• Korea-Australia Rheology Journal
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• v.20 no.2
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• pp.59-63
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• 2008

A theoretical model was developed to describe the flow behavior of a filled polymer in the packing stage of reaction injection molding and predict the residual stress distribution of thin injection-molded parts. The model predictions were compared with experiments performed for phenol-formaldehyde resin filled with wood dust and cured by urotropine. The packing stage of reaction injection molding process presents a typical example of complex non-isothermal flow combined with chemical reaction. It is shown that the time evolution of pressure distribution along the mold cavity that determines the residual stress in the final product can be described by a single 1D partial differential equation (PDE) if the rheological behavior of reacting liquid is simplistically described by the power-law approach with some approximations made for describing cure reaction and non-isothermality. In the formulation, the dimensionless time variable is defined in such a way that it includes all necessary information on the cure reaction history. Employing the routine separation of variables made possible to obtain the analytical solution for the nonlinear PDE under specific initial condition. It is shown that direct numerical solution of the PDE exactly coincides with the analytical solution. With the use of the power-law approximation that describes highly shear thinning behavior, the theoretical calculations significantly deviate from the experimental data. Bearing in mind that in the packing stage the flow is extremely slow, we employed in our theory the Newtonian law for flow of reacting liquid and described well enough the experimental data on evolution of pressure.

• Polymer(Korea)
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• v.25 no.1
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• pp.15-24
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• 2001

In this study, the effects of different glycol molar ratios of unsaturated polyester(UPE) resins on the curing behaviors were investigated. The cross linking process was checked or monitored by differential scanning calorimetry(DSC) and by viscoelastic properties of rigid-body pendulum model. The knife-edge from which the pendulum is suspended, is immersed in a reaction mixture, and the change of the viscoelastic behavior brings on those of the period(T) and logarithmic decrement(${\Delta}$) of the damped free oscillations of the pendulum. The values of T and ${\Delta}$ obtained are related to the dynamic modulus(E') and modulus loss(E'). The information on the viscoelastic behavior of unsaturated polyester(UPE) resins during the curing process are shown to illustrate the usefulness of the techniques. As the content of NPG in a propylene glycol(PG)/NPG glycol mixture increased, both the cycle time during cure and the change of damping during cure of UPE resin decreased.

• Journal of muscle and joint health
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• v.9 no.1
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• pp.53-67
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• 2002

Osteoporosis is a age-related metabolic disorder. Currently there is no cure, but there are measures that can prevent or deter the development of osteoporosis. Futhermore lifestyle among risk factors of osteoporosis may be modifiable. Osteoporotic preventive health promotion behavior may be more effective at early adult when make formation of peak bone mass. The purpose of this study was to identify of relation between the demographic variable, osteoporosis-related lifestyles and the health promotion behavior of University and College Female Students. The results were followed: 1. Demographic variables according to the health promotion behavior were significantly difference with age, body height, religion and income. 2. Osteoporosis-related lifestyles according to the health promotion behavior were significantly difference with element school milk intake, current milk intake, exercise and caffeine intake. 3. Health promotion behavior was positively correlation with age, body weight, height income, element school and current milk intake and exercise.

• Macromolecular Research
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• v.9 no.6
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• pp.319-326
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• 2001

Fatigue crack growth (FCG) behavior of natural rubber/ethylene-propylene-diene rubber (NR/EPDM) blend vulcanizates under dynamic tearing condition was investigated by using a fracture mechanics approach. It appeared that variation of crack growth rate with blend compositions was dependent on the level of imposed tearing energy G. At low tearing energy region, the FCG rates of the blend were lower as the EPDM content was increased, while at high tearing energy region, the trend was reversed. Over the measured range of tearing energy G, all blend compositions showed the lower crack growth rates compared to the average of properties of component elastomers. When the blends were thermally aged, the fatigue resistance of the blends was deteriorated in proportion to the concentration of EPDM phase. Fatigue crack growth behavior of the blends was supposed to be associated with the inhomogeneities of the crosslink structure of the blends arising from cure incompatibility of the EPDM and NR when they are sulphur cured.

• Elastomers and Composites
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• v.41 no.3
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• pp.147-156
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• 2006

To investigate the influence of the foaming temperature and carbon black content on the cure behaviors and foaming characteristics of the foams. natural rubber (NR) was foamed at five temperature zones (145, 150, 155, 160 and $165^{\circ}C$) and different feeding ratios of the carbon black. A decreasing trend of the scorch time, $t_{s2}$ and cure time, $t_{90}$ was observed upon increasing foaming temperature and carbon black content. The optimal temperature for vulcanization and foaming of NRs in this study was considered to be $165^{\circ}C$ where density of the loomed NRs is lower than those at other four temperature regions. The rule rate index of the NRs foamed at $145^{\circ}C$ is smaller than those at 150, 155, 160 and $165^{\circ}C$. The results of the expansion ratio and micrographs of the foamed NRs were founded to support the density characteristics. The thickness of each of the struts formed inside the rubber matrix decreases with increasing the foaming temperature, while it increases with increasing the carbon black content.

• Elastomers and Composites
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• v.34 no.3
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• pp.253-261
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• 1999

The cure properties of rubber compounds containing different adhesive compositions were examined. As the amounts of tannin were increased in the adhesive composition, the scorch time was increased and cure rate was decreased due to the size and shape of tannin molecules. Also, the effect of adhesive composition on the adhesion between rubber and fiber was examined by TCAT(Tire Cord Adhesion Test), The reinforcing cords used in this study were mon ofilaments of nylon 610 and nylon 66. According to the results, the optimum adhesion strength between rubber and fiber could be obtained with adhesives whose molar ratios of formaldehyde/resorcinol were above 5/1 in the recipes. Although the level of dip pick-up(DPU) on the reinforcing cord affects the adhesion strength, the DPU of nylon 610 monofilament did not affect the adhesion strength because the level of DPU was constant regardless of the adhesive compositions. In this case, the adhesion strength with the adhesive composition could be explained with the behavior of tannin in the adhesive.

• Korean Journal of Materials Research
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• v.2 no.3
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• pp.191-196
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• 1992

The new epoxy resin, diglycidyl ether of bisphenol A(DGEBA)/4, 4'-methylene dianiline (MDA)/succinonitrile system, containing the reactive additive succionitrile was investigated through the impact test and the stress-strain test on the basis of the behavior of cure reaction and the cure mechanism. The new epoxy resin system, having the different succinonitrile contents, were cured at $80^{\circ}C$for 1.5 hour and then in order to cure completely at $150^{\circ}C$ for 1 hour. It was shown that as the succinonitrile content increased, impact strength was gradually increased, tensile strength was decreased, almost constantly Young's modulus was sustained and elongation was increased until the succinonitrile content was increased to 10phr, and then decreased. From the experimental results, it can be concluded that the chemical bonding length between the main chains was extended by adding the reactive additive succinonitrile. It was also found that the flexibility of epoxy resin was improved by adding the succinonitrile.

• Composites Research
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• v.15 no.6
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• pp.8-15
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• 2002

In this work, the effect of biodegradable poly(butylene succinate)(PBS) in difunctional epoxy(21:P) resin was investigated in terms of rheological properties, cure kinetics, thermal stabilities, and mechanical interfacial properties. Rheological properties of the blend system were measured under isothermal condition using a rheometer. Cross-linking activation energies($\textrm{E}_c$) were determined from the Arrhenius equation based on gel time and curing temperature. The $\textrm{E}_c$ was increased in the presence of 10 wt% PBS as compared with neat 2EP. From the DSC results of the blends, the cure activation energies($\textrm{E}_a$) showed a similar behavior with $\textrm{E}_c$ due to the increased intermolecular interaction between 2EP and PBS. The decomposed activation energies($\textrm{E}_t$) for the thermal stability derived from the integral method of Horowitz-Metzger equation, were also increased in 10 wt% PBS. In addition, 20 wt% PBS showed the highest critical stress intensity factor($\textrm{E}_{IC}$). which was explained by increasing the fracture toughness of the 2EP/PBS blend systems.

• Proceedings of the KWS Conference
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• 2010.05a
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• pp.78-78
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• 2010

모바일 정보통신기기를 중심으로 패키지의 초소형화, 고집적화를 위해 플립칩 공법의 적용이 증가되고 있고 있으며 접속피치의 미세화에 따라 솔더 및 언더필을 사용하는 C4 공법보다 ACA(Anisotropic Conductive Adhesive), NCA (Non-conductive Adhesive) 등의 접착제를 이용하는 칩본딩 공법에 대한 요구가 증가하고 있다. 특히, NCA 공법의 경우 산업 현장의 대량생산에 대응하기 위해서는 접착제의 속경화 특성이 요구되어 진다. 일반적으로 접착제의 경화거동은 DSC(Differential Scanning Calorimeter)를 사용해 확인하지만, 수초 이내에 경화되는 접착제의 경우는 적용되기 어렵다. 본 연구에서는 이러한 전자패키지용 접착제의 속경화 거동을 효과적으로 평가할 수 있는 방법을 조사 하였다. 실험에서 사용된 접착제는 에폭시계 레진 기반에 이미다졸계 경화제를 사용한 기본적인 포뮬레이션을 사용하였고, 경화시간은 160^{\circ}C에서 1분 이내에 경화되는 특성을 가지고 있다. 경화 거동을 확인하기 위해서 isothermal DSC와 DEA(Dielectric Analysis)의 두가지 방법을 사용해 비교하였다. 두 실험 방법 모두 $160^{\circ}C$를 유지하며 경화 거동을 확인하였고, DoC(Degree of Cure)의 측정오차를 비교 분석하였다. DEA는 이온 모빌리티 변화에 따른 유전손실율을 측정하는 방법으로 80~90% 이후의 경화도는 측정되지 않았지만, 수초 이내에 경화되는 속경화 특성을 평가하기에 적합한 것으로 확인되었다.

• Composites Research
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• v.17 no.5
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• pp.47-53
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• 2004

In this work, two thermal latent catalysts, i.e., N-benzylpyrazinium hexafluoroantimonate (BPH) and benzyl-2,5-dimethylpyrazinium hexafluoroantimonate (BDPH), were synthesized. The cure behaviors and thermal stabilities of diglycidylether of bisphenol A (DCEBA) epoxy resins initiated by 1 wt.% of the catalysts were investigated by DSC, NIR, TCA, and DMA Latent properties of the catalysts were examined by conversion of epoxy resins using NIR from $100^{\circ}C$ to $180^{\circ}C$ From the resultes of near-IR, DGEBA/BPH system showed higher conversion than that of DGEBA/BDPH system. The thermal stabilities of DGEBA/BDPH system based on the initial decomposition temperature (IDT) and integral procedural decomposition (IPDT) were relatively lower than those of DCEBA/BPH system. These could be attributed to the hindered structure of BDPH, resulting in decreasing the thermal stability in the DGEBA/BDPH system.