• Fibers and Polymers
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• 제6권1호
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• pp.13-18
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• 2005

PLA/LPCL/HPCL blend fibers composed of poly (lactic acid) (PLA), low molecular weight poly ($\varepsilon$-caprolactone) (LPCL), and high molecular weight poly ($\varepsilon$-caprolactone) (HPCL) were prepared by melt blending and spinning for bioab­sorbable filament sutures. The effects of blending time and blend composition on the X-ray diffraction patterns and tensile properties of PLA/LPCL/HPCL blend fibers were characterized by WAXD and UTM. In addition, the effect of in vitro degra­dation on the weight loss and tensile properties of the blend fibers hydrolyzed during immersion in a phosphate buffer solu­tion at pH 7.4 and 37$^{\circ}C$ for 1-8 weeks was investigated. The peak intensities of PLA/LPCL/HPCL blend fibers in X-ray diffraction patterns decreased with an increase of blending time and LPCL contents in the blend fibers. The weight loss of PLA/LPCL/HPCL blend fibers increased with an increase of blending time, LPCL contents, and hydrolysis time while the tensile strength and modulus of the blend fibers decreased. The tensile strength and modulus of the blend fibers were also found to be increased with an increase of HPCL contents in the blend fibers. The optimum conditions to prepare PLA/LPCL/HPCL blend fibers for bioabsorbable sutures are LPCL contents of $5 wt\%, HPCL contents of $35 wt\%, and blending time of 30 min. The strength retention of the PLA/LPCL/HPCL blend fiber prepared under optimum conditions was about $93.5\% even at hydrolysis time of 2 weeks.

• 대한기계학회논문집A
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• 제36권12호
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• pp.1585-1590
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• 2012

플라스틱 소재는 온도, 습도 및 자외선 등 다양한 환경의 영향으로 인해 기계적 물성변화가 심하기 때문에 체결부의 견고함이 느슨해지고 형태의 변형에 의해 부품간의 마찰 등을 유발하여 잡음이 발생하게 된다. 따라서, 본 논문에서는 자동차 칵핏 모듈에 사용되는 다양한 플라스틱 소재에 대해 온도변화에 따른 동 특성시험을 통해 유리전이온도, 저장탄성계수, 손실계수 등을 측정하여 상온 및 열화조건에 따른 물성변화를 파악하였다. 시험결과, 온도가 높을수록 저장탄성계수는 감소하고 손실계수는 증가하는 경향을 나타내었다.

• Journal of the Korean Wood Science and Technology
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• 제24권1호
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• pp.81-86
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• 1996

This study was performed to evaluate the reduction in bending properties of radiata pine sapwood associated with incipient brown-rot decay. Decayed bending specimens by Tyromyces palustris and Gloeophyllum trabeum for varoious periods were tested destructively. Brown-rot decay by T. palustris and G. trabeum caused serious reduction in bending properties at very early stages of decay, with about 30 percent decrease in bending strength observed for only 1~2 percent weight loss. In general, the reduction in bending properties caused by T. palustris was somewhat greater than that by G. trabeum. Work to maximum load was reduced most severely and rapidly from the onset of decay, while modulus of elasticity showed a much more moderate rate of reduction. Modulus of rupture was affected by decay to a greater extent than was modulus of elasticity. Since a relatively strong correlation between weight loss and bending strength was observed, the residual strength of decayed wood can be predicted by weight loss due to decay. The results of this study indicate that very early stages of brown-rot decay reduce the bending strength significantly. Thus, it is recommended that all load-bearing members in wooden structures, especially those that are periodically wetted, should be inspected regularly to prevent a sudden failure even though there are no definite signs of decay.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 추계 학술발표회 논문집
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• pp.425-428
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• 2006

In order to estimate the reduction of laodbearing capacity, followed by the attributive change of heat while high strength concrete structure is revealed on fire it is necessary to evaluate, it is necessary to evaluate the property of material under high temperature such as thermal conductivity, specific heat, compressive strength, modulus of rigidity and diminution figure. Therefore, this study is for the purpose of presenting evaluation data for the analysis of thermal behavior about the high strength concrete material under high temperature, through the experiment by manufacturing concrete(40, 50, 60, 80, 100 MPa) commonly used in the construction field. As a result of the study, in the case of physical attribute, it demonstrates a greater fluctuation of change than the one of 30 MPa concrete. In case of specific heat, the high strength concrete, shown the serious diminution between $500{\sim}600^{\circ}C$, presents the thermal change area corresponding to the change of high strength concrete. In compressive strength, regardless of intensity of concrete, all of them show the first intensity loss between normal temperature and $100^{\circ}C$, the dramatic loss beyond $400^{\circ}C$. The concrete weighing above 50 MPa shows a twice lower dramatic intensity loss than the one weighing $30{\sim}40MPa$. The concrete ranging from $60{\sim}80MPa$, shows the biggest diminution of modulus of elasticity under $400^{\circ}C$, which implies the structural unstability of temperature.

• 유변학
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• 제10권4호
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• pp.227-233
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• 1998

잠재성 경화제인 N-benzylpyrazinium hexafluoroantimonate(BPH)를 Cycloaliphatic계 에폭시 (CAE)/DGEBA계 에폭시의 혼합물에 1 mol% 첨가 시킨 후 혼합 조성비에 따른 유변학적 특성과 경화 동력학에 대해 연구하였다. 잠재특성은 등온 DSC를 이용하여 각각 $150^{\circ}C$와 $50^{\circ}C$의 반응 온도에 대한시간의 함수로서 전화량을 구하여 측정하였다. 블렌드 시스템의 유변학적 특성은 레오미터를 사용한 등온 실험을 통하여 storage modulus (G'), loss modulus (G") 그리고 damping factor (tan$\delta$)를 구한 후 이들 데이터로부터 겔화 시간을 측정하였다. 겔화 시간과 경화 온도를 Arrenius equation에 적용시킨 결과 가교 활성화 에너지 ($E_c$)를 구할 수 있었으며 겔화 시간과 활성화 에너지 모두 DGEBA의 함량이 증가할수록 증가하였다. 경화 활성화 에너지 ($E_a$)를 동적 DSC를 이용하여 Kissinger method에 의해 구하였는데 활성화 에너지는 CAE의 함량이 증가할수록 감소함으로써 높은 반응성을 나타내었는데, 이는 짧은 반복 단위와 단순한 곁사슬기 그리고 반응 매질 내의 점도 등에 기인한다.기인한다.

• 폴리머
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• 제25권1호
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• pp.15-24
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• 2001

본 연구에서는 불포화 폴리에스테르 수지의 글리콜 몰비에 따른 경화거동을 실험하였다. 경화과정은 Tanaka 강체진자(rigid-body pendulum)형 점탄성 모델과 differential scanning calorimetry(DSC)법을 이용하였다. 강체진자의 회전축부에 수지막을 형성하여 자유진동을 시키면 수지막의 점탄성 변화에 응답하여 pendulum의 진동주기 T 및 대수 감쇄율 ${\Delta}$가 변화한다. Pendulum의 회전축부에 있어서의 수지막의 역학적인 응답을 pendulum의 진동 운동으로 취급하고 T 및 ${\Delta}$를 이용, 수지막의 dynamic modulus(E') 및 modulus loss(E')을 구하는 계산식을 만들었다. 이 측정법과 계산식을 이용하여 불포화 폴리에스테르 수지의 경화과정에 있어서의 점탄성 변화를 추적하여 수지막의 경화성의 차이를 알 수 있었다. Neopentyl glycol(NPG)의 몰비가 증가할수록 진동주기의 감소폭 기울기에 의한 경화반응속도가 느리고, damping 값에 의한 점도값의 상승속도가 감소하는 경화거동을 고찰하였다.

• 한국군사과학기술학회지
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• 제26권3호
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• pp.262-272
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• 2023

A polymer-based mechanical low-pass filter(m-LPF) for high-g accelerometers makes it possible to remove high-frequency transient noises from acceleration signals, thus ensuring repeatable and reliable measurement on high-g acceleration. We establish a prediction model for performance of m-LPF by combining a fundamental vibration model with the fractional derivative standard linear solid(FD SLS) model describing the storage modulus and loss modulus of polymers. Here, the FD SLS model is modified to consider the effect of m-LPF shape factor (i.e., thickness) on storage modulus and loss modulus. The prediction accuracy is verified by comparing the displacement transmissibility(or cut-off frequency) estimated using our model with that measured from 3 kinds of polymers(polysulfide rubber(PSR), silicone rubber(SR), and polydimethylsiloxane(PDMS)). Our findings will contribute a significant growth of m-LPF for high-g accelerometers.

• Korea-Australia Rheology Journal
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• 제18권2호
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• pp.67-81
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• 2006

Using a strain-controlled rheometer, the dynamic viscoelastic properties of aqueous xanthan gum solutions with different concentrations were measured over a wide range of strain amplitudes and then the linear viscoelastic behavior in small amplitude oscillatory shear flow fields was investigated over a broad range of angular frequencies. In this article, both the strain amplitude and concentration dependencies of dynamic viscoelastic behavior were reported at full length from the experimental data obtained from strain-sweep tests. In addition, the linear viscoelastic behavior was explained in detail and the effects of angular frequency and concentration on this behavior were discussed using the well-known power-law type equations. Finally, a fractional derivative model originally developed by Ma and Barbosa-Canovas (1996) was employed to make a quantitative description of a linear viscoelastic behavior and then the applicability of this model was examined with a brief comment on its limitations. Main findings obtained from this study can be summarized as follows: (1) At strain amplitude range larger than 10%, the storage modulus shows a nonlinear strain-thinning behavior, indicating a decrease in storage modulus as an increase in strain amplitude. (2) At strain amplitude range larger than 80%, the loss modulus exhibits an exceptional nonlinear strain-overshoot behavior, indicating that the loss modulus is first increased up to a certain strain amplitude(${\gamma}_0{\approx}150%$) beyond which followed by a decrease in loss modulus with an increase in strain amplitude. (3) At sufficiently large strain amplitude range (${\gamma}_0>200%$), a viscous behavior becomes superior to an elastic behavior. (4) An ability to flow without fracture at large strain amplitudes is one of the most important differences between typical strong gel systems and concentrated xanthan gum solutions. (5) The linear viscoelastic behavior of concentrated xanthan gum solutions is dominated by an elastic nature rather than a viscous nature and a gel-like structure is present in these systems. (6) As the polymer concentration is increased, xanthan gum solutions become more elastic and can be characterized by a slower relaxation mechanism. (7) Concentrated xanthan gum solutions do not form a chemically cross-linked stable (strong) gel but exhibit a weak gel-like behavior. (8) A fractional derivative model may be an attractive means for predicting a linear viscoelastic behavior of concentrated xanthan gum solutions but classified as a semi-empirical relationship because there exists no real physical meaning for the model parameters.

• Journal of the Korean Wood Science and Technology
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• 제32권5호
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• pp.29-38
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• 2004

본 연구에서는 생분해성 고분자인 polybutylene succinate-adipate (PBS-AD)에 옥수수 전분을 충전제로 첨가한 생분해성 복합재의 열적성질에 대해 고찰하였다. 열분석은 온도에 대한 함수로서 복합재 물질의 화학적 성질과 중량 감소율을 측정할 수 있는 분석적인 방법으로 사용되고 었다. 옥수수 전분의 열안정성은 순수한 생분해성 고분자인 PBS-AD보다 낮았다. 옥수수 전분의 함량이 증가할수록 생분해성 복합재의 열안정성과 열분해 온도는 감소하였고 회분의 함량은 증가하였다. 이것은 생분해성 복합재의 계면에서의 결합려이 옥수수 전분의 혼합비율이 증가할수록 감소하였기 때문이다. 옥수수 전분의 함량이 증가할수록 생분해성 복합재의 유리전이온도(T_g) 와 용융온도(T_m) 에는 큰 변화가 없었다. 옥수수 전분이 혼합된 생분해성 고분자 복합재의 저장 탄성율(E')과 손실 탄성율(E") 값은 PBS-AD보다 높았다. 이 결과는 옥수수 전분의 첨가로 인하여 생분해성 복합재의 강성이 증가하였기 때문이다. 고온에서 생분해성 고분자 복합재의 감소된 저장 탄성율 값은 온도가 증가할수록 고분자 사슬의 운동성이 증가하기 때문이다. 위의 결과들로부터, 옥수수 전분이 생분해성 고분자 복합재를 제조하는데 충전제로서 사용이 가능하다고 예상할 수 있었으며 옥수수 선분과 생분해성 고분자의 계면에서의 결합력을 향상시키기 위하여 결합제의 사용이 요구된다.

• Journal of the Korean Wood Science and Technology
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• 제35권5호
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• pp.76-86
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• 2007

This study was conducted to investigate the effects of formaldehyde to urea (F/U) mole ratio on thermomechanical curing of UF resin adhesives with different F/U mole ratios. Thermomechanical curing of these UF resin adhesives was characterized using parameters of dynamic mechanical analysis (DMA) such as the gel temperature, maximum storage modulus, and peak temperatures of storage and loss modulus. As the F/U mole ratio decreased, the gel temperature of UF resin adhesives increased. The maximum storage modulus as an indicator of the rigidity of UF resin adhesives decreased with decreasing F/U mole ratio. The peak temperature of tan $\delta$ increased with decreasing F/U mole ratio, indicating that the vitrification occurred faster for high F/U mole ratio of UF resin adhesives than for the one of lower F/U mole ratio. These results partially explained the reason why UF resin adhesives with lower F/U mole ratio resulted in relatively poor adhesion performance when they were applied.