Non-isothermal Crystallization (non-isothermal + crystallization)

Distribution by Scientific Domains

Selected Abstracts

Unique Orientation Textures Induced by Confined Crystal Growth of Poly(vinylidene fluoride) in Oriented Blends with Polyamide 6

Akira Kaito
Abstract Unique orientation textures have been induced by the confined crystal growth of PVDF in drawn films of PVDF/PA6 blends. Oriented films of PVDF/PA6 blends were prepared by uniaxially drawing melt-mixed blends. The drawn films with fixed lengths were heat-treated at 180,C for 3 minutes to melt the PVDF component, followed by non-isothermal crystallization of PVDF at a cooling rate of 0.5,C,,min,1. The crystal orientation was studied by WAXD. When PVDF was melted and recrystallized in the drawn films of the PVDF/PA6,=,50/50 blend at a slow cooling rate, the crystal b- axis of the , -crystalline form of PVDF was oriented in the drawing direction, forming orthogonal orientation textures. SEM showed that stretched domains of PVDF with diameters of 0.2,0.5 m were dispersed in the PA6 phase in the drawn films of the PVDF/PA6,=,50/50 blend. Spatial confinement of the crystal growth resulted in the alignment of the crystal b- axis along the long axis of the domains, because PVDF is crystallized in thin cylindrical domains. The orientation behavior is different from the oriented crystallization of PVDF/PA11 (Y. Li, A. Kaito, Macromol. Rapid Commun. 2003, 24, 255), in which transcrystallization from the interface causes the a- axis orientation to be in the drawing direction. It is thought that the domain size influenced the mechanism of oriented crystallization and the resultant crystal orientation. [source]

Study on the Phase Behavior of High Density Polyethylene , Ethylene Octene Copolymer Blends

Daniela Mileva
Abstract The processes of melting and crystallization of blends based on HDPE and EOC were investigated. DSC thermograms showed that a separate crystallization and co-crystallization occurred in the blends studied. Avrami approach was used to analyze the kinetics of crystallization in the blends. It is shown that the Avrami exponent depends on the EOC concentration of the samples studied. The difference in the Avrami parameters for HDPE, EOC and the blends indicated that the nucleation mechanism and dimension of the spherulite growth of the blends were different from that of HDPE to some extent. The crystal growth was examined in the context of the Lauritzen-Hoffman theory. DSC traces obtained at different cooling rates were used for analyzing the non-isothermal crystallization. It was found that the Ozawa model was rather inapplicable for the materials studied. In contrast, the Avrami equation modified by Jeziorny can be used more efficiently to describe the non-isothermal crystallization behavior of HDPE-EOC blends. [source]

Effect of zirconium dioxide on crystallization and melting behavior of flame sprayed polyamide 1010

Yadong Li
The crystallization and melting behavior of flame sprayed Polyamide 1010 (PA1010) containing zirconium dioxide (ZrO2) were investigated using differential scanning calorimeter (DSC). ZrO2 has a heterogenous nucleation effect on PA1010, leading to a moderate increase in the crystallization temperature and a decrease in the supercooling temperature. A modified Avrami theory could be successfully used to well describe the early stages of non-isothermal crystallization of PA1010 and its composite coatings. A study of the nucleation activity, which indicated the influence of the filler on the polymer matrix, revealed that the zirconium dioxide nanoparticles had a good nucleation effect on PA1010. POLYM. COMPOS., 2008. 2008 Society of Plastics Engineers. [source]

Variation of non-isothermal crystallization behavior of isotactic polypropylene with varying ,-nucleating agent content

Linli Xu
Abstract The non-isothermal crystallization behavior, the crystallization kinetics, the crystallization activation energy and the morphology of isotactic polypropylene (iPP) with varying content of ,-nucleating agent were investigated using differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The DSC results showed that the Avrami equation modified by Jeziorny and a method developed by Mo and co-workers could be successfully used to describe the non-isothermal crystallization process of the nucleated iPPs. The values of n showed that the non-isothermal crystallization of ,- and ,-nucleated iPPs corresponded to a tridimensional growth with homogeneous and heterogeneous nucleation, respectively. The values of crystallization rate constant showed that the rate of crystallization decreased for iPPs with the addition of ,-nucleating agent. The crystallization activation energy increased with a small amount (less than 0.1 wt%) of ,-nucleating agent and decreased with higher concentration (more than 0.1 wt%). The changes of crystallization rate, crystallization time and crystallization activation energy of iPPs with varying contents of ,-nucleating agent were mainly determined by the ratio of the content of ,- and ,-phase in iPP (,-PP and ,-PP) from the DSC investigation, and the large size and many intercrossing lamellae between boundaries of ,-spherulites for iPPs with small amounts of ,-nucleating agent and the small size and few intercrossing bands among the boundaries of ,-spherulites for iPPs with large amounts of ,-nucleating agent from the SEM examination. Copyright 2010 Society of Chemical Industry [source]

The turning point on plots of log , and log t of Mo's equation

Jian-bin Song
Abstract BACKGROUND: Mo's equation based on the Avrami equation and Ozawa equation has been successfully used in non-isothermal crystallization kinetics by many researchers. However, in recent years we have found that plots of log ,,log t of Mo's equation are not straight lines, but there appears a turning point at , = 7 C min,1 or so. The aim of this article is to analyze in detail the reason for the occurrence of this turning point by studying the non-isothermal crystallization of poly(vinylidene fluoride) (PVDF) using differential scanning calorimetry. RESULTS: A turning point at about 7 C min,1 appeared on plots of log ,,log t. The cooling rate where the turning point occurred showed little change with increasing relative crystallinity, but the temperature decreased. It is noted that this turning-point temperature is lower than transition temperature of regime I , II reported for PVDF. CONCLUSION: We deemed that the occurrence of turning points on plots of log ,,log t of Mo's equation can be ascribed to the different crystallization regimes based on the Hoffman nucleation theory, and presumed that the turning point corresponded to transition of regime I , II. Finally, we considered that Mo's equation should be analyzed using two beelines, instead of one beeline. Copyright 2009 Society of Chemical Industry [source]

Thermal properties and non-isothermal crystallization behavior of biodegradable poly(p -dioxanone)/poly(vinyl alcohol) blends

Zhi-Xuan Zhou
Abstract Blends of two biodegradable semicrystalline polymers, poly(p -dioxanone) (PPDO) and poly(vinyl alcohol) (PVA) were prepared with different compositions. The thermal stability, phase morphology and thermal behavior of the blends were studied by using thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). From the TGA data, it can be seen that the addition of PVA improves the thermal stability of PPDO. DSC analysis showed that the glass transition temperature (Tg) and the melting temperature (Tm) of PPDO in the blends were nearly constant and equal to the values for neat PPDO, thus suggesting that PPDO and PVA are immiscible. It was found from the SEM images that the blends were phase-separated, which was consistent with the DSC results. Additionally, non-isothermal crystallization under controlled cooling rates was explored, and the Ozawa theory was employed to describe the non-isothermal crystallization kinetics. Copyright 2006 Society of Chemical Industry [source]

Modification of the thermal properties and crystallization behaviour of poly(ethylene terephthalate) by copolymerization

Darwin P, R Kint
Abstract Poly(ethylene terephthalate) (PET) is a widely used polyester, which can be crystallized from the melt over a wide range of supercooling conditions or, alternatively, quenched into the amorphous state and, subsequently, crystallized by thermal treatment above the glass-transition temperature. It is well known that the crystallization of PET can be hindered by means of copolymerization or reactive blending. The incorporation of comonomeric units into the polymer backbone leads to an irregular chain structure and thereby inhibits regular chain packing for crystallization. The crystallization of PET copolyesters is strongly influenced by the chain microstructure regarding comonomer distribution, randomness and length of the crystallizable ethylene terephthalate sequences. This paper is mainly devoted to the thermally induced crystallization behaviour of PET and to reviewing the efforts that have been made in the last decade to modify the glass-transition and melting temperatures, the crystallinity and the crystallization rate of this polyester. Furthermore, some illustrative experimental data obtained from isothermal and non-isothermal crystallization of PET are included in this study. 2003 Society of Chemical Industry [source]