Evaluation of HFC-245fa as an Alternative Blowing Agent for Extruded Polystyrene
Bibliographic record
Abstract
The need for replacing conventional CFCs with alternative blowing agents has led to the development of many candidates. Among those, HFC-245fa is targeted as one of the most promising for the replacement of HCFC-141b in polyurethane foams. However, the low thermal conductivity of HFC-245fa and its interesting near room-temperature boiling point may render it suitable for other applications such as polystyrene insulating foam board manufacturing. This work investigates the use of HFC-245fa as a potential physical blowing agent for extruded thermoplastic foams. The process was monitored using ultrasonic probes, which reveals information on the solubility behavior of the gas in the molten state. Results showed that at 190°C, HFC-245fa could be incorporated in molten polystyrene up to about 7 wt.% and generate homogeneous solutions. Higher concentrations revealed evidence of heterogeneous conditions as seen in the attenuation signal. Three concentrations of blowing agent (5, 6 and 7 wt.%) were used to produce foam samples at lower extrusion temperatures. Increasing the concentration of blowing agent or nucleating agent greatly affected the expansion profile of the foam samples. Thus, lower densities could be achieved by using an optimal combination of both.
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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 | 0.000 |
| 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) | 0.001 | 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".