Detection of divergences in polyethylene resins fabrication by means of the modified stepwise isothermal segregation technique
✍ Scribed by D. Gueugnaut; D. Rousselot
- Publisher
- John Wiley and Sons
- Year
- 1999
- Tongue
- English
- Weight
- 286 KB
- Volume
- 73
- Category
- Article
- ISSN
- 0021-8995
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✦ Synopsis
The selective crystallization behavior of a series of commercial mediumand high-density polyethylene resins has been studied by means of an original modified procedure of the stepwise isothermal segregation technique using differential scanning calorimetry. The technique consists of a sequenced multiple-stage stepwise thermal treatment of the materials allowing separation of the macromolecules with respect to their length-to-branching content and distribution. It is assumed that such a separation process gives an image of the proportion of specific crystallizable species, which are in turn responsible for slow crack growth resistance of the resins under study. A drift molecular parameter is calculated from a combination of the crystallization data at 119°C and 114°C. This molecular parameter is capable of revealing some divergences regarding the fabrication of a commercial polyethylene resin within a decade. Such divergences are well correlated with premature brittle failures under hydrostatic pressure testing of a series of correctly extruded pipes. Furthermore the drift molecular parameter allows a ranking of different medium-to high-density polyethylene resinsthe lower this parameter the better the slow crack growth resistance of the materials.