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This study proposes that green composites using recycled plastic bags (PEr) extruded with pineapple fiber waste (PR) from a juice industry to increase pineapple’s economic value stimulate practices that prioritize recycling and development of new materials. PEr composites were prepared using PR as a filler, using different fiber loadings of 5, 10, and 15 wt%, and the use of a coupling agent, prepared via extrusion and injection molding. The samples were investigated by Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis, inflammability, mechanical tests (tensile, impact, and shore hardness), scanning electron microscopy, and water absorption tests. FTIR results demonstrated that the addition of PR to the PEr caused a decrease in the characteristic bands of neat PEr, evidencing the chemical interactions. Thermal analysis showed that the addition PR decreased composites' thermal stability, causing relatively higher percentages of char compared to neat PEr, which increased the burning rate of composites, except for PEr/15PR and PEr/5PR-C. Green composites exhibited higher tensile modulus and hardness than PEr, but the impact tests presented a decrease in the fibers' addition to the PEr due to the reduction of toughness and resilience. SEM of fractured surface composites presented microcracks, voids, and fibers breakage in the interface. The composites showed low water absorption (up to 0.804%). The coupling agent’s use presented a low influence on the mechanical and thermal properties and a slight decrease in water absorption. These results demonstrate o potential of the reuse of plastic bags and industrial waste for green composites.

Australian palm residues are generated by palm heart industry in large quantities and are considered an underused material with a composition rich in lignocellulosic structures. This residue is generally utilized as briquettes for energy or sheep feed; however, few works investigate this residue as composite fillers. This work aimed to revalue Australian palm residues (PR) by preparing polypropylene composites through melt mixing, using different fiber contents (0, 5, 10, 20, and 30 wt%), and evaluate the statistical influence of fibers (residues) alkali treatment (MPR) in composites mechanical properties. PR and MPR were evaluated by FTIR, XRD, SEM, TGA, and composites were assessed using thermal and mechanical analysis, in which ANOVA statistical analysis was applied. The residues addition increased the mechanical properties and their treatment enhanced the stiffness of the composites compared to pristine PP. However, ANOVA demonstrated that at low residues contents, surface treatment does not increase fiber-matrix interactions effectively, then tensile properties were statistically similar to PP. Considering tensile properties, 20% MPR showed statistically distinct properties, with significative enhancements; no filler contents dependence was verified. Flexural properties were more sensitive to residue loading, and composites with 30% PR and MPR presented superior mechanical performance. This difference is associated with a higher sensitivity of tensile stress towards fiber-matrix interactions, which was improved with fiber treatment. Also, the residues content and treatment influenced the composites' thermal stability, with better results for PP-MPR. Results indicate that palm residue is an excellent filler for improving composites' thermal and mechanical properties, with a greener character.