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This work evaluates a new eco-friendly surface treatment method for coir fibres based on sodium bicarbonate (NaHCO3). The fibres are treated with 10 wt% NaHCO3 solution for different periods of time (24, 96 and 168 h). A 2141 Full Factorial Design is established to investigate the effect of the type of matrix (epoxy and polyester) and treatment time (24, 96 and 168 h) on the mechanical properties of coir fibre composites. X-Ray diffraction (XRD) analysis reveals that the treatment does not promote a complete change of cellulose-I into cellulose-II. However, the degradation of hemicellulose and pectin of the fibre surface is evidenced by the thermogravimetric (TGA) curves. The chemical treatment contributes to increase the fibre density and to reduce its thermal stability. Single fibre tensile tests reveal a gradual increase in the elastic modulus attributed to the treatment time factor. Epoxy composites presented higher tensile and flexural strength in comparison to polyester composites, which exhibit higher tensile and flexural modulus. The alkaline treatment does not affect the mechanical strength of the composites. However, higher tensile and flexural moduli are obtained when the treatment time increases to 96 or 168 h. The proposed treatment proves to be feasible and efficient to increase the stiffness of coir fibre composites, besides being less damaging to the environment after disposal when compared to strongly alkaline solutions such as NaOH.

This work focuses on the fabrication and characterisation of epoxy composites reinforced with natural fibre layers extracted from the inner bast (phloem) of the papaya plant (Carica papaya) under tensile and three-point bending loading. The papaya phloem is composed of fibrous laminas that wrap and reinforce the stem of the plant. A set of quasi-periodically arranged holes disrupt the continuity of these layers, through which the branches emerge. The fibres in each layer constitute an anisotropic honeycomb-like structure, whose elongated cells align along a single preferential direction. Papaya-reinforced epoxy composites are fabricated by hand lay-up and evaluated using two full-factorial designs based on the fibre-to-load direction in longitudinal (0°) and transverse (90°) conditions, for configurations without holes and alternating holes. Composites made with randomly-oriented short fibres are also evaluated along with the first experiment. The tensile and flexural properties obtained are compared to other materials in the literature to assess its potential as a structural material. The results show that the papaya bast fibre layers can be a promising reinforcement for polymeric composites.

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.

Currently many works of art made of soapstone and recognized as cultural patrimony of humanity are in an advanced stage of degradation. Hence, it is necessary to interrupt this process and recover the deteriorated parts. Composite materials consisted of steatite particles and epoxy polymer are designed and characterised for their application in the repair of sculptures made of soapstone. The material applied in restorations should provide coloration and texture similar to soapstone besides structural requirements. The degree of similarity of the artificial material to the rock is enhanced by the proper selection of the particle size range and the increase of steatite incorporation in the composites. A statistical methodology based on the mixture design is used to optimize the relative amount of three particle size fractions of steatite particles in order to maximise the proportion of the dispersed phase in the composites. The maximum particle packing density (1.50 g/cm³) is obtained for a ternary mixture, composed of 62% of coarse particles (1.18 mm - 0.60 mm), 6% of medium sized particles (0.60 mm - 0.30 mm) and 32% of fine particles (0.30 mm - 0.15 mm). In this manner, the fabrication of composites based on an epoxy polymer matrix with 70wt% of incorporated steatite particles has been possible, increasing the maximum amount by 10% as used in previous works.

This work investigates the effect of using functionalised poly-diallyldimethylammonium chloride (PDDA) silica micro and nanoparticles on the apparent density, tensile and flexural strength and modulus of hybrid glass fibre reinforced composites. The work is carried out using a Design of Experiment (DoE) approach on a population of 60 composite specimens produced according the size of the nanoparticles and their weight fraction. A 2% of weight fraction of functionalised silica nanoparticles is shown to reduce the flexural strength and density of the composites, but to maximise significantly both the tensile, flexural modulus and tensile strength of the hybrid glass fibre materials.

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.