Highly exfoliated montmorillonite (MMT) clay reinforced thermoplastic polyurethane elastomers (TPUs) were prepared by an in situ solution polymerization method. By using small amount of 4,4'-methylenediphenyl diisocyanate (MDI) modified pristine clay (MDI-MMT) as fillers, the mechanical properties of TPUs were greatly improved. For example, with the addition of only 1.0 wt% of MDI-MMT, the resultant TPU/MDI-MMT nanocomposites showed approximately 36% increase in initial Young's modulus, 70% increase in tensile strength and 46% increase in ultimate elongation at break as compared with those of neat TPU. Detailed study showed that, owing to the strong covalent bonding between the MMT sheets and TPU matrix, MMT sheets were highly exfoliated during the polymerization process, and the highly exfoliated MMT sheets gave rise to the greatly improved mechanical properties and thermomechanical properties of TPU/MDI-MMT nanocomposites. The present work demonstrates that the in situ preparation of TPU/MDI-MMT nanocomposites by using MDI-MMT as fillers is a highly efficient method for reinforcing TPU.
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