Wide-angle X-ray Diffraction Profiles Research Articles

A nonequilibrium constitutive equation for tensile behavior of polyolefinic thermoplastic vulcanizates

Polyolefinic thermoplastic vulcanizates (TPVs) composed of iPP (isotactic polypropylene) and crosslinked EPDM (ethylene-propylene-diene rubber) prepared by dynamic vulcanization process exhibit rubber domains dispersed in the iPP matrix, even though the EPDM component is the major component. Here we proposed a kinetic nonequilibrium constitutive equation that considers the transition of the mechanical nature from plasto-rigid deformation to rubbery deformation during uniaxial extension to explore the origin of the thermoplastic elastomer behavior of TPV (thermoplastic vulcanizate) materials. Fitting of the constitutive equation to the experimental stress‒strain curves quantitatively revealed the critical transition point of the mechanical properties. The transition shifted to higher strains with decreasing EPDM content. In situ wide-angle X-ray diffraction profiles monitored during the uniaxial extension confirmed the mechanical transition process.

Formation and Distribution of the Mesophase in Ultrasonic Micro-Injection-Molded Isotactic Polypropylene

The influence of mold temperature and filling velocity on the formation and distribution of the mesophase in ultrasonic micro-injection-molded isotactic polypropylene (iPP) was explored using a wide-angle X-ray diffraction (WAXD) technique. A Gaussian fitting method was used to decompose one-dimensional WAXD profiles into quantitative fractions of the crystalline lamellae, mesophase, and amorphous phase. It was found that the mesophase formation can only be detected up to a mold temperature of 60 °C due to its low thermal stability. Moreover, the content of the mesophase decreases distinctly as the filling velocity is increased. The component is mainly located in the core layer after examining the distribution of each crystal form along the thickness direction, irrespective of mold temperature and filling velocity. All these findings can be attributed to the correlation between the degree of molecular orientation and the cooling rate. A high cooling rate occurred during the micro-injection molding process produces the result that there is less time for the polymeric chains with a low level of orientation to crystallize into a well-ordered structure, thus yielding many mesophase crystals with a paracrystalline smectic arrangement especially in the core layer. Finally, a diagram for mesophase formation was constructed in mold temperature–filling velocity space, which offers a detailed road map for regulating mesophase fraction in ultrasonic micro-injection molding operations.

Constituent Isomerism-Induced Quasicrystal and Frank–Kasper σ Superlattices Based on Nanosized Shape Amphiphiles

Naturally, subtle variations in the chemical structures of constituent molecules may significantly affect their multiscale spatial arrangements, properties, and functions. Deceptively simple spheri...

Mesophase in melt-spun poly(ϵ-caprolactone) filaments: Structure–mechanical property relationship

Fine poly(ϵ-caprolactone) (PCL) filaments (diameter: 59–92 μm) were successfully melt-spun with modified drawing setups to prevent draw instabilities. Depending on the production parameters, different mechanical properties were obtained (tensile strength: 302–456 MPa, elongation at break: 69–88%). These variations are related to subtle structural differences, which we have analyzed with wide-angle x-ray diffraction (WAXD) and small-angle x-ray scattering (SAXS). SAXS was used to determine crystal widths and the spacing between crystals along the filament axis. Additionally, 2D WAXD patterns were simulated and WAXD profiles were fitted. The detailed 2D WAXD analysis revealed that a highly-oriented non-crystalline mesophase is present in drawn PCL filaments, which is most-likely situated in-between PCL crystals. A large amount of this mesophase (>16%), combined with high crystalline orientation and perfect crystals, led to higher tensile strength values. We also confirmed that PCL chains pack with non-planar chain conformations in the unit cell.

A Study on Blend Ratio-dependent Far-IR and Low-frequency Raman Spectra and WAXD Patterns of Poly(3-hydroxybutyrate)/poly(4-vinylphenol) Using Homospectral and Heterospectral Two-dimensional Correlation Spectroscopy.

An intensive analysis of far-infrared (far-IR), low-frequency Raman, and wide angle X-ray diffraction (WAXD) data has been performed by two-dimensional correlation spectroscopy (2D-COS) as a function of the blend ratio of poly(3-hydroxybutyrate)/poly(4-vinylphenol) (PHB/PVPh). Homospectral 2D-COS revealed that a weak band at 128 cm-1 in the far-IR spectra appeared more clearly in the 2D correlation spectra. Heterospectral 2D-COS (far-IR/low-frequency Raman and far-IR/WAXD) provided very important results that were hardly detected in the conventional 2D-COS. A far-IR peak at 130 cm-1 in the heterospectral 2D-COS had negative correlations with the peaks in the low-frequency Raman spectra at 81, 100, and 110 cm-1 and WAXD profile 8.78 and 11.01°. These results indicated that those peaks have different origins; the 130 cm-1 peak comes from the intermolecular C=O···H-O hydrogen bond between PHB and PVPh, while those for low-frequency Raman and WAXD peaks are the features of PHB crystalline structure.

Periodic introduction of aromatic units in polypeptides via chemoenzymatic polymerization to yield specific secondary structures with high thermal stability

Polypeptides containing periodic aromatic residues in their main chains were synthesized via papain-catalyzed chemoenzymatic polymerization of tripeptide ester monomers under moderate conditions in aqueous buffers. As the monomer, 4-aminobenzoic acid (Abz) was modified with Gly or Ala at the N- and C-termini to mitigate the poor substrate specificity of papain to unnatural amino acids. The tripeptide esters, namely, GlyAbzGly and AlaAbzAla ethyl esters, can be recognized and polymerized by papain, resulting in the polypeptides poly(GlyAbzGly) and poly(AlaAbzAla), respectively, with periodic sequences containing Abz units every three residues. Copolymerization of tripeptide esters with Gly or Ala ethyl ester also proceeded in the presence of papain. The secondary structures of the Abz-containing polypeptides were investigated by IR and wide-angle X-ray diffraction (WAXD) analysis. The WAXD profile of poly(GlyAbzGly) was similar to that of polyGly, whereas poly(AlaAbzAla) adopted a sheet-like structure similar to the β-sheet of polyAla. Thermal analysis of Abz-containing polypeptides revealed that the high thermal stability of the Abz-containing polypeptides is related to the distinct sequences that periodically include Abz residues.

Ambidextrous Chirality Transfer Capability from Cellulose Tris(phenylcarbamate) to Nonhelical Chainlike Luminophores: Achiral Solvent-Driven Helix-Helix Transition of Oligo- and Polyfluorenes Revealed by Sign Inversion of Circularly Polarized Luminescence and Circular Dichroism Spectra.

We investigated whether helicity and/or chirality of cellulose tris(phenylcarbamate) (CTPC) can transfer to noncharged, nonhelical oligo- and polyfluorenes when CTPC was employed as a solution processable homochiral platform of a D-glucose-skeletal polymer. Noticeably, CTPC revealed the solvent-driven, ambidextrous intermolecular helicity/chirality transfer capability to these fluorenes. The chiroptical inversion characteristics of circularly polarized luminescence (CPL) and the corresponding CD spectra were realized by solely choosing a proper achiral solvent and/or achiral cosolvent. When the solution of PF6 and CTPC in tetrahydrofuran (THF) was cast on a quartz substrate, the dissymmetry ratio of CPL (gCPL) from the polymer film showed gCPL = +2.1 × 10-3 at 429 nm. Conversely, when dichloromethane (DCM) was used as the solvent, the CPL sign was inverted to gCPL = -2.4 × 10-3 at 429 nm. The dissymmetry ratio of Cotton CD band (gCD) from the THF solution was gCD = +3.2 × 10-3 at 392 nm; conversely, from the DCM, the CD sign inverted to gCD = -0.8 × 10-3 at 371 nm. The sign and magnitude of the gCD values were interpreted to a London dispersion term (δd) of Hansen solubility parameter (δ) of the casting solvents rather than a dipole-dipole interaction term (δp) and a hydrogen bonding interaction term (δh) of the δ values and dielectric constant (ε). Analysis of solvent-driven changes in FTIR spectra, wide-angle X-ray diffraction profiles, and differential scanning calorimetry diagrams indicated that solvent driven on-off switching of multiple hydrogen bonds due to three urethane groups of CTPC play the key for the inversion. Intermolecular CH/π and π-π interactions among phenyl rings and alkyl groups were assumed to be crucial for helicity/chirality transfer capability based on molecular mechanics and molecular dynamics simulations of PF6-CTPC hybrids. These chiroptical inversion characteristics arose from solvent-driven order-disorder transition characteristics of the CTPC helix rather than a helix-helix transition of CTPC itself.

Multiple Melting Behavior of High-Speed Melt Spun Polylactide Fibers

ABSTRACTHigh-speed melt spinning of polylactide (PLA) was conducted and the structure and multiple melting behavior of the as-spun fibers were investigated. In the analysis of temperature modulated differential scanning calorimetry (TMDSC) thermograms for the as-spun PLA fibers taken-up at 1 and 6 km/min, the peaks around the melting temperature region in the reversing heat flow (RHF) and nonreversing heat flow (NRHF) curves were mainly separated into (1) a pair of an endothermic peak (Peak L) in RHF and an exothermic peak (Peak R) in NRHF in a low temperature region, (2) an endothermic peak (Peak M) both in RHF and NRHF (only in RHF for PLA fiber spun at the low-speed) in an intermediate temperature region, and (3) an endothermic peak (Peak H) both in RHF and NRHF in a higher temperature region. Wide-angle X-ray diffraction (WAXD) measurements were conducted during the heating process of the as-spun fibers cut into powders. In the case of fibers obtained at 1 km/min, disordered crystals, i.e. α′-form crystals, were formed through cold crystallization followed by a disorder-to-order phase transition, i.e. α′ to α crystalline modification, with partial melting of the α′ crystals around 148.5°C in the temperature range of Peaks R and L. Finally, the α form crystals melted above 169.4°C, in the temperature range of Peak H. On the other hand, the PLA crystals generated by the orientation-induced crystallization during the spinning process at a spinning velocity of 6 km/min did not show a WAXD profile of perfect α form crystals but showed an intermediate structure having lattice spacings between the α′ and α forms. Such intermediate crystals did not transformed into α form crystals during the heating process.

Insights into the structural and physicochemical properties of small granular starches from two hydrophyte duckweeds, Spirodela oligorrhiza and Lemna minor

The structure and physicochemical properties of starches from two hydrophyte duckweeds, Spirodela oligorrhiza and Lemna minor, were investigated and compared in this study. The amylose content and average size of starches were determined to be 20.85%, 4.70 μm and 27.77%, 6.17 μm for Spirodela oligorrhiza and Lemna minor, respectively. The average chain length of two duckweed starches was measured to be around DP 28. The chain length distribution was observed to be greatly different from other reported starches for the high proportion of long chains (DP ≥ 37) over 50%. Wide-angle X-ray diffraction profiles of the two starch samples displayed typical B-type diffraction pattern. The gelatinization enthalpy-changes (ΔHgel) of two starch samples was about 10.40 J/g for two duckweed starches. The present results suggested the potential utilization of small granular starches from duckweed in functional foods and dietary supplement products.

Improved expansion ratio and heat resistance of microcellular poly(L-lactide) foam via in-situ formation of stereocomplex crystallites

It is critical to broaden the applications of poly(L-lactic acid) foams by improving heat resistance properties. The stereocomplex crystallites that are formed by melt blending of poly(L-lactic acid)/polylactide possess high melting point of about 220℃ and thus exhibit high heat resistance; therefore, the introduction of stereocomplex crystallites tends to improve the thermal stability of poly(lactic acid) foam. Unfortunately, using the solid-state foaming method, it was found that the expansion ratio of the obtained poly(lactic acid) foams was compromised with the value of 1.7 times once the stereocomplex crystallites were formed during the sample saturation stage. In this study, by applying a high compression molding temperature of 230℃, the as-prepared poly(L-lactic acid) and poly(L-lactic acid)/polylactide blends were amorphous. After being CO2 saturated at a mild condition, the specimens were foamed at 90–160℃. The wide-angle X-ray diffraction profiles presented that the stereocomplex crystallites and PLA homocrystals were in-situ generated during the foaming process. It is observed that the in-situ formed stereocomplex crystallites could act as the physical cross-linking agent to stabilize the nucleated bubbles and suppress cell coalescence, resulting in the increased expansion ratio (with value of about 23.6–25.6 times) and cell density, especially at high foaming temperatures and extended foaming time. Furthermore, the in-situ formed stereocomplex crystallites during the foaming increased the heat resistance performance of poly(L-lactic acid) foams. This novel crystallization control method helps us to find a balance point in preparing poly(L-lactic acid) foam with high expansion ratio, well-defined cell structure and high heat resistance performance.

Overcoming the Fundamental Challenges in Improving the Impact Strength and Crystallinity of PLA Biocomposites: Influence of Nucleating Agent and Mold Temperature.

Poly(lactic acid) (PLA), one of the widely studied renewable resource based biopolymers, has yet to gain a strong commercial standpoint because of certain property limitations. This work is a successful attempt in achieving PLA biocomposites that showed concurrent improvements in impact strength and heat deflection temperature (HDT). Biocomposites were fabricated from a super toughened ternary blend of PLA, poly(ether-b-amide) elastomeric copolymer and ethylene-methyl acrylate-glycidyl methacrylate and miscanthus fibers. The effects of varying the processing parameters and addition of various nucleating agents were investigated. Crystallinity was controlled by optimizing the mold temperature and cycle time of the injection process. With the addition of 1 wt % aromatic sulfonate derivative (Lak-301) as a nucleating agent at a mold temperature of 110 °C, PLA biocomposites exhibited dramatic reduction in crystallization half time to 1.3 min with crystallinity content of 42%. Mechanical and thermal properties assessment for these biocomposites revealed a 4-fold increase in impact strength compared to neat PLA. The HDT of PLA biocomposites increased to 85 °C from 55 °C compared to neat PLA. Crystallization behavior was studied in detail using differential scanning calorimetry and was supported with observations from wide-angle X-ray diffraction profiles and polarized optical microscopy. The presence of a nucleating agent did not alter the crystal structure of PLA; however, a significant difference in spherulite size, crystallization rate and content was observed. Fracture surface morphology and distribution of nucleating agent in the PLA biocomposites were investigated through scanning electron microscopy.

Crystallization and Crystalline Structure of Syndiotactic Polypropylene and Syndiotactic-Poly(1-Butene) Blend

The crystallization and crystalline structure of syndiotactic-polypropylene (sPP) and syndiotactic-poly(1-butene) (sPB) blend containing 10 (Bl-10), 25 (Bl-25), 50 (Bl-50), 75 (Bl-75), and 90 (Bl-90) wt% of sPB, have been investigated by means of differential scanning calorimetry (DSC), FT-IR, and wide-angle X-ray diffraction (WAXD) analyses. The melt-crystallization behavior of the blend samples was studied by DSC on the cooling process at constant rates. Bl-50, Bl-75, and Bl-90 showed lower crystallization temperatures than the neat sPP. sPP in Bl-75 showed the lowest crystallization rate among the blend samples. Bl-90 showed a two-phase molten state, and sPP in Bl-90 crystallized via two-stepprocess. Time evolution of FT-IR spectroscopy at room temperature detected conformational transformation of the sPP polymer chain in the blend samples of Bl-50 and Bl-75. The absorption peaks intensity in the FT-IR spectra derived from the helical conformations in the crystalline phase decreased, and the planar zigzag conformations in the amorphous and mesophase phases decreased over the crystallization time. The time evolution of the WAXD profile of Bl-90 indicated that sPP in the blend accelerated the crystallization of sPB. The crystallized Bl-10, Bl-25, and Bl-50 samples showed diffraction peaks in WAXD profiles and melting endothermic peak in DSC profiles derived from only the sPP crystal. The crystallinity and melting temperature of sPP in the crystallized Bl-10, Bl-25, and Bl-50 samples were almost independent of the sPB content. Both the crystalline structure of sPP and sPB were detected in Bl-75 and Bl-90. Bl-75 showed the lowest crystallinity and melting temperature of sPP among the blend samples.

Physical properties of poly(tetrahydrofuran)-block-poly(2-ethyl-2-oxazoline) triblock copolymer

ABA-type triblock copolymers (PEOxz-PTHF-PEOxz) composed of poly(tetrahydrofuran) (PTHF) and poly(2-ethyl-2-oxazoline) (PEOxz) were synthesized by cationic sequential polymerization. Differential scanning calorimetry and wide-angle X-ray diffraction analyses revealed that PEOxz-PTHF-PEOxzs produced a microphase separation structure, which consisted of a partially crystallized amorphous PTHF phase containing PEOxz chains on both ends. Tensile testing showed that PEOxz-PTHF-PEOxz exhibited tough mechanical properties that differed from those of the brittle PTHF homopolymer. Thus, it was suggested that the amorphous PTHF/PEOxz phase played a role in physically cross-linking the moieties via entanglement, resulting in a PEOxz-PTHF-PEOxz material with tough mechanical properties and the ability to be cold-drawn. Linear ABA-type triblock copolymer with poly(tetrahydrofuran) (PTHF) and poly(2-ethyl-2-oxazoline) (PEOxz) was synthesized by a one-pot sequential copolymerization, utilizing the living cationic polymerization of both monomers. Films of the ABA-type copolymer configure PTHF pure phase and mixing phase of PTHF and PEOxz, which was attributed by differential scanning calorimetry thermograms and wide-angle X-ray diffraction profiles.

Preparation and morphology of different types of cellulose spherulites from concentrated cellulose ionic liquid solutions

Spherulites of microcrystalline cellulose (MCC) have been prepared by using the vapor precipitation procedure with proper humidity at various temperatures from concentrated microcrystalline cellulose/1-allyl-3-methylimidazolium chloride (MCC/AMIMCl) solutions, for which AMIMCl is an ionic liquid, a good solvent for dissolving MCC. Four different types of MCC spherulites have been investigated by using polarizing optical microscopy (POM), scanning electron microscopy (SEM) and wide-angle X-ray diffraction (WAXD) technique. POM observations reveal four types of MCC spherulites, i.e., negative and positive banded spherulites, and negative and positive non-banded spherulites, depending on MCC concentration and crystallization temperature (Tc). For banded spherulites, both the band spacing and sizes of spherulites evidently increase with increasing Tc for each MCC/AMIMCl solution. The sizes of spherulites increase with increasing MCC concentration at a given Tc. The findings imply that MCC concentration plays a key role in MCC chain reorganizations into positive or negative spherulites, while the crystallization temperature mainly affects the MCC crystalline lamellar twisting for the formation of banded spherulites. SEM observation reveals that the formation of negative and positive banded spherulites is due to different lamellar twisting directions and the formation of non-banded spherulites is due to the formed radiating fibrillar textures. WAXD profiles confirm that all the four types of MCC spherulites formed are in the crystalline form of cellulose II family, exhibiting more intense and sharper diffraction peaks than those of cellulose II family obtained by the dissolution/precipitation process.

Structural investigation of Poly(ethylene terephthalate)/Poly(trimethylene terephthalate) transesterificated blends

Wide-Angle X-ray Diffraction (WAXD) and Small-Angle X-ray Scattering analyses were carried out to evaluate the evolution of the crystalline and supermolecular structure of poly(ethylene terephthalate) (PET) blended with poly(trimethylene terephthalate) (PTT). The conditions adopted in preparing the PET/PTT 50/50 blend induce transesterification between the polyesters; these reactions produce a new molecular characteristics based on PET/PTT copolymer that exhibits its own WAXD profile. The PET/PTT 50/50 copolymers prepared by melt mixing of the homopolymers for increasing times evidence spherulitic morphology and an evolution of the crystalline structure in terms of crystallinity and crystal dimensions. The periodicity of the transesterificated samples is intermediate between the long periods observed for pure PET and pure PTT. For the PET/PTT 50/50 copolymers the value of periodicity and lamellar thickness increase with the increasing of the processing time.

Electrochemical Synthesis of Mesoporous Pt–Au Binary Alloys with Tunable Compositions for Enhancement of Electrochemical Performance

Mesoporous Pt-Au binary alloys were electrochemically synthesized from lyotropic liquid crystals (LLCs) containing corresponding metal species. Two-dimensional exagonally ordered LLC templates were prepared on conductive substrates from diluted surfactant solutions including water, a nonionic surfactant, ethanol, and metal species by drop-coating. Electrochemical synthesis using such LLC templates enabled the preparation of ordered mesoporous Pt-Au binary alloys without phase segregation. The framework composition in the mesoporous Pt-Au alloy was controlled simply by changing the compositional ratios in the precursor solution. Mesoporous Pt-Au alloys with low Au content exhibited well-ordered 2D hexagonal mesostructures, reflecting those of the original templates. With increasing Au content, however, the mesostructural order gradually decreased, thereby reducing the electrochemically active surface area. Wide-angle X-ray diffraction profiles, X-ray photoelectron spectra, and elemental mapping showed that both Pt and Au were atomically distributed in the frameworks. The electrochemical stability of mesoporous Pt-Au alloys toward methanol oxidation was highly improved relative to that of nonporous Pt and mesoporous Pt films, suggesting that mesoporous Pt-Au alloy films are potentially applicable as electrocatalysts for direct methanol fuel cells. Also, mesoporous Pt-Au alloy electrodes showed a highly sensitive amperometric response for glucose molecules, which will be useful in next-generation enzyme-free glucose sensors.

Ionically Self-Assembled Thermotropic Liquid Crystalline Complexes of Linear Polysiloxane and Dendritic Amphiphiles

A series of polyelectrolyte-dendritic amphiphilic complexes with high degrees of substitution were prepared by ionic self-assembly of the polyelectrolyte poly (3-aminopropyl) methylsilane hydrochloride (PSI) with dendritic 3,4,5-tris(n-alkan-1-yloxy)-benzoic acid potassium salt [(3,4,5)nG1-COOK, n = 8, 10, 12, 14, and 16, where n was the number of carbon atoms in the alkyl tail]. These complexes PSI-(3,4,5)nG1 were characterized with wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS), Fourier transform infrared (FT-IR), thermogravimetry (TG), differential scanning calorimetry (DSC), and polarized optical microscopy (POM). WAXD profiles indicated a transition from liquid crystalline (n = 8, 10) to crystalline phase (n = 12, 14, and 16) in the PSI-(3,4,5)nG1 resulted from the dendritic amphiphiles at room temperature. PSI-(3,4,5)nG1 (n = 8, 10) were found to be in the hexagonal columnar (Φh) liquid crystalline phase, with the lattice parameter a = 3.05, 3.35 nm for n = 8, 10, respectively. On the other hand, PSI-(3,4,5)nG1 (n = 12, 14, and 16) formed end-to-end bilayer lamellar crystalline structures with the long periods d = 4.56, 5.04, and 5.68 nm for n = 12, 14, 16, respectively, at room temperature. An ionic thermotropic liquid crystalline state was obtained from PSI-(3,4,5)nG1 at temperatures: (a) below the clearing point Ti (n = 8, 10), and (b) between the melting point Tm and Ti (n = 12, 14, and 16). This research provides an easy way to obtain complexes with high degrees of substitution through the self-assembly of the linear polysiloxane and dendron amphiphiles, and demonstrates that the alkyl tail lengths of the bound dendritic amphiphiles play an important role in determining the mesomorphous structure for the polyelectrolyte-dendritic amphiphile complexes.

Mechanical Properties and Ordered Structure of Bacterial Poly<i>(3-Hydroxybutyrate-<i>Co</i>-3-Hydroxyhexanoate</i>) Fibers Stretched after Isothermal Crystallization near Tg

Biodegradable fibers of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) were prepared by melt spinning, followed by one-step-drawing with small crystal nuclei grown after isothermal crystallization near the glass transition temperature (Tg) and annealing at room temperature under tension. This new drawing technique is a very attractive method for obtaining flexible fibers from low-molecular-weight biopolyesters produced by recombinant bacteria. The ordered structure of PHBHHx fibers was investigated by tensile measurement, scanning electron microscopy, and wide-angle X-ray diffraction (WAXD). The tensile strength of 10 times one-step-drawn fiber after isothermal crystallization increased to 100 MPa. The WAXD profiles of PHBHHx fibers showed sharp reflections corresponding to highly oriented α-form (21 helix conformation) crystal.

In Situ synthesis of inorganic filler-filled polyethylene using polyethersulfone-supported TiCl4 catalyst system

In situ ethylene polymerizations with inorganic fillers were performed using catalyst based on titanium tetrachloride supported on polyethersulfone. The inorganic fillers used were MgO, TiO2, and CaCO3, which were pretreated with cocatalyst (methylaluminoxine) for better dispersion onto the polymer matrix. The formation of polyethylene (PE) within the whole matrix was confirmed by Fourier transform infrared studies. The wide-angle X-ray diffraction profile of the synthesized PEs indicated the presence of crystalline region. It was found that the nature of inorganic filler did not have any remarkable effect on the melting characteristics of the polymer, but the degree of crystallinity of PE was found to be higher for TiO2-filled PE. The amount of filler incorporated into the matrix was also evaluated through thermogravimetric analysis, where TiO2-filled PE showed ∼ 49% of filler material, which was also reflected in the higher productivity obtained by this system. The morphology of the filler-filled PEs was different, whereas the elemental dispersion was found to be uniform on the surface as elucidated through energy-dispersive X-ray spectroscopy. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Crystallization behavior of isotactic propylene‐1‐hexene random copolymer revealed by time‐resolved SAXS/WAXD techniques

AbstractThe crystallization behavior of isotactic propylene‐1‐hexene (PH) random copolymer having 5.7% mole fraction of hexene content was investigated using simultaneous time‐resolved small‐angle X‐ray scattering (SAXS) and wide‐angle X‐ray diffraction (WAXD) techniques. For this copolymer, the hexene component cannot be incorporated into the unit cell structure of isotactic polypropylene (iPP). Only α‐phase crystal form of iPP was observed when samples were melt crystallized at temperatures of 40 °C, 60 °C, 80 °C, and 100 °C. Comprehensive analysis of SAXS and WAXD profiles indicated that the crystalline morphology is correlated with crystallization temperature. At high temperatures (e.g., 100 °C) the dominant morphology is the lamellar structure; while at low temperatures (e.g., 40 °C) only highly disordered small crystal blocks can be formed. These morphologies are kinetically controlled. Under a small degree of supercooling (the corresponding iPP crystallization rate is slow), a segmental segregation between iPP and hexene components probably takes place, leading to the formation of iPP lamellar crystals with a higher degree of order. In contrast, under a large degree of supercooling (the corresponding iPP crystallization rate is fast), defective small crystal blocks are favored due to the large thermodynamic driving force and low chain mobility. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 26–32, 2010