Relationship between cooling rate and crystallization behavior of hydrogenated sunflowerseed oil

The relationship between cooling rate and crystallization behavior of hydrogenated sunflowerseed oil and its thermal properties during melting were investigated by differential scanning calorimetry and x-ray diffraction. At crystallization, temperature peaks and area percents of components with higher melting points were found to be greater when cooling rate was slower. When samples were melted, total enthalpies were similar at all rates. According to the chemical composition of the analyzed samples, the components with higher melting points were found in samples with a higher saturated fatty acid content. Changes in the profile of melting curves might be due to differences in triglyceride intersolubility.     

Crystallization kinetics of fully hydrogenated palm oil in sunflower oil mixtures

The crystallization kinetics of mixtures of fully hydrogenated palm oil (HP) in sunflower oil (SF) was studied. The thermal properties and phase behavior of this model system were characterized by means of differential scanning calorimetry and X-ray diffraction. From the melting enthalpy and clear point of HP, it was possible to calculate the supersaturation at a given temperature for every composition of the model system. Supersaturation of the model system for the β′ but not for the α polymorph yielded the β′ polymorph, while supersaturation for the α polymorph yielded a mixture of mainly β and some β′ polymorphs. The crystallization kinetics of HP/SF mixtures were determined by pulsed wide-line proton nuclear magnetic resonance for various initial supersaturations in the β′ polymorph. The determined curves were modeled by a modified classical nucleation model and an empirical crystal growth function, which are both functions of supersaturation. Heterogeneous nucleation rates in the β′ polymorph yielded a surface Gibbs energy for heterogeneous nucleus formation of 3.8 mJ·m⁻². About 80% of the triglyceride was assumed to be in a suitable conformation for incorporation in a nucleus. Induction times for isothermal crystallization in the β′ polymorph yielded a surface free energy for heterogeneous nucleus formation of 3.4 to 3.9 mJ·⁻².     

mLLDPE非等温结晶动力学研究

利用差示扫描量热仪(DSC)研究了茂金属线性低密度聚乙烯(mLLDPE)和传统线性低密度聚乙烯(LLDPE)的非等温结晶行为。采用Jeziorny法和莫志深法对所得的数据进行了分析。结果表明,采用莫志深法处理数据可得到较好的线性关系,且mLLDPE在相同的相对结晶度下的结晶速率低于LLDPE。     

Crystallization kinetics,melting behavior,and morphologies of poly(butylene succinate) and poly(butylene succinate)‐block‐poly(propylene glycol) segmented copolyester

This article investigated the crystallization kinetics, melting behavior, and morphologies of poly(butylene succinate)(PBS) and its segmented copolyester poly(butylene succinate)‐block‐poly(propylene glycol)(PBSP) by means of differential scanning calorimetry, polarized light microscopy, and wide angle X‐ray diffraction. Avrami equation was used to describe the isothermal crystallization kinetics. For nonisothermal crystallization studies, the Avrami equation modified by Jeziorny, and the model combining Avrami equation and Ozawa equation were employed. The results showed that the introduction of poly(propylene glycol) soft segment led to suppression of crystallization of PBS hard segment. The melting behavior of the isothermally and nonisothermally crystallized samples was also studied. Results showed that the isothermally crystallized samples exhibited two melting endotherms, whereas only one melting endotherm was shown after nonisothermal crystallization. The spherulitic morphology of PBSP and wide angle X‐ray diffraction showed that the polyether segments were excluded from the crystals and resided in between crystalline PBS lamellae and mixed with amorphous PBS. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

丙烯酰胺的结晶动力学

采用MSMPR连续结晶器研究了丙烯酰胺的成核 -生长动力学。实验结果表明 ,丙烯酰胺的晶体生长基本符合生长速率与粒度无关的ΔL定律。在小于 1 0 0 μm的晶体粒度范围内 ,存在大量的细小晶粒 ,分析了产生这种现象的 4种可能原因。得到结晶温度分别为 1 0、1 5、2 0℃时 ,丙烯酰胺的成核 -生长动力学模型分别为 :n0 =1 2 6× 1 0 - 5G3 6 6 、n0 =3 92× 1 0 - 5G2 92 、n0 =7 65× 1 0 - 5G3 31 。在 1 0～ 2 0℃内 ,丙烯酰胺的成核 -生长动力学级数为 4 30。动力学级数对温度敏感性较小 ,不能通过调节晶浆密度来控制晶体产品的主粒度。进行了丙烯酰胺结晶的应用研究 ,完成了连续三步式结晶新工艺的概念设计。     

Crystallization behavior and morphology of polylactic acid (PLA) with aromatic sulfonate derivative

This article provides a detailed investigation of crystallization behavior and morphology of polylactic acid (PLA) in the presence of a nucleating agent: potassium salt of 5‐dimethyl sulfoisothalate, an aromatic sulfonate derivative (Lak‐301). Isothermal crystallization kinetics of PLA melt mixed with Lak at concentrations of 0.25–1 wt % was investigated at a range of crystallization temperature, 140–150 °C. To gain further insight on the effect of Lak, nonisothermal differential scanning calorimetry (DSC), wide angle X‐ray diffraction (WAXD), polarized optical microscope (POM), heat deflection temperature (HDT), and rheology were also performed. At 0.25 wt % Lak, crystallinity of PLA increased from 10% to 45%, and in 1 wt % Lak, maximum crystallinity of 50% was achieved. With 1 wt % Lak, crystallization half time reduced to 1.8 min from 61 min for neat PLA at 140 °C. The isothermal crystallization kinetics was analyzed using Avrami model. Values of the Avrami exponent for PLA with Lak were mainly in the range of 3 indicating a three dimensional crystal growth is favored. Crystallization rate was found to increase with increase in Lak content. Observation from POM confirmed that the presence of Lak in the PLA matrix significantly increased the nucleation density. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43673.     

结晶动力学研究进展

综述了溶液结晶动力学及聚合物结晶动力学的现状及进展,并对其研究中存在的缺陷与不足进行了评述.     

聚四氟乙烯/聚苯酯复合材料非等温结晶动力学研究

通过冷压烧结的方法制备了聚四氟乙烯/聚苯酯（PTFE/POB）复合材料。采用差示扫描量热法（DSC）研究了PTFE/POB复合材料的非等温结晶行为,并利用Jeziorny法对所得DSC数据进行分析。结果表明,随着冷却速率的增加,结晶峰向低温方向移动,结晶温度范围增大,结晶度下降;Jeziorny方程能够较好地描述PTFE/POB复合材料的非等温结晶动力学;POB有异相成核作用,改善了PTFE的结晶性能,提高了PTFE的结晶速率。     

Spherulitic Morphology and Crystallization Kinetics of Poly(vinylidene fluoride)/Poly(vinyl acetate) Blends

Spherulitic morphology and crystallization kinetics of the blends of poly(vinylidene fluoride) (PVDF) and poly(vinyl acetate) (PVAc) prepared by solution casting films have been investigated by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The results suggested that PVAc was mainly segregated into the interlamellar and/or interfibrillar regions due to the volume-filling spherulitic morphology observed. As for the results of crystallization kinetics, it was found that both the PVDF spherulitic growth rate (G ^PVDF) and the overall crystallization rate constant (k _n ) were depressed with either the addition of PVAc component or the increase of crystallization temperature (T _c). The kinetics retardation was attributed to the decrease in PVDF molecular mobility and dilution of PVDF concentration due to the addition of PVAc, which has a higher glass transition temperature (T _g).     

Crystallization behavior of PHA/PEDEA oligoester blends

The crystallization behavior of oligoester blends prepared from crystalline poly(hexanediol adipate) (PHA) and amorphous poly(ethylene diethylene glycol adipate) (PEDEA) was studied using POM, WAXD, and DSC. The crystal form of both PHA and the blends are spherulites. The crystallinity, melting enthalpies, and crystallization rate increased with increased PHA content in the blends. Two sharp diffraction peaks of each blend were detected at the same position, where, respectively, 2θ = 21.3° and 24.1°. The research on the crystallization kinetics showed that the Avrami exponent of all the oligoester blends is approximately 4. It was demonstrated that the crystallization mechanism of PHA is not disturbed by amorphous PEDEA. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1363–1368, 2002; DOI 10.1002/app.10268     

Crystallization and melting behavior of iPP studied by DSC

This article is a part of a study of model and bulk composites, based on isotactic polypropylene (i-PP) and glass (or carbon) fibers, produced from knitted textile preforms of hybrid yarns. First, we report the results on crystallization and fusion of textile-grade i-PP, used for the processing of hybrid yarns and the corresponding knitted fabrics. The kinetics of the crystallization process, in the dynamic and isothermal regime, was followed by DSC, and the results were analyzed by Avrami, Ozawa, and Harnisch-Muschik methods. Isothermal crystallization of i-PP was carried out at 388–400 K, and values for the Avrami exponent ranging from 1.93 to 4.39 were determined. The equilibrium melting temperature was determined by the Hoffman-Weeks method, and γ = 2.54 was found. Double melting peaks were observed both when the crystallization was performed at lower temperatures (isothermal regime) and at higher cooling rates (nonisothermal regime). A single melting peak appeared upon melting following isothermal crystallization at 400 K. The nonisothermal kinetics data showed that the peak crystallization temperature changes from 377 to 386 K as the cooling rate decreases from 20 to 3 K/min. Applying the Ozawa method, a value of the exponent n = 2.33 was determined, which is in agreement with the results for isothermal crystallization at 391–400 K. The Harnisch-Muschik approach was also applied to compare the results for n, and a similar trend in the results of isothermal and nonisothermal crystallization was found, due to the predominant homogeneous mechanism of nucleation at lower cooling rates (lower isothermal T_c) in spite of being heterogeneous at higher cooling rates (higher isothermal T_c). © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 395–404, 1998     

聚甲醛等温结晶动力学研究

采用差示扫描量热法(DSC)研究了纯聚甲醛和加入成核剂氮化硼(BN)的聚甲醛等温结晶动力学,采用Avrami方程和L H方程得到了在不同结晶温度下的K、t1/2、n和σe值,探讨了成核剂BN对聚甲醛的结晶成核作用。实验证明,加入氮化硼后,聚甲醛的结晶峰温度和起始结晶温度提高,结晶过程为异相三维生长过程,结晶速率明显加快,半结晶时间和表面自由能下降,说明BN是一种较好的成核剂。     

Influence of Hydroxyvalerate Content on the Crystallization Kinetics of Poly(hydroxybutyrate-co-hydroxyvalerate)

Influence of hydroxyvalerate (HV) content on the crystallization kinetics of hydroxybutyrate (HB) units in random poly(hydroxybutyrate-co-hydroxyvalerate) (P(HB-co-HV)) copolymers has been studied by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). It was found that the crystallization kinetics of HB units was strongly affected by the presence of the ethyl side chain of HV units whether under the non-isothermal or isothermal crystallization conditions. The spherulitic growth rate (G) and overallall crystallization rate (k _n ) of HB units decreased with increasing HV content. Both G and k _n exhibited the maxima, G ^max and k _n ^max, which showed a gradual shift toward lower temperatures with increasing HV content, which may be attributed to the depression in the equilibrium melting point (T _m ⁰) and nucleation factor (K _g). The temperature corresponding k _n ^max was different from G ^max due to the depression of nucleation rate with the degree of undercooling was more susceptible than that of the growth rate. According to the Lauritzen–Hoffman theory of secondary nucleation, the crystallization of HB units in P(HB-co-HV) copolymers was similar to that of neat PHB as regime III and n=4 growth process.     

电石渣在不同气氛下析晶动力学研究

以电石渣为研究对象,通过热分析对不同气氛下的电石渣热分解过程进行了研究,并对电石渣热分解产生的产物采用熔融法制备CaO-Al2O3-SiO2系微晶玻璃.通过差热分析并利用修正后的Johnson-Mehl-Avrami(JMA)方程和Augis-Bennett方程,分析了不同气氛下电石渣制备微晶玻璃过程中的析晶规律.结果表明:不同气氛下对电石渣的失重率有所不同,在氮气气氛下,电石渣总失重率为22.66％:而在空气气氛下电石渣的总失重率为24.54％.并对以电石渣为原料制备微晶玻璃过程中不同气氛下的析晶行为进行了探讨,在氮气气氛下的析晶活化能310.99kJ/mol低于在空气气氛下的析晶活化能353.43 kJ/mol,根据Augis-Bennett方程对不同气氛下的晶化机制进行研究,发现氮气气氛下其晶化机制以三维体积晶化方式进行,而在空气气氛下则以二维晶化方式进行.     

UHMWPP／UHMWPE合金纤维非等温结晶动力学研究

运用DSC手段研究了UHMWPP／UHMWPE合金纤维的等温结晶行为，对所得的实验数据用修正Avrami方程的Jeziorny法进行处理，发现随冷却速率的提高，半结晶的时间t1/2缩短，表明冷却速率加快时，结晶速率也随之加快，纯UHMWPP主要是以三维球晶的方式进行结晶生长，UHMWPE的加入起到核剂的作用，随着成核剂含量的增加，UHMWPP的结晶维数将降低.     

生物大分子结晶过程的动力学

阐述了生物大分子结晶的一般过程,分析了结晶的机制和动力学.     

Crystallization and melting behavior of biodegradable poly(ethylene succinate‐co‐6 mol % butylene succinate)

The crystallization, melting behavior, and spherulitic growth kinetics of biodegradable poly(ethylene succinate‐co‐6 mol % butylene succinate) [P(ES‐co‐6 mol % BS)] were investigated and compared with those of the homopolymer poly(ethylene succinate) (PES) in this work. The crystal structure of P(ES‐co‐6 mol % BS) was the same as that of neat PES, but the crystallinity decreased slightly because of the incorporation of the butylene succinate content. The glass‐transition temperature decreased slightly for P(ES‐co‐6 mol % BS) compared to that for neat PES. The melting point of P(ES‐co‐6 mol % BS) decreased apparently; moreover, the equilibrium melting point was also reduced. Two melting endotherms were found for P(ES‐co‐6 mol % BS) after isothermal crystallization; this was ascribed to the melting, recrystallization, and remelting mechanism. The spherulitic growth rate of P(ES‐co‐6 mol % BS) was slower than that of neat PES at a given crystallization temperature. Both neat PES and P(ES‐co‐6 mol % BS) exhibited a crystallization regime II to III transition; moreover, the crystallization regime transition temperature of P(ES‐co‐6 mol % BS) shifted to a low temperature compared with that of neat PES. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

生物基尼龙56的等温结晶性能研究

采用差示扫描量热仪和带有热台的偏光显微镜对生物基尼龙56的等温结晶性能进行了研究。用Avrami方程对等温结晶过程及其动力学进行了分析,得出Avrami指数(n值)在2.30~3.37之间,推测其晶体生长方式为三维球状生长;采用Arrhenius方程计算了生物基尼龙56的等温结晶活化能(ΔE)为-99.04 kJ/mol。偏光显微镜研究证实了上述推测,同时发现球晶半径与结晶时间呈线性关系,求得了球晶的生长速率。     

聚丙烯／滑石粉复合材料的等温结晶动力学

用差示扫描量热法(DSC)研究聚丙烯(PP)及PP／滑石粉复合材料的等温结晶过程。用Avrami方程全面分析PP／滑石粉的等温结晶动力学，并由此获得相关的动力学参数；用Kissinger方程研究滑石粉对PP／滑石粉复合材料结晶活化能的影响。研究表明：加入滑石粉后明显提高PP／滑石粉复合材料的结晶速率和结晶度；证明滑石粉能促进PP材料的结晶，并在PP结晶过程中起到异相成核作用。PP／滑石粉复合材料的等温结晶过程属于典型的异相成核机理。     

五水柠檬酸钠连续结晶动力学研究

研究了五水柠檬酸钠的连续结晶过程。利用马尔文激光粒度分析仪对不同温度和停留时间下连续结晶过程产品的粒度分布进行分析。通过实验数据和粒度无关生长模型,分别计算了连续结晶过程中五水柠檬酸钠晶体生长与成核速率方程。研究表明,在33.3℃的连续结晶过程中,五水柠檬酸钠的成核速率较生长速率对溶液的过饱和度变化更敏感,增加溶液过饱和度更易形成较小粒度的晶体。