Primary polymer recycling involves the reprocessing of defective parts and scraps in a processing line. The critical limitation for excessive use of primary recycling consists of the need to maintain ...the properties of the polymer above the required minimum level. The polymer degradation during the extrusion occurs by the combination thermal, oxidative and mechanical degradation. This work investigated the degradation of HDPE (High Density Polyethylene). Green HDPE (PV) and petrochemical HDPE (PN) were processed five times in a single-screw extruder and the flow rate, crystallinity and impact strength properties were evaluated. The increase in the number of reprocessing cycles increased the flow index and crystallinity values. The increase in the degree of crystallinity of the polymer, verified by the DSC analysis, evidenced the degradation of the material associated to the decrease of the size of the main chain (chain scission mechanism). The impact strength showed no significant change after five reprocessing cycles. Contrary variations were found in the crystallinity index considering the first and fifth processing, suggesting a change in the predominant mechanism of degradation.
This paper reports the state of art review for processing techniques used in recycling of thermoplastics polymers with different types of reinforcements, especially for additive manufacturing (AM) ...applications. In last two decades, some studies have reported use of primary (1°), secondary (2°), tertiary (3°) and quaternary (4°) ways to process polymeric materials from recycling view point. But hither to little has been reported on standardisation of 1°/2°/3°/4° routes in AM applications. The present study bridges the gaps for use of 1°/2°/3°/4° routes as an industrial processing standard with low cost AM technology (which have been presented as four case studies for field engineers).
The present work aims at evaluating the behaviour of various grades of high and low density polyethylene subjected to continuous injection moulding operations. It is based on a wide range of ...experimental techniques that allowed the establishment of relationships between the observed property changes and the structural modifications developed in the polymers. The study confirmed the coexistence of two distinct degradation mechanisms, crosslinking and chain scission, that occur due to thermo-oxidative reactions arising during the different injection moulding stages. The relative importance of these two mechanisms depends on the material structure and on the processing conditions used. It was also possible to confirm that the polyethylenes with lower molecular mass show low sensitivity to degradation during reprocessing. Furthermore, the more branched polymers (as is the case of LDPE) also proved to be less sensitive to thermo-degradation phenomena. Overall, it was concluded that the primary recycling of polyethylene, if performed under well controlled conditions, will lead to only minor material property losses.
Polymeric nanocomposites are novel materials of huge interest owing to their favourable cost/performance ratio with low amount of nanofillers, improved thermal resistance, flame retardancy and ...mechanical properties in relation to their matrices. In this work, composites based on post-industrial waste or primary recycled poly(butylene terephthalate) and 5 wt.% of organic modified montmorillonite clays were melt compounded using a twin-screw extruder. A 22 factorial experimental design was used to study the compounding and processing variables: Organic modified montmorillonite with one or two hydrogenated tallow (initial basal spacing) and screw speed of the extruder. X-ray diffraction and transmission electron microscopy suggest that a partial exfoliation of the organoclay in the recycled poly(butylene terephthalate) matrix was achieved for organic modified montmorillonite with lower initial basal spacing. On the other hand, formulations containing organic modified montmorillonite with higher initial basal spacing showed only intercalated structure. The recycled poly(butylene terephthalate)–organic modified montmorillonite nanocomposites did not drip flaming material during burning tests. Storage of dynamic-mechanical, tensile and flexural moduli of the recycled poly(butylene terephthalate)–organic modified montmorillonite were improved when compared with both virgin and recycled poly(butylene terephthalate)s, mainly for nanocomposites formulated at a lower initial basal spacing organoclay. This could be related to a better diffusion of polymer into organic modified montmorillonite layers compared with the higher initial basal spacing organoclay. The improvements on the physical properties of recycled poly(butylene terephthalate) showed the feasibility to add value to primary recycled engineering thermoplastics with a very small amount of organic modified montmorillonite.
