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All issues / Volume 10 (2016) / Issue 8 (August)

“Waking sleeping beauty”: Regeneration of vulcanized rubber by triggering dynamicity of the inherent sulfur network
M. Q. Zhang
Vol. 10., No.8., Pages 627-627, 2016
DOI: 10.3144/expresspolymlett.2016.57
This is an editorial article. It has no abstract.
Semiconducting, biodegradable and bioactive fibers for drug delivery
M. M. Perez-Madrigal, E. Llorens, L. J. del Valle, J. Puiggali, E. Armelin, C. Aleman
Vol. 10., No.8., Pages 628-646, 2016
DOI: 10.3144/expresspolymlett.2016.58
In this work we present the drug release properties and morphological studies of fibers formed by mixing different ratios of poly(lactic acid) (PLA) and poly(3-thiophene methyl acetate) (P3TMA) loaded with four drugs (ciprofloxacin, chlorhexidine dihydrochloride, triclosan and ibuprofen sodium salt). Thus, the main aim of this study is to prove that the excellent cellular response of PLA-P3TMA biocompatible scaffolds can be successfully combined with essential applications as drug carrier and delivery systems. Atomic force microscopic (AFM) and scanning electron microscopic (SEM) micrographs of PLA-P3TMA fibers indicate that the presence of the conducting polymer inside the PLA matrix affects the surface morphology, resulting in a significant increment of the bulk conductivity with respect to PLA fibers. Electrospun hybrid fibers of PLA and P3TMA successfully load both hydrophilic and hydrophobic drugs, the release profiles depending on the release environment (i.e. the release rate increases with the hydrophobicity of the medium). Finally, our results prove that the antibacterial activity of the drugs is not affected by their interactions with the PLA-P3TMA matrix.
Influence of reprocessing on fibre length distribution, tensile strength and impact strength of injection moulded cellulose fibre-reinforced polylactide (PLA) composites
N. Graupner, K. Albrecht, G. Ziegmann, H. Enzler, J. Muessig
Vol. 10., No.8., Pages 647-663, 2016
DOI: 10.3144/expresspolymlett.2016.59
The present study focuses on the reprocessing behaviour of recycled injection moulded polylactide (PLA) composites. The composites are reinforced with regenerated cellulose fibres (lyocell) of variable fineness and a fibre mass content of 30%. They were reprocessed up to three times. The influence of reprocessing on the fibre length distribution and the resulting composite mechanical properties (tensile and impact strength) was analysed. While the first reprocessing cycle does not affect the mechanical characteristics of the neat PLA matrix, the strength of the composites decreases significantly due to a decreasing fibre aspect ratio. It was shown that fibres having a larger cross-sectional area display a lower aspect ratio than finer fibres, after reprocessing. This phenomenon leads to a larger decrease in tensile strength of composites reinforced with coarser fibres when compared to composites reinforced with finer fibres. A comparison of virgin composites and threefold reprocessed composites with a similar fibre length distribution resulted in a significantly higher tensile strength compared to the virgin sample. This result leads to the conclusion that not only the fibre length is drastically reduced by reprocessing but also that the fibres and the matrix were damaged.
Evaluating a simple blending approach to prepare magnetic and stimuli-responsive composite hydrogel particles for application in biomedical field
H. Ahmad, M. S. Sultana, M. A. Alam, M. M. Rahman, K. Tauer, M. A. Gafur, M. K. Sharafat
Vol. 10., No.8., Pages 664-678, 2016
DOI: 10.3144/expresspolymlett.2016.60
The inclusion of super paramagnetic iron oxide (Fe3O4) nanoparticles in stimuli-responsive hydrogel is expected to enhance the application potential for cellular therapy in cell labeling, separation and purification, protein immobilization, contrasting enhancement in magnetic resonance imaging (MRI), localized therapeutic hyperthermia, biosensors etc. in biomedical field. In this investigation two different magnetic and stimuli-responsive composite hydrogel particles with variable surface property were prepared by simply blending Fe3O4/SiO2 nanocomposite particles with stimuli-responsive hydrogel particles. Of the hydrogel particles prepared by free-radical precipitation polymerization poly(styrene-N-isopropylacrylamide-methyl methacrylate-polyethylene glycol methacrylate) or P(S-NIPAM-MMA-PEGMA) was temperature-sensitive and poly(S-NIPAM-methacrylic acid-PEGMA) or P(S-NIPAM-MAA-PEGMA) was both temperature- and pH-responsive. The morphological structure, size distributions and volume phase transitions of magnetic and stimuli-responsive composite hydrogel particles were analyzed. Temperature-responsive absorptions of biomolecules were observed on both magnetic and stimuli-responsive Fe3O4/SiO2/P(S-NIPAM-MMA-PEGMA) and Fe3O4/SiO2/P(S-NIPAM-MAA-PEGMA) composite hydrogel particles and separation of particles from the dispersion media could be achieved by applying magnetic field without time consuming centrifugation or decantation method.
Synergistically improved thermal conductivity of polyamide-6 with low melting temperature metal and graphite
Y. C. Jia, H. He, P. Yu, J. Chen, X. L. Lai
Vol. 10., No.8., Pages 679-692, 2016
DOI: 10.3144/expresspolymlett.2016.61
Low melting temperature metal (LMTM)-tin (Sn) was introduced into polyamide-6 (PA6) and PA6/graphite composites respectively to improve the thermal conductivity of PA6 by melt processing (extruding and injection molding). After introducing Sn, the thermal conductivity of PA6/Sn was nearly constant because of the serious agglomeration of Sn. However, when 20 wt% (5.4 vol%) of Sn was added into PA6 containing 50 wt% (33.3 vol%) of graphite, the thermal conductivity of the composite was dramatically increased to 5.364 versus 1.852 W·(m·K)–1 for the PA6/graphite composite, which suggests that the incorporation of graphite and Sn have a significant synergistic effect on the thermal conductivity improvement of PA6. What is more, the electrical conductivity of the composite increased nearly 8 orders of magnitudes after introducing both graphite and Sn. Characterization of microstructure and energy dispersive spectrum analysis (EDS) indicates that the dispersion of Sn in PA6/graphite/Sn was much more uniform than that of PA6/Sn composite. According to Differential Scanning Calorimetry measurement and EDS, the uniform dispersion of Sn in PA6/graphite/Sn and the high thermal conductivity of PA6/graphite/Sn are speculated to be related with the electron transfer between graphite and Sn, which makes Sn distribute evenly around the graphite layers.
Synthesis of polyisobutylene-polycaprolactone block copolymers using enzyme catalysis
M. Castano, A. Alvarez, M. L. Becker, J. E. Puskas
Vol. 10., No.8., Pages 693-700, 2016
DOI: 10.3144/expresspolymlett.2016.62
The synthesis of poly(isobutylene-b-ε-caprolactone) diblock and poly(ε-caprolactone-b-isobutylene-b-ε-caprolactone) triblock copolymers was accomplished using a combination of living carbocationic polymerization of isobutylene (IB) with the ring-opening polymerization (ROP) of ε-caprolactone (ε-CL). OH-PIB-allyl was prepared by living carbocationic polymerization of IB initiated with 1,2-propylene oxide/TiCl4 followed by termination with allyltrimethylsilane. Hydroxyl telechelic HO-PIB-OH was obtained by living IB polymerization initiated by 2,4,4,6-tetramethyl-heptane-2,6-diol/TiCl4, termination with allyltrimethylsilane and subsequent thiol-ene click reaction with mercaptoethanol. The structure of the hydroxyl PIBs was confirmed by 1H NMR (proton Nuclear Magnetic Resonance spectroscopy). OH-PIB-allyl and HO-PIB-OH were then successfully used as macroinitiators for the polymerization of ε-CL catalyzed by Candida antarctica Lipase B (CALB), yielding poly(ε-caprolactone-b-isobutylene) diblock and poly(ε-caprolactone-b-isobutylene-b-ε-caprolactone) triblock copolymers, respectively. Differential Scanning Calorimetry (DSC), Transition Electron Microscopy (TEM) and Atomic Force Microscopy (AFM) demonstrated that the amorphous PIB and the semicrystalline PCL block segments phase separated, creating nanostructured phase morphology.
Molecular orientation behavior of isotactic polypropylene under uniaxial stretching by rheo-Raman spectroscopy
T. Kida, Y. Hiejima, K.-H. Nitta
Vol. 10., No.8., Pages 701-709, 2016
DOI: 10.3144/expresspolymlett.2016.63
The molecular orientation behavior of isotactic polypropylene (iPP) is investigated by using in situ Raman spectroscopy under tensile tests. A versatile method of the tilt-angle correction for the orientation parameters is newly developed, where the molecular orientation in highly oriented specimens is assumed to be entropically favorable. The real-time changes of orientation parameters and orientation distribution functions are determined for the molecular chain axis of iPP during uniaxial stretching. The molecular orientation remains random in the elastic region, and increases after the first yield point. In the yielding region, a broad distribution of orientation toward an intermediate angle of 30–70° from the stretching direction is observed. This is interpreted as reorientation of the crystalline chains being hindered by rigid, bulky lamellar cluster units. After the yielding region, orientation toward the stretching direction proceeds rapidly, approaching highly oriented states.
Thermal sensitivity of carbon nanotube and graphene oxide containing responsive hydrogels
E. Manek, B. Berke, N. Miklosi, M. Sajban, A. Doman, T. Fukuda, O. Czakkel, K. Laszlo
Vol. 10., No.8., Pages 710-720, 2016
DOI: 10.3144/expresspolymlett.2016.64
Comparative investigations are reported on poly(N-isopropylacrylamide) (PNIPA) gels of various carbon nanotube (CNT) and graphene oxide (GO) contents synthesized under identical conditions. The kind and concentration of the incorporated carbon nanoparticles (CNPs) influence the swelling and stress-strain behaviour of the composites. Practically independently of the filler content, incorporation of CNPs appreciably improves the fracture stress properties of the gels. The time constant and the swelling ratio of the shrinkage following an abrupt increase in temperature of the swelling medium from 20 to 50 °C can be adjusted by selecting both the type and the amount of nanoparticle loading. This offers a means of accurately controlling the deswelling kinetics of drug release with PNIPA systems, and could be employed in sensor applications where fast and excessive shrinkage are a significant drawback. Both CNTs and GO enhance the infrared sensitivity of the PNIPA gel, thus opening a route for the design of novel drug transport and actuator systems. It is proposed that the influence of the CNPs depends more on their surface reactivity during the gel synthesis rather than on their morphology. One of the important findings of this study is the existence of a thermally conducting network in the GO filled gels.
Published by:

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