The main goal of this research is to study the development of crystalline morphology and compare it to various mechanical properties of microfibrillar composites (MFCs) based on polypropylene (PP) and poly(ethylene terephthalate) (PET), by adding a functional compatibilizer and a non-functional rubber in two different steps in the processing sequence. The MFCs were prepared at a weight ratio of 80/20 PP/PET by twin screw extrusion followed by cold drawing and injection moulding. The non-functionalized polyolefin-based elastomer (POE) and the functional compatibilizer (i.e., POE grafted with maleic anhydride (POE-g-MA)) were added in a fixed weight percentage at two stages: during extrusion or during injection moulding. The morphology observations showed differences in crystalline structure, and the PP spherulite size was reduced in all MFCs due to the presence of PET fibrils. Their relationship with the mechanical performances of the composite was studied by tensile and impact tests. Adding the functional compatibilizer during extrusions showed better mechanical properties compared to MFCs. Overall, a clear relationship was identified between processing, structure and properties.

This work aims at presenting a new strategy for the use of cork by-products on the development of sustainable composites with potential applications in rotational molding. In this study, different cork granulometries (0.15–3 mm) and matrix/cork ratios (90/10, 85/15, 80/20) are analyzed to access the processability of medium-density polyethylene (MDPE) with cork by rotational molding. The influence of processing parameters, such as the mold peak internal air temperature (PIAT) (200–240°C), is analyzed and correlated with the aesthetics, morphological and mechanical properties of the parts. The aim is to obtain a complete understanding of the processing–structure–property relationships. Defect-free parts are obtained with thin granulometric cork powders at a maximum of 10% by weight in PE/cork composites. The increase in cork content reduces the sintering capability and increases the porosity, wall thickness, and surface defects, simultaneously weakening the mechanical properties. The increase in PIAT favors a more compact structure and reveals better impact properties. All the parts are soft on touch and transmit the comfort and sensation of warm feeling of the cork. Moreover, lightweight parts and hydrophobic surfaces are achieved from the cork intrinsic properties. As a natural material, cork darkens its color with temperature, which is attributed to the reactions of the extractives within the components of cork, with no degradation associated. The work shows that polymer cork composites (CPC) are suitable for rotational molding within the processing window characteristic of PE, to achieve innovative and sustainable products with unique aesthetics and functionalities given by the cork material.