Xiaoping Cui

Electroactive shape memory cyanate/polybutadiene epoxy composites filled with carbon black

Electroactive shape memory composites were synthesized using polybutadiene epoxy (PBEP) and bisphenol A type cyanate ester (BACE) filled with different contents of carbon black (CB). Dynamic mechanical analysis (DMA), scanning electron microscopy (SEM), electrical performance and electroactive shape memory behavior were systematically investigated. It is found that the volume resistivity decreased due to excellent electrical conductivity of CB, in turn resulting in good electroactive shape memory properties. The content of CB and applied voltage had significant influence on electroactive shape memory effect of developed BACE/PBEP/CB composites. Shape recovery can be observed within a few seconds with the CB content of 5 wt% and voltage of 60 V. Shape recovery time decreased with increasing content of CB and voltage. The infrared thermometer revealed that the temperature rises above the glass transition temperature faster with the increase of voltage and the decrease of resistance.

The effects of carbon fiber on electroactive shape memory behaviors of cyanate/polybutadiene epoxy/carbon black composites

Electroactive shape memory composites were synthesized using polybutadiene epoxy and bisphenol A-type cyanate ester filled with 2 wt% carbon fiber; 3 wt% carbon fiber; 4 wt% carbon fiber; 4 wt% carbon black; 4 wt% carbon black and 0.3 wt% carbon fiber; 4 wt% carbon black and 0.5 wt% carbon fiber; 4 wt% carbon black and 0.8 wt% carbon fiber. Mechanical, electrical performance, and electroactive shape memory behavior were systematically investigated by dynamic mechanical analysis and scanning electron microscopy. It is found that the volume resistivity sharply decreased due to excellent electrical conductivity and synergic effect of carbon black and carbon fiber, in turn resulting in good electroactive shape memory properties. The content of carbon fiber and applied voltage had significant influence on electroactive shape memory effect of the developed bisphenol A-type cyanate ester/polybutadiene epoxy/carbon black/carbon fiber composites. Shape recovery can be observed within a few seconds with carbon black content of 4 wt%, carbon fiber content of 0.5 wt%, and voltage of 60 V. Shape recovery time decreased with the increase content of carbon fiber and voltage.

Synthesis, characterisation and enhanced properties of polyimide/mica hybrid films

ABSTRACT Polyimide/mica (PI/mica) hybrid films were prepared from pyromellitic dianhydride/4,4-bis(3-aminophenoxy)biphenyl (PMDA/4,3-BAPOBP) and mica in a solution of N,N-dimethylacetamide. The structure–property relationships of the composites were studied by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, ultraviolet–visible spectroscopy and differential scanning calorimetry. FTIR indicated successful preparation of PI/mica hybrid films. XRD and SEM results indicated that the mica was well dispersed in the PI matrix. The dependence of morphology, glass transition temperatures (Tg), dielectric properties and mechanical properties at room temperature of the hybrid films on the content of mica was discussed. It was observed that Tg, the breakdown strength and tensile strength of the hybrid films, could be simultaneously increased when the mica content was lower than 8 wt-%. Meanwhile, the dielectric constant and dielectric loss of PI/mica hybrid films increased with the increase in the mica content.

Mechanical and dielectric properties of polyimide/silica nanocomposite films

Polyimide/silica (PI/silica) nanocomposite films were successfully prepared via in situ dispersive polymerisation and thermal imidisation. In order to obtain homogeneous nanoscale dispersibility and good compatibility with the PI matrix, hydrophobic aerosil was selected as the nanosilica precursor. 4,4-Bis(3-aminophenoxy)biphenyl (4,3-BAPOBP) was used as diamine to improve the processability of PI. The PI/silica nanocomposite films were characterised using Fourier transform infrared spectroscopy, scanning electron microscopy and differential scanning calorimetry. The mechanical and dielectric properties of the films were also measured. The results demonstrate that the tensile strength and breakdown strength of films can be markedly improved by the addition of appropriate amounts of silica to the PI matrix. At a silica content of 4.0 wt-%, the tensile strength and the breakdown strength of the films increased by 21 and 13%, respectively, compared with the neat PI. Thus, it is feasible to use nanosilica to improve the properties of PI.

Effect of alumina on the structure and properties of polyimide matrix films

To improve the properties of polyimide (PI), different mass fractions of alumina (Al2O3) nanoparticles, unmodified or modified by KH550, were incorporated into PI matrix to form PI/Al2O3 hybrid films by in situ polymerisation. The effects of Al2O3 additives on the structure, dielectric and mechanical properties of the films were studied. Fourier transform infrared spectroscopy confirmed the successful preparation of PI/Al2O3 hybrid films, and the microstructures of the samples showed a more uniform dispersion of the modified Al2O3 nanoparticles than the unmodified ones in the matrix. The dielectric constant of the films increased with increasing filler content, and the maximum electrical breakdown strength of 311 MV m−1 was obtained with a filler content of 8.0 wt-% modified Al2O3 in the matrix. Both unmodified and modified Al2O3-reinforced PI hybrids demonstrated improved mechanical properties compared with the PI matrix. Moreover, the properties of films with Al2O3 modified by KH550 were better.