Crystallization Behavior (crystallization + behavior)

Distribution by Scientific Domains
Distribution within Polymers and Materials Science

Kinds of Crystallization Behavior

  • nonisothermal crystallization behavior

  • Selected Abstracts

    Crystallization Behavior of Poly(, -caprolactone) Grafted onto Cellulose Alkyl Esters: Effects of Copolymer Composition and Intercomponent Miscibility

    Ryosuke Kusumi
    Abstract Graft copolymers of CA and CB with PCL were prepared at compositions rich in PCL. Kinetic DSC data were analyzed in terms of a folded-chain crystallization formula expanded for a binary mixing system of amorphous/crystalline polymers. The order of crystallization rates was plain PCL,>,CA- g -PCL (DS,=,2.98),>,CB- g -PCL (DS,=,2.1,2.95),>,CA- g -PCL (DS,=,2.1,2.5), and the fold-surface free energy of the PCL crystals obeyed the reverse order. POM revealed a generally tardy growth of spherulites for all the graft copolymers. The slower crystallization process may be ascribed primarily to the compulsory effect of anchoring PCL chains onto the semi-rigid cellulose backbone. Intercomponent miscibility of the CA/PCL and CB/PCL pairs was also taken into consideration. [source]

    Unusual Crystallization Behavior in Nylon-6 and Nylon-6/Montmorillonite Nanocomposite Films

    Zhudi Zhao
    Abstract Summary: The crystallization behavior of nylon-6 and nylon-6/montmorillonite nanocomposite films with different heat histories was investigated by wide-angle X-ray diffraction (WAXD). For nylon-6 films isothermally crystallized above 170,C or annealed at 200,C and then quenched in ice water, a crystalline peak appeared at 2,,=,28.5. This crystalline peak was strong in intensity for the former and weak for the latter. However, for nylon-6 films cooled in air after isothermal crystallization or annealing, no crystalline peak at 2,,=,28.5 was observed in the WAXD patterns. For nylon-6/montmorillonite nanocomposite films annealed above 140,C, a crystalline double peak was observed between the ,1 and ,2 peaks. The possible origins of the peak at 2,,=,28.5 and the crystalline double peak are discussed. WAXD patterns of isothermally crystallized nylon-6/montmorillonite nanocomposite films. [source]

    Effect of EPDM on Morphology, Mechanical Properties, Crystallization Behavior and Viscoelastic Properties of iPP+HDPE Blends

    Nina Vranjes
    Abstract Summary: Blends of isotactic polypropylene (iPP) and high density polyethylene (HDPE) with and without ethylene-propylene-diene (EPDM) terpolymer as compatibilizer were systematically investigated to determine the influence of the EPDM on blends properties. The morphology was studied by Scanning Electron Microscopy (SEM). Mechanical properties of investigated systems: tensile strength at break, elongation at break, yield stress and Izod impact strength were determined. Crystallization behavior was determined by Differential Scanning Calorimetry (DSC). Dynamic Mechanical Analysis (DMA) was used to determined the storage modulus (E,), loss modulus (E,), and loss tangent (tan ,). The PP+HDPE blend revealed poor adhesion between PP and HDPE phases. Finer morphology was obtained by EPDM addition in PP+HDPE blends and better interfacial adhesion. Addition of HDPE to PP decreased tensile strength at break, elongation and yield stress. Decrease of tensile strength and yield stress is faster with EPDM addition in PP+HDPE blends. Elongation at break and impact strength was significantly increased with EPDM addition. The addition of EPDM in PP+HDPE blends did not significantly change melting points of PP phase, while melting points of HDPE phase was slightly decreased in PP+HDPE+EPDM blends. The EPDM addition increased the percentage of crystallization (Xc) of PP in PP+HDPE blends. The increase of Xc of HDPE was found in the blend with HDPE as matrix. Dynamical mechanical analysis showed glass transitions of PP and HDPE phase, as well as the relaxation transitions of their crystalline phase. By addition of EPDM glass transitions (Tg) of HDPE and PP phases in PP+HDPE blends decreased. Storage modulus (E,) vs. temperatures (T) curves are in the region between E,/T curves of neat PP and HDPE. The decrease of E, values at 25,C with EPDM addition in PP+HDPE blends is more pronounced. [source]

    Crystallization behavior of Sb70Te30 and Ag3In5Sb60Te32 chalcogenide materials for optical media applications

    M. L. Lee
    Abstract Addition of In and Ag into eutectic Sb70Te30 fast-growth material was studied. We explored the optical transitions and crystallization kinetics of Sb70Te30 and Ag3In5Sb60Te32 recording films. The results showed that Ag3In5Sb60Te32 has a higher crystallization temperature but a similar melting point compared to Sb70Te30. In both the crystalline and amorphous states, addition of Ag and In increased the refractive index and decreased the extinction coefficient of Sb70Te30. Ag3In5Sb60Te32 has better thermal stability and a lower crystallization speed than Sb70Te30 film. ( 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Crystallization behavior and mechanical properties of polypropylene/modified carbon black composites

    POLYMER COMPOSITES, Issue 4 2009
    Ping Zhu
    Carbon black (CB) modified with small organic molecules was filled in polypropylene (PP) matrix. The crystallization behavior and mechanical properties of PP/modified CB (MCB) composites were investigated. Compared with the original CB, MCB could be dispersed uniformly in smaller particle sizes in PP matrix, and MCB could act as a more effective nucleating, toughening, and reinforcing agent when it was filled in PP at low concentrations. Further increasing of MCB particles in PP matrix resulted in the decrease of impact and tensile strength of PP/MCB composites. It was inferred from DSC results that the existence of CB vand MCB in PP matrix could result in the decrease of crystallite size and degree of perfection of PP. POLYM. COMPOS., 2009. 2008 Society of Plastics Engineers [source]

    Crystallization behaviors of carbon fiber reinforced BN-Si3N4 matrix composite

    Bin Li
    Abstract The crystallization behaviors of a new carbon fiber reinforced composite with a hybrid matrix comprising BN and Si3N4 prepared by precursor infiltration and pyrolysis were investigated by Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscopy. The results show that the as-received composite is almost amorphous, and its main composition is BN and Si3N4. When heat treated at 1600C, the composite is crystallized and shows a much better crystal form. When heat treated at 2100C, Si3N4 in the matrix is decomposed, and BN exhibits a relatively complete crystallization. The existence of B4C and SiC is detected, which indicates the interfacial chemical reactions between nitride matrices and carbon fibers. The surface morphology of carbon fibers in the composite changed significantly when heated from 1600 to 2100C, which also proved the occurrence of interfacial chemical reactions. ( 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    How do crystal lattice contacts reveal protein crystallization mechanism?

    Christo N. Nanev
    Abstract The nature of crystal lattice contacts is discussed because they reflect the selection of the most appropriate (for the given set of conditions) contact patches on the surface of protein molecules. The conclusion is that, along with chemical composition, the protein structure at the crystal lattice contacts is the key to crystallization behavior. The reason is that most stable are conformations, which do not only maximize the number of the bonds but simultaneously minimize van der Waals repulsions. A plausible explanation of the crystallization slot that exists for proteins is given on this basis. ( 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Effect of Ce, Sb, and Sn on Solarization and Crystallization of an X-Ray-Irradiated Photosensitive Glass

    Mohamad Hassan Imanieh
    The effect of Ce, Sb, and Sn photosensitive elements, individually and in combination with each other, on solarization and crystallization of an X-ray irradiated and a nonirradiated lithium silicate-based glass were investigated. According to the results, considering the crystallization behavior of the nonirradiated glasses, they were divided into Ce-bearing and Ce-free groups, in which the former group showed a clearer solarization tendency that manifested as an appearance of an absorbance peak at 318 nm in the spectrophotometry experiment. However, the results showed that in the irradiated glasses, the presence of Sb was more important in terms of improvement in crystallization view. Antimony decreased the differential thermal analysis (DTA) crystallization peak temperature from 655C to 594C and, in combination with the two other elements, changed the surface crystallization mechanism to a bulk one. The reactions that seemed to be responsible for the above-mentioned observations were discussed by spectrophotometry, DTA, X-ray diffraction, and scanning electron microscopic methods. [source]

    Preparation of Machinable Fluoramphibole Glass,Ceramics from Soda-Lime Glass and Fluormica

    Weiyi Zhang
    A novel route, directly mixing fluormica crystals with recycled soda-lime glass powder and then sintering, is proposed to fabricate machinable fluoramphibole glass,ceramics. The effect of fluormica addition on the sinterability, reactive crystallization behavior, strength, and machinability of the material was investigated. The relative densities of the glass,ceramics decreased with increasing fluormica content. An interaction between fluormica crystals and glass powder occurred during the sintering process. Diopside was formed in the glass,ceramics with 20 wt% fluormica, and fluorrichterite was formed in the glass,ceramics with more than 30 wt% fluormica. Machinability and strength of the glass,ceramics were improved with increasing crystalline phase content. [source]

    The continuous cooling transformation (CCT) as a flexible tool to investigate polymer crystallization under processing conditions

    V. Brucato
    Abstract An experimental route for investigating polymer crystallization over a wide range of cooling rates (from 0.01 to 1000C/s) and pressures (from 0.1 to 40 MPa) is illustrated, using a method that recalls the approach adopted in metallurgy for studying structure development in metals. Two types of experimental setup were used, namely an apparatus for fast cooling of thin films (100,200 ,m thick) at various cooling rates under atmospheric pressure and a device (based on a on-purpose modified injection molding machine) for quenching massive samples (about 1,2 cm3) under hydrostatic pressure fields. In both cases, ex situ characterization experiments were carried out to probe the resulting structure, using techniques such as density measurements and wide-angle x-ray diffraction (WAXD) patterns. The cooling mechanism and temperature distribution across the sample thickness were analyzed. Results show that the final structure is determined only by the imposed thermal history and pressure. Experimental results for isotactic polypropylene (iPP), poly(ethylene terephthalate) (PET), polyamide 6 (PA6), and syndiotactic polystyrene (sPS) are reported, showing the reliability of this experimental approach to assess not only quantitative information but also a qualitative description of the crystallization behavior of different classes of semicrystalline polymers. The present study gives an opportunity to evaluate how the combined effect of the cooling rate and pressure influences the crystallization kinetics for various classes of polymer of commercial interest. An increase in the cooling rate translates into a decrease in crystallinity and density, which both experience a sudden drop around the specific "crystallizability" (or "critical cooling rate") of the material examined. The exception is sPS where competition among the various crystalline modifications determines a minimum in the plot of density vs. cooling rate. As for the effect of pressure, iPP exhibits a "negative dependence" of crystallization kinetics upon pressure, with a decrease of density and degree of crystallinity with increasing pressure, owing to kinetic constraints. PA6 and PET, on the other hand, due to thermodynamic factors resulting in an increase in Tm with pressure, exhibits a "positive dependence" of crystallization kinetics upon pressure. Finally, recent original results concerning sPS have shown that the minimum in the density vs. cooling rate curve shifts toward larger cooling rates upon increasing pressure. 2009 Wiley Periodicals, Inc. Adv Polym Techn 28:86,119, 2009; Published online in Wiley InterScience ( DOI 10.1002/adv.20151 [source]

    Polylactide copolymers: Effect of copolymer ratio and end capping on their properties

    D. M. Bigg
    Abstract Racemic copolymers of polylactic acid were investigated to determine the effect of copolymer ratio on melting point, degree of crystallinity, mechanical properties, and processing behavior. The copolymer ratio was found to have a strong influence on the crystallization behavior of the polymer. In addition to the ratio of the L -form to a random mixture of the D and L forms of the lactic acid in the copolymer, the effect of the polymer's molecular weight was examined. The copolymers were produced from the lactide form of the monomer to achieve weight average molecular weights above 100,000. The molecular weight had a profound influence on processability and rate of crystallization. Other notable factors influencing the properties and processing of the copolymers were the concentration of residual monomer in the polymer, the processing time-temperature history, and the extent of molecular weight degradation during processing. An important factor in the commercial development of biodegradable polymers is the ability to control the rate of degradation. Ideally, the polymer should not degrade during functional use, but degrade quite rapidly when discarded. This paper discusses various aspects associated with the control of the rate of degradation of polylactide copolymers; both from the perspective of stabilizing the polymer during processing and product use, and subsequently accelerating the rate of degradation after disposal. Of particular interest are the influences of molecular weight, crystallinity, end capping, and plasticization. 2005 Wiley Periodicals, Inc. Adv Polym Techn 24:69,82, 2005; Published online in Wiley InterScience ( DOI 10.1002/adv.20032 [source]

    Rotationally molded polyethylene: Structural characterization by x-ray and microhardness measurements

    Maria Clara Cramez
    Rotationally molded polyethylene (PE) blended in two ways (turbo blending and extrusion) with nucleating and nonnucleating pigments is structurally characterized by wide- and small-angle x-ray scattering (WAXS and SAXS, respectively), DSC and microhardness measurements. Morphological observations are performed by polarized light microscopy. The melting temperature and the degree of crystallinity (from both DSC and WAXS) remain essentially constant regardless of sample preparation and type of pigment. The same holds for the crystal sizes from WAXS and the lamella thickness from SAXS. Only the values of microhardness depend on the type of pigment, increasing about 10% when a nucleating type is used. The almost constant values of these properties, contrasting to the spherulitic morphology, are explained by the fact that the processing conditions in rotational molding are very favorable for crystallization. As a consequence, optimal crystalline structure is achieved, which masks significantly the effect of pigments and blending conditions on the crystallization behavior of polyethylene. 2001 John Wiley & Sons, Inc. Adv Polym Techn 20: 116,124, 2001 [source]

    Crystallization and melting behavior of HDPE in HDPE/teak wood flour composites and their correlation with mechanical properties

    Kamini Sewda
    Abstract The nonisothermal crystallization behavior and melting characteristics of high-density polyethylene (HDPE) in HDPE/teak wood flour (TWF) composites have been studied by differential scanning calorimetry (DSC) and wide angle X-ray diffraction (WAXD) methods. Composite formulations of HDPE/TWF were prepared by varying the volume fraction (,f) of TWF (filler) from 0 to 0.32. Various crystallization parameters evaluated from the DSC exotherms were used to study the nonisothermal crystallization behavior. The melting temperature (Tm) and crystallization temperature (Tp) of the composites were slightly higher than those of the neat HDPE. The enthalpy of melting and crystallization (%) decrease with increase in the filler content. Because the nonpolar polymer HDPE and polar TWF are incompatible, to enhance the phase interaction maleic anhydride grafted HDPE (HDPE-g-MAH) was used as a coupling agent. A shift in the crystallization and melting peak temperatures toward the higher temperature side and broadening of the crystallization peak (increased crystallite size distribution) were observed whereas crystallinity of HDPE declines with increase in ,f in both DSC and WAXD. Linear correlations were obtained between crystallization parameters and tensile and impact strength. 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source]

    Mechanical and thermal properties of poly(butylene succinate)/plant fiber biodegradable composite

    Zhichao Liang
    Abstract Biodegradable polymeric composites were fabricated from poly(butylene succinate) (PBS) and kenaf fiber (KF) by melt mixing technique. The mechanical and dynamic mechanical properties, morphology and crystallization behavior were investigated for PBS/KF composites with different KF contents (0, 10, 20, and 30 wt %). The tensile modulus, storage modulus and the crystallization rate of PBS in the composites were all efficiently enhanced. With the incorporation of 30% KF, the tensile modulus and storage modulus (at 40C) of the PBS/KF composite were increased by 53 and 154%, respectively, the crystallization temperature in cooling process at 10C/min from the melt was increased from 76.3 to 87.7C, and the half-time of PBS/KF composite in isothermal crystallization at 96 and 100C were reduced to 10.8% and 14.3% of that of the neat PBS, respectively. SEM analysis indicates that the adhesion between PBS and KF needs further improvement. These results signify that KF is efficient in improving the tensile modulus, storage modulus and the crystallization rate of PBS. Hence, this study provides a good option for preparing economical biodegradable composite. 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source]

    Study on the long-term thermal-oxidative aging behavior of polyamide 6

    Ying Shu
    Abstract The long-term thermal-oxidative aging behavior of polyamide 6 (PA6) was studied by comparison with the stabilized sample in this work. The variation of mechanical properties of the pure and the stabilized samples of PA6 with aging time at 110C, 130C, and 150C were investigated, respectively. The aging mechanism of PA6 under heat and oxygen was studied in terms of the reduced viscosity, crystallization behavior, dynamic mechanical behavior, and chemical composition through the methods of polarized light microscopy (PLM), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), X-ray photoelectron energy spectrum (XPS), and so on. The results indicated that at the initial stage of aging, the molecular crosslinking reaction of PA6 dominated resulting in the increase of the mechanical strength, reduced viscosity, and the glass transition temperature of the sample. And the molecular degradation dominated in the subsequent aging process resulting in the decrease of the melting temperature, the increase of the crystallinity, and the formation of the oxides and peroxides products. 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

    Nonisothermal and isothermal crystallization kinetics of nylon-12

    Neil L. A. McFerran
    Abstract The isothermal and nonisothermal crystallization behavior of Nylon 12 was investigated using differential scanning calorimetry (DSC). An Avrami analysis was used to study the isothermal crystallization kinetics of Nylon 12, the Avrami exponent (n) determined and its relevance to crystal growth discussed and an activation energy for the process evaluated using an Arrhenius type expression. The Lauritzen and Hoffman analysis was used to examine the spherulitic growth process of the primary crystallization stage of Nylon 12. The surface-free energy and work of chain folding were calculated using a procedure reported by Hoffmann and the work of chain folding per molecular fold (,) and chain stiffness of Nylon 12 (q) was calculated and compared to values reported for Nylons 6,6 and 11. The Jeziorny modification of the Avrami analysis, Caz and Chuah average Avrami parameter methods and Ozawa equation were used in an attempt to model the nonisothermal crystallization kinetics of Nylon 12. A combined Avrami and Ozawa treatment, described by Liu, was used to more accurately model the nonisothermal crystallization kinetics of Nylon 12. The activation energy for nonisothermal crystallization processes was determined using the Kissinger method for Nylon 12 and compared with values reported previously for Nylon 6,6 and Nylon 11. 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

    Effects of silver nanoparticles on the dynamic crystallization and physical properties of syndiotactic polypropylene

    Dong Wook Chae
    Abstract The effects of silver (Ag) nanoparticles on the physical properties of syndiotactic PP (sPP) were investigated concentrating on the isothermal melt crystallization behavior under shear. sPP with 5 wt % Ag nanoparticles presented higher crystallization temperature (Tc) and heat of crystallization (,Hc) than pure sPP. At 90C, the Ag nanoparticles had little effect on the induction time of crystallization but a little increased the half-time (t1/2) for the crystallization. At 100C, however, the induction time was decreased with increasing the Ag content and the t1/2 was decreased up to the Ag content of 0.5 wt %. DSC melting endotherms exhibited double melting peaks when crystallized at 90C under shear but a single melting peak when crystallized at 100C. The WAXD patterns exhibited that the presence of Ag nanoparticles did not produce any change in the crystal structure of sPP. The tensile strength of sPP is little changed up to the Ag content of 0.1 wt % but it was decreased with further addition. In addition, the introduction of less than 0.1 wt % Ag increased the elongation at break, but further addition decreased it abruptly. 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

    Synthesis and crystallization behavior of acetal copolymer/silica nanocomposite by in situ cationic ring-opening copolymerization of trioxane and 1,3-dioxolane

    Lanhui Sun
    Abstract The acetal copolymer/silica nanocomposite was prepared by in situ bulk cationic copolymerization of trioxane and 1,3-dioxolane in the presence of nanosilica. The crystallization behavior of acetal copolymer/silica nanocomposite was studied by AFM, DSC, XRD, and CPOM, and the macromolecular structure of acetal copolymer/silica nanocomposite was characterized by FTIR and 1H-NMR. The 1H-NMR results showed that the macromolecular chain of acetal copolymer had more than two consecutive 1,3-dioxolane units in an oxymethylene main chain, while that of acetal copolymer/silica nanocomposite had only one 1,3-dioxolane unit in an oxymethylene main chain. There existed interaction between the macromolecular chains and nanoparticles (such as hydrogen bonds and coordination). On one hand, nanoparticles acted as nucleation center, which accelerated the crystallization rate but reduced the crystallinity. The spherulite sizes also decreased with addition of nanoparticles attributed to the nucleation effect. On the other hand, the presence of nanoparticles interrupted the spherical symmetry of the crystallite. In conclusion, the high surface energy and small scale of nanoparticles have a prominent impact on the polymerization mechanism and crystallization behavior of nanocomposite. 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

    Blends of high density polyethylene and ethylene/1-octene copolymers: Structure and properties,

    Rameshwar Adhikari
    Abstract The morphology formation in the blends comprising a high density polyethylene (HDPE) and selected ethylene/1-octene copolymers (EOCs) was studied with variation of blend compositions using atomic force microscopy (AFM). The binary HDPE/EOC blends studied showed well phase-separated structures (macrophase separation) in consistence with individual melting and crystallization behavior of the blend components. For the blends comprising low 1-octene content copolymers, the lamellar stacks of one of the phases were found to exist side by side with that of the another phase giving rise to leaflet vein-like appearance. The formation of large HDPE lamellae particularly longer than in the pure state has been explained by considering the different melting points of the blend components. The study of strain induced structural changes in an HDPE/EOC blend revealed that at large strains, the extensive stretching of the soft EOC phase is accompanied by buckling of HDPE lamellar stack along the strain axis and subsequent microfibrils formation. 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1887,1893, 2007 [source]

    Modeling the crystallization of proteins and small organic molecules in nanoliter drops

    AICHE JOURNAL, Issue 1 2010
    Richard D. Dombrowski
    Abstract Drop-based crystallization techniques are used to achieve a high degree of control over crystallization conditions in order to grow high-quality protein crystals for X-ray diffraction or to produce organic crystals with well-controlled size distributions. Simultaneous crystal growth and stochastic nucleation makes it difficult to predict the number and size of crystals that will be produced in a drop-based crystallization process. A mathematical model of crystallization in drops is developed using a Monte Carlo method. The model incorporates key phenomena in drop-based crystallization, including stochastic primary nucleation and growth rate dispersion (GRD) and can predict distributions of the number of crystals per drop and full crystal size distributions (CSD). Key dimensionless parameters are identified to quickly screen for crystallization conditions that are expected to yield a high fraction of drops containing one crystal and a narrow CSD. Using literature correlations for the solubilities, growth, and nucleation rates of lactose and lysozyme, the model is able to predict the experimentally observed crystallization behavior over a wide range of conditions. Model-based strategies for use in the design and optimization of a drop-based crystallization process for producing crystals of well-controlled CSD are identified. 2009 American Institute of Chemical Engineers AIChE J, 2010 [source]

    Preparation and characterization of poly(butylene terephthalate)/poly(ethylene terephthalate) copolymers via solid-state and melt polymerization

    M. A. G. Jansen
    Abstract To increase the Tg in combination with a retained crystallization rate, bis(2-hydroxyethyl)terephthalate (BHET) was incorporated into poly(butylene terephthalate) (PBT) via solid-state copolymerization (SSP). The incorporated BHET fraction depends on the miscibility of BHET in the amorphous phase of PBT prior to SSP. DSC measurements showed that BHET is only partially miscible. During SSP, the miscible BHET fraction reacts via transesterification reactions with the mobile amorphous PBT segments. The immiscible BHET fraction reacts by self-condensation, resulting in the formation of poly(ethylene terephthalate) (PET) homopolymer. 1H-NMR sequence distribution analysis showed that self-condensation of BHET proceeded faster than the transesterification with PBT. SAXS measurements showed an increase in the long period with increasing fraction BHET present in the mixtures used for SSP followed by a decrease due to the formation of small PET crystals. DSC confirmed the presence of separate PET crystals. Furthermore, the incorporation of BHET via SSP resulted in PBT-PET copolymers with an increased Tg compared to PBT. However, these copolymers showed a poorer crystallization behavior. The modified copolymer chain segments are apparently fully miscible with the unmodified PBT chains in the molten state. Consequently, the crystal growth process is retarded resulting in a decreased crystallization rate and crystallinity. 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 882,899, 2007. [source]

    Shape-memory polymer networks from oligo(,-caprolactone)dimethacrylates

    Andreas Lendlein
    Abstract Polymer networks showing a thermally induced shape-memory effect were prepared through the crosslinking of oligo(,-caprolactone)dimethacrylates under photocuring with or without an initiator. The influence of the molecular weight of the oligo(,-caprolactone)dimethacrylates and the initiator concentration on the macroscopic properties of the polymer networks was investigated. The isothermal and nonisothermal crystallization behavior of the polymer networks was evaluated as a basic principle of the functionalization process. Shape-memory properties such as the strain fixity and strain recovery rate were quantified with cyclic thermomechanical tensile experiments for different maximum elongations. 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1369,1381, 2005 [source]

    Ring-opening polymerization and block copolymerization of L -lactide with divalent samarocene complex

    Dongmei Cui
    Abstract Divalent samarocene complex [(C5H9C5H4)2Sm(tetrahydrofuran)2] was prepared and characterized and used to catalyze the ring-opening polymerization of L -lactide (L-LA) and copolymerization of L-LA with caprolactone (CL). Several factors affecting monomer conversion and molecular weight of polymer, such as polymerization time, temperature, monomer/catalyst ratio, and solvent, were examined. The results indicated that polymerization was rapid, with monomer conversions reaching 100% within 1 h, and the conformation of L-LA was retained. The structure of the block copolymer of CL/L-LA was characterized by NMR and differential scanning calorimetry. The morphological changes during crystallization of poly(caprolactone) (PCL)- b -P(L-LA) copolymer were monitored with real-time hot-stage atomic force microscopy (AFM). The effect of temperature on the morphological change and crystallization behavior of PCL- b -P(L-LA) copolymer was demonstrated through AFM observation. 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2667,2675, 2003 [source]

    Fabrication of Nitrogen-Containing Cordierite Ceramics

    Noritaka Saito
    We have investigated the crystallization behavior of cordierite-based oxynitride glass prepared by melting a powder mixture of cordierite and silicon nitride. The results indicated that two polymorphs exist: a stable ,-form, which has a low coefficient of thermal expansion, and a metastable ,-form. The time,temperature,transformation diagram of the crystallization of the ,-form shows a typical C-shaped curve that has a nose around 1420 K. Above 1373 K, the ,-form can be directly obtained by the isothermal crystallization of the oxynitride glass and the ,-form inverts to the ,-form at temperatures below 1273 K. We also have fabricated an ,-cordierite ceramic that has a nitrogen content of 1.55 mass%, which is much lower than the content of the batch composition (5 mass%); this is mainly owing to the decomposition reaction of nitrogen in the oxynitride melts and glasses during heat treatment. However, the fabricated nitrogen-containing ,-cordierite ceramics showed the coefficient of thermal expansion of 10,7 K,1, which is comparable with that of the oxide ,-cordierite ceramics. Moreover, Young's modulus of the ,-cordierite ceramics improved with the incorporation of nitrogen. [source]

    Preparation of Ba6,3xNd8+2xTi18O54 via Ethylenediaminetetraacetic Acid Precursor

    Yebin Xu
    Ba6,3xNd8+2xTi18O54 ceramic powders were synthesized by the modified Pechini method using ethylenediaminetetraacetic acid (EDTA) as a chelating agent. A purplish red, molecular-level, homogeneously mixed gel was prepared, and transferred into a porous resin intermediate through charring. Single-phase and well-crystallized Ba6,3xNd8+2xTi18O54 powders were obtained from pulverized resin at a temperature of 900C for 3 h, without formation of any intermediate phases. Meanwhile, the molar ratio of EDTA to total metal cation concentration had a significant influence on the crystallization behavior of Ba6,3xNd8+2xTi18O54. The Ba6,3xNd8+2xTi18O54 (x= 2/3) ceramics prepared via EDTA precursor have excellent microwave dielectric characteristics: ,= 87, Qf= 8710 GHz. [source]

    Fabrication and properties of nano-ZnO/glass-fiber-reinforced polypropylene composites

    Yi-Hua Cui
    Polypropylene (PP) is widely used in many fields, such as automobiles, medical devices, office equipment, pipe, and architecture. However, its high brittle transformation temperature, low mechanical strength, dyeing properties, antistatic properties, and poor impact resistance, considerably limit its further applications. Nano-ZnO treated by KH550 coupling agent and glass fibers (GFs) were introduced in order to improve the mechanical performance and flowability of PP in this research. The crystallization behavior and microstructure of nano-ZnO/GFs/PP hybrid composites were analyzed by differential scanning calorimetry, transmission electron microscopy, and scanning electron microscopy. The effect of crystallization behavior on the mechanical properties of the nanocomposites was investigated and analyzed. The results indicated that nano-ZnO surface-coupled by KH550 could be uniformly dispersed in the PP matrix. The incorporation of nano-ZnO and GFs resulted in increases of the crystallization temperature and crystallization rate of PP and a decrease of the crystallization degree. The introduction of nano-ZnO and GFs also enhanced the tensile strength and impact toughness of the hybrid composites and improved their fluidity. Composites containing 2% of nano-ZnO and 40% of GFs possessed the optimum mechanical properties. J. VINYL ADDIT. TECHNOL., 2010. 2010 Society of Plastics Engineers [source]

    Isolated Ethylene Units in Isotactic Polystyrene Chain: Stereocontrol of an Isospecific Post-Metallocene Titanium Catalyst

    Carmine Capacchione
    Abstract Summary: Copolymerization of styrene with small amounts of ethylene using the catalyst system dichloro{1,4-dithiabutanediyl-2,2,-bis(4,6-di- tert -butyl-phenoxy)}titanium/methylaluminoxane results in the unprecedented formation of isotactic polystyrene containing isolated ethylene units. 13C NMR spectroscopic analysis of the copolymer indicates that an "enantiomorphic site" control mechanism for isospecific propagation is operating. DSC measurements also indicate the presence of isolated ethylene units which modify the crystallization behavior of the isotactic polystyrene. Schematic representation of the copolymerization of styrene with small amounts of ethylene using dichloro{1,4-dithiabutanediyl-2,2,-bis(4,6-di-tert-butyl-phenoxy)}titanium/methylaluminoxane as catalyst system. [source]

    Miscibility and Physical Properties of Poly(3-hydroxybutyrate -co- 3-hydroxyhexanoate)/Poly(ethylene oxide) Binary Blends

    Fang Yu
    Abstract In order to improve some inferior physical properties of bacterial poly(3-hydroxybutyrate -co- 3-hydroxyhexanoate) [P(3HB -co- 3HHx)] by blending with PEO, the miscibility, spherulite morphology, crystallization behavior and mechanical properties of P(3HB -co- 3HHx)/PEO binary biodegradable polymer blends were investigated. A good miscibility between P(3HB -co- 3HHx) with a 3HHx unit content of 11 mol-% and PEO in the amorphous state was found when the PEO weight fraction was 10,wt.-%, while the miscibility decreased dramatically when the PEO weight fraction exceeded 20,wt.-%. Strongly depending on the blend composition, the mechanical properties of P(3HB -co- 3HHx) was found to be significantly improved by blending with PEO with a weight fraction of ,5,17.5,wt.-%. [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]

    Biodegradable Polylactide and Its Nanocomposites: Opening a New Dimension for Plastics and Composites

    Suprakas Sinha Ray
    Abstract The academic and industrial aspects of the preparation, characterization, mechanical and materials properties, crystallization behavior, melt rheology, and foam processing of pure polylactide (PLA) and PLA/layered silicate nanocomposites are described in this feature article. Recently, these materials have attracted considerable interest in polymer science research. PLA is linear aliphatic thermoplastic polyester and is made from agricultural products. Hectorite and montmorillonite are among the most commonly used smectite-type layered silicates for the preparation of nanocomposites. Smectites are a valuable mineral class for industrial applications because of their high cation exchange capacities, surface area, surface reactivity, adsorptive properties, and, in the case of hectorite, high viscosity, and transparency in solution. In their pristine form, they are hydrophilic in nature, and this property makes them very difficult to disperse into a polymer matrix. The most common way to overcome this difficulty is to replace interlayer cations with quaternized ammonium or phosphonium cations, preferably with long alkyl chains. In general, polymer/layered silicate nanocomposites are of three different types: (1) intercalated nanocomposites, in which insertion of polymer chains into the layered silicate structure occurs in a crystallographically regular fashion, regardless of polymer to layered silicate ratio, with a repeat distance of few nanometer; (2) flocculated nanocomposites, in which intercalated and stacked silicate layers are sometimes flocculated due to the hydroxylated edge,edge interactions between the silicate layers; (3) exfoliated nanocomposites, in which individual silicate layers are uniformly distributed in the polymer matrix by average distances that totally depend on the layered silicate loading. This new family of composite materials frequently exhibits remarkable improvements in its material properties when compared with those of virgin PLA. Improved properties can include a high storage modulus both in the solid and melt states, increased flexural properties, a decrease in gas permeability, increased heat distortion temperature, an increase in the rate of biodegradability of pure PLA, and so forth. Illustration of the biodegradability of PLA and various nanocomposites. [source]