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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 investigates the effect of eco-friendly chemical treatments on the mechanical and physical properties of composite laminates based on sisal fibres. A 2231 full-factorial design is conducted to test the influence of chemical solution types, fibre treatment time, and polymer matrix type on the mechanical and morphological characterisation of the composites. Chemical treatments remove impurities from fibre surfaces, and enhance fibre-matrix adhesion. The treatments, especially with sodium carbonate (Na2CO3), also progressively reduce the hemicellulose fibre content. Polyester composites made with sisal fibres treated with Na2CO3 for 96h achieve enhanced strength and stiffness under tensile, compressive and impact loads. The results evidence the feasibility and efficiency of the proposed eco-friendly treatments for natural fibres and the application of renewable fibre laminates in secondary structural applications.

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.

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.

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.

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.

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.