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Green plastics are constantly being used to minimize the negative impacts of the polymers made of fossil fuels such as petroleum. Non-renewable petroleum-based products are employed in wide range of human activities, yet plastic waste accumulation represents a serious issue for the environment (Mohd Rafee et al., 2019). On the other hand, the use of natural fibres in composite materials, such as sisal fibres, in substitution for synthetic fibres, has increased considerably. The aim of this study was to develop a low-cost manufacturing process of composites with reuse of polyethylene bags made of sugarcane ethanol (green polyethylene) reinforced with sisal fibres. The hot compression moulding (185 °C) was used to mould composite structural board. Tensile tests were conducted to evaluate the influence of the reinforcement configuration on the mechanical properties of the composites, considering two arrangements: woven fibres in (0°/90°) and randomly arranged. The results indicated that the use of woven sisal fibres in (0°/90°) as reinforcement of the green HDPE showed an increase in the tensile strength (33.30%) in contrast to the pure traditional HDPE. Randomly arranged sisal fibre-reinforced green HDPE composites showed higher modulus of elasticity than pure traditional HDPE (76.83%). Composites with woven sisal fibres showed higher values for tensile strength and ultimate strain, and lower modulus of elasticity than composites with randomly arranged sisal fibres. In addition, failure modes of the composites were observed. The results showed the viability of producing these composites by the developed equipment and the potential use of these materials as structural components.

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.

In recent years, green composites based on thermoplastic matrices from renewable sources, and reinforced with natural fibres, have gained significant importance in different industrial applications, due to lower environmental impacts and production costs than traditional composites. This work investigates the manufacturing process, fibre/matrix integration and mechanical properties of a novel environmentally friendly green composite with a recyclable biobased polymer from a renewable source and a biodegradable natural fibre. Untreated woven sisal fibres reinforced post-consumer green polyethylene composites were evaluated in terms of flexural, tensile and impact properties. Traditional and green high-density polyethylene (HDPE), originated from sugarcane ethanol, were utilised as matrices of the investigated composites. Woven sisal fibres were arranged in two different stacking sequences, i.e. [0°/90°] and [± 45°], being incorporated into the HDPE with a mass percentage proportion of 30/70 (fibre/matrix). A low-cost manufacturing process based on the hot compression moulding was used to produce the composites. The results were analysed by a factorial design to identify the effects of polyethylene type and the use of woven sisal fibres, considering the [0°/90°] and [± 45°] orientations. Thermal gravimetric analysis was used to verify the thermal stability of the sisal fibre. The topographic surface of sisal fibres was observed by scanning electron microscopy. The results showed that the use of green polyethylene reinforced with untreated woven sisal fibres achieved higher flexural modulus (35%), flexural strength (13%), tensile strength (39%) and ultimate strain (68%) than traditional polyethylene without reinforcement. The green composite presented promising mechanical results to replace materials from non-renewable sources and can reduce manufacturing costs of the final product. These composite materials can be efficient for structural applications such as insulated panels, drywall and partitions for furniture.

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.

The hybrid configuration of bio-reinforced composites has established a new extended boundary for the development of pro-ecological technologies due to light weight, moderate specific strength, low cost, environmental benefits, and potential applications of natural components. This work investigates the physical and mechanical properties of hybrid composites made of sisal/glass fibres and Portland cement inclusions. A full factorial design was generated to identify the effects of the stacking sequence and cement particles on the flexural strength, flexural stiffness, apparent density, apparent porosity and water absorption of the composites. The significant contributions of these main factors and their interactions were determined via Design of Experiments (DoE) and Analysis of Variance (ANOVA). The fracture features and damage mechanisms of hybrid composite were also reported. The inclusion of cement microparticles led to an increased apparent porosity, as well as enhanced water absorption, flexural stiffness and flexural strength of the hybrid composites. The mechanical properties were strongly dependent on the fibre stacking sequence, which accounts for approximately 98% of the effects observed. Moreover, the stacking sequence affected the damage mechanism of the bio-composites. Finally, the replacement of glass fibres by unidirectional sisal reinforcements may potentially improve the specific properties in structural applications with an environmental sustainable footprint.

Rapid prototyping for material deposition or additive manufacturing has been widely used for short time production of parts with complex geometry in small series. The three-dimensional printing process needs post-processing to improve the strength, stiffness and/or surface finish of the parts. Printed parts in pristine condition are generally very brittle with a porous structure, so infiltrates have been introduced to improve their mechanical and physical characteristics. This work investigates the effect of two infiltrates, epoxy polymer and cyanoacrylate, under a vacuum pressure system on the mechanical properties of powder-based composites made by three-dimensional printing. Samples printed under pristine and infiltrated conditions were tested under tensile, flexural, compressive and impact loadings. The infiltrated samples achieved superior mechanical properties, especially when the epoxy polymer was applied via a vacuum system. The microstructural analysis showed that the infiltrates were not able to penetrate the entire sample, revealing a porous structure in the centre, mainly when the cyanoacrylate was used. The epoxy polymer infiltrate was able to substantially increase the mechanical performance of three-dimensional samples, being a promising material when higher structural requirements are required.

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.

Cementitious composites are low cost and readily manufactured materials which can be used for specialist applications such as the production of aerostatic porous bearings. A design of experiment was used to identify the effects of superplasticizer additions and carbon nanotube inclusions on the physical and mechanical properties of cementitious composites which can be applied as porous restrictor in aerostatic thrust bearings. The presence of carbon nanotubes was able to increase the bulk density, the compressive strength and the modulus of elasticity, and also decrease the apparent porosity of the composites. The composite made with 0.4 wt.% of superplasticizer and 0.05 wt.% of carbon nanotubes achieved acceptable properties for the use as double-layered porous restrictor in aerostatic thrust bearings.

Over the years, with the increasing development of engineering materials, the emergence of new composites, fiber metal laminated, biomaterials, metal alloys etc., and with demand for products less expensive, less polluting and more efficient, the manufacturing engineering also needs to develop to be able to process these new materials. Materials and tool geometries, intelligent mechanisms, modular machines, also follow this setting. To that end, this work comes to raise the main parameters that influence in the hole quality surface of finished product. Were used two polymeric materials, ultra high molecular weight polyethylene (UHMW-PE) and polytetrafluoroethylene (PTFE), two feed rates, three rotations and three tool geometries, allowing to identify which of these parameters have greater influence on the thrust force and the characteristics of the finished product and dimensional deviation.

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.

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.

The development of new materials based on industrial wastes has been the focus of much research for a sustainable world. The growing demand for tyres has been every year exacerbating environmental problems due to indiscriminate disposal in the nature, making a potentially harmful waste to public health. The incorporation of rubber particles from scrap tyres into polymeric composites has achieved high toughness and moderate mechanical properties. This work investigates the geometric effects (thickness, width and internal cell angle) of auxetic structures made of recycled rubber composites based on experimental and numerical data. The response surface models integrated with the swarm intelligence and finite element analysis were proposed in order to obtain a range of solutions that provides useful information to the user during the selection of geometric parameters for reentrant cells. The results revealed the cell thickness ranges from 39-40 mm and 5.98-6 mm, and the cell angle range from -0.01 to -0.06º maximize the ultimate strength. The same parameters were able to optimize the modulus of elasticity of rubber auxetic structures, excepting for the angle factor which must be set between -30º and 27.7º. The optimal Poisson's ratio was found when the cell angle ranged from -30º to -28.5º, cell width ranged from 5-5.6 mm and 2 mm in thickness.

Timber is the oldest construction materials in the world, have been widely used in structures in addition to having a high longevity, if treated properly (maintenance). If this does not occur, the wood deteriorates due to the action of insects, fungi and other aggressive agents. There are several materials and techniques used to reinforce the damaged parts. This paper presents an experimental study ofEucalyptus grandis and Pinus elliiottiitimber beams rein forced with sisal fibres laminated composite materials. The co mposite material and the wood were prepared for testing. In order to simulate the defect, some parts were cracked. The study was to determine the maximu m load (rupture) applied on the timberin the conditions: without defect, with defect and without composite and with defect and with composite, aiming to verify the efficiency of the laminate as reinforcement in the wooden beams. The experimental results indicate the possible use of the laminated composite as reinforcement, presenting considerable increase in the maximu m strength supported by the timber when compared to unreinforced cracked condition, being more efficient for the Pinus elliiottii species.

In today's modern world the composite materials have been widely used not only for aerospace/aeronautics, but also automotive, sports and construction industries. The flexural strength of laminated composites depends on the characteristics of dispersive and matrix phases, considering the presence of tensile and co mpressive loadings. For this reason, the addition of particles into the matrix phase has been investigated to enhance its stiffness and consequently the elastic modulus of the composite. Th is work investigates a glassfibre co mposite reinforced with silicon carbide part icles. The following responses were evaluated: apparent density, water absorption, flexural strength, modulus of elasticity. The results were compared to those manufactured with no silicon carbide particles. It was observed that the silicon carbide particles provided the increase of the apparent density and flexu ral strength of the composites.