Mechanical behavior of polyurethane composites with nanosized fillers

This paper reports the results of a study on the structure and properties of elastomeric nanocomposites based on polyurethane, which is of special interest due to its heterogeneous structure. So, the unfilled polyurethane also can be considered as a nanocomposite with complex mechanical behavior. Our study was performed on unfilled polyurethane and polyurethane filled with carbon particles of various morphologies: 1) few-layer graphene; 2) multi-walled carbon nanotubes; 3) diamond charge (detonation nanodiamonds). The content of filler in composites was 0.5 and 4 phr. Analysis of the mechanical behavior of the materials under consideration was carried out on the basis of the results of classical uniaxial tensile tests and cyclic experiments with increasing amplitude of deformation. The results obtained demonstrated that the incorporation of even a small filler amount in a polyurethane matrix leads to a significant change in the mechanical properties of the material. First of all, the stiffness of the material decreases in all cases. Secondly, the rupture (tensile failure) of the filled material significantly increases (almost in all cases) as compared to the unfilled polyurethane. The true stresses in some materials also increase at the time of sample’s rupture. A series of tearing tests were performed to gain a deep insight into the peculiarities of the failure mechanisms of materials. It was established that an increase in the macro-fracture of the unfilled material (until its rupture) is insignificant. In the materials reinforced with nanofillers, the growth of macrofractures takes a longer time, and they propagate to a much greater extent. Numerical calculations were carried out to give an explanation for the reduction in the polyurethane stiffness and the macrofracture growth retardation when the filler is added to polyurethane. It was hypothesized that a soft interfacial layer is formed near the particle surface. Furthermore, the finite element model proposed here can be used to explain the growth of deformations at the moment of rupture for filled polyurethane systems.