Huifeng Tan

Enhanced toughness and shape memory behaviors of toughed epoxy resin

This paper reports on an approach to enhance the toughness of shape memory epoxy by using polypropylene glycol diglycidyl ether (G) as the toughening agent. The mechanical properties and shape memory behavior of the toughened resin systems with different loading level of G were studied, respectively. Results of the torsional braid analysis (TBA) test indicated that G had good compatibility with the epoxy resin matrix and induced a decrease in the glass transition temperature, Tg, of the toughened systems when compared to that of the neat resin system; and the decrease in Tg scaled with the content of G added in the system. Impact strength tests showed that the impact strength was improved significantly by adding G into the resin system and it increased by a factor of 13.7 for the system with 13 wt.% content of G. In addition, the toughened systems were found to yield during the impact strength test whereas brittle fracture occurred for the neat epoxy resin system; this behavior could be further confirmed by the results of scanning electron microscopy (SEM). In the shape memory behavior tests, strain fixity ratio reached as high as 98.9% for toughened systems with 7, 9, 11, 13, and 15 wt.% of G. Toughened systems also displayed changed shape recovery behavior that was comparable with that of the neat epoxy resin system during shape memory process.

UV-protective treatment for Vectran® fibers with hybrid coatings of TiO2/organic UV absorbers

The high performance of Vectran® fiber makes its application as an envelope material for airship feasible. The ultraviolet (UV) resistance of this fiber, however, is poor, and UV irradiation in the stratospheric environment causes rapid fiber aging. To protect Vectran® fibers from UV irradiation, we prepared TiO2 nanosols via a sol–gel method and added benzotriazole UV-1130, triazine Tinuvin® 477, and hindered amine Tinuvin® 123 to them to form organic/inorganic hybrid coatings. Fiber specimens were subjected to accelerated aging using a xenon arc weatherometer. Mechanical measurements as well as surface morphology and chemical composition analyses were performed to evaluate the UV-protective performance of different coatings. Hybrid coatings performed better than TiO2 coatings in protecting fibers from UV. Among the hybrid coatings obtained, UV-1130 especially reinforced the UV-protective ability of the TiO2 coating because of its strong UV absorbance. Although the performances of Tinuvin® 477 and Tinuvin® 123 were below optimal when combined with TiO2 alone, both hybrids exhibited excellent synergistic effects when used together with UV-1130 and improved the UV-protective ability of the resultant hybrid coatings.

Effect of accelerated xenon lamp aging on the mechanical properties and structure of thermoplastic polyurethane for stratospheric airship envelope

This study aimed to investigate the effect of artificial weathering test on the photoaging behavior of TPU films. Changes in mechanical properties, morphology and chemical structures are studied by tensile test, scanning electron microscopy, atomic force microscopy, Fourier-transformed infrared, and X-ray photoelectron spectroscopy. The results show that the photoaging negatively affects the initial modulus and stress at break values of TPU films. The surface of the specimen that is exposed to irradiation becomes rough, and some visible micro-defects such as blisters and voids can be detected. The morphology of the fracture surfaces illustrates that irradiation reduces the plasticity but increases the brittleness of the TPU films. The chemical structure analyses of the accelerated aged films prove that chemical structural changes in TPU films occur. The irradiation may break the long molecular chains on the surface of the specimens and form the low-molecular weight oxygen-containing groups. The number of chain scissions increases with the increase in exposure time.

Effect of clay modification on the morphological, mechanical, and thermal properties of epoxy/polypropylene/montmorillonite shape memory materials

A series of montmorillonite (DK2) modified shape memory polyurethane-epoxy (UEP) composites had been prepared. The effect of DK2 modification on the morphological, mechanical and thermal properties of epoxy/polypropylene/Montmorillonite nano-composites were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), tensile test, scanning electron microscope (SEM) and dynamic mechanical analysis (DMA). The shape memory performance was investigated by fold-deploy shape memory tests. The XRD and TEM results indicated the formation of exfoliated structure for epoxy/polypropylene nano-composites had been prepared using 2~ 3wt.% DK2. On the other hand, a mixture of intercalated and exfoliated structure was found in 4~5wt.% DK2/ epoxy/polypropylene polymers. Further more, the toughness, tensile strength, enlongation at break had been improved by adding DK2, while glass transition temperature, storage modulus and shape recovery ratio was unaffected. The composite materials possessed excellent shape memory properties, they could fully recover their original shapes within 3 min under the maximum bending angle of 180°, and there were little effect by fold-deploy ten times.

Experimental study of inflatable deployment process of folded membrane tubes

There has been a lot of attention recently on space inflatable deployment structures. One of the challenges is to control the dynamic properties of the structures during the inflation and deployment. Inflatable tubes used to deploy and support space structures are a key component for many space inflatable structures. In this paper, an inflation deployment experimental system in equivalent micro gravity environment is established based on air track which evidently avoid disturbance of contact sensor to the inflation deployment process. The impact of dynamic properties from three different kinds of gas flow, variable geometry size and if there is added mass on deployable end. Dispersion of the experimental data is analyzed. The experimental results indicate that the inflation deployment experimental system in equivalent micro gravity environment is feasible and effective. Results also show that deployment velocities of the folded tube are a function of the tube diameter, gas flow, and the added mass on the deployable end.

Pullout behavior of large-diameter collapsed double-walled carbon nanotubes

The pullout behavior of large-diameter collapsed double-walled carbon nanotubes (DWCNT) was studied by molecular dynamics simulations and compared with those in the circular cross-sectioned state. The pullout force-displacement curves of both are in good agreement with the same mean value of the pullout force during the steady pullout stage. The pullout force was mainly due to the formation of new surfaces; the friction between nested walls was negligible. The effects of different chiral combinations and inter-wall spacings on the pullout behavior for both section situations were investigated. The commensurate (zigzag/zigzag or armchair/ armchair) bi-tube systems have a larger fluctuation in the pullout force. The smaller interspacing implies lower mean pullout force with stronger fluctuations.

Buckling delamination induced microchannel: Flow regulation in microfluidic devices

The buckling delamination induced microchannel is employed to regulate fluid flow as a microvalve which can be utilized in microfluidic devices. This microvalve consists of a soft substrate and a stiff thin film, between which there is a pre-set small imperfection. Two critical strain values, namely, on-off strain and failure strain, have been proposed to determine the working strain interval using analytical predictions. Within this interval, the cross-sectional area of the microchannel can be controlled and predicted by different compressive strains of the film/substrate system. The fluid flow rate within this microchannel can be then estimated by both analytical and numerical simulations and adjusted to satisfy different values by alternating the compressive strain. In addition, a demonstrative experiment has been taken to verify the feasibility of this approach. This flexible microvalve has potential in the application where the use of traditional rigid microvalves is improper in flexible microfluidic...