NR nanocomposites reinforced with

A comparison of the mechanical properties of NR/CNT and NR/CB composites with 25 phr of filler is shown in Table 1.12. NR/CNT nanocomposites exhibit marked enhancement of Shore A hardness, tensile modulus and tensile strength by 16, 32 and 10%, respectively, as compared to NR composites reinforced with the same filler loading of CB. This may be due to the strong... 

However, NR composites and nanocomposites reinforced with CNTs are seldom prepared via melt blending because it is difficult to disperse CNTs into the NR matrix. 

NR Composites and Nanocomposites Reinforced with Natural Mineral Fillers... 

Das et further used a series of long chain fatty acids to modify OMMT, and subsequently utilized them as reinforcing fillers to prepare NR nanocomposites by melt blending. They found that mechanical properties of NR nanocomposites with modified OMMT were remarkably improved. Thomas et reported that NR nanocomposites with outstanding gas barrier properties had been prepared with OMMT via a melt mixing technique. They found that the permeability decrease of the NR nanocomposites had a good qualitative correlation with the volume of the constrained region. 

Another promising approach to preparation of novel NR composites and nanocomposites with excellent properties is to adopt hybrid fillers because each reinforcing agent can retain its inherent advantages, which imparts a synergistic effect between hybrid fillers to reinforce NR nanocomposites. 

A similar sol-gel process method, via NR rubber solution, was also conducted to study the effect of in situ silica content, which was varied from 15 to 65 phr, on the cure characteristics and mechanical, dynamic mechanical and thermal properties of the silica-NR nanocomposite.Both the Mooney viscosity and cure time of the sol-gel silica-NR compound increased with increasing silica contents and were lower than those of the commercial silica-filled NR compound at the same amount of silica. This is attributed to the fewer amounts of silanol groups in the sol-gel silica as compared to the commercial silica. Better reinforcement of the in situ silica, compared to the normal silica, was confirmed when higher moduli and improved compression set were observed for the sol-gel silica NR vulcanizate. This observation is consistent with the Guth and Gold equation as well as the TEM micrographs results. The sol-gel silica vulcanizate has lower storage modulus but better thermal stability then the commercial silica vulcanizate. 

The achievement of a high degree of exfoliation of layered clay minerals in nonpolar rubber matrices, such as NR, is still a major issue. This chapter presents a brief overview of studies of clay reinforcement in NR both in micro and nano scale. Although quite a lot of studies have been reported in the field of NR reinforcement with simple organoclay (OMt), plenty of scope still exists to improve the dispersion of MMT followed by property enhancement. Better dispersion and improvement in dilferent properties was observed in the case of EOMt-filled NR nanocomposites. 

The Mullins effect is characterized by stress softening. In order to demonstrate the presence of the Mullins effect in NR nanocomposites, three successive tensile cycles were performed for each sample. For the unfilled NR matrix, curves corresponding to the successive cycles were perfectly superposed, to a few per cent (6-8%) (Figure 14.22(a)).For nanocomposites, a significant decrease in G o can be observed between the first and the second cycle, for films reinforced with 30 wt% starch nanocrystals (Figure 14.22(b)).Similar to the Payne effect, the magnitude of the Mullins effect also increases with filler content. Furthermore, this increase was almost proportional to the filler content. 

When 1 wt% of CNTs were added to the rubber the stress level for the nanocomposite material increased from 0.2839 to 0.56413 MPa. At 10 wt% of CNTs the stress value obtained reached 2.55 MPa which is nine times that of pure NR." Nanocomposites of NR reinforced with SiC nanoparticles and single-walled carbon nanotubes were synthesized and processed using toluene as the solvent." Both types of nanocomposite showed an increase in initial modulus with increasing filler content, with a maximum initial modulus at 1.5% filler content. The tangent modulus at 200% strain further confirms the enhancement of reinforcement by the nanofillers at 1.5% content. 

Crosslinked NR nanocomposites were prepared with montmorillonite. Morphology was characterized using transmission electron microscopy (TEM), wide-angle X-ray scattering (WAXS), and dynamic mechanical analysis (DMA). X-ray scattering patterns revealed clay intercalation and TEM showed dispersion with partial delamination. The loss modulus peak broadened with clay content, while Tg remain constant. Montmorillonite reinforced the rubber. The DMA exhibited non-linear behaviour typified as a Payne effect (see Section 20.11) that increased with clay content and was more pronounced for this type of nanocomposite. Viscoelastic behaviour was observed under large strains via recovery and stress relaxation. ... 

Very interesting studies of natural rubber reinforcement with ZnO nanoparticles were performed by scientists from India, under the direction of Sabu Thomas [62]. The goal of these studies was to characterize the viscoelastic behavior and reinforcement mechanism of ZnO nanoparticles introduced into the rubber matrix. They have presented a constrained polymer model based on a rubbery region and a ZnO nanoparticle. Very interestingly, the authors presented a core-shell morphology model and constrained polymer model to explain the constrained polymer chains in NR/ZnO nanocomposites [62]. Thanks to this research and the proposed models, it is possible to understand the behavior of nanofillers in the polymer matrix and maybe in the future to develop an ideal nanofiller for use in the rubber matrix. 

Chemical pretreatments with amines, silanes, or addition of dispersants improve physical disaggregation of CNTs and help in better dispersion of the same in rubber matrices. Natural rubber (NR), ethylene-propylene-diene-methylene rubber, butyl rubber, EVA, etc. have been used as the rubber matrices so far. The resultant nanocomposites exhibit superiority in mechanical, thermal, flame retardancy, and processibility. George et al. [26] studied the effect of functionalized and unfunctionalized MWNT on various properties of high vinyl acetate (50 wt%) containing EVA-MWNT composites. Figure 4.5 displays the TEM image of functionalized nanombe-reinforced EVA nanocomposite. 

---