低硅SAPO-34分子筛的复合模板剂法合成及其对甲醇制烯烃的催化性能

系统考察了模板剂比例和晶化条件对复合模板剂(三乙胺+四乙基氢氧化铵)法合成低硅SAPO-34分子筛的影响;评价了合成产物对甲醇制烯烃的催化性能.结果表明,190℃晶化时不易合成低硅SAPO-34分子筛,而170℃晶化、模板剂组成为2Et3N+0.3TEAOH时可合成纯相SAPO-34分子筛.较高温度晶化时,延长晶化时间,SAPO-34有向SAPO-5转晶的趋势,而较低温度晶化时则相反.与晶化3 d的分子筛样品相比,170℃晶化5 d后的分子筛样品的比表面积较大、强酸中心较多、弱酸中心较少、对甲醇制烯烃反应的催化寿命较长.     

Molecular segregation and nucleation of poly(ethylene oxide) crystallized from the melt. I. Calorimetric study

Thermal analysis is used to elucidate the fusion of fractions of poly(ethylene oxide) of from 3500 to 5000000 molecular weight. In addition, the equilibrium and nonequilibrium phase diagrams of binary mixtures of these fractions have been studied. Complete segregation from high-molecular-weight polymer is possible up to at leat 20000 molecular weight. This segregation is not governed by the melting/crystallization equilibrium, but rather by molecular nucleation. Over a broader crystallization temperature range three regions can be identified. At low crystallization temperature, solid solutions result, at higher temperature one finds an intermediate type of crystallization, and ultimately one reaches complete, eutectic segregation. This work will be followed by analysis of the kinetics of crystallization.     

链缠结对聚合物结晶行为的影响

链缠结是聚合物分子链相互作用的一种形式 ,它主要影响分子链的长程运动 .自链缠结的概念被提出以来 ,人们对聚合物粘弹性、流变行为和网络平衡力学等进行了理论研究和实验验证 .然而 ,在聚合物结晶领域 ,链缠结对结晶过程的影响一直存在着很大的争论 .Flory等 [1] 认为 ,聚合物结晶时分子链根本没有足够的时间进行构象调整 ,分子链进入晶格后 ,使大量的缠结链段被挤入非晶区 ,并由此建立了聚合物结晶“插线板”模型 .Hoffman等 [2 ]根据单根分子链从过冷熔体“卷饶”到晶体前沿所需的时间进行估算 ,结果比 Flory预言的快约 3～ 5个数量级…     

The influence of recycled material on the crystallization kinetics of thermoplastic polymers

The injection moulding of semi-crystalline thermoplastic polymers requires an exact knowledge of the thermodynamic data and of the crystallization kinetics. The behaviour of the polymer melt during rapid cooling in the mould determines, to a great extent, the quality and usability of a final product. Technical raw materials are often equipped with nucleating agents in order to obtain crystallization within the desired temperature range and at the required rate. The use of recycled material (regranulate) shows an analogous effect such as the addition of nucleating agents, i.e. crystallization begins at a higher temperature and a higher crystallization rate is detected compared to materials without added regranulate. Heat flux DSC was used to study the crystallization of polyamides, polyolefins and polyoxymethylene during cooling at various cooling rates. Although the temperature gradients and pressures which occur in the proceesing machine cannot be realised in DSC tests, the DSC results reproduce the direction of influence of the regranulate additive very clearly.     

Modulated temperature DSC measurements relating to the cold crystallization process of poly(ethylene terephtalate)

The modulated temperature differential scanning calorimetric method (MT-DSC) yields three temperature dependent signals, an underlying heat capacity curve from the underlying heat flow rate (corresponding to the conventional DSC signal), and a complex heat capacity curve with a real part (storage heat capacity) and an imaginary part (loss heat capacity). These curves have been measured in the cold crystallization region for poly(ethylene terephtalate) with a modified Perkin-Elmer DSC-7. The underlying curve shows the well known large exothermic crystallization peak. The storage heat capacity shows a step change which reproduces the change in heat capacity during crystallization. This curve may be used as baseline, to separate the crystallization heat flow rate from the underlying heat flow rate curve. The loss heat capacity curve exhibits a small exothermic peak at the temperature of the step change of the storage curve. It could be caused by changes of the molecular mobility during crystallization.Dedicated to Professor Wunderlich on the occasion of his 65th birthday     

An efficient organic additive to control the crystallization rate of aliphatic polyketone: A non-isothermal crystallization kinetics study

Three types of organic compounds—two carboxylic acids and an anhydride, were used as additives for polyketone(PK). The effect of the additive structure and their feed ratios on the melting temperature, crystallization temperature, and crystallization rate of PK were studied. We found that the crystallization temperature could be reduced significantly by introducing a small quantity of organic additive, in particular, an anhydride. On addition of 1 phr of anhydride, the crystallization temperature was reduced by 10.7 ℃. Therefore, the non-isothermal crystallization kinetics of aliphatic PK/anhydride blends with various feed ratios was investigated using DSC. The results were analyzed by various theoretical models, such as Avrami, Ozawa and combined Avrami-Ozawa models.     

Investigation of polyamide 12 isothermal crystallization through the application of the phase-field model

Crystallization of polyamide 12 (PA12) is an essential process requiring thorough investigation for evaluating the mechanical properties after the polymer parts are manufactured. The change in crystallization temperature results in different crystallization behaviors for PA12. Hence, the crystal morphology of PA12 achieved provides important information about crystallization behavior, especially for those produced through additive manufacturing due to its heterogenous cooling rate in a single print bed. Considering the need of investigating PA12 crystallization using phase-field modeling, this paper aims to simulate the spherulite morphology of PA12 undergoing isothermal crystallization. This model is compared with the spherulite morphologies obtained from the optical microscopy test. The model shows that PA12 spherulites have thicker dendrites when the isothermal temperature is higher. The present phase-field model can determine the spherulite morphologies of bulk printed PA12 based on the crystallization condition and be used to evaluate the properties of the printed part.     

ZSM-5分子筛结晶度及晶粒大小的影响因素

以硅溶胶为硅源,偏铝酸钠为铝源,用晶种法制备ZSM-5分子筛.考察了物料混合方式、陈化时间、晶化时间、晶化温度、碱度和水量等对ZSM-5分子筛相对结晶度和晶粒大小的影响.用X射线衍射仪(XRD)、扫描电子显微镜(SEM)和激光粒度分析等对所合成样品进行了表征.结果表明:在一定的高碱度条件下形成高浓度的硅铝酸盐凝胶,才能合成出晶化良好的样品,ZSM-5分子筛是按固相机理形成的;合成ZSM-5分子筛的相对结晶度和平均颗粒度均随晶化温度的升高及硅铝酸盐凝胶浓度的增加而增大,在室温陈化24 h、180℃晶化12～24 h时相对结晶度最高,平均颗粒度基本上与陈化时间无关.     

Nucleation of crystallization in molten isotactic polybutene-1

Droplet experiments have been performed on polybutene-1. It was found that this polymer can be cooled to room temperature without homogeneous nucleation of crystallization. It was also found that when the polymer was heterogeneously nucleated, form I (as well as form II) could be crystallized directly from the melt. The melting point of droplets crystallized in form I near room temperature decreased with increasing crystallization temperature, while the melting point of the droplets crystallized in form I at the highest temperatures increased with increasing crystallization temperature. There was a broad minimum at about 60°C. in the melting point versus crystallization temperature curve.     

Prediction of the induction period of crystallization of naproxen in solid dispersion using differential scanning calorimetry

The induction period of crystallization of amorphous naproxen in solid dispersion was measured by DSC. Hydroxypropylmethylcellulose acetate succinate LG (HPMCAS-LG) was selected as a polymer of solid dispersion, because of the excellent inhibitory effect of crystallization. Naproxen was chosen as a model drug having poor water solubility and poor physical stability of glassy state. The prediction of crystallization of amorphous naproxen in solid dispersion at the desired storage temperature or the desired polymer content was carried out. If the storage condition satisfied the requirement that was either more than 90% of HPMCAS-LG content at 333 K or below storage temperature of 301 K for 50% HPMCAS-LG content, the induction period of crystallization of naproxen in solid dispersion would be more than 1 year. The storage period of amorphous drug in solid dispersion of desired storage temperature and desired drug content might be predictable from measurement data of induction period of crystallization.     

Study of the crystallization behaviors of isotactic polypropylene with sodium benzoate as a specific versatile nucleating agent

Sodium benzoate (SB), a conventional nucleating agent of α‐phase isotactic polypropylene (iPP) was discovered to induce the creation of β‐phase iPP under certain crystalline conditions. Polarized optical microscopy (POM) and wide angle X‐ray diffraction (WAXD) were carried out to verify the versatile nucleating activity of SB and investigate the influences of SB's content, isothermal crystallization temperature, and crystallization time on the formation of β‐phase iPP. The current experimental results indicated that, under isothermal crystallization conditions, SB showed peculiar nucleating characteristics on inducing iPP crystallization which were different from those of the commercial β form nucleating agent (TMB‐5). The content of β crystal form of iPP nucleated with SB (PP/SB) increased initially with the increase of crystallization temperature, nucleating agent (SB) percentage or crystallization time, reached a maximum value, and then decreased as the crystallization temperature, nucleating agent percentage or crystallization time further increased. While the content of β crystal form of iPP nucleated with TMB‐5 (PP/TMB‐5) showed a completely different changing pattern with the crystallization conditions. The obvious difference of the two kinds of nucleating agents on inducing iPP crystallization can be explained by the versatile nucleating ability of SB. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1183–1192, 2008     

Effects of crystallization temperature and blend ratio on the crystal structure of poly(butylene adipate) in the poly(butylene adipate)/poly(butylene succinate) blends

The effects of crystallization temperature and blend ratio on the polymorphic crystal structures of poly(butylene adipate)(PBA) in poly(butylene succinate)(PBS)/poly(butylene adipate)(PBS/PBA) blends were studied by means of differential scanning calorimetry(DSC), wide-angle X-ray diffraction(XRD) and atomic force microscopy(AFM). It was revealed that the polymorphism of PBA can be regulated by the blend ratio even in a non-isothermal crystallization process. The results demonstrate that high temperature favors flat-on α crystals, while low temperature contributes to edge-on β crystals. It was also found that the effect of blend ratio on the crystallization mechanism of PBA is well coincident with that of the crystallization temperature. The increment of PBS content in the PBS/PBA blend gives rise to more β-form crystals of PBA. For those PBS/PBA blends with low PBA content, the interlamellar phase segregation of PBA makes its molecular chains so difficult to diffuse from one isolated microdomain to another that high crystallization temperature and sufficiently long crystallization time will be required if the PBA α-type crystals are targeted.     

热致型液晶聚合物的等温和非等温晶化动力学

利用等温和非等温方法详细研究了芳香族聚酯──热致型聚合物对，对’－联苯二甲酸二辛酯的结晶相和液晶相形成机理，并计算了相变过程中的表面自由能与温度系数，研究结果表明：从介晶相开始的结晶过程是二维异相成核、三维线性增长的，而从各向同性液相开始的液晶相形成过程则是二维异相成核二维线性增长的．对两个晶化过程的表面自由能的研究表明，该聚合物液晶相形成过程的相转变表面自由能比结晶过程小得多，预示了它将具有更大的晶化速率．研究还发现，该聚合物的液晶相形成过程具有比结晶过程大得多的温度敏感性．     

Effects of stereo-defect distribution and molecular mass in the non-isothermal crystallization behavior of β-nucleated isotactic polypropylene

In this study, based on the synthesis of two Ziegler–Natta iPP with nearly same average isotacticity but different uniformities of stereo-defect distribution, we further prepared two series of β-iPP with different molecular masses by addition of different concentration of peroxide. We investigated the combination effects of stereo-defect distribution and molecular mass on the non-isothermal crystallization behavior and polymorphic composition behavior of β-iPP by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), and scanning electron microscope (SEM). The results of non-isothermal crystallization kinetics revealed that the iPP molecular mass has only slight influence on the crystallization temperature of β-iPP, while the uniformity of stereo-defect distribution not only evidently influences the crystallization temperature, but also affects the dependency of crystallization temperature on cooling rate. β-iPP with less uniformity of stereo-defect distribution leads to higher dependency of crystallization temperature on the cooling rate. The calculation of crystallization activation energy ΔE showed that the lower the molecular mass, the lower the ΔE, indicating that it is easier for the occurrence of crystallization. Meanwhile, iPP with more uniform stereo-defect distribution has lower ΔE. Moreover, both stereo-defect distribution and molecular mass are important factors in determining the polymorphic composition. A more uniform stereo-defect distribution is more favorable for the β-phase crystallization; the lower the molecular mass, the harder for β-phase crystallization to take place. However, compared with iPP molecular mass, the uniformity of stereo-defect distribution is the first-order factor in determining the β-phase crystallization of iPP. Moreover, the thermal stability and the dependency of β-phase proportion on the cooling rate are also found to be highly dependent on the iPP molecular mass.     

聚丙烯-g-聚氨酯共聚物组成对其结晶行为的影响

接枝共聚物;聚丙烯-g-聚氨酯共聚物组成对其结晶行为的影响     

Interpretation of the nonisothermal crystallization kinetics of polypropylene using a power law nucleation rate function

A nucleation rate function is proposed for use in analyzing the overall crystallization kinetics of polymers. This function allows for the possibility that the nucleation rate varies substantially during the crystallization. This feature is particularly useful in analyzing nonisothermal crystallization, but it can be used to analyze isothermal crystallization as well. The nucleation rate function was used in the derivation of a modified transformation kinetics equation of the Avrami type. The modified Avrami equation was found to be suitable for kinetics analysis for the data obtained from nonisothermal crystallization at rapid cooling rates. Kinetics parameters used to describe nonisothermal crystallization under rapid cooling rates are presented and discussed. These include crystallization induction time, plateau (crystallization) temperature, crystallization half-time, crystallization rate constant, Avrami index, and newly defined quantities called nucleation index, geometric index, and nucleation rate constant. The procedure used to obtain the nucleation rate constant and nucleation index for the nucleation rate function is described and illustrated by application to the analysis of the crystallization kinetics of polypropylene. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1077–1093, 1997     

Influence of ozonized kraft lignin on the crystallization of CaCO3

Results are reviewed from a study examining how structural modifications introduced by ozonization enhance the influence of kraft lignin on the crystallization of CaCO(3). Ozone treatment of kraft lignin in an aqueous environment is shown to increase its carboxylic acid and overall oxygen content and reduce its molecular weight. Calcium concentration and temperature were monitored in heated supersaturated solutions containing ozonized kraft lignins to gauge their influence on CaCO(3) crystallization processes. The presence of kraft lignin raises the temperature necessary to induce crystallization. This effect is shown to level off at relatively low lignin concentrations and be dependent on the extent of ozone treatment the kraft lignin has undergone. A linear correlation is found between crystallization temperatures and the carboxylic acid content of ozonized lignin samples indicating the introduction of these functional groups plays an important role in enhancing its inhibitory effect. Scanning electron microscopy images of crystals grown in the presence of kraft lignins show significant morphological modifications. These are consistent with specific or pseudo specific interactions between the lignin and crystal faces of calcite to inhibit growth parallel to its c axis. The influence over crystal morphology demonstrated by modified kraft lignin increases with increasing ozonization. Also presented here are crystallization temperature data for a range of kraft lignin ultrafiltration fractions, which indicate that the optimal (nominal) molecular weight of kraft lignin for inhibiting the crystallization of CaCO(3) lies between 5000 and 10000.     

Influence of crystallization conditions on the crystalline transformation behavior of nylon 10 14

Three kinds of nylon 10 14 crystals with different perfections were prepared under various crystallization conditions. The Brill transition behavior of these nylon 10 14 crystals was investigated by variable-temperature X-ray diffraction. It was found that the crystallization conditions influence the Brill transition temperature greatly. The Brill transition temperature of the lamellar crystals grown from dilute solution is so high that no Brill transition temperature can be observed before melting. However, for crystals postannealed at 125 °C, the Brill transition temperature is as low as 130 °C. The results show that the Brill transition behavior of nylons is strongly dependent on the crystallization conditions, for example, the perfections of the crystals.     

高分子液晶态有序性对其结晶过程的影响

采用退偏振光强度法、ＳＡＬＳ和ＰＯＭ测定了高分子液晶态有序微区结构随体系温度变化的规律,并用ＤＳＣ法研究具有不同有序微区结构尺寸的液晶态的结晶过程．结果发现,高分子液晶态有序性或有序微区结构是随着体系退火温度和时间的变化而变化．同时从相应的不同有序性为起始态进行结晶时,其结晶速率明显不同．并讨论了高分子液晶态的结晶机理