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Natural fibre-based composites have been investigated as a viable ecological alternative to conventional materials, combining low-cost and sustainable features to engineering products. In tropical countries, such as Brazil, there are many lignocellulosic residues that are discarded in nature, polluting the environment, such as the Tucuma fruit, which generates about 50 tonnes/month of solid waste only in the city of Manaus (State of Amazonas). This work investigates a novel wood-plastic composite (WPC) made from recycled polypropylene (PP) and Tucuma endocarp powder (TEP) without coupling agents that encompasses social and environmental issues. WPCs are composed of 10, 20, 30, 40 and 50 wt% of TEP combined with PP by injection moulding, being characterised by SEM, FTIR, flammability, water absorption, ageing, tensile, compressive, three-point bending, impact and scratch tests. TEP does not react to the matrix phase, presenting 49.4 % and 37.4 % of cellulose and lignin, respectively. In general, the incorporation of TEP not only increases the elastic modulus and the dynamic friction coefficient, but also reduces the strength and the burning rate of WPCs. WPC preserves its physical integrity after ageing, absorbing up to 1.6 % of water. Composites made with 20 wt% of TEP can be considered promising materials to be used as wood plastic for sustainable engineering applications.

This work evaluates an epoxy composite reinforced with curauá fibres and/or organophilic clay. Epoxy polymers reinforced with nano-clays are also assessed. Composites are manufactured by cold pressing using fibres in pristine and treated conditions. Three levels of the factors NaOH solution (2.5, 5 and 10%) and immersion time (2, 4 and 10 hours) are investigated. Nano-clays are incorporated at the levels of 2.5, 5 and 10 wt.%. The morphology and crystallinity of the treated fibres are evaluated by scanning electron microscopy and X-ray diffraction, respectively. Tensile, three-point bending and impact tests are performed to characterise the composites. Tensile strength, flexural strength and impact resistance are increased by 24%, 44% and 47%, respectively, when compared to untreated fibre composites. The highest tensile and flexural strengths are achieved by hybrid composites containing 5 wt.% of nano-clay and 20 wt.% of curauá fibres treated with 5% NaOH for 4 hours. In contrast, the highest tensile modulus is achieved when hybrid composites are made from untreated fibres and 10 wt.% of nanoparticles. The highest impact resistance is obtained by curauá composites, without particles, composed of fibres treated with 5% NaOH for 4 hours. The inclusion of nano-clay leads to reduced impact resistance values.

Natural fibres have many advantages over synthetic ones, making them attractive for reinforcing polymer materials. This work evaluates the use of an Amazonian plant, namely Curauá (Ananas erectifolius), as a reinforcement phase of biocomposites fabricated by cold pressing. Curauá fibres have been shown to be a promising fibre for composite materials, especially due to their higher elastic modulus than other plant species. An L9 Taguchi design is used to investigate the effect of fibre fraction, NaOH concentration and immersion time on the tensile properties of biocomposites. Statistical models are able of predicting and revealing the optimal composition of the biocomposites. The tensile strength of Curauá biocomposites is significantly affected by the fibre fraction, followed by the factors of immersion time and NaOH concentration. High tensile strength is obtained by adding 25 wt.% of Curauá fibres treated under different conditions. There is an interaction between NaOH concentration and the immersion time; a higher concentration requires less time or vice versa to achieve ideal roughness, promoting strong fibre/matrix adhesion.

This work investigates a hybrid polyester composite consisted of Curaua natural fibres and organophilic clay nanoparticles. A Taguchi method is used to identify the effects of fibre fraction (10, 20 and 30 wt%), alkaline treatment concentration (NaOH, 2.5, 5 and 10 wt%), treatment time (2, 4 and 8 h) and nanoparticle content (2.5, 5 and 10 wt%) on the mechanical behaviour of the hybrid composites under tension and three-point bending. X-ray, FTIR and microstructural analysis are performed to assess the treated and untreated fibre surfaces. The optimum combination of the process parameters for the tensile and flexural properties is: fibre content at 30 wt%, NaOH concentration at 5 wt%, treatment time at 8 h and nanoclay inclusions at 5 wt%. A mean tensile and flexural strength of 36.13 MPa and 32.55 MPa are obtained, which represents percent increases of 39.22 % and 25.43 % compared to the polyester polymer in pristine condition.