Abstract
In this study, we have investigated the relationship between the spherulitic morphology and the dynamic tensile response of polyurethane reinforced with Halloysite nanotubes (HNTs). The polyurethane prepolymer is partially silane end-capped and filled with only 0.8 wt.% of acid-treated Halloysite nanotubes. The resultant nanocomposite material presents a 35% higher spall strength compared to the neat polyurethane and 21% higher fracture toughness. We show evidence that the HNTs are not the toughening phase in the nanocomposite, but rather it is their influence on the resultant spherulitic structures which alters the polymer microstructure and leads to a tougher dynamic response. Microstructural characterization is performed via Scanning Electron Microscopy, Atomic Force Microscopy and Field Emission Scanning Electron Microscopy, and crystallinity examination via X-ray diffraction. The spherulitic structures present a brittle fracture character, while the interspherulitic regions are more ductile and show large deformation. The nanocomposite presents a finer and more rigid spherulitic structure, and a more energy dissipative fracture mechanism characterized by a rougher fracture surface with highly deformed interspherulitic regions.
Highlights
In this study, we have investigated the relationship between the spherulitic morphology and the dynamic tensile response of polyurethane reinforced with Halloysite nanotubes (HNTs)
Polyurethane (PU) based materials can be optimized for a wide range of stress and strain rate conditions, as they can be synthesized with different compositions and macromolecular structural organization
In our previous work[27], we have described the synthesis process and characterization of HNT-PU nanocomposites based on PU prepolymer partially end-capped with a secondary aminoalkoxysilane, and an acid-treated
Summary
We have investigated the relationship between the spherulitic morphology and the dynamic tensile response of polyurethane reinforced with Halloysite nanotubes (HNTs). Sun et al.[8] studied the molecular dependencies of the high-strain-rate impact response of PUs and polyureas using a laser-induced particle impact test under strain rate magnitudes between 106 and 1 08 s−1 Their results showed that more intense hydrogen bonding between hard and soft segments led to greater dynamic strengthening and stiffening. The quasi-static response of the polymer was evaluated via uniaxial compression tests, and high-strain-rate compression tests were conducted using a split Hopkinson pressure bar with strain rates varying from 103 and 104 s−1 Their characterization indicated that an increase in phase mixing and hydrogen bonding between hard and soft segments, which was controlled by altering the soft segment molecular weight, resulted in increased strain rate sensitivity of the PU. The model predictions for uniaxial loading–unloading responses under different strain rates followed the same trends observed experimentally
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