Vulcanized nanocomposites

They have studied the properties of NR-epoxidized natural rubber (ENR) blend nanocomposites also. Vulcanization kinetics of natural mbber-based nanocomposite was also smdied. The effect of different nanoclays on the properties of NR-based nanocomposite was studied. The tensile properties of different nanocomposites are shown in Figure 2.7 [33]. 

Novel room-temperature-vulcanized silicone mbber-organo-MMT nanocomposites were prepared by a solution intercalation process by Wang et al. [104]. A new strategy was developed by Ma et al. [105] to prepare disorderly exfoliated nanocomposites, in which a soft siloxane surfactant with a weight-average molecular weight of 1900 was adopted to modify the clay. 

Fig. 18 Variation of a tan 8 versus temperature, and b log E versus temperature for different fluorocarbon rubber nanocomposites (V refers to vulcanized samples)...

Recent work by Lukehart et al. has demonstrated the applicability of this technique to fuel-cell catalyst preparation [44g,h]. Through the use of microwave heating of an organometallic precursor that contains both Pt and Ru, PtRu/Vulcan carbon nanocomposites have been prepared that consist of PtRu alloy nanoparticles highly dispersed on a powdered carbon support [44g]. Two types of these nanocomposites containing 16 and 50 wt.% metal with alloy nanoparticles of 3.4 and 5.4 nm, respectively, are formed with only 100 or 300 s of microwave heating time. The 50 wt.% supported nanocomposite has demonstrated direct methanol fuel-cell anode activity superior to that of a 60 wt.% commercial catalyst in preliminary measurements. 

The photooxidation of vulcanized ethylene-propylene-diene monomer/montmor-illonite nanocomposite as well as EPDM/nanocomposite with stabilizers was recently reported [105]. The photooxidation products were not changed in the presence of the nanofiller. However, the presence of MMt was observed to dramatically enhance the rate of photooxidation of EPDM with a shortening of the oxidation induction time, leading to a decrease in the durability of the nanocomposites. On the other side, it was observed that addition of stabilizers, either Tinuvin P or 2-mercaptobenzimidazole, was efficient in inhibiting the degradation effect of MMt. 

TPV nanocomposites of LLDPE/reclaimed rubber with nanoclay and 1 wt.% MA-grafted PE and curative were prepared using a Brabender internal mixer at 170°C (Razmjooei et al., 2012). Contents of the reclaimed rubber, nanoclay, and compatibilizer were varied up to 30, 7, and 21 wt.%, respectively. The blends without the compatibilizer were also prepared. Morphological, thermal, and mechanical properties of the nanoclay-reinforced TPV nanocomposites indicated intercalation and partial exfoliation by the high-shear stress during mixing with the reclaimed rubber. Vulcanization of rubber phase led to an increase of viscosity. The size of rubber particles in TPV was reduced with the addition of nanoclay and compatibilizer. 

Polyolefin must be modified to make it become polarized. This polarized polyolefin can then be processed to synthesize a nanocomposite. Rubber does not need to be modified to synthesize a nanocomposite. If we take EPDM as an example, EPDM can be mixed with C18-Mt, and this mixture is intercalated in the clay gallery during vulcanization. When the vulcanization... 

Molesa et al. [61] compared compounded styrene-butadiene nanocomposites with polymer nanocomposites that were prepared by blending the latex with an aqueous dispersion of the montmoriUonite. The loading of the dispersed phase was at 10 phr. The initial results are consistent with the information found above. The flocculated rubber nanocomposite from the aqueous blend has superior strength properties when vulcanized and compared with the rubber nanocomposite prepared by compounding. MontmoriUonite that was organically treated demonstrated superior tensile strength when compared with rubber compounded with sUica. 

Natural Rubber-Based Composites and Nanocomposites Table 1.2 Properties of pure NR and vulcanized NR. 

In modern vulcanization processes, NR is generally compounded (either under high or low temperature) with 0.5 to 1 wt% of accelerators, different concentrations of CBs (which act as a filler) (up to 45 wt% for tyre manufacturing), low concentrations of aromatic amines and phenols for antioxidation purposes and 5-8 wt% of sulfur. These types of vuleanized NR are commonly known as NR composites (when the filler dimension is on the microscale) or NR nanocomposites (when the filler dimension is on the nanoscale). NR-based composites or nanocomposites will be discussed in more detail in the following sections. 

Salvetat et al manufactured NR/MWCNT nanocomposites according to the following steps the first step is the carboxylation of MWCNTs in the presence of nitric acid. The activated MWCNTs were dispersed by sodium dodecyl sulfate (SDS) in water, and the dispersion was then added to the ammonia solution containing pre-vulcanized NR, the mixture was stirred, sonicated, and dried to obtain the composite films. The NR nanocomposites showed a very large increase in both tensile strength and storage modulus in the rubbery region at room temperature. 

Recently, it has been used as a nanofiller to impart good mechanical, thermal and electrical properties of NR nanocomposites. Ozbas et fabricated NR/ functionalized graphene sheets (FGS) nanocomposites by solution mixing. The detailed procedure was stated as follows NR compounds were completely dissolved in TFIF with the aid of a magnetic stirring bar. Then, the required amount of FGS suspended in TFIF was added to the NR solution with stirring. After mixing the FGS-NR-TFIF solution for an hour with a stir bar, THF was removed by evaporation at room temperature under vacuum. The uncured NR/FGS nanocomposites were further vulcanized by hot compression moulded technique. 

Pasquini et al. reported that cellulose whiskers with high aspect ratio extracted directly from cassava bagasse were used to prepare NR nanocomposite films by mixing with the NR latex emulsion. The mixtures were cast on Teflon plates and dried overnight to obtain composite films. These NR nanocomposite films were not vulcanized by standard process. They found that a significant increase of the storage tensile modulus was observed upon filler addition by dynamic mechanical analysis. 

Abraham et al. reported that films of pre-vulcanized NR nanocomposite were fabricated by casting and evaporating a mixture of NR latex and aqueous suspension of cellulose nanofibrils (CNF). By this method, the CNF were evenly distributed in the NR composites. The increase of CNF content in the NR matrix caused the increasing the Young s modulus and tensile strength of materials, but the decreasing characteristic rubber elongation. The enhancements in mechanical and dynamic mechanical properties were attributed to the formation of a Zn ellulose complex and the three dimensional network of the CNF in the NR matrix as a result of the deprotonation of the cellulose. 

Wirasate et al also prepared NR nanocomposites using pristine Na -MMT or OMMT as reinforcing agent by a conventional mechanical mixing method. They found that both Na -MMT and OMMT could accelerate the vulcanization reaction of NR. The abrasion resistance of NR was improved by the addition of either Na" -MMT or OMMT. OMMT-filled NR composites showed better abrasion resistance than those of Na -MMT filled NR composites. Meanwhile, they had also found that the addition of Si69 to NR resulted in improvement of the abrasion resistance of the NR/Na -MMT composites due to the reduction in Na -MMT particle size. Particle size and dispersion of OMMT remained the same by the addition of Si69, thus the abrasion resistance, abrasion pattern and mechanical properties were not affected. 

Wu et al. reported that a new kind of NR/organo-vermiculite (OVMT) nanocomposite was prepared via a melt process in a HAAKE mixer. The resultant mixtures were further pressed to vulcanize at 140 °C, and vulcanized sheets were obtained. The vermiculite (VMT) was intercalated by cetyl-trimethylammonium bromide with a ball mill method to obtain used OVMT. The results showed that the intercalation led to an increase in the dfooj) of VMT from 1.46 nm to 4.51 nm. Meanwhile, they found that the tensile strength and the elongation at break of the NR/OVMT nanocomposites loading 15 phr of the OVMT reached 28.4 MPa and 623.2%, respectively. The 300% modulus, tear strength and hardness (Shore A) of the nanocomposites increased with the increase in OVMT loading. The thermal properties of the NR/OVMT nanocomposites were also improved. 

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