• Composites Research
• /
• v.17 no.6
• /
• pp.37-43
• /
• 2004

To determine the effect of chain length and chemical structure of linear amine curing agents on thermal and mechanical properties, a standard bifunctional linear DGEBF epoxy resin was cured with EDA and HMDA having amine group at the both ends of main chain in a stoichiometrically equivalent ratio in condition of preliminary and post cure. From this work, the effect of linear amine curing agents on the thermal and mechanical properties is significantly influenced by numbers of carbon atoms of main chain. In contrast, the results show that the DCEBF/EDA system having two carbons had higher values in the thermal stability, density, shrinkage (%), grass transition temperature, tensile modulus and strength, flexural modulus and strength than the DGEBF/HMDA system having six carbons, whereas the DGEBF/EDA cure system had relatively low values in maximum ekothermic temperature, maximum conversion of epoxide, thermal expansion coefficient than the DGEBF/HDMA cure system. These findings indicate that the packing capability (rigid property) in the EDA structure affects the thermal and mechanical properties predominantly. It shows that flexural fracture properties have a close relation to flexural modulus and strength.

• Corrosion Science and Technology
• /
• v.14 no.5
• /
• pp.213-217
• /
• 2015

Recently, household electronic industries require environmentally-friendly and highly functional steels in order to enhance the quality of human life. Customers especially require both excellent corrosion and abrasion resistant anti-fingerprint steels for digital TV panels. Thus POSCO has developed new functional electro-galvanized steels, which have double coated layers with organic-inorganic composites on the zinc surface of the steel for usage as the bottom chassis panel of TVs. The inorganic solution for the bottom layer consists of inorganic phosphate, magnesium, and zirconium compounds with a small amount of epoxy binder, and affords both improved adhesion properties by chemical conversion reactions and corrosion resistance due to a self-healing effect. The composite solution for the top layer was prepared by fine dispersion of organic-inorganic ingredients that consist of a urethane modified polyacrylate polymer, hardener, silica sol and a titanium complex inhibitor in aqueous media. Both composite solutions were coated on the steel surface by using a roll coater and then cured through an induction furnace in the electro-galvanizing line. New anti-fingerprint steel was evaluated for quality performance through such procedures as the salt spray test for corrosion resistance, tribological test for abrasion resistance, and conductivity test for surface electric conductance regarding to both types of polymer resin and coating weight of composite solution. New composite coated anti-fingerprint steels afford both better corrosion resistance and abrasion properties compared to conventional anti-fingerprint steel that mainly consists of acrylate polymers. Detailed discussions of both composite solutions and experimental results suggest that urethane modifications of acrylate polymers of composite solutions play a key role in enhanced quality performances.

• Tribology and Lubricants
• /
• v.37 no.4
• /
• pp.125-128
• /
• 2021

A means of enhancing the performance of triboelectric nanogenerators (TENGs) is increasing the differences in work functions between contacting materials. Hexagonal boron nitride (h-BN) exhibits excellent mechanical properties and high chemical stability as well as a high work function. As a result, engineers in the field of energy harvesting have envisioned using h-BN in the electrification layer in TENGs. For the industrial application of h-BN in TENGs, large-scale production is necessary, and h-BN is generally exfoliated and dispersed in various solvents. In this study, we evaluate the performance of a TENG with h-BN nanoflakes in the polyimide (PI) layer. To synthesize a PI composite containing h-BN nanoflakes, h-BN powders are exfoliated and dispersed in poly(amic acid) (PAA), which is the precursor of PI. Then, h-BN dispersion is spin-coated onto the PI film and cured for 2 h under 300℃. This composite material can then be used for the electrification layer in TENGs. Below the electrification layer, an aluminum foil is placed and used as an electrode. When the contact and separation processes with polyethylene terephthalate are repeated, the fabricated TENG shows a maximum power density of 190.8 W/m². This study shows that h-BN is a promising material for enhancing the performance of the electrification layer in TENGs.

• Journal of the Korean Wood Science and Technology
• /
• v.38 no.4
• /
• pp.333-340
• /
• 2010

The Korean Dendropanax lacquer, made from a natural resinous sap from Dendropanax orbifera Lev., was used as a golden and transparent varnish for the traditional artifacts (armor uits, helmets, arrowheads, etc.) to make them be brilliant golden color. The cured film of the acquer has excellent protective properties such as weatherability, water resistance, and nticorrosive. But, one of disadvantages is that takes a long time and much energy to fulfill curing the lacquer. The chemical constituents of the lacquer contained conjugated diene compounds s the photopolymerizable monomers. These monomers easily polymerized in sunlight to form olden-colored, hard-coating films in a short time. Photooxidation may be one of the most mportant reactions in the chemistry of the lacquer. Although the Korean Dendropanax Lacquer hould be dried to a thoroughly dry stage to achieve optimal film properties, curing with elevated emperatures may be required for the protracted curing time at atmospheric temperature. So we ntended to accelerate the curing rate of the lacquer by dual curing of thermal and radiation uring. The effect of thermal initiator on the thermal curing reaction was evaluated by monitoring he changes in double bond peak with FT-IR. Then the curing rate of the lacquer blended with hermal initiator and photoinitiator together was measured during dual curing using a RPT with V spot curing machine. Thermal initiator not only accelerated the curing rate but also improved he physical property. And the curing rate of the Korean Dendropanax lacquer was improved by ual curing method of thermal and UV curing. According to these results, the application area of he Korean Dendropanax lacquer could be expanded to surface coatings for electronic devices uch as mobile phones or electronics.

• Journal of the korean academy of Pediatric Dentistry
• /
• v.30 no.3
• /
• pp.530-539
• /
• 2003

The aim of this study was to evaluate the resistance to degradation of four commercial composite resins in an alkaline solution. The brands studied were Charisma, Filtek P 60, Palpique Estelite, and Spectrum. Preweighed discs of each brand were exposed to 0.1N NaOH solution at $60^{\circ}C$. After 2 weeks they were removed, neutralized with HCl, washed with water and dried. Resistance to degradation was evaluated on the basis of following parameters: (a) mass loss(%) - determined from pre-and post-exposed specimen weights; (b) Si loss(ppm) - obtained from ICP-AE analysis of solution exposed to specimens; and (c) degradation depth(${\mu}m$) - measured SEM and CLSM from polished circular sections of exposed specimens. The results were as follows: 1. The sequence of mass loss was in descending order by Palpique Estelite, Filtek P 60, Charisma, and Spectrum. 2. The sequence of the degree of degradation layer depth was in descending order by Filtek P 60, Charisma, Palpique Estelita, and Spectrum. 3. The sequence of the Si loss was in descending order by Chrisma, Spectrum, Palpique Estelite, and Filtek P 60. 4. The correlation coefficient between mass loss and degradation layer depth was relatively high(r=0.704, p<0.05). 5. When observed with SEM, destruction of bonding was observed between resin matrix and filler. 6. When observed with CLSM, degradation layer depth of composite resin surface was observed.

• Composites Research
• /
• v.12 no.4
• /
• pp.71-78
• /
• 1999

To determine the effect of chemical structure of linear amine curing agents on thermal and mechanical properties, standard epoxy resin DGEBA was cured with diaminodiphenyl methane (DDM), diaminodiphenyl sulphone (DDS) in a stoichiometrically equivalent ratio. From this work, the effect of aromatic amine curing agents. In contrast, the results show that the DGEBA/DDS cure system having the sulfone structure between the benzene rings had higher values in the conversion of epoxide, density, shrinkage (%), glass transition temperature, tensile modulus and strength, flexural modulus and strength than the DGEBA/DDM cure system having methylene structure between the benzene rings, whereas the DGEBA/DDM cure system presented higher values in the maximum exothermic temperature, thermal expansion coefficient, and thermal stability. These results are caused by the relative effects of sulfone group having strong electronegativity and methylene group having (+) repulsive property and stem from the effect of the conversion ratio of epoxide group. The result of fractography shows that the each grain size of the DDM/DGEBA system with feather-like structure is larger than that of the DDS/DGEBA system.