The properties of nitrile rubber (NBR) reinforced by multiwalled carbon nanotube (MWCNT), conductive carbon black (CCB), carbon black (CB), and precipitated silica (PSi) were investigated via viscoelastic behavior, bound rubber content, electrical properties, cross-link density, and mechanical properties. The filler content was varied from 0 to 15 phr. MWCNT shows the greatest magnitude of reinforcement considered in terms of tensile strength, modulus, hardness, and abrasion resistance followed by CCB, CB, and PSi. The MWCNT filled system also exhibits extremely high levels of filler network and trapped rubber even at relatively low loading (5 phr) leading to high electrical properties and poor dynamic mechanical properties. Although CCB possesses the highest specific surface area, it gives lower level of filler network than MWCNT and also gives the highest elongation at break among all fillers. Both CB and PSi show comparable degree of reinforcement which is considerably lower than CCB and MWCNT.

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Attempts to enhance dispersion degree of multi-walled carbon nanotubes (CNT) in nitrile rubber (NBR) matrix, and to improve the NBR-CNT interaction were carried out by different approaches, namely, sonication and chemical treatments of CNTs with nitric acid (HNO3), nitric-sulfuric acid mixture (HNO3/H2SO4) and potassium permanganate (KMnO4). Rheological behavior of NBR/CNT composites was monitored as an indication of filler dispersion degree using the Rubber Process Analyzer (RPA2000) via the alteration in Payne effect. Results gained reveal the magnitude of Payne effect in the following order: untreated system> sonicated system> HNO3 system> HNO3/H2SO4 KMnO4 system, implying a significant improvement in the state-of-mix of NBR/CNT composites by sonication and/or chemical treatment of CNT prior to being mixed with NBR. The SEM results demonstrate the highest magnitude of CNT dispersion in the system with HNO3 followed by the sonicated system untreated system, HNO3/H2SO4 KMnO4. The SEM results suggest that the surface treatment of CNT with HNO3 yields highest magnitude of improvement in CNT dispersion. Poor CNT dispersion after treatment with HNO3/H2SO4 or KMnO4 is due probably to the re-agglomeration of CNT during the drying stage after the chemical treatment process.

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 (HNO 3 ), nitric-sulfuric acid mixture (HNO 3 /H 2 SO 4 ) and potassium permanganate (KMnO 4 ). 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 HNO 3 , but relatively poor interaction with NBR. The HNO 3 /H 2 SO 4 or KMnO 4 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.