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.

It has been known in the industrial sector that in closely intermeshing counterrotating twin screw extruders, large separating forces develop in the calender gap, which push the screws towards the barrel wall. The result is significant wear in the region defined by 30°- and 60°-degree angles from the vertical. In the present investigation, pressures were measured around the barrel in extrusion of two rigid PVC resins in a laboratory extruder of 55 mm diameter and the forces on the screw core were determined. Numerical flow simulations were also carried out using the power-law viscosity parameters of the resins. From the experimental results, it was determined that the resultant forces are in the 30 degree angle direction, and from the computer simulations, the angle is between 18° and 25°. It is argued that the resultant force angle will be somewhat larger in large diameter extruders, due to the additional contribution of gravity.