Rheological properties of maleated natural rubber/polypropylene blends with phenolic modified polypropylene and polypropylene-g-maleic anhydride compatibilizers

Maleated natural rubber was prepared using natural rubber (air-dried sheet) and maleic anhydride by a melt mixing process under high shearing action. Two types of blend compatibilizers: graft copolymer of polypropylene and maleic anhydride (PP-g-MA), and phenolic modified polypropylene (Ph-PP) were also synthesized in a molten state. The 60/40 MNR/PP blends were later prepared by a melt mixing process using PP-g-MA and Ph-PP at various loading levels of 3, 5, 10, 15 and 20 wt% of PP. Shear flow properties of the blends were later characterized. We found that the apparent shear stress and shear viscosity increased with an increase in apparent shear rate over a range of loading levels of compatibilizers of 0-5%. This may be attributed to the chemical interaction between different phases of the blend caused by compatibilizers. They consist of segments chemically reactive to their respective counterparts in the polymer pairs. The increase in chemical interaction between the interface caused an improvement of interfacial tension and led to decreasing size of dispersed domains of the minor phase (PP) in the MNR matrix. Increasing loading level of compatibilizers higher than 5 wt% caused a decreasing trend of the flow properties. This may be attributed to the formation of micelles dispersed in the MNR matrix. Therefore, the apparent shear stress and shear viscosity decreased because the micelles act as a lubricant in the polymer melt flow. The log additive rules was applied to the flow properties and it was found that the 60/40 MNR/PP blends with PP-g-MA and Ph-PP compatibilizers indicated positive deviation blends. That is, the blends were partially compatible blends. The power law equation was also applied to the shear flow properties. We found that at a loading level of compatibilizers of 5 wt%, the lowest n value was observed. This indicates the highest pseudoplasticity of the polymer melts.