Thermal and mechanical properties of the polymers synthesized by the sequential polymerization of propylene and 1‐hexadecene

The block copolymer of poly(1‐hexadecene) (PHD) and polypropylene (PP) was effectively synthesized by the sequential polymerization of propylene and 1‐hexadecene by using highly isospecific TiCl₃/Cp₂Ti(CH₃)₂ (Cp = cyclopentadienyl). The block copolymers had two separate melting temperatures of constituent blocks. The modulus of PHD–PP block copolymer was enhanced as the content of sequentially polymerized PP block was increased. The elongation at break showed positive deviation at the intermediate compositions from the simple additive values of constituent homopolymers. Shape memory effect which utilizes the crystalline PHD block as a reversible phase and the crystalline PP block as a fixed structure was examined. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1709–1715, 2002; DOI 10.1002/app.10551     

Synthesis and physicochemical characterization of amphiphilic block copolymer self‐aggregates formed by poly(ethylene glycol)‐block‐poly(ϵ‐caprolactone)

Diblock copolymers with different poly(ε‐caprolactone) (PCL) block lengths were synthesized by ring‐opening polymerization of ε‐caprolactone in the presence of monomethoxy poly(ethylene glycol) (mPEG‐OH, MW 2000) as initiator. The self‐aggregation behaviors and microscopic characteristics of the diblock copolymer self‐aggregates, prepared by the diafiltration method, were investigated by using ¹H NMR, dynamic light scattering (DLS), and fluorescence spectroscopy. The PEG–PCL block copolymers formed the self‐aggregate in an aqueous environment by intra‐ and/or intermolecular association between hydrophobic PCL chains. The critical aggregation concentrations of the block copolymer self‐aggregate became lower with increasing hydrophobic PCL block length. On the other hand, reverse trends of mean hydrodynamic diameters were measured by DLS owing to the increasing bulkiness of the hydrophobic chains and hydrophobic interaction between the PCL microdomains. The partition equilibrium constants (K_v) of pyrene, measured by fluorescence spectroscopy, revealed that the inner core hydrophobicity of the nanoparticles increased with increasing PCL chain length. The aggregation number of PCL chain per one hydrophobic microdomain, investigated by the fluorescence quenching method using cetylpyridinium chloride as a quencher, revealed that 4–20 block copolymer chains were needed to form a hydrophobic microdomain, depending on PCL block length. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3520–3527, 2006     

Encapsulation mechanism of N2 molecules into the central hollow of carbon nitride multiwalled nanofibers

Nitrogen molecules have been encapsulated into the central hollows of vertically aligned carbon nitride (CN) multiwalled nanofibers by dc plasma-enhanced chemical vapor deposition with C₂H₂, NH₃, and N₂ gases on a Ni/TiN/Si(1 0 0) substrate at 650 °C. X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure spectra showed the existence of nitrogen molecules in CN nanofibers. Elemental mapping images with electron energy loss spectroscopy of the CN nanofiber and catalyst metal, and optical emission spectroscopy spectra of the plasma showed the distribution of nitrogen atoms and molecules in the CN nanofiber, catalyst metal, and gaseous precursor, respectively. These studies showed that atomic nitrogen diffused into the catalytic metal particle because of the concentration gradient and then saturated at the bottom of the particle. Saturated nitrogen atom participated in the formation of the CN nanofiber wall but most of nitrogen was trapped in the central hollow of the nanofiber as molecules.     

Experimental analysis of bubble mode in a plate-type absorber

An experimental analysis of ammonia-water absorption was performed in a plate-type absorber. The flow of water and ammonia gas was performed in the bubble mode. The experiments were made to examine the effects of solution flow rate and gas flow rate on the performance of the absorber. It was found that the increase of solution flow rate rarely affected the mass transfer, but improved the heat transfer. As the gas flow rate increased, slugging occurred in the bubble mode and influenced the thermal boundary layer. Finally, the results were converted into dimensionless numbers to elucidate physical phenomena and plotted as Sherwood number versus Reynolds number for mass transfer performance and Nusselt number versus Reynolds number for heat transfer performance.     

Durable antimicrobial treatment of cotton fabrics using N‐(2‐hydroxy)propyl‐3‐trimethylammonium chitosan chloride and polycarboxylic acids

N‐(2‐hydroxy)propyl‐3‐trimethylammonium chitosan chloride (HTCC), a water‐soluble chitosan quaternary ammonium derivative, was used as an antimicrobial agent for cotton fabrics. HTCC has a lower minimum inhibition concentration (MIC) against Staphylococcus aureus, Klebsiella pneumoniae, and Escherichia coli compared to that of chitosan; however, the imparted antimicrobial activity is lost on laundering. Thus crosslinking agents were utilized to obtain a durable antimicrobial treatment by immobilizing HTCC. Several crosslinkers such as dimethyloldihydroxyethylene urea (DMDHEU), butanetetracarboxylic acid (BTCA), and citric acid (CA) were used with HTCC to improve the laundering durability of HTCC treatment by covalent bond formation between the crosslinker, HTCC and cellulose. The polycarboxylic acid treatment was superior to the DMDHEU treatment in terms of prolonged antimicrobial activity of the treated cotton after successive laundering. Also, the cotton treated with HTCC and BTCA showed improved durable press properties without excessive deterioration in mechanical strength or whiteness when compared to the citric acid treatment. With the addition of only 0.1% HTCC to BTCA solutions, the treated fabrics showed durable antimicrobial activity up to 20 laundering cycles. The wrinkle recovery angle and strength retention of the treated fabrics were not adversely affected with the addition of HTCC. Therefore, BTCA can be used with HTCC in one bath to impart durability of antimicrobial activity along with durable press properties to cotton fabric. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1567–1572, 2003     

Rheology-processing-property relationships in tubular blown film extrusion. I. High-pressure low-density polyethylene

Three different grades of high-pressure low-density polyethylene resin were used to establish relationships between tubular film blowability and the molecular parameters, namely, the molecular weight distribution (MWD) and the degree of long-chain branching (LCB), and also between the processing conditions and the mechanical properties of the tubular blown films produced. For the study, both the shearing and elongational flow properties of the resins were determined. During the tubular film blowing experiment we measured the freeze-line position, the tubular bubble diameter, the takeup speed, the axial tension, the pressure inside the tubular bubble, and the mass flow rate of the resin. The thickness of the tubular blown films was measured from the samples collected. In order to determine the tubular film blowability, we measured the maximum takeup speed at which the tubular blown bubble broke, for various blowup ratios. The measurements described above permitted us to calculate the tensile stresses at the freeze line, in both the machine and transverse directions, and they were found to be correlatable to the processing conditions employed. It has been found that the tubular film blowability is increased as the resin's MWD becomes narrower and the degree of LCB is less. It has been found further that a resin having lower elongational viscosity tends to give a greater draw-down ratio, indicating a better tubular film blowability. Finally, the tensile properties of the tubular blown films were found correlatable to the processing variables, namely, blowup and takeup ratios.     

Energetic surface heterogeneity of nanocrystalline TiO<Subscript>2</Subscript> films for dye-sensitized solar cells

Dye sensitized solar cells (DSSCs) have been receiving significant attention because they have many advantages compared to conventional organic solar cells. It has been known that the photovoltaic characteristics of DSSC are highly dependent on the adsorption properties of dyes on TiO₂ films. To analyze the surface heterogeneity of TiO₂ surfaces, single-phase anatase nanocrystallite titanium films were prepared by sol-gel method using the hydrolysis reaction of titanium tetraisopropoxide under acidic condition and characterized by XRD, FE-SEM and BET analysis. The adsorption energy distribution functions were calculated by the generalized nonlinear regularization method. It was found that the shape and the intensity of the adsorption energy distribution curve determined were highly related with the physical properties (i.e., geometrical heterogeneity) and chemical characteristics (i.e., energetic heterogeneity) of nanocrystalline TiO₂ for DSSC.     

Modeling and economic analysis of CO<Subscript>2</Subscript> separation process with hollow fiber membrane modules

The main purpose of the study was to develop a model using ASPEN and Excel simulation method to establish optimum CO₂ separation process utilizing hollow fiber membrane modules to treat exhaust gas from LNG combustion. During the simulation, optimum conditions of each CO₂ separation scenario were determined while operating parameters of CO₂ separation process were varied. The characteristics of hollow fibers membrane were assigned as 60 GPU of permeability and 25 of selectivity for the simulation. The simulation results illustrated that 4 stage connection of membrane module is required in order to achieve over 99% of CO₂ purity and 90% of recovery rate. The resulted optimum design and operation parameters throughout the simulation were also correlated with the experimental data from the actual CO₂ separation facility which has a capacity of 1,000 Nm³/day located in the Korea Research Institute of Chemical Technology. Throughout the simulation, the operating parameters of minimum energy consumption were evaluated. Economic analysis of pilot scale of CO₂ separation plant was done with the comparison of energy cost of CO₂ recovery and equipment cost of the plant based on the simulation model. This work was presented at the 6 ^th Korea-China Workshop on Clean Energy Technology held at Busan, Korea, July 4–7, 2006.     

Electromechanical behavior of hybrid carbon/glass fiber composites with tension and bending

To understand the smart (i.e., good memory) characteristics of hybrid composites of carbon fibers (CFs) and glass fibers (GFs) with epoxy resin as a matrix, the changes in the electrical resistance of composites with tension and on bending were investigated. The electrical resistance behavior of composites under tension changed with the composition of the CF/GF, as well as with the applied strain. The fractional electrical resistance increased slowly with increasing strain within a relatively low strain region. However, with further loading it increased stepwise with the strain according to the fracture of the CF layers. The strain sensitivity of the samples increased with increasing CF weight percentage, and the samples incorporating more than 40 wt % CF showed a strain sensitivity higher than 1.54 for a single CF. The changes in the fractional electrical resistance with bending were not so dominant as those with tension. This difference was attributed to the action of two cancelling effects, which are the increasing and decreasing fractional electrical resistance due to tension and compression with bending, respectively. On recovery from a large applied bending, the fractional electrical resistance decreased slowly with unloading because of the increase of contacts between the fibers that resulted from the reorganization of ruptured CFs during the recovery. Even the composites incorporating a relatively small CF content showed an irreversible electrical resistance with both tension and bending. However, the strain sensitivity being larger with tension than with bending is ascribed to the difference in their mechanical behaviors. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2447–2453, 2002