• 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.

• 폴리머
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• 제39권2호
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• pp.268-274
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• 2015

In this paper, the isothermal crystallization kinetics of a functional PP (FPP) with different grafting yields (GY)-methacryloxyethyltrimethyl ammonium chloride (DMC) grafted PP were investigated by differential scanning calorimetry (DSC). The results showed that the crystallization rate of FPP (GY=4.83%) was the highest for all of the studied samples. Furthermore, for the FPP with different GY, the value of $t_{1/2}$ became longer with increasing the grafting yield (GY). The possible explanation was that the quaternary ammonium groups introduced affected the crystallization process of the FPP in two opposite directions, i.e. promoting the nucleation and hindering the transport of the chain molecules towards the growing nuclei. Polarized optical micrographs showed that the DMC chains acted as nucleating agents, which accelerated the nucleation. In addition, the results showed the FPP had lower nucleation free energy than the PP. This study would be useful for designing the processing parameters of the grafted 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.

• 한국재료학회지
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• 제1권3호
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• pp.151-155
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• 1991

시차주사 열분석기를 이용하여 poly(ethylene oxide)(PEO)/poty(styrene-co-acrylic acid) (SAA) blonds에 대한 등온 결정화 속도를 blend의 조성, 사용한 SAA의 공중합조성 및 결정화 온도에 따라 조사하였다. 실험결과는 Avrami 방정식을 이용하여 분석하였다. Avrami지수는 결정화 온도에 관계없이 거의 모든 blend 시료에서 2의 값을 나타내었다. 결정화 속도는 blend시료의 SAA 함량 및 사용한 SAA 공중합체의 아크릴산함량이 증가함에 따라 급격히 느려졌다.

• 한국세라믹학회지
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• 제32권12호
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• pp.1331-1336
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• 1995

The glass-ceramics for ferro-electric were made from compositions of 70PbO.16TiO2.8SiO2.4B2O3.2AlPO4 (wt%) and 67.5PbO.20TiO2.8.5SiO2.2B2O3.2AlPO4 (wt%). The crystallization kinetics for PbTiO3 crystalline phase formation from glass was studied using non-isothermal DSC techniques. The values of activation energy, ΔE using variables of heating rate and temperature were calculated at various reaction fractions obtained from peak area over DSC. The results indicated that activation energy was lowest at 60% reaction fractions and the activation energy of glass containing 20.0 wt% TiO2 is higher than that of glass containing 16.0 wt% TiO2. The crystallization mechanism was three dimensional growth (n=4).

• 한국자기학회지
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• 제5권5호
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• pp.511-514
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• 1995

The crystallization kinetics of $Fe_{73.5}Si_{13.5}B_{9}Cu_{1}Nb_{3}$ amorphous alloy has been investigated using differential scanning calorimetry (DSC). The crystallization process had two stages, i.e. precipitation of the $\alpha$-Fe(Si) solid solution and the tetragonal borides. The isothermal transformation data of the amorphous alloy has been fitted successfully to the generalized Johnson-Mehl-Avrami equation. The mean time exponent, n, obtained is close to 2.5. The value of n=2.5 may be interpreted as being due to a diffusion-controlled transformation process with a constant nucleation rate, one likely transformation mode for the crystallization of metallic amorphous alloys. The activation energy of the overall crystallization process deduced from the time to 50% crystallization are about 81 kcal/mole. The value is of the same order as those estimated from viscous flow.

• 폴리머
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• 제36권6호
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• pp.803-809
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• 2012

에틸렌-테트라플르오르에틸렌(ETFE) 공중합체의 비등온 결정화 거동을 DSC와 imaging FTIR을 이용하여 살펴보았다. 변형 비등온 Avrami 분석 결과, DSC에 의한 열분석의 경우 상대적으로 적은 결정화 엔탈피 변화로 인하여 Avrami 식에 의한 ln[-ln(1-X(t))] vs. ln(t) 곡선이 선형을 이루지 못하는 반면, 결정화에 의한 IR 흡수 강도 image의 변화에 의한 분석 방법인 imaging FTIR의 경우보다 선형적인 결과를 얻음에 따라 imaging FTIR이 ETFE 비등온 결정화 연구에 보다 효과적임을 알 수 있었다. 이와 함께 비등온 결정화에 의한 ETFE의 광학특성을 살펴본 결과, 서냉에 의하여 형성된 ETFE 결정의 빛 산란에 의하여 haze가 증가하며 따라서 투명도가 감소함을 알 수 있으며 비등온 결정화에 의하여 최대 8%의 투과도 감소가 일어남을 확인할 수 있었다. 이상의 결과로부터 결정화를 조절하는 냉각속도가 유리 대체 소재로 사용되고 있는 ETFE 필름의 광투과도 조절에 주요한 가공 변수임을 확인할 수 있었다.

• 한국세라믹학회지
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• 제53권1호
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• pp.24-33
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• 2016

The grafting reaction for maleic anhydride (MA) onto high density polyethylene (HDPE) was investigated from solution process with initiators. The chemical modification of neat HDPE was carried out with various contents of MA (3-21 wt.%) and initiator (0.2-1 wt.%) at different temperature ($80-130^{\circ}C$). The grafting degree was obtained from the titration and the highest grafting degree was 3.1%. The grafting degree increased as the content of MA and initiator increased, however, the highest grafting degree was demonstrated for a particular content of MA and initiator. In the non-isothermal crystallization kinetics, the Ozawa model was unsuitable method to investigate the crystallization behavior of MA onto HDPE, whereas the Avrami and Liu models found effective. The crystallization rate was accelerated as the cooling rate increased, but postponed by combination of MA onto neat HDPE backbone.

• 한국섬유공학회:학술대회논문집
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• 한국섬유공학회 1993년도 ACT 93
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• pp.825-829
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• 1993

• 대한금속재료학회지
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• 제46권6호
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• pp.338-344
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• 2008

The crystallization kinetics of the $Cu_{43}Zr_{43}Al_7Be_7$ bulk metallic glass were studied by differential scanning calorimetry(DSC) in the continuous heating and isothermal annealing modes. Only one major peak could be detected on the DSC traces of $Cu_{43}Zr_{43}Al_7Be_7$ bulk amorphous alloy, and the activation energy for crystallization corresponding to the peak determined by the Kissinger method was resulted of 239 kJ/mol. The isothermal kinetic, analyzed by the Johnson-Mehl-Avrami equation yielded values for the Avrami exponents in the range 1.69 to 2.37, which implied a crystallization governed by a three-dimensioned growth. Primary phases were essentially the cubic structure CuZr together with the $Cu_{10}Zr_7$ phase. At higher temperature, the CuZr disappeared while the $Cu_{10}Zr_7$ became predominant. After long term annealing at 731 K, the phases were $Cu_{10}Zr_7$, $Cu_2ZrAl$ and $Al_3Zr_5$.