BIOPLASTICS | COMPOUNDING


Figure 1: The effect of talc filler level on Mw retention


technology the Mw retention was at least 95% up to the 50% fill rate with a drop to 88% at 60% fill. When compared with the TSE samples, a significant improvement in Mw retention was seen. This was attributed to the combination of lower melt tempera- tures, shorter residence time, and the more efficient shear imparted in the CP relative to the TSE. Higher fill levels are believed to be possible, say the authors. It is also possible to use process aids where the application permits, which could further increase fill levels while potentially preserving Mw. Lower processing temperatures directly impacts


Figure 2: The effect of talc filler level on melt temperature Figure 3: Specific energy vs talc filler level


Mw retention in PLA-based compounds. Compar- ing the data in Figure 1 and Figure 2, there appears to be a correlation between lower processing temperatures and improved Mw retention in the CP. Similar results are anticipated as these studies are expanded to larger machines. Figure 3 shows the specific energy (SEI) required per kilogram expressed in kW-h/kg. When evaluat- ing the CP curve, a gradual increase in SEI is seen as filler level is increased. In the TSE curve, a decrease in SEI is observed, which can be explained by noting the change in Mw in the TSE samples. This is attributed to the lower loss in Mw reducing energy requirements when filler levels are increased. The authors postulate that an equivalent Mw between the two processes would result in similar slopes and separation on both lines as filler levels are in- creased. Formulating with process aids may have further benefit in increasing the amount of filler used when considering creation of masterbatches. Natureworks and Farrel Pomini intend to run


further studies on larger production size machines to validate the findings remain consistent with the results of the study. However, they say that these initial indications show the FCM is very well suited to processing PLA and mineral filled PLA compounds.


Source: Natureworks/Farrel Pomini


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