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Poly(glycerol sebacate) (PGS) is a novel polymeric material intended for applications in tissue engineering (TE). This study involves synthesizing the PGS prepolymer (pPGS) and subsequent manufacturing of porous PGS-based scaffolds with an addition of hydroxyapatite (HAp) by means of thermally induced phase separation followed by thermal cross-linking and salt-leaching (TIPS-TCL-SL). The study aims to investigate the effect of the apatite filler content on properties and morphology of porous PGS/HAp scaffolds. The emphasis is put on the mechanical behavior of the material characterized by means of compression tests and dynamic thermal mechanical analysis (DMTA). In addition to the reference polymer scaffold, the composites with filler contents of 10, 20 and 30 wt% have been examined. Our research revealed that the HAp content does not affect the mechanical properties in a directly proportional manner. The 30 wt% addition of HAp resulted in frayed structure and decrease in the mechanical parameters in comparison to other tested specimens. On the other hand, an addition of 10% did not sufficiently boost the properties. Therefore, a 20% addition of HAp was concluded to have superior mechanical properties in comparison to other analyzed specimens. A similar relationship results from the DMTA studies. Moreover, the strain sweep and frequency sweep tests confirmed the stability of the mechanical parameters in various conditions, as well as the elastomeric nature of the materials. Finally, the material did not exhibit cytotoxicity against standard L929 fibroblasts and cells readily populated the scaffolds. [Display omitted] [ABSTRACT FROM AUTHOR]

The efficient utilization of lignin in 3D printing had attracted increasing attention using this abundant and eco-friendly material. However, the large-scale utilization of lignin in 3D printing remains a great challenge due to its inherent brittleness and non-thermoplasticity. In this study, thermoplastic polyurethane (TPU) was introduced to regulate the rheological properties of lignin for 3D printing. The Lignin/TPU composite of 3D printing exhibited a smooth surface, non-plastic, warm wood touch, and natural color at 50 wt% lignin loading. To further improve the mechanical properties of the composite, carbon fiber (CF) was added to the Lignin/TPU composite. The resulting CF/Lignin/TPU composites possessed 1.7 times higher tensile strength and 2.4 times higher elongation at break compared to Lignin/TPU composite. Meanwhile, the smooth surface of filament and dense interlayer bonds of printed specimens are also achieved. This work provides new insights to realize the high-value utilization of lignin and expands the practical application of lignin in 3D printing. [Display omitted] • TPU imparts lignin flexibility and thermoplastic properties. • Up to 50 wt% lignin composites available for 3D printing • The addition of carbon fiber enhances the mechanical properties of the composite. • Excellent interlayer bonding properties of 3D printed specimens after CF addition [ABSTRACT FROM AUTHOR]

Triply periodic minimum surface (TPMS) porous structures with large cavity ratios and excellent mechanical properties are highly desirable in engineering applications. This study proposes a method for optimizing the structural performance by controlling the orientation of unit cells based on three typical TPMS porous structures with similar porosity. Quasi-static compression tests were conducted on structures with different orientations to comprehensively investigate and verify their deformation behavior, mechanical properties, and energy absorption. The results showed that changing the orientation of unit cells was an effective way to improve the performance of Diamond, Gyroid, and Primitive porous structures, and even to achieve predictable failure behavior by optimizing the orientation of Diamond structures. The morphology of their fracture surfaces was characterized, and the mechanism of their mixed brittle and ductile deformation was identified. Overall, the findings of this work have significant implications for the future development and expansion of TPMS porous structures. [ABSTRACT FROM AUTHOR]

In the present investigation, novel photoluminescent and transparent biocomposite films based on chitosan reinforced with styrylbenzothiazolium- g -cellulose nanocrystal for anti-counterfeiting applications were successfully prepared by casting solvent. Three novel styrylbenzothiazolium derivatives were synthesized by Knoevenagel condensation and characterized by FTIR, 1H, 13C NMR and photoluminescence analysis. These photochromic compounds have been used to functionalize cellulose nanocrystal and the resulting fluorescent photonic materials were characterized by FTIR, 13C-CP/MAS NMR as well as photoluminescent analysis to confirm the successful grafting. It can be concluded that the addition of 5 wt% of fluorescent modified CNC to chitosan matrix increase the photoluminescent properties as well as improved the mechanical properties of the Cs/CNC-dye biocomposite films. These photoluminescent biocomposite film hold promising applicative value in anti-counterfeiting material in large-scale. [Display omitted] [ABSTRACT FROM AUTHOR]

• The mixture of boric acid and borax slow down PLA's fire speed by roughly 66 %. • Thermal degradation temperature lowered by the addition of boron compounds to PLA. • Flexural and Young's modulus prominently rise by roughly 20 % and 22 %, respectively. • 5 wt% boron compounds reinforced composites have better mechanical–thermal results. This study aims to understand how ulexite, boric acid-borax mixtures (1:1), and zinc borate fillers affect the thermal and mechanical properties of the poly (lactic acid) (PLA). For this purpose, three different boron fillers were added to the PLA matrix at four different concentrations of 3 %, 5 %, 8 %, and 12% wt. UL-94 test was conducted to comprehend the impacts of boron fillers on the fire resistance of the biocomposites. Thermogravimetric analysis was applied to determine the thermal stability, mass loss, and decomposition temperature of the samples. The biocomposite's significant mechanical properties, such as tensile strength, flexural strength, Young's modulus, and elongation at break, were assessed using tensile and three-point bending tests. Although the tensile and flexural strengths of PLA reduced, flexural and Young's modulus rose by roughly 20 % and 22 %, respectively, with rising boron filler rates. [ABSTRACT FROM AUTHOR]

Greener and more mechanically robust 3D-printed structures were obtained by adding tannin to acrylate resin. Mimosa tannin particles (5–25 wt %) were incorporated into an acrylate resin formulated and 3D-printed to fabricate tannin-reinforced composites using stereolithography. FTIR spectroscopy and printing parameters highlighted the photoblocking behavior of the tannin particles by adsorption in the UV range and a reddening phenomenon characteristic of phenolic compounds. Tannin-containing samples showed a low penetration depth (from 322 to 127 µm), thus improving the resolution control in the resin tank. The glass transition temperature decreased with the incorporation of stiff tannin microparticle, evidencing change in relaxation time, while mechanical properties improved with increasing tannin content. For instance, the inclusion of 10 wt % tannin improved tensile strength, ductility, and Young's modulus by 110 %, 80 %, and 32 %, respectively. The high resolution and improved mechanical performance demonstrate the promising use of tannin as a bio-based ingredient to produce accurate and reinforced structures. [Display omitted] • Condensed tannin was used to enhance the stiffness of a photosensitive resin. • The presence of a tannin filler allowed for better printing accuracy. • The stiff tannin microparticles increased the tensile strength by up to 110 %. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel inverse biological crossed-lamellar structure was synthesized in CFRP. • This is the first non-biological prototype crossed-lamellar structure in the literature. • The tailored inverse-biologic crossed-lamellar structure is designed to achieve higher load-carrying capacity and stiffness. The remarkable toughness of Strombus gigas shell arises from its microstructure. In this study, inspired by the biologic crossed-lamellar microstructure of Strombus gigas shell, we prepared a novel carbon fiber reinforced polymer (CFRP) composite with inverse-biologic crossed-lamellar structure by replacing the inner and outer layers with the "tough" middle structure. The influences of the alternating arrangement of crossed-lamellar three-layer structure on the mechanical responses, including toughening mechanisms and biological mechanism, were studied. Experimental and numerical results indicated that as burrowing mollusks, Strombus gigas shells require a balance of certain load-carrying capacity and stronger protection function. Meanwhile, the tailored inverse-biologic structure achieved higher load-bearing capacity and stiffness. Additionally, the Bouligand-ply design strategy was proposed as an alternative to the traditional angle-ply design for the crossed-lamellar structure. By changing the laying-up form and pitch angle of the middle layer, a significant improvement in both load-bearing and energy dissipation capacity of the structures was achieved. The paper provides valuable insights for the design of high-performance biomimetic crossed-lamellar structures and holds great potential for the customization of fiber-reinforced composites. [ABSTRACT FROM AUTHOR]

Nanostructured materials are difficult to prepare rapidly and at large scale. Melt-processed polymer-clay nanocomposites are an exception, but the clay content is typically below 5 wt%. An approach for manufacturing of microfibrillated cellulose (MFC)/kaolinite nanocomposites is here demonstrated in pilot-scale by continuous production of hybrid nanopaper structures with thickness of around 100 μm. The colloidal nature of MFC suspensions disintegrated from chemical wood fiber pulp offers the possibility to add kaolinite clay platelet particles of nanoscale thickness. For initial lab scale optimization purposes, nanocomposite processing (dewatering, small particle retention etc) and characterization (mechanical properties, density etc) were investigated using a sheet former (Rapid Köthen). This was followed by a continuous fabrication of composite paper structures using a pilot-scale web former. Nanocomposite morphology was assessed by scanning electron microscopy (SEM). Mechanical properties were measured in uniaxial tension. The fire retardancy was evaluated by cone calorimetry. Inorganic hybrid composites with high content of in-plane oriented nanocellulose, nanoclay and wood fibers were successfully produced at pilot scale. Potential applications include fire retardant paperboard for semi structural applications and as reinforcement mats in molded thermoset biocomposites. [ABSTRACT FROM AUTHOR]

This work deals with fibrous biocomposites prepared by using nettle and poly(lactic acid) fibers and employing carding and compression-molding processes. The role of carding process in determining the tensile strength of the biocomposites was analyzed. The tensile, bending and impact properties of the biocomposites were found to increase initially with the increase of nettle fiber content till 50 wt% and decrease afterwards. The thermogravimetric analysis inferred that the thermal stability of the biocomposites increased with the increase of nettle fiber content. The dynamic mechanical analysis showed that the biocomposites exhibited high storage modulus, low loss modulus, and low damping factor. Further, the biocomposites exhibited excellent biodegradability and their biodegradability increased with the increase of nettle fiber content. Overall, the biocomposite prepared with equal weight proportion of nettle and poly(lactic acid) showed high potential for automotive dashboard panel application. [ABSTRACT FROM AUTHOR]

Natural fibers are not as rigid as glass or carbon fibers. During composites extrusion and injection molding, they tend to bend and twist in the polymeric matrix, thus resulting in fiber waviness and decreased mechanical properties of natural fiber composites. The most widely used models for the estimation of interfacial shear strength (IFSS) and elastic modulus, which consider the fiber aspect ratio and mechanical properties of the fiber and matrix, do not consider these important features. In order to account for fiber waviness, an effective fiber length is proposed in this paper. The undulation of the fibers is approximated with a sinusoidal arc along with a calculated new length. The proposed correction factor depends on the wavelength and amplitude of the wave approximating the fiber. To verify this method, blends of polylactic acid (PLA) and polycarbonate (PC) (prepared with and without an interchange reactions catalyst) with addition to various percentages of cellulosic fibers (5 wt%, 10 wt% and 15 wt%) have been prepared and characterized. It has been demonstrated that by considering the corrected length values, it is possible to predict the mechanical properties and the effective reinforcement attained in the composites by using the most widely used models. In particular, the prediction of the elastic modulus is slightly affected by this correction, whereas the calculation of IFSS is strongly dependent on it. [ABSTRACT FROM AUTHOR]

In the research, paper was successfully coated with curdlan and chitosan (CR/CH) coating solutions at different ratios (CR/CH ≈ 10:0, 8:2, 6:4, 5:5, 2:8, 4:6, 0:10% w/w). The novelty of this paper is in the use of combination of curdlan and chitosan, which led to a positive effect on the mechanical and water barrier properties. The tensile properties were improved when the ratio between polymers was 5:5. Coated papers were further investigated for their bursting strength, tear and bending resistance. Pure curdlan coating worsen the tensile and moisture properties and allowed to prepare the blend coatings with different amounts of chitosan. The equilibrium thickness of coatings as a function of curdlan content and tensile strength has shown a decrease in tensile strength. This has resulted in reduction of tensile strength especially at higher thickness. The resulting blend curdlan/chitosan coatings exhibited good water barrier and mechanical properties and could be used in many fields. [ABSTRACT FROM AUTHOR]

Biocomposites have major advantage in term of weight saving thanks to lower densities compared to conventional materials; this property also allows a reduction of environmental impacts which is beneficial for the automotive industry. In addition, they maintain rather good mechanical properties after recycling cycles which makes possible to consider other end-of-life scenarios than incineration or landfill. In this work, we studied two potential routes for the recycling of moulding wastes from poly-(propylene)-flax nonwovens. By representing close to 25%-wt, these wastes are a major industrial problem, inducing additional recycling or treatment costs. In a first step, the parts were grinded and reincorporated at different weight fractions into virgin nonwovens. Up to 30%-wt of reincorporated wastes, results showed good mechanical performances for recycled nonwovens, especially in bending mode. In a second stage, scraps were grinded and then compounded for injection moulding applications. Their good rheological behavior and ability to conserve fibre lengths during extrusion made possible to formulate competitive materials in terms of tensile performances. [ABSTRACT FROM AUTHOR]

This work aims the manufacture of injection molded polylactic acid (PLA)-based magnetic biocomposites, presenting an alternative approach to enhance the magnetic susceptibility of PLA-based biocomposites without resorting to the exclusive incorporation of magnetic nanoparticles whose long-term side effects are still unclear. Magnetic biocomposites were obtained by incorporating 5 wt% of iron doped biphasic calcium phosphate (FeBCP) powders into the PLA matrix and compared with similar composites containing 2 and 5 wt% of non-doped BCP powder, as well as neat PLA. The chemical, thermal, mechanical, and magnetic performances were evaluated. Biodegradability according to two sterilization methods used and cytotoxicity were also assessed. The composites with FeBCP exhibited a typical ferromagnetic-like behavior and presented a superior tensile strength even with low concentrations of FeBCP, when compared to PLA or non-doped composites, besides being cytocompatible. The presented proof of concept paves the way for future developments of new magnetic PLA-based biocomposites for biomedical applications. [Display omitted] • New generation of magnetic PLA-based composites preventing the use of MNP. • Magnetic BCP powders improved the mechanical performance of PLA-based composites. • Homogeneous distribution of magnetic BCP-based powders within PLA matrix was attained. • BCP powders improved the thermal stability of PLA. [ABSTRACT FROM AUTHOR]

Composite materials based on renewable agricultural and biomass feedstocks are increasingly utilized as these products significantly offset the use of fossil fuels and reduce greenhouse gas emissions in comparison with conventional petroleum-based materials. However, the inclusion of natural fibers in polymers introduces several challenges, such as excess water absorption and poor thermal properties, which need to be overcome to produce materials with comparable properties to the conventional composite materials. Instead of using rather expensive chemical and physical modification methods to eliminate these aforementioned challenges, a new trend of utilizing waste, residues, and process by-products in natural fiber-polymer composites (NFPCs) as additives or reinforcements may bring considerable enhancements in the properties of NFPCs in a sustainable and resilient manner. In this paper, the effects of waste materials, residues or process by-products of multiple types on NFPCs are critically reviewed and their potential as NFPC constituents is evaluated. [ABSTRACT FROM AUTHOR]

In this present work a highly flexible electromagnetic interference (EMI) shielding composite was prepared from industrial crop for advanced engineering applications. The EMI shielding composite product was further tested for its effectiveness on high frequency bands of 8–20 GHz. Through pyrolysis, the leftover rubber seed hulls were converted into carbon dots (C-dots). The composites were characterized after being made using the solution casting process. The inclusion of carbon dots increased the relative permittivity up to 9.4 with the lowest loss factor of 0.62 at 8 GHz, according to the findings. The hysteresis loop showed a broader "S" curve for cobalt with biochar at a 2 vol% concentration. Additionally, the composite contains 3 vol% of cobalt/carbon dots records a maximum tensile strength of 54.7 MPa, modulus of 0.88 GPa, and % of elongation of 128.7. However, the composite contains 5 vol% of cobalt/carbon dots (PBC4) had a total EMI shielding effect of − 54.3 dB at 20 GHz. These enhanced EMI shielding composites with highly retained flexibility could be employed as a protective material in telecommunication; chip sets manufacturing, defense and medical applications. • Carbon dots were successfully prepared from waste rubber seed hulls. • Cobalt/C-dots compound structure PVA composite prepared. • Measurement of total EMI shielding efficiency is improved for 2 vol% Co/C-dots. • The total EMI shielding up to − 54.7 dB was measured for Ku band. • The tensile and hardness properties measures 45% of improvement. [ABSTRACT FROM AUTHOR]

Engineered bamboo scrimber has processed from the raw bamboo culm into a compressed or laminated product with thermosetting resin in the density range of 800–1200 kg/m 3 . The present work investigates the mechanical properties of commercially available engineered bamboo scrimber and compares the results of present work with the existing results in the literature. The main aim of this work is to investigate the influence of bamboo scrimber densities on the mechanical properties. The strength and modulus properties in tensile, compression, shear and flexural were evaluated using the specimens of three different densities. The dynamic modulus of elasticity of bamboo scrimber beams were evaluated using ultra-sonic pulse method. According to the present results it can be concluded that the density have significant influence on the mechanical properties of bamboo scrimber. The long term water absorption was also conducted to analysis the weight gained by the bamboo scrimber having different densities and the results revealed that density of specimen’s influences the water absorption. [ABSTRACT FROM AUTHOR]

The production of ligno-cellulosic biomass-based composites requires the development of new methodologies to evaluate the reinforcement potential of a given biomass, such as miscanthus studied in the work. Miscanthus stems from thirteen genotypes were broken into elongated fragments and mixed with polypropylene composites in an internal mixer. The aim is to find the best protocol able to discriminate miscanthus genotypes for their reinforcement capability. The following process parameters were optimized in order to maximize the reinforcement effect of the stem fragment filler: mixing parameters (mixing time, rotor speed and chamber temperature), temperature, fragment content, size and length distributions and coupling agent. The relationship between the process parameters and the mechanical properties of composites were analyzed to evaluate the influence of genotype on reinforcement performance, showing the robustness of the protocol in effectively discriminating genotypes according to their reinforcing capacity. [ABSTRACT FROM AUTHOR]

[Display omitted] • Waste coffee grounds improve the flame retardancy and reduce toxic gases emissions of epoxy composites. • Reducing the size of coffee grounds further improves the flame. • Reduced size coffee grounds can achieve similar peak heat release rate reduction as commonly used inorganic flame retardants. • A micro mechanical finite element model has been developed to predict the tensile strength of particle/epoxy composites. Waste coffee grounds, a biomaterial with high carbon content, have been suggested as a non-toxic organic flame retardant due to their high char forming and radical scavenging properties. Herein, investigations are conducted on the effects of waste coffee grounds, especially their concentration and particle size, on the mechanical properties, flame retardancy, toxic gas production of epoxy composites. Results reveal that reducing average size of the waste coffee grounds from 46 µm to 16 µm, using freeze-milling or filtering, can reduce peak heat release rate and total heat release of their epoxy composites by 52.0% and 33.7% respectively, exceeding the effectiveness of other bio-based flame retardants such as chitosan, lignin and seashell. More importantly, the fine coffee grounds can achieve the same performance as aluminium trihydrates, the most widely used non-bio flame retardant. Furthermore, the burning rates and emissions of toxic gas have also been greatly reduced, almost entirely suppressing the highly toxic NO 2 gas. The findings provide new insights into the effect of particle size of waste coffee grounds on both the mechanical properties and flame retardancy performnance of epoxy composites. [ABSTRACT FROM AUTHOR]

Commingled plant and polypropylene fibres (PP) nonwovens are attractive for automotive industry because of their interesting mechanical performances combined with good acoustical properties. This double function is achieved thanks of controlled porosity within the composite material. Indeed, from a same material, different functions (acoustic or mechanical) can be obtained by only varying the compaction rate during moulding. This study aims to highlight the necessity of a very large porosity volume fraction (60%) to reach good acoustic properties and understand the mechanical effect behind it. By combining tensile testing, acoustic absorption measurement and scanning electron imaging analysis, the microstructure, acoustic and mechanical properties have been investigated and were found to be intimately related to the material porosity content. As expected, when increasing porosity level from 5 to 60%, the material behaviour change and its tensile properties (modulus, strength and elasticity domain) drop drastically to a point where the material is no longer elastic (70% porosity) due to a modification of the material microstructure involving different failure mechanisms. [ABSTRACT FROM AUTHOR]

Environmental awareness of the global waste problem has driven the development of new green composites made from either renewable or biodegradable materials. Among the variety of available green composites, natural composites based on poly-lactic acid (PLA) have shown noteworthy performance due to their short degradation time after disposal, good strength, and ease of processing by conventional methods. In particular, green composites manufactured with PLA matrix reinforced with Manicaria Saccifera fabric (MF) display mechanical properties that have shown to be very competitive compared with similar materials. In this study, the tensile properties of a green composite of PLA reinforced with MF are optimized by using a Taguchi method approach. The processing parameters, fabric chemical treatment parameters, compression molding parameters, and fiber content are analyzed simultaneously to yield the optimum biocomposite properties. The predicted optimum parameters are experimentally verified. Tensile tests and scanning electron microscope (SEM) analysis are used. Significant improvements on both the tensile strength (114.2%), and the elastic modulus (120.6%) of the biocomposite are achieved. [ABSTRACT FROM AUTHOR]

• The study aims to use agricultural waste deriving from production processes. • Acoustical, mechanical and thermal properties were studied. • Good sound absorption properties with low thicknesses and air–gap behind the sample. • Acceptable mechanical and thermal properties for their use as ceiling tile. • Possible alternative to traditional materials used for noise control applications. This work deals with experimental research about acoustic panels made of agricultural waste to be used as ceiling tiles, providing a sustainable and environmentally friendly alternative to traditional building materials. The raw materials used in this work were rice husk, vine pruning residues, cork (white cork, virgin cork, and expanded cork), and prickly pear. All of them were bonded with a water-based acrylic resin in different proportions. The obtained panels were mechanically, thermally and acoustically tested. The flexural and the dynamic modulus of elasticity, as well as other important physical properties, such as open porosity, tortuosity or flow resistivity, and thermal conductivity, were obtained. The sound absorption coefficient of the biocomposites was experimentally measured, using an impedance tube, and modeled, using the Zwikker and Kosten model, over the frequency range from 200 Hz to 6400 Hz. The results showed values of sound absorption coefficients close to 0.80 and acceptable flexural strength for their use as suspended ceiling tiles. Therefore, these new categories of biocomposites provide sustainable bio-based materials that can be an alternative to the traditional acoustic ceiling panels, mainly composed of synthetic fibers or foams and petroleum-based resins. [ABSTRACT FROM AUTHOR]

Soy-castor oil-based polyurethane acrylate prepolymer (SCPUA) was synthesized by using epoxidized soybean oil and ricinoleic acid as raw materials, and a cost-effective halogen-free flame retardant phosphorous silicon methacrylate monomer (PSMAM) was also synthesized and used as an efficient reactive diluent to mix with SCPUA to develop a novel vegetable oil-based UV-curable coating system. Benefited from the addition of PSMAM, the limiting oxygen index (LOI) of the coatings reaches up to 23%, and the coatings can self-extinguish instantly (within 1 s) after removing from flame, indicating that these coatings possess remarkable flame-retardant performance. Also, the flame-retardant mechanism is proposed, and it reveals that PSMAM promotes the formation of a dense and continuous char layer on the coating surface to serve as a heat and oxygen barrier, thus providing the coatings with remarkable flame retardancy. Besides, the use of PSMAM can improve the thermal stability of the coatings. More strikingly, these coatings exhibit excellent hardness (6H), flexibility (2 mm), adhesion (4B) and remarkable acid and alkali resistance as well as boiling water resistance. Therefore, excellent performances and cost-effective feature as well as the facile synthesis process make these newly-developed halogen-free flame-retardant vegetable-oil based UV-curable coatings more potential for practical applications. [Display omitted] • An efficient reactive flame retardant active diluent was prepared from GPTES. • A novel soybean-castor oil-based PUA with high bio-content was synthesized. • The composite UV-cured films had showed excellent flame retardant properties. • The bio-based coatings showed great potential to replace the traditional coatings. [ABSTRACT FROM AUTHOR]

Highlights: [•] Coir-polypropylene biocomposites were manufactured using hot press technique. [•] OH groups in raw coir cellulose were converted to OH−Cr groups during treatment. [•] SEM indicates improved interfacial adhesion between coir and PP upon treatment. [•] Chemically treated composites yielded the best set of mechanical properties. [ABSTRACT FROM AUTHOR]

Abstract: For the first time, biocomposites from wheat by-products, i.e. wheat gluten and wheat straw fibers, were prepared using a thermomechanical process. Three types of wheat straw fibers displaying contrasted sizes (median diameter d 50 =1.1mm, 62μm and 8μm), morphologies and surface reactivities were prepared by successive grinding processes (cut milling (CM), impact milling (IM) and ball milling (BM), respectively). The main objectives of the present study were (i) to gain further scientific knowledge about the impact of fibers characteristics on the mechanical properties of these composite materials, and (ii) to evaluate in which extent the addition of wheat straw fibers could decrease the final cost of materials without altering their mechanical properties. Mechanical properties were assessed through tensile tests and discussed in relation to the structure of materials, especially to the interfacial adhesion between the fiber and the matrix. Globally, an increasing fiber content up to 11.1vol% led to an increase in both the Young''s modulus and the stress at break, and to a reduction in the strain at break. Experimental Young''s moduli were well predicted by the Tsai–Pagano model for the three types of fibers. Data of specific mechanical energy consumed upon processing, contact angle measurements and observations of cryo-fractured surfaces allowed to demonstrate that the adhesion at the interface wheat straw fiber/wheat gluten was improved by (i) an increased hydrophobicity of wheat straw fibers, which was induced by successive grinding, and (ii) a higher specific surface of fibers which was favoured in the case of small fibers. The interfacial adhesion was improved in the order BM>IM>CM whereas the fiber aspect ratio decreased in the order CM>IM>BM. Thus, a competition between these parameters could occur, explaining why no significant difference in reinforcing effect was achieved between the three types of fibers. Finally, the reinforcing effect of wheat straw fibers was also ascribed to a deplasticizing effect, which was particularly pronounced for BM wheat straw fibers. [Copyright &y& Elsevier]

Abstract: This work describes a truss-core structure made of hemp/epoxy biocomposite based on a topology with auxetic (negative Poisson’s ratio) characteristics. Epoxy-based composites with 25wt.% of hemp yarns have been manufactured and characterized with tensile and flexural tests. Truss-core hexagonal chiral panels with the biocomposite core have been produced using a Resin Transfer Molding technique. The panels have been subjected to standard transverse shear tests, and their properties predicted with a Finite Element nonlinear modeling. The results show that the hexachiral biocomposite truss core exhibits specific shear modulus and strength significantly higher compared to the ones observed in previous demonstrators made of polymeric core. [Copyright &y& Elsevier]

Abstract: The effective elastic behaviour of a biopolymer composite with random microstructure is studied. The effective elasticity modulus is computed as function of the protein fraction with the hypothesis of an imperfect interface. This interface is handled considering normal and tangential stiffness parameters. The methodology assumes the direct import of real microstructures of starch–protein (zein) composite, obtained using Confocal Laser Scanning Microscopy (CLSM), into a finite element model. A static linear analysis is conducted to determine the influence of interface rigidities, zein fraction and interface quantity on the effective properties. Predictions show that the effective modulus is nonlinearly correlated to the product of stiffness parameters for which the normal stiffness is the most influential parameter. The effective property dependence with respect to interface related variables and zein fraction shows a logarithmic influence of the stiffness parameters when increasing zein fraction. [Copyright &y& Elsevier]

Abstract: In this work, a starch-based biopolymer was reinforced with flax strands. Composite materials at different fiber content were obtained by means of high-shearing mixing followed by injection molding processing. The evaluation of the mechanical properties gave a significant increase of the strength and stiffness of composites with the percentage of flax strands. The enhancement was analyzed in terms of compatibility and extension of the adhesion at fiber–matrix interface. The intrinsic mechanical properties of the reinforcement were measured and the behavior of the obtained composites was studied in terms of the modified rule of mixtures and the modified Halpin–Tsai equations. [Copyright &y& Elsevier]

Abstract: Thermoplastics reinforced by natural fibres are mainly used for fitting-up products in the automotive industry. The aim of this work is to study the tensile properties of natural fibre-biopolymer composites in order to determine whether or not, biocomposites may replace glass fibre reinforced unsaturated polyester resins. The materials used are flax fibre, polylactic acid (PLA), l-polylactide acid (PLLA), poly(3-hydroxylbutyrate) (PHB), polycaprolactone and starch thermoplastic (MaterBi® Z), poly(butylene succianate) (PBS) and poly(butylene adipate-co-terephtalate) (PBAT). The tensile properties of the flax fibres have already been determined [C. Baley, Analysis of the flax fibres tensile behaviour and analysis of the tensile stiffness increase, Comp Part A 2002;33:939–948]. The composites are manufactured using a film stacking technique. After studying the processing parameters, these are then adapted to each thermoplastic composites. Test samples are cut out from the composites to test their mechanical properties under tensile loading conditions. These tensile properties are then compared to those of similar polypropylene flax composites. Preliminary results show that the tensile properties are improved with the fibre volume fraction. The tensile strength and Young’s modulus of PLLA and PLA flax composites are greater than those of similar PP/flax fibre composites. The specific tensile strength and modulus of flax fibre/PLLA composite have proved to be very close to those of glass fibre polyester composites. [Copyright &y& Elsevier]

Abstract: This paper is focused on the analysis of the thermal and mechanical behaviour of processed biocomposites (biodegradable composites). These materials have been created by extrusion and injection moulding. The matrix, a biodegradable and aromatic copolyester (polybutylene adipate-co-terephthalate), has been fully characterised (NMR, SEC). The lignocellulosic materials used as fillers are a by-product of an industrial fractionation process of wheat straw. Different filler fractions have been selected by successive sieving, and then carefully analysed (granulometry, chemical structure). Cellulose, lignin, and hemicellulose contents have been determined through different techniques. The biocomposites thermal behaviour has been investigated by TGA (thermal degradation) and DSC (transition temperatures, crystallinity). These materials present good mechanical behaviour due to high filler-matrix compatibility. The impacts of filler content, filler size and the nature of each fraction have been analysed. To predict the mechanical behaviour, Takayanagi’s equation seems to provide an accurate answer to evaluate the modulus in a range, 0–30wt% of fillers. [Copyright &y& Elsevier]

• Bamboo advantages including growing fast, strong mechanical properties, and low-cost. • Plantation, harvesting and processing of bamboo has global socio-economic benefits. • The increase in the alkali concentration reduces wax, ash contents, and cellulose. • There is an optimum NaOH concentration level, immersion time, and temperature level. • Excessive alkali concentration damaged the fibers and affects the mechanical properties. Applying bamboo fibers into the composite reinforced concrete governs some significant drawbacks, including inadequate adhesion between fiber and matrix interface, and hydrophilic nature. Thus, the mercerization of bamboo fibers is suggested to overcome these limitations. In this review, the thermal and mechanical properties of alkalized bamboo fibers have been evaluated. It was concluded that alkalization treatment of bamboo fibers could provide enhanced bio-composites properties up to a great extent. Besides, the betterment of the thermal stability and mechanical properties of the alkalized bamboo fibers and its composite depends closely on the temperature level, immersion time, and NaOH concentration percentage. [ABSTRACT FROM AUTHOR]

• The effect of open-hole on mechanical properties of flax laminates was investigated. • Strain field around hole was analysed using Digital image correlation. • Acoustic emission was used to monitor the progressive damage during tensile testing. • Acoustic events were classified to calculate the contribution of each damage modes. • SEM pictures were used to visually identify the damage mechanisms. The present paper is dedicated to the assessment of the damage taking place in open-hole flax bio-epoxy laminates with different stacking sequences. Tensile test results have shown significant effects of the open hole on the performance of the laminate. Moreover, strain maps have allowed to detect the onset of cracks and to discuss their contribution to the laminates failure. For unidirectional laminate, splitting was observed as the main damage at the hole boundary along the fiber orientation and parallel to the loading axis. However, the [0 90] 6s laminate failure has caused by the onset of subsurface cracks in the 90° plies. Even if the tensile strength was decreased, the strain fields result has shown a less hole sensitive behavior of the [0 +45 90 −45] 3s laminate. Finally, damage monitoring using acoustic emission has shown a significant increase of the fiber-matrix debonding and fiber breakage contribution to the laminate failure. [ABSTRACT FROM AUTHOR]

Despite various properties and functionalities of natural fillers, their use as a toughening agent in biocomposites is hindered because of their hydrophilicity. Synthetic and costly functionalization agents such as silanes are generally used to reduce the hydrophilicity of natural fillers. Herein the performance characteristics of epoxy biocomposites are evaluated by replacing silane functionalized bamboo micron fibers (BMFs). An efficient and eco-friendly method to functionalize BMFs using tannic acid (TA) is proposed in this work to prepare toughened biocomposites. The TA akin to the silanes reduces the liquid retention value of the BMFs by ~30%. However, silane functionalized BMFs is found to offer limited resistance to mechanical constraint in the biocomposites. The TA treatment helped regain the capability of BMFs to offer stiffness modulation at the interfaces within the epoxy network. Even though the polysiloxane oligomers on BMFs significantly improves the tensile strength of the biocomposites by ~26% but the TA coated BMF showed their considerable capacity to increase the tensile strength by ~19%. Noteworthy improvement in the fracture toughness and fracture energy by ~60%, and ~212% respectively is demonstrated by the biocomposites prepared using TA treated BMFs. Our work shows that TA can be a safe, natural, and eco-friendly alternative functionalization agent for natural fillers and to exhibit the untapped nature of TBMFs in toughening the epoxy biocomposites. Image 1 • Green process of functionalizing bamboo micron fibers (BMFs) by Tannic acid (TA). • TBMFs based composites demonstrate a significant increase in Young's modulus (E) than the other composite samples. • Improved fracture toughness by ~60% and fracture energy by ~212% in comparison to the neat epoxy. • Reduction in moisture retention for TBMF as well as for the composites. [ABSTRACT FROM AUTHOR]

• A cyclic hydrothermal ageing alters non-embedded flax fibers and flax/epoxy composite. • The ageing induces a drop of composite's moduli after the first cycles of exposure. • A drop of composite's tensile stress and strain happen after long time exposure. • Mechanical properties changes are linked to morphological and chemical evolutions. • Composite's mechanical properties changes are of low amplitude, which is promising. The use of vegetal fibers to reinforce polymeric matrix composites is challenging and goes with questions of durability issues, especially when exposed to damp conditions. The aim of this study is to quantify, up to 1 year, the impact of humidification/drying cycles, i.e. 3.5 days at 90% HR and 3.5 days at 40% HR, both at 55 °C, on the longitudinal mechanical properties of a unidirectional flax/epoxy composite. Then, by a multi-scale analysis, the objective is to identify the causes of mechanical properties evolutions. According to the results of this study, a cyclic hygrothermal ageing induces irreversible degradations of fibers (matrix-embedded or not) and interfaces within the composite. Indeed fiber/fiber and fiber/matrix debondings have been observed by morphological analyses and a loss of fibers hydrophilic components has been highlighted by chemical and microstructural characterizations. A plasticization of flax fibers has also been shown during this kind of ageing. All these modifications induce a drop of composite's moduli after the first cycles of exposure and a decrease of ultimate tensile stress and strain after long time exposure. But these mechanical properties evolutions are much lower than the values found in the literature. Decreases of about -10% for the modulus and about -14% for the ultimate tensile stress have been recorded after 1 year of exposure and 52 cycles of ageing. Thus, this study highlighted that a well manufactured flax/epoxy composite is resistant to a cyclic hygrothermal ageing. These results are therefore promising for the development of this type of bio-based materials on a larger scale. [ABSTRACT FROM AUTHOR]

This study investigates the evolution of hygromechanical properties of flax/PP nonwoven composites in a wide range of environmental Relative Humidity (RH) conditions from 10 to 98% RH. The influence of microstructure with various porosity content (Φ = 5, 30, 50%) on the mechanical and hygroscopic behaviours is studied and compared to glass/PP composites as a baseline. No significant changes in the moisture content and mechanical properties of glass-fibre reinforced composites are observed. For flax fibre nonwoven composites, the porosity greatly impacts the kinetic of sorption with moisture saturation varying from 9 h to 15 days with decreasing voids. Hygroscopic expansion is hardly modified by the porosity content while anisotropic expansion is always observed. Tensile behaviour and properties are slightly changed over a range of 10–75%RH but negatively impacted between 75% and 98% RH. Interestingly, unlike the tangent tensile modulus and strain at rupture of flax/PP composites, the yield strength exhibits a non-monotonic trend with an optimal value over 50% RH; compressive stresses at the fibre/matrix interface induced by flax fibres hygroexpansion are proposed to explain this trend. • Evolution of hygromechanical properties of flax/PP non-woven composites was investigated. • A large range of porosity (5, 30, 50%) and humidity (10–98%) was explored. • The kinetic sorption behaviour was greatly impacted by porosity content. • Tensile behaviour and properties are slightly changed over a range of 10–75%RH. [ABSTRACT FROM AUTHOR]