Natural nanocomposite structures

And in eompletion of the present seetion let us note one more important feature of natural nanocomposites structure. In Refs. [24,25] the interfacial regions absence in amorphous glassy polymers, treated as natural nanocomposites, was shown. This means, that such nanocomposites structure represents a nanofiller (nanoclusters), immersed in matrix (loosely packed matrix of amorphous polymer structure), that is, unlike polymer nanocomposites with inoiganic nanofiller (artificial nanocomposites) they have only two structural components. 

Hence, the stated above results demonstrated, that the adhesion level between natural nanocomposite structural components depended on nanoclusters and loosely packed matrix structures closeness. This level change can result to pol5mier elasticity modulus significant increase. A number of this effect practical realization methods was considered [50]. 

The nature of the organomodifier plays a role in the existence of true nanocomposite structures (intercalated for 15A and 30B, exfoliated for 25A, microcomposite for 10A), cone calorimeter results associated with x-ray diffraction (XRD) suggest that increased flame retardancy are more dependent on physical and thermal cross-linking of clay particles and polymer chains than on formation of nanocomposite structure. However, it can be concluded that the role of clay is crucial since PHRR values are reduced up to 70% in the presence of clays. 

Nanotube nanocomposites with a large number of polymer matrices have been reported in the recent years. The composites were synthesized in order to enhance mechanical, thermal and electrical properties of the conventional polymers so as to expand their spectrum of applications. Different synthesis route have also been developed in order to achieve nanocomposites. The generated morphology in the composites and the resulting composite properties were reported to be affected by the nature of the polymer, nature of the nanotube modification, synthesis process, amount of the inorganic filler etc. The following paragraphs review the nanocomposites structures and properties reported in a few of these reports and also stress upon the future potential of nanotube nanocomposites. 

Georgy V. Kozlov, DSc, is a Senior Scientist at UNIID of Kabardino-Balkarian State University in Nal chik, Russian Federation. His scientific interests include the structural grounds of properties of polymeric materials of all classes and states physics of polymers, polymer solutions and melts, and composites and nanocomposites. He proposed to consider polymers as natural nanocomposites. He is the author of more than 1500 scientific publications, including 30 books, published in the Russia, Ukraine, Great Britain, Germany, Holland, and USA. 

The primary problem in synthetic and natural nanocomposites is the establishment of a correlation between the molecular structure and the properties of the materials obtained, which indeed is a part of the fundamental content-structure-property problem. It seems to us that one of the ways of solving this problem is to investigate the catalytic properties of polymer-immobilized metal complexes, clusters and nanoparticles in different organic synthesis reactions as a function of their molecular organization (see Chapters 11 and 12). 

For preparation of such nanocomposites based on organoclays have to be used layered natural inorganic structures as montmorillonite [4, 5, 6], hectorite [3], vermiculite [7], saponin [8], kaolin, etc. Length of these layers about 220 nm, and thickness - Inm [9,10]. 

In a novel application of BC, Grande et al. (2009) added starch to the culture medium of cellulose-producing bacteria in order to introduce the granules into the forming network of cellulose which allowed the preservation of the natural ordered structure of cellulose nanofibers. Microscopic analysis revealed that starch acted as a matrix which filled the voids in the BC network. Using MCF as reinforcement, the nanocomposites showed considerable improvement in mechanical properties. 

Lately it was offered to consider polymers amorphous state stmcture as a natural nanocomposite [6]. Within the frameworks of cluster model of polymers amorphous state stmcture it is supposed, that the indicated structure consists of local order domains (clusters), immersed in loosely packed matrix, in which the entire polymer free volume is concentrated [7, 8]. In its turn, clusters consist of several coUinear densely packed statistical segments of different macromolecules, that is, they are an amorphous analog of crystallites with stretched chains. It has been shown [9] that clusters are nanoworld objects (tme nanoparticles-nano clirsters) and in case of polymers representation as natural nanocomposites they play nanofiller role and loosely packed matrix-nanocomposite matrix role. It is significant that the nanoclusters dimensional effect is identical to the indicated effect for particulate filler in polymer nano composites sizes decrease of both nano clusters [10] and disperse particles [11] resrdts to sharp enhancement of nanocomposite reinforcement degree... 

The authors of Ref [9] conducted cross-linked polymers microhardness description within the frameworks of the fractal (structural) models and the indicated parameter intercommunication with structure and mechanical characteristics clarification. The epoxy polymers structure description is given within the frameworks of the cluster model of polymers amorphous state structure [10], which allows to consider polymer as natural nanocomposites, in which nanoclusters play nanofiller role (this question will be considered in detail in chapter fifteen). 

At amorphous glassy polymers as natural nanocomposites treatment the estimation of filling degree or nanoclusters relative fraction (p j has an important significance. Therefore, the authors of Ref. [27] carried out the comparison of the indicated parameter estimation different methods, one of which is EPR-spectroscopy (the method of spin probes). The indicated method allows to study amorphous polymer structural heterogeneity, using radicals distribution character. As it is known [28], the method, based on the parameter - the ratio of spectrum extreme components total intensity to central component intensity-measurement is the simplest and most suitable method of nitroxyl radicals local concentrations determination. The value of dipole-dipole interaction is directly proportional to spin probes concentration C [29] ... 

Thus, the Ref [27] results showed, that the obtained by EPR method natural nanocomposites (amorphous glassy polymers) structure characteristics corresponded completely to both the cluster model theoretical calculations and other authors estimations. In other words, EPR data are experimental confirmation of the cluster model of polymers amorphous state structure. 

In this theme completion an interesting structural aspect of intercomponent adhesion in natural nanocomposites (polymers) should be noted. Despite the considered above different mechanisms of reinforcement and nanoclusters-loosely packed matrix interaction realization the common dependence is obtained for the entire studied temperature range of... 

Hence, the stated above results have demonstrated, that intercomponent adhesion level in natural nanocomposites (polymers) has structural origin and is defined by nanoclusters relative fraction. In two temperature ranges two different reinforcement mechanisms are realized, which are due to large friction between nanoclusters and loosely packed matrix and also perfect (by Kemer) adhesion between them. These mechanisms can be described successfully within the frameworks of fractal analysis. 

Hence, the presented above results have shown that elasticity modulus of amorphous glassy polycarbonate, considered as natural nanocomposite, are defined completely by its suprasegmental structure state. This state can be described quantitatively within the frameworks of the cluster model of polymers amorphous state structure and characterized by local order level. Natural nanocomposites reinforcement degree can essentially exceed analogous parameter for artificial nanocomposites [56]. 

It has been shown earlier on the example of PC, that the value is defined completely by natural nanocomposite (polymer) structure according to the Eq. (15.32) (see Fig. 15.26). 

Yanovskii, Yu. G., Bashorov, M. T., Kozlov, G. V., Kamet, Yu. N. (2012). Polymeric Mediums as Natural Nanocomposites Intercomponont Interactions Geometry. Proceedings of All-Russian Conf. Mechanics and Nanomechanics of Structurally-Complex and Heterogeneous Mediums Achievements, Problems, Perspectives . Moscow, IPROM, 110-117. 

Bashorov, M. T, Kozlov, G. V., Zaikov, G. E., Mikitaev, A. K. (2009). Polymers as Natural Nanocomposites Adhesion between Structural Components. Khimicheskaya... 

From wood to blood vessels [8-10], nature uses composites to create nanocomposite structures such as wood (essentially cellulose-reinforced fibrils bound together by lignin and hemicellulose matrix), and bones (this basic structure of all vertebrates is made of collagen fibrils embedded in an inorganic apatite matrix) [11-13]. All that scientists need to do is to try to mimic nature or to exploit these natural biocomposites in order to develop novel materials that can be suitable to our needs without being harmful to the environment... 

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