Determination of lamellar twisting manner in a banded spherulite with scanning microbeam X-ray scattering

We investigated lamellar twisting manner in a banded spherulite, the blend of poly-(?-caprolactone) and poly-(vinyl butyral), with scanning microbeam X-ray diffraction. We obtained the diffraction contour intensity map with a scanning pitch of 1 μm by employing a rotation of a spherulite around its radial direction along which the microbeam scans. The results confirm that the twisting manner depends on the crystallization temperature and that it changes from continuous twisting to step-wise twisting with the increase of crystallization temperature. Moreover, we observed that the phase of long-period lamellar twisting advanced by about 15° compared to that of short-period lamella. In addition, it was confirmed that c-axis of packing structure was normal to lamella, which was represented by dominant short-period lamella.     

Growth process of homogeneously and heterogeneously nucleated spherulites as observed by atomic force microscopy

A poly(bisphenol A octane ether) (BA-C8) was synthesized. The isothermal spherulitic growth process was studied in situ using atomic force microscopy (AFM) at room temperature. For spherulites formed by homogeneous nucleation, the growth process includes the birth of a primary nucleus, the development of a founding lamella and the growth of the founding lamella into a spherulite. An embryo below a critical size is unstable. A stable embryo grows into a founding lamella. There is only one founding lamella in each spherulite. All other lamellae originate from this founding lamella. Two eyes can be seen at the center of a spherulite. For spherulites formed through heterogeneous nucleation, many lamellae grow at the nucleus surface and propagate outward radially. The spherulites acquire spherical symmetry at the early stage of crystallization. No eyes are found for this kind of spherulites.     

Spatial distribution of lamella structure in PCL/PVB band spherulite investigated with microbeam small- and wide-angle X-ray scattering

The microbeam small- and wide-angle X-ray scattering (SAXS/WAXS) technique gives the novel information about micron-scale structural inhomogeneity of polymer crystal. By using this technique, we have studied structural inhomogeneity of lamella within the band spherulite of miscible polymer blend poly(ε caprolactone) (PCL)/poly(vinyl butyral) (PVB) and the structure development of lamella during crystallization. It is known that PCL/PVB forms very large spherulites (∼several mm in radius) with highly regular band structure because of low frequency of nucleation and that PCL/PVB crystallized at 41 °C has at least two kinds of lamella structure (150 Å, 180 Å). With an X-ray microbeam initially fixed outside near the growth front of the band spherulite, we have observed the lamella formation at the local point and have found that the larger long period grows before the appearance of the shorter long period. We have also observed that the orientation of lamella with the larger long period is different from that of lamella with the shorter long period from SAXS experiment with an X-ray microbeam scanning the band spherulite along its radial direction. Further, the discontinuity in lamella twisting was observed from scanning microbeam WAXS. Based on the experimental results, we propose two possible spatial distribution models. The result of PCL/PVB crystallized at 35 °C was also discussed.     

Poly(ε-caprolactone)/poly(ethylene oxide) diblock copolymer. I. Isothermal crystallization and melting behavior

The isothermal crystallization and melting behavior of the poly(ε-caprolactone)(PCL)/poly(ethylene oxide)(PEO) diblock copolymer has been studied by WAXD, SAXS, and DSC methods. Only the PCL block is crystallizable; the PEO block of weight fraction 20% cannot crystallize, although its corresponding homopolymer has strong crystallizability. The long period, amorphous layer, and crystalline lamella of the PCL/PEO block copolymer all increase with the rise in the crystallization temperature, and the thickness of the amorphous layer is much larger than that of crystalline lamella due to the existence of the PEO block in the amorphous region. The isothermal crystallization of the PCL/PEO block copolymer is investigated by using the theory of Turnbull and Fischer. It is found that the amorphous PEO block has a great influence on the nucleation of PCL block crystallization, and the extent of this influence depends on crystallization conditions, especially temperature. The outstanding characteristics are the phenomenon of the double melting peaks in the melting process of the PCL/PEO block copolymer after isothermal crystallization at different temperatures and the transformation of melting peaks from double peaks to a single peak with variations in the crystallization condition. They are related mainly to the existence of the PEO block bonding chemically with the PCL block. In summing up results of investigations into the crystallization and melting behavior of the PCL/PEO block copolymer, it is interesting to notice that when the PCL/PEO block copolymer crystallizes at three different crystallization temperatures, i.e., below 0°C, between 0 and 35°C, and above 35°C, the variation of peak melting temperature is similar to that of overall crystallization rates in the process of isothermal crystallization. The results can be elucidated by the effect of the PEO block on the crystallization of the PCL block, especially its nucleation. © 1996 John Wiley & Sons, Inc.     

不同熔融混炼条件下PET的降解行为和结晶行为

采用不同预处理条件对聚对苯二甲酸乙二醇酯（PET）切片进行熔融混炼,考察了不同熔融混炼条件下PET的降解行为和结晶行为。结果表明,不同条件的熔融混炼过程均导致PET降解,而降解速率和样品含水率密切相关;PET的降解不仅导致其结晶速率提高,也将导致其球晶晶片厚度增加和结晶度增大;PET的结晶峰值温度（Tcp）、结晶起始温度（Tonset）和结晶结束温度（Tendset）与其特性黏度\[η\]之间存在相关关系,表现为\[η\]越小,Tcp越高,结晶速率越快。     

Young modulus and degree of crystallization of highly‐elongated polyoxymethylene

The physical structure of polyoxymethylene (POM) drawn into two steps by a press and a simultaneous biaxial drawing machine was studied and the drawing dependency on the degree of the crystallization, the orientation, and the modulus were analyzed. The stretching ratio by the press reached 6.0 and the tensile modulus of elasticity increased from 2.5 to 4.5 GPa. However, the degree of crystallization decreased slightly. The rupture elongation increased in the lower drawing region and it peaked when the drawing ratio was 1.7. The film stretched by 2 times was drawn by the biaxial drawing machine. The high tensile modulus of elasticity was obtained and the maximum value was 11.5 GPa at 14 times of the drawing ratio. The lamella structure of POM was supposed to loosen and become oriented to the drawing axis ambiguously by the first drawing. The lamella was highly oriented by the second stretching procedure. The tensile strength and the elongation as well as the modulus were analyzed as a function of the degree of the stretching and the crystallization. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1223–1227, 2006     

Extended-chain lamellar packing of poly(3-butylthiophene) in single crystals

We developed an approach, i.e. solvent-assist crystallization (SAC), for growing high quality single crystals of head-to-tail regio-regular poly(3-butylthiophene) (P3BT). By means of atomic force microscopy, electron diffraction and X-ray diffraction, we found that P3BT macromolecules formed lamella single crystals through gradient crystallization, and in the single crystals, molecules packed normal to the lamella with extended-chain conformation with alkyl side chains in the growth front during crystallization.     

Highly Reactive Remelted Belite

Remelted belite showed higher hydration activity and better grindability than the quenched material. Both properties were closely related to the belite microtextures induced by the remelting reaction; after the reaction, the belite showed disintegration of the intracrystalline lamella structure, inclusion of the liquid exsolved on the former lamella boundaries, and crystallization of the liquid during further cooling. The fractures easily penetrated the remelted crystal grains upon grinding, probably along the disintegrated lamella boundaries and/or along the inclusions. The resulting fragments were irregular in shape with high specific surface area, leading to the high hydration activity of the remelted belite.     

Morphology and melting behaviour of poly(vinylidene fluoride) crystallized from the melt

The influence of crystallization temperature on the melting behaviour and the morphology of poly(vinylidene fluoride) (PVF₂) has been investigated. The DSC endotherms of PVF₂ crystallized from the melt show at least two peaks. The peak areas depend on the thermal history of the samples and the heating scan rate. The area of the first peak was found to increase as the crystallization temperature or the scan rate increased. The double peak configuration was attributed to a melting–recrystallization process. Electron microscopy supports these results, for which only one type of lamella was found in the spherulitic structure.     

Experimental study on the effect of molecular weight and chemical composition distribution on the mechanical response of high-density polyethylene

This article aims to appraise the effect of microstructure comprising molecular weight distribution and chemical composition distribution on the mechanical properties of high-density polyethylene (HDPE). HDPE resins were synthesized using several titanium–magnesium-supported Ziegler–Natta catalysts in the industrial gas phase reactor under the same polymerization condition. Gel permeation chromatography and crystallization elution fractionation (CEF) were conducted on the resins to characterize the molecular weight and comonomer distribution. Crystallization, thermal and rheological behavior were evaluated following differential scanning calorimetry, polarization light microscopy, and rheometric mechanical spectrometry. The resins with higher soluble fraction in trichlorobenzene below 80°C (highly branched low molecular weight chains) exhibited longer crystallization time based on the crystallization kinetic obtained from the Avrami model. Rheological determination of the molecular weight between entanglements (M_e) and the average lamella thickness based on the Gibbs–Thomson equation revealed that the entanglement density and impact strength decreased, and the average lamella thickness increased with an increase in the ratio of CEF eluted fraction below 80°C to the crystallizable fraction in the range of 80–90°C.     

Poly[(3‐hydroxybutyrate)‐co‐(3‐hydroxyvalerate)]/layered double hydroxide nanocomposites

BACKGROUND: The thermomechanical performance of poly[(3‐hydroxybutyrate)‐co‐(3‐hydroxyvalerate)] (PHBV) is associated with its crystallization. Enhanced nucleation using a stearate‐functionalized synthetic layered double hydroxide (LDH) presents a potential solution. RESULTS: PHBV crystallization varied with concentration of LDH. At lower LDH concentration, thermal history‐induced cold crystallization was present. The extent of this order–disorder transition decreased with increasing LDH concentration and was completely eliminated at 7 wt% LDH. PHBV did not have a melt recrystallization peak but the introduction of LDH resulted in an increasingly pronounced melt recrystallization with increasing LDH concentration. Polarized optical microscopy coupled with differential scanning calorimetry and wide angle X‐ray diffraction (WAXD) analysis indicated increased lamella thickness in the nanocomposites compared to pure PHBV. WAXD and transmission electron microscopy showed that the nanocomposites had an intercalated but aggregated dispersion. CONCLUSION: The concentration of nanofiller provides unique effects in PHBV. Mechanical performance was found to scale with composition as determined using dynamic mechanical analysis and tensile testing. Copyright © 2008 Society of Chemical Industry     

Nanoscale Phase Separation in Lithium Niobium Silicate Glass by Femtosecond Laser Irradiation

Understanding the phase transformation in glass and the morphology of related nanostructure after femtosecond laser irradiation is of great importance for fabricating functional optics, in which glass crystallization is involved to obtain nonlinear optical properties. We report on the crystallization inside lithium niobium silicate glass induced by fs laser irradiation. Energy‐dispersive X‐ray spectroscopy coupled to scanning transmission electron microscopy (STEM/EDS) and transmission electron microscopy confirm a nanoscale phase separation whereby LiNbO₃ crystals are embedded in lamella‐shaped frames of amorphous SiO₂. The obtained nanostructure may have applications in fabricating second‐order nonlinear optical devices.     

Thermal analysis of poly(phenylene sulfide). II: Non-isothermal crystallization

The non-isothermal crystallization of Fortron poly(phenylene sulfide), PPS, was examined to better understand its behavior during injection molding. The nonisothermal Avrami formalism was applied to this system, but this method was found to be questionable because of the sometimes severe curvature that appears in the plots of the transformed data. A method of ranking crystallization rates at low cooling rates by plotting the peak in the crystallization exotherm versus the cube root of cooling rate has been considered and shown to have limitations at the higher cooling rates of interest. The growth rate expression developed by J. D. Hoffman for polymer crystallization of chain folded lamella in three dimensions has been used to simulate crystallization exotherms. It was found that this could only fit the data at low cooling rates. At high cooling rates it was necessary to use a growth rate expression developed by Calvert and Ulhmann for polymer crystallization without chain folding. When this is used to describe a two dimensional growth geometry, close agreement in the positions of high cooling rate exotherms could be obtained. The implication is that a change in crystallization mechanism is possible as the conditions go from low to high cooling rates.     

云母微晶玻璃析晶动力学的研究

采用差热分析的方法，对ＴｉＯ２作为晶核剂的氟金云母生晶玻璃的析晶动力学参数进行了测定。结果表明：ＴｉＯ２使原始玻璃在晶化过程中产生了先析相钛酸镁，降低了氟金云母相的析晶活化能；氟金云母晶体以二维片层状方式生长，其生长过程受界面过程控制。     

On crystallization phenomena in polytetrafluoroethylene

The crystal thickness of PTFE has been measured for a variety of crystallization conditions. It increases with the temperature and time of crystallization as well as molecular weight, and also with the temperature and time of annealing. The data are fitted by the kinetic theory of chain folding as well as are those for chain-folded polyethylene. On this basis PTFE may be regarded as a chain-folded polymer whose large thickness derives essentially from its low entropy of fusion. It is also suggested that a single theory of polymeric crystallization may be able to predict the crystal thicknesses not only of PTFE and chain-folded polyethylene but also of chain-extended polyethylene, but it would have to be a theory in which account were taken of lamellar thickening behind the narrowed growing edge of a lamella.     

Understanding the effect of silica nanoparticles and exfoliated graphite nanoplatelets on the crystallization behavior of isotactic polypropylene

This study explores how the presence of nanofillers with different structural and chemical characteristics, specifically silica nanoparticles and exfoliated graphite nanoplatelets (GNP), alters the crystallization behavior and polymorphism of a semicrystalline polymer, such as polypropylene (PP). The main focus of this research is to investigate how silica and GNP affect the nucleation and growth of PP crystals during isothermal crystallization. The nonisothermal crystallization behavior, including crystal structures, crystallization temperature, and rate, is also determined. PP composites with nanomaterial content up to 7 wt% were produced by melt mixing and injection molding. Both silica and graphite were found to be effective nucleating agents, significantly increasing the crystallization rate during isothermal crystallization, with greater changes observed in case of GNP composites. The effect of filler type and amount on the PP polymorphism and lamella thickness was studied by X‐ray diffraction and modulated differential scanning calorimetry. Both silica and graphite were found to be effective nucleating agents for the less common β‐phase of PP crystals even at low nanomaterial concentration. α‐?crystal perfection and the recrystallization of the β‐form in the α‐form and/or at the transcrystalline regime were found to be responsible for the recrystallization occurring upon melting in nanocomposites at high silica or medium GNP content. POLYM. ENG. SCI., 55:672–680, 2015. © 2014 Society of Plastics Engineers     

Formation mechanism, chain folding, and growth behavior of the intriguing fiber-like crystal of poly (ethylene oxide-b-ε-caprolactone) block copolymer in ultrathin films

The morphologies, crystallization behavior and chain orientation of a highly asymmetric poly (ethylene oxide-b-ε-caprolactone) (PEO-b-PCL) block copolymer ultrathin films were investigated by using wide-angle X-ray diffraction (WAXD), atomic force microscopy (AFM) and grazing incidence X-ray diffraction (GIXRD) techniques. It is shown that the intriguing fiber-like crystal which seems to be an individual flat-on lamella was first observed in PEO-b-PCL ultrathin film according to our knowledge. The possible mechanism of forming the fiber-like crystals is chiefly ascribed to the rather low molecular weight of PEO-b-PCL and the mutual interaction between crystallization and microphase separation. At the same time, solution concentration and substrate surface energy play a crucial role. Subsequently, chain folding of the fiber-like crystal of PEO-b-PCL in ultrathin films was deduced based on the cell parameters and the lamellar thickness. Isothermal crystallization tests revealed that in the whole growth process, the crystal growths can be divided into two stages, both of which followed the diffusion-limited (DL) mechanism.     

Morphology of syndiotactic polypropylene/alumina nanocomposites

The effect of the addition of 50 nm spherical alumina nanoparticles with hydrophilic or hydrophobic surfaces on the morphology of syndiotactic polypropylene (sPP) was investigated. The filler content in the nanocomposites was 3 wt%. Polarized Optical Microscopy and Small Angle Light Scattering (SALS) studies showed that sPP and the nanocomposites form hedrites. The addition of alumina nanoparticles significantly increased the number of hedrites. A higher number of nucleation sites in the nanocomposites promote a higher crystallization rate, and thus hedritic growth was stopped at the early stage of crystallization. Quantitative evaluations by SALS analysis show that the object size is decreased by not only the crystallization conditions but also the presence of Al₂O₃ nanoparticles. A small amount of Al₂O₃ nanoparticles did not noticeably affect the crystallinity of sPP, but increased the melting point. Transmission Electron Microscopy images showed that the lamellar thickness did not change significantly with the incorporation of nanoparticles. The lamella thickness, however, depends on cooling rates. X-ray diffraction characterization indicated that the sPP and the nanocomposites were crystallized in disordered “form I”. The incorporation of alumina nanoparticles had a small effect on the crystal structure of syndiotactic polypropylene.     

碳纤维增强聚醚醚酮的非等温结晶行为与力学性能

利用聚酰亚胺(PI)作为碳纤维(CF)界面改性剂,制备了界面改性碳纤维增强聚醚醚酮(MCF/PEEK)复合材料。采用差示扫描量热仪(DSC)讨论了CF及其界面改性对PEEK非等温结晶行为的影响机制与作用规律,并基于莫志深法研究了MCF/PEEK的非等温结晶动力学;借助DSC和小角X射线散射仪(SAXS)表征不同降温速率下PEEK基体的结晶结构,采用万能试验机评价了MCF/PEEK的力学性能。结果发现:CF对PEEK的结晶有较为明显的异相成核促进作用,经过PI界面改性之后成核作用有所下降,但结晶行为仍较纯PEEK更容易发生,整体结晶速率更快;随冷却速率的增大,基体结晶度、片晶厚度与长周期均减小,MCF/PEEK的拉伸强度与模量也显著减小,层间断裂韧性提高。     

聚乙烯薄膜拉伸过程中结构变化的原位研究

使用差示扫描量热分析(DSC)研究了其拉伸前后结晶动力学与热力学行为的区别,使用同步加速器小角X射线散射(SAXS)和广角X射线衍射(WAXD)研究了薄膜拉伸过程中晶体结构、尺寸和长周期的变化。结果表明,拉伸使薄膜结晶度提高;拉伸过程中,二维散射图案发生明显变化,片晶结构被破坏后高应力诱导下重新结晶,拉伸使薄膜晶体取向度和晶体尺寸明显增大;随拉伸进行,纵向(拉伸方向)和45°方向的长周期先增大后减小,而横向一直呈下降趋势。聚乙烯工业缠绕膜通常在拉伸应变1.5倍附近下使用,此时薄膜纵向上已经高度取向并形成了拉伸诱导结晶,从而在纵向上有较高的力学强度。而横向上片晶结构尚未完全破坏,仍保持着一定的力学性能,因此综合使用性能较好。