• Korean Chemical Engineering Research
• /
• v.60 no.2
• /
• pp.202-207
• /
• 2022

The study on electrode degradation of Proton Exchange Membrane Fuel Cell (PEMFC) was mainly studied on the particle growth and active area reduction of Pt on the electrode. The degradation of the electrode catalyst Pt in contact with the membrane affects the deterioration of the polymer membrane, but there are not many studies related to this. In this study, the phenomenon of the deposition of deteriorated Pt inside the polymer membrane during the accelerated electrode catalyst degradation test and its effects were studied. The voltage change (0.6 V ↔ 0.9 V) was repeated up to 30,000 cycles to accelerate the platinum degradation rate. When the voltage change cycle was repeated while oxygen was introduced into the cathode, the amount of Pt deposited inside the film was larger than when nitrogen was introduced. As the number of voltage change cycles increased, the amount of Pt deposited inside the membrane increased, and Pt dissolved in the cathode moved toward the anode, showing a uniform distribution throughout the membrane at 20,000 cycles. In the process of the accelerated electrode catalyst degradation test, the hydrogen crossover current density of the membrane did not change, and it was confirmed that the deposited Pt did not affect the durability of the membrane.

• Applied Chemistry for Engineering
• /
• v.16 no.4
• /
• pp.496-501
• /
• 2005

The thermal degradation of ABS in the presence of iron-based metal catalysts has been studied by thermogravimetric analysis (TGA). The reaction of iron-based metal catalysts (ferric nitrate nonahydrate, ammonium ferric sulfate dodecahydrate, iron sulfate hydrate, ammonium ferric oxalate, iron(II) acetate, iron(II) acetylacetonate and ferric chloride) with ABS has been found to occur during the thermal degradation of ABS. In a nitrogen atmosphere, char formation was observed, and at $600^{\circ}C$ approximately 3~23 wt% of the reaction product was non-volatile char. The resulting enhancement of char formation in a nitrogen atmosphere has been primarily due to the catalytic crosslinking effect of iron-based metal catalysts. On the other hand, char formation of ABS in air at high temperature by iron-based metal catalyst was unsuccessful due to the oxidative degradation of the char.

• Korean Chemical Engineering Research
• /
• v.58 no.1
• /
• pp.59-63
• /
• 2020

Radical scavenger is used to improve the durability of PEMFC polymer membrane. In this study, we investigated whether fucoidan extracted from seaweed as a radical scavenger prevents electrochemical degradation through Fenton and OCV Holding experiments. Fucoidan has an antioxidant effect, protecting the polymer membrane from hydrogen peroxide and oxygen radicals, reducing the degradation rate to 1/10. Fucoidan has been shown to be more effective than MnO₂, which is used as a radical scavenger. In the PEMFC cell, the accelerated durability evaluation method (OCV Holding) showed that fucoidan reduced the hydrogen permeability of the polymer membrane by 12% and enhanced the performance by 29.1% compared to without radical scavenger. And fucoidan was found to be more effective in the cathode side ionomer than the anode side.

• Proceedings of the Korean Fiber Society Conference
• /
• 2003.10b
• /
• pp.209-210
• /
• 2003

The durability and anti-microbial stability of plastics, which have been thought to be favorable characteristics, cause ecoloical problems due to non-degradation after disposal. For a possible solution of these ecological and environmental problems, the biodegradable polymers. especially aliphatic polyesters, have been widely investigated. Poly(tetramethylene succinate)(PTMS) is one of the most promising biodegradable polyesters. (omitted)

• Proceedings of the Korean Fiber Society Conference
• /
• 2001.10a
• /
• pp.25-28
• /
• 2001

Polymer blending constitutes a most useful method for the improvement or modification of the physicochemical properties of polymeric materials. Some of the polymer blends exhibit unusual properties, unexpected from homopolymers. An important property of a polymer blend is the miscibility of its component, because it affects the mechanical properties, the morphology, its permeability and degradation [1, 2]. (omitted)

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2005.07a
• /
• pp.657-658
• /
• 2005

Flame retard of polymers was studied for prevention from burning by various additives stimulated the char formation during heating and thermal degradation of polymer materials. Forming char have high porosity, low thermal conductivity and act as thermal shield for heat transmission from the flame to the polymer and. oxygen towards the polymer. The results showed that various additives may regulate the processes of intumecsence. The efficient fire protective intumescent char was result of processes of melting, gas evolution, cross-linking, carbonization etc.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.14 no.1
• /
• pp.241-250
• /
• 1990

Characteristic relaxation time and characteristic diffusion time of viscoelastic fluids are determined experimentally by measuring the zero-shear-rate viscosity by falling ball viscometer and the infinite-shear-rate viscosity by capillary tube viscometer. Fluids used in experiments are aqueous solutions of polyacrylamide Separan AP-273 and the polymer concentrations range from 300 to 2000 wppm. A newly designed laser beam and timer system is employed to overcome the difficulty in measuring terminal velocities of the low concentration solutions. Ball removal device is prepared to remove the dropped ball from the bottom of cylinder without disturbing the testing fluid. In order to measure the zero-shear-rate viscosity, densities of hollow aluminium balls are adjusted very close to the densities of testing fluids. Characteristic diffusion time, which is ball viscometer. However, terminal velocity of a needle by falling ball viscometer is not affected by the time interval of dropping needles and characteristic diffusion time is not measured with a dropping needle. Powell-Eyring model predicts the highest values of the characteristic relaxation times among models used for heat transfer experimental works for a given polymer solution. As degradation of a polymer solution continues, the zero-shear-rate viscosity decreases more seriously than the infinite-shear-rate viscosity. Characteristic relaxation times of polymer solutions decreases as degradation continues.

• Macromolecular Research
• /
• v.15 no.4
• /
• pp.363-369
• /
• 2007

Novel biodegradable elastic hydrogels, based on hydrophilic and hydrophobic polymer blocks, were synthesized via the radical crosslinking reaction of diacrylates of poly(ethylene glycol) (PEG) and poly(${\varepsilon}-caprolactone$) (PCL). PEG and PCL diols were diacrylated with acryloyl chloride in the presence of triethylamine, with the reaction confirmed by FT-IR and $^1H-NMR$ measurements. The diacrylate polymers were used as building-blocks for the syntheses of a series of hydro gels, with different block compositions, by simply varying the feed ratios and molecular weights of the block components. The swelling ratio of the hydrogels was controlled by the balance between the hydrophilic and hydrophobic polymer blocks. Usually, the swelling ratio increases with increasing PEG content and decreasing block length within the network structure. The hydrogels exhibited negative thermo-sensitive swelling behavior due to the coexistence of hydrophilic and hydrophobic polymer components in their network structure, and such thermo-responsive swelling/deswelling behavior could be repeated using a temperature cycle, without any significant change in the swelling ratio. In vitro degradation tests showed that degradation occurred over a 3 to 8 month period. Due to their biodegradability, biocompatibility, elasticity and functionality, these hydrogels could be utilized in various biomedical applications, such as tissue engineering and drug delivery systems.

• Macromolecular Research
• /
• v.12 no.5
• /
• pp.466-473
• /
• 2004

We have used FT-IR spectra to explain the effects of hydrogen bonding between chitosan and polycaprolactam (PA6). A dynamic mechanical analysis study suggested that the optimum chitosan and PA6 miscibility under the conditions of this experiment were obtained at a blending ratio of 40:60. We studied the thermal degradation of chitosan blended with PA6 (chitosan/PA6) by thermogravimetric analysis and kinetic analysis (by the Ozawa method). Dry chitosan and PA6 exhibited a single stage of thermal degradation and chitosan/PA6 blends having> 20 wt% PA6 exhibited at least two stages of degradation. In chitosan/PA6 blends, chitosan underwent the first stage of thermal degradation; the second stage proceeded at a temperature lower than that of PA6, because the decomposition product of chitosan accelerated the degradation of PA6. The activation energies of the blends were between 130 and 165 kJ/mol, which are also lower than that of PA6.

• Korean Chemical Engineering Research
• /
• v.45 no.4
• /
• pp.345-350
• /
• 2007

During PEMFC operation, OCV(open circuit voltage) and low humidity conditions accelerate the degradation of perfluorosulfonic acid membrane. There have been no studies that clearly explain why these conditions accelerate the membrane degradation. In this study, the hydrogen permeability through the membrane, I-V polarization of MEA, fluoride emission rate(FER) and $H_2O_2$ concentration in condensed water were measured during cell operation under OCV and low relative humidity(RH). The experimental results were evaluated with oxygen radical mechanism the most commonly known for membrane degradation. It seems that low RH of anode is a good condition for $H{\cdot}$ radical formation on the Pt catalyst and the OCV condition accelerate the $H{\cdot}$ to form $HO_2{\cdot}$ radical attacking the polymer membrane.