Micromechanics of ultra-toughened electrospun PMMA/PEO fibres as revealed by in-situ tensile testing in an electron microscope

A missing cornerstone in the development of tough micro/nano fibre systems is an understanding of the fibre failure mechanisms, which stems from the limitation in observing the fracture of objects with dimensions one hundredth of the width of a hair strand. Tensile testing in the electron microscope is herein adopted to reveal the fracture behaviour of a novel type of toughened electrospun poly(methyl methacrylate)/poly(ethylene oxide) fibre mats for biomedical applications. These fibres showed a toughness more than two orders of magnitude greater than that of pristine PMMA fibres. The in-situ microscopy revealed that the toughness were not only dependent on the initial molecular alignment after spinning, but also on the polymer formulation that could promote further molecular orientation during the formation of micro/nano-necking. The true fibre strength was greater than 150 MPa, which was considerably higher than that of the unmodified PMMA (17 MPa). This necking phenomenon was prohibited by high aspect ratio cellulose nanocrystal fillers in the ultra–tough fibres, leading to a decrease in toughness by more than one order of magnitude. The reported necking mechanism may have broad implications also within more traditional melt–spinning research

Using various techniques to characterize oxidative functionalized and aminosilanized carbon nanotubes for polyamide matrix

The main purpose of this study was to reveal usability of various characterization techniques for certain aspects of surface functionalized multi-walled carbon nanotubes. Surfaces were first oxidative functionalized by sulphuric acid/nitric acid mixture, then aminosilanized by gamma-aminopropyltriethoxysilane. Chemical groups formed on carbon nanotubes due to these surface treatments were characterized by X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy and also energy dispersive spectroscopy. Morphological changes and crystal structure of surface-treated carbon nanotubes were analyzed by scanning electron microscopy and X-ray diffraction, respectively. Thermogravimetric analysis was also used to observe thermal degradation of the chemical groups formed on the nanotube surfaces. In the second part of the study, Polyamide-6 nanocomposites were produced by using unmodified and surface functionalized carbon nanotubes. Transmission electron microscopy indicated that surface functionalization improves distribution of carbon nanotubes in the matrix, while flexural tests revealed that strength and modulus values could be increased as much as 30% and 40%, respectively, due to enhanced interfacial bonding between the matrix and nanotubes