Carbon nanomaterial/thermoplastic polyurethane composites for sports application : preparation, characterization and simulation
Date of Issue2016-05-05
School of Materials Science and Engineering
Carbon nanomaterials have been widely studied in various fields since their discovery. Their ultrahigh surface-to-volume ratios, low density, as well as outstanding thermal and mechanical properties, make them excellent candidates as nanofillers for high-performance and light-weight polymer composites. The major objectives of this project include two aspects: i) preparation of polyurethane (PU)-based composites reinforced by chemically functionalized multi-walled carbon nanotubes (MWCNTs) and graphene oxide (GO), respectively, with improved mechanical properties and thermal stability; ii) conducting the finite-element analysis (FEA) with Abaqus/Standard to study the mechanical performance of PU and the GO/PU composite under conditions of large-deflection bending typical for shoe soles. First, MWCNTs were covalently functionalized to fabricate thermoplastic PU-based composites with enhanced performance. Polycaprolactone diol (PCL), as one of PU’s monomers in this work, and was selectively used to functionalize MWCNTs to prepare MWCNT-PCL so as to realize a good compatibility between the nanofillers and PU matrix. Besides, the raw MWCNTs and carboxylic acid groups functionalized MWCNTs (MWCNT-COOH) served as control. It was found that both MWCNT-COOH and MWCNT-PCL showed better dispersion states in the PU matrix, as well as improved interfacial interactions with the matrix. In terms of mechanical properties and thermal stability, MWCNT-PCL/PU composite exhibited the greatest extent of improvement with addition of 1 wt% MWCNT-PCL. The achieved remarkable reinforcement effect of MWCNT-PCL was attributed to their homogeneous dispersion in the PU matrix and strong interfacial interactions with the matrix. Then, GO, with abundant oxygen functional groups, was studied as nanofiller for PU-based composites. To achieve a well exfoliated and stable GO suspension in an organic solvent (dimethylformamide, DMF), 4, 4′- methylenebis (phenyl isocyanate) (MDI) and PCL, two monomers for synthesizing PU, were selectively used to functionalize GO. The obtained functionalized GO (FGO) could form homogeneous dispersions in the DMF solvent and PU matrix, as well as provide a good compatibility with the PU matrix. The most efficient improvement of mechanical properties was achieved when 0.4 wt% FGO was added into the PU matrix. Regarding the thermal stability, PU filled with 1 wt% FGO showed the largest extent of improvement. The improved dispersion of FGO in the PU matrix and strong interfacial interactions between them could contribute to the improvement in mechanical properties and thermal stability of FGO/PU composites. Thermoplastic PU elastomers are used as shoe-sole materials due to many excellent properties but their inelastic deformation is a serious deficiency for such applications. Hence, GO was introduced into the synthesized thermoplastic PU to produce a GO/PU composite material with enhanced properties. Plastic behavior of this composite was assessed in cyclic tensile tests, demonstrating reduction of irreversible deformations with the addition of GO. Additionally, in order to evaluate mechanical performance of PU and the GO/PU composite under conditions of large-deflection bending typical for shoe soles, finite-element simulations with Abaqus/Standard were conducted. An elastic-plastic finite-element model was developed to obtain detailed mechanical information for PU and the GO/PU composite. The numerical study demonstrated that the plastic area, final specific plastic dissipation energy and residual height for PU specimens were significantly larger than those for the GO/PU composite. Besides, the addition of GO into the PU matrix greatly delayed the onset of plastic deformation in PU in a large-deflection bending process. The finite-element analysis provided quantification of the effect of GO enhancement on the large-deflection bending performance of PU for regimes typical for shoe soles and can be used as a basis for optimization of real composite products.