Effect of mechanical recycling on molecular structure and rheological properties of high-density polyethylene (HDPE)
Bibliographic record
Abstract
This study investigates the degradation of high-density polyethylene (HDPE) during successive closed-loop mechanical recycling via multiple extrusion. The main objective is to perform a comprehensive analysis of the rheological property changes associated with molecular characteristics. High temperature size exclusion chromatography (SEC) was performed first showing that more than 95% mass recovery was obtained after every mechanical recycling generation, thus excluding the possibility of extensive crosslinking in the rHDPE investigated. Then, small amplitude oscillatory shear (SAOS) measurements revealed significant increases of the zero-shear viscosity (ηo) by up to six-times, especially at a later stage between the 4th and 8th recycling cycles. Additionally, the van Gurp-Palmen (v-GP) plots suggest long chain branching due to the generation of free radicals during mechanical recycling, as radicals are created by chain scission. Extensional rheological measurements showed no detectable strain hardening effect, which is in contradiction with the hypothesis of an ill-defined long chain branched structure. This assumption is further corroborated through nuclear magnetic resonance (NMR) analyses, which detect branching sites in both 13C and 1H spectra. Moreover, the ‘branch-on-branch’ (BoB) constitutive model yields insights into the molecular topologies present within the recyclates, including different structures such as star-shaped and comb-type configuration. Overall, this study provides in-depth insights into topological changes during the mechanical recycling of HDPE, most likely from linear to a randomly branched, star-like structure, which is of fundamental interest for polyolefin polymer reprocessing; i.e. HDPE recycling.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".