Melting Temperature (melting + temperature)

Distribution by Scientific Domains
Distribution within Polymers and Materials Science

Kinds of Melting Temperature

  • equilibrium melting temperature
  • high melting temperature
  • lower melting temperature

  • Selected Abstracts

    Measurement of the Electric Resistivity of Metals up to and Above the Melting Temperature,

    R. Brandt
    A device for high-accuracy measurements of electric resistivity is introduced by the authors. Also, a layout for its use in high-temperature experiments presented to record resistivity changes around the melting temperature. A demonstration of the apparatus' precision (performed on steel samples at low temperature, with a deviation of merely 0.5 % from reference date) is given and first high-temperature results are discussed. [source]

    Functionalized polypropylenes in the compatibilization and dispersion of clay nanocomposites

    POLYMER COMPOSITES, Issue 4 2006
    C. Varela
    The preparation of polypropylene (PP) nanocomposites was studied using clay and three types of modified PP (m-PP) as compatibilizers: diethyl maleate grafted PP (PP- g -DEM), maleic anhydride grafted PP (PP- g -MA), and PP grafted with carbamyl maleamic acid (PP- g -UMA). The clay was made organophylic by an acid treatment with octadecylamine. PP functionalization and blending were carried out in an internal mixer. Blends of PP containing 20 and 40 wt% each of the modified PP and 5 wt% of organophilic clay (IMt), in each case, were prepared. Samples were characterized by transmission electron microscopy (TEM), differential scanning calorimetry (DSC), optical microscopy, and mechanical testing. The presence of tactoid, intercalated and exfoliated structures was observed by TEM in all the samples containing clay and modified PP, which also showed improved mechanical properties with tensile modulus as much as three times that of PP. Melting temperature did not vary significantly with the addition of clay. However, because of the clay's nucleating effect, an increase in the crystallization temperature was observed, accompanied by a slight decrease in the degree of crystallinity. The best results were obtained when PP- g -MA was used as the compatibilizer; intermediate results were obtained with the use of PP- g -UMA, followed by the results obtained when PP- g -DEM was used. Property enhancements were obtained when a higher percentage of modified PP was employed. POLYM. COMPOS., 27:451,460, 2006. 2006 Society of Plastics Engineers [source]

    Aminoglycoside,Quinacridine Conjugates: Towards Recognition of the P6.1 Element of Telomerase RNA

    CHEMBIOCHEM, Issue 2 2006
    Markus Kaiser Dr.
    Abstract A modular synthesis has been developed which allows easy and rapid attachment of one or two aminoglycoside units to a quinacridine intercalator, thereby leading to monomeric and dimeric conjugates. Melting temperature (Tm) experiments show that the tobramycin dimeric conjugate TD1 exhibits strong binding to the P6.1 element of human telomerase RNA. By contrast, tobramycin alone is much less efficient and the monomeric compound TM1 elicits a poor binding ability. Monitoring of the interaction by an electrophoretic mobility shift assay shows a 1:1 stoichiometry for the binding of the dimeric compound to the hairpin structure and confirms the lower affinity for a control duplex. Protection experiments with RNase T1 indicate interaction of the drug both in the stem and in the loop of the hairpin. Taken together, the data suggest a binding of TD1 inside the hairpin at the stem-loop junction. The same trends are observed with paromomycin and kanamycin analogues but with a lower affinity. [source]

    Oligonucleotide N3,,P5, Phosphoramidates and Thio -Phoshoramidates as Potential Therapeutic Agents

    Abstract Nucleic acids analogues, i.e., oligonucleotide N3,,P5, phosphoramidates and N3,,P5, thio -phosphoramidates, containing 3,-amino-3,-deoxy nucleosides with various 2,-substituents were synthesized and extensively studied. These compounds resist nuclease hydrolysis and form stable duplexes with complementary native phosphodiester DNA and, particularly, RNA strands. An increase in duplexes' melting temperature, ,Tm, relative to their phosphodiester counterparts, reaches 2.2,4.0 per modified nucleoside. 2,-OH- (RNA-like), 2,- O -Me-, and 2,- ribo -F-nucleoside substitutions result in the highest degree of duplex stabilization. Moreover, under close to physiological salt and pH conditions, the 2,-deoxy- and 2,-fluoro-phosphoramidate compounds form extremely stable triple-stranded complexes with either single- or double-stranded phosphodiester DNA oligonucleotides. Melting temperature, Tm, of these triplexes exceeds Tm values for the isosequential phosphodiester counterparts by up to 35. 2,-Deoxy-N3,,P5, phosphoramidates adopt RNA-like C3,- endo or N -type nucleoside sugar-ring conformations and hence can be used as stable RNA mimetics. Duplexes formed by 2,-deoxy phosphoramidates with complementary RNA strands are not substrates for RNase H-mediated cleavage in vitro. Oligonucleotide phosphoramidates and especially thio -phosphoramidates conjugated with lipid groups are cell-permeable and demonstrate high biological target specific activity in vitro. In vivo, these compounds show good bioavailability and efficient biodistribution to all major organs, while exerting acceptable toxicity at therapeutically relevant doses. Short oligonucleotide N3,,P5, thio -phosphoramidate conjugated to 5,-palmitoyl group, designated as GRN163L (Imetelstat), was recently introduced as a potent human telomerase inhibitor. GRN163L is not an antisense agent; it is a direct competitive inhibitor of human telomerase, which directly binds to the active site of the enzyme and thus inhibits its activity. This compound is currently in multiple Phase-I and Phase-I/II clinical trials as potential broad-spectrum anticancer agent. [source]

    Synthesis and MALDI-TOF analysis of dendritic-linear block copolymers of lactides: Influence of architecture on stereocomplexation

    Alexandre Richez
    Abstract Formation of a stereocomplex from polylactide copolymers can be tuned by changing the size and the chain topology of the second block in the copolymer. In particular, the use of a dendritic instead of linear architecture is expected to destabilize the cocrystallisation of polylactide blocks. With this idea in mind, dendritic-linear block copolymers were synthesized by ring-opening polymerization (ROP) of lactides using benzyl alcohol dendrons of generation 1,3 as macroinitiators and stannous octoate as catalyst. Polymers with controlled and narrow molar mass distribution were obtained. The MALDI-TOF mass spectra of these dendritic-linear block copolymers show well-resolved signals. Remarkably, 10% or less of odd-membered polymers are present, indicating that ester-exchange reactions which occur classically parallel to the polymerization process, were in these conditions, very limited. Thermal analysis of polyenantiomers of generation 1,3 and the corresponding blends were examined. The blend of a pair of enantiomeric dendritic-linear block copolymers exhibit a higher melting temperature than each copolymer, characteristic for the formation of a stereocomplex. Melting temperatures are strongly dependent on the dendron generation. 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6782,6789, 2006 [source]

    Polyamides X.34: A New Class of Polyamides with Long Alkane Segments

    Moritz Ehrenstein
    Abstract A new series of semi-crystalline polyamides (PA), which comprise extended aliphatic segments between the amide moieties and which display an interesting amphiphilic character has been synthesized and characterized. The polymers PA-2.34, PA-4.34, PA-8.34, PA-10.34, and PA-12.34 were prepared by melt-polycondensation of salts of tetratriacontanedioic acid and the respective short-chain diamine. The thermal properties of these polymers were investigated by differential scanning calorimetry, thermogravimetric analysis, and dynamic mechanical thermal analysis. The new polyamides exhibit melting temperatures that depend on the length of the diamine and range between 166 (PA-12.34) and 190,C (PA-2.34). Solid transitions were observed between 38 and 57,C. The materials displayed a rather limited solubility in common polyamide solvents, but readily dissolved in alkylsulfonic acids. All members of the series formed thermo-reversible gels in the highly polar sulfuric acid and 1,2,3,4-tetrahydronaphthalene, reflecting their interesting amphiphilic character. Young's moduli and tensile strengths of melt-processed, isotropic films of the polyamides investigated were in the range of 0.5,0.7 GPa and 20.30 MPa, respectively, independent of the length of the diamine used. Melting temperatures of polyamides PA-X.34 (x) and 1,2,3,4-tetrahydronaphthalene/PA-X.34 gels (37.5 wt.-% polyamide, determined from the second DSC heating scans) (+). [source]

    Synthesis and Hybridization Properties of Modified Oligodeoxynucleotides Carrying Non-Natural Bases

    Anna Avi
    Abstract The impact of the presence of nonnatural bases on the properties of oligodeoxynucleotides has been studied. First, oligodeoxynucleotides carrying 2,-deoxyzebularine were prepared, and the stability of duplexes carrying this analogue was determined by DNA melting experiments. Melting temperatures and thermodynamic data indicated the preference of 2,-deoxyzebularine for 2,-deoxyguanosine, which behaves as a 2,-deoxycytidine analogue, forming a less stable base pair due to the absence of the amino group at position 4. Moreover, the duplex,hairpin equilibrium of a self-complementary oligodeoxynucleotide carrying several natural and nonnatural bases including 2,-deoxyzebularine as a central mispair, was studied. Depending on the base present in the middle of the sequence, it is possible to affect the stability of the bimolecular duplex modulating the duplex,hairpin equilibrium. Magnesium ions were shown to stabilize preferentially the bimolecular duplex form. The results indicate the importance of the modifications and the role of cations in shifting the structural equilibrium. [source]

    Metal-Assisted Hybridization of Oligonucleotides, Evaluation of Circular 2,- O -Me RNA as Ligands for the TAR RNA Target

    Laurence Zapata
    Abstract Two complementary oligonucleotides were conjugated with terpyridine ligands at their nearby 5,- and 3,-ends. Addition of a stoichiometric amount of a transition metal (Zn2+, Fe2+) resulted in a large increase in the melting temperature of the duplex. The conjugation of TPY to stem-loop oligomers provided an efficient procedure for the cyclisation of the oligomer after the addition of metal ions. Such a short stem-loop oligomer was designed to target the HIV-1 TAR RNA through loop,loop interactions. The addition of Zn2+ ions yielded a good ligand (Kd = 30 nM) for this RNA structural element. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]

    Measurement of the Electric Resistivity of Metals up to and Above the Melting Temperature,

    R. Brandt
    A device for high-accuracy measurements of electric resistivity is introduced by the authors. Also, a layout for its use in high-temperature experiments presented to record resistivity changes around the melting temperature. A demonstration of the apparatus' precision (performed on steel samples at low temperature, with a deviation of merely 0.5 % from reference date) is given and first high-temperature results are discussed. [source]

    Improving thermostability and catalytic activity of pyranose 2-oxidase from Trametes multicolor by rational and semi-rational design

    FEBS JOURNAL, Issue 3 2009
    Oliver Spadiut
    The fungal homotetrameric flavoprotein pyranose 2-oxidase (P2Ox; EC catalyses the oxidation of various sugars at position C2, while, concomitantly, electrons are transferred to oxygen as well as to alternative electron acceptors (e.g. oxidized ferrocenes). These properties make P2Ox an interesting enzyme for various biotechnological applications. Random mutagenesis has previously been used to identify variant E542K, which shows increased thermostability. In the present study, we selected position Leu537 for saturation mutagenesis, and identified variants L537G and L537W, which are characterized by a higher stability and improved catalytic properties. We report detailed studies on both thermodynamic and kinetic stability, as well as the kinetic properties of the mutational variants E542K, E542R, L537G and L537W, and the respective double mutants (L537G/E542K, L537G/E542R, L537W/E542K and L537W/E542R). The selected substitutions at positions Leu537 and Glu542 increase the melting temperature by approximately 10 and 14 C, respectively, relative to the wild-type enzyme. Although both wild-type and single mutants showed first-order inactivation kinetics, thermal unfolding and inactivation was more complex for the double mutants, showing two distinct phases, as revealed by microcalorimetry and CD spectroscopy. Structural information on the variants does not provide a definitive answer with respect to the stabilizing effects or the alteration of the unfolding process. Distinct differences, however, are observed for the P2Ox Leu537 variants at the interfaces between the subunits, which results in tighter association. [source]

    Crystal structure of highly thermostable glycerol kinase from a hyperthermophilic archaeon in a dimeric form

    FEBS JOURNAL, Issue 10 2008
    Yuichi Koga
    The crystal structure of glycerol kinase from the hyperthermophilic archaeon Thermococcus kodakaraensis (Tk-GK) in a dimeric form was determined at a resolution of 2.4 . This is the first crystal structure of a hyperthermophilic glycerol kinase. The overall structure of the Tk-GK dimer is very similar to that of the Escherichia coli glycerol kinase (Ec-GK) dimer. However, two dimers of Ec-GK can associate into a tetramer with a twofold axis, whereas those of Tk-GK cannot. This may be the reason why Tk-GK is not inhibited by fructose 1,6-bisphosphate, because the fructose 1,6-bisphosphate binding site is produced only when a tetrameric structure is formed. Differential scanning calorimetry analyses indicate that Tk-GK is a highly thermostable protein with a melting temperature (Tm) of 105.4 C for the major transition. This value is higher than that of Ec-GK by 34.1 C. Comparison of the crystal structures of Tk-GK and Ec-GK indicate that there is a marked difference in the number of ion pairs in the ,16 helix. Four ion pairs, termed IP1,IP4, are formed in this helix in the Tk-GK structure. To examine whether these ion pairs contribute to the stabilization of Tk-GK, four Tk-GK and four Ec-GK derivatives with reciprocal mutations at the IP1,IP4 sites were constructed. The determination of their stabilities indicates that the removal of each ion pair does not affect the stability of Tk-GK significantly, whereas the mutations designed to introduce one of these ion pairs stabilize or destabilize Ec-GK considerably. These results suggest that the ion pairs in the ,16 helix contribute to the stabilization of Tk-GK in a cooperative manner. [source]

    Characterization and mode of action of an exopolygalacturonase from the hyperthermophilic bacterium Thermotoga maritima

    FEBS JOURNAL, Issue 21 2005
    Leon D. Kluskens
    An intracellular pectinolytic enzyme, PelB (TM0437), from the hyperthermophilic bacterium Thermotoga maritima was functionally produced in Escherichia coli and purified to homogeneity. PelB belongs to family 28 of the glycoside hydrolases, consisting of pectin-hydrolysing enzymes. As one of the few bacterial exopolygalacturonases, it is able to remove monogalacturonate units from the nonreducing end of polygalacturonate. Detailed characterization of the enzyme showed that PelB is highly thermo-active and thermostable, with a melting temperature of 105 C and a temperature optimum of 80 C, the highest described to date for hydrolytic pectinases. PelB showed increasing activity on oligosaccharides with an increasing degree of polymerization. The highest activity was found on the pentamer (1000 Umg,1). In addition, the affinity increased in conjunction with the length of the oligoGalpA chain. PelB displayed specificity for saturated oligoGalpA and was unable to degrade unsaturated or methyl-esterified oligoGalpA. Analogous to the exopolygalacturonase from Aspergillus tubingensis, it showed low activity with xylogalacturonan. Calculations on the subsite affinity revealed the presence of four subsites and a high affinity for GalpA at subsite +1, which is typical of exo-active enzymes. The physiological role of PelB and the previously characterized exopectate lyase PelA is discussed. [source]

    Neuroserpin Portland (Ser52Arg) is trapped as an inactive intermediate that rapidly forms polymers

    FEBS JOURNAL, Issue 16 2004
    Implications for the epilepsy seen in the dementia FENIB
    The dementia familial encephalopathy with neuroserpin inclusion bodies (FENIB) is caused by point mutations in the neuroserpin gene. We have shown a correlation between the predicted effect of the mutation and the number of intracerebral inclusions, and an inverse relationship with the age of onset of disease. Our previous work has shown that the intraneuronal inclusions in FENIB result from the sequential interaction between the reactive centre loop of one neuroserpin molecule with ,-sheet A of the next. We show here that neuroserpin Portland (Ser52Arg), which causes a severe form of FENIB, also forms loop-sheet polymers but at a faster rate, in keeping with the more severe clinical phenotype. The Portland mutant has a normal unfolding transition in urea and a normal melting temperature but is inactive as a proteinase inhibitor. This results in part from the reactive loop being in a less accessible conformation to bind to the target enzyme, tissue plasminogen activator. These results, with those of the CD analysis, are in keeping with the reactive centre loop of neuroserpin Portland being partially inserted into ,-sheet A to adopt a conformation similar to an intermediate on the polymerization pathway. Our data provide an explanation for the number of inclusions and the severity of dementia in FENIB associated with neuroserpin Portland. Moreover the inactivity of the mutant may result in uncontrolled activity of tissue plasminogen activator, and so explain the epileptic seizures seen in individuals with more severe forms of the disease. [source]

    Temperature-Resolved Local and Macroscopic Charge Carrier Transport in Thin P3HT Layers,

    Patrick Pingel
    Abstract Previous investigations of the field-effect mobility in poly(3-hexylthiophene) (P3HT) layers revealed a strong dependence on molecular weight (MW), which was shown to be closely related to layer morphology. Here, charge carrier mobilities of two P3HT MW fractions (medium-MW: Mn,=,7,200 g mol,1; high-MW: Mn,=,27,000 g mol,1) are probed as a function of temperature at a local and a macroscopic length scale, using pulse-radiolysis time-resolved microwave conductivity (PR-TRMC) and organic field-effect transistor measurements, respectively. In contrast to the macroscopic transport properties, the local intra-grain mobility depends only weakly on MW (being in the order of 10,2 cm2 V,1 s,1) and being thermally activated below the melting temperature for both fractions. The striking differences of charge transport at both length scales are related to the heterogeneity of the layer morphology. The quantitative analysis of temperature-dependent UV/Vis absorption spectra according to a model of F. C. Spano reveals that a substantial amount of disordered material is present in these P3HT layers. Moreover, the analysis predicts that aggregates in medium-MW P3HT undergo a "pre-melting" significantly below the actual melting temperature. The results suggest that macroscopic charge transport in samples of short-chain P3HT is strongly inhibited by the presence of disordered domains, while in high-MW P3HT the low-mobility disordered zones are bridged via inter-crystalline molecular connections. [source]

    Masking selected sequence variation by incorporating mismatches into melting analysis probes,

    HUMAN MUTATION, Issue 3 2006
    Rebecca L. Margraf
    Abstract Hybridization probe melting analysis can be complicated by the presence of sequence variation (benign polymorphisms or other mutations) near the targeted mutation. We investigated the use of "masking" probes to differentiate alleles with similar probe melting temperatures. Selected sequence variation was masked by incorporating mismatches (deletion, unmatched nucleotide, or universal base) into hybridization probes at the polymorphic location. Such masking probes create a probe/target mismatch with all possible alleles at the selected polymorphic location. Any allele with additional variation at another site is identified by a lower probe melting temperature than alleles that vary only at the masked position. This "masking technique" was applied to RET protooncogene and HPA6 mutation detection using unlabeled hybridization probes, a saturating dsDNA dye, and high-resolution melting analysis. Masking probes clearly distinguished all targeted mutations from polymorphisms when at least 1 base pair (bp) separated the mutation from the masked variation. We were able to mask polymorphisms immediately adjacent to mutations, except in certain cases, such as those involving single-base deletion probes when both adjacent positions had the same polymorphic nucleotides. The masking probes can also localize mutations to specific codons or nucleotide positions. Masking probes can simplify melting analysis of complex regions and eliminate the need for sequencing. Hum Mutat 27(3), 269,278, 2006. 2006 Wiley-Liss, Inc. [source]

    The Planck,Benzinger thermal work function in the condensation of water vapor

    Paul W. Chun
    Abstract Based on the Planck,Benzinger thermal work function using Chun's method, the innate temperature-invariant enthalpy at 0 K, ,H0(T0), for the condensation of water vapor as well as the dimer, trimer, tetramer, and pentamer form in the vapor phase, was determined to be 0.447 kcal mol,1 for vapor, 1.127 for the dimer, 0.555 for the trimer, 0.236 for the tetramer, and 0.079 kcal mol,1 for the pentamer using ,G(T) data reported by Kell et al. in 1968 and Kell and McLaurin in 1969. These results suggest that the predominant dimeric form is the most stable of these n -mers. Using Nemethy and Scheraga's 1962 data for the Helmholtz free energy of liquid water, the value of ,H0(T0) was determined to be 1.21 kcal mol,1. This is very close to the value for the energy of the hydrogen bond EH of 1.32 kcal mol,1 reported by Nemethy and Scheraga, using statistical thermodynamics. It seems clear that very little energy is required for interconversion between the hypothetical supercooled water vapor and glassy water at 0 K. A hypothetical supercooled water vapor at 0 K is apparently almost as highly associated as glassy water at that temperature, suggesting a dynamic equilibrium between vapor and liquid. This water vapor condensation is highly similar in its thermodynamic behavior to that of sequence-specific pairwise (dipeptide) hydrophobic interaction, except that the negative Gibbs free energy change minimum at ,Ts,, the thermal setpoint for vapor condensation, where T,S = 0, occurs at a considerably lower temperature, 270 K (below 0C) compared with ,350 K. The temperature of condensation ,Tcond, at which ,G(T) = 0, where water vapor begins to condense, was found to be 383 K. In the case of a sequence-specific pairwise hydrophobic interaction, the melting temperature, ,Tm,, where ,G(Tm) = 0 was found to be 460 K. Only between two temperature limits, ,Th, = 99 K and ,Tcond, = 383 K, where ,G(Tcond) = 0, is the net chemical driving force favorable for polymorphism of glassy water and hypothetical supercooled water vapor. Analysis of the water vapor condensation process based on the Planck,Benzinger thermal work function confirms that a thermodynamic molecular switch occurs at 10 K, wherein a change of sign in [,Cp(T)]cond leads to a true negative minimum in the Gibbs free energy of vapor condensation, and hence a maximum in the related equilibrium constant, Kcond. 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [source]

    Molecular dynamics of phase transitions in clusters of alkali halides

    Pedro C. R. Rodrigues
    Abstract Molecular dynamics simulations of unconstrained alkali halide clusters with 8, 64, 216, 512, 1000, 1728, 2744, 4096, 5832, and 8000 ions have been carried out using the Born,Mayer,Huggins potential. All the clusters exhibit first-order melting and freezing transitions. The melting temperature increases with the number of ions and approaches the melting temperature of the bulk. Clusters with a number of ions less than approximately 1000 present hysteresis cycles and practically do not have phase coexistence. Clusters with a number of ions over 1000 present phase coexistence during a significant part of the transition region and hysteresis is progressively eliminated as the clusters size increases. It is suggested that hysteresis is an intrinsic characteristic of small clusters. In the transition regions the calculations have been performed by fixing the total energy of the clusters. It is shown that such a technique provides a better way of analyzing the transition mechanism than the usual procedure of fixing the temperature by ad hoc rescaling the velocities or by using canonical molecular dynamics or Monte Carlo. A detailed analysis of the melting transition is presented. The effects of interfaces and impurities are discussed. A method based on the velocity autocorrelation functions is proposed, in order to determine the molar fraction of the ions present in the solid and liquid phases as well as to produce colored snapshots of the phases in coexistence. The overall agreement of the estimated melting points and enthalpies of melting with the experiment is fairly good. The estimated melting point and enthalpy of melting for KCl in particular are in excellent agreement with the experimental values. 2001 John Wiley & Sons, Inc. Int J Quantum Chem 84: 169,180, 2001 [source]

    A novel process for continuous thermal embossing of large-area nanopatterns onto polymer films

    Matthew D. Fagan
    Abstract Hot embossing and nanoimprinting processes are being widely practiced in industry. Fast and reliable production of micro/nanofeatured patterns on large-area polymer films is of a great importance. In this study, a novel roll-to-roll thermal imprinting process was developed, capable of providing a mold-heating rate of 125C/s with sufficient temperature control to produce large-area patterns continuously at a rapid production rate. With this new process, selected micro/nano patterns were produced on a polyethylene terephthalate film at a production rate exceeding 1 m/min. The roller mold temperature played a profound role in affecting the replication quality. To achieve good feature transfer properties, an elevated roller mold temperature approaching the melting temperature of the polymer was found to be critical. Microcavity filling time calculation further revealed that the elevated roller mold temperature is also necessary for achieving a rapid film feed rate as desired in the continuous roll-to-roll process. 2010 Wiley Periodicals, Inc. Adv Polym Techn 28:246,256, 2009; Published online in Wiley InterScience ( DOI 10.1002/adv.20167 [source]

    Electrical and thermal properties of nylon 6/calcium carbonate composites

    M. A. Moussa
    Abstract Several polymer composites formed from nylon 6/CaCO3 with different ratios and particle sizes were prepared using modified and unmodified CaCO3 as inorganic filler. The modification of CaCO3 surfaces was carried out by adsorption of oleic acid from toluene. TGA and DSC measurements show that the glass transition temperatures reduced by the presence of inorganic filler, whereas the melting temperature did not influenced. In all prepared polymer composites, the presence of filler accelerates the degradation process of the polymer. Dielectric properties of the investigated samples were studied in the frequency range from 45 Hz to 1 MHz and at temperatures ranging between 50 and 200C. The presence of CaCO3 led to a remarkable decrease in the conductivity of nylon 6. 2010 Wiley Periodicals, Inc. Adv Polym Techn 28:257,266, 2009; Published online in Wiley InterScience ( DOI 10.1002/adv.20165 [source]

    Physical characterization of starch extrudates as a function of melting transitions and extrusion conditions

    Stphanie Blanche
    Abstract The objective of this study was to investigate the relationships between starch melt transition characteristics, extrusion conditions, and final product properties. Cornstarch was extruded using a corotating twin-screw extruder at varying moisture content, medium/high screw configuration, and 300/400-rpm screw speeds. Extrudates were evaluated for bulk density, expansion ratio, cell structure, bending strength, thermal and pasting properties. Temperature change (,T) was defined as the temperature difference between the native starch melting temperature and its melt temperature just behind the die during extrusion at a given moisture content. ,T was significantly affected by starch moisture content and mechanical shearing, which controlled the melting behavior of the starch in the barrel. Amylose,lipid complex formation during extrusion increased as ,T increased and leveled off at ,T of about 20C. Pasting peak viscosity of the starch extrudates decreased as ,T increased and leveled off at ,T of about 15C. Within the same range of mechanical shearing intensity, extrudate bulk density and bending strength decreased linearly as ,T increased. Extrudate expansion was negatively correlated to bulk density. 2004 Wiley Periodicals, Inc. Adv Polym Techn 23: 277,290, 2004; Published online in Wiley InterScience ( DOI 10.1002/adv.20017 [source]

    Effect of solid state grinding on properties of PP/PET blends and their composites with carbon nanotubes

    Ozcan Koysuren
    Abstract In this study, it was aimed to improve electrical conductivity and mechanical properties of conductive polymer composites, composed of polypropylene (PP), poly(ethylene terephthalate) (PET), and carbon nanotubes (CNT). Grinding, a type of solid state processing technique, was applied to PP/PET and PP/PET/CNT systems to reduce average domain size of blend phases and to improve interfacial adhesion between these phases. Surface energy measurements showed that carbon nanotubes might be selectively localized at PET phase of immiscible blend systems. Grinding technique exhibited improvement in electrical conductivity and mechanical properties of PP/PET/CNT systems at low PET compositions. Ground composites molded below the melting temperature of PET exhibited higher tensile strength and modulus values than those prepared above the melting temperature of PET. According to SEM micrographs, micron-sized domain structures were obtained with ground composite systems in which PET was the minor phase. 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source]

    Reduction in tactoid size as a means for reinforcing high-density polyethylene/montmorillonite nanocomposites

    Carla Marega
    Abstract Nanocomposites were prepared by adding montmorillonite clay to a high-density polyethylene matrix. Their structure, morphology, thermal behavior, and physical, mechanical properties were studied. The filler did not alter much the structure and morphology of the matrix, with the exception of a disruptive effect on the lamellar stacks. The crystallization behavior, equilibrium melting temperature, and work of chain folding of the nanocomposites were also unaltered with respect to that of the PE base polymer. However, significant improvements in physical,mechanical properties were observed. The reason for this increase in performance was ascribed to the interaction between the filler and the matrix, especially because of a reduction in size of the original tactoids to stacks of just a few layers, albeit not intercalated. 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source]

    Improvement of the thermal stability of polyhydroxybutyrates by grafting with maleic anhydride by different methods: Differential scanning calorimetry, thermogravimetric analysis, and gel permeation chromatography

    Shinn-Gwo Hong
    Abstract The crystallization and thermal degradation behaviors of polyhydroxybutyrate (PHB) grafted with maleic anhydride (MA) by different techniques were analyzed with differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and gel permeation chromatography (GPC). The results of DSC, TGA, and GPC analyses indicated that the grafting method could affect the crystallization rate, crystallinity, and thermal stability of PHB because of changes in the molecular weight of PHB and the amount of MA grafted during the reaction. The reduction of the molecular weight of PHB that reacted during the processing followed this order of methods: melt grafting > solvent grafting > mechanical grafting. However, the grafting ratio of MA followed this order of methods: melt grafting > mechanical grafting > solvent grafting. All three grafting methods significantly improved the thermal stability, therefore increasing the crystallization rate and melting temperature of the as-received PHB. A grafting ratio of MA as low as 0.07 wt % could result in a significant improvement in the heat resistance of PHB. 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

    Poly(butylene terephthalate)/clay nanocomposite compatibilized with poly(ethylene- co -glycidyl methacrylate).


    Abstract Poly(butylene terephthalate) (PBT)/clay nanocomposite was prepared by blending PBT and commercial modified montmorillonite clays via a extruder by using poly(ethylene- co -glycidyl methacrylate) (PEGMA) as a compatibilizer (PBT/PEGMA/Clay). PEGMA and clay were also blended with PBT to prepare PBT/PEGMA and PBT/Clay, respectively. The morphology was investigated by wide-angle X-ray diffraction (WAXD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The clays were aggregated together and phase separation was observed in PBT/Clay. The clays were exfoliated in PBT/PEGMA/Clay. The equilibrium melting temperature was estimated by linear and nonlinear Hoffman-Weeks relation. The influence of the PEGMA and clay on the PBT crystallizable ability was also investigated by Avrami model and undercooling (difference between crystallization and equilibrium melting temperature). Hoffman-Lauritzen relation was used to estimate chain fold surface free energy. The exfoliated silicates cause a large number nucleus center to enhance the crystallization in PBT/PEGMA/Clay. The presence of PEGMA can react with the PBT and an increase in viscosity would reduce molecular mobility and crystallization in PBT/PEGMA. The aggregated clays have a confinement effect on the segmental motion of PBT and hinder the crystallization in PBT/Clay. 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

    Surface modification of starch nanocrystals through ring-opening polymerization of ,-caprolactone and investigation of their microstructures

    Hassan Namazi
    Abstract Bionanoparticles of starch obtained by submitting native potato starch granules to acid hydrolysis conditions. The resulted starch nanoparticles were used as core or macro initiator for polymerization of ,-caprolactone (CL). Starch nanoparticle- g -polycaprolactone was synthesized through ring-opening polymerization (ROP) of CL in the presence of Sn(Oct)2 as initiator. The detailed microstructure of the resulted copolymer was characterized with NMR spectroscopy. Thermal characteristic of the copolymer was investigated using DSC and TGA. By introducing PCL, the range of melting temperature for starch was increased and degradation of copolymer occurred in a broader region. X-ray diffraction and TEM micrographs confirmed that there was no alteration of starch crystalline structure and morphology of nanoparticles, respectively. 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [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]

    Compatibility of liquid deproteinized natural rubber having epoxy group (LEDPNR)/poly (L -lactide) blend

    Phan Trung Nghia
    Abstract Reaction after mixing of liquid epoxidized natural rubber/poly(L -lactide) blend was performed to enhance the compatibility of the blend. The liquid epoxidized natural rubber was prepared by epoxidation of deproteinized natural rubber with peracetic acid in latex stage followed by depolymerization with peroxide and propanal. The resulting liquid deproteinized natural rubber having epoxy group (LEDPNR) was mixed with poly(L -lactide) (PLLA) to investigate the compatibility of the blend through differential scanning calorimetry, optical light microscopy, and NMR spectroscopy. After heating the blend at 473 K for 20 min, glass transition temperature (Tg) of LEDPNR in LEDPNR/PLLA blend increased from 251 to 259 K, while Tg and melting temperature (Tm) of PLLA decreased from 337 to 332 K and 450 to 445 K, respectively, suggesting that the compatibility of LEDPNR/ PLLA blend was enhanced by a reaction between the epoxy group of LEDPNR and the ester group of PLLA. The reaction was proved by high-resolution solid-state 13C NMR spectroscopy. 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

    Preparation and properties of physically crosslinked sodium carboxymethylcellulose/poly(vinyl alcohol) complex hydrogels

    Congming Xiao
    Abstract A series of physically crosslinked complex hydrogels of poly(vinyl alcohol) (PVA) and sodium carboxymethylcellulose (CMC) were prepared via physical mixing and a freeze/thaw technique. The morphology of the CMC/PVA complex gels was analyzed with differential scanning calorimetry and wide-angle X-ray diffraction. It was found that the crystallinity and melting temperature of the complex gels decreased, whereas the glass-transition temperature increased, with an increase in the content of CMC. The reswelling of the complex gels was pH-responsive and relied on the content of CMC and the freeze/thaw cycles. A network structure model of the complex gel was presented. PVA crystalline regions served as physical crosslinks; the interaction between CMC and PVA resulted in intramolecular entanglements. It was also found that the model drug hemoglobin was released completely from the complex hydrogels in 4 h, and its release rate increased with an increase in the content of CMC. 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

    Effect of chain architecture on biaxial orientation and oxygen permeability of polypropylene film

    P. Dias
    Abstract Films of two isotactic propylene homopolymers prepared with different catalysts and a propylene/ethylene copolymer were biaxially oriented under conditions of temperature and strain rate that were similar to those encountered in a commercial film process. The draw temperature was varied in the range between the onset of melting and the peak melting temperature. It was found that the stress response during stretching depended on the residual crystallinity in the same way for all three polymers. Biaxial orientation reduced the oxygen permeability of the oriented films, however, the reduction did not correlate with the amount of orientation as measured by birefringence, with the fraction of amorphous phase as determined by density, or with free volume hole size as determined by PALS. Rather, the decrease in permeability was attributed to reduced mobility of amorphous tie molecules. A single one-to-one correlation between the oxygen permeability and the intensity of the dynamic mechanical ,-relaxation was demonstrated for all the polymers used in the study. 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

    Evaluation of the crystallization kinetics and melting of polypropylene and metallocene-prepared polyethylene blends

    Mohammad Razavi-Nouri
    Abstract The kinetics of the isothermal crystallization of a polypropylene (PP) random copolymer containing 5 mol % ethylene, a metallocene linear low-density polyethylene (m -LLDPE) with 3.3 mol % hexene-1 as a comonomer, and three blends were studied with differential scanning calorimetry at temperatures sufficiently high to prevent any crystallization of m-LLDPE. The analysis was carried out with the Avrami equation. The overall crystallization rate and the equilibrium melting temperature of the PP copolymer decreased with increasing amounts of m-LLDPE in the blends. The former was attributed to the effect of m-LLDPE in reducing the number of primary nuclei, and the latter was attributed to a lowering of the fold surface energy due to the limited partial miscibility of the blend components. 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 634,640, 2007 [source]