Effect Of Crystalline Morphology Research Articles

Dielectric properties dependent on crystalline morphology of PP film for HVDC capacitors application

In this paper, the effects and mechanism of crystalline morphology on dielectric loss and breakdown strength of PP film were studied. The crystalline morphology was modified by adding the β-nucleating agent (β-NA). The crystalline types and crystalline morphologies of samples were analysed by the X-Ray diffraction (XRD) and the polarized optical microscopy (POM), respectively. The current integration, representing the dielectric loss, was investigated using the Q(t) method. The DC conductivity was measured at temperature from 25 to 85 °C. The effects of crystalline morphology on the trap energy level distribution were analysed by the isothermal discharge current (IDC). The DC breakdown strength was tested using a pair of ball-plate electrodes at 85 °C. The results of XRD and POM indicate that the addition of β-NA introduced β-spherulites in PP film and the spherulite size of samples with β-NA are smaller the spherulites size of PP without β-NA. The results of IDC indicate that the special structure of β-spherulites introduced deep trap energy levels. The results of Q(t) and DC conductivity indicate that β-spherulites can effectively suppress the current though samples. Besides, the addition of β-nucleating agent increases the DC breakdown strength at 85 °C.

The Effect of the Cooling Process on the Crystalline Morphology and Dielectric Properties of Polythene.

In this study, LDPE samples were prepared by melt blending with different cooling processes, which were natural air cooling, rapid air cooling, water cooling and oil cooling, respectively. According to polarization microscope (PLM) and differential scanning calorimeter (DSC) tests of these four low-density polyethylene (LDPE) samples, the effect of different cooling processes on polythene crystalline morphology could be studied. According to conductivity, dielectric frequency spectra and space charge tests, the effect of crystalline morphology on dielectric macroscopic properties could be explored. The microstructure characteristic results indicated the cooling medium significantly affected polythene crystalline morphology. When the samples were produced with natural air cooling, the crystalline grain size was large. On the other hand, after rapid air cooling, water cooling and oil cooling processes, the samples’ crystalline grain dispersed uniformly, and the grain sizes were lower. The space charge testing results indicate the samples produced with water cooling and oil cooling processes restrained the electrode injection in the process of pressurization. During short-circuits, the rates of charge release of these two samples were fast, and the remaining space charges were fewer. The conductivity and dielectric frequency spectra testing results indicated the conductivities of samples produced with water cooling and oil cooling processes were both less than those of samples produced with a natural air cooling process. Besides, with increasing experimental frequency, the relative dielectric constants of all testing samples decreased. Among them, the relative dielectric constant of the LDPE sample with the natural air cooling process was the largest. However, the crystalline structures of samples produced with rapid air cooling and water cooling processes were close, which restrained the movement of polymer macromolecule chains. Thus, the dielectric constants were lower. Additionally, because of the influence of relaxation polarization and dipole polarization, the dielectric losses of LDPE with water cooling and oil cooling processes increased to varying degrees.

Effect of Crystallinity on Water Vapor Sorption, Diffusion, and Permeation of PLA-Based Nanocomposites.

The effects of crystalline morphology and presence of nanoparticles such as cellulose nanofibers (CNFs), organically modified nanoclay (C30B), or a combination of both on water vapor sorption and diffusion in polylactide (PLA) were evaluated by a quartz spring microbalance (QSM). It was found that the large spherulite size induced by high-temperature processing leads to an increase in water sorption and a substantial reduction of diffusion with increasing crystallinity. Contrarily, small-sized spherulites, arising after low-temperature processing during solvent-casting, showed a different behavior with a slight decrease in both water vapor sorption and diffusion with increasing crystallinity. These observations suggest that solvent-casting at low temperatures should not be used to predict the properties a material will show after industrial-scale processing. From the analysis of the nanocomposite materials, it was concluded that nanoparticles affected the material′s properties not only by themselves but also by modifying the crystalline morphology. Interestingly, this led to CNF showing similar performance to C30B, decreasing water diffusivity (21 vs 27%) on isothermally crystallized materials despite its less favorable geometry. Additionally, the incorporation of 1 wt % CNF and C30B decreased water vapor transmission rate (WVTR) by 24% under an amorphous state but by 44% in a crystallized state, which makes hybrid CNF/C30B composites a promising food packaging material.

Effect of Crystalline Morphology on Electrical Tree Growth Characteristics of High-Density and Low-Density Polyethylene Blend Insulation

The electrical tree initiation and propagation behaviors are a key issue for the polyethylene-based cable insulation. This paper focuses on the effect of crystalline morphology on electrical tree growth characteristics of high-density and low-density polyethylene (HDPE/LDPE) blend insulation. In this paper, the electrical tree growth characteristics of HDPE/LDPE blends with HDPE mass fractions of 0, 10, 15, 20 wt% are investigated under repetitive impulse voltage at 40, 60, 80 °C. It is found that with the rise of HDPE content from 0 to 15 wt%, the growth rate and accumulated damage of electrical tree decreases, with the morphology of electrical tree tending to bush tree. The increasing of voltage amplitude improves the energy of injected charge while the temperature rise leads to the relaxation of molecular chain, which both result in the promotion of collision ionization, thus increasing the density of electrical tree. Compared with branch tree, bush tree illustrates better inhibition of discharge tracks due to uniform electric field at the end of branches. The crystalline characteristics of HDPE/LDPE blends indicate that the crystallinity increases with the addition of HDPE, and the blend comprising 15 wt% HDPE in an LDPE matrix apparently reduces the average size of spherulites and improves the distribution of spherulites evenly. The upsurge of crystal-amorphous interface leads to the increase of deep trap energy level density and the decrease of carrier mobility. Carrier injection and migration at the interface between crystalline and amorphous regions are restrained, thus inhibiting the growth of electrical tree. It is concluded that the crystalline morphology modified by polymer blending has a significant effect on the electrical tree growth characteristics.

Oriented polypropylene cast films consisted of β-transcrystals induced by the nucleating agent self-assembly and its homogeneous membranes with high porosity

In this article, the crystalline morphology of the cast film was controlled by the nucleating agent self-assembled into supramolecular structures at different temperature fields. Subsequently, the effect of crystalline morphology and orientation on porosity and uniformity of microporous membranes was investigated. The morphology of β nucleating agent (NA) networks changes from needle-like agglomerates into flower-like frameworks as PP melt temperature increases. As a result, the crystalline morphology of the cast film changed from β-transcrystals (β-TCs) organized along extrusion direction into random β flower-like crystals with the die temperature increases. Furthermore, microporous membranes with high porosity and uniform micropores distribution could be obtained from the oriented sample consisted of β-TCs. It may relate to the structure that lamellae on β-TCs were usually loosely-packed and lamellae between nearby β-TCs were mutually interdigitated. This work established a relationship between the crystalline structure of cast films and the performance of microporous membranes, which afforded a new insight to obtain PP microporous membranes with excellent performance.

Effect of Crystalline Morphology on Mechanical Properties of PPB Polymer Nanofiber Composite

In this work, the effects of crystalline morphology on the mechanical properties of polycaprolactone/polyvinyl alcohol/ butterfly pea extract (PPB) nanofiber composite were investigated. Biopolymer nanofiber composite of PPB was fabricated by electrospinning technique using polycaprolactone concentration and distance of nozzle to ground collector of 7 wt% and 20 cm, respectively. The influence of applied voltage (vary from 15-25 kV) on the stress-strain curves was also observed. The structure and morphology of electrospun PPB nanofibers were investigated by x-ray diffraction (XRD) and scanning electron microscopy (SEM). It was found that, the degree of crystallinity increased with applied voltage and the mechanical properties was affected by the morphology of PPB nanofiber.

β/α Transformation of β-polypropylene during tensile deformation: effect of crystalline morphology

In this work, the β/α transformation of β-nucleated iPP at different tensile strains has been analyzed. The crystalline morphology of iPP is controlled by the content of β-phase nucleating agent (β-NA), namely, well-developed β-spherulites induced by critical content of β-NA and bundle-like morphology without distinctly developed spherulites by supercritical content of β-NA. It is interesting to observe that the crystalline morphology of β-iPP exhibits great influence on the β/α transformation process during deformation. For well-developed β-spherulites, the content of β-iPP increases at relatively low tensile strain and then decreases gradually with the further increase of tensile strain. However, for bundle-like morphology, the content of β-iPP decreases monotonically with the increase of tensile strain. More important, well-developed β-spherulites, which have integrated crystalline structures, exhibit much smaller degree of β/α transformation as compared with bundle-like morphology at the same tensile strain, leading to more β-iPP maintaining and participating in the deformation process at high strain and consequently, resulting in better ductility. The results of this study further show the importance of crystalline morphology in determining the ductility of β-nucleated iPP on the one hand. On the other hand, this work provides the illuminating explanation for the reason why the well-developed β-spherulites exhibits more excellent ductility compared with the bundle-like morphology.

The effect of crystalline morphology on the degradation of polycaprolactone in a solution of phosphate buffer and lipase

AbstractThe degradation of polycaprolactone (PCL) in a solution of lipase and phosphate buffer has been characterized using a combination of differential scanning calorimetry (DSC) and electron microscopy. The molecular weight of the polymer initially appeared to determine the degradation rate while the degree of crystallinity was found to increase with time. Samples of PCL were also conditioned using DSC to specify a known degree of crystallinity. This approach enabled the effects of molecular weight and degree of crystallinity on the degradation to be separated. It was observed that an increase in either molecular weight or degree of crystallinity reduced the rate of degradation. The work presented in this paper addresses a significant limitation associated with the characterization of “as received” samples and provides a more detailed understanding of the effect of polymer morphology on the degradation process. Copyright © 2008 John Wiley & Sons, Ltd.

323 トコフェロール添加UHMWPEの疲労特性向上における結晶形態の影響(GS-9:バイオマテリア,一般セッション,学術講演)

323 トコフェロール添加UHMWPEの疲労特性向上における結晶形態の影響(GS-9:バイオマテリア,一般セッション,学術講演)

Effects of crystalline morphology on the impact behavior of polypropylene

A series of notched impact tests were made to polypropylene (PP) materials of different crystalline morphology through a certain effective filled nucleating agent (0.1–2 wt.%) and subsequent heat-treatment. A maximum of impact strength exists at the 0.4 wt.% filled quantity of the nucleating agent. It was shown that when the filled quantity of the nucleating agent was below 0.4 wt.%, the spherulite size decreased and the crystallinity increased. The impact strength was controlled mainly by the spherulite size, but when it went beyond 0.4 wt.%, the decline tendency of the spherulite size decreased and tended towards progressive stabilization, the crystallinity still increased and the rising gradient increased. Therefore, crystallinity is the decisive factor in strength property. This illustrates that the appearance of a maximum of impact strength is due to the comprehensive result of the spherulite size and the crystallinity. The succeeding heat-treatment only affected the crystallinity. The spherulite size showed basically little change. The impact strength can be described by a quantitative formula. The fracture surface was composed of the expanding zone, the arc stripe zone and the last fracture zone. The fractal dimension of the expanding zone exists at a maximum at the 0.4 wt.% filled quantity of the nucleating agent. The size of the arc stripe has nothing to do with the quantity of nucleating agent.

Hydrolytic degradation behavior of poly(butylene succinate)s with different crystalline morphologies

The effect of crystalline morphology on the hydrolytic degradation behavior of poly(butylene succinate) (PBS) in an alkaline solution was investigated by using scanning electron microscopy, gel permeation chromatography, and weight loss measurement. Morphological changes were induced on PBS samples by different thermal treatments (i.e., melt quenching or isothermal crystallization) at a constant overall degree of crystallinity. It was found that even with a similar degree of crystallinity, the hydrolytic degradation rate of an isothermally crystallized sample at 60°C was higher than that of a melt-quenched sample. This was due to the difference in the internal morphology of the spherulites: the internal structure of spherulite in an isothermally crystallized sample consists of coarse and loosely packed fibrils whereas a melt-quenched sample contains finer and tightly packed fibrils. This result suggested that the internal structure of the spherulite of PBS samples plays an important role in the hydrolytic degradation for this experimental condition. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1025–1033, 2001

The effect of crystalline morphology of poly (butylene terephthalate) phases on toughening of poly(butylene terephthalate)/epoxy blends

In an effort to investigate the effect of the crystalline morphology of a poly(butylene terephthalate) (PBT) phase on the toughening of PBT/epoxy blends, the blends, having different degrees of perfectness of the PBT crystalline phase, were prepared by blending PBT and epoxy at various temperatures ranging from 200 to 240 °C. As the blending temperature decreases, the degree of perfectness of the PBT crystalline phase increases as a result of the increase of crystal growth rate. For PBT/epoxy blends, the change in crystalline morphology induced by processing may be the most important cause for the dependency of the fracture energy on blending temperatures. It has been found that PBT phases with a well-developed Maltese cross are most effective for epoxy toughening. This dependency reveals the occurrence of a phase transformation toughening mechanism. Also, the higher relative enhancement of fracture energy of a higher molecular weight epoxy system is further indirect evidence for a phase transformation toughening mechanism. Some other toughening mechanisms observed from the fracture surfaces, such as crack bifurcation, crack bridging, and ductile fracture of PBT phases, have been found to also be affected by the blending temperatures.

Preparation of poly(l-lactide) microspheres of different crystalline morphology and effect of crystalline morphology on drug release rate

Abstract The physicochemical properties of progesterone-loaded poly(l-lactide) microspheres prepared by the solvent evaporation method were studied, focusing on the crystallinity of the polymer matrices. The solvent evaporation process was found to govern the physical characteristics of microspheres. Solvent removal at atmospheric pressure yielded microspheres of crystalline polymer matrices, while faster solvent removal under a reduced pressure gave microspheres of amorphous polymer matrices. The crystallinity of the polymer matrices was closely correlated with the morphology and physical properties of microspheres, and affected the drug release rate. The microspheres of crystalline polymer matrices had rough surfaces with large surface areas, and exhibited a rapid drug release. In contrast, the microspheres of amorphous polymer matrices had smooth surfaces with smaller surface areas, and provided a slower drug release. The results of X-ray powder diffraction, differential scanning calorimetry and Fourier-transform infra-red spectroscopy suggested that progesterone formed a molecular dispersion in the amorphous polymer matrices.

Miscible blends and block copolymers. Crystallization, melting, and interaction

The effects of crystalline morphology and its kinetics on the melting point depression and thermodynamic interactions in miscible blends are theoretically analyzed and experimentally compared four PED/PMMA and PVF 2 blends. As the concentration of PMMA increases, the thickness of folded-chain lamellae becomes thinner and the rate of crystallization slows down. These results in an increase in the concentration-dependent interaction parameter at their melting temperatures