IV.1 Non-reactive compatibilization

We studied the influence of different non-reactive compatibilizers, EVA, Kraton, MAPE and  EXACT 0210 (ethylene octene copolymer, 1-octene ) on the tear strength of the EMA and rubber blends. The results are shown in figure 4.1.


fig 4.1 Comparison of tear strength between different non-reactive compatibilizers

It can be seen form the figure that EXACT was the best compatibilizer in EPDM waste rubber/EMA compared to others. That is, in EMA15wt% + compabilizer 10wt% blends, EXACT increased the tear strength to 16.47 MPa, compared to 9.70 MPa with EVA and 9.62 MPa with Kraton, and the percentage is 70% and 71% respectively; in EMA15wt% + compatibilizer 15wt% blends, EXACT increased the tear strength 88% compared to MAPE (18.29 Vs. 9.74 MPa).

We can also see from the figure that the mechanical properties were not increased enough by just adding EXACT, EMA or LDPE. It is necessary to use thermoplastic polymer and compatibilizer to achieve the expected properties.

The compatibilization effect of EXACT on the recycled EPDM rubber/EMA was investigated in detail. The mechanical properties changes as the content of EXACT increases (Figure 4.2 to Figure 4.6, the dashed line represents value of blue and black reference material (reference material supplied by Ecorub AB).


Figure 4.2: Tensile strength of recycled EPDM rubber/EMA blends compatibilized by EXACT

It has been found during the experiment that the total amount of EMA and EXACT should be at least 15wt%; otherwise the blends can not be pressed to a plate strong enough to be tested.

It could be seen that the tensile strength and the elongation at break increased obviously as the EMA increased, and increased as the content of EXACT in the beginning and then decreased after an optimum value. The variations of Young’s modulus with the content of EXACT are not easy to explain. In the case of 15wt% EMA, young’s modulus were improved as increased the content of EXACT was increased, and in the case of 10wt% EMA and 20wt% EMA, there exists a maximum value of the modulus as the content of EXACT increased. The tear strength was improved with increasing the concentration of compatibilizer and EMA, and a small decrease was observed for 20wt% EMA blends.

Finally, the hardness did not change much as the EXACT and EMA increased.

We could also see that there exist maximum values in the tensile strength and elongation at break (Figure 4.2 and Figure 4.3): 7.5wt% EXACT in the case of 10wt% EMA, 25wt% EXACT in the case of 15wt% EMA and 15wt% EXACT in the case of 20wt% EMA. There is a critical volume of compatibilizer in each of the blend component. Nguyen [19] also found a critical value in the compatibilization of waste tire rubber/EMA blends.

This phenomenon was also investigated by other researchers [20, 21]. A possible mechanism for maximum values in tensile strength and strain at break might be the formation of a compatibilizer multilayer structure in the interphase [21]. Thus, in stead of going into a single layer at the interface, resulting in a higher volume fraction, the additional compatibilizer might simply form additional lamellae. The effective interfacial tension would then remain more or less constant.

Favis et al. [20] explained that the obtained maximum values were due to the fact that dispersed phase had reached critical domain size which could be ascribed to the balance of viscous forces tending to break the dispersed drop, and interfacial tension forces tending to resist deformation and disintegration. Noolandi and co-workers [22] noted that
modulus increased with the increase in compatibilizer concentration, reaching maximum at a critical volume fraction, which is sufficient to saturate the interphase surfaces. They proposed that micelle formation would be energetically favorable when the concentration of the compatibilizer became sufficiently high, thus, the concentration of compatibilizer in the
interphase region could be expected to remain approximately constant, with the interfacial tension correspondingly unchanged.


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