Extrudates wavy surfaces

The control compounds gave extrudates with a smooth surface, but the 67% silica compound extruded with a wavy surface. The 100% silica compound was extruded through the Monsanto extruder but was too stiff to feed into the NRM extruder. Therefore,... 

Figure 12.11 Extrudates of compound 3 with wavy surfaces.

Figure 12.12 Extrudates of compound 4 with wavy surfaces.

During extrusion of polymer melts with high throughputs, the elastic melt properties can also lead to elastic instabilities which can result in surface distortions of the extrudate. One example are wavy distortions also described as sharkskin. Depending on the polymer, this can also lead to helical extrudate structures (stick-slip effect) or to very irregular extrudate structures (melt fracture) at even higher throughput rates [10]. 

The question remains, as to whether or not the gel and long branch formation resulting from the reaction between TESPT and NR may be responsible at least as a part of the extrusion problem. This question may be answered by what is shown in Eigures 12.11 and 12.12 that when the dump temperature is higher, the waviness of the extrudate surface is more extensive. 

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