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All issues / Volume 1 (2007) / Issue 5 (May)

Emerging nanostructured polymeric materials
J. Seppala
Vol. 1., No.5., Pages 252-252, 2007
DOI: 10.3144/expresspolymlett.2007.38
The present status and key problems of carbon nanotube based polymer composites
J-H. Du, J. Bai, H-M. Cheng
Vol. 1., No.5., Pages 253-273, 2007
DOI: 10.3144/expresspolymlett.2007.39
The state-of-art and key problems of carbon nanotube (CNT) based polymer composites (CNT/polymer composites) including CNT/polymer structural composites and CNT/polymer functional composites are reviewed. Based on the results reported up to now, CNTs can be an effective reinforcement for polymer matrices, and the tensile strength and elastic modulus of CNT/polymer composites can reach as high as 3600 MPa and 80 GPa, respectively. CNT/polymer composites are also promising functional composite materials with improved electrical and thermal conductivity, etc. Due to their multi-functional properties, CNT/polymer composites are expected to be used as low weight structural materials, optical devices, thermal interface materials, electric components, electromagnetic absorption materials, etc. However, the full potential of CNT/polymer composites still remains to be realized. A few key problems, such as how to prepare structure-controllable CNTs with high purity and consistently dependable high performance, how to break up entangled or bundled CNTs and then uniformly disperse and align them within a polymer matrix, how to improve the load transfer from matrix to CNT reinforcement, etc, still exist and need to be solved in order to realize the wide applications of these advanced composites.
Synthesis and ring-opening metathesis polymerization (ROMP) of new N-fluoro-phenylnorbornene dicarboximides by 2nd generation ruthenium alkylidene catalysts
J. Vargas, A. A. Santiago, R. Gavino, A. M. Cerda, M. A. Tlenkopatchev
Vol. 1., No.5., Pages 274-282, 2007
DOI: 10.3144/expresspolymlett.2007.40
The synthesis of new N-3,5-bis(trifluoromethyl)phenyl-endo-norbornene-5,6-dicarboximide (TFMPhNDI, 2a), N-4-fluorophenyl-endo-norbornene-5,6-dicarboximide (FPhNDI, 2b) and N-2,2,6,6-tetramethylpiperidyl-endo-norbornene-5,6-dicarboximide (TMPNDI, 2c) monomers was carried out. Polynorbornene dicarboximides were obtained via ring opening metathesis polymerization (ROMP) using a second generation ruthenium alkylidene catalyst (1,3-dimesityl-4,5-dihydroimidazol-2-ylidene) (PCy3Cl2Ru=CHPh) (I). Poly-TMPNDI which bears a piperidyl moiety showed the highest Tg and Td compared to the polymers bearing fluoro-aryl moieties. Thermal stability of Poly-TFMPhNDI (3a) was enhanced after hydrogenation with Wilkinson´s catalyst.
Effects of dynamical cure and compatibilization on the morphology and properties of the PP/epoxy blends
X. L. Jiang, K. Sun, Y. X. Zhang
Vol. 1., No.5., Pages 283-291, 2007
DOI: 10.3144/expresspolymlett.2007.41
In this paper, effects of dynamical cure and compatibilization on the morphology and properties of the PP/epoxy blends were studied. The addition of maleic anhydride-grafted polypropylene (MAH-g-PP) and dynamical cure of epoxy by dicyanamide give rise to decrease the average diameter of epoxy particles in the PP/epoxy blends. The epoxy particles in the PP/epoxy blends can act as effective nucleating agents, accelerating the crystallization of PP component. The dynamical cure and compatibilization increase the kinetic constant K(T) of PP crystallization in the PP/epoxy blends. Dynamical cure of the epoxy resin leads to an improvement in the modulus and strength of the PP/epoxy blends, and the addition of MAH-g-PP results in an increase in the impact strength. Dynamic mechanical thermal analysis (DMTA) results indicate that the addition of MAH-g-PP improves the compatibility between PP and epoxy resin, and the storage modulus of the PP/epoxy blends increase by dynamical cure. Thermogravimetric analysis (TGA) results show dynamical cure of epoxy and addition of MAH-g-PP improved the thermal stability of the PP/epoxy blends. Wide-angle X-ray diffraction (WAXD) analysis shows that the PP/epoxy blends have the same crystalline structure as pure PP, indicating dynamical cure and compatibilization do not disturb the crystalline structure of the PP/epoxy blends.
Preparation of porous carbon particle with shell/core structure
Y. B. Jiang, L. H. Wei, Y. Z. Yu, T. Zhao
Vol. 1., No.5., Pages 292-298, 2007
DOI: 10.3144/expresspolymlett.2007.42
Porous carbon particles with a shell/core structure have been prepared successfully by controlled precipitation of the polymer from droplets of oil-in-water emulsion, followed by curing and carbonization. The droplets of the oil phase are composed of phenolic resin (PFR), a good solvent (ethyl acetate) and porogen (Poly(methyl methacrylate), PMMA). The microstructure was characterized in detail by scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption, and thermo gravimetric analysis (TGA). The obtained carbon particles have a capsular structure with a microporous carbon shell and a mesoporous carbon core. The BET surface area and porous volume are calculated to be 499 m2g-1 and 0.56 cm3g-1, respectively. The effects of the amount of porogen (PMMA), co-solvent (acetone) and surfactant on the resultant structure were studied in detail.
Surface modification and micromechanical properties of jute fiber mat reinforced polypropylene composites
X. Y. Liu, G. C. Dai
Vol. 1., No.5., Pages 299-307, 2007
DOI: 10.3144/expresspolymlett.2007.43
A new treating method using sodium hydroxide (NaOH) and Maleic anhydride-grafted polypropylene (MPP) emulsion was introduced to treat jute fiber mat in order to enhance the performance of jute/polypropylene (PP) composite prepared by film stacking method. The surface modifications of jute fiber mat have been found to be very effective in improving the fiber-matrix adhesion. It was shown that treatments changed not only the surface topography but also the distribution of diameter and strength for the jute fibers, which was analyzed by using a two-parameter Weibull distribution model. Consequently, the interfacial shear strength, flexural and tensile strength of the composites all increased, but the impact strength decreased slightly. These results have demonstrated a new approach to use natural materials to enhance the mechanical performances of composites.
Synthesis and characterization of electrical conducting chitosan-graft-polyaniline
A. Tiwari, V. Singh
Vol. 1., No.5., Pages 308-317, 2007
DOI: 10.3144/expresspolymlett.2007.44
A mucopolysaccharide, chitosan was grafted with polyaniline through oxidative-radical copolymerization using ammonium persulfate in acidic medium. The grafting conditions were extensively studied by varying grafting parameters. All the findings have been discussed and proposed a plausible mechanism for the graft copolymerization. The representative chitosan-graft-polyaniline (Ch-g-PANI) was characterized using UV-vis, FTIR, TGA, X-ray diffraction and Scanning electron microscopy taking chitosan as reference. Ch-g-PANI exhibited electrical conductivity, which increases with the extent of grafting onto chitosan backbone. Its electrical conductivity is further influenced by pH and showed pH switching electrical conduction behavior when exposed to NN3/HCl vapors. The application of conducting biomaterial such as Ch-g-PANI in the electronic devices especially for the fabrication of sensor devices would be attractive not only in terms of product cost and environmental safety but also from a materials science point of view.
The effect of fiber oxidation on the friction and wear behaviors of short-cut carbon fiber/polyimide composites
X. R. Zhang, X. Q. Pei, Q. H. Wang
Vol. 1., No.5., Pages 318-325, 2007
DOI: 10.3144/expresspolymlett.2007.45
Pitch-based short-cut carbon fibers were treated by HNO3 oxidation, thereafter the treated (CFN) and untreated carbon fibers (CF) were incorporated into polyimide (PI) matrix to form composites. The carbon fibers before and after treatment were examined by Fourier Transform Infrared Spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM). The friction and wear behaviors of PI composites sliding against GCr15 steel rings were evaluated on an M-2000 model ring-on-block test rig, which revealed that small incorporation of carbon fibers can decrease the friction coefficient and improve the wear resistance of PI composites, and that the reinforcement effect of treated carbon fibers was better than that of the untreated ones. It was found that the optimum content of carbon fibers is 15 wt% when a thin and continuous transfer film was formed on the counterpart surface during the friction process. With further increasing content of carbon fibers, the friction coefficient increased and the wear resistance reduced owing to the drop out of carbon fibers from PI matrix. Besides, the friction coefficient of the PI composites decreased and the wear resistance improved with increasing load, while for the pure PI, its wear resistance decreased drastically owing to the micro-melting and mechanical deterioration caused by friction heat under a higher load.
Improvement of thermal properties and flame retardancy of epoxy-amine thermosets by introducing bisphenol containing azomethine moiety
X. H. Zhang, L. H. Huang, S. Chen, G. R. Qi
Vol. 1., No.5., Pages 326-332, 2007
DOI: 10.3144/expresspolymlett.2007.46
A novel bisphenol 1, 4'-bis{4-[(4-hydroxy) phenyliminomethylidene] phenoxy} benzene (BHPB), which contains azomethine moiety and flexible aromatic ether linkage, was synthesized and introduced into the curing system composed of diglycidyl ether of bisphenol A (DGEBA) and diamine. The curing behavior of DGEBA/diamine changed dramatically due to the introduction of BHPB. The resultant epoxy thermosets containing BHPB had high Tgs (127-160 °C), high Td, 5% (>=330°C) and high integral procedure decomposition temperature (IPDT) values (662-1230°C) and good flame retardancy for their high Limited Oxygen Index (LOI) values (above 29.5).
Published by:

Budapest University of Technology and Economics,
Faculty of Mechanical Engineering, Department of Polymer Engineering