DSC Measurements (dsc + measurement)

Distribution by Scientific Domains

Selected Abstracts

Crosslinking of elastomers upon ageing: a kinetic approach based on crystallinity changes followed by DSC

Mohamed Baba
Abstract It was observed that crosslinking reactions resulting both from peroxide decomposition or photoageing at wavelengths longer than 300,nm involve a drastic decrease of the crystallinity of some dienic elastomers, such as polybutadienes (rich in cis 1,4 and 1,2 microstructures) and polycyclo-octene. By comparing precisely the rate of decomposition of dicumyl peroxide and that of the crystallinity decrease, it was possible to show that the kinetics of crystallinity loss observed upon ageing can be identified with that of the crosslinking of elastomers. The results indicate that the crosslinking process can be followed directly by DSC measurement of the crystallization/melting cycle. 2003 Society of Chemical Industry [source]

Control of orientation for carbazole group in comb copolymers arranged by method of organized molecular films

Hiroko Hoshizawa
Abstract We investigated the molecular orientation of organized molecular films with regard to solid-state structures for newly synthesized comb copolymers with N -vinylcarbazole (NVCz) by in-plane and out-of plane X-ray diffraction (XRD), differential scanning calorimetry (DSC), and atomic force microscopy (AFM). In the bulk state, hydrogenated and fluorinated comb copolymers form side-chain crystals for a two-dimensional lattice spacing of 4.2 and 5.0,, respectively. The findings suggest that the carbazole rings in the main-chain are arranged in opposition to each other. From the results of the DSC measurement, sharp-shaped melting peaks appear on the relatively lower temperature side of the thermograms. This result supports the formation of side-chain crystals in the synthesized comb copolymers. These monolayers of the copolymers on the water surface were extremely condensed, except for the fluorocarbon:NVCz,=,1:1 copolymer. From the in-plane XRD measurement of multilayers on solids, the changes in the two-dimensional lattice structure of fluorinated comb copolymer films containing NVCz units, as opposed to their bulk state, were confirmed. It seems that these structural changes are caused by the stronger ,,, interaction between the carbazole rings rather than the van der Waals interaction between fluorocarbons. Copyright 2007 John Wiley & Sons, Ltd. [source]

Influence of the atmosphere on the growth of LiYF4 single crystal fibers by the micro-pulling-down method

D. Maier
Abstract Micro-pulling-down growth of LiYF4 single crystal fibers have been performed under different gas atmospheres using stoichiometric LiYF4 single crystal pieces from prior Czochralski experiments as starting material. Completely transparent and phase pure LiYF4 single crystal fibers could be obtained after evacuation of the recipient to 210 -6 mbar and subsequent filling with pure (99.995%) CF4 gas. Using a gas mixture of 5% CF4 in Argon or pure 5N Argon leads to the formation of micro crystallites of oxofluorides on the surface. Evacuating only to 3 10 -3 mbar leads, independently of atmosphere, to completely white fibers that are heavily contaminated with oxofluorides. DSC measurements of the completely transparent fiber grown under pure CF4 atmosphere reveal congruent melting behavior. ( 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [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 (www.interscience.wiley.com). DOI 10.1002/adv.20165 [source]

Method to describe curing in large epoxy samples

Krzysztof Kasza
Abstract Curing kinetics models used in numerical simulations describe the exothermic chemical reaction of thermosetting materials. The mathematical formula known as Kamal's model is discussed in the following paper. Traditionally, the coefficients of Kamal's equations are estimated based on differential scanning calorimetry (DSC) measurements and results from an experimental verification of such created curing kinetics model are presented. Furthermore, an inverse analysis is proposed for additional adjustment of the model. The new coefficients thus found provide better accuracy in the computer simulations. The methodology of development of the curing kinetics model is proposed as an alternative solution to the standard DSC measurements. Particularly, it could be useful for materials with a complex structure, such as composites. 2010 Wiley Periodicals, Inc. Adv Polym Techn 28:267,275, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20162 [source]

Curing behavior of a novel polytriazole resin

Liqiang Wan
Abstract The curing behavior of a novel low temperature curing polytriazole resin, prepared from p -xylylene diazide and N,N,N,,N, -tetrapropargyl- p,p, -diaminodiphenylmethane, was investigated by DSC and rheological analyses. The kinetics of the curing of the resin was studied by nonisothermal and isothermal DSC measurements and the kinetics parameters were obtained. The values of apparent activation energy Ea of the curing reaction obtained by nonisothermal and isothermal DSC are 80.7 and 75.3 kJ/mol, respectively. The curing of the resin was traced by the isothermal rheological analysis. The gelation times of the resin at 70, 75, 80, and 85C are about 200, 150, 110, and 75 min, respectively. The viscosity equation for the resin was found as follows: 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 [source]

Influence of the remelting process on the fatigue behavior of electron beam irradiated UHMWPE

J. A. Purtolas
Abstract Electron beam irradiation at doses below 150 kGy is a widely used technique to obtain highly crosslinked ultra-high-molecular-weight polyethylene (UHMWPE). Its current use in total joint replacement components may improve wear resistance and decrease UHMWPE particle debris. However, currently used post-irradiation thermal treatments, which aim to decrease the free radicals within the material, introduce microstructural changes that affect UHMWPE mechanical properties, particularly the fatigue strength. This influence may be crucial in total knee replacements, where fatigue-related damage limits the lifespan of the prosthesis. Therefore, more studies are required to understand UHMWPE fatigue after current crosslinking protocols. This study was planned to evaluate the influence of UHMWPE remelting after irradiation on the material fatigue resistance. The remelting was achieved at 150C for 2 h on UHMWPE previously irradiated at 50, 100, and 150 kGy. Fatigue evaluation included short-term tests under cyclic tensile stress with zero load ratio, R = 0, and 1 Hz. In addition, stress-life testing was performed using 12% yield as the criterion for failure. Near-threshold fatigue crack propagation experiments were also performed at a frequency of 5 Hz, and crack length was measured in nonthermally treated and remelted irradiated UHMWPE. Crystallinity percentage was calculated from DSC measurements. The results pointed out that irradiation positively contributed to total life analysis, but the further remelting process decreased the flaw initiation resistance. On the other hand, both processes negatively affected the fatigue resistance of notched components. From a clinical point of view, the results suggest that the material fatigue behavior should be carefully studied in new UHMWPE to avoid changes related to material processing. 2005 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2006 [source]

Microstructure of ball milled and compacted Co,Ni,Al alloys from the , range

Summary Two powder alloys from the , phase region of compositions Co28.5Ni36.5Al35 and Co35Ni30Al35 were ball milled for 80 h in a high energy ball mill. The formation of amorphous structure was observed after 40 h of milling and further milling did not change their structure. The analytical and high-resolution transmission electron microscopy (TEM, HREM) examination of powder structure showed that nanoparticles of L10 phase of size of about 5 nm were present within the amorphous matrix. The vacuum hot pressing of the milled powders under pressure of 400 MPa at 700C for 12 min resulted in the formation of compacts with density of about 70% of the theoretical one. The additional heat treatment at 1300C for 6 h followed by water quenching, led to significant improvement of density and induced the martensitic transformation manifested by a broad heat effect. The characteristic temperatures of the transformation were determined using DSC measurements, which revealed only small differences within the examined alloys compositions. TEM structure studies of heat-treated alloys allowed to identify the structure of an ordered , (B2) phase and L10 martrensite. [source]

Characterization of amorphous API:Polymer mixtures using X-ray powder diffraction

Ann Newman
Abstract Recognizing limitations with the standard method of determining whether an amorphous API,polymer mixture is miscible based on the number of glass transition temperatures (Tg) using differential scanning calorimetry (DSC) measurements, we have developed an X-ray powder diffraction (XRPD) method coupled with computation of pair distribution functions (PDF), to more fully assess miscibility in such systems. The mixtures chosen were: dextran,poly(vinylpyrrolidone) (PVP) and trehalose,dextran, both prepared by lyophilization; and indomethacin,PVP, prepared by evaporation from organic solvent. Immiscibility is detected when the PDF profiles of each individual component taken in proportion to their compositions in the mixture agree with the PDF of the mixture, indicating phase separation into independent amorphous phases. A lack of agreement of the PDF profiles indicates that the mixture with a unique PDF is miscible. In agreement with DSC measurements that detected two independent Tg values for the dextran,PVP mixture, the PDF profiles of the mixture matched very well indicating a phase separated system. From the PDF analysis, indomethacin,PVP was shown to be completely miscible in agreement with the single Tg value measured for the mixture. In the case of the trehalose,dextran mixture, where only one Tg value was detected, however, PDF analysis clearly revealed phase separation. Since DSC can not detect two Tg values when phase separation produces amorphous domains with sizes less than approximately 30 nm, it is concluded that the trehalose,dextran system is a phase separated mixture with a structure equivalent to a solid nanosuspension having nanosize domains. Such systems would be expected to have properties intermediate to those observed for miscible and macroscopically phase separated amorphous dispersions. However, since phase separation has occurred, the solid nanosuspensions would be expected to exhibit a greater tendency for physical instability under a given stress, that is, crystallization, than would a miscible system. 2008 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 97:4840,4856, 2008 [source]

Core-shell particles with glycopolymer shell and polynucleoside core via RAFT: From micelles to rods

Samuel Pearson
Abstract Amphiphilic block copolymers were synthesized via the reversible addition fragmentation chain transfer (RAFT) copolymerisation of 2-methacrylamido glucopyranose (MAG) and 5,- O -methacryloyl uridine (MAU). Homopolymerisations of both monomers using (4-cyanopentanoic acid)-4-dithiobenzoate (CPADB) proceeded with pseudo first order kinetics in a living fashion, displaying linear evolution of molecular weight with conversion and low PDIs. A bimodal molecular weight distribution was observed for PMAU at low conversions courtesy of hybrid behavior between living and conventional free radical polymerization. This effect was more pronounced when a PMAG macroRAFT agent was chain extended with MAU, however, in both cases, good control was attained once the main RAFT equilibrium was established. A stability study on PMAU found that its hydrolysis is diffusion controlled, and is accelerated at physiological pH compared with neutral conditions. Self-assembly of four block copolymers with increasing hydrophobic (PMAU) block lengths produced micelles, which demonstrated an increased tendency to form rods as the PMAU block length increased. Interestingly, none of the block copolymers were surface-active. An initial assessment of PMAU's ability to bind the nucleoside adenosine through base pairing was highly promising, with DSC measurements indicating that adenosine is fully miscible in the PMAU matrix. 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1706,1723, 2009 [source]

Acid-labile, thermoresponsive (meth)acrylamide polymers with pendant cyclic acetal moieties

Xiao-Nan Huang
Abstract Acid-labile, thermoresponsive polymers with pendant six-membered cyclic acetal groups were prepared by radical polymerization of two monomers, N -(2,2-dimethyl-1,3-dioxan-5-yl) methacrylamide (NDMM) and N -(2,2-dimethyl-1,3-dioxan-5-yl) acrylamide (NDMA). The aqueous solution properties of the polymers, PNDMM and PNDMA, were studied by turbidimetry, 1H NMR, fluorescence, and DSC measurements. It is found that both polymers show sensitive and reversible phase transitions with distinct lower critical solution temperatures (LCST). Below their LCSTs, there are still some polymer aggregates as evidenced by measurements of pyrene excitation spectra and urea effects on the cloud points (CP) of polymers. The salting effect of six inorganic sodium salts on the phase transition behavior of PNDMM was investigated by turbidimetric approach. The salting-out to salting-in effect is in the order of SO42, > F, > Cl, > Br, > I, > SCN,, following the Hofmeister's series. pH-dependent hydrolysis of PNDMM and PNDMA was studied by turbidimetric and 1H NMR methods. They are both pH-sensitive and their hydrolysis rates significantly increase with decreasing pH value. The CP of PNDMM gradually increases with the acid-triggered hydrolysis of the acetal groups and the hydrolyzed polymer with , 30% hydrolysis degree does not show thermally induced phase transition. 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4332,4343, 2008 [source]

Syntheses of multicyclic poly(ether sulfone)s from 5,5,,6,6,-tetrahydroxy-3,3,3,,3,-tetramethyl spirobisindane and 4,4,-bis(4-chlorophenyl) sulfones

Hans R. Kricheldorf
Abstract 5,5,,6,6,-Tetrahydroxy-3,3,3,,3,-tetramethyl spirobisindane (TTSBI) was polycondensed with 4,4,-dichlorodiphenyl sulfone (DCDPS) or with 4,4,-bis(4-chlorophenyl sulfonyl) biphenyl (BCSBP) in DMSO. Concentration and feed ratio were optimized to avoid gelation and to obtain a maximum yield of multicyclic polyethers free of functional groups. Regardless of these reaction conditions, only low fractions of perfect multicycles were obtained from DCDPS apparently due to steric hindrance of ring closure. Under the same conditions high fractions of perfect multicycles were achieved with the longer and more flexible DCSBP. The reaction products were characterized by MALDI-TOF mass spectrometry, 1H-NMR spectroscopy viscosity, and DSC measurements. Relatively low glass transition temperatures (Tgs , 160,175 C) were found. 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3732,3739, 2008 [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]

Experimental Study on Phase Transformation Between MgB2 and MgB4

S. C. Yan
Using X-ray diffraction (XRD), scanning electron microscope (SEM), and differential scanning calorimetry (DSC), we have investigated the reaction between MgB4 and Mg in its solid, liquid, and gas physical states. The XRD results indicate that the reaction of MgB4+Mg=2MgB2 always occurs independently of the different states of Mg. DSC measurements show that the solid,solid reaction MgB4(s)+Mg(s)=2MgB2(s), the Mg melting Mg(s),Mg(l), and the Mg volatilization occur in turn with increasing temperature for mixed (MgB4+Mg) powder with a nominal stoichiometry of MgB2. SEM observations indicate that the resulting synthesized MgB2 samples, obtained from the MgB4+Mg mixtures, have a denser microstructure than those obtained directly from Mg+B mixtures. On the basis of XRD, DSC, and SEM results, a kinetic model for the reaction between MgB4 and Mg is proposed. [source]

Synthesis and Structure/Property Relationships of Regioselective 2- O -, 3- O - and 6- O -Ethyl Celluloses

Hiroshi Kamitakahara
Abstract Regioselectively ethylated celluloses, 2- O - (1), 3- O - (2), and 6- O -ethyl- (3) celluloses were synthesized via ring-opening polymerization of glucopyranose orthopivalate derivatives. The number-average degrees of polymerization (DPns) of compounds 1 and 2 were calculated to be 10.6 and 49.4, respectively. Three kinds of compound 3 with different DPns were prepared: DPns,=,12.9 (3-1), 60.3 (3-2), and 36.1 (3-3). The 2- O -, 3- O -, and 6- O -ethylcelluloses were soluble in water, confirmed by NMR analysis. Furthermore, the 3- O - (2), and 6- O -ethyl- (3-2) celluloses showed thermo-responsive aggregation behavior and had a lower critical solution temperature (LCST) at about 40,C and 70,C, respectively, based on the results from turbidity tests and DSC measurements. The 6- O -ethyl-cellulose (3-3) with DPn,=,36.1 and DPw,=,54.6 showed gelation behavior over approx 70,C, whereas the 6- O -ethyl-celluloses 3-1 and 3-2 with lower and higher molecular weight, such as DPns 12.9 and 60.3, did not show gelation behavior at this temperature. It was revealed that the position of ethyl group affected the phase transition temperature. According to our experiments, the 3- O -ethyl and 6- O -ethyl groups along the cellulose chains caused the thermo-responsive property of their aqueous solutions. The appropriate DP of the regioselective 6- O -ethyl-cellulose existed for gelation of the aqueous solution. [source]

Fabrication of Aromatic-Aliphatic Aminoketone Polymers with Terminal Fluorine Groups

Susann Anders
Abstract A procedure for synthesis aromatic-aliphatic PAK, completely functionalized with p- fluorophenyl terminal groups, is presented. This synthesis uses the nucleophilic aromatic substitution of DFB with various secondary aliphatic diamines [CH3NH(CH2)mNHCH3] (m,=,3, 6, and 8) and cesium fluoride as the base catalyst in the melt. The linearity and the complete functionalization of the PAK compounds with p- fluorophenyl terminal groups are demonstrated with the aid of MALDI TOF mass spectrometry. PAK compounds are semi-crystalline as shown by WAXS and DSC measurements. The degree of crystallinity ranges between 2 and 25%. Nucleophilic aromatic substitution reactions in the fluorine end groups are demonstrated by reaction of PAK (m,=,6) with the strong S- nucleophile mercaptoacetic acid. [source]

Multicyclic Poly(ether sulfone)s Derived from Tris(4-hydroxyphenyl)ethane

Mazen Garaleh
Abstract Polycondensations of 4,4,-difluorodiphenylsulfone with tris(4-hydroxy phenyl)ethane were performed in DMSO with variation of feed ratio and concentration. For feed ratios of 1.0:1.3,1.0:1.5, soluble multicyclic poly(ether sulfone)s were obtained when the monomer concentration was below 0.05 M. The conversions were never complete under standard conditions, and doubling the reaction time yielded perfect multicyclic products free of endgroups; however, a small fraction of the product was crosslinked under these conditions. Quite similar results were obtained with 4,4,-dichlorodiphenylsulfone at higher temperatures. When K2CO3 was replaced by tertiary amines, conversions and molecular weights were lower. The multicyclic poly(ether sulfone)s were characterized by MALDI-TOF mass spectrometry, SEC, and DSC measurements. Broad molecular weight distributions with polydispersities in the range of 2.4,3.9 were found, and, surprisingly, two glass transitions were detectable in the DSC heating curves. [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]

Physical Properties of PBMA- b -PBA- b -PBMA Triblock Copolymers Synthesized by Atom Transfer Radical Polymerization

Luis Martn-Gomis
Abstract The physical properties of well-defined poly(butyl methacrylate)- block -poly(butyl acrylate)- block -poly(butyl methacrylate) (PBMA- b -PBA- b -PBMA) triblock copolymers synthesized by atom transfer radical polymerization (ATRP) are reported. The glass transition and the degradation temperature of copolymers were determined by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). DSC measurements showed phase separation for all of the copolymers with the exception of the one with the shortest length of either inner or outer blocks. TGA demonstrated that the thermal stability of triblock copolymers increased with decreasing BMA content. Dynamic mechanical analysis was used for a preceding evaluation of adhesive properties. In these block copolymers, the deformation process under tension can take place either homogeneously or by a neck formation depending on the molecular weight of the outer BMA blocks and on the length of the inner soft BA segments. Microindentation measurements were also performed for determining the superficial mechanical response and its correlation with the bulk behavior. Stress-strain curves for the different PBMA- b -PBA- b -PBMA specimens at room temperature and at 10 mm/min. [source]

Antifreeze Properties of Polyglycidol Block Copolymers

Eti Baruch
Abstract In this paper, we describe a new biomimetic approach to the synthesis of block copolymers with antifreeze properties. Our approach focuses on the design of block copolymers that mimic the structure and functionality of antifreeze proteins. Hyperbranched copolymers containing poly(ethylene oxide)-polyethyleneimine blocks and polyglycidol side chains were synthesized and their antifreeze properties were studied. It is shown that these block copolymers can lower the freezing point of water up to 0.8,C at a relatively low concentration (1 mg,,mL,1). From DSC measurements it is proven that polyglycidol block copolymers slow down the crystallization kinetics of ice and lead to changes in the ice crystal morphology, as observed by cryo-optical microscopy. [source]

Effect of clay exfoliation and organic modification on morphological, dynamic mechanical, and thermal behavior of melt-compounded polyamide-6 nanocomposites

Smita Mohanty
Abstract Polyamide-6/clay nanocomposites were prepared employing melt bending or compounding technique followed by injection molding using different organically modified clays. X-ray diffraction and transmission electron microscopy were used to determine the molecular dispersion of the modified clays within the matrix polymer. Mechanical tests revealed an increase in tensile and flexural properties of the matrix polymer with the increase in clay loading from 0 to 5%. C30B/polyamide-6 nanocomposites exhibited optimum mechanical performance at 5% clay loading. Storage modulus of polyamide-6 also increased in the nanocomposites, indicating an increase in the stiffness of the matrix polymer with the addition of nanoclays. Furthermore, water absorption studies confirmed comparatively lesser tendency of water uptake in these nanocomposites. HDT of the virgin matrix increased substantially with the addition of organically modified clays. DSC measurements revealed both , and , transitions in the matrix polymer as well as in the nanocomposites. The crystallization temperature (Tc) exhibited an increase in case of C30B/polyamide-6 nanocomposites. Thermal stability of virgin polyamide-6 and the nanocomposites has been investigated employing thermogravimetric analysis. POLYM. COMPOS., 28:153,162, 2007. 2007 Society of Plastics Engineers [source]

Molecular orientation, crystallinity, and flexural modulus correlations in injection molded polypropylene/talc composites

Marcia Cristina Branciforti
Abstract In order to promote better understanding of the structure-mechanical properties relationships of filled thermoplastic compounds, the molecular orientation and the degree of crystallinity of injection molded talc-filled isotactic polypropylene (PP) composites were investigated by X-ray pole figures and wide-angle X-ray diffraction (WAXD). The usual orientation of the filler particles, where the plate planes of talc particles are oriented parallel to the surface of injection molding and influence the orientation of the , -PP crystallites was observed. The PP crystallites show bimodal orientation in which the c - and a*-axes are mixed oriented to the longitudinal direction (LD) and the b -axis is oriented to the normal direction (ND). It was found that the preferential b -axis orientation of PP crystallites increases significantly in the presence of talc particles up to 20,wt% in the composites and then levels-off at higher filler content. WAXD measurements of the degree of crystallinity through the thickness of injection molded PP/talc composites indicated an increasing gradient of PP matrix crystallinity content from the core to the skin layers of the molded plaques. Also, the bulk PP crystallinity content of the composites, as determined by DSC measurements, increased with talc filler concentration. The bulk crystallinity content of PP matrix and the orientation behavior of the matrix PP crystallites and that of the talc particles in composites are influenced by the presence of the filler content and these three composite's microstructure modification factors influence significantly the flexural moduli and the mechanical stiffness anisotropy data (ELD/ETD) of the analyzed PP/talc composites. Copyright 2009 John Wiley & Sons, Ltd. [source]

X-ray diffraction study of the phase transition of K2Mn2(BeF4)3: a new type of low-temperature structure for langbeinites

A. Guelylah
The potassium manganese tetrafluoroberyllate langbeinite compound has been studied in the temperature range 100,300,K. Using DSC measurements, a phase transition has been detected at 213,K. The space group of the low-temperature phase was determined to be P1121 using X-ray diffraction experiments and optical observations of the domain structure. The b axis is doubled with respect to the prototypic P213 cubic phase. Lattice parameters were determined by powder diffraction data [a = 10.0690,(8), b = 20.136,(2), c = 10.0329,(4),, , = 90.01,(1)]. A precise analysis of the BeF4 tetrahedra in the low-temperature phase shows that two independent tetrahedra rotate in opposite directions along the doubled crystallographic axis. A symmetry mode analysis of the monoclinic distortion is also reported. This is the first report of the existence of such a phase transition in K2Mn2(BeF4)3 and also of a new type of low-temperature structure for langbeinite compounds. [source]

Physicochemical studies on the biopolymer inulin: A critical evaluation of its self-aggregation, aggregate-morphology, interaction with water, and thermal stability

BIOPOLYMERS, Issue 9 2009
Abhijit Dan
Abstract Physicochemical properties viz., aggregation, molar mass, shape, and size of chicory inulin in solution were determined by fluorimetry, DLS, SLS, TEM, and viscometry methods. The thermal stability of the biopolymer was examined by TGA, DTA, and DSC measurements. The water vapor adsorption of desiccated inulin was also studied by the isopiestic method, and the data were analyzed in the light of the BET equation. On the basis of the obstruction to ion conductance by the inulin aggregates in solution and analysis of the data, the extent of hydration of inulin in solution was estimated. The result was coupled with the intrinsic viscosity, [,], of inulin to ascertain the shape of the biopolymer aggregates in aqueous solution. The critical aggregation concentration (cac) of inulin in aqueous as well as in salt solution was assessed by fluorimetry. The weight average molar mass, , of inulin monomer and its aggregate was found to be 4468 and 1.03 106 g/mol, respectively, in aqueous solution. This aggregated mass was 2.4 106 g/mol in 0.5M NH4SCN solution. The [,] values of the soft supramolecular aggregates in solution (without and with salt) were small and comparable with globular proteins evidencing spherical geometry of the biopolymer aggregates as supported by the TEM results. In DMSO, rod-like aggregates of inulin was found by the TEM study. The [,] of the biopolymer in the DMSO medium was therefore, higher than that in the aqueous medium. Unlike aqueous medium, the aggregation in DMSO was not associated with a cac. 2009 Wiley Periodicals, Inc. Biopolymers 91: 687,699, 2009. This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source]