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This is the first attempt to combine disposed bottle caps and natural fibres into sandwich panels. A full factorial design is performed to identify the effects of the skin type (aluminium or coir fibre reinforced laminates) and bottle cap core packing (cubic and orthotropic) on the mechanical properties of the proposed panels. The coir fibre composite skin provides maximum core shear strength, 29 % higher than the aluminium-based panels, in cubic packing, while the flexural modulus is reduced by 45 %. An interlocking effect between the skin and the core is evidenced when coir fibre composites are used. In addition, the cubic cell packing increases the specific mechanical properties, even though with a higher density. The results highlight a promising association of green components and plastic bottle caps for secondary structural applications.

Cementitious composites reinforced with silica, silicon carbide or carbon microfibres are designed, manufactured, characterised and tested as porous restrictor for aerostatic bearings. Carbon microfibres are residues obtained from the cutting process of carbon fibre-reinforced polymers. Porosity, permeability, flexural strength and stiffness are quite relevant in the design of aerostatic porous bearings. A 3141 full factorial design is carried out to identify the effects of particle inclusion and water-to-cement ratio(w/c) factors on the physical and mechanical properties of cementitious composites. Higher density material is achieved by adding silicon carbide. Higher porosity is obtained at 0.28 w/c level when silica and silicon carbide are used. Carbon microfibres are not effective under bending loads. Higher compressive strength is reached especially when silica particles are combined with 0.33 or 0.35 w/c. According to the permeability coefficient values the cementitious composites consisted of CMF (0.28 w/c), silica (0.30 w/c) or silicon carbide (0.30 w/c) inclusions are promising as porous restrictor; however, carbon microfibre porous bearings achieved the lowest air gap variation under the tested working conditions.

A full factorial design (2 231 ) has been used to investigate the effect of the use of sodium hydroxide fibre treatment, Portland cement and uniaxial pressure on the physical and mechanical properties of hybrid short coir fibre reinforced composites (HSCoirFRCs). The response variables considered in this work were the apparent density, porosity, tensile and flexural strength , the modulus of elasticity and the Charpy impact resistance. The alkali treatment contributed not only to reduce the apparent porosity , but also to increase the mechanical properties of the HSCoirFRCs. A reduction of the impact resistance and an increase of the apparent density was also identified after treatment. Cold pressing significantly affected the physical and mechanical properties of the HSCoirFRCs. Higher pressure levels enhanced the wettability of the fibres and, consequently, the mechanical performance of the composites. The incorporation of cement microparticles as a second reinforcement phase was however not effective, leading to decreased strength and an increased apparent density of the materials. The HSCoirFRC structure can be considered an economical and sustainable alternative for future secondary structural parts in lightweight transport applications.

Over the last few decades, a significant amount of research has been focused on the use of natural fibres as reinforcement in polymers, due to their intrinsic properties such as sustainability, easy availability and processing, biodegradability and moderate mechanical strength. Among natural fibres, coir is a low-cost fibre extracted from coconut palm which is extensively produced in Brazil. A full factorial design was carried out to investigate the effects of the manufacturing and composition parameters on the mechanical and physical properties of short coir fibre–reinforced composites (SCoirFRCs). The random short fibres were mixed with epoxy polymer and compacted by uniaxial pressure. The physical and mechanical responses, namely, apparent density, impact resistance, flexural strength and modulus, were investigated under a design of experiment approach. SCoirFRCs fabricated with 35% of fibre volume fraction, 375 g/m2 of fibre grammage and HY956 epoxy hardener type achieved higher flexural modulus and impact resistance, while those consisting of 30 vol% of coir fibres, HY956 type and 300 g/m2 of grammage revealed higher flexural strength. The findings revealed that the mechanical properties of SCoirFRCs are substantially dominated by the properties of the matrix phase and fibre wettability.

This work investigates the effect of silica nanoparticles functionalized with poly-diallyldimethylammonium chloride (PDDA) and silica microparticle inclusions (1.0 wt% and 3.5 wt%) on the impact resistance of hybrid carbon fibre reinforced composite laminates (HCFRCs) and tensile modulus of particle reinforced polymers (PRPs) via Full-Factorial Design of Experiments. The data were analysed with Analysis of Variance (ANOVA). The inclusion of particles led to reduced impact absorption of HCFRCs, except for composites with 1.0 wt% of silica in microscale, which provides an increase of 11.75% in the impact resistance. Microstructural analysis of fractured impact samples revealed pull-out as the predominant fracture mode in 1.0 wt% silica microparticle composites. Such mechanism leads to impact energy dissipation which may explain the increased impact resistance of these samples.

Surface modification induced by sodium carbonate on coir fibres was studied in view of its application as a reinforcing agent in polyester and epoxy polymer fibre-reinforced composites. Coir fibres were treated with a 10 wt% sodium carbonate solution for different periods of time (24, 96 and 168 h) at room temperature. The surface treatment was evaluated by scanning electron microscopy, X-ray diffraction and thermogravimetric analysis. Tensile, flexural and impact properties of treated and untreated coir fibre-reinforced composites were compared. Coir-reinforced epoxy and polyester composites were manufactured by the uniform dispersion of randomly oriented coir fibres within the polymeric matrix. Tensile and flexural modulus of coir-reinforced polyester composites increased nearly 28% and 25%, respectively after 96 h of coir treatment. An analogous increase of 31% and 17% was obtained for coir-reinforced epoxy composites. In addition, coir-polyester composites achieved superior tensile (∼17%) and flexural (∼5%) modulus and impact strength (∼193%) compared with coir-epoxy-derived composites. In contrast, coir-epoxy composites led to superior tensile and flexural strength. The experimental results revealed that sodium carbonate solution effectively removes hemicellulosic compounds, promotes swelling and increases superficial roughness of the fibres, improving the mechanical properties (modulus and strength) of the coir-reinforced composites studied.

The work describes the manufacturing and testing of novel hybrid epoxy/carbon fibre composites with silica micro and poly-diallyldimethylammonium chloride-functionalised nanoparticles. A specific chemical dispersion procedure was applied using the poly-diallyldimethylammonium chloride to avoid clustering of the silica nanoparticles. The influence of the various manufacturing parameters, particles loading, and mechanical properties of the different phases has been investigated with a rigorous Design of Experiment technique based on a full factorial design (2131). Poly-diallyldimethylammonium chloride-functionalised silica nanoparticles were able to provide a homogenous dispersion, with a decrease of the apparent density and enhancement of the mechanical properties in the hybrid carbon fibre composites. Compared to undispersed carbon fibre composite laminates, the use of 2 wt% functionalised nanoparticles permitted to increase the flexural modulus by 47% and the flexural strength by 15%. The hybrid carbon fibre composites showed also an increase of the tensile modulus (9%) and tensile strength (5.6%).

International audience; This work investigates the effects of ageing on autoclaved composites made with unidirectional prepreg epoxy and flax tape in environments with 50% and 100% of relative humidity. A Design of Experiment (DoE) has been used first to determine the effect of the ageing time (0,2, 4, 6, 8 and 16 days), type of bending (3-point and 4-point bending) and fibre orientation (longitudinal and transverse) on the water absorption and flexural properties of 50% saturated composites. A second experiment at 100% humidity has been also performed to further characterise the composites and to identify the equivalent ageing time that provides the mechanical behaviour of the 50% humidity samples after sixteen days. The water absorption and apparent porosity levels increase progressively with the ageing time, in particular for the case of transverse laminates; these features compromise the flexural properties of the composites. The laminates subjected to 4-point bending showed increased water absorption levels and improved flexural properties compared to the samples under 3-point bending. The flexural properties of flax composites at 50% humidity after 16 days are equivalent to those shown by composites immersed in water for less than one day.

Fibre metal laminates (FMLs) have been widely used to manufacture airframe components. This work describes novel sisal fibre reinforced aluminium laminates (SiRALs) that have been prepared by cold pressing techniques and tested under tensile, flexural and impact loading. The pristine sisal fabric and the sisal fibre reinforced composites (SFRCs) were also tested to understand the difference in mechanical performance of the sisal fibre metal laminates. The SiRALs achieved not only the highest modulus and strength, but also the highest specific properties. The mean specific tensile strength and modulus of the SIRALs reached increases of 132% and 267%, respectively, when compared to the sisal fibre reinforced composites (SFRCs). Moreover, the mean specific flexural strength and modulus of the SiRALs were significantly higher than SFRCs, revealing increases of 430% and 973%, respectively. A delamination fracture mode was noted for SiRALs under bending testing. The SiRALs can be considered promising and sustainable composite materials for structural and multifunctional applications.

Hybrid Glass Fibre Reinforced Composites (HGRFCs) made with unidirectional glass fibres and silica or cement microparticles inclusions were investigated in order to improve their performance under flexural and impact loadings. Two full factorial designs were conducted to evaluate (i) the effect of the particle weight fraction on the compressive modulus of epoxy polymer (2131) and (ii) the effect of the number of layers and type of particle (32) on the apparent density, flexural modulus and strength of HGFRCs. Composites with higher flexural properties were evaluated under impact loading via one-way analysis. TGA and FTIR analyses were used to verify the effect of ceramic particles within the polymeric phase. A microstructural analysis (SEM) was performed to verify the fracture mode and better assess the mechanical performance of HGFRCs.

Fiber-reinforced composites (FRCs) have been used to replace conventional materials in a wide range of applications in transportation and civil engineering. The dispersion of nanoparticles and microparticles into epoxy matrix phase has been widely investigated to enhance the mechanical properties of hybrid FRCs. The nanoparticles generate large attractive forces among themselves, providing a significant tendency to agglomerate. A chemical treatment based on diallyldimethylammonium chloride (PDDA) was evaluated to disperse the silica nanoparticles within the epoxy polymer. A microstructural analysis was conducted to better assess the results. Experimental analysis was carried out based on the analysis of variance (ANOVA) and Tuckey test in order to verify the effect of PDDA treatment, silica particle size (micro and nano), and silica particle inclusion (1, 2, and 3.5 wt.%) on the mechanical properties of epoxy polymer commonly used as matrix phase in FRCs. The PDDA treatment was able to disperse the silica nanoparticles. The incorporation of 1 wt. % of silica micro or 1 and 2 wt. % of nanoparticles slightly improved the tensile strength and modulus of the epoxy polymer.