Rubber blends surface morphology

Thomas, S., Gupta, B. R., De, S. K., Mechanical properties, surface morphology and failure mode of gamma-ray irradiated blends of polypropylene and ethylene-vinyl acetate rubber. Polymer Degradation and Stability 1987,18(3), 189-212. 

Blended matrices of maleated natural rubber and poly(methyl methacrylate) were prepared by mechanical mixing, and the fractured surface morphology of... 

Fig. 11.38 Blend 2 at 140°C and 120 rpm. Early morphology development reveals rough PS surfaces and fingers indicative of the rubber-like nature of PS at 140°C. [Reprinted by permission from the Proceedings of the Seventh Semi-annual Meeting of the Polymer Mixing Study, Polymer Processing Institute, Hoboken, NJ (1993).]...

For the morphological analysis of the binary blends (materials DZ and NZ), the samples were cryofractured in liquid nitrogen and the rubber phase was dissolved after exposure at 140°C for 6 hours to xylene vapour. After the chemical treatment, the surfaces were gold-sputtered for SEM observation. 

Figure 15.7a shows that the two phases are with irregular domain sizes and shapes. This indicates that the NR/EPDM blends were completely immiscible, large EPDM domains being dispersed in the NR matrix. The average domain size of the dispersed phase was 4.1 pm. The compatibility of the NR/EPDM system was improved by the addition of a compatibilizer, as can be seen in Fig. 15.7b-g the treatment resulted in noticeable surface hardening, and the physical changes in the surface were expected to influence physically both the deformation and adhesion of the two mbbers, that is, the compatibilizers improved both the morphology and compatibility of the blends because of the reduction in the interfacial tension between EPDM and NR rubbers. The size of the dispersed phase (EPDM) domain decreased with the addition of compatibilizers, and no gross phase separation was present in the blends (Fig. 15.7). For NR/BR/EPDM, the domain size was approximately 3.8-1.26 pm NR/PVC/EPDM, 2.7-0.75 pm NR/chlorosulfonated PE/EPDM, 2-0.75 pm NR/p-radiation/EPDM 4-1.5 pm and NR/MAH/EPDM. 1-0.25 pm. These results are in agreement with the observations of Anastasiadas and Koberstein (58) and Meier (59), who reported that compatibilizers reduced the phase domain size.

Bitinis et developed for the first time a novel and industrially scalable PLA-NR blend prepared by melt mixing blends at 5,10 and 20 wt% of natural rubber to analyze the effect of the NR concentration on the blend morphology. Figure 7.5 shows SEM micrographs of the blends fracture surfaces where it is observed that the size of the rubber particles is similar for 5 and 10 wt% but increases for the blend at 20 wt% from 1.15 to 2.00 pm. In general, in an immiscible binary polymer blend, the size of the dispersed phase increases as a function of the concentration of the minor phase in the blend, due to coalescence phenomena. ... 

---