The dispersion of CNT in TPU matrix with different preparation methods: solution mixing vs melt mixing

Melt mixing and solution mixing are two commonly used methods for the preparation of polymer nanocomposites. In this work, thermoplastic polyurethane (TPU) composites with unmodified MWCNTs and carboxyl MWCNTs (MWCNT-COOH) were prepared using melt mixing and solution mixing. The dispersion of filler in TPU matrix and the macro-properties of composites under different processing conditions were systematically investigated. It was found that for pristine MWCNTs, a better dispersion was obtained using solution method at relatively low content of fillers (≤2.5 wt%); but when the content of MWCNT was above 2.5 wt%, melt mixing under high shear force was more effective to achieve a homogeneous dispersion. The similar result was confirmed in TPU/MWCNT-COOH composites, with the critical concentration shifted to 5.0 wt%, indicating that the interaction between CNT and TPU also played role on the dispersion of CNT in TPU matrix via solution mixing. Our finding is important for the preparation of polymer/CNT nanocomposites with good dispersion depending on the filler content and mixing methods. [Display omitted] •The dispersion state of CNT in TPU matrix with solution and melt mixing was compared.•The effect of the concentration and the surface modification of CNT on the dispersion of CNT in TPU matrix was studied.•Melt mixing under high shear force with unmodified MWCNTs is a better way to obtain high-performance composites.