Rheology and processing of high-density polyethylenes (HDPEs) : effects of molecular characteristics
Bibliographic record
Abstract
In this study, the linear viscoelastic properties of two series of Ziegler-Natta and metallocene HDPEs (ZN-HDPEs and m-HDPEs respectively) of broad molecular weight distribution (MWD) have been studied. Relationships between the zero-shear viscosity and molecular weight (Mw) and molecular weight distribution show that the breadth of the molecular weight distribution (MWD) for m-HDPEs plays a significant role. Other interesting correlations between the crossover modulus and steady state compliance with MWD of both these classes of polymers have also been derived. Finally, the steady-shear viscosities from capillary rheometry are compared with LVE data to check the applicability of the empirical Cox-Merz rule. It is shown that the original Cox-Merz rule is approximately applicable for HDPEs for narrow to moderate MWD and fails for those HDPEs having a wide MWD due to the occurrence of wall slip. The processing behavior of both series of HDPEs was investigated. Their melt fracture behaviour was studied primarily as a function of Mw and MWD, and operating conditions i.e. temperature and geometrical details and type of die (capillary, slit and annular). It is found that sharkskin and other melt fracture phenomena are very different for these two classes of polymers, although their rheological behaviors are nearly the same for many of these. It is also found that critical conditions for the onset of various melt fracture phenomena depend significantly on the type of die used for their study. The slip behaviour of these resins was also studied as a function of Mw and MWD. It is found that the slip velocity increases with decrease of Mw, which expected to decay to zero as the Mw approaches a value with characteristic molecular dimension similar to surface asperities. For HDPEs that exhibit stick-slip transition (narrow to moderate MWD), the slip velocity has been found to increase with increase of polydispersity. The opposite dependence is shown for HDPEs of wider molecular weight distribution that do not exhibit stick-slip transition. A criterion is also developed as to the occurrence or not of the stick-slip transition which is found to depend strongly on Mw and its distribution.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| 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) | 0.000 | 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 teacher head, 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".