Crystallization of filled nylon 6 III. Non-isothermal crystallization

Summary DSC data on crystallization kinetics from the melt at different cooling rates of nylon 6 containing various amonts of untreated and surface-treated fillers, were analyzed in terms of a modified Kolmogorov-Avrami equation. It was established that mechanism of crystallinity development in molten nylon 6 does not change appreciably in presence of aminosilane-treated glass beads and small amounts of untreated glass beads, whereas time exponentn was found to decrease with increasing filler content in samples containing untreated glass beads and Aerosil. On the other hand, dependence of temperature of the onset of crystal nucleation on cooling rate obeyedm = 2 law for pure nylon 6 and samples containing surface-treated filler, whilem = 4 law seemed to hold for samples containing large amounts of untreated fillers at low cooling rates (m is the exponent at degree of supercooling). It was concluded that although isothermal conditions of crystallization should be preferred for further quantitative investigations of polymer-filler interactions in highly filled polymer melts, the above results qualitatively are consistent with trends discovered in isothermal crystallization experiments.     

Polymeric nature of selenium crystallization. II. Crystallization kinetics and secondary crystallization

The crystallization of elemental selenium has been studied in light of present concepts of crystallization in organic polymers. Bulk-crystallization kinetic data as measured by a dynamic density technique and spherulite growth-rate data as measured by optical microscopy are presented for the temperature range 70°C to 160°C. Plots of extent of isothermal crystallization versus time were sigmoidal in shape. Spherulite growth rates were constant for a given temperature and reached a maximum at approximately 130°C. Evidence is presented for secondary crystallization in selenium, and a model is proposed for destruction of chain folds with interlamellar crystallization during the spherulitic-to-“metallic” transformation above 100°C.     

聚对苯甲酰胺存在下尼龙6的结晶化

用解偏振光强度法和DSC等方法研究了少量聚对苯甲酰胺(PBA)对尼龙6结晶化过程和热行为的影响.利用Avrami方程处理解偏振光强度法的实验结果,得到了尼龙6及含PBA 1%、2%尼龙6的n值分别为3.3、1.6、1.7.DSC结果表明,尼龙6中掺入少量的PBA会使结晶度提高,X射线衍射显示,当尼龙6中加入少量PBA后,晶格结构并未改变。     

Solvent-induced crystallization. I. Crystallization kinetics

The kinetics of crystallization of quenched poly(ethylene terephthalate) (PET) films during the imbibition of methylene chloride (MeCl₂) vapor is studied by density measurements. The effects of film thickness (0.0025–0.086 cm) and temperature (0–38°C) were examined. The data suggest that MeCl₂ transport controls the crystallization in thick films and at elevated temperatures, but that spherulite growth controls in thin films and at reduced temperatures. The application of a mathematical model developed previously supports this mechanistic interpretation of the data.     

Transient and athermal effects in the crystallization of polymers. I. Isothermal crystallization

The isothermal crystallization of poly(propylene) and poly(ethylene terephthalate) was investigated with differential scanning calorimetry and optical microscopy. It was found that the induction time depends on the cooling rate to a constant temperature. The isothermal crystallization of the investigated polymers is a complex process and cannot be adequately described by the simple Avrami equation with time‐independent parameters. The results indicate that crystallization is composed of several nucleation mechanisms. The homogeneous nucleation occurring from thermal fluctuations is preceded by the nucleation on not completely melted crystalline residues that can become stable by an athermal mechanism as well as nucleation on heterogeneities. The nucleation rate depends on time, with the maximum shortly after the start of crystallization attributed to nucleation on crystalline residues (possible athermal nucleation) and on heterogeneities. However, the spherulitic growth rate and the exponent n do not change with the time of crystallization. The time dependence of the crystallization rate corresponds to the changes in the nucleation rate with time. The steady‐state crystallization rate in thermal nucleation is lower than the rate determined in a classical way from the half‐time of crystallization. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1835–1849, 2002     

Grafting Vinyl Monomers onto Nylon 6 Fiber. II. Graft Copolymerization of Methyl Methacrylate onto Nylon 6 Fiber by Photoirradiation in the Presence of Fructose

Photopolymerization of methyl methacrylate (MMA) onto nylon 6 fiber by UV radiation in alcoholic solutions of water-methanol, water-ethanol, and water-n-propanol in the presence of fructose was investigated. The effects of monomer concentration, time of polymerization, fructose concentration, and effect of media have also been studied. Graft add-on (GAO) % greatly enhanced with an increase in monomer concentration and time. With fructose concentration it increases up to 15 mmol/L of fructose and thereafter falls. The GAO in the media is in the following order: W + M + F > W + E + F > W + P + F(W = water; M = methanol; E = ethanol; P = n-propanol). A probable mechanism has been suggested. It appears that the active site is formed on MMA which abstracts an H-atom from the nylon 6 backbone, giving rise to graft of MMA by mutual combination.     

Crystallization of polymers in variable external conditions IV. Isothermal crystallization in the presence of variable tensile stress or hydrostatic pressure

General equations of crystallization in variable conditions have been applied to isothermal crystallization affected by variable tensile stress or hydrostatic pressure. In a system under stress, the crystallization rate involves relaxational and athermal effects, and is controlled by the normal stress difference and the stress rate. Similarily, pressure effects include the hydrostatic pressure and its rate of change. Received: 1 December 1998 Accepted in revised form: 23 March 1999     

Modeling Equilibrium Behavior of Nylon 6, Nylon 6,6 and Nylon 6/6,6 Copolymer

Nylon 6 and nylon 6,6 reaction equilibria depend in a complex way on water concentration and temperature. For example, data sets from six research groups reveal that the apparent equilibrium constant for polycondensation increases with water at low water concentrations, reaches a maximum, and then decreases as the water concentration rises further. In this article, semi‐empirical expressions are proposed to describe the experimentally observed equilibrium behavior for the five main reactions that occur during nylon 6 and nylon 6,6 polymerization. Nine side reactions involving amidine ends, cyclopentanone ends, and hydrated carboxyl ends are used to develop expressions that account for the influence of both water and temperature on these equilibrium constants. Excellent fit to the data, over the entire range of the available nylon 6 and nylon 6,6 literature data, suggests that the proposed equations will be helpful for modeling reaction equilibria for nylon 6/6,6 copolymerization.     

A new look at the crystallization of polyethylene. II. Crystallization from the melt at low supercoolings

This article is part of the general project laid out in Part I (ref. 9) and is concerned with obtaining information on primary (unthickened) crystals of polyethylene formed at low supercoolings. For this, a technique had to be devised by which crystallization could be speeded up so as to eliminate or at least reduce lamellar thickening. Indeed we were able to increase the rate of crystallization by an order of magnitude using a technique which we have called enhanced self-nucleation. Using this technique we find that when viewed under an optical microscope, spherulites crystallize uniformly over the field of view, and not, as is usual, by a radial growth process. Isothermal crystallization in bulk linear polyethylene has been studied by means of the enhanced self-nucleation technique as a function of crystallization time by using Raman LAM and melting points to assess variations of fold length Data have been obtained at very much shorter times than before. At short times, we find a constant fold length; at longer times the crystals thicken linearly with the logarithm of time. Values of the initial fold length for crystallization temperatures between 118 and 130°C are presented. Associated with the thickening at short times we find an induction time which increases with temperature.     

尼龙66/SiO2纳米微粒复合材料的结晶行为

采用双螺杆熔融共混法制备了尼龙66/S iO2纳米微粒复合材料,用X射线衍射法和示差扫描量热法比较了干态和湿态两种制备条件下复合材料的结晶行为;并用修正的Avram i方程的Jeziorny法研究了纳米复合材料的非等温结晶动力学行为.     

Isothermal crystallization of propylene-1-decene copolymers

The isothermal crystallization and subsequent melting behavior of one propylene homopolymer and three propylene-1-decene copolymers with different comonomer contents prepared by metallocene catalyst were studied using differential scanning calorimetry (DSC). It is found that the Avrami exponent of the propylene copolymers decreases gradually with the increase of comonomer content, from 3.0 for the propylene homopolymer to 1.4 for the copolymer with 7.83 mol% 1-decene units. Higher comonomer content also weakens the dependence of crystallization rate constant and crystallization halftime on temperature. Double melting peaks, which correspond to α and γ crystal phases, respectively, are observed for all copolymers under isothermal crystallization. The result shows that higher crystallization temperature is favorable to the segregation of α and γ crystal phases, resulting in higher proportion of γ crystal phase. This revised version was published online in July 2006 with corrections to the Cover Date.     

Studies on crystalline forms of nylon 6. II. Crystallization from the melt

The relative amounts of the α and the γ crystalline forms of nylon 6 obtained from the melt under different crystallization conditions have been studied by an x-ray diffraction procedure by comparison with a calibration curve obtained from the diffraction of standard samples. The weight fraction of the α form decreases with increasing crystallization temperature and that of the γ form increases. Growth of the α form is predominant in crystallization at 100°C and of the α form at 200°C. The amount of the α form tends to increase on annealing at 200°C for specimens crystallized at any temperature.     

尼龙1010结构与性能研究进展（下）：结晶,熔融,性质,改性

本文介绍了尼龙１０１０的结晶过程与动力学、晶体的熔融与转化；并论述了其稀溶液、热降解与动态力学性质及共聚、共混、填充、增强、交联改性方面的研究进展。     

Effect of highly filled ferrites on non-isothermal crystallization behavior of polyamide 6 bonded ferrites

The aim of this study is to characterize the non-isothermal crystallization of polyamide 6 bonded highly filled ferrites which were prepared by the melt extrusion. Especially, the effect of ferrite concentration and its surface property on the non-isothermal crystallization were investigated by means of differential scanning calorimetry. The highly filled ferrite particles acting as obstacles could severely hinder the motion of surrounding chain segments, which were irrespective of surface nature. The ferrite could be modified by silane and obtain a visually enhanced interaction with polymer matrix which evoked the heterogeneous nucleation. Increasing this enhanced interfacial area between polymer-particle can promote the heterogeneous nucleation. However, a strong interaction can slow the motion of surrounding chain segments of particles, thereby producing a competitive effect on the crystallization rate and crystallinity. The plot of crystallization activation energy against concentration also can evaluate dispersion performance of hydrophilic fillers within hydrophobic polymer.     

Solvent-induced crystallization. II. Morphology

The Morphology of quenched poly(ethylene terephthalate) (PET) films crystallized by low-molecular-weight organic penetrants is studied by scanning electron microscopy. Films with thicknesses from ca. 1 mil (0.0025 cm) to ca. 35 mil (0.1 cm) were exposed to methylene chloride (MeCl₂) and N,N-dimethylformamide (DMF) in the temperature ranges 0–38°C and 22–70°C, respectively. The effects on the surface and internal structures of contact with liquids and saturated vapors were examined. Severe porosity at the surface results from contact with the liquids, but only minor surface roughness appears following contact with vapors. Internal porosity developed in the thinnest films (ca. 1 mil) during crystallization in liquid environments. Here, the internal void fraction is greatest along the film centerline and decreases with increasing crystallization temperature. A mathematical model discussed previously accounts for the observed behavior.     

Crystallization of oriented smectic polypropylene I. Thermally induced crystallization

The crystallization induced by thermal treatments of smectic polypropylene fibres has been studied. Analysis was carried out detecting the density and X-ray diffractograms. Density and diffraction data disagree on two important aspects: the critical temperature necessary to activate the crystallization process, and the effects of annealing time on the growth process. The first point seems to suggest that the observed densification at the lower temperatures is related to phenomena differing from a crystallization process, while the observed effects of the annealing time can be explained by assuming that the anisotropy of the fibre structure induces anisotropy in the phase transition and growth process. On the other hand, density and diffraction data agree in indicating that the rate and degree of crystallization increase on increasing the crystallization temperature.     

尼龙1010非等温结晶动力学过程的计算机模拟

根据Ъорохоъский提出的相似于Avrami方程的近似公式 X =1 -exp[-Z(at) n],采用加权最小二乘法 ,对尼龙 1 0 1 0非等温结晶动力学过程进行了模拟 ,编制了模拟非等温结晶动力学过程的软件。该软件可用于精确处理结晶动力学参数 ,也可用于计算机辅助教学。     

尼龙1O1O非等温结晶动力学过程的计算机模拟

根据ъорοхоъский提出的相似于Avrami方程的近似公式X=1-exp[-Z(at)n],采用加权最小二乘法,对尼龙1010非等温结晶动力学过程进行了模拟,编制了模拟非等温结晶动力学过程的软件.该软件可用于精确处理结晶动力学参数,也可用于计算机辅助教学.     

可分散性纳米SiO2/尼龙1010复合材料的结晶行为

采用熔融共混法制备了可分散性纳米SiO2/尼龙1010复合材料.通过X射线衍射和差示扫描量热法对尼龙1010及其复合材料的结晶行为进行了研究.结果表明,SiO2的加入作为结晶的异相成核点,使复合材料的结晶温度升高,熔融温度降低,使其结晶度稍有降低;SiO2的加入并没有改变尼龙1010的结晶形态,只是使尼龙1010的晶格尺寸发生了一定程度的改变.