Volume 17, Issue 1 - Special Issue: Polymers and Composite Materials (PCM 2016) / Guest Editor: Esteban Broitman

To enhance the physical properties of copolymer-polyamide (CO-PA), a sequence of nanocomposites based upon CO-PA and chemically reduced graphene oxide (CRGO) nanoplatelets were prepared by in-situ reduction using hydrazine hydrate. Graphene oxide (GO), prepared by the improved Hummers method, was used to fabricate CRGO nanaoplatelets. Atomic-force microscopy (AFM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) analysis showed that the thickness and the width of GO was about 0.9 nm and 1 μm, respectively. An abundance of oxygen-containing functional groups were introduced onto the GO sheets. XRD and SEM analysis showed that CRGO nanoplatelets were well dispersed in the CO-PA matrix with the appropriate CRGO content. TGA and DSC analysis demonstrated that CRGO nanoplatelets can significantly improve the thermal stability, glass-transition temperature, crystallization temperature of the composites. The mechanical properties of the nanocomposites were improved significantly with the appropriate increment of CRGO nanoplatelets content, though the elongation at break of the composites decreased with the increase of CRGO nanoplatelets content. The electrical conductivity test showed a significant increase in electrical conductivity from an insulator to almost a semiconductor with increasing CRGO nanoplatelets content. And at 1.0 wt% CRGO content, the electrical percolation threshold of the nanocomposites was found.

A series of fluorescent carbazole-containing star polymers with different arms were successfully synthesized using 9-(4-vinylbenzyl)9H-carbazole (VBCz) as monomer and multifunctional bromide as initiators via atom transfer radical polymerization (ATRP). The effect of the poly(9-(4-vinylbenzyl)-9H-carbazole) (PVBCz) star polymer architecture on their optical and electrochemical properties was investigated. All of the PVBCz star polymers absorbed light in the range of 280–360 nm both in solution and as polymer films. Meanwhile, the star polymers exhibited maximum fluorescent emission at 350 nm in solution, while at 406 nm as films. Moreover, the star polymers with different arm numbers showed different photoluminescence quantum efficiency and highest and lowest occupied molecular orbital (HOMO, LOMO, respectively) energy levels. It is proved that the PVBCz star polymers exhibited different photoelectronic properties by varying the molecular architectures.

This study demonstrates that different modification pulse voltages affect the wetting property of the surface of polyamide 6 (PA6) with a certain regularity. Broadly, the hydrophilic property of PA6’s surface increases with increasing pulsed voltage. Based on scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) analysis, this paper discusses the mechanism by which high current pulsed electron beam (HCPEB) etching modification influences the surface wettability of PA6. Within a certain range below 28 kV, this effect is caused by an increase of in surface roughness due to HCPEB bombardment of the surface. Within a certain range above 28 kV, HCPEB changes the surface morphology, resulting in changes to the wetting property. Furthermore, by using various pulsed voltages to modify the PA6 surface, this study investigated the ability of the Wenzel model to explain changes in the water contact angle and wetting property of PA6’s surface.

The waterborne polyurethane (WPU) was synthesized with isophorone diisocyanate (IPDI), polyethyleneglycol-400 (PEG-400), polyethyleneglycol-2000 (PEG-2000), dimethylolpropionic acid (DMPA) and trimethylolpropane (TMP) in this work. And the hydroxyethyl methacrylate (HEMA), butyl acrylate (BA) and methyl methacrylate (MMA) followed to modify the WPU by physical mixing and chemical integration to obtain the polyurethane/polyacrylate (PU/PA) and crosslinked polyurethane-acrylate (LPUA), respectively. Fourier transform infrared (FTIR) spectroscopy confirmed the presence of functional groups of LPUA. Thermogravimetric analysis (TGA) illustrated that the heat resistance of LPUA was better than that of PU/PA and WPU. And the effect of acrylate used to modify WPU on LPUA is also discussed. Lastly, LPUA was combined with Basic Red 1# to prepare fluorescent composite which could be used to dye cotton fabric. Such properties of fluorescent composite such as washing color fastness, heat-resistance were studied.

A new type of medicated polymeric composite consisting of acyclovir (ACY), polyvinylpyrrolidone K60 (PVP) and polyethylene glycol 6000 (PEG) with core-shell structure were prepared by a coaxial electrospinning process. The composites could enhance the dissolution of the poorly water-soluble drug. The shell layers were formed from a spinnable working fluid containing the filament-forming PVP and citric acid while the core parts were prepared from an un-spinnable co-dissolving solution composed of ACY, sodium hydrate and PEG. Scanning electron microscope and transmission electron microscope observations demonstrated that the composites had a homogeneous linear topography with a slippery surface, a diameter of 670±130 nm, and an obvious core-shell structure. X-ray diffraction (XRD) and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy results demonstrated that the drug and citric acid contained in the core and shell parts were in an amorphous status. In vitro dissolution experiments exhibited that ACY was able to be free within 1 min, and the dissolution media were neutral due to acid-basic action within the core-shell structures. The medicated nanocomposites resulted from a combined usage of hydrophilic polymeric excipients PVP and PEG could provide a new solution to the problem associated with the dissolution of poorly water-soluble drugs.

Insulating paper is a traditional insulation material used for transformer insulation. Transformer development is not only limited to small sizes and large capacities, but also limited to insulation life as insulating paper cannot withstand high temperatures. Therefore, recent studies have focused on improving the performance of insulation paper and discovering better insulation materials. In this study, two types of polymeric materials, polycarbonate (PC) and polyester film (PET), were chosen for comparative analysis. In order to test whether these two materials could be used in oil-immersed transformers, the PC and PET were placed in transformer oil for thermal aging at 110°C and 130°C, respectively. The thermal cracking processes and fragmentation mechanisms of the PC, PET, and insulation paper were analyzed using thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), and atomic force microscopy (AFM), as well as their degrees of polymerization and surface morphologies. According to the test results, the initial thermal decomposition temperature of PC and PET are higher than insulation paper and exhibited a better thermal resistance. PC and PET have the potential to substitute insulation paper for large capacity power transformer.

Epoxy polymer with damage indicating ability was very usable for ships and bridges to detect the cracks at an early stage and to prevent corrosion. 2′, 7′-dichlorofluorescein (DCF), as a damage indicator, was used to report the mechanical damage of epoxy-amine polymer by a strong color change from a light yellow to bright red due to the molecular structure transition from the acid molecular form to the base ion form. The effect of water on damage indicator and damaged epoxy-amine polymer film was evaluated by an immersion test and the properties were characterized by ultraviolet-visible spectrophotometry (UV-Vis), scanning electronic microscopy (SEM), energy dispersive X-ray spectrometer (EDS), zeta potential and thermal gravimetric analysis (TGA). The results showed that DCF was an easy, stable and permanent indicator for epoxy-amine polymer and the water only had a slight influence on the indication stability of damaged epoxy polymer.

Thermosensitive PNIPAM-coated Au nanoparticles (AuNPs@P(NIPAM-co-MADMAC)) were synthesized by the radical “grafting through” copolymerization of 4-methacryloyloxy-4′-dimethylaminochalcone (MADMAC), MAEL-capped AuNPs and N-isopropylacrylamide (NIPAM) using azobisisobutyronitrile (AIBN) as the initiator. AuNPs@P(NIPAM-co-MADMAC) were characterized by transmission electron microscopy (TEM), ultraviolet-visible (UV-Vis) spectroscopy, thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), 1 H nuclear magnetic resonance (NMR), and Fourier transform infrared (FTIR) spectroscopy. AuNPs@P(NIPAM-co-MADMAC) exhibited thermo-sensitivity from poly(NIPAM-co-MADMAC) chains and sensitive fluorescence from the MADMAC group. AuNPs@P(NIPAM-co-MADMAC) showed weak fluorescence after the temperature increased from 25°C to 45°C, or after β-cyclodextrin (β-CD) was added. Furthermore, it exhibited strong fluorescence when the solvent was changed to ethanol or chloroform.

The crystallization and orientation of isotactic polypropylene (iPP) molded by rapid heat cycle molding (RHCM) and conventional injection molding (CIM) were studied. Due to the varying cooling rates and shearing, the molded parts exhibited a multilayered structure (skin, shear and core) across the part thickness, reflecting different degrees of crystallization and lamellae orientation of iPP. The morphology evolution of RHCM products was discussed based on the comparative research of morphology and structure at multiple sites on the RHCM and CIM specimens. Scanning electron microscopy (SEM) and wide angle X-ray diffraction (WAXD) were used to analyze the thickness, crystallinity and lamellae orientation of these three distinct layers. The crystallization and lamellae orientation of iPP correlated strongly with the multilayered structure. In the RHCM process, one side of the mold is equipped with the rapid heat cycle function. The thickness and lamellae orientation next to the heated surface were less than that of the opposite skin layer without heating. Meanwhile, the crystallinity was greater than that of the opposite skin layer.

The molecular chains of a highly oriented polymer lie in the same direction. A highly oriented polymer is an engineering material with a high strength-to-weight ratio and favorable mechanical properties. Such an orthotropic material has biaxially arranged molecular chains that resist stress in the tensile direction, giving it a high commercial value. In this investigation, finite element analysis (FEA) was utilized to elucidate the deformation and failure of a highly oriented polymer. Based on the principles of material mechanics and using the FEA software, Abaqus, a solid model of an I-beam was constructed, and the lengths of this beam were set based on their heights. Three-point bending tests were performed to simulate the properties of the orthotropic highly oriented polymer, yielding results that reveal both tension failure and shear failure. The aspect ratio that most favored the manufacture of an I-beam from highly oriented polymers was obtained; based on this ratio, a die drawing mold can be developed in the future.

This paper employs differential scanning calorimetry (DSC) to investigate the reactions of hydroxyl-terminated polybutadiene (HTPB) binder and isophorone isophorone diisocyanate (IPDI) with two different cure catalysts, namely, dibutyl tin dilaurate (DBTDL) and stannous octanoate (TECH). This study evaluates the effects of two cure catalysts (i.e. DBTDL and TECH) on rate constants of the polyurethane cure reactions. Throughput the study, the kinetic parameters and the curing reaction rate equations are obtained. The present work concludes that both catalysts had a catalytic effect on the HTPB-IPDI system, but that the catalytic effect of DBTDL was higher than that of TECH. The binder system with the TECH catalyst displayed a longer pot-life and lower toxicity compared with the DBTDL. Additionally, this study investigates the binder system’s viscosity build-up at 35°C and the viscosity build-up results were in agreement with the DSC analysis results.

In order to study the effect of composite clays on the mechanical properties, water absorption and salt tolerance of a hydrogel, a poly(acrylic acid-co-acrylamide)/bentonite/kaolin composite hydrogel was prepared. Acrylic acid and acrylamide have been used as water absorbent monomers. N,N′-methylene bisacrylamide was used as a crosslinking agent while potassium persulfate was used as an initiator. The water preserving capability, repeated water absorption, salt resistance and the mechanical properties of the composite hydrogel are analyzed and discussed. The results show that a small quantity of bentonite can increase the storage modulus of the composite hydrogel, whereas the excess clay had an unfavorable effect on the mechanical strength of the composite hydrogel. Both bentonite and kaolin significantly improved the water preserving capability, repeated water absorption and salt resistance of the composite hydrogel. Optimum values for the amounts of bentonite and kaolin were found to be 10% and 5%, respectively.