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All issues / Volume 7 (2013) / Issue 10 (October)

Cell-instructive hydrogels to assemble in biofluids
C. Werner
Vol. 7., No.10., Pages 805-805, 2013
DOI: 10.3144/expresspolymlett.2013.77
This is an editorial article. It has no abstract.
Surface and thermomechanical characterization of polyurethane networks based on poly(dimethylsiloxane) and hyperbranched polyester
M. V. Pergal, J. V. Dzunuzovic, R. Poreba, D. Micic, P. Stefanov, L. Pezo, M. Spirkova
Vol. 7., No.10., Pages 806-820, 2013
DOI: 10.3144/expresspolymlett.2013.78
Two series of polyurethane (PU) networks based on Boltorn® hyperbranched polyester (HBP) and hydroxyethoxy propyl terminated poly(dimethylsiloxane) (EO-PDMS) or hydroxy propyl terminated poly(dimethylsiloxane) (HPPDMS), were synthesized. The effect of the type of soft PDMS segment on the properties of PUs was investigated by Fourier transform infrared spectroscopy (FTIR), contact angle measurements, surface free energy determination, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), dynamic mechanical thermal analysis (DMTA) and differential scanning calorimetry (DSC). The surface characterization of PUs showed existence of slightly amphiphilic character and it revealed that PUs based on HP-PDMS have lower surface free energy, more hydrophobic surface and better waterproof performances than PUs based on EO-PDMS. PUs based on HPPDMS had higher crosslinking density than PUs based on EO-PDMS. DSC and DMTA results revealed that these newlysynthesized PUs exhibit the glass transition temperatures of the soft and hard segments. DMTA, SEM and AFM results confirmed existence of microphase separated morphology. The results obtained in this work indicate that PU networks based on HBP and PDMS have improved surface and thermomechanical properties.
Crystallization kinetics and morphology of melt spun poly(ethylene terephthalate) nanocomposite fibers
R. R. Hegde, G. S. Bhat, B. Deshpande
Vol. 7., No.10., Pages 821-831, 2013
DOI: 10.3144/expresspolymlett.2013.79
Natural nanoclay closite Na+ incorporated melt spun poly(ethylene terephthalate) (PET) fibers were investigated for crystallization kinetics and morphology. Nature of clay dispersion and nanocomposite morphology were assessed using wide angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM). Fiber mechanical properties were measured using single fiber tensile test. Combination of scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) was used to investigate the fiber failure mode. Among nanocomposite PET fibers, sample with 1% clay performed better. WAXD and TEM micrographs of the fibers revealed intercalated and delaminated morphology. Size of agglomerate increased with percentage of add-on. SEM surface images showed significant variation in fiber diameter, voids and imperfections. Cross-sections of fractured surfaces revealed the presence of clay agglomerates at failure spots. Nanoclay reinforcement did not incur mechanical property benefits due to increase in voids and agglomerates in fiber section, especially at loading levels higher than one percent.
Metal adsorption behavior of 2,4-dinitrophenyl hydrazine modified polyacrylonitrile nanofibers
S. Jitjaicham, P. Kampalanonwat, P. Supaphol
Vol. 7., No.10., Pages 832-841, 2013
DOI: 10.3144/expresspolymlett.2013.80
Electrospun polyacrylonitrile nanofiber mats (es-PAN nanofiber mats) were surface modified by 2,4-dinitrophenyl-hydrazine (2,4-DNPH) to yield the metal ion adsorption material (es-PAN-DNPH nanofiber mats) and were investigated their adsorption behaviors. Functional modification of the es-PAN nanofiber mats and conventional polyacrylonitrile fibers (c-PAN fibers) were prepared by using 4% (w/v) of 2,4-DNPH in 1,2-ethandiol at 110°C for 6 h to obtained c-PAN-DNPH fibers. The average diameter of the es-PAN-DNPH nanofiber mats was 0.25 µm, which was comparatively smaller than the es-PAN precursor. Their functional groups were confirmed by Fourier transform infrared spectroscopy (FT-IR) and their adsorption behaviors to trace Ag(I), Bi(III), Ga(III), and In(III) from aqueous solutions and were investigated by the induced couple plasma technique. The FT-IR spectra showed the existence of NN=C–NHNH–, O=C–NHNH–, and –NO2 functional groups for metal complexes. The adsorption capacities of the obtained es-PAN-DNPH were 7.14 to 36.36% higher than those of c-PAN-DNPH fibers. All adsorption plots onto es-PAN-DNPH nanofiber mats and c-PANDNPH fibers followed the Langmuir isotherm and indicated monolayer adsorption characteristics.
Synthesis and characterization of naphthalene diimide polymers based on donor-acceptor system for polymer solar cells
Q. Xu, J. Wang, S. Chen, W. Li, H. Wang
Vol. 7., No.10., Pages 842-851, 2013
DOI: 10.3144/expresspolymlett.2013.81
Three donor-acceptor (D–A) naphthalene diimide copolymers, poly{thieno[3,2-b]thiophene-diyl-alt-N,N'-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)}(P1), poly{4,8-dioctyloxybenzo[1,2-b;3,4-b']dithiophene-diyl-alt-N,N!-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)}(P2), and poly{4,8-bis(2-ethylhexyloxy)benzo[1,2-b:4,5-b']dithiophene-diyl-alt-N,N'-bis(2-octyldodecyl) -naphthalene-1,4,5,8-bis(dicarboximide)}(P3), were synthesized by Stille coupling reaction. All copolymers showed good solubility in common organic solvents with broad absorption region and narrow optical band gap. The electrochemical properties of the polymers can be adjusted by changing the donor segment. P1 showed n-type characteristic while P2 and P3 showed p-type characteristic. All-polymer solar cells using P3HT as the donor and P1 as the acceptor were fabricated and the highest power conversion efficiencies (PCEs) of 0.068% were obtained under the preliminary condition. Moreover, p-type naphthalene diimide copolymers (P2 and P3) based on D–A system were used as donors to fabricate bulk heterojunction polymer solar cells (BHJ, PSCs) for the first time, and the maximum power conversion efficiencies PCEs were about 0.021 and 0.017%, respectively.
Development of bio-based thermoplastic polyurethanes formulations using corn-derived chain extender for reactive rotational molding
B. J. Rashmi, D. Rusu, K. Prashantha, M-F. Lacrampe, P. Krawczak
Vol. 7., No.10., Pages 852-862, 2013
DOI: 10.3144/expresspolymlett.2013.82
Partly bio-based segmented thermoplastic polyurethane (TPU) formulations were developed to fulfill the requirements of the reactive rotational molding process. They were obtained by one-shot bulk polymerization between an aliphatic diisocyanate (1,6-hexamethylene diisocyanate), a polyether polyol as macrodiol (polyethylene glycol) and a biobased corn-derived 1,3-propanediol as chain extender (CE), in presence of a catalyst, at an initial temperature of 45°C. Equivalent TPU formulations with classical petroleum-based 1,3-propanediol were also prepared for a purpose of comparison. TPU with different soft to hard segment (SS/HS) ratios were synthesized by varying the macrodiol and CE concentrations in the formulations. For each formulation, the evolution of the reaction temperature as a function of time was monitored and the kinetics of polymerization was studied by Fourier Transform infrared spectroscopy in attenuated total reflection mode (FTIR-ATR). The morphology, thermal properties, solubility in different solvents and tensile properties of the final products were analyzed. All synthesized polyurethanes are 100% linear polymers and the extent of microphase separation, as well as the thermal and mechanical properties highly depends on the HS content, and glass transition temperature and Young modulus can be tuned by adjustment of the SS/HS ratio. All results indicate that petrochemical CE can be replaced by its recently available corn-derived homologue, without sacrificing any use properties of the final polyurethanes.
Tensile properties of in-situ precipitated polydimethylsiloxane networks
Y-L. Yue, C. Zhang, H. Zhang, D-H. Zhang, X. Chen, Y-F. Chen, Z. Zhang
Vol. 7., No.10., Pages 863-872, 2013
DOI: 10.3144/expresspolymlett.2013.83
Tensile propertiesof polydimethylsiloxane (PDMS) networks filled with in-situ precipitated silica were investigated. Experimental results showed that increasing the swelling time of cured rubber sheets in tetraethoxysilane (TEOS) solution or elevating the humidity and temperature of precipitation reaction atmosphere can render to a positive reinforcing effect. Moreover the in-situ precipitation method can be used to further enhance the tensile properties of fumed silica filled PDMS networks. The reinforcement introduced by the in-situ precipitated silica gel particles can probably be attributed to the adsorption of polymer chains onto silica surface, the pinning effect of polymer chains within gel particles, and the fillerfiller gel structure among gel particles.
Processing – morphology – property relationships of polyamide 6/polyethylene blend–clay nanocomposites
R. Scaffaro, L. Botta, M. C. Mistretta, F. P. La Mantia
Vol. 7., No.10., Pages 873-884, 2013
DOI: 10.3144/expresspolymlett.2013.84
In this work, we studied the effect of the method of preparation and of reprocessing on the morphology and, consequently, on the physical properties of polyamide 6 (PA6)/ high density polyethylene (HDPE)-clay nanocomposite blends in the presence of different compatibilizers. In particular, the nanocomposites were obtained by melt mixing using a corotating twin screw extruder (E1). The blends thus obtained were re-extruded (E2) under the same operating conditions. Moreover, blends with the same final composition were produced using a masterbatch of the compatibilizer with the clay prepared in a separated stage in a batch mixer (MB). All the materials were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffractometry (XRD) analyses. In addition, the rheological behaviour and the, tensile and impact, properties were evaluated. The XRD and TEM analysis showed that re-extrusion slightly improves the morphology of the nanocomposites. A further improvement of the morphology, in terms of lower clay dimension and better dispersion, was observed in the MB blends. The results of the mechanical tests showed that reprocessing (E2) induced an increase of all the properties for all the three systems. A further general increase of the mechanical properties was showed by the MB blends.
Published by:

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