Dispersion enhancement of multi-walled carbon nanotubes in nitrile rubber

A study of reinforcement mechanism of multi-walled carbon nanotubes (MWCNT) in nitrile rubber (NBR) matrix was carried out. Attempts to enhance the dispersion degree of MWCNT and the NBR-MWCNT interaction were conducted using numerous approaches, namely, sonication and chemical treatments of MWCNT with nitric acid (HNO₃), nitric-sulfuric acid mixture (HNO₃/H₂SO₄) and potassium permanganate (KMnO₄). Rheological behavior, dynamic properties and electrical properties of MWCNT/NBR vulcanizates were monitored. Results gained reveal the magnitude of Payne effect increases with MWCNT content and mixing time. The expanded MWCNT and continuous-network formation are observed with an increase in mixing time, yielding enhanced mechanical properties and electrical properties. With MWCNT modification, a significant reduction in the state-of-mix of MWCNT composites is exhibited. SEM results demonstrate the highest magnitude of MWCNT dispersion in the system with HNO3, but relatively poor interaction with NBR. The HNO₃/H₂SO₄ or KMnO₄ system demonstrates poor MWCNT dispersion after treatment which is probably due to the compaction of MWCNT during the drying stage after the chemical treatment process, giving the detrimental effect to mechanical and electrical properties of vulcanizates.