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Mechanical recycling of Polypropylene: effect of a repair additive on flow characteristics and processability
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A simulation study of the microstructure evolution of PP-LDHs nanocomposites in melt compounding
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Melt compounded PP-LDHs nanocomposites: a simulation study of the microstructure evolution
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Towards effective recycling routes for polypropylene: influence of a repair additive on flow characteristics and processability
Full text linkPlastic recycling is a key aspect to achieve effective polymer circularity, especially for polyolefins for which usually the mechanical recycling is considered a downcycling process. This downcycling phenomenon arises from the progressive deterioration of the polymer microstructure during reprocessing, resulting in a gradual loss
of processability and properties, ultimately compromising the possibility of using recycled polyolefins for applications with high engineering requirements.
In this work, the effects of the thermomechanical degradation on the microstructure of polypropylene (PP) were assessed by subjecting the polymer to multiple extrusion cycles. The objective is investigating the evolution of the molecular weight and of the macromolecular architecture of PP typically occurring in a mechanical recycling process. Furthermore, a commercially available additive capable of restoring the PP molecular weight was introduced, with the purpose of proposing an effective upcycling strategy for achieving recycled PP with enhanced processability.
In particular, the effects of the additive were evaluated following two different strategies that simulate pre-consumer or post-consumer mechanical recycling. The obtained results indicated that the introduction of the additive can effectively prevent the decrease of the molecular weight of reprocessed PP, also inducing some melt structuring phenomena associable with the introduction of some long chain branching and/or crosslinking. Finally, it was demonstrated that different macromolecular architectures for recycled PP can be achieved depending on the residence time during the processing in presence of the additive, opening new perspectives toward
Fused Filament Fabrication (FFF) with PP-based composites: effect of fillers on thermal conductivity and flammability
Full text linkDelving into Process–Microstructure–Property Relationships in Cast-Extruded Polylactic Acid/Talc Composite Films: Effect of Different Screw Designs
Full text linkIn the context of polymer-based composites, the knowledge of the correlations between the processing conditions, the microstructure, and the final properties is essential to tailor polymeric systems for specific applications. Specifically concerning the extrusion process, an accurate design of the screw profile allows for achieving composites with modulable microstructures, according to the specific properties required by the intended application. In this work, films of polylactic acid-based composites with 5 wt.% of talc were obtained by means of a single-screw extruder equipped with a flat die and a calender unit. Three different screw profiles, namely a general-purpose compression screw, a screw with a reverse flow zone, and a barrier screw, were employed for the production of films. The ability of the screw profile in varying the degree of filler dispersion and distribution was assessed through morphological and rheological analyses, demonstrating that the barrier screw is more able in disaggregating the talc lamellae. Due to the achieved microstructures, films produced using this screw profile exhibited superior barrier properties, with a decrease of about 27% in the oxygen permeability as compared to unfilled PLA. However, a concurrent decrease in material ductility as compared to the other films was observed. Finally, the thermoformability of the composites was assessed; also in this case, trays with more precise edges and corners were obtained for the film formulated through the barrier screw
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