Effect of nano-MMT addition sequence on properties of polypropylene/thermoplastic polyurethane blends

Polypropylene (PP)/thermoplastic polyurethane (TPU) blends and their nano-montmorillonite (MMT)-reinforced composites with different MMT addition sequences were prepared via melt blending. This study investigated the effect of MMT addition sequence on morphological evolution, thermal properties, rheological behavior, and mechanical properties of the PP/TPU/MMT ternary system. Key results are as follows: compared with the PP70 %/TPU30 % binary blend, the size of the TPU dispersed phase in composites decreased after introduction of nano-MMT. Among composite systems, the sample where TPU was pre-mixed with 3 % MMT followed by blending with PP exhibited the narrowest TPU droplet size distribution, with its average diameter reduced by one-third relative to the unfilled PP70 %/TPU30 % blend. X-ray diffraction (XRD) analysis revealed that the diffraction peak of MMT in this system shifted to a lower angle (3.496°), indicating partial intercalation/exfoliation of nano-clay. Differential scanning calorimetry (DSC) results demonstrated that the inhibitory effect of this system on PP crystallization was weaker than that of other composites. Additionally, this system showed the optimal tensile strength and tensile modulus. Thermogravimetric analysis (TGA) indicated that the system where PP was pre-mixed with 3 % MMT followed by blending with TPU had the best thermal stability, yet its mechanical properties were the worst.