber coating.Microdebonding tests were performed to assess the fiber/matrix interfacial properties in terms of interfacial shear strength.A full recovery of the interfacial properties was obtained via thermal interfacial healing by Joule effect. [ABSTRACT FROM AUTHOR]

This work aims at developing multifunctional thermoplastic laminates combining structural and heat storage/management functions. The laminates are constituted by paraffin microcapsules as phase change materials (PCM), continuous carbon fibers, and a novel thermoplastic liquid methyl methacrylate resin (Elium), processable as a thermoset. The characterization aims to study how the paraffin microcapsules influence the thermo‐mechanical properties and thermal management performance of Elium and of the relative composite laminates. For the Elium/PCM systems, the phase change enthalpy increased with the experimental PCM concentration up to 101 J/g, but the mechanical properties decreased concurrently. The melting enthalpy of the laminates also increased with the microcapsule amount, up to 66.8 J/g, which indicates that the mild conditions applied in the processing of the liquid resin allow the integrity of the microcapsules to be preserved. This is also confirmed by the improved thermal management performance observed through thermal camera imaging measurements. Microscopy techniques showed that the PCM phase is preferentially distributed in the interlaminar region, which accounts for the observed decrease in the interlaminar strength and the flexural properties with an increase in the PCM content. These results show a potential for the future development of multifunctional thermoplastic composites with elevated thermal energy storage capabilities. POLYM. COMPOS., 40:3711–3724, 2019. © 2019 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

Multifunctional self‐healing composites have great potential in several applications, i.e., from automotive to aerospace. This study examines the self‐healing behavior of carbon fiber reinforced composites by depositing jet‐spun cyclic olefin copolymer (COC) meshes on dry carbon fiber plies before lamination with epoxy resin (EP). Three different laminates were prepared, including neat EP/CF and two composites with 4 wt.% and 8 wt.% of COC in the form of a jet‐spun network as a healing agent. The introduction of COC mesh reduced flexural stress by 26% and interlaminar shear strength by 50%. Mode I interlaminar fracture toughness (GI) was evaluated and specimens were mended at 110°C by resistive heating generated by an electrical current flowing within the samples. The laminates containing 8 wt% COC reported a healing efficiency, evaluated as the ratio between the GI and as the ratio of the maximum load (PMAX) of virgin and healed samples, of 9.4% and 33.7%, respectively. Fractography analysis highlighted the poor adhesion between the COC mesh and EP matrix, and several COC microfibers were trapped inside the epoxy matrix, hindering their diffusion inside the crack zone, which limited the healing capability of the prepared laminates. [ABSTRACT FROM AUTHOR]

The elevated brittleness of commercial grades of poly(lactic acid) (PLA) may limit their use in several engineering applications. Therefore, the aim of this work is to develop a PLA‐based material possessing well‐balanced stiffness and toughness. Composites were prepared by blending PLA with increasing contents (from 10 to 30 wt%) of a thermoplastic polyurethane (TPU) and a fixed concentration (5 wt%) of carbon fibers (CFs), to tune the mechanical properties of the resulting materials. In order to increase the interfacial adhesion between CFs and polymeric phase, CFs were subjected to an acidic modification, by treating them in solution of H2SO4 and HNO3. The prepared composites were characterized from a chemical, rheological, morphological, and thermo‐mechanical point of view. Fourier transform infrared spectroscopy showed that the fiber surface reactivity was significantly enhanced by the acid treatment, with the introduction of reactive functional groups on CFs. Rheological and dynamic‐mechanical tests confirmed that the introduction of acid‐treated CFs implied strong fiber–matrix interactions. Thanks to the presence of the acid treated CFs, an important increase in tensile modulus and maximum stress was obtained for all the compositions. In particular, samples containing 10 wt% of TPU showed +74% tensile modulus and +43% maximum stress with respect to the unfilled blends. Moreover, the elongation at break of PLA was significantly improved (+81%) with the addition of 30 wt% of TPU. It was therefore demonstrated that the adopted approach could be effective for the preparation of novel PLA‐based materials with tailorable and well‐balanced properties that could find application in various technological fields. [ABSTRACT FROM AUTHOR]

Mechanical properties of starch‐grafted‐polypropylene/kenaf fibers (KF) composites were investigated and compared to different theoretical models. In this work, the composites were prepared via melt compounding and compression molding processes at different KF loadings, that is, 10, 20, and 30 wt%. Tensile, fracture toughness and fatigue tests were performed. Generally, the mechanical properties increased with increasing kenaf fiber loadings. This is attributed to the good filler‐matrix interactions between KF and starch‐grafted‐polypropylene, as observed by scanning electron microscopy. Tensile properties were modeled using the rule of mixture, the Kelly‐Tyson and the Halpin‐Tsai models. Fatigue data were also modeled using different theoretical models to fit both S–N and normalized S–N curves with simple linear model and Boltzmann sigmoidal function. POLYM. COMPOS., 39:3289–3299, 2018. © 2017 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

The present work deals with the characterization of multi‐walled carbon nanotubes (MWCNTs) filled and unfilled short carbon fiber reinforced epoxy resin composites. Short carbon fibers (10 mm) were selected at various processing stages such as (i) white color polyacrylonitrile fibers (PAN); (ii) pre‐carbonized carbon fibers (Precarb‐CF); (iii) oxidized carbon fibers (OCF); (iv) fully carbonized carbon fibers (CF‐low); and (v) sized carbon fibers (CF Sized). The investigated composites were characterized by three points bending test, hardness test, dynamic mechanical thermal analysis (DMTA), electrical conductivity test, thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). The results show that the mechanical and electrical properties of the investigated materials markedly depend on the type of short carbon fibers and on the presence of MWCNTs. POLYM. COMPOS., 39:E817–E825, 2018. © 2016 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

Electrically conductive composites of thermoplastic polyurethane (TPU), poly(vinylidene fluoride) (PVDF), and carbon black‐polypyrrole (CB‐PPy) were prepared by melt compounding followed by compression molding or by filament production followed by fused filament fabrication (FFF). The storage modulus (G′) and complex viscosity (η*) of the composites increased with the addition of CB‐PPy leading to a more rigid material. The electrical and rheological percolation threshold of composites were 5 and 3 wt%, respectively. In fact, composites with 5 wt% or more CB‐PPy content display G′ higher than G″ indicating a solid‐like behavior. Furthermore, the addition of CB‐PPy increased the electrical conductivity of all composites. However, the electrical conductivity values of composites containing 5 and 6 wt% of CB‐PPy produced by compression molding are one and seven order of magnitude higher than those of FFF composites with same composition. Compression molded and 3D printed composites with 6 wt% of CB‐PPy displayed high sensitivity/gauge factor, large measurement range and reproducible piezoresistive response during 100 loading‐unloading cycles for both processing methods. The results presented in this study demonstrated the potential use of FFF for producing piezoresistive flexible sensors based on PVDF/TPU/CB‐PPy composites. [ABSTRACT FROM AUTHOR]

In this study, the effects of various types of commercial graphene nanoplatelets (XG Sciences xGnP M5, C300, C500, and C750) on the thermal, electromagnetic shielding (EMI SE), electrical and mechanical behavior of an acrylonitrile–butadiene–styrene (ABS) copolymer matrix were investigated. The selected nanofillers were characterized and compared in term of surface area, different oxygen content, dimension and density (X‐ray photoelectron spectroscopy, scanning electron microscopy, and helium pycnometry). Graphene nanoplatelets were dispersed in ABS by direct melt compounding at 2, 4, and 8 wt%. Melt flow index (MFI) values almost linearly decreased with all the type of xGnPs, especially with the highest surface area nanofiller (C750). Moreover, EMI SE of neat ABS was improved from −0.7 dB to −2.5 dB (increase more than 3 times) for xGnP (C300, C500, and C750) and to −6.2 dB (increase about 9 times) for xGnP‐M5, in agreement with proportional reduction of electrical resistivity. xGnP‐M5 also resulted in being most effective in enhancing the tensile modulus which improved up to 64%, while a maximum increment of about 20% was obtained with the others xGnP nanoparticles. However, yield stress slightly decreased for xGnP‐M5 (about −9%) and remained fairly constant for others nanofillers. Halpin–Tsai model used to predict the tensile modulus of the nanocomposites suggested that graphene nanoplatelets were randomly oriented in the ABS matrix in a three‐dimensional (3D) manner. POLYM. COMPOS., 40:E285–E300, 2019. © 2017 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

Electrically conducting fibers were prepared through in situ oxidative polymerization of pyrrole (Py) in the presence of peach palm fibers (PPF) using iron (III) chloride hexahydrate (FeCl3·6H2O) as oxidant. The polypyrrole (PPy) coated PPF displayed a PPy layer on the fibers surface, which was responsible for an electrical conductivity of (2.2 ± 0.3) × 10−1 S cm−1, similar to the neat PPy. Electrically conductive composites were prepared by dispersing various amounts of PPy-coated PPF in a polyurethane matrix derived from castor oil. The polyurethane/PPy-coated PPF composites (PU/PPF–PPy) exhibited an electrical conductivity higher than PU/PPy blends with similar filler content. This behavior is attributed to the higher aspect ratio of PPF–PPy when compared with PPy particles, inducing a denser conductive network formation in the PU matrix. Electromagnetic interference shielding effectiveness (EMI SE) value in the X-band (8.2–12.4 GHz) found for PU/PPF–PPy composites containing 25 wt% of PPF–PPy were in the range −12 dB, which corresponds to 93.2% of attenuation, indicating that these composites are promising candidates for EMI shielding applications. [ABSTRACT FROM AUTHOR]

Viscoelastic properties of nanocomposite fibers of high density polyethylene (HDPE) and organically modified hydrotalcite were studied. Neat and nanofilled HDPE fibers (with nanofiller content between 0.5 and 3 wt%) were produced by melt spinning and hot-drawing at different draw ratios up to 20. Effect of temperature on storage modulus, loss modulus, and creep compliance were compared. Rising nanofiller content and/or drawing ratio accounted for an increase in storage modulus in the glassy (i.e., below the γ transition at 2100°C) as well as in the rubbery state of noncrystalline regions. The α relaxation temperature readoff for the maximum of the loss modulus peak ranged from 20 to 60°C being dependent on frequency, filler content and draw ratio. Sumita model was successfully applied to evaluate the effective volume fraction of the dispersed phase; maximum fraction of immobilized matrix was observed for the composite with 1 wt% of nanofiller. Creep behavior was evaluated by fitting experimental data with the Burgers model. The addition of a small amount of well-dispersed hydrotalcite (0.5-1 wt%) had a beneficial effect on the creep resistance of drawn fibers at room temperature as well as at 70°C. TEM analysis evidenced a good dispersion of 0.5% nanofiller in as-spun fibers and improved interfacial adhesion after drawing. The best mechanical properties were observed for the composition with 1 wt% of hydrotalcite, due to combined effects of nanofiller reinforcement and stiffening produced by hot drawing. [ABSTRACT FROM AUTHOR]