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 past years, the use of additive manufacturing technology and the capability of different core cell geometry have significantly contributed to the development of advanced components based on lightweight structures and high mechanical strength. This work shows a numerical and experimental analysis of the mechanical behaviour of new sandwich panels, with cores manufactured by the fused deposition modeling (FDM) method. PLA and ABS polymeric cores with 2024-T3 aluminium alloy sheets as facings are analyzed. Three core shapes are investigated: out-of-plane hexagonal honeycomb, S-shape corrugated, and in-plane hexagonal honeycomb. Using a full factorial design, the experimental conditions are tested under three-point bending, Charpy impact and ballistic tests. Numerical modelling using Ansys Software is performed to obtain the energy absorbed and the failure mode of the panels in the ballistic tests. The experimental ballistic tests are made in a new piezoelectric sensor-based monitoring system. In the bending tests, sandwich panels with in-plane hexagonal honeycomb PLA core showed the highest average values for flexural modulus and flexural strength. On the other hand, ABSAL panels with S-shape corrugated cores had higher energy absorbed in the Charpy impact. Numerical analysis of ballistic impact showed greater energy absorption by ABSAL panels. The experimental tests validated the numerical simulations, showing high energy absorption by the in-plane hexagonal honeycomb core, with concentrated fractures in the region close to the impact, and good impact resistance by panels with out-of-plane hexagonal honeycomb and S-shape corrugated ABS cores. The feasibility of producing sandwich panels with 3D-printed polymeric cores and 2024-T3 aluminium alloy facings achieves suitable mechanical properties for structural applications, especially when lightness, stiffness, and high energy-absorption capabilities are required.

Waste from the processing of hardwood and coniferous wood generated in the timber industries is difficult to dispose of and can cause considerable environmental impacts, such as soil and groundwater contamination. In this context, composites with varying concentrations of polypropylene, maleated polypropylene, and particulate Eucalyptus and Pinus waste were produced in a twin screw extruder and injection molded as test bodies for tensile and flexural tests. The morphology of the composites was investigated via scanning electron microscopy. The thermal properties were identified through differential scanning calorimetry. The tensile and flexural results for the two waste formulations indicated that the addition of vegetable fillers increased the modulus of elasticity and bending, and the compatibilizer provided increased resistance to stress and maximum deflection. The scanning electron micrographs illustrated the wetting of the cellulosic charge by the thermoplastic polymer with the compatibilizer, which corroborated the possible occurrence of an esterification reaction and hydrogen bonding interactions in the matrix-particle interface. The incorporation of waste in the composite resulted in the reduction of the degree of crystallinity of polypropylene, regardless of the use of the compatibilizer. This was explained by the barrier capacity of the charge, which prevented the growth of the crystals.

The need for studies aiming at the selection of materials for such application is preponderant, be-cause a large increase in the focus on vehicle weight reduction by the automotive industry in recent years. In environmental and commercial terms, this reduction provides lower energy consumption and better vehicle performance, as well as limiting pollutant emissions. The present work has the objective to select the best materials in substitution of the metals and glass used in doors, hood and windows, respectively, of sports cars to decrease the weight/power ratio and consequently improvement of performance. With the aid of Ashby maps simulated through the CES EduPackTM 2018 program, maximizing the limit of tensile strength and minimizing density, it was possible to analyze that carbon fiber composites obtained values of merit index of up to eleven times greater than the value obtained by carbon steels. Already in substitution of the glass, the acrylic obtained a index of merit about three times greater. At the same time, the tensile strength, fracture toughness, density and cost of the possible materials obtained in the previous method were obtained through the Pugh matrix, the exchanges for composites of glass fiber and polycarbonate obtained outstanding responses.

The feasibility of using epoxidized waste cooking oils as a partial replacement for synthetic resins in the manufacture of lignocellulosic composites where the reinforcement is comprised of mechanically ground wood from civil construction waste wood (CCWW) was investigated. For this study, the wood-epoxy composite was prepared using the thermo-curing technique, and wood particle contents of 20 and 30% (m/m) were studied with a matrix comprised of 50% epoxidized vegetable oil and 50% petroleum-based epoxy resin. The specific mass of the composites was in the range of 1130 to 1380 kg/m³, with the lowest value for the highest content of wood particles. Fourier transform infrared spectroscopy was successfully used to monitor the epoxidation of the vegetable oils and the subsequent curing of the epoxy resins and particleboards. Thermal stability of the composite was dictated by its lignocellulosic content, and significant mass losses occurred at temperatures higher than 300 °C, regardless of the wood particles content. The introduction of CCWW particles into the polymeric matrices did not promote the desired effect of improving the mechanical properties in regard to those of the cured blend of epoxy resins. However, the produced particleboards still met the standards of the American National Standards for general purpose boards in regard to their physical and mechanical properties (e.g., density, tensile strength). Hence, the use of wood waste and waste cooking oil to produce particleboards was deemed justified within the framework of a cascading lifecycle-extended service for both wastes.