Modulus in HDPE Blends

Modulus of HDPE, TOPAS® COC, and HDPE-COC Blend at 23°C, 80°C, and 100°C.

Introduction

TOPAS® COC 6013F-04 is an amorphous polyolefin with a glass transition temperature (T_g) of 138°C. A High Density Polyethylene (HDPE) with a density of 0.960g/cc has a crystalline melting point of approximately 131°C. As the temperature increases, the physical properties of COC 6013F-04 are retained more so than they are in the HDPE material. To demonstrate this, the modulus of 6013S-04, a 0.960g/cc HDPE, and an 80% HDPE, 20% 6013S-04 blend were measured at 23°C, 80°C and 100°C.

Results

The modulus of 6013S-04 is 3x higher than the HDPE at 23°C. The gap between the two materials widens as the temperature increases with the COC being 22x higher modulus than the HDPE at 100°C. Then adding 20% 6013S-04 to the HDPE resulted in a 2x higher modulus at 100°C than HDPE alone. The collected modulus data can be found below in Table 1.

Table 1: Tensile modulus of COC 6013S-04, HDPE, and an 80% HDPE, 20% 6013S-04 blend at three temperatures: 23°C, 80°C, and 100°C.

Analysis

While the modulus of the HDPE and COC blend is twice as high neat HDPE at 100°C, it might be expected that it should be even higher. It is likely that having the COC and HDPE blended together compromises the ability of the COC to retain a high modulus as the temperature rises. This is because the blend of the two materials results in a dispersed COC phase that reinforces the HDPE phase rather than the formation of co-continuous phases of rigid COC and HDPE. If a coextrusion utilizing a discrete layer of COC was evaluated instead of a melt blend of HDPE and COC, then higher modulus values for the HDPE and COC combination would have been achieved.

Implications

This data illustrates how TOPAS® COC can be used to increase the high temperature performance of polyolefin materials. For applications where high modulus is required even as the temperature is increased, consider adding discrete layers of TOPAS® COC 5013 or 6013 to deliver the performance needed.  

Material Note

This study evaluated TOPAS® COC 6013S-04, an injection molding grade comparable to 6013F-04, which is a film grade. Regarding the results presented in this study, 6013S-04 can be considered identical to 6013F-04.

Additionally, the HDPE evaluated is an injection molding grade with a melt index of 8g/10 minutes at 190°C with a 2.16kg weight. The modulus results presented for the HDPE may differ for lower melt index resins, particularly at higher temperatures, but not significantly.

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