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Wide Angle X-ray Diffraction (wide + angle_x-ray_diffraction)
Selected AbstractsEthylene propylene diene terpolymer/ethylene vinyl acetate/layered silicate ternary nanocomposite by solution methodPOLYMER ENGINEERING & SCIENCE, Issue 7 2006H. Acharya A new ternary nanocomposite has been developed using ethylene propylene diene terpolymer (EPDM), ethylene vinyl acetate (EVA-45) copolymer, and organically modified layered silicate (16 Me-MMT) from sodium montmorillonite (Na+ -MMT). Wide angle X-ray diffraction and transmission electron microscopic analysis confirmed the intercalation of the polymer chains in between the organosilicate layers and the nanoscale distribution of 16 Me-MMT in polymer matrix, respectively. The measurement of mechanical properties for 2,8 wt% of 16 Me-MMT loadings showed a significant increase in tensile strength, elongation at break, and modulus at different elongations. Such an improvement in mechanical properties has been correlated based on the fracture behavior of nanocomposite by SEM analysis. Thermal stability of EPDM/EVA/layered silicate ternary nanocomposites also showed substantial improvements compared with the neat EPDM/EVA blend, confirming thereby the formation of a high performance nanocomposite. POLYM. ENG. SCI., 46:437,843, 2006. © 2006 Society of Plastics Engineers [source] Isotactic polypropylene solidification under pressure and high cooling rates.POLYMER ENGINEERING & SCIENCE, Issue 11 2000A master curve approach Solidification in industrial processes very often involves flow fields, high thermal gradients and high pressures: the development of a model able to describe the polymer behavior becomes complex. Recently a new equipment has been developed and improved to study the crystallization of polymers when quenched under pressure. An experimental apparatus based on a modified, special injection moulding machine has been employed. Polymer samples can be cooled at a known cooling rate up to 100°C/s and under a constant pressure up to 40 MPa. Density, Micro Hardness (MH), Wide angle X-ray diffraction (WAXD), and annealing measurements were then used to characterize the obtained sample morphology. Results on one iPP sample display a lower density and a lower density dependence on cooling rate for increasing pressure. Micro hardness confirms the same trend. A deconvolution technique of WAXD patterns is used to evaluate the final phase content of samples and to assess a crystallization kinetics behavior. A master curve approach to explain iPP behavior under pressure and high cooling rates was successfully applied on density results. On the basis of this simple model it is possible to predict the final polymer density by superposition of the effect of cooling rate and the effect of pressure in a wide range of experimental conditions. [source] Phase transition behavior and structure of the thermotropic liquid crystal 6-{[(4,-{[(undecyl)carbonyl]oxy}biphenyl-4yl)carbonyl]oxy}-1-hexyneCRYSTAL RESEARCH AND TECHNOLOGY, Issue 9 2006Leijing Liu Abstract The phase transition behaviors and corresponding structures of 6-{[(4,-{[(undecyl)carbonyl]oxy}biphenyl-4yl)carbonyl]oxy}-1-hexyne (A4EE11) were investigated using differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and wide angle X-ray diffraction (WAXD). In comparison with the published homologues, 5-{[(4,-heptoxy-biphenyl-4-yl)carbonyl]oxy}-1-pentyne (A3EO7) which shows a monotropic smectic A (SmA) phase and a metastable monotropic smectic C (SmC) phase; 5-{[(4,-heptoxy-biphenyl-4-yl)oxy]carbonyl}- 1-pentyne (A3E'O7) that exhibits three enantiotropic stable liquid crystalline (LC) phases, SmA phase, SmC phase and smectic X (SmX) phase; 5-{[(4,-heptoxy-biphenyl-4-yl)carbonyl]oxy}-1-undecyne (A9EO7) which has a monotropic SmA phase and a metastable crystal phase, A4EE11 integrates the enantiotropy, monotropy and metastability of the LC phases of those three compounds. Upon cooling from isotropic state to room temperature, in the temperature range of 62.0 to 58.5°C, A4EE11 shows an enantiotropic smectic A (SmA) phase with a layer spacing d=32.69Å. Further lowering the temperature, it enters into a metastable monotropic smectic B (SmB) phase with a longer layer spacing d=34.22Å which has a tendency towards crystallization. The metastability of the liquid crystalline phase may associate to the linkage order of the ester bridge between the mesogenic core and the flexible spacer. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Crystallization and melting behavior of HDPE in HDPE/teak wood flour composites and their correlation with mechanical propertiesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2010Kamini 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] Evaluation of the potential of polymeric carriers based on chitosan- grafted -polyacrylonitrile in the formulation of drug delivery systemsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2010A. A. Sarhan Abstract Graft copolymerization of chitosan with acrylonitrile (AN) was carried out by free radical polymerization using KMnO4 and oxalic acid as a combined redox initiator system. Graft copolymerization was confirmed by Fourier transform infrared spectra (FTIR), proton nuclear magnetic resonance spectra (1H-NMR), thermal gravimetric analysis (TGA) measurements, and wide angle X-ray diffraction (WAXD). In addition, further modification of the cyano groups of the grafted copolymers was performed by partial hydrolysis into carboxylic function groups with various extents. The extent of hydrolysis was monitored using FTIR spectroscopy. The potential of the hydrolyzed and unhydrolyzed grafted copolymers as polymeric carriers for drug delivery systems was extensively studied by preparation of tablets incorporated with methyl orange (MO) as a drug model. In vitro drug release was carried out in simulated gastric and intestinal conditions. The effects of grafting percentage (GP) and the extent of hydrolysis on the release kinetics were evaluated. Release continued up to 24 h for both hydrolyzed and unhydrolysed chitosan- g -PAN copolymers. The nature of drug transport through the polymer matrices was studied by comparing with power law or Kormeyer-Peppas equation. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Crystalline morphology and dynamical crystallization of antibacterial ,-polypropylene compositeJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2008Xin Chen Abstract The crystalline morphology and dynamical crystallization of antibacterial polypropylene composite and pure polypropylene were investigated via differential scanning calorimeter (DSC), wide angle X-ray diffraction (WAXD), and real-time hot-stage optical microscopy (OM). The results reveal that the crystalline morphology of antibacterial PP composites changes with variations of the crystallization conditions and compositions. The crystalline phase consists of both ,-PP and ,-PP crystals. The content of ,-PP decreases with the increase in antibacterial agent content and cooling rate. With the addition of ,-nucleating agent, the morphologies of all dynamically crystallized antibacterial PP composites show no obvious spherulitic morphology, and the decrease of crystal perfection and the increase of nucleation density of antibacterial PP composite system could be observed. With the increase of antibacterial agent content, the overall crystallization rates of the antibacterial PP composite increase dramatically, while the content of ,-PP in all antibacterial PP composite decrease distinctly under given cooling conditions. These results can be explained by the interruptive effect of antibacterial agent on interactions of ,-nucleating agent components and the obstructing effect of antibacterial agent on the mobility of PP chains in melts. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Crystallization, orientation morphology, and mechanical properties of biaxially oriented starch/polyvinyl alcohol filmsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008Jing Wang Abstract Biaxially oriented starch/polyvinyl alcohol (PVA) films were prepared by stretching starch/PVA blend precursor films that were fabricated by extrusion casting via a twin-screw extruder. Investigations on crystallization, orientation morphology, and mechanical properties of extrusion cast and stretched starch/PVA films were carried out by using differential scanning calorimetry, scanning electron microscope, wide angle X-ray diffraction (WAXD), and tensile testing. The fresh extrusion-cast starch/PVA films, which were almost amorphous, can crystallize spontaneously when aged at room condition. A good compatibility between starch and PVA was obtained by extrusion-casting technology. The well-developed molecular orientation, which did not occur along the machine direction during the extruding process, was observed in stretched film samples. Stretching unaged films can induce crystallization and the orientation of crystalline structures during stretching, resulting in the changes in diffraction peaks of WAXD patterns. The effect of stretch ratio and the orientation distribution in the plane of the film on mechanical properties of stretched films was studied, and the equal biaxially oriented films were found to exhibit in-plane isotropy. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Synthesis and characterization of poly(butylene terephthalate)/mica nanocomposite fibers via in situ interlayer polymerizationJOURNAL OF APPLIED POLYMER SCIENCE, Issue 2 2007Jin-Hae Chang Abstract Intercalated nanocomposites consisting of poly(butylene terephthalate) (PBT) incorporated between mica layers were synthesized from dimethyl terephthalate (DMT) and 1,4-butanediol (BD) by in situ interlayer polymerization. PBT nanocomposites of varying organoclay content were melt-spun to produce monofilaments. The samples were characterized using wide angle X-ray diffraction, electron microscopy, thermal analysis, and tensile testing. Some of the clay particles were found to be well dispersed in the PBT matrix, but other clay particles were agglomerated at a size level greater than approximately 20 nm. The glass transition temperatures (Tg) and the thermal degradation properties (TDi) of undrawn PBT hybrid fibers were found to improve with increases in the clay content. At draw ratio (DR) = 1, the ultimate tensile strengths of the hybrid fibers increased with the addition of clay up to a critical content and then decreased. However, the initial moduli monotonically increased with increases in the amount of organoclay in the PBT matrix. The ultimate strengths were found to decrease linearly with increases in DR from 1 to 18. In contrast to the trend for the tensile strengths, the initial moduli of the hybrid fibers increased only slightly with increases in DR up to 18. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 [source] Effect of an organic dicarboxylic acid salt on fractionated crystallization of polypropylene dropletsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2007Y. Jin Abstract The effect of a particulate nucleating agent on fractionated crystallization of polypropylene (PP) was studied. A novel method utilizing breakup of PP nanolayers was used to obtain a dispersion of PP droplets in a polystyrene (PS) matrix. An assembly with hundreds of PP nanolayers alternating with thicker PS layers was fabricated by layer-multiplying coextusion. The concentration of an organic dicarboxylic acid salt (HPN) nucleating agent in the coextruded PP nanolayers was varied up to 2 wt %. When the assembly was heated into the melt, interfacial driven breakup of the thin PP layers produced a dispersion of PP particles in a PS matrix. Analysis of optical microscope images and atomic force microscope images indicated that layer breakup produced a bimodal particle size distribution of submicron particles and large, micron-sized particles. Almost entirely submicron particles were obtained from breakup of 12 nm PP layers. The fraction of PP as submicron particles dropped dramatically as the PP nanolayer thickness increased to 40 nm. Only large, micron-sized particles were obtained from 200 nm PP nanolayers. The crystallization behavior of the particle dispersions was characterized by thermal analysis and wide angle X-ray diffraction. Only part of the PP was nucleated by HPN. It was found that HPN was not effective in nucleating the population of submicron particles. The particulate HPN was too large to be accommodated in the submicron PP particles. On the other hand, the amount of nucleated crystallization qualitatively paralleled the fraction of PP in the form of large, micron-sized particles. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007 [source] Microencapsulation of a functional dye and its UV crosslinking controlled releasing behaviorJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 14 2009Gangqiang Li Abstract A new family of microcapsules containing photopolymerizable tripropylene glycol diacrylate (TPGDA) was synthesized by using interfacial polymerization. The release behavior of encapsulated dye could be controlled easily by changing the crosslink density of network formed from TPGDA. The chemical structure and properties of microcapsules were characterized by Fourier Transform infrared spectroscopy, scanning electron microscope, differential scanning calorimetry, optical microscope, wide angle X-ray diffraction and UV-visible spectrophotometer. The results demonstrate that the higher agitation rate results in a smaller particle size with a narrow size distribution. When core/shell ratio is low, the surface of the microcapsules becomes smooth. Additionally, it was found that UV radiation time is most effective factor to change the CC double bond conversion ratio. After microcapsules were synthesized, the release speed could be changed according to requirement by exposing them to UV light for minutes. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3630,3639, 2009 [source] Supramolecular inclusion complexes of star-shaped poly(,-caprolactone) with ,-cyclodextrinJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 2005Lu Wang Abstract Both star-shaped poly(,-caprolactone) (PCL) having 4 arms (4sPCL) and 6 arms (6sPCL) and linear PCL having 1 arm (LPCL) and 2 arms (2LPCL) were synthesized and then investigated for inclusion complexation with ,-cyclodextrin (,-CD). The supramolecular inclusion complexes (ICs) were in detail characterized by 1H NMR, differential scanning calorimetry, thermogravimetric analysis, wide angle X-ray diffraction, solid-state carbon nuclear magnetic resonance spectroscopy using cross-polarization and magic-angle spinning, and Fourier transform infrared, respectively. The stoichiometry (CL:CD, mol:mol) of all ICs increased with the increasing branch arm of PCL polymers, and it was in the order of ,-CD-6sPCL1 ICs > ,-CD-4sPCL ICs > ,-CD-2LPCL ICs > ,-CD-LPCL ICs. All analyses indicated that the branch arms of star-shaped PCL polymers were included into the hydrophobic ,-CD cavities and their original crystalline properties were completely suppressed. Moreover, the ICs of star-shaped PCL with ,-CD had a channel-type crystalline structure similar to that formed between the linear PCL and ,-CD. Furthermore, the thermal stability of the free PCL polymers probably controlled that of the guest polymers included in the ICs. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4721,4730, 2005 [source] Crystallization of Poly(, -caprolactone)/Poly(vinyl chloride) Miscible Blends Under Strain: The Role of Molecular WeightMACROMOLECULAR RAPID COMMUNICATIONS, Issue 18 2006Yubao Zhang Abstract Summary: The effect of poly(, -caprolactone) (PCL) molecular weight on the orientation of crystalline PCL in miscible poly(, -caprolactone)/poly(vinyl chloride) (PCL/PVC) blends, melt crystallized under strain, has been studied by a combination of wide angle X-ray diffraction (WAXD) and small angle X-ray scattering (SAXS) studies. An unusual crystal orientation with the b-axis parallel to the stretching direction was observed in miscible PCL/PVC blends with PCL of high molecular weight (>21,000). SAXS showed the presence of nanosize confined PCL in the PCL/PVC blends, which could be preserved at temperatures higher than the Tm of PCL but lower than the Tg of PVC. A mechanism based on the confinement of PCL crystal growth was proposed, which can explain the formation of b-axis orientation in PCL/PVC blends crystallized under strain. SAXS pattern of stretched PCL/PVC blend after annealing at 90,°C for 5 min. [source] Polycarbonate Crystallization by Vapor-Grown Carbon Fiber with and without Magnetic FieldMACROMOLECULAR RAPID COMMUNICATIONS, Issue 13 2003Tatsuhiro Takahashi Abstract Polycarbonate (PC)/vapor-grown carbon fiber (VGCFÔ) composite was prepared through melt compounding. It was unexpectedly found from differential scanning calorimetry (DSC) and wide angle X-ray diffraction (WAXD) that the crystallization of PC was substantially accelerated in the presence of the ordered graphite surface of VGCFÔ. To make an aligned structure of PC crystallization together with the orientation of VGCFÔ, a magnetic field of 2.4 T was applied to the composite under several temperature profiles. The WAXD pattern revealed that not only dispersed VGCFÔ but also matrix PC crystallization was magnetically aligned through the optimization of processes. The evidence for PC crystallization by VGCFÔ with and without magnetic force is described. Optical micrograph (a) and WAXD pattern (b) of PC/VGCFÔ (95:5 wt. ratio) composite which was treated under a magnetic field (vertical direction) of 2.4 T under an optimized heating profile. [source] Mechanical and thermal properties of polypropylene nanocomposites using organically modified Indian bentonitePOLYMER COMPOSITES, Issue 3 2010Hasmukh A. Patel We report preparation and characterization of nanoclay from Indian bentonite and imported nanoclays, and their compounding with polypropylene (PP) and maleic anhydride-grafted PP (MA-g-PP) in twin screw extruder. The compounded polymer/nanoclay nanocomposites (PNCs) are molded into a standard specimen for studying its tensile, flexural and impact strength. A wide angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM) study demonstrates intercalation of PP in nanoclays rather than exfoliation for both, indigenous and imported nanoclays. The tensile modulus increased by 41 and 39% for PNC1 (PNC with imported nanoclay) and PNC2 (PNC with indigenous nanoclay) with respect to PP. The flexural modulus for PNC1 and PNC2 also increases by 23 and 22% due to incorporation of 5% nanoclay in PP along with 5% MA-g-PP. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers [source] Simultaneously improving the toughness, flexural modulus and thermal performance of isotactic polypropylene by ,-, crystalline transition and inorganic whisker reinforcementPOLYMER ENGINEERING & SCIENCE, Issue 2 2010Yewen Cao Magnesium salt (M-HOS) whisker and ,-nucleating agent were introduced into polypropylene and their effects on the crystalline structures, morphologies, mechanical properties, and thermal resistance of polypropylene (PP) were investigated. The results of wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), and polar optical microscopy (POM) examinations suggested that the presence of the whisker did not cause any negative effect on the occurrence of ,-modification, and ,-phase became absolutely dominant form in ,-nucleated samples. The mechanical and thermal properties tests demonstrated that there is an excellent synergy between the ,-nucleating agent and the whisker. For PP composite containing 0.1 wt% of the ,-nucleating agent and 10 wt% of the whiskers, the Izod notched impact strength, elongation at break, flexural modulus, and heat deflection temperature were increased by 108, 194, 31, and 40%, respectively, compared with those of neat PP. By combining the toughening effect of ,,, transition with the reinforcing effect of the whisker, simultaneous improvement in toughness, flexural modulus, and thermal performance of PP was successfully achieved. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers [source] Simultaneous stretching and static electric field poling of poly(vinylidene fluoride-hexafluoropropylene) copolymer filmsPOLYMER ENGINEERING & SCIENCE, Issue 10 2007Yan Huan Poly(vinylideneflouride-hexafluoropropylene) (PVDF-HFP) copolymer films were simultaneously stretched and static electric poled (SSSEP) in seriate mode. The experimental results exhibited that SSSEP greatly enhanced the piezoelectric properties of the PVDF-HFP films and slightly increased the dielectric properties of the films. The maximum piezoelectric coefficient d33 24 pC/N higher than the reported was obtained in these films under optimum condition. Based on the wide angle X-ray diffraction results, the SSSEP films showed more organized crystalline structure than the only stretched films. POLYM. ENG. SCI., 47:1630,1633, 2007. © 2007 Society of Plastics Engineers [source] Epoxy nanocomposites curing by microwavesPOLYMER ENGINEERING & SCIENCE, Issue 8 2006Nurseli Uyan In this work, chemically modified sodium montmorillonite and epoxy monomer were used to prepare nanocomposites in two consecutive stages. In the first stage, dodecylamine, octadecylamine, hexadecylamine, and hexadecyltrimethyl ammonium bromide were used to prepare various organophilic clays. In the second stage, the bisphenol-A based epoxy monomer and predetermined amounts of organoclay were mixed together and then cured by an aliphatic polyamine for 20 min under microwave at 400 W. Furthermore, ,-, diacrylate poly(dimethylsiloxane) was added to the mixture before the curing process to modify the toughness of the samples. The mixture was poured into the poly(tetrafluoroethylene) mold; the epoxy resin/curing agent ratio was maintained as 2/1. The clear films formed after microwave irradiation were removed from the mold, cooled, and then stored in a cool and dry medium until characterization. The samples were analyzed by wide angle X-ray diffraction, differential scanning calorimetry, and mechanical tests. Surfaces of the cold fractured samples were also observed under the scanning electron microscope. The results revealed that microwave curing of the samples of 5% organoclay and 5% siloxane showed improvement in mechanical properties. POLYM. ENG. SCI. 46:1104,1110, 2006. © 2006 Society of Plastics Engineers [source] Melt processing of PA-66/clay, HDPE/clay and HDPE/PA-66/clay nanocompositesPOLYMER ENGINEERING & SCIENCE, Issue 6 2004Mahmood Mehrabzadeh Polyamide 66/clay, high-density polyethylene (HDPE)/clay and HDPE/PA66/clay nanocomposites were prepared, using a twin-screw extruder. The nanocomposites were characterized by means of transmission electron microscopy (TEM), scanning electron microscopy (SEM), wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), optical microscopy and tensile testing. Effects of processing conditions and clay modifier were evaluated. The results show that exfoliation in the twin-screw extruder is enhanced by the incorporation of mixing and shearing elements and high residence times. Compatibility of the clay modifier with the polymer matrix plays an important role in exfoliation. Clay does not influence the crystal form, melting temperature or crystallinity of PA-66 and HDPE. However, it acts as a nucleation agent, increases marginally the crystallization temperatures, and reduces the crystallite size. Clay in the blend nanocomposites acts as a compatibilizer and changes the morphology of the blend. TEM micrographs suggest the presence of an exfoliated structure in PA-66 and an intercalated structure in HDPE. Polym. Eng. Sci. 44:1152,1161, 2004. © 2004 Society of Plastics Engineers. [source] Comparison of structure development in injection molding of isotactic and syndiotactic polypropylenesPOLYMER ENGINEERING & SCIENCE, Issue 8 2002Dongman Choi A comparative study of the crystallization and orientation development in injection molding isotactic and syndiotactic polypropylenes was made. The injection molded samples were characterized using wide angle X-ray diffraction (WAXD) techniques and birefringence. The injection molded isotactic polypropylene samples formed well-defined sublayers (skin, shear and core zones) and exhibited polymorphic crystal structures of the monoclinic ,-form and the hexagonal ,-form. Considerable amounts of ,-form crystal were formed in the shear and core zones, depending on the injection pressure or on the packing pressure. The isotactic polypropylene samples had relatively high frozen-in orientations in the skin layer and the shear zone. The injection molded syndiotactic polypropylene exhibited the disordered Form I structure, but it did not appear to crystallize during the mold-filling stage because of its slow crystallization rate and to develop a distinct shear zone. The core zone orientation was greatly increased by application of high packing pressure. The isotactic polypropylene samples exhibited much higher birefringence than the syndiotactic polypropylene samples at the skin and shear layers, whereas both materials exhibited similar levels of crystalline orientation in these layers. [source] Development of orientation and mechanical properties of extrusion cast polyamide 11 films in biaxial stretching processPOLYMER ENGINEERING & SCIENCE, Issue 5 2002Sangkeun Rhee The development of orientation of extrusion cast polyamide 11 films in the biaxial stretching process was studied with birefringence and wide angle X-ray diffraction (WAXD) pole figures. White-Spruiell biaxial orientation factors of the crystalline phase were calculated with the pole figure data. Both biaxially stretched films were developed. Planarity of hydrogen bonding planes with respect to the film surface was observed from WAXD pole figures. Mechanical properties of the films were studied. Tensile strength and elongation at break were successfully correlated with the out-of-plane birefringences. [source] Polyimide nanocomposites: Comparison of their properties with precursor polymer nanocompositesPOLYMER ENGINEERING & SCIENCE, Issue 12 2001Jin-Hae Chang A precursor poly(amic acid) was obtained by solution polymerization of pyromellitic dianhydride and benzidine in N, N-dimethylacetamide. Poly(amic acid)/Organoclay hybrids were prepared by the solution intercalation method with dodecylamine-montmorillonite. A polyimide hybrid was obtained from poly(amic acid) hybrid by heat treatment at various temperatures. The film type polyimide hybrids showed better thermal properties than poly(amic acid) hybrids. Also, the thermal stability of the two polymer hybrids were enhanced linearly with increasing clay content from 0 to 8 wt%. Tensile properties and gas barriers of the hybrids, however, were enhanced remarkably compared to pristine polymers. Intercalations of the polymer chains in clar were examined through wide angle X-ray diffraction (XRD) and electron microscopy (SEM and TEM). Transmission electron microscopy revealed that a partially exfoliated structure had been obtained from polyimide/organo-clay hybrids. [source] Microstructural effects on hot drawing syndiotactic styrene P-methyl styrene copolymerPOLYMER ENGINEERING & SCIENCE, Issue 10 2001R. J. Yan Crystalline syndiotactic styrene/p-methyl styrene copolymer (SPMS) has been oriented by tensile drawing at various temperatures between the glass transition and crystalline melting point. The microstructural changes resulting from drawing have been studied using differential scanning calorimetry (DSC) and wide angle X-ray diffraction (WAXD). WIth increasing draw temperature, both melting temperature and crystalline dimensions of the oriented samples increase. The heat of fusion increases with increasing draw temperature up to ,200°C. It also increases with draw ratio and draw rate, while the crystalline width increases only with draw ratio. THe amorphous fraction shows a clear glass transition, the temperature of which (Tg) increases with draw ratio. However, Tg decreases somewhat with increasing draw temperature. This is interpreted in terms of the stretching of the randomly coiled amorphous phase molecules. [source] Large-scale extrusion processing and characterization of hybrid nylon-6/SiO2 nanocompositesPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 4 2004Monserrat García Abstract Solution impregnations, pulltrusion and film stacking are widely used methods to prepare thermoplastic composite materials. Extruders are used to melt the polymer and to incorporate fibers into the polymer in order to modify physical properties. In this article, the compounding of colloidal silica nanoparticles filled polyamide-6 (PA-6) is achieved using a twin-screw extruder, which has a significant market share due to its low cost and easy maintenance. The experiments were performed at 250 rpm and the bulk throughput was 6,kg,h,1 with a pump pressure of 30 bars. The composites were characterized with nuclear magnetic resonance (NMR), wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). As determined by WAXD, the PA-6 showed higher amounts of , -phase when compared to other synthesis methods such as in situ polymerization. TEM pictures showed that the silica particles aggregated nevertheless, upon addition of 14% (w/w) silica the E-modulus increased from 2.7 to 3.9,GPa indicating that an effective mechanical coupling with the polymer was achieved. The behavior, illustrated with dynamic mechanical analysis (DMA) curves, indicated that in general when a filled system is compared to unfilled material, the values of the moduli (E, and E,) increased and tan , decreased. Determination of molecular mass distribution of the samples by means of size exclusion chromatography (SEC) coupled to a refractive index (RI), viscosity (DV) and light scattering (LS) detector revealed that the addition of silica did not decrease the average molecular weight of the polymer matrix, which is of importance for composite applications. Copyright © 2004 John Wiley & Sons, Ltd. [source] An efficient approach to synthesize polysaccharides- graft -poly(p -dioxanone) copolymers as potential drug carriersJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 2009Fang Lu Abstract Starch and poly(p -dioxanone) (PPDO) are the natural and synthetic biodegradable and biocompatible polymers, respectively. Their copolymers can find extensive applications in biomedical materials. However, it is very difficult to synthesize starch- graft -PPDO copolymers in common organic solvents with very good solubility. In this article, well-defined polysaccharides- graft -poly(p -dioxanone) (SAn -PPDO) copolymers were successfully synthesized via the ring-opening polymerization of p -dioxanone (PDO) with an acetylated starch (SA) initiator and a Sn(Oct)2 catalyst in bulk. The copolymers were characterized via Fourier transform infrared spectroscopy, 1H NMR, gel permeation chromatography, thermogravimetric analysis (TG), differential scanning calorimetry, and wide angle x-ray diffraction. The in vitro degradation results showed that the introduction of SA segments into the backbone chains of the copolymers led to an enhancement of the degradation rate, and the degradation rate of SAn -PPDO increased with the increase of SA wt %. Microspheres with an average volume diameter of 20 ,m, which will have potential applications in controlled release of drugs, were successfully prepared by using these new copolymers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5344,5353, 2009 [source] | ||||||||||