This work describes the development of a sustainable and low-cost sandwich composite structure made from aluminium skins and bonded to a tubular core with epoxy resin. The core is made from disposed plastic bottle caps. An analysis of variance (ANOVA) has been performed to determine the significance of the orientation of the bottle caps in the core, the use and type of adhesive over the bulk density and the mechanical properties of the sandwich panels. The results show that a core topology made from an alternated orientation of the bottle caps provides an enhancement of the resistance in the face skins and the core. The use of the epoxy adhesive between adjacent bottle caps also gives an increase of the maximum resistance of the panel.

This work further investigates the manufacture and characterisation of a sustainable sandwich panel made from aluminium skins and a recycled thermoplastic bottle cap core, an innovative concept proposed in a previous paper. A full factorial design based on Design of Experiments (DoE) and Analysis of Variance (ANOVA) techniques has highlighted the complex influence of three manufacturing parameters (type of polymeric adhesive, adhesive layer thickness layer and core packing topology) on the absolute and specific physical and flexural properties of the panels. The ANOVA revealed that the use of higher amount of epoxy polymer led to enhanced panel strength and stiffness. The cell packing topology, however, did not provide a significant effect on most panel properties. Discarded bottle caps have proven to be a promising lightweight and inexpensive honeycomb component for structural applications.

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The effects of sucrose (S) and pectin (P) concentrations and the ratio between two distinct pectins (R) on the rheological behavior of diluted pectin systems were evaluated simultaneously using the surface response methodology. The systems were composed of a mixture of two high methoxy pectins with different degree of methyl esterification values (HM1/HM2) and of a mixture of a high-methoxy with an amidated low-methoxy pectin (HM1/ LMA). For the HM1/HM2 systems, the multivariate analysis showed that the sucrose and pectin concentrations exerted statistically significant (p<0.05) linear effects on the consistency index k and viscosity, the influence of pectin being about five times higher than that of sucrose. The pectin concentration and the ratio between the different pectins were shown to be significant with respect to the rheological parameters of the HM1/LMA systems. Evaluating the influence of the ratio between the different pectins, a synergistic effect on the structure reinforcement was observed when mixing HM1 and LMA in similar proportions, indicating the importance of the presence of hydrophobic interactions between methyl ester groups in addition to the stronger hydrogen bonding in junction zone stabilization. In general, the conditions in which hydrogen bonds were favored in relation to hydrophobic interactions led to systems with higher pseudoplasticity.

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.

A sandwich panel based on upcycled bottle caps core and sustainable components is investigated to contribute to advances in lightweight and environmentally friendly structural solutions.Ecological alternatives to the panel skin and adhesive, such as a recycled PET-bottle foil and a castor oil bio-polyurethane, respectively, are tested and compared to commercial components (aluminium skin and epoxy polymer). Bottle caps are characterised using a small punch test specially developed to obtain the properties of the bottle caps. Additionally, low-cost reinforcement (Portland cement) is added to adhesives to enhance the mechanical behaviour of the panel. The sustainable panels achieve enhanced efficiency compared to aluminium-based panels for core shear strength and stiffness, besides having similar specific flexural properties compared to those of epoxy-based PET panels. Despite their higher strength and stiffness, epoxy polymer-based panels show visible adhesive peeling off to bottle caps core and aluminium skin. In contrast, the biopolymer exhibits larger deformation and debonding of both substrates, indicating a progressive and ductile failure. The satisfactory efficiency of sustainable panels confirms the promising reuse of recycled bottle caps in structural applications.

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