• Korea-Australia Rheology Journal
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• 제17권1호
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• pp.21-25
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• 2005

Rheological properties and crystallization kinetics of the polypropylene (PP) block copolymer and recycled PP block copolymer were studied by advanced rheometric expansion system (ARES), differential scanning calorimetry (DSC), and optical microscopy. In the study of the dynamic rheology, it is observed that the storage modulus and loss modulus for the PP block copolymer and recycled PP block copolymer did not change with frequency. In the study of the effect of the repeated extrusion on the crystallization rate, half crystallization time of the PP samples was increased with the number of repeated extrusion in isothermal crystallization temperature ($T_c$). From the isothermal crystallization kinetics study, the crystallization rate was decreased with the increase of the number of repeated extrusion. Also, from the result of Avrami plot, the overall crystallization rate constant (K) was decreased with the increase of the number of the repeated extrusion. From the study of the optical microscopy, the size of the spherulite of the PP samples did not change significantly with the number of repeated extrusion. However, it was clearly observed that the number of the spherulite growth sites was decreased with the number of repeated extrusion. From the results of the crystallization rate, isothermal crystallization kinetics, Avrami plots, and optical microscopy, it is suggested that the crystallization rate of the PP block copolymer is decreased with the increase of the number of repeated extrusion.

• 공업화학
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• 제4권1호
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• pp.94-102
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• 1993

제올라이트 A의 결정화 과정에서 온도, $Na_2O$와 $SiO_2$ 조성의 영향을 조사하였다. 각 결정화 조건에서 결정화 곡선과 최종 생성물의 결정크기 분포를 조사하고 반응 경로 모델을 이용하여 결정화 속도를 구하였다. 결정화 과정은 길이 성장 속도상수가 결정 크기와 무관하게 일정하고 무정형 고형 겔과 용해된 반응물이 평형을 이룬다는 가정으로 잘 모사되었으며, 실험결과와 비교하여 길이성장 속도상수 등을 결정할 수 있었다. 온도가 높아지면 길이성장 단계와 용해된 반응물의 분율이 커져서 결정화 속도가 커졌다. 반면 $Na_2O/H_2O$ 몰비가 커지면 성장단계는 촉진되지 않으나 용해된 반응물의 분율이 커졌으며 핵심생성이 촉진되었다. $SiO_2/Al_2O_3$ 몰비에 따라 용해된 반응물 분율과 핵심생성 속도가 달라진다. 각 결정화 조건에서 제올라이트 A의 길이성장 속도상수는 $0.07{\sim}0.24{\mu}m{\cdot}min^{-1}$로 추정되었으며 겉보기 활성화에너지는 $49kJ{\cdot}mol^{-1}$이었다.

• Macromolecular Research
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• 제11권1호
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• pp.25-35
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• 2003

A series of random poly(ethylene-co-1,4-butylene terephthalate)s (PEBTs), as well as poly(ethylene terephthalate) (PET) and poly(1,4-butylene terephthalate) (PBT), were synthesized by the bulk polycondensation. Their composition, molecular weight, and thermal properties were determined. All the copolymers are crystallizable, regardless of the compositions, which may originate from both even-atomic-numbered ethylene terephthalate and butylenes terephthalate units that undergo inherently crystallization. Non-isothermal crystallization exotherms were measured over the cooling rate of 2.5-20.0 K/min by calorimetry and then analyzed reasonably by the modified Avrami method rather than the Ozawa method. The results suggest that the primary crystallizations in the copolymers and the homopolymers follow a heterogeneous nucleation and spherulitic growth mechanism. However, when the cooling rate increases and the content of comonomer unit (ethylene glycol or 1,4-butylene glycol) increases, the crystallization behavior still becomes deviated slightly from the prediction of the modified Avrami analysis, which is due to the involvement of secondary crystallization and the formation of relatively low crystallinity. Overall, the crystallization rate is accelerated by increasing cooling rate but still depended on the composition. In addition, the activation energy in the non-isothermal crystallization was estimated.

• 폴리머
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• 제31권5호
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• pp.385-392
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• 2007

Poly (N-vinylpyrrolidone) (PVP) groups were grafted onto a poly(3-hydroxybutyrate-co-3-hydroryvalerate) (PHBV) backbone in order to modify its properties and synthesize a novel biocompatible copolymer. The crystallization behavior of PHBV and grafted PHBV was investigated by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). During the cooling-induced crystallization process, the crystallization temperature and the crystallization rate of the grafted PHBV decreased with increasing PVP weight fraction. On the heating scans of all grafted PHBV samples, a new crystallization exothermic peak appeared at almost the same temperature, suggesting the operation of a recrystallization process, while the melting temperature ($T_m$) and the apparent enthalpy of fusion (${\Delta}H_f$) were not affected by graft modification. During the isothermal crystallization process at the same temperature, the presence of side PVP groups decreased the spherulitic growth rate and the spherulitic band spacing with increasing PVP weight fraction in samples.

• Elastomers and Composites
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• 제51권1호
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• pp.56-62
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• 2016

The isothermal crystallization behaviors of blends of poly(ethylene naphthalate) (PEN) and a thermotropic liquid crystalline polymer (TLCP) were investigated by differential scanning calorimetry (DSC) as functions of crystallization temperature and blend composition. Avrami analyses were applied to obtain information on the crystal growth geometry and the factors controlling the rate of crystallization. The crystallization kinetics of the PEN/TLCP blends followed the Avrami equation up to a high degree of crystallization, regardless of crystallization temperature. The calculated Avrami exponents for PEN/TLCP revealed three-dimensional growth of the crystalline region in each blend. The crystallization rate of each blend increased as the crystallization temperature decreased, and decreased as the TLCP content increased. The crystallization of PEN in the blend was affected by the addition of TLCP, which acts as a nucleating agent.

• 한국산학기술학회논문지
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• 제7권4호
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• pp.559-566
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• 2006

폴리(에틸렌 테레프탈레이트)와 액정 폴리에스테르의 블렌드를 등온 결정화 거동에 대하여 연구하였다. 블렌드내의 PET의 결정화 거동을 나타내주는 결정화 속도나 결정이 어떤 모양으로 성장하는가에 대한 정보를 얻기위해 Avrami 식을 이용하였다. 블렌드내 PET의 결정화는 결정화온도에 무관하게 높은 결정화도에 이르기까지 Avrami 식에 잘 적용됨을 알 수 있었으며 Avrami 지수값, n이 2를 나타냄으로써 블렌드내의 PET의 결정이 1차원적으로 성장함을 알 수 있었고, 결정화 온도가 높을수록 결정화 속도가 느려짐을 조사 결과 확인하였다.

• 전자공학회논문지D
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• 제34D권4호
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• pp.33-39
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• 1997

The crystallization temperature of an amorphous silicon (a-Si) can be lowered down to 400.deg. C by a new method : Double-metal induced lateral crystallization (DMILC). The a-Si film was laterally crystallized from Ni and Pd deposited area, and its lateral crystallization rate reaches up to 0.2.mu.m/hour at that temperature and depends on the overlap length of Ni and Pd films; the shorter the overlap length, the faster the rate. Poly-Silicon thin film transistors (poly-Si TFT's) fabricated by DMILC at 400.deg. C show a field effect mobility of 38.5cm$^{3}$/Vs, a minimum leakage current of 1pA/.mu.m, and a slope of 1.4V/dec. The overlap length does not affect the characteristics of the poly-Si TFT's, but determines the lateral crystallization rate.

• Korea-Australia Rheology Journal
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• 제21권2호
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• pp.135-141
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• 2009

Effect of activation energy and crystallization kinetics of polyethylenes (PEs) on the dynamics and stability has been investigated by changing rheological properties and crystallization rate in film casting process. The effect of changes of these properties has been shown using a typical example of short-chain branching (SCB) in linear polyethylenes. SCBs in linear polymers generally lead to the increase of the flow activation energy, and to the decrease of the crystallization rate, making polymer viscosity lower in the case of equivalent molecular weight. In general, the increment of the crystallinity of polymers under partially crystallized state helps to enhance the process stability by increasing tension, and lower fluid viscoelasticity possesses the stabilizing effect for linear polymers. It has been found that the fluid viscoelasticity plays a key role in the control of process stability than crystallization kinetics which critically depends on the cooling to stabilize the film casting process of short-chain branched polymers operated under the low aspect ratio condition.

• 자원환경지질
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• 제32권2호
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• pp.203-208
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• 1999

The main objective of this study is to suggest a new assessment method of the influence of weathering due to salt crystallization on the engineering property of rock. For this purpose, various sources of salt and salt crystallization were investigated, and artificially accelerated weathering tests were carried out. In natural envionment, weathering rate is very slow and weathering process involves complex mechanisms. Therefore artificial weathering test is essential for systematic analysis. Arificial weathering test is defined as test which controls weathering rate and agents by controlling arificial environmental condition. In this study, salt crystallization test was selected among various artificial weathering test methods, for its important role in weathering. Change of various stone properties were detexted. The change of physical properties by salt crystallization were observed as follows : 72% in Brazilian tensile strength and 72% in Slake durability. These results explain the importance of salt crystallization in the mechanical behaviour and properties of stone.

• 대한화학회지
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• 제32권3호
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• pp.276-284
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• 1988

1,3-propane diol, 1,5-pentane diol, 1,6-hexane diol, 분자량이 300인 poly(ethylene glycol)등을 제 3의 디올로 사용하여 poly(ethylene terephthalate)를 개질하여 개질된 copolyester의 결정화 거동을 비교하였다. 개질된 copolyester 중 제 3의 디올 함량이 약 4몰%인 경우 유리전이온도 부근에서 승온시키면서 유리전이온도로 부터 일정 온도 위에서의 결정화 속도를 비교하거나, 녹는점 부근에서 등온 결정화시켜 동일 과냉각 상태에서의 결정화 속도를 비교하면 가해진 디올의 길이가 짧을수록 결정화 속도가 크게 촉진되었다. 이에 반해 녹는점 부근에서 강온시키면서 동일 과냉각 상태에서의 결정화 속도를 비교하면 가해진 디올의 길이가 길수록 결정화 속도가 크게 촉진되었다.