Measurement of adsorption characteristics of alumina and activated carbon using a quartz crystal resonator with <Emphasis Type="Italic">i</Emphasis>-butane

A new device for measuring the pore characteristics of adsorbents is developed for fast measurement and convenient sample handling. The proposed device utilizes a quartz crystal resonator capable of detecting the change of mass loading in nanogram scale. The measured material is coated on the electrode surface of the resonator, and the change of resonant frequency of the resonator at different pressures of adsorbate gas is converted into the adsorbed amount used in the computation of the adsorption surface area and pore size. For the performance evaluation of the device, alumina and activated carbon are tested with the adsorbate, i-butane. The experimental results show that the proposed device gives comparable measurements with some deviation to the reference values of the adsorption characteristics. It is proved that the device is relatively simple and requires short measurement time and the mild condition of sample handling.     

Crystallization behavior of polyamide 11/multiwalled carbon nanotube composites

Differential scanning calorimetry (DSC) was used to investigate the isothermal and nonisothermal crystallization kinetics of polyamide11 (PA11)/multiwalled carbon nanotube (MWNTs) composites. The Avrami equation was used for describing the isothermal crystallization behavior of neat PA11 and its nanocomposites. For nonisothermal studies, the Avrami model, the Ozawa model, and the method combining the Avrami and Ozawa theories were employed. It was found that the Avrami exponent n decreased with the addition of MWNTs during the isothermal crystallization, indicating that the MWNTs accelerated the crystallization process as nucleating agent. The kinetic analysis of nonisothermal crystallization process showed that the presence of carbon nanotubes hindered the mobility of polymer chain segments and dominated the nonisothermal crystallization process. The MWNTs played two competing roles on the crystallization of PA11 nanocomposites: on the one hand, the MWNTs serve as heterogeneous nucleating agent promoting the crystallization process of PA11; on the other hand, the MWNTs hinder the mobility of the polymer chains thus retarding the crystal growth process of PA11. The activation energies of PA11/MWNTs composites for the isothermal and nonisothermal crystallization are lower than neat PA11. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Isothermal and nonisothermal crystallization of poly(aryl ether ketone ketone) with all‐para phenylene linkage

Isothermal and nonisothermal crystallization behavior for PEKK(T) was studied using differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and electron diffraction (ED). In the isothermal crystallization process, the Avrami parameters obtained were n = 2.33–2.69, which shows crystal growth of two‐dimensional extensions consistent with our observations by TEM. The lamellar thickness increases with the crystallization temperature of PEKK(T) crystallized isothermally from the melt. However, for the nonisothermal crystallization of PEKK(T), the results from the modified Avrami analysis show two different crystallization processes. Avrami exponents n₁ = 3.61–5.30, obtained from the primary crystallization process, are much bigger than are the secondary n₂ = 2.26–3.04 and confirmed by the observation of the spherulite morphology. PEKK(T) crystallized isothermally from the melt possesses the same crystal structure (Form I) as that from nonisothermal melt crystallization. The results from TEM observation show that the spherulite radius decreases with an increasing cooling rate. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3431–3438, 2001     

PA11/白炭黑纳米复合材料非等温结晶动力学研究

采用原位聚合法制备了聚酰胺(PA)11/白炭黑纳米复合材料,利用差示扫描量热仪研究了PA11纳米复合材料的非等温结晶过程,用经Jeziorny修正的Avrami方程、Mo法对其非等温结晶动力学进行了分析,计算并得到了非等温结晶动力学参数。结果表明,Avrami方程、Mo法都适用于处理PA11及其纳米复合材料的非等温结晶过程;在非等温结晶过程中,PA11及其纳米复合材料都包括初期结晶和二次结晶两个阶段;Avrami方程和Mo法表明,白炭黑含量较低时可提高复合材料的结晶速率,含量过高时则阻碍晶体的生长。     

Measurement of thermal property of polystyrene using dual quartz crystal resonators

A new device using dual quartz crystal resonators is proposed to determine the thermal property and morphological change of polystyrene. The resonators are installed in a small aluminum cell directly heated and air cooled according to the programmed temperature variation. The resonant frequencies of the dual resonators-one for reference and the other for sample-are measured and analyzed for the morphological change while their temperature varies. The temperatures of the changes are compared with the DSC thermogram and previously reported studies, and it is found that the measurements are comparable to those of the DSC. The proposed device is simple and easy to construct, and a portable system is available with some modification.     

The influence of talc as a nucleation agent on the nonisothermal crystallization and morphology of isotactic polypropylene: The application of the Lauritzen–Hoffmann,Avrami, and Ozawa theories

A new method is proposed, which can be used to analyze the influence of different additives and fillers on the nonisothermal crystallization of polymers. The composites of talc in isotactic polypropylene (i‐PP) were prepared using a corotating twin‐screw extruder. The compounds were subsequently dried and injection molded. PP morphology and talc dispersion were visualized using optical microscopy and computed tomography. Wide‐angle X‐ray scattering and small‐angle X‐ray scattering measurements provided an insight into the crystal structure of PP. The data obtained from nonisothermal DSC measurements were fitted to the Avrami model for the nonisothermal case. The calculated Avrami's exponent (n), which takes into account the influence of talc on the nucleation and growth of the PP crystals, was used in the combination of Lauritzen–Hoffman and Ozawa models to calculate the nucleation parameter (K_g). A good agreement was found between the model predictions and literature values. The examination shows that the developed model extension gives an expected trend in the case of i‐PP filled with talcs from the same origin but with different particle sizes. Furthermore, it is shown that delaminated talc with a higher specific surface is more efficient in nucleation of i‐PP. Thus, the introduced model extension could be a useful tool for comparing of nucleation ability of different additives in the crystallization of polymers. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Thermal properties and crystallization behavior of ultrafine fully‐vulcanized powdered rubber particle toughened polypropylene

Thermal properties and crystallization behavior of ultrafine fully‐vulcanized powdered rubber (UFPR) toughened polypropylene (PP) were studied by Differential scanning calorimetry (DSC) and Wide angle X‐ray diffraction (WAXD) measurements. It was found that the fraction of β‐form in the PP crystal increased at first, then sharply deceased up to zero with increasing UFPR content. This trend did not rely on isothermal crystallization temperature. Moreover, DSC measurements implied that UFPR particles addition affected both isothermal and nonisothermal crystallization behaviors, including the crystallization temperature and the half‐time of crystallization. Furthermore, WAXD test results indicated that the addition of UFPR induced the orientation of the crystallites more or less. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

PEN非等温冷结晶动力学的研究

采用差示扫描量热(DSC)法对聚萘二甲酸乙二醇酯(PEN)的非等温冷结晶动力学进行研究;通过改变升温速率,讨论了PEN冷结晶起始温度与峰顶温度之间存在差值的原因;对比了两种不同的冷结晶起始点的确定方法对冷结晶动力学常数的影响。结果表明:以DSC曲线偏离基线作为PEN冷结晶的起始点,得到的表观Avrami指数很大;用基线延长线与DSC曲线的切线的交点作为冷结晶的起始点和结束点,得到的表观Avrami指数为2.55,且不随升温速率的变化而变化,与等温熔融热结晶方法得到的结果接近,具有相似的结晶生长方式。     

Crystallization behavior of polytetrafluoroethylene (PTFE)

For some polymers such as PTFE, the crystallization is so rapid that it is difficult to observe isothermal crystallization by differential scanning calorimetry (DSC). In this investigation, first, isothermal crystallization kinetics of PTFE was followed by DSC and the results were analyzed by the Avrami method, which showed that PTFE crystallizes one‐dimensionally from preexisting nuclei, presumably impurities. Furthermore, the crystallization activation energy, the equilibrium melting point, and the nucleation rate parameter K_g were calculated in the isothermal crystallization. Second, nonisothermal crystallization was also studied and the result was in accordance with the results of isothermal crystallization. Then, the Kissinger method was used to investigate the activation energy of PTFE in the nonisothermal crystallization. Third, the effect of glass fiber (used as filling) was investigated on crystallization of PTFE matrix. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 990–996, 2002     

The DSC thermal analysis of crystallization behavior in palm oil

Polymorphic behavior of palm oil crystals was studied by DSC isothermal analysis and microscopic observation. Different crystal forms developed specific spherulites depending on the degree of super-cooling from the melt. The A-form crystal was capable of forming a dotted spherulite and the B-form crystal of forming a dendritic spherulite. Experimental results of B form crystallization studied by the DSC and a microscope under kinetic conditions were evaluated using Avarami’s theory, since the behavior of the oil during crystallization related well to that of high polymers. The crystallization process was divided into nucleation and crystal-growth phases to facilitate a theoretical treatment similar to that of high polymers, providing crystals possessing overall structural regularity.     

Investigation of nonisothermal crystallization of hydroxyapatite/ethylene‐vinyl acetate (HA/EVA) composite

Hydroxyapatite/ethylene‐vinyl acetate (HA/EVA) composites were prepared by injection molding and characterized by X‐ray diffraction (XRD) and attenuated total multiple reflection infrared (ATR‐IR) spectroscopy. The nonisothermal crystallization behavior of HA/EVA composites at different cooling rates and with different HA content were examined by differential scanning calorimetry (DSC). The results exhibit the occurrence of interaction between HA and EVA, and the HA particles in EVA matrix act as effective nucleation agent. The addition of HA influences the mechanism of nucleation and growth of EVA crystallites. HA particles, as nucleus, are efficient to promote EVA crystallization at early stage but prevent EVA crystal growth in the late stage. The EVA crystallization in the composite is mainly through heterogeneous nucleation. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

PA11/SiC复合材料非等温结晶动力学研究

通过熔融共混法制备了尼龙11/碳化硅(PA11/SiC)复合材料,利用差示扫描量热仪(DSC)研究了该复合材料的非等温结晶过程,且采用Avrami方程修正的Jeziorny法和Mo法对其非等温结晶动力学进行了研究,并计算得到相关非等温结晶动力学参数。结果表明:Jeziorny法和Mo法都适用于处理PA11及PA11/SiC复合材料的非等温结晶过程,其分析结果均显示,SiC的加入影响了PA11复合材料的非等温结晶行为,少量(1%)SiC的加入促进了PA11复合材料的成核及晶体生长,提高了结晶速率;由Jeziorny法可知,PA11及其复合材料的非等温过程可分为初期结晶和二次结晶两个阶段,在二次结晶阶段,结晶方式为一维线性、二维盘状和三维球晶生长并存。     

Nonisothermal melt and cold crystallization kinetics of poly(aryl ether ketone ether ketone ketone)

Nonisothermal melt and cold crystallization kinetics of poly(aryl ether ketone ether ketone ketone) (PEKEKK) were investigated by differential scanning calorimetry (DSC). The Avrami equation modified by Jeziorny could only describe the primary stage of nonisothermal crystallization kinetics of PEKEKK. Also, the Ozawa equation could not describe its nonisothermal crystallization behavior. A convenient and reasonable kinetic approach was used to describe the nonisothermal crystallization behavior. The crystallization activation energy were estimated to be −264 and 370 KJ/mol for nonisothermal melt and cold crystallization by the Kissinger method. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2865–2871, 2000     

Crystallization kinetics modeling of high density and linear low density polyethylene resins

This paper describes isothermal and nonisothermal crystallization kinetics of a Ziegler‐Natta catalyzed high density polyethylene (HDPE) and linear low density polyethylene (LLDPE) resins. Standard techniques such as differential scanning calorimetry (DSC) and light depolarization microscopy (LDM) techniques were used to measure isothermal kinetics at low supercoolings. DSC was also used to measure nonisothermal crystallization kinetics at low cooling rates. Extrapolation of isothermal crystallization half‐times of Z‐N catalyzed LLDPE resin using the isothermal half‐time analysis led to erroneous predictions, possibly due to Z‐N LLDPE consisting of a mixture of molecules having different amounts of short chain branching (comonomer). However, predicted reciprocal half‐times at high supercoolings, using isothermal half‐time analysis and using nonlinear regression of nonisothermal crystallization kinetics measured at low cooling rates using the differential Nakamura model, of the HDPE were similar to measured reciprocal half times at high supercoolings of a similar HDPE by Patki and Phillips. It is also shown that the differential Nakamura model can be effectively used to model nonisothermal crystallization kinetics of HDPE resins. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Ultrasonic characterization of the crystallization behavior of poly(ethylene terephthalate)

On the basis of the previous observations that the ultrasonic signals are sensitive to the crystallization of polymers (Tatibouet and Piché, Polymer 1991, 32, 3147), we have expanded our efforts to study the detail relationship between the ultrasonic signals and crystallization process in this work. The nonisothermal and isothermal crystallization of virgin poly(ethylene terephthalate) (PET) and PET samples after degradation were studied by using a specially designed pressure‐volume‐temperature (PVT) device, with which an ultrasonic detector was combined. The results showed that the evolution of the ultrasonic signals not only can be used to probe the crystallization process but also can qualitatively characterize the crystallization rate, crystallinity, crystallite size, and amorphous. DSC measurement was used to verify such results. Ultrasonic signals could be as a complementary tool to polymer chain movement and well be applied to characterize the crystallization behavior. Furthermore, the ultrasonic measurement has the potential use to characterize crystallization of products in‐line during processing (i.e., injection molding, micromoulding). © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

聚乙二醇增塑聚乳酸的非等温结晶动力学研究

采用DSC方法对聚乙二醇(PEG)增塑聚乳酸的非等温结晶动力学进行了研究。结果表明,PEG的加入明显提高了聚乳酸的结晶速度。对所得数据分别用Ozawa方程和莫志深方法进行了处理,发现在给定温度范围里非等温结晶时,PLA/PEG主要是以均相成核的三维生长方式结晶;PLA的结晶速度随着PEG分子质量的增加而升高。     

Thermal and crystallization behavior of alloys of polyphenylene sulfide and high-density polyethylene

The thermal and crystallization behavior of alloys of two semicrystalline thermoplastics, namely, polyphenylene sulfide (PPS) and high-density polyethylene (HDPE) were studied by differential scanning calorimetry (DSC). The presence of a second component in the alloy was found to influence the nonisothermal crystallization process of both the component polymers. The crystallization temperature of PPS in the DSC cooling scan is significantly affected, whereas there is little variation in case of HDPE in the composition range studied. The morphological changes observed in both PPS and HDPE are similar. These include larger crystallite size, a narrower crystallite size distribution, and a lower degree of crystallinity in the alloys as compared to the homopolymers. The isothermal crystallization of the component polymers in the alloys is significantly different from that of the homopolymer. The composition dependence of the overall rate of isothermal crystallization is explained in terms of the competing processes of nucleation and crystal growth. The results show that blending of a high melting polymer with a low melting polymer accelerates the crystallization of the high melting polymer, even at low levels of about 10% of the lower melting component.     

Crystal shape monitoring and supersaturation measurement in cooling crystallization with quartz crystal oscillator

A crystallization monitoring system using a quartz crystal oscillator was utilized to predict different shapes of crystal formation by measuring crystal growth rate and to measure supersaturation. Applying different rates of cooling, crystal formation of different shapes was induced, and the frequency variation of the oscillator and the crystal shape observed with an SEM were compared to determine how the frequency variation can be interpreted for the prediction of produced crystal shape. The experimental results obtained from the crystallization of potassium nitrate and cupric sulfate solutions showed that the proposed frequency measurement technique could be applied in the prediction of crystal shape of cooling crystallization processes. In addition, supersaturation was determined from the measurements of solution and coolant temperatures.     

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。     

The effects of crystallization condition on the microstructure and thermal stability of istactic polypropylene nucleated by β‐form nucleating agent

This article deals with the crystallization behaviors of original (prepared in a torque rheometer), DSC crystallization and mold crystallization (quenching and slow nonisothermal crystallization) of isotactic polypropylene (iPP) mixed with β‐form nucleating agent. The microstructure and thermal stability of these samples were investigated. The wide angle X‐ray diffraction (WAXD) results indicate that fast cooling is favorable for β‐form iPP formation. With slower cooling rate and higher concentration of nucleating agent, the lamellar thickness and stability of crystal0s were enhanced. Polarized optical microscopy (POM) and scanning electron microscopy (SEM) both showed that rapid crystallized samples gave rise to tiny spherulites, whereas under slow crystallization condition, nucleated samples could be fully developed in the form of dendritic or transcrystalline structures, depending on the nucleating agent concentration. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011