Study on the formation of beta-crystal during the crystallization process of polypropylene reactor granule

A notable amount of PP beta-crystal (30%, by X-ray diffraction pattern) has been found in the PP samples as polymerized at normal static isothermal crystallization conditions without using any extra nucleating agents. Existence of catalyst residues in the sample is decisive, which slows down the crystallization rate facilitating the formation of beta-form spherulites. Comparatively, high molecular weight PP favors the formation of beta-form spherulites, deducting from no beta-crystal detected in the degraded samples. Finally, high isotacticity is also required for obtaining qualitative beta-form spherulites, demonstrated by increased beta-crystal content after removal of weak crystalline fraction of the sample.

Thermal stability, crystallization, structure and morphology of syndiotactic 1,2-polybutadiene/organoclay nanocomposite

Syndiotactic 1,2-polybutadiene/organoclay nanocomposites were prepared and characterized by thermogravimetry analysis (TGA), X-ray diffraction (XRD), polarized optical microscopy (POM), and differential scanning calorimetry (DSC), respectively. The XRD shows that exfoliated nanocomposites are formed dominantly at lower clay concentrations (less than 2%), at higher clay contents intercalated nanocomposites dominate. At the same time, the XRD indicates that the crystal structures of sPB formed in the sPB/organoclay nanocomposites do not vary, only the relative intensity of the peaks corresponding to (0 1 0) and (2 0 0)/(1 1 0) crystal planes, respectively, varies. The DSC and POM indicate that organoclay layers can improve cooling crystallization temperature, crystallization rate and reducing the spherulite sizes of sPB. TGA shows that under argon flow the nanocomposites exhibit slight decrease of thermal stability, while under oxygen flow the resistance of oxidation and thermal stability of sPB/organoclay nanocomposites were significantly improved relative to pristine sPB. The primary and secondary crystallization for pristine sPB and sPB/organoclay (2%) nanocomposites were analyzed and compared based on different approaches.

Crystallization kinetics and morphology of nylon 1212

The isothermal and non-isothermal crystallization processes of nylon 1212 were investigated by polarized optical microscopy. The crystal growth rates of nylon 1212 measured in isothermal conditions at temperatures ranged from 182 to 132 degreesC are well comparable with those measured by non-isothermal procedures (cooling rates ranged from 0.5 to 11 degreesC/min). The kinetic data were examined with the Hoffman-Lauritzen nucleation theory on the basis of the obtained values of the thermodynamic parameters of nylon 1212. The classical regime I --> II and regime II --> III transitions occur at the temperatures of 179 and 159 degreesC, respectively. The crystal growth parameters were calculated with (100) plane assumed to be the growth plane. The regime I --> II --> III transition is accompanied by a morphological transition from elliptical-shaped structure to banded spherulite and then non-banded spherulite. The development of morphology during isothermal and non-isothermal processes shows a good agreement.

Primary and secondary crystallization kinetic analysis of nylon 1212

The isothermal and non-isothermal melt-crystallization kinetics of nylon 1212 were investigated by differential scanning calorimetry. Primary and secondary crystallization behaviors were analysed based on different approaches. The results obtained suggested that primary crystallization under isothermal conditions involves three-dimensional spherulite growth initiated by athermal nucleation, while under non-isothermal conditions, the mechanism of primary crystallization is more complex. Secondary crystallization displays a lower-dimensional crystal growth, both in the isothermal and non-isothermal processes. The crystallite morphology of nylon 1212, isothermally crystallized at various temperatures, was observed by polarized optical microscopy. The activation energies of crystallization under isothermal and non-isothermal conditions were also calculated based on different approaches.

Crosslinking of poly[(3-hydroxybutyrate)-co-(3-hydroxyvalerate)] using dicumyl peroxide as initiator

In order to modify poly [(3-hydroxybutyrate)-co-(3-hydroxyvalerate)] (PHBV), the crosslinking of this copolymer was carried out at 160degreesC using dicumyl peroxide (DCP) as the initiator. The torque of the PHBV melt showed an abrupt upturn when DCP was added. Appropriate values for the gel fraction and crosslink density were obtained when the DCP content was up to 1 wt% of the PHBV. According to the NMR spectroscopic data, the location of the free radical reaction was determined to be at the tertiary carbons in the PHBV chains. The melting point, crystallization temperature and crystallinity of PHBV decreased significantly with increasing DCP content. The effect of crosslinking on the melt viscosity of PHBV was confirmed as being positive. Moreover, the mechanical properties of PHBV were improved by curing with DCP. When 1 wt% DCP was used, the ultimate elongation of PHBV increased from 4 to 11 %. A preliminary biodegradation study confirmed the total biodegradability of crosslinked PHBV.

Formation of a unique crystal morphology for the poly(ethylene glycol)-poly(epsilon-caprolactone) diblock copolymer

The crystallization behaviors of the poly(ethylene glycol)-poly(epsilon-caprolactone) diblock copolymer with the PEG weight fraction of 0.50 (PEG(50)-PCL50) was studied by DSC, WAXD, SAXS, and FTIR. A superposed melting point at 58.5 degrees C and a superposed crystallization temperature at 35.4 degrees C were obtained from the DSC profiles running at 10 degrees C/min, whereas the temperature-dependent FTIR measurements during cooling from the melt at 0.2 degrees C/min showed that the PCL crystals formed starting at 48 degrees C while the PEG crystals started at 45 degrees C. The PEG and PCL blocks of the copolymer crystallized separately and formed alternating lamella regions according to the WAXD and SAXS results. The crystal growth of the diblock copolymer was observed by polarized optical microscope (POM). An interesting morphology of the concentric spherulites developed through a unique crystallization behavior. The concentric spherulites were analyzed by in situ microbeam FTIR, and it was determined that the morphologies of the inner and outer portions were mainly determined by the PCL and PEG spherulites, respectively. However, the compositions of the inner and outer portions were equal in the analysis by microbeam FTIR.

Crystallization behavior of carbon nanotubes-filled polyamide 1010

The nanocomposites of polyamide1010 (PA1010) filled with carbon nanotubes (CNTs) were prepared by melt mixing techniques. The isothermal melt-crystallization kinetics and nonisothermal crystallization behavior of CNTs/PA1010 nanocomposites were investigated by differential scanning calorimetry. The peak temperature, melting point, half-time of crystallization, enthalpy of crystallization, etc. were measured. Two stages of crystallization are observed, including primary crystallization and secondary crystallization. The isothermal crystallization was also described according to Avrami's approach. It has been shown that the addition of CNTs causes a remarkable increase in the overall crystallization rate of PA1010 and affects the mechanism of nucleation and growth of PA1010 crystals. The analysis of kinetic data according to nucleation theories shows that the increment in crystallization rate of CNTs/PA1010 composites results from the decrease in lateral surface free energy.

Investigation on isothermal and non-isothermal crystallization kinetics of poly (epsilon-caprolactone)

The crystallization kinetics and the development of lamellar structure during the isothermal crystallization of poly (epsilon-caprolactone) (PCL) were investigated by means of differential scanning calorimetry (DSC) and real-time synchrotron small angle X-ray scattering (SR-SAXS) techniques, respectively. The Avrami analysis was performed to obtain the kinetics parameters. The value of Avrami index, n, is about 3, demonstrating a three-dimensional spherulitic growth on heterogeneous nuclei in the process of isothermal crystallization. The activation energy and the surface free energy of chain folding for isothermal crystallization were determined according to the Arrhenius equation and Hoffman-Lauritzen theory, respectively. In the process of nonisothermal crystallization of PCL, the value of Avrami index, n, is about 4, which demonstrates a three-dimensional spherulitic growth on homogeneous nuclei. In addition, lamellar parameters were obtained from the analysis of SR-SAXS data.

Melting behaviors, isothermal and non-isothermal crystallization kinetics of nylon 1212

Isothermal crystallization, subsequent melting behavior and non-isothermal crystallization of nylon 1212 samples have been investigated in the temperature range of 160-171 degreesC using a differential scanning calorimeter (DSC). Subsequent DSC scans of isothermally crystallized samples exhibited three melting endotherms. The commonly used Avrami equation and that modified by Jeziorny were used, respectively, to fit the primary stage of isothermal and non-isothermal crystallizations of nylon 1212. The Avrami exponent n was evaluated, and was found to be in the range of 1.56-2.03 for isothermal crystallization, and of 2.38-3.05 for non-isothermal crystallization. The activation energies (DeltaE) were determined to be 284.5 KJ/mol and 102.63 KJ/mol, respectively, for the isothermal and non-isothermal crystallization processes by the Arrhenius' and the Kissinger's methods.

The preparation of phenolic resin/montmorillonite nanocomposites by suspension condensation polymerization and their morphology

Phenolic resin/clay nanocomposites were prepared using a suspension condensation polymerization method that was suitable to both novolac and resole. Natural montmorillonite and two kinds of organic modified montmorillonite were adopted to investigate the effect of modification on the final morphology of the nanocomposites. X-ray diffraction (XRD) measurements and Transmission Electron Microscope (TEM) observations showed that clay platelets were easier to be exfoliated or intercalated in novolac than in resole because novolac usually has a linear structure. The modifier with a phenyl ring was more compatible with novolac (or resole) than the aliphatic type modifier. The influence of curing on the morphology was studied as well. An exfoliation-adsorption and in situ condensation mechanism was proposed on the formation of the nanocomposites.

Non-isothermal crystallization behavior and kinetics of metallocene short chain branched polyethylene

The non-isothermal crystallization behavior and kinetics of metallocene short chain branched polyethylene were investigated via DSC at cooling rates from 2.5 to 20 degreesC/min, and subsequent heating at rate of 10 degreesC/min. To verify the effect of molecular weight and branching content on crystallization, three group samples were chosen: (1) linear polyethylene with low molecular weight and high molecular weight; (2) low molecular weight polyethylene with low branching content and high branching content; (3) high molecular weight polyethylene with low branching content and high branching content. The results show that crystallization temperature, crystallinity, melting temperature and crystallization rate are highly branching content-dependent. Molecular weight effect is less important, compared to branching content. A dramatic decrease of crystallization temperature, crystallinity, crystallization rate and melting temperature was observed for branched samples. The non-isothermal kinetics was analyzed via the methods, developed by Gupta and Mo Zhi-shen, and good agreement was obtained.