Effects of Plasticizers on the Rheological Behavior of Ethylene- Vinyl Acetate (EVA) Copolymer Using an Online Capillary Rheometer

The objective of this work is to find an appropriate ethylene vinyl acetate (EVA) copolymer-plasticizer blend for potential use in further extrusion-based additive manufacturing (AM) processes, such as FGF technology applications. Plasticizers, as additives, soften the materials and improve material flow in polymer processing systems. In the current work, plasticizers used were paraffin oil (PO), triethyl citrate (TEC), and di(propylene glycol) dibenzoate (DPGDB). The plasticizer concentrations used in the blends were 1, 3, 5 and 7 phr (parts per hundred resin). Increasing plasticizer content resulted in an increase in the melt flow rate (MFR) compared to the non-plasticized EVA; however, the rate of increase was strongly influenced by the type of plasticizer used. DSC results showed a reduction in melt temperature and an increase in degree of crystallinity. Viscosity measurements for blends with 5 and 7 phr were made using an online capillary rheometer. Bagley and Rabinowitsch corrections were applied to obtain the true shear viscosity. A noticeable drop in the viscosity with increasing shear rate in both plasticized and non-plasticized EVA has been detected; however, variation in viscosity was observed with changes in processing temperatures regardless of the plasticizer type and content within the measured shear-rate range.