Interface Tailoring And Development Of High-Performance Clay-Rubber Nanocomposites

"The nano-compositing technique based on separation of clay nano-platelets by rubber latex particles in aqueous clay nano-suspension", (abr. LCM), is a facile and highly effective nano-compounding method brought forward by Dr. Zhang Li-Qun. Especially, LCM is considered as one of the most important methods to prepare layered silicate/rubber nanocomposites. In this paper, clay/rubber nanocomposites (i.e. MMT/SBR, NR nanocomposites) were prepared through LCM, while the interface of the nanocomposites was carefully designed by introducing various organic modifiers, in order to improve both the clay dispersion and inter facial adhesion of the nanocomposites, and above all, to improve the mechanical properties of the nanocomposites. In addition, the combined effect of nano-clay and nano-carbon black on the properties of rubber (NR) nanocomposites was investigated to provide useful results relevant to the industrialization of clay/rubber nanocomposites.In this paper, mainly two modification methods were adopted to tailor the interface of the clay/SBR nanocomposites. The first one was melt organic modification, in which the clay/SBR nanocomposites were prepared firstly through regular LCM, and then the organic modifiers were added to the nanocomposites during the conventional melt compounding. After blending on the mixers and vulcanization, the final clay/SBR nanocomposites with improvements on the interfacial adhesion were obtained. The effects of C16 (hexadecyl trimethyl ammonium bromide) and KH550 (3-aminopropyltrithoxy silane) on the structures and properties of the nanocomposites were studied and compared, and it was found that both modifiers could well improve the interfacial adhesion between the clay and rubber, resulting better mechanical properties of the nanocomposites. The difference was that, C16 could only form physical interaction with rubber macromolecules that could only benefit the tensile strength of the nanocomposites, but KH550 developed connections between the clay and rubber macromolecules through chemical bonding, which offered much better results from the modification, increasing both the stress at certain strain and tensile strength of the nanocomposites. In second stage, the addition amounts of silane coupling agents (KH550 and Si69: bis-(3-triethoxysilyl propyl)-tetrasulfide) on the structures and properties of the nanocomposites were carefully investigated. The results showed that, with increase of silane coupling agents, the modulus increased, but the ultimate elongation decreased, resulting in better tensile strength at small loading but decreased strength at large loading. The optimum dosage of silane coupling agents was found at 4phr, and it could also be concluded that KH550 gave better outcome of modification than Si69.The second modification method was in-situ organic modification during LCM, invented firstly by author, in which the organic modification was carried out before the co-coagulation step of LCM. This method could well improve the nanocomposite interfaces and increase the mechanical properties of the resulted nanocomposites. In a typical procedure, the organic modifier was added into the clay aqueous suspension to in-situ modify the clay nano-platelets, then mixed the suspension with SBR latex before adding flocculants to co-coagulate clay and rubber. The obtained clay/SBR nanocompounds were dried, further mixed using traditional mixers and vulcanized to give the nanocomposites. Herein, quaternary ammonium salts with long alkyl chain and silane coupling agents were mainly utilized as organic modifiers. The effects of modifier type and loading level on the structures and properties of the nanocomposites were studied, and the modification mechanism was thoroughly discussed. It was found that, in the clay aqueous suspension, the organic modifiers could be adsorbed onto the clay nano-platelets through ionic exchange reaction, in which the originally inorganic clay acquired certain organic characteristics. When the flocculants were introduced into the mixture of modified clay and rubber latex, the organic modifier molecules and flocculants both could be intercalated into the clay galleries, and the competition between the two affected the final structure and properties of the nanocomposites. With relatively large loading of organic modifier, they could be well intercalated into clay layers, rather than flocculants, which then led to the intercalation of rubber macromolecules. Therefore in the final nanocomposites there were modifier intercalated structures and rubber macromolecules intercalated sturetures, which definitely improved the clay dispersion in rubber matrix and the interfacial adhesion. Consequently, the mechanical performance was significantly enhanced. Besides, comparing these two types of organic modifiers, the quaternary ammonium salts could only form physical interaction with rubber macromolecules, while silane coupling agents helped to construct chemical linked interface, particularly with both KH550 and Si69, a quite stronger interfacial adhesion was achieved. The in-situ modification was found to be more efficient in promoting the interfacial interaction and mechanical properties of the nanocomposites than the first method, melt organic modification.Finally, in application studies on the clay/rubber nanocomposites prepared by LCM, other nano-filler could be incorporated into the master batch to give the joint reinforced rubber nanocomposites. In this paper, the combined effects of nano-clay and nano-carbon black on the properties of rubber (NR) nanocomposites was systematically investigated. The results showed that two nano-fillers were uniformly dispersed in the NR matrix at the nano-scale, and the carbon black particles filled into the space between clay layers. At the same total filling amount, combining clay and carbon black could increase the filler volume fraction in the nanocomposites, improve the processability, dynamic and mechanical properties of the nanocomposites.