Reactive extrusion of PA6 – different ways to increase the viscosity

Depending on processing, different requirements are placed on plastic melt. While in injection molding polyamide (PA) with low viscosities is generally processed, higher viscosities are required for extrusion or thermoforming. In order to increase the molar mass and hence the viscosity of PA, the solid-state post-condensation is used, which is however time-consuming and thus expensive. An alternative method is reactive extrusion. In doing so, so-called chain extenders are added during compounding and thus simultaneously to the metering of further additives. In this work, PA6 with different chain extenders is compared. The different chain extenders either connect polymer chains linearly or act as a backbone and polymer chains are grafted onto. The compounding is carried out in a twin-screw extruder. The changes in the viscosity are examined by means of plate-plate rheometer and those of molar mass by means of gel permeation chromatography (GPC). It can be shown that a significant increase in the viscosity due to the chain extension occurs. The measurements of the GPC confirm the increase of the molar mass, whereby even a bimodal distribution of the molar mass occurs during grafting. The reactive extrusion is thus a cost-effective alternative to increase the viscosity of PA6 and thereby to increase its range of application.Depending on processing, different requirements are placed on plastic melt. While in injection molding polyamide (PA) with low viscosities is generally processed, higher viscosities are required for extrusion or thermoforming. In order to increase the molar mass and hence the viscosity of PA, the solid-state post-condensation is used, which is however time-consuming and thus expensive. An alternative method is reactive extrusion. In doing so, so-called chain extenders are added during compounding and thus simultaneously to the metering of further additives. In this work, PA6 with different chain extenders is compared. The different chain extenders either connect polymer chains linearly or act as a backbone and polymer chains are grafted onto. The compounding is carried out in a twin-screw extruder. The changes in the viscosity are examined by means of plate-plate rheometer and those of molar mass by means of gel permeation chromatography (GPC). It can be shown that a significant increase in the viscosity ...