Gelation of poly(vinyl chloride) inside a single screw extruder and its effect on product properties

Abstract

Two resin formulations were extruded through a single screw extruder, equipped with a single flighted screw, rotating at 10 rpm, at different barrel temperature settings, which resulted in different melt temperatures measured in the adapter zone. The extrudates were subsequently subjected to assessments of the gelation level by three different methods: differential scanning calorimetry (DSC), capillary rheometry (CR), and solvent absorption (SA). The pros and cons of these methods are discussed. It appears that DSC is the most accurate technique for the quantitative determination of the gelation degree (GD), with the drawback that the specimen size is very small. The CR technique, based on measurement of entrance pressure, is also capable of providing reasonable estimates of GD, with some potential inaccuracies as a result of difficulties associated with measurement or assessment of temperature rise. The SA technique provided qualitative assessments of GD in agreement with the other two methods. Ultimate tensile strength, elongation at break, solid density, and color change were also measured and were correlated to melt temperatures and the corresponding GD. Extruded specimens having GDs in the range of 60%-90% possessed satisfactory properties for both resin formulations. J. VINYL ADDIT. TECHNOL., 25:E174-E180, 2019.

Application of fracture mechanics for the characterization of PVC pipes. I. Evaluation of the applicability of the EWF technique in specimens produced directly from pipes

“…In the case of the degree of gelation, it is observed that the pipe samples exhibit very different values. U‐PVC‐1 is in the lower limit established in the literature ( DG ~60%), [ 8,10 ] and M‐PVC‐2 appears to have been gelled in excess ( DG >90%).…”

“…[ 5 ] It is widely accepted that an adequate gelation level of a U‐PVC composition is between 60 and 90%. [ 8,10 ] In this situation, the primary particles exhibit a high degree of cohesion with the presence of extremely strong bonding forces, with the persistence of small structural voids that act as stress relievers. [ 11 ]…”

“…In this case, the degree of gelation achieved during processing is no longer the only governing factor that guarantees product performance and durability. In addition, DCMT is to be banned from international standards in the near future due to its toxicity, [ 8 ] as the author has been observing in ISO/TC 138 discussions, and new PVC processing quality assessment techniques proposed today for its replacement, such as uniaxial tensile testing and DSC, are still under evaluation of practical applicability.…”

“…The DSC test, on the other hand, brings the challenge of relying on the result for the degree of gelation of a product of large dimensions—the external diameters of PVC pipes reach ~1600 mm in some places in the world, with thicknesses that reach tens of millimeters—from testing a small sample of a few milligrams. [ 8 ]…”

The Role of Calender Gap in Barrel and Screw Wear in Counterrotating Twin Screw Extruders

“…The stabilizer package also includes lubricants. These PVC formulations are commercial grades used for cable duct (resin A) and window profile (resin B) extrusion applications [ 18 ]. The formulations were mixed in a Zeppelin Reimelt Henschel FML10/KM 23 hot-cold mixer (Kassel, Germany).…”