Kyung-Ho Chung

Introductory behavior of rubber concrete

This article introduces a new type of concrete, the so-called rubber concrete, and thereupon presents a way of modification of waste rubber to construction articles. The conventional cement concrete is made by mixing cement with sand and pebbles, but the rubber concrete proposed here virtually excludes cement completely. The manufacturing process of rubber concrete can be divided into two methods, which are designated for dry and wet processes, but this article focused just on the dry process. The physical properties of rubber composite increased with the silane treatment of added aggregates, but the volume of the aggregate might not be a critical factor affecting the compressive strength in the range of the aggregate contents used in this study, that is, the interfacial adhesion between the matrix rubber and the aggregates was a key factor to improve the mechanical properties of rubber concrete. The compressive strength of rubber concrete was about 89 MPa and the Poissons ratio, which is the ratio of compressive-to-tensile strength, was 5.5%. From the viewpoint of the compressive strength and the Poissons ratio, rubber concrete had better properties than those of conventional cement concrete.

Enhanced adhesion of steel filaments to rubber via plasma etching and plasma-polymerized coatings

Zinc-plated steel filaments were coated with RF plasma polymers of acetylene or butadiene in order to enhance adhesion to rubber compounds. Plasma polymerization was carried out as a function of the plasma power, deposition time, and gas pressure. In order to maximize adhesion, argon plasma etching was performed and carrier gases such as argon, nitrogen, and oxygen were used. Plasma polymer coatings were characterized by FT-IR, Alpha-Step, and a dynamic contact angle analyzer. The adhesion of steel filaments was evaluated via a tire cord adhesion test (TCAT). The best results were obtained from a combined process involving argon etching (90 W, 10 min, 30 mTorr) and acetylene plasma polymer coating (10 W, 30 s, 30 mTorr) with argon carrier gas (25/5, acetylene/argon). These samples exhibited a pull-out force of 285 N, which is comparable to that from the brass-plated steel filament (290 N).

Fabrication and properties of magnetorheological elastomers based on CR/ENR self-crosslinking blends

Magnetorheological elastomers (MREs) are intelligent materials, which are widely used as dampers to eliminate vibration. In this study, a new kind of MREs was designed using carbonyl iron particles (CIPs), carbon black (CB) and self-crosslinking blends, which were fabricated by reacting polychloroprene rubber with epoxidized natural rubber (CR/ENR blends). The interaction mechanism among CIPs, CB and a matrix in the fabrication process was discussed in detail. The morphology of isotropic MREs (i-MREs) and anisotropic MREs (a-MREs) was observed by scanning electron microscopy (SEM). The effect of CIP volume content on the mechanical properties of MREs was investigated. The effect of CIP volume content on the shear storage modulus, MR effect and loss factor was studied using a modified dynamic mechanical analyzer (DMA). The results revealed that the chain-like distribution of CIPs became more pronounced with increasing CIP content in a-MREs, whereas CIPs distributed uniformly in i-MREs. CIPs and CB bonded well with the rubber matrix as a result of their surface attraction effect to CR and ENR molecular chains. Therefore, MREs had excellent mechanical properties. The promoting effect of CB and CIPs on the self-crosslinking reaction was verified by crosslink density assessment. The shear storage modulus of MREs increased with the increase of CIP content, and the MR effect of i-MREs remarkably increased, while a-MREs decreased due to the obvious increase in initial storage modulus with increasing CIP content. The loss factor of MREs decreased obviously with the increase of CIP content.

Structure of Regenerated Cellulose Fibers from DMAc/LiCl Solution

Solutions of celtulose (Cell) in dimethylacetamide (DMAc)/lithium chloride (LiCl) solvent are spun and annealed. The resulting fibers show various polymorphs with the different coagulants and annealing temperatures. Prior to annealing, as-spun fibers show Cell III morphology without differentiating the kind of coagulants. Fibers annealed at 170°C show Cell IV morphology and have better tensile strength than fibers annealed at 190°C, which show Cell III morphology.

Formation of core–shell structured complex microparticles during fabrication of magnetorheological elastomers and their magnetorheological behavior

To improve mechanical and magnetorheological properties of magnetorheological elastomers (MREs), a facile method was used to fabricate high-performance MREs which consisted of the core?shell complex microparticles with an organic-inorganic network structure dispersed in an ethylene propylene diene rubber. In this work, the proposed magnetic complex microparticles were in situ formed during MREs fabrication as a result of strong interaction between matrix and CIPs using carbon black as a connecting point. The morphology of both isotropic (i-MREs) and anisotropic MREs (a-MREs) was observed by scanning electron microscope (SEM). The effects of carbonyl iron particle (CIP) volume content on mechanical properties and hysteresis loss of MREs were investigated. The effects of CIP volume content on the shear storage modulus, MR effect and loss tangent were studied using a modified dynamic mechanical analyzer under applied magnetic field strengths. The results showed that the orientation effect became more pronounced with increasing CIPs in the a-MREs, whereas CIPs distributed uniformly in the i-MREs. The tensile strength, tear strength and elongation at break decreased with increasing CIP content up to 40 vol.%, while the hardness increased. It is worth noting that the tensile strength of i-MREs and a-MREs containing 40 vol.% CIPs still had high mechanical properties as a result of good compatibility between complex microparticles and rubber matrix. The MR performance of shear storage modulus and damping properties of MREs increased remarkably with CIP content due to strong dipole?dipole interaction of complex microparticles. Besides, the hysteresis loss increased with increasing CIP content as a result of magnetic field induced interfacial sliding between complex microparticles.

Vertical distraction osteogenesis using a titanium nitride–coated distractor

OBJECTIVES The purpose of this study was to examine the effect of using a titanium nitride (TiN)-coated vertical distractor on osseointegration after implantation. STUDY DESIGN Four adult mongrel dogs, weighing 9-10 kg, were used in this study. The lower premolars were extracted, and vertical distraction was performed after 10 weeks using 8 distraction devices (left, 4 titanium; right, 4 nitrified). A 7-day latency period was allowed before distraction began. The distraction device was activated at a rate of 0.5 mm twice a day for 5 days. After completing distraction, the device was removed after a consolidation period of 6 weeks and 24 implants were installed. The dogs were killed after 4 or 8 weeks. Histologic examinations were performed. RESULTS The implant success rate was 100% in all of the study groups. Direct bone contact was achieved, and there were no significant differences between the control and experimental groups in the implantation area. CONCLUSION The results suggested that the nitrified distraction device does not negatively affect osseointegration in the vertical distraction osteogenesis; therefore, it has the advantageous potential to substitute for the conventional distractor.

Preparation of Copoly(styrene/butyl methacrylate) Beads and Composite Particles containing Carbon Black with Hydrophobic Silica as a Stabilizer in Aqueous Solution

ABSTRACT ：A suspension copolymerization of styrene and butyl methacrylate (BMA) in the aqueous phase was conductedat a selected temperature between 65 and 95℃. Hydrophobic silica was selected as a stabilizer and azobisisobutyronitrile(AIBN) as an initiator. Optimum dispersion of silica in water was obtained at pH 10 while polymerization reaction wasrun at pH 7. TGA and EDS measurements revealed that 90% of silica functioned as a stabilizer and 10% were incorporatedinto polymeric particles. Average particle diameter decreased with increasing amounts of stabilizer. Molecular weights displayedan increase when the stabilizer concentration reached 1.67 wt%. An increase in the initiator concentration and/or reaction temperature raised the reaction rate but decreased molecular weights. Particle diameter was nearly independent of the initiatorconcentration and reaction temperature. An increase in the BMA proportion decreased the glass transition temperature andincreased the particle diameter with irregularity in shape. Incorporation of carbon black into the particles composed ofstyrene and BMA prolonged the reaction time before reaching completion. We have confirmed that a suspension copolymeriza-tion of styrene and BMA with hydrophobic silica as a stabilizer can produce spherical composite particles with 1-30 ㎛ in diameter containing carbon black.요 약：물을 반응매체로 하고 스티렌과 부틸메타크릴레이트 (BMA)를 단량체로 하여 65℃에서 95℃ 사이의 선택된온도에서 현탁중합을 실시하였다. 소수성 실리카를 안정제로, azobisisobutyronirile (AIBN)을 개시제로 선택하였다.안정제의 최적 분산은 pH 10에서 이루어졌으며 반응은 pH 7에서 진행하였다. TGA 및 EDS 측정으로 사용 한 실리카의 90%는 안정제로 10%는 입자 내로 유입되는 것으로 분석되었다. 안정제의 농도가 증가할수록 평균입경은 감소 하였다. 분자량은 안정제의 농도가 1.67 wt%에 이르며 증가하였다. 개시제의 농도 및/혹은 반응온도의 상승에 따라반응속도는 증가하였으나 분자량은 감소하였다. 입자의 입경은 개시제의 농도 및 반응온도에 거의 무관하였다. BM A의 비가 증가하면서 유리전이온도는 감소하였으며 불규칙한 형상의 입자가 증가하였다. 카본블랙을 함유하는 스티렌/BMA의 중합반응은 반응완료에 보다 많은 시간이 소요되었다. 소수성 실리카를 안정제로 하는 현탁중합반응을 이용하여 카본블랙을 함유하는 평균입경이 1-30 ㎛의 구형 폴리(스티렌-BMA) 공중합체 복합체 입자를 합성할 수 있다는 사실을 확인하였다.

Preparation of Monodisperse Poly(Methacrylic acid) with a Water-Soluble Initiator by Solution Polymerization in the Aqueous Phase

Solution polymerization was conducted with water-soluble methacrylic acid (MAA) as a monomer and potas- sium persulfate (KPS) as an initiator at a selected temperature between 70 and 90 . When the ratio between MAA and water was reduced or initiator concentration increased, molecular weights decreased. Molecular weights of poly(methacrylic acid) (PMAA) showed nearly no dependence on reaction temperature. The Weissenberg effect was observed in most polymer- ization reactions, while its effect weakened at 90 . The polydispersity index was less than 1.5 in most of the reactions. An increase in the stirring speed produced PMAAs with increasing molecular weights. When the stirring speed reached 800 rpm, we retrieved a monodisperse PMAA with both the number and weight average molecular weights of 791,000 g/mol. The glass transition temperature was found to be 162 .

Interfacial Adhesion and Mechanical Properties of Magneto-rheological Elastomer Based on the Natural Rubber with Different Curing System

Vulcanization is an important procedure for elastomers processing. The effects of vulcanization system on the interfacial interaction and mechanical properties of magneto-rheological elastomers (MREs) based on natural rubber (NR) have not been researched, even though, there were many researches focusing on the natural rubber based MREs. In this work, sulfur and dicumyl peroxide (DCP) acted as curing agents preparing MREs based on NR. Scanning electron microscopy was used to characterize the interfacial adhesion of carbonyl iron particles (CIPs) in the matrix. Crosslink density provided evidence that the MREs with DCP system had higher crosslink density than that of MREs with sulfur system. The tensile strength of MREs with DCP system increased, while that of MREs with sulfur system decreased, when 30 vol% of CIPs filled into NR. Finally, the magneto-induced dynamic mechanical properties were tested using a modified dynamic thermo-mechanical analysis under magnetic fields.