Influence of Carbon Nanotubes on the Mechanical Properties of Cross-Linked Polyurethanes
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INFLUENCE OF CARBON NANOTUBES ON THE MECHANICAL PROPERTIES OF CROSS-LINKED POLYURETHANES Е. А. Lysenkov,1,2 Z. О. Haholkina,3 E. V. Lobko,3 M. H. Tkalich,3 and V. V. Klepko3
UDC 539.199: 541.64
By the methods of electron microscopy, dynamic mechanical analysis, and transmission of ultrasound, we study the principal mechanical characteristics of systems based on cross-linked polyurethanes and carbon nanotubes. It is shown that they exhibit the percolation behavior and, in the region of percolation transition (0.4–1%), their mechanical characteristics undergo abrupt changes. In this case, the decisive influence is exerted by the aggregates of carbon nanotubes. As the percolation threshold is reached, we observe the formation of a branched network of carbon nanotubes and the tensile strength, the modulus of elasticity, and the velocity of ultrasound significantly increase in the investigated materials. Keywords: carbon nanotubes, polyurethanes, polymeric nanocomposites, mechanical properties of polymers, percolation behavior.
As one of the main trends in the development of new types of polymeric composite materials, one can mention the development of so-called polymeric nanocomposites in which the range of particle sizes of the filler or of the reinforcing element lies within the nanometer range. In some cases, this enables us to create materials with unique complexes of consumer and operating properties [1]. In these systems, metal oxides, layered silicates, aerosil, etc. are used as fillers. Carbon nanotubes (CNT) also prove to be promising. Thus, carbon nanotubes and nanofibers attract significant attention of the researchers. Due to the ability to exhibit of semiconducting properties, they can be used as emission displays, data-storage devices, etc. [2]. Moreover, the CNT are fairly hard and elastic and, therefore, can be used as constituents of various nanocomposites. As a result of addition of relatively small amounts of CNT, the properties of polymeric materials (conductivity, heat conduction, and mechanical strength) undergo substantial changes due to the formation of a continuous (percolation) cluster [3, 4]. Since the interaction of the polymeric matrix with CNT is weaker than the Van-der-Waals forces between the nanotubes, the CNT are susceptible to the formation of agglomerates in the composites. In this case, the nanotubes cannot increase the strength of the composite and, therefore, their uniform distribution in the polymeric matrix is the main factor for the nanohardening of the polymer. Polyurethanes are the most promising polymers, which have a number of important operating properties (strength, elasticity, hardness, tribologic stability, thermal stability, lyochemical stability, etc.) [5–7] and, hence, are used as coatings, adhesives, flexible and hard foams, elastomers, thickeners, fillers, etc. [8, 9]. There are numerous works devoted to the analysis of the influence of CNT on the mechanical properties of polymeric systems and, in particular of polyurethane (PU) systems. The mechanical properties
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