Nanofillers surface modification

M. Tanahashi, Development of fabrication methods of filler/polymer nanocomposites With focus on simple melt-compounding-based approach without surface modification of nanofillers. Materials, 3 (3), 1593-1619,2010. 

The thermal stability of nanocomposites containing cyanate ester/MWCNTs was found to be dependent on the surface modification of CNTs [93]. The results showed that the presence of unmodified MWCNTs in the nanocomposites produced a decrease of the initial decomposition temperature and a char yield similar to the neat resin. On the contrary, the initial decomposition temperature increased with 20 °C in the presence of modified MWCNTs. Moreover, the char yield of the nanocomposites containing modified MWCNTs was much higher than that of the cyanate ester resin. These results proved that the nature of carbon nanofiller is important for developing new nanocomposites with enhanced thermal properties. 

An alternative method of producing natural rubber based clay reinforced nanocomposites with outstanding properties is by using a spray drying technique. In this technique the siUcate layers of clay will be well dispersed in an irradiated polymer latex and this mixture will be sprayed through hot air to produce micrometre-sized liquid droplets. When the solvent is fully evaporated, micrometre-sized polymer spheres with delaminated clay silicate layers on their surface are produced. These spheres can later be melt blended with natural rubber to produce ternary nanocomposites. It is noteworthy that exfoliation of nanofillers can still be achieved without modification of the nanofiller surface, thus the expensive modification process can be eliminated. 

The hydrophilic surface of the cellulose-based nanoreinforcements leads to poor interaction between matrix and the filler [29]. Furthermore, the chemical compatibility is very important in controlling the dispersion and the adhesion among them. Therefore, it is common to see weak filler-matrix interactions when hydrophilic whiskers were added to hydrophobic matrices [4]. The miscibility of cellulose nanofillers with hydro-phobic matrices can be improved by various surface modifications, for example, esterification and acylation. The increment in the filler/matrlx compatibility produces the enhancement of mechanical and thermal properties but also enhances the barrier properties [30]. 

Surface modification of the nanofiller will be a challenge in the preparation of new types of rubber nanocomposites. Furthermore, the modification of various nanofillers using other nanofiUer systems will be a key to obtaining materials with designed properties. The interactions at the interface between the nanofillers and the matrix are one of the most important factors connected with the production of the new improved polymeric nanocomposites. Understanding the modification of the nanofiller in the polymer matrix, as well as the mechanical behavior in dynamic mode, leads to the possibility of producing new rubber nanocomposites, for example, for tire applications, where enhanced rolling resistance would improve traction [17]. 

In rubber-rubber blend nanocomposites, nanoparticles are incorporated into a blend which can significantly affect the properties of the matrix. The properties of these composites depend on the type of nanoparticles that are incorporated, their size and shape, their concentration and their interactions with the polymer matrix. It is difficult to produce monodispersed nanoparticles in a rubber blend because of the agglomeration of nanoparticles. This problem can be overcome by modification of the surface of the nanoparticles. Surface modification improves the interfacial interactions between the nanoparticles and the polymer matrix. Nanofillers when added to blend systems are known to cause a considerable change in dynamic properties. 

With the objective of a successful and economical recycling process in which the recycled polymer has largely acceptable properties, considerable effort must be made to encompass all the aspects of recycling in future studies to enhance the competitiveness of these systems. The first step could be the improvement of interfacial adhesion in prepared nanocomposites to achieve better physical and mechanical properties from recycled polymer wastes. Many procedures such as compatibilisation, functionalisation and surface modification could be developed in the future. Furthermore, the addition of effective nanofillers including available nanofillers or a combination of nanofillers will provide further progress and new opportunities in these systems. In addition, the development of fabrication techniques and also, the optimisation of available methods such as melt mixing should be performed, due to its important role in the final properties of recycled products. 

Table 5.1 Surface Modification of Nanofillers for Controlling Structure and Properties ...

TGA is most commonly used for evaluation thermal stability of nanocomposites filled with montmorillonite, clay, or carbon nanotubes. High-resolution TGA is applicable while determining the presence of any excess of surface modification molecules unbound to the surface. It is very important to know this parameter, especially if the nanofiller is to be added to pol5mier at high temperatures. In such a situation, modification molecules may have lower thermal degradation, which will negatively affect the properties of the nanocomposite. The commercially treated filler, in comparison with the second one, clearly exhibits an extra degradation peak at lower temperature, which indicates the presence of modification molecules not bonded with filler surface... 

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