Polymers2013, 5(4), 1380-1391; doi:10.3390/polym5041380 - published online 5 December 2013 Show/Hide Abstract
Abstract: Pure polyamide 6 (PA6) and polyamide 6/carbon nanotube (PA6/CNT) composite samples with 0.5 weight percent loading of pristine or functionalized CNTs were made using a solution mixing technique. Modification of nanotube surface as a result of chemical functionalization was confirmed through the presence of lattice defects as examined under high-resolution transmission electron microscope and absorption bands characteristic of carboxylic, sulfonic and amine chemical groups. Microstructural examination of the cryogenically fractured surfaces revealed qualitative information regarding CNT dispersion within PA6 matrix and interfacial strength. X-ray diffraction studies indicated formation of thermodynamically more stable α-phase crystals. Thermogravimetric analysis revealed that CNT incorporation delayed onset of thermal degradation by as much as 70 °C in case of amine-functionalized CNTs, thus increasing thermal stability of the composites. Furthermore, addition of amine-functionalized CNTs caused an increase in crystallization and melting temperatures from the respective values of 177 and 213 °C (for neat PA6) to 211 and 230 °C (for composite), respectively.
Polymers2013, 5(4), 1362-1379; doi:10.3390/polym5041362 - published online 4 December 2013 Show/Hide Abstract
Abstract: Hyperbranched polyimide–silica hybrids (HBPI–silica HBDs) and hyperbranched polyimide–silica composites (HBPI–silica CPTs) were prepared, and their general and gas transport properties were investigated to clarify the effect of silica sources and preparation methods. HBPI–silica HBDs and HBPI–silica CPTs were synthesized by two-step polymerization of A2 + B3 monomer system via polyamic acid as precursor, followed by hybridizing or blending silica sources. Silica components were incorporated by the sol-gel reaction with tetramethoxysilane (TMOS) or the addition of colloidal silica. In HBPI-silica HBDs, the aggregation of silica components is controlled because of the high affinity of HBPI and silica caused by the formation of covalent bonds between HBPI and silica. Consequently, HBPI-silica HBDs had good film formability, transparency, and mechanical properties compared with HBPI-silica CPTs. HBPI-silica HBD and CPT membranes prepared via the sol-gel reaction with TMOS showed specific gas permeabilities and permselectivities for CO2/CH4 separation, that is, both CO2 permeability and CO2/CH4 selectivity increased with increasing silica content. This result suggests that gas transport can occur through a molecular sieving effect of the porous silica network derived from the sol-gel reaction and/or through the narrow interfacial region between the silica networks and the organic matrix.
Polymers2013, 5(4), 1352-1361; doi:10.3390/polym5041352 - published online 3 December 2013 Show/Hide Abstract
Abstract: This paper describes the results of experimental testing of glass fiber reinforced plastic (GFRP) composite beam strengthened reinforced concrete (RC) slabs with two symmetrical openings. Specimens, one-half scale, have been designed and fabricated to reflect the most common RC bathroom slab used in school buildings. The specimen had dimensions of 2000 mm (width) × 150 mm (thickness) × 3000 mm (length) were used with the two openings of 300 mm × 400 mm. The aim of this study is to investigate the most effective strengthening method using GFRP composite beams in slabs with openings for enhancing the load-carrying capacity and stiffness. Test results showed that the strengthened slabs seems to increase the load-carrying capacity by 29%, 21% and 12% over that of the control specimen for diagonal, parallel and surround strengthening respectively. Furthermore, test results showed that the diagonal-strengthened system is one of the most effective methods for strengthening an RC slab with openings in terms of load-carrying capacity, stiffness and crack patterns.
Polymers2013, 5(4), 1339-1351; doi:10.3390/polym5041339 - published online 29 November 2013 Show/Hide Abstract
Abstract: In order to further improve the biocompatibility of xylitol based poly(xylitol sebacate) (PXS) bioelastomer, a novel kind of amino acid based poly(xylitol glutamate sebacate) (PXGS) has been successfully prepared in this work by melt polycondensation of xylitol, N-Boc glutamic acid and sebacic acid. Differential scanning calorimetry (DSC) results indicated the glass-transition temperatures could be decreased by feeding N-Boc glutamic acid. In comparison to PXS, PXGS exhibited comparable tensile strength and much higher elongation at break at the same ratio of acid/xylitol. The introduction of glutamic acid increased the hydrophilicity and in vitro degradation rate of the bioelastomer. It was found that PXGS exhibited excellent properties, such as tensile properties, biodegradability and hydrophilicity, which could be easily tuned by altering the feeding monomer ratios. The amino groups in the PXGS polyester side chains are readily functionalized, thus the biomelastomers can be considered as potential biomaterials for biomedical application.
Polymers2013, 5(4), 1325-1338; doi:10.3390/polym5041325 - published online 19 November 2013 Show/Hide Abstract
Abstract: Transparent, conductive films were prepared by compositing poly(3-hexylthiophene) (P3HT) nanofibers with poly(methyl methacrylate) (PMMA). The transparency, conductivity, atmospheric stability, and mechanical strength of the resulting nanofiber composite films when doped with AuCl3 were evaluated and compared with those of P3HT nanofiber mats. The conductivity of the nanofiber composite films was 4.1 S∙cm−1, which is about seven times lessthan that which was previously reported for a nanofiber mat with the same optical transmittance (~80%) reported by Aronggaowa et al. The time dependence of the transmittance, however, showed that the doping state of the nanofiber composite films in air was more stable than that of the nanofiber mats. The fracture stress of the nanofiber composite film was determined to be 12.3 MPa at 3.8% strain.
Polymers2013, 5(4), 1272-1324; doi:10.3390/polym5041272 - published online 18 November 2013 Show/Hide Abstract
Abstract: The morphological and structural features of the conjugated polymer films play an important role in the charge transport and the final performance of organic optoelectronics devices [such as organic thin-film transistor (OTFT) and organic photovoltaic cell (OPV), etc.] in terms of crystallinity, packing of polymer chains and connection between crystal domains. This review will discuss how the conjugated polymer solidify into, for instance, thin-film structures, and how to control the molecular arrangement of such functional polymer architectures by controlling the polymer chain rigidity, polymer solution aggregation, suitable processing procedures, etc. These basic elements in intrinsic properties and processing strategy described here would be helpful to understand the correlation between morphology and charge transport properties and guide the preparation of efficient functional conjugated polymer films correspondingly.