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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.

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.

The cutting fluids contributed for removing chips, cooling, and lubricating, on the other hand, are harmful to the environment. The minimum quantity lubrication technique (MQL) in machining operations proved to be suitable in addition to minimizing the environmental impact. The present work is focused on the drilling of electrolytic copper using biodegradable oil as cutting fluids applied by the MQL technique. The specific cutting pressure, burr height, and maximum diameter were measured varying the cutting parameters, cutting speed, feed, and lubrication condition (dry, flooded, and MQL). A statistical analysis was utilized to determine the influence of cutting parameters in the variables measured. The results indicated that the second-order interactions have a significant influence on the specific cutting pressure and in burr height. The lowest burr height was obtained using flood and MQL. The MQL system demonstrated the lowest specific cutting pressure, while the flood exhibited the best performance for diameter analysis. In addition to this, it can be confirmed that the MQL technique may replace the flooding drilling (abundant flow), minimizing the environmental impact.

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.

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.

Applications for composite materials are constantly increasing because of their lightweight combined with a high modulus of elasticity. Thus, the drilling of such materials is cause for concern for the scientific community since these components need generally to be fixed and assembled. Dimensional variations and the presence of burr are some of the problems that commonly arise due to the drill action in the composite material. Such problems should be minimized because it can compromise the quality of the final product. The present work studies the drilling of a sandwich composite material consisting of aluminium and polyethylene core (PEALL). The drilling tests were carried out using a TiO2-coated high-speed steel drills (HSS drills) deposited by sol–gel process. In order to optimize the hole quality, the influences of the TiO2 coating and the drilling parameters (speed and feed) are analysed. The thrust force, burr height and maximum diameter are collected to statistical study (analysis of variance (ANOVA)). The results underline that the TiO2-coated tool exhibits the best performance and improves the hole quality. Thus, the sol–gel method is a promising technique to coat the complex geometries of the HSS tools.

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.

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.

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.