Predicting glass fibers breakage during twin screw extrusion

Glass fibers are compounded with polymers to enhance their mechanical performance since the 1960′s. This performance improvement is depending on the fibers length. Indeed, the longer the fiber is, the more resistant the composite will be. As they are processed by twin screw extrusion, the key point of the process is to save the fibers length (shear rate, pressure… generated by twin screw cause severe breakages of the fibers).

Glass fibers

Glass fibers

Conveying Screw

Conveying screw

The stake of this study is to monitor and control the glass fiber breakage in a corotating twin screw extruder (TSE) by the integration of a theoretical model in Ludovic®, a 1D-simulation software.

The material is a Polyamide 12 reinforced with 30 wt% of glass fibers (both supplied by Arkema). The fibers have an initial length of 3.38 mm and a diameter of 10 µm. Compounding was performed using a laboratory corotating TSE with a diameter of 24 mm. The screw profile is shown in figure 1.

profil vis

Before glass fibers introduction, conveying elements in blue allow the solid transport of PA 12 and its rise in temperature, then kneading blocks in green have the role of melting and mixing PA 12. After the introduction of the glass fibers (secondary feeding zone), kneading blocks have to ensure the mixing and dispersion of fibres in the molten matrix. The last conveying elements convey the molten PA 12 with the dispersed glass fibers to the extrusion die. Compounding was performed at 2 extreme operating conditions, i.e. high screw speed coupled with low throughput and low screw speed coupled with high throughput.

The integration of the modified Shon-Liu-White model allows to determine glass fibers average length along the screw profile (Figure 2).

comparison simu vs experi

Ludovic® computation provides trends of the glass fibers length evolution along the screw for the 2 extreme operating conditions. The comparison between computation and experiments confirms that the modified Shon-Liu-White model underestimates the fiber breakage and it has to be adjusted for more accuracy.

As a conclusion, in this study Ludovic® has been able to integrate mathematical model to analyze the specific phenomenon of glass fibers breakage along corotating twin screw extruder. The philosophy of this 1D-code is to embedded models able to give trends and relevant information about the phenomena occuring in the machine.

*based on “Influence of Extrusion Conditions on Fiber Breakage along the Screw Profile during Twin Screw Compounding of Glass Fiber-reinforced PA” by J. Ville (Polytechs), F. Inceoglu, N. Ghamri and J-L. Pradel (Arkema), R. Valette and B. Vergnes (Cemef – Mines ParisTech) (Polymer Processing – 2013).

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