Advanced Materials Research Vols. 47-50

Abstract: In this paper, effort has been undertaken to study the fracture behavior of thermoplastic/elastomer (PP/SBS) dynamically vulcanized blends by analyzing the EWF test results. PP/SBS blends were prepared with concentrations of SBS of 15, 30 and 40 wt%. Deeply double edged notched tension (DDENT) specimens were cut from injection molded plaques for fracture testing. It should be noted that the incorporation of SBS to PP seems to enhance fracture toughness, thus the specific essential work (we) increases with elastomer content. The elastomer particles contribute to the energy dissipation at the fracture surface and in the outer plastic zone in which various types of deformation might have been at work. Also, it seems that the fracture toughness value levels-off from 30 wt% rubber on. In addition, the incorporation of SBS triggers a considerable plastic deformation, since the non-essential work ( βwp) increases compared to the value of pure PP. Nonetheless, a decrease in βwp is present with increasing amount of rubber. So the EWF method revealed that the dynamic vulcanization method can impair fracture resistance to PP/SBS blends.

Abstract: To provide epoxy based composites with self-healing ability, two-component healing system consisting of urea-formaldehyde walled microcapsules containing epoxy (30~70µm in diameter) and CuBr2(2-MeIm)4 (the complex of CuBr2 and 2-methylimidazole) latent hardener was synthesized. When cracks were initiated or propagated in the composites, the neighbor micro-encapsulated epoxy would be damaged and released. As the latent hardener is soluble in epoxy, it can be well dispersed in epoxy composites during composites manufacturing, and hence activate the released epoxy wherever it is. As a result, repair of the cracked sites is completed through curing of the released epoxy. The present work indicated that the plain weave glass fabric laminates using the above self-healing epoxy as the matrix have been provided with self-healing capability.

Abstract: For purposes of developing a novel self-healing chemistry for polymer composites, melamine-formaldehyde (MF) resin-walled microcapsules containing styrene were prepared by in-situ polymerization in an oil-in-water emulsion. Chemical structure of the microcapsules was identified by Fourier-transform infrared spectroscopy (FTIR) and proton magnetic resonance spectroscopy (1H NMR), respectively. In addition, scanning electron microscope (SEM) and optical microscope (OM) were used to investigate morphology and geometry of the product. The effects of dispersion rate, weight ratio of core to shell and emulsifier concentration were carefully analyzed. It was found that poly(melamine-formaldehyde) (PMF) microcapsules containing styrene were successfully synthesized through the proposed technical route, and their mean diameters fall in the range of 20~71 µm. The rough surface of the microcapsules is composed of agglomerated PMF nanoparticles. Both core content and size of the microcapsule can be adjusted by selecting different processing parameters. The highest loading of styrene in the capsules is about 60% and the emulsifier with lower molecular weight used to result in higher core content. In terms of differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), thermal behavior and storage stability of the capsules were studied. The results indicated that the microcapsules can be handled up to 72 oC.

Abstract: For purposes of developing a novel epoxy with low viscosity and high activity, N,N-diglycidyl-furfurlamine (DGFA) was successfully synthesized through a two-step reaction between 2-furfurylamine and epichlorohydrin involving ring-opening and ring-closure mechanisms. The product structure was verified by FTIR, 1H-NMR, 13C-NMR and elemental analysis, respectively. Its viscosity was found to be 0.02 Pa·s at 25oC. To understand its curing behavior, exothermic habit of the model mixture of DGFA and the curing agent methylhexahydrophthalic anhydride (MHHPA) at stoichiometric ratio of epoxy ring/anhydride of 1:0.8 was inspected with DSC. By changing the heating rates from 2.5 to 15oC/min, activation energy for consolidation of the resin was estimated to be 46.2 kJ/mol, which is much lower than the value involved in curing of diglycidyl ether of bisphenol A catalyzed by anhydride. Besides, thermal decomposition performance of cured version of the newly synthesized epoxy was also examined. The predominant pyrolysis took place at around 330-390oC as a result of chain scission of epoxy. The cured resin possesses comparable mechanical properties as conventional diglycidyl ether of bisphenol A. Its flexural strength and modulus are 111MPa and 3.6GPa, respectively. Evidently, the resultant epoxy is provided with balanced properties for practical applications.

Abstract: A novel flame retardant polymethylsilsesquioxane (PMSQ) was successfully obtained via combination of non-hydrolytic and hydrolytic sol-gel routes. Chemical structure of the resultant PMSQ was determined by nuclear magnetic resonance spectroscopy, Fourier-transform infrared spectrometry and powder X-ray diffraction, respectively. All the measurements demonstrated that the product possessed regular structure with chain-to-chain width of 0.87nm and chain thickness of 0.40nm. Weight average molecular weight of PMSQ was measured to be 3.5×105 using gel permeation chromatography. Numerical simulations of the molecular structure suggested that PMSQ should exhibit cis-isotactic configuration and double helical conformation at undisturbed condition.

Abstract: The acrylic acid and silicone are common dielectric elastomer materials. These actuators have shown excellent activate properties including large strains up to 380% and high energy densities up to 3.4 J/g, high efficiency, high responsive speed , good reliability and durability, etc. When a voltage is applied on the compliant electrodes of the dielectric elastomers, the polymer shrinks along with the electric field and expands in the plain area which erects the orientation of the line. In this paper, we synthesize a novel silicone dielectric elastomer with high dielectric constant, large strain and high force output. Pre-strain and certain driving electric field are applied on the novel silicone film, respectively. The strain responsing to the Maxwell stress is measured. Using the large deformation theory of finite element method to simulate the deformable behavior of materials, the simulation results agree with the experiment. The coupling effect of the mechanics and electric fields applied on the electrode of the dielectric elastomers is inverstigated. The finite element simulation of large deformation theory can be used to describe the dielectric elastomers materials large deformation that induced by the static electric field.

Abstract: Polybenzimidazole (PBI) and vapor grown carbon nanofibers (VGNFs) nanocomposites were developed successfully by using ultrasonic mixing followed by hot compress. The contents of VGNFs used were 0.5wt%, 1wt%, 2wt% and 5wt%. The mechanical properties of neat PBI and PBI/VGNFs nanocomposites were discussed and the results were that the Young’s modulus, tensile strength, storage modulus and hardness were improved after adding VGNFs. Microscopic analysis showed that the dispersion of VGNFs in nanocomposites with a lower amount was considered to be uniform.

Abstract: Based on Laminate plate theory, a formulation, including the effects of shear deformation and rotary inertia on the characterization of plate wave propagation, was derived. The characteristics of plate waves propagating were investigated and the influences of frequency, plate thickness and propagating direction were clearly known. A health monitoring system was built and the plate waves generated by lead break source were received by acoustic emission (AE) sensors. By the wavelet transform [1], the time-frequency domain of AE signal was derived. For a certain frequency, the first peak of the magnitude of wavelet transform indicates the arrival times of plate waves. The locations of lead break source and the delaminations of plate were compared with the predictions of theory.

Abstract: A graded titania film was formed on chemically polished NiTi shape memory alloy (SMA) by a novel deposition-assisted advanced oxidation method in a modified Fenton’s reagent containing titanium tetrachloride and then characterized by SEM and XPS. The effects of the titania film on leaching of harmful Ni ions from the NiTi substrate in simulated body fluids (SBF) is assessed by inductively-coupled plasma mass spectrometry (ICPMS). The results indicate that a thick and dense titania film was successfully fabricated in this in situ advanced oxidation reaction assisted with an additional deposition process by the hydrolysis of titanium tetrachloride on NiTi. The titania film can dramatically reduces Ni leaching from NiTi. XPS depth profiles show that the film possesses a smooth graded interfacial structure that boost mechanical stability.

Abstract: Electro-Fenton process as a modified Fenton’s oxidation method in waster water treatment can provide a stable hydroxyl radical (·OH) source by continuous reaction of electrochemically generated H2O2 with Fe2+ ions for surface oxidation modification of NiTi shape memory alloy (SMA). In this work, effects of electro-Fenton process on blood compatibility and nickel suppression of NiTi SMA were investigated by SEM and XPS, inductively-coupled plasma mass spectrometry (ICPMS), hemolysis analysis and blood platelet adhesion test. It is found that electro-Fenton process is a notably effective way to impede out-diffusion of Ni from NiTi SMA in simulated body fluids during the entire ten week immersion period. It can also improve the hemolysis resistance and thromboresistance of biomedical NiTi SMA. The improvement of blood compatibility and nickel suppression of NiTi SMA can be attributed to the formation of surface titania film with a Ni-free zone near its top surface by electro-Fenton process.